Sugar Gliders

“Morgana Mo” by H. Schofield (CC BY 2.0)

Petaurus breviceps  

Sugar gliders are a very popular pet in many homes across the globe. The cute face and quirky personality makes them interesting and fun pets for those who have the time and patience for these fascinating critters. They do require a lot of attention and can be quite vocal about this. Remember to always get them in pairs for lonliness is a terrible burden to bear.


These small adorable creatures are actually part of the marsupial family which means that although they may resemble a flying squirrel, they are not rodents. As marsupials, the females have a pouch which will carry and protect their joeys (babies) until they are ready to venture out into the world. The females also have two uteruses and vaginas allowing them to have 1-2 joeys at a time. The pouch can be found in the belly button region and I would not recommend trying to poke it. The female also has four nipples for nursing her young within this pouch. They become sexually mature around eight months.

“Sugar Glider Babies” by Robert Nelson (CC BY2.0)

The male sugar gliders also have some unique features such as the forked penis and a testicle sac that becomes visible when it matures. The testicles are attached to the body via a chord that does not contain nerve endings making it virtually painless to neuter the animals. They also have a scent gland atop their head and a smaller one on their chest and when the male is not neutered it will typically look like a bald spot due to the oils that are excreted for marking territory and marking the other gliders in their social group. Marking the other gliders allows the dominant male to recognize his group members by scent. The male gliders will also have a cloaca, a common chamber into which the rectum, bladder, and reproductive system empty, and then excreted through a vent opening found at the base of the tail. The males become sexually mature around a year and can be neutered at five to six months.

“Petaurus breviceps male ” by
Dawson at English Wikipedia (CC BY 2.5)

Both male and female gliders will have large eyes that protrude from the sides of their head due to their nocturnal nature. This enables them to have a large field of vision which helps them detect predators and navigate. The eyes appear to be black but are simply a very dark brown. Some gliders will have a thin blue iris. It is believed that gliders only see greys and red as suggested by the amount of cones and rods that have been identified in their eyes. It has also been observed that gliders excrete a white, milky substance from their eyes that is used for grooming.

These marsupials also have a very sensitive nose with cute wiskers. Gliders’ ears are disproportionate to the size of their heads however, the ears are able to move independently which makes them excellent listeners. Males tend to weigh 100-160g whereas females tend to be smaller and weigh in at 80-130g. Standard fur colors are grey with a black dorsal stripe and white underbelly. Female dorsal stripes are typically thinnner than the males. Captive and domesticated gliders come in a variety of colors including albino.

“White Sugar Glider” by Dave Hogg (CC BY 2.0)

A cool thing about gliders is that they have four hands instead of feet. These are used for grabbing and holding onto food stuffs and for climbing and gliding. Each of these hands have an opposable thumb and each finger have claws to help with latching onto things, the lower hands have fingers that are fused together for grooming and a padded thumb for holding onto branches or cage walls. It is absolutely adorable when they grab for treats that are being handed to them.

“Sugar Glider” by George Grinsted (CC BY-SA 2.0)

Watching gliders eat is really fun because of how they hold their food and take bites of fruit or treats. They have two small cute front teeth and two much longer lower teeth which are used for scooping fruit or sap. They can often be seen turning the food in their small hands to access the various sides of the food pieces. Luckily their teeth do not continue to grow so they will not chew nor be destructive. They use their long tongues for drinking water and juices, as well as for grooming. It is very cute when they lick pieces of their food to taste them before grabbing and eating it.

“Patagium” by Phil and Lisa (CC 2.0)

They are called gliders because they have what is called a patagium, which is the extra skin between their front and back arms that extend making them look like cute squares. They are not actually wings but they do allow the suggies to glide from one branch to another. When the glider is in this positon it is called an airfoil. The gliders’ tail is about haf the length of their bodies and is primarily used as a steering mecanism when they glide. Sometimes they will use their tails to carry small twigs but they are unable to hang from a branch using their tail. They use their hands to climb and hang from the cage and or branches.


Sugar gliders are very social creatures. In the wild they typically live in groups of 6-10 gliders. They are originally from Australia and New Guinea but can now be found in homes across the globe. When adopting a glider, it is always important to get them in pairs, a lone glider that is not given LOTS of attention will become extremely stressed out. If they are the same gender then it is ok to house them together. If there is a male and a female it is important that you neuter the male before housing them together. Breeding gliders requires a license. Always have more females than males and monitor dominant and aggressive behaviors between individuals.

Social Grooming: gliders will often groom each other by licking and running their hands through one another’s fur. As discussed in the Anatomy section, the gliders hands have extra padding on the thumbs to aid in this. Not only does the practice keep the colony clean but is also a bonding activity for its members.

Gliders are very playful creatures and pets and with their curious nature they can often find themselves in trouble if not properly supervised in a glider proofed room. In the wild they rely on their instincts for survival but as pets it is the owners responsibility to ensure their safety. Gliders can be seen exploring, climbing, jumping, and gliding during the night when they are typically active. They enjoy time out of the cage as well and will climb on EVERYTHING and chew cords if they are not watched. If you have the ability to install perches in your home for them to play on while out of the cage make sure that they have a safe landing space for when they glide down.

Handling pet gliders is a really important aspect of the bonding process and should be done daily. The bonding process establishes trust and love between owner and pet. Gliders that are not frequently handled do become nippy, as discusssed previously they do have long sharp teeth that can make you bleed. However, these teeth are small and it does not hurt that bad. Try not to flinch or pull away when the glider does bite, fast movements may frighten them. Handling the gliders also socializes the creatures and ensures that they are recieving enough attention. Once the gliders have bonded with you, it is a lot of fun to play with them and have them glide to you.

“Sugar gliders gliding” by reptile maniac (CC BY 2.0)

Gliders prefer to climb and jump instead of crawling on the ground where they would be easy targets for predators. They like to be up high and will often climb up to your shoulder or onto your head, be careful because they may try to glide from your head to another location. They are able to glide up to 50 meters in the wild in search of food. They are able to climb up a variety object, for example, my suggie climbed up a lamp post and also a tapestry in my room.

Gliders are known to love pouches. They will curl up in your pocket and snooze if you let them. Pouches are ideal for sleeping as it allows them to cuddle together in a safe space. Cage pouches are available online and in many pet stores. Travel pouches are ideal to assist in bonding and taking your gliders on the go. Like cage pouches they are available commercially and it keeps them cozy and warm, I usually put a small blanket into the travel pouch for them to curl up in as well. Do not take them outside in bad weather becuase they may become ill.


Crabbing: this noise typically indicates that the glider is frightened or agitated. Sometimes they will crab as a warning signal or a cry for attention. It can be compared to locusts or screeching and each glider sounds different, having its own variation in pitch.

“Sugar Glider Crabbing” by Tia (CC BY 2.0)

Barking: the bark sounds like a puppy yipping. Like the crabbing, the pitch and tone are unique to each glider. They will bark when they want attention, are excited, bored, annoyed, or are calling to their owner or colony members. It is also used as a warning call to other gliders in the colony to signl that there is a predator nearby. It may also occur at night if something strange such as a light or sound occur that startle the glider.

“Sugar Glider Barking” by Sirens of the Sea (CC BY 2.0)

Crying: is similar to whining. It is typically only made by joeys or a newer glider that misses its colony. Should the glider do this, try to give them attention and love to cheer them up.

Chattering/Chirping: is a noise that sounds like a mix between a chirp, teeth chattering, and low pitched squeaks. It is used to communicate with other gliders and with their owners.

Purring: sounds similar to a small drumbeat or cat’s purr. It means that the glider is happy but it is very faint and can only be heard when extremely close to it.

Hissing: It sounds like a sneeze but it is actually the sound that is made when the glider is grooming itself. The glider will spit into its hands which produces the sound and then run them through its fur or a colony member’s fur to clean them. The hissing sound can also be heard when they are newly introduced to one another and when the gliders wrestle together.

Sneezing: This is very similar to the hissing but sounds much more like an actual sneeze that a cat would make. Sneezing can occur due to an upper respiratory infection, especially if the glider has been in cold temperatures. The glider should be taken to your exotic veterinarian for treatment.

Singing: Typically only done by female gliders to their joeys.

“Sugar Glider Noises” by Elissa Brianne (CC by 2.0)

The Cage

The cage should be large enough for the gliders to climb and jump around. Typically a couple of platforms and hanging toys are good to have in there as well. The cage can be lined with shredded paper or pine bedding. Spot cleaning the cage daily is important to ensure that the gliders do no become ill. Cage covers or clean blankets can be used to keep the enclosure dark while they sleep during the day.

Toys should be cleaned and varied weekly to mentally stimulate the gliders. Hanging scavenger toys are a fun way to treat your gliders and to encourage their curiosity. A wheel is a nice addition for exercise. Gliders will also need a couple of pouches for sleeping in. Pouches, tents, and hammocks as well as cage toys can be purchased commercially and online.

The cage should also have multiple food dishes that are sturdy so that they do not tip over if the gliders leap away from them after grabbbing a bite to eat. A sturdy water dish or a water bottle that attaches to the side of the cage are also necesary. Filtered water should be used.

The gliders should be kept in temperatures between 75° F-80° F but can tolerate 65° F-90° F. I also like to keep small blankets in the cage pouches for them to snuggle up in. I often use old socks that have gotten holes in them because my gliders like to curl up in those and its really cute.


“Enjoying a meal” by Alex Archambault (CC BY 2.0)

Sugar gliders are nocturnal and will need fresh food when they first wake up, so I typically feed mine around 9pm. They are omnivores and will eat a variety of items. In the wild the often choose to consume tree sap from acacia trees and the gum of eucalyptus plants. Nectar and pollen from flowers as well as insects are regularly consumed. Wild sugar gliders rarely eat fruit whereas pet gliders are often overfed fruits and underfed nectar and protein sources. The ideal sugar glider diet is varied and cannot be narrowed down to only two or three items.

Your glider’s diet shoud consist of 25% protein such as cooked eggs, cooked lean meat, crickets, mealworms, and pelleted diets that are available online and in most pet stores. Another 25% should be grean leafy vegetables with a small amount of fruit such as berries, apples, and carrots. The other 50% of their diet should be a pelleted nectar source. Vitamin and mineral powder supplements containing calcium are also required.

Sugar gliders do have a sweet tooth so they love getting treats. Honey sticks made for gliders are a great way to bond with the glider while letting them enjoy a tasty snack. Treats should not be fed to gliders in large quantities. Popular treats for gliders include almonds, peanuts, plain cheerios, and yogurt drops. Placing these items into scavenger toys or offering them by hand to your gliders is a great way to bond and get them to enjoy coming up to you.


Make sure to find an exotic pet veterinarian that can do regular checkups for your gliders. Gliders are awesome pets and it is our job to keep them happy and healthy. Occasionally gliders will get bacterial or parasitic infections that will require medication, traumatic injuries that need surgery, or sadly they have organ failure or cancer. More common health problems include obesity, malnutrition, metabolic bone disease, dental problems, and stress related diseases.

“Boom! It is a Sugar Glider” by Joe McKenna (CC BY 2.0)

Obesity in gliders is due to a lack of space and the ability for the glider to exercise. Gliders that eat excess amounts of proteins, fats, and treats will often become obese and exhibit behaviors such as lethargy, heart disease, and arthritis. Thankfully this is easily reversed by increasing the glider’s daily amount of exercise, decreasing the amount of proteins being served, and decreasing the portion sizes while maintaining a balanced diet.

The signs of malnourishment in gliders are weakness, weight loss, dehydration and an inability to stand or climb. This can lead to more serious problems such as broken bones, bruising, and pale gums. If this happens to your glider, you should seek help from your veterinarian.

Metabolic bone disease, also called nutritional osteodystrophy, is a type of malnutrition due to low levels of calcium in the blood. This can lead to the glider having seizures. The treatment for this is a long term administration of calcium with supportive care.

Always check with your veterinarian if you have health related questions about your pets. Sugar gliders make great pets if you know how to treat them. Glide on!!!

“Parsnipkitty” by H. Schofield (CC BY 2.0)
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Heather Schofield, Althia Rickard, Malisa Rai

April 20th, 2018

Bio 345 – Animal Behavior


 Betta splendens are model organisms for understanding aggressive behavior in aquatic species. Aggressive displays have been well documented and include the opercula display and hitting with the tail. These behaviors have evolutionary contexts that have created differences in the frequencies that these behaviors are displayed in the presence of various audience types. Male betta fish were observed without bystanders and with different gendered bystanders to determine differences between these displays. There were significantly less gill flares in the presence of a female bystander. The presence of a male bystander saw significantly less tail flicking. The data suggested that gill flaring is typically more common in the presence of other males whereas tail beating is more closely associated with the presence of a female bystander. It is believed that tail beating evolved from an aggressive display to a courtship display due to chase away selection.


Communication between animals occurs in a variety of forms, such as auditory, electrical, or visual signals. The use of signals allows animals to send information to one another and modify behaviors based upon the understanding of those signals[7]. A few common reasons that animals interact are for mate attraction, territory or predator defense, and social integration. Aggressive behavior in animals is common for defensive mechanisms and acquiring resources [6]. Sometimes these signals accurately depict an animal’s true size and ability which is called honest signaling. When the signals are misleading this is described as dishonest signaling, however, evolution tends to favor honest signaling [8]. Gill flaring, also called the opercula display, is an honest signal that male Betta splendens use to intimidate an opponent and suggest fighting ability and strength. This behavior of gill flaring is energetically costly because the display prevents the fish from using the gills to obtain oxygen which requires stamina [10]. Traits that are used for communication are evolutionarily and historically limited based upon the phylogeny of the species. Only a pre-existing trait such as physiological abilities and behaviors can become an evolutionary adaptation. These become incorporated into the larger population if they increase the overall fitness of the individuals with that trait [8].

Another aspect of communication is eavesdropping where an individual receives information about another from a signal that was not intended for it. This is seen in a variety of animals and often the eavesdropper behavior toward the signaler is influenced by the signal that was intercepted. An example of eavesdropping is when snakes use the mating calls of frogs to find their prey [9]. Other studies on eavesdropping as a communication mechanism have suggested that male Betta splendens alter their aggression displays depending on the context of the situation. It was found that the sex of a bystander, among other contextual elements, has significant effects on the display behavior of Betta splendens. The males showed different levels of aggression depending on the presence or absence of an audience, the gender of the audience, their own reproductive state, and the amount of resources held [2].

Siamese fighting fish, Betta splendens, are a model organism for observing fish aggression. Typical aggressive behaviors that have been previously documented on Betta splendens include, but are not limited to, gill flaring, fin spreading, tail beating, and biting. Physical displays such as tail beating and biting only occur when the benefits of territoriality outweigh the costs of potential harm of fighting [4].Tail beating has been more closely associated with courtship rituals and therefore are thought to occur more often in the presence of female Betta Splendens. The gill flaring behavior was shown to be greatest in the presence Betta splendens who were males [3]. This suggests that there may in fact be a gender-based bystander effect on the aggression displays in male Betta splendens.

This study aimed to investigate aggressive behaviors in male Betta Splendens to determine the response to the presence and absence of different gendered bystanders. This was done to shed light on the evolutionary and historical outcomes of specific aggressive behaviors in Betta splendens. We hypothesize that Betta splendens will have differential aggressive displays that are dependent on the gender of the bystander. We predicted that if a male Betta Splendens is placed in a tank with a mirror, it would display more gill flaring than tail flicking when there is a male Betta Splendens bystander. We also predicted that if a male Betta Splendens is placed in a tank with a mirror, it would display more tail beating than gill flaring when there is a female Betta Splendens bystander.


Study Species:

Five mature male crowntail Betta splendens and one mature elephant ear female from the local Petco were purchased. The males varied in size, shape, and color to be representative of the variation observed in male betta fish. They are naturally found in freshwater ponds of Southeast Asia. Captive-bred and wild males both exhibit strong and stereotyped aggression in defending their territories against intruding male conspecifics.  Each male fish was assigned a number for later identification.

Housing and Care:

 All fish were kept in a small isolated glass fish bowl with about 700mL of lukewarm tap water and black pebbles for resting on. These fishbowls were initially housed on the fourth floor of the KSC Putnam Science Center in the greenhouse and then later moved to the greenhouse office for a cooler environment. The water in all fish bowls and the experimental tank was treated with  API  Splendid Betta Complete Water Conditioner from Petco to prepare the  tanks for suitable living conditions [4].  The conditioner is used to remove chemicals from the treated tap water because these chemicals are toxic to fish [5]. Fish bowls remained segregated to prevent interactions. Fish were fed generic betta fish food from Petco daily. Fish bowls were cleaned every other day or more often if needed, all water was treated with the API conditioner before fish were placed into the water. The water was maintained at about neutral pH and the water temperature was held at room temperature.

The female betta perished the day after purchase and was replaced with a similar elephant ear female at Petco. Male #1 perished after the self-trials and was removed from the experimental data set. He was not replaced and the trials continued with only Male #2, #3, #4, #5, and the female. It was believed that the heat of the greenhouse caused these fatalities and the fish were moved inside to the greenhouse office to remain cooler.

Experimental Tank Set-up:

A half-gallon tank with a divider was filled with tap water and treated with conditioner. One male betta was placed into a plastic bag and allowed to acclimate to side A of the experimental tank. An opaque cover was placed over the divider to prevent interactions prior to the trials (Figure 1). A male or female betta acclimated to side B, the bystander side. After each trial the tank was emptied and cleaned and the water was treated with API conditioner.

Figure 1: Experimental half-gallon tank with a divider. Side A will contain the male Betta that will be exposed to the mirror. Location of the mirror is shown on the back wall of side A.  Side B will be used to house the bystander that will be male or female.

Experimental Design:

A small mirror was attached to the wall of the experimental tank on side A. Male betta #2 was allowed to acclimate to the experimental tank on side A. Then for five minutes, male aggressive displays of gill flaring and tail flicking were counted and recorded. Three trials of solitary displaying, trials without bystanders, were done for each fish. These trials served as a control to compare solitary versus bystander behaviors.

Male #3 was placed on side B of the experimental tank and was allowed to adjust to the new environment. The opaque cover for the divider prevented interactions. Once both fish in side A and B, separated by the opaque divider, were acclimated to the water, the trial began. The opaque divider was removed so that the bystander was visible. For five minutes, the number of tail flicking and gill flaring that betta #2 displayed were recorded.

After the five minutes the fish were placed in their respective fish bowls for acclimation while the experimental tank was cleaned. Male #2 was put back into side A to be tested with male #4 and this was repeated for male #5 and the female betta. All five males were tested in side A for solitary mirror displays and bystander effects. Each male was tested with the female three times. Each set of male trials (#2, 3, 4, 5) was a replicate experiment.    

Focal Betta Behaviors:

This study aimed to investigate the differences in gill flaring and tail beating behaviors of male betta fish when exposed to either a male or female bystander betta fish. The behaviors are described in Table 1. These behaviors were chosen because they are easily spotted and have been described in published papers on this species.

Table 1: Descriptions of aggressive betta fish behaviors derived from primary literature search [3] and observations.

Behavior: Description:
Gill Flaring Opercula display, extension of gills
Tail Beating Using the tail to hit or attempt to hit an opponent or object


Statistical Analysis 

            The averages of each trial condition (self, male bystander, female bystander) were calculated with standard deviations and standard errors using Microsoft Excel. A One-Way ANOVA with post hoc comparisons were done for gill flares and for tail beats using an online calculator. The post hoc comparisons were used to determine the significance of the data between the different trial conditions. The average number of gill flares for each trial condition (self, male bystander, female bystander) were calculated and compared. The average tail beats for each trial condition were calculated and compared. The significance of each type of trial condition was calculated for each behavior (gill flaring or tail beating).


            Gill flaring behavior appeared to decrease in frequency in the presence of a female bystander. The statistical analysis indicated that there were significant differences between the average number of the two aggressive displays with a male versus a female bystander for the three different trial conditions. The results showed that there were significantly less gill flares in the trials that had the female bystander (P= 0.0023, F=6.762, Figure 2) as compared to a male bystander and the self-trials. Gill flares for the self-trials and male bystander trials were not significantly different suggesting that it was the presence of the female creating the differences. The different letters above the data bars indicate if the data sets are significantly different.


Figure 2: Average number of Gill Flares exhibited by the focal male Betta during the five- minute trials. For the three trial conditions the F value = 6.7622 and P-value = 0.0023. A male Betta splendens was in the experimental tank with a mirror on side A and observed for five minutes displaying to a mirror with either nothing, a male bystander, or a female bystander in side B of the experimental tank. The number of gill flares in the female bystander trial condition was significantly less than the other two trial conditions.

The self-trials and female bystander trials appeared to have similar means for tail beating when displayed graphically. There was a significant difference between the number of tail beats in the presence of a male versus a female bystander (P=0.0015, F=7.3241, Figure 3). There were greater tail beating events in the presence of the female bystander and the self-trials when compared to the male bystander trials. This data showed that in the presence of male bystanders there were a greater number of gill flares and that there were more tail beatings in the presence of the female bystander.

Figure 3: Average number of Tail Beats exhibited by the focal male Betta during the five-minute trials. F-value = 7.3241. P-value = 0.0015. A male Betta splendens was in the experimental tank with a mirror on side A and observed for five minutes displaying to a mirror with either nothing, a male bystander, or a female bystander in side B of the experimental tank. Male bystander trial conditions had significantly less tail beating events than the other two trial conditions.


Aggressive behaviors are typically seen in response to territory defense and mate acquisition. These behaviors have evolutionary contexts that has been selected for over thousands of years. The Betta splendens is a classic fish pet that has been studied extensively for their aggressive behaviors. It has been proposed that there is gender based bystander effects that determine the frequency that specific aggressive behaviors are displayed due to the audience effect [1]. This study aimed to investigate whether there was a gender bias for gill flaring and tail beating in male Betta splendens. Various colored and sized males were observed displaying to a mirror without a bystander, with a male bystander, and with a female bystander.

It had been hypothesized that there would be greater gill flare displays in the presence of male bystander whereas a female bystander would induce more tail beatings. The experimental trials supported this hypothesis. The male bystander trials displayed significantly more gill flares compared to the female bystander suggesting that gill flaring is typically used as an aggressive defense against invaders. The female bystander trials showed significantly more tail beatings suggesting that this behavior has both aggressive and mating evolutionary contexts. This suggests that there are differences in aggressive displays due to the presence of different gendered bystanders. Future experiments or observations could look at how or if closely related species exhibit the same aggressive behaviors based upon the sex of bystanders or if this is unique to Betta splendens.


[1] Claire Doutrelant, Peter K. McGregor, Rui F. Oliveira; The effect of an audience on intrasexual communication in male Siamese fighting fish, Betta splendens, Behavioral Ecology, Volume 12, Issue 3, 1 May 2001, Pages 283–286,

[2] Dzieweczynski, Teresa L., et al. “Audience Effect Is Context Dependent in Siamese Fighting Fish, Betta Splendens .” OUP Academic, Oxford University Press, 29 Sept. 2005,

[3] Dzieweczynski, Teresa, et al. “Opponent Familiarity Influences the Audience Effect in Male–Male Interactions in Siamese Fighting Fish.” Animal Behaviour, Academic Press, 15 Mar. 2012,

[4] Egar M. J, Lynn E. S, Ramenofsky. M, Sperry S. T, Walker G. B. (2007). “Fish on Prozac: a simple, noninvasive physiology laboratory investigating the mechanisms of aggressive behavior in Betta Splendens.” American physiological society. Retrieved from

[5] Mohrman, Eric. “What Does Conditioner Do for an Aquarium?” Pets, The Nest, 2007,

[6] Romano, Donato, et al. “Multiple Cues Produced by a Robotic Fish Modulate Aggressive Behaviour in Siamese Fighting Fishes.” Scientific Reports, Nature Publishing Group UK, 2017,

[7] Rosenthal, Gil G. “Spatiotemporal Dimensions of Visual Signals in Animal Communication.”Annual Review of Ecology, Evolution, and Systematics, vol. 38, 2007, pp. 155–178. Illiad, doi:10.1146/annurev.ecolsys.38.091206.095.

[8] Schofield , Heather. “Communication Between Animals.” Schofield Investigations, KSC Open , 1 Mar. 2018.

[9] Strauss, Amy. “Eavesdropping in the Animal Kingdom: Sneaky Creatures Just Trying to Get Ahead.” Thats Life Science, 5 Sept. 2017,

[10] Verbeek, Peter, et al. “Differences in Aggression between Wild-Type and Domesticated Fighting Fish Are Context Dependent.” Animal Behaviour, vol. 73, no. 1, 2007, pp. 75–83., doi:10.1016/j.anbehav.2006.03.012.










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Final Review

Population and Community Ecology Final Review

Dr. Hayes, KSC 

The final exam is cumulative and will include topics covered in the first semester. To review these please visit the Midterm Review.

Metapopulations and allee effects

  • Population growth trajectory for density independent growth is an exponential growth curve. dN/dt=rN
  • Population growth trajectory for negative density dependent growth. Logistic, S-shaped curve. dN/dt=rN(1-N/K)
  • Relationship of Per capita population growth and N:
  • Logistic models show population regulation.
  • Positive density dependence: when small populations show a lower per capita growth rates than bigger populations do. This is not a straight line-right skewed graph, the smaller population has an increasing per capita growth until it reaches a larger size when the negative density dependence takes over.
  • Allee Effect– due to positive density dependence.
    • Mechanisms:
      • Problems finding a mate at low densities.
      • Group formation-foraging success, detection, avoidance, saturation of predators.

Smaller populations at a greater risk for extinction than larger ones

  • Environmental changes can decrease population growth rates
    • Habitat loss, hunting, invasive species
  • Due to Allee Effect (smaller dN/dt)
  • More sensitive to randomness
    • Environmental stochasticity-good years and bad years
    • Demographic stochasticity- randomness that occurs when rates are applied to whole numbers. Ie. Average number of children an individual has, do not expect same outcome in each case.
  • Genetic reasons-inbreeding, inbreeding depression (reduction of fitness due to deleterious recessive traits that are passes to these offspring that have low fitness-lower birthrates and higher death rates occur), loss of genetic diversity.
  • Genetic rescue- introduce new individuals to increase genetic diversity.

Conservation of Genetic Diversity

  • Genetic diversity within individuals (heterozygosity) the proportion of gene loci in an individual that contains alternative forms of alleles.
  • Genetic diversity among individuals within a population
  • Smaller populations are more likely to become extinct-allele affects are more deleterious
  • Low genetic diversity-all are affected by the same abiotic/biotic factors, cannot respond to change
  • Florida Panthers-last surviving subspecies of puma found in southern North America. Only two populations: one in the everglades and the other is outside of Miami. Down to 25 animals total in 1990’s. Due to fitness consequences of inbreeding caused by very low populations (high parasites, low sperm counts, bobbed tails)
    • Four females from the texas subspecies were brought in which brought the population size from -30% yearly to +20%. Survivors were the pure hybrids who had the highest fitness. Florida offspring had lowest fitness. The backcrosses (hybrid+Miami/ hybrid+everglades) had an intermediate fitness.
    • Bring in new alleles to a population is called a “genetic rescue” to help stop the extinction vortex.

Interspecies Interactions

  • How do they affect each other?
  • What is the direction of the effect?
  • Competition: (-/-) negative effect on each individual on the other because they share a limiting resource.
  • Predation: (-/+) one individual (the predator) captures and kills another individual (prey); each predator kills multiple prey in their lifetime.
    • Exploitative interactions (predators, grazing, parasites (do not always kill host), pathogens(microorganisms/fungi), parasitoids (lay eggs on host, always kill host)).
    • Hairworm Life cycle- cricket drinks water that contains larva, larva grows inside cricket/eats it, when ready to emerge it influences behavior of host to make it jump into water because it makes it really thirsty through chemical manipulations. The drowned cricket will harbor the eggs of the next generation of parasites and infect the water supply.
  • Parasites influencing host behavior:
    • Cold or flu: symptoms of flu
      • Fever-indicates illness
      • Sneeze/cough- spreads illness
    • Rabies: increases aggressive behaviors to increase transmission through biting
    • Toxoplasmosis: due to protozoan parasite. Toxoplasma gondii infects warm blooded animals; primary host – cats
      • Mice that are infected behave differently. Will head toward smell of cat in a T-Maze.
  • Commensalism: (+/0) one species gains something, the other species is not affected
  • Dispersal mechanism
    • Plants
    • Barnacles on whale
    • Artic fox follows the polar bear
  • Mutualism: (+/+) both species have a net positive benefit from the interaction.
    • Flowers must produce excess pollen so that bees come and make honey, pollen is also spread.
    • Goby and alpheid shrimp

“blind goby and his shrimp” by Chris Thompson (CC reuse allowed) 

  • A positive effect that one individual has on another is called Facilitation
  • Interaction Web: diagram that shows the direction (sometimes strength) of interactions between pairs of species- includes consumption (predator/prey), competition, and facilitation.
  • The world is green because the predators keep the herbivores in check- “Green World Hypothesis”. Predators regulate herbivore populations-prevents them from eating all the plants
  • Paine: what happens if you remove the predator starfish? Within a year and a half- the number of species on the rocks decrease, mussels (the starfish prey) overtook the area. A single species of starfish controlled the composition of the area. “Keystone Species and Trophic Cascades”. These species have a huge impact on the ecosystems while other species do not……Not all species have the same impact on the food web. Remove the predator- the system simplifies itself.
    • Another experiment: sea urchins eat all the kelp. Why is nothing controlling the urchin populations? Loss of otters due to the fur trade caused urchins to take over. Sea otters control urchin populations, without otters the urchins will eat all of the kelp. Sea otters are keystone species-regulate the costal systems.
    • Otter populations decline due to orcas starting to eat otters. Whales that orcas normally eat were on the decline due to hunting. Otter populations in areas where orcas had no access remained the same.
  • Removal of predators has broad effects on the variation and number of species within a population.
  • Keystone Species: A species that has a disproportionate effect on the species within the community. Are often predators, less abundant within the community (rare).
  • Trophic Cascade: predator has a negative effect on herbivore which has a negative effect on the autotroph. The predator has a positive effect on the autotroph. The presence of the predator creates a diverse community.
  • Bottom up process: resources regulate abundance of a species
  • Top Down process: predators regulate their prey abundance and have positive effects on the prey of their prey. Reintroduction of wolves to Yellowstone.
  • Apparent Competition: a predator or pathogen that affects two different prey species, the two-prey species have a negative indirect interaction on each other. If one species increases in abundance, predation for the other decreases. They have an inverse relationship.
  • Coevolution: obligate and host-specific for parasites and hosts
  • Evolution of reduced virulence: rabbit populations in Australia- biological control via the introduction of a pathogen. In 1950 a virus was released and killed 99.8% of the rabbits. 600 million rabbits declined to 200 rabbits within two years. The rabbits became resistant to the lab strain and the virus became less virulent over time.

The Paradox of the Plankton

  • Refers to a paper by G. E Hutchinson (1961)
  • Points out the clash between observed diversity of photosynthetic plankton and Gause’s Principle of Competitive exclusion. How can so many species filling the same niche survive together?
  • To resolve the paradox: how do you explain the maintenance of diversity?
    • Isoclines are arranged for stable coexistence

Maintenance of species Diversity:

  • Intraspecific competition > interspecific competition (Connell 1978 Science)
  • Gradual change in the environment. The competitive rank varies with changing environmental conditions. Fluctuating pattern of who is the dominant competitor.
    • Species must not decline to extinction before the environment changes to favor it again.
  • Circular Networks: competitive hierarchy. A > B > C > A. A nontransitive network is independent from environmental conditions.
    • Similar to frequency dependent selection
  • Compensatory mortality on most dominant species. The mortality in competitive dominant Is greatest because it is more abundant.
    • Frequency dependent
    • Source of mortality….
      • Pathogen/host, predator/prey, disturbances
  • Predation:
    • Keeps population level of the dominant competitor below that which would cause competitive exclusion.
    • Creates patchiness in the environment- opens up spaces and resource that reduces the strength of competition.
    • Proportional predation: generalist predator that eats prey as they are encountered. The most abundant species/competitive dominant will be encountered more often and eaten.
    • “Switching” behaviors: predator prefers the prey species that is most abundant. The most common species eaten disproportionately more than uncommon ones. Rare species will become more abundant than the other and the predator switches to eating that species.
  • Keystone Predators: predator prefers the competitive dominant. By consuming the dominant competitor, biodiversity is maintained.
  • Janzen-Connell Hypothesis: to explain the diversity in tropical forests.
    • Seed dispersal patterns- interspecific interactions
      • Pathogens and parasites on seed. Specialization of parasite/pathogen will spread from the parent tree. So that seed mortality occurs most often to those seeds that are closest to the parent tree. Patchwork of differential mortality and species diversity.
    • Intermediate Disturbance Hypothesis: proposed to explain the maintenance of species diversity
      • Predicts that species diversity will be greatest at intermediate levels of disturbance (Intensity/frequency of disturbance)
        • The competitive dominants will survive when there are low disturbances
        • The most resistant will survive at high disturbances
      • Disturbances: abiotic factor that causes death/decreased fitness/population size of some individuals but not necessarily all.

Metapopulation Dynamics:

Assumptions of exponential and logistics population growth models:

  1. Populations are closed, no immigration/emigration
  2. All individuals contribute equally to the population growth, K (carrying capacity).
    1. Age, size, sex are not considered
  3. Effect of adding or losing an individual has an instantaneous effect on dn/dt
    1. Delayed density dependence with a time lag-new dynamics such as damped oscillations, chaos

How are populations connected to each other?

  1. Species occur in nature as networks of populations whose temporal and spatial dynamics are interconnected by dispersing individuals
  2. “metapopulation coined by Levins (1969)
    1. Meta: analysis of several analysis’s, a population of populations, etc.
      1. Scale out
    2. Many populations or suitable habitat patches are connected by dispersal across intervening matric of unsuitable habitat.

Metapopulation: a group of populations linked together by immigrations and emigrations and dispersal, able to persist despite local extinctions because of frequent recolonization events.

Model metapopulation dynamics:

  • P= fraction of occupied patches
  • Change in % occupied = births – deaths (pf occupied patches)
  • dP/dt = c(P)(1-P) – eP
  • c = “per patch” colonization rate à
    • c(P)(1-P) is representative of birth rate
      • c(P)= occupied patches
      • (1-P) = unoccupied patches
    • e = “per patch” extinction rate
  • When set equal to ZERO….find the equilibrium
    • P = 1- e/c
  • Metapopulation will persist if e/c is less than one ( extinction rate is less than colonization rate) (e<c )
  • What affects c and e?   (will be on the final exam)
    • Matrix habitat: the group of habitat patches within an unsuitable environment.
    • Distance between patches
    • Size of patches
    • Less hospitable matrix decreases C
    • Increase the distance between patches decreases C d
    • Make the patches smaller will increase e, decrease c
    • Destroy patches will increase e
  • Patches that are sinks will only thrive if there are sources from which migrants come from.
  • Patch area determines population size due to K.
    • The bigger patches have larger populations, have larger colonization rates.
    • Small patches are more likely to go extinct, due to small population size, inbreeding, etc.
  • Which patches are occupied changes on an almost yearly basis.

Demography and Life Tables

  • Age structure: relative proportion of different age classes within a population
    • Size structure, stage structure
  • Population pyramid: separate sexes left/right, youngest are on bottom of pyramid.
  • Shape of pyramid describes the metapopulation
    • Pointy means rapid growth
    • Mound is stable growth
    • Smaller base indicates shrinking populations (bulbous)

Life tables:

  • X= age
  • Nx= number of individuals of age X
  • Fx= per capita fecundity of age X (average births per female age X)
  • Survivorship and survival rate
  • X=0 is the 1st age class (from birth up to the first age class)
  • X=3 is the 4th age class

****common to typically only use females since they are the ones that give births***

Cohort Life Table:

  • Cohort= group of individuals experiencing something together
  • Derived from a single group over time from birth. Monitor growth, survival, death as the group ages

Static Life Table:

  • Longer living organisms
  • Counts of individuals of different age classes at a single time step.
  • Used to infer past survivorship


  • Survivorship: (lx) the probability of surviving from birth to the beginning of age class X
    • Lx=Nx/N0
  • Survival Rate: (Sx) the proportion of individuals of age X that survive to the beginning of the next age class, (X+1).
    • Sx= Nx+1/N
  • Different species have different mortality curves.
    • Type 1: most die late in life (humans)
    • Type 2: die at uniform rate-likelihood of dying is constant
    • Type 3: most die at young age (sea turtles)
  • Fecundity (Fx) is the average number of offspring produced by a female while she is in a certain age class (per capita rate)


  • 1000 female fish as newborns are marked (cohort approach-following these organisms throughout life)
  • One week only 200 alive
  • At two weeks 40 alive
  • At 3 weeks 8 alive
  • At 4 weeks none were alive
  • Each female fish reproduces 200 eggs in their 4th week


X (week) Nx lx (Nx/N0) Sx (Nx+1/Nx) Fx R0
0 1000 1.0 (from birth to birth) 0.2 0 0
1 200 0.2 0.2 0 0
2 40 0.04 0.2 0 0
3 8 0.008 0 200 (0.008)(200)
4 0 0
= 1.6


  • R0 is the net reproductive rate = ∑lxFx
  • R0 > 1 indicates a growing population
  • Population projections: use time step table
  • PVA: population viability analysis

Matrix Models:

  • Age specific survival and fecundity X vector of individuals within each age structure
  • Fecundities are top row
  • Survival rates are elements of sub diagonal


Age 0 Age 1 Age 2 Age 3
Age 0 F0 F1 F2 F3
Age1 S0 0 0 0
Age 2 0 S1 0 0
Age 3 0 0 S2 0


  • Age Is not always the best indicator of demographic change.
  • Vital rates might be related to size or developmental stage.
  • Stage-Based Matrix Models


  • Seed → seedling → small adult → large adult
  • Egg/hatching → small juvenile → large juvenile → subadult → adult
  • Egg → pupa → cocoon → butterfly
  • Calf → immature female → mature female ⇔ mature female with a calf (reversal and changed can occur)

Example of matrix modeling:

  • Invasive bullfrogs
  • Negative effect on native fauna
  • Focus on removing tadpoles and breeding adults
  • Sensitivity Analysis: lambda was most influential by % tadpoles who metamorphize fastest. Concluded that removing the organisms before metamorphosis and the adults will fix the problem.


  • (-/-) interaction. The negative effect on each individual on the other because they share a limiting resource.
  • Scramble Competition: divisible resources
  • Contest Competition: resources cannot be divided between all of the individuals
  • Exploitative Competition: Negative effects on both species are due to their effect on the shared resource. Indirect effect due to effect on the abundance of the shared resource.
  • Interference Competition: physically interact with one another
  • Strength of competition between two species will depend on how limiting the resource is. How much overlap in resource use is there between species.
    • Density dependence and genetic diversity
    • Character displacement: niche portioning with a genetic component. Two species are found in sympatry where they mix but are allopatric in the rest of their habitats. Where species do not overlap in habitat will be more genetically similar but the populations that do overlap will be different à allows for variation in resource use and decreased competition/sharing of resources. A shift in the genetic composition due to competition (selection acts to reduce the strength of competition.
      • Evolutionary change in species traits that act to minimize competition.
    • Gausse’s Principle of competitive exclusion: species occupying the same niche cannot coexist in a stable environment. One is better adapted to access the resource. Often seen as a negative (inverse) relationship in abundance.
      • Gradient in density
      • Patchy/clumped
      • Apparent competition: two prey species negatively affect each other because they are a resource to a shared enemy.
    • Competitive Release: change in distribution when separate and together. Distribution of species changes when a potential competitor is removed.
    • Competition effects:
      • populations:
        • Abundance/density
        • Distribution
        • Demographic
      • Individuals:
        • Behavioral-feeding, foraging
        • Physiological- growth and reproductive
        • Morphological- body size and biomass

Modeling Competition:

Lotka and Volterra

Basic Approach:

  1. Derive an equation for population growth in the presence of competition
  2. Define the values at which population growth stops: set the equation to zero, plot isoclines (line of sameness) in phase space.
  3. Understand the zones, predict the outcome. If one species’ N goes to zero then you can conclude that there is competitive exclusion. Determine relative population size of each species. Plot the two isoclines together. IF the isoclines do not cross…the species on the outside always outcompetes the other.

Derive Equation:

  • Population growth with negative density dependence: logistic equation
    • dN/dt=rN(1-N/K)
  • Population growth with negative density dependence and competition: Lotka-Volterra equation
    • dN1/dt=r1N1[1-(αN2+N1/K1)]
    • dN2/dt=r2N2[1-(βN1+N2/K2)]
  • α = the competition coefficient
  • β = competition coefficient

Set the equations equal to zero

  • 0= 1 – (αN2+N1/K1)
  • 1= (αN2+N1/K1)
  • K1 = αN2+N1

The equation of the line that describes the isocline for species 1:

N2 = (-1/α) N1 + K1

Y  =   m   X     +   b

Isocline for species 2:

N2 = K2 – βN1

“Isoclines” by WikiMedia Commons (CC BY-SA 4.0)

  • In an unstable coexistence, “r” per capita population growth rate has an effect on the outcome.
  • Two species cannot use the same limiting resource in the same way and coexist in a stable environment indefinitely.
  • When the strength of interspecific competition is weaker (smaller βand α) than intraspecific competition, then coexistence in more likely.
  • Outcome of competition is determined by the relationship between the two species’ carry capacity (K) and the competition coefficients, not the per capita growth rate (r) or initial population sizes (N)


  • (-,+) immediate consumption of one organism (prey) by another (predator), predator individual consumes many prey individuals in its lifetime.
  • Effects of Predation on Prey:
    • Population response: change in population size/density, distribution/range, age/size/genetic distribution, change in population dynamics (population regulation).

Modeling predator-prey dynamics:

  • Without a predator the prey will grow exponentially
  • For Prey:
    • dN/dt = rN – (predation rate)( # predators) (N of prey)
    • 0 = rN – (predation rate)( # predators) (N of prey)
    • rN = (predation rate)( # predators) (N of prey)
    • # of Predators = r/predation rate
  • Without prey the predators will experience population decline.
  • For Predators:
    • dN/dt = (conversion rate)(N of prey)( N of predators) – (predators)(death rate)

Create Equation:

  • Prey: dx/dt = αx – βxy
  • Predator: dy/dt = δxy – γy
  • αx= exponential growth of prey species
  • βxy= predation rate by predator
  • δxy= consumption of prey
  • γy= death rate

Set Equal to 0

  • 0 = αx – βxy
  • Y= α/β (zero growth for prey species) – prey abundance is dependent only on the predator abundance
  • Predator population is dependent on prey abundance
  • Cyclic changes in abundance


Huffaker’s Mites Experiment:

  • Introduced the prey mite onto orange and then a few days later he added a predator.
    • Predators rapidly consumed all prey
  • Created patches in the orange by covering them. The predator mites ate all the prey mites.
  • Then created barriers and found some oscillations in dynamics for 7 months before the predator consumed all the prey.
  • Coexistence was not maintained.
  • Conclusions:
    • Oscillations are seen in predator-prey relationships
    • Very difficult to create coexistence
    • Factors that lead to longer oscillations: increasing dispersal of prey and slowed dispersal of predators, smaller surface area, increased DD of prey, barriers and refuge
    • Space is critical

“Huffaker’s Balancing Act” by Ecomotion Studios (Standard YouTube License)

Isle Royale:

  • Predator prey dynamics in a natural island system
  • Moose have been present for over 100 years
  • Wolves were introduced in 1950 due to ice bridges
  • 1958 biologists began studying the island.
  • Data shows that as moose populations increase the predation rate decreases. This is a positive density dependent relationship, an allee affect.
  • Low populations of moose are more vulnerable to predation events.
  • An increasing predation rate negatively affects the moose population growth rate. Supports the theory that wolves have a top-down effect on the moose density.
  • Predator preference determines the predator’s effect on the community and population dynamics.
    • Keystone predation
    • Switching predators
  • Studies showed that wolves typically prey on the calves and old moose.
    • Wolves affect dn/dt of moose due to consuming calves.

Adaptions from Predation Events:

  • Predation can affect the traits of individuals, both within their lifetimes and in forms of selection across generations.
  • Adaptations in prey species to avoid predators – structural defenses
  • Silica on grass as a defense against herbivores
    • Predators will adapt such as horses who feed on the grass- teeth continually grow throughout the lifetime.
  • Camouflage: cryptic coloration (occurs in both prey and predators)
  • Batesian mimicry: a harmless animal looks like a poisonous/dangerous animal
  • Mullerian mimicry: a poisonous species looks like another poisonous/dangerous species
  • Chemical defenses: bright coloration (aposomatic) indicates poisonous species – can be mimicked by other species.
  • Secondary metabolites in plants: phenolics, terpenes, and alkaloids (cafferine, cocaine, nicotine, morphine) to kill off predators
  • Constitutive defenses: the defense mechanism/trait is always expressed
  • Induced defenses: trait is only expressed if/when there a cue/signal
    • Nicotine acts like acetylcholine and kills insects. Clipping/grazing on the tobacco leaves induces the roots to produce more nicotine and send them to the leaves.
    • Induced responses are common in plants due to their relationship with grazers who do not completely kill the plant. Animal predators kill the prey immediately.
    • They can be reversible or irreversible traits
  • Why aren’t all defenses constitutive?
    • Life history theory: a trait will become fixed in a population unless there is a cost associated with it.
    • There must be reliable cues
  • When a plant is grazed on (tissue damage), hormones are released to signal the presence of a grazer and the plant will upregulate its defenses. The wound on the plant will release VOC (volatile organic compounds) that signals to other plants to increase their own secondary metabolite.
    • There is also communication between plants via mycorrhizal networks (within the soil). Fungal species attaches to the roots and connects them to other plants.
    • The VOC can also signal to an enemy of the grazer- attract the predator of you predator

Facilitation and Mutualism:

  • Facilitation: a positive interaction between two individuals
  • Mutualism: two different species facilitate each other, typically involved the exchange of protection for resources (Ants that farm aphids, lichens)
  • Facilitation is strongest when there is abiotic stress.
  • Consumer pressure and abiotic stress are inversely related
  • Associational Defense is highest in response to large consumer density. (Safety in numbers)


  • Individuals of different species, living in the same place at the same time, some interact strongly with each other, some do not.
  • Frederic Clements: “organismic” view”, community is like a super organisms, tightly bound functional unit with discrete boundaries, that communities were predictable due to conditions. Deterministic-the output is due to the factors of the input.
  • Henry Gleason: “Individualistic”, communities are fortuitous associations of species, adaptations allowed them to live under particular biotic/abiotic conditions found in a place, the role of chance
  • Robert Whittaker (1970): environmental gradient analysis and tested mountain ranges, the Gleason model was shown to be more accurate.
  • Ecotone: there is a boundary between 2 community types, set by an abrupt change in abiotic conditions
  • Succession: the change is species composition over time after a disturbance
    • Primary Succession: sequence of communities developing on a newly exposed habitat devoid of life and soil
    • Secondary Succession: recovery of a disturbed site that has soil and perhaps seeds
    • Chronosequence: space for time substitution
    • Pioneer Species: first stage in succession
    • Climax Community: final stage of recovery of an ecosystem
  • Disturbance: an abiotic event that kills or damages some individuals but may allow others to grow and reproduce.
  • Succession is explained by:
    • Type of interaction between early and late stage prganims
    • Which species can establish directly after the disturbance
      • Facilitation Model: (Clements) only pioneer species are able to survive the early abiotic conditions. These species modify the environment so that other species to establish. Later species typically are better competitors and outcompete the pioneers.
        • Primary succession on a rock exposed by glacier recession. Lichens live on the rocks which allows for mosses etc.
      • Tolerance Model: any species can establish (no pioneers, just good dispersers), there is no facilitation between species. There is a sequence of change reflects who gets there first and who can outcompete those who have been established. Stable when no new species can invade. Later species are better competitors and can tolerate lower resource levels.
      • Inhibition Model: any species can establish, no facilitation. Early colonists make the habitat less suitable for others. Priority effects- dependent on who got to the habitat first, replacement occurs when the species dies or there is a disturbance.
        • Marine fouling organism. Bryozoans inhibit colonization by sponges and tunicates.
        • Alternate stable states: when two ecological communities can form under very similar environmental conditions.
      • Stability: the ability of an ecological community to defy change (resistance) or rebound from change (resilience) after a disturbance.
        • Threshold– tipping point, change in abiotic factors that lead to a change in community structure.
        • Hysteresis: different pathways to create biological communities.

Species Diversity and its Effect on Ecosystem Function and Stability:

  • Diversity has been observed to produce more productive and stable communities.
  • Effect of Diversity on Productivity: Tilman Cedar Creek LTER experiment
    • 168 9X9 meter plots
    • Treatment: 1, 2, 4, 8, 16 different savanna species planted into the plots
    • Weeded to maintain the treatments over time
    • Primary Productivity: accumulation of biomass, rate that new plant growth is produced
      • Study saw that over time there is an increase in biomass, plots with multiple species saw greater increase in biomass.
    • Stability: study saw that the more diverse plots were stable over time
      • WHY?….
    • Complementarity: different species vary in traits and how they utilize resources. This creates less competition for resources. Traits are complementary to one another.
    • Portfolio Effect: diversity of species stabilizes productivity of a community during changing environmental factors. Monocultures can be wiped out due to a large negative disturbance.
    • Sampling Effect: diverse plots have a greater likelihood of containing species that are inherently better suited to an environment/have a greater productivity rate.

Diversity within a Population:

Plant Genetic Diversity Predicts Community Structure and Governs an Ecosystem Process

  • By Crutsinger et. al.
  • Genetic Diversity affects community structure → richness of arthropods; herbivores/predators
  • Genetic Diversity affects ecosystem function → ANPP above ground annual primary productivity, the measure of the annual plant growth
  • Solidago altissi was studied à differential genotypes for the plant, reproduces clonally.
    • 21 genotypes of the plant
  • Experimental Design:
    • Plots with 12 individuals
    • 1, 3, 6, or 12 genotypes in each plot
  •  Results:
    • Monoculture plots showed greater variability biomass, herbivore richness, and predator richness
    • Diverse plots showed greater species richness in consumer species
  • Discussion:
    • Many Individuals Hypothesis: Greater genetic diversity lead to greater productivity, and increased herbivore and predator richness. There were greater population sizes and increased consumer species richness. Rarefication of the data supported this hypothesis.
    • Resource Specialization Hypothesis: Increased plant diversity leads to an increase in the types of available resources which will lead to an increased abundance of specialist consumers.

Foundation Species:

  • A species that creates a habitat, a species that creates biogenic structures
  • For Example: sea grass, kelp forests, and coral reefs
  • Genetic Diversity of these species creates ecosystem stability/productivity

Fragmentation and Habitat Loss:

  • Effects on Species Diversity: Large creatures/predators are more likely to be disrupted/lost
  • Heterozygosity: genetic diversity within individuals- genes that contain alternative forms of alleles
  • Fragmentation tends to  diversity between population because it can decrease genetic flow but within a population there is a decrease in genetic diversity.
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The Cat’s Meow

“Newly Adopted Kitten” by Ben N (CC BY 2.0)

A small kitten will meow at its mother to signal to her that he is hungry or cold. But as he grows his meows will change to the more advanced manners of communication such as tail and ear flicking that older cats do. Adult cats do not meow at each other. They will hiss, growl, or yowl at one another to indicate anger or fear or a desire to mate. Cats have modified their behavior with humans however, since we are unable to understand the nuances of each ear twitch cats will actually meow at humans during kittenhood and throughout adulthood.

A cat’s meow is an active effort to acheive communication with humans. Often cats will meow to get attention, food, or to be let outside. They will often meow if they are lonely as well so that you spend more time with them. Cats also make other noises as well such as purring and thrilling/chirrups to indicate that they are content. Thrilling has also been suggested to be form of greeting to humans as it is a blend of a purr and soft meow. Maine Coon cats have been known to chirp at birds as well. These noises that they make are not actual communication in the sense that we think of. Humans use words to get ideas across but meows are not like that. Their tone, pitch, length, and frequncy is not exact words or demands but merely a noise they have learned will elicit a response from their owner. Through the thousands of years that cats ghave been at our side, they have evolved responses to interact with their human counterparts.

“Cat” by Stefan Muth (CC BY-SA 2.0)

So what noises can cats make? There are over 100 different noises that our feline compnaions can make. This impressive becuase dogs only make about 10 noises and cats specifically use the majority of these noises to interact with humans. Aside from mewoing, growling, hissing, purring, thrilling, and chirping, cats can also caterwaul which is a wail that they make when attempting to attract a mate. To hear these interesting noises check out this website.

Another reason a cat will meow or be vocal is when it is in pain. A cat’s pain tolerance and ego are high so if the cat is crying and groaning frequently, will not walk around or does so infrequently, is not eating/drinking, or appaers to be in distress a visit to the vet would be a a good idea. Cats meow to indicate needs, desires, fear, and pain. It is important for humans to pay close attention to and learn what they sounds and behaviors indicate so that they may interact more effectivley with their pets.

“Cats” by test_t51 (CC BY 1.0)

Housecats and ferals meow….so do large cats? Well, it depends on the species. Lions roar and purr. A tiger cannot roar or purr but they chuff. Caws are aggressive calls, such as a low growl of  a lynx that are done to fend off other lynx in their territory. This caw is an aggressive display that prevents a physical  altercation that would ultimately result in the death of one cat, it is less energetically costly to caw at a threat to estabish stregth and dominance. Lynx are also known to wail and bark. The variety of sounds that not only housecats but lareger, exotic species can make demonstrates the extensiuve evolutionary development of feline vocalization. While we may not understand every noise, cat lovers everywhere continue to learn and interact with their fluffy companions.

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Nature vs Nurture

The development of an organism is an interactive process between genes and the environment

As an organism develops….

  • Genetic information interacts with changing internal and external environemnts
  • Genes become turned on and off by signals (expressed/repressed)
    • Signals are internal/cellular/chemical or external environmental stimuli (neurochemical/hormonal)
  • These interactions alter the assembly of the organism- its neural networks as well as other aspects of its physiological/anatomical systems
  • Central Dogma: DNA  → Transcription →  RNA  → translation → protein →  gene expressed

“Honey Bee (Apis mellifera linnaeus)” by Jim (CC BY 2.0)

Development of worker behavior in honey bees:

  • Variation in tasks is age dependent (cleaning, feeding, packing pollen, foraging). Younger bees work within the nest as nurses and then transition with age to become foragers.
  • Gene activity varies in the brains of “nurse” bees and “foragers”. Opposite gene activation patterns were observed in the analysis of their gene expression.
  • The Juvenile Hormone (JH): low concentrations are found in nurse bees, there are increased levels in the forager bee. A nurse bee treated with JH will begin to forage. Remove the JH glands of a forager and it will revert to nursing behaviors.
    • Hormonal influence on gene expression.
  • JH gene boosts at about 3 weeks. This is activated by the social behavior of their environment.
    • In the presence of foragers, the nurses had lower levels of JH
    • In the absence of foragers, the nurses had higher levels of JH
    • When older bees are added the colony, the young bees remain nurses. The presence of many foragers inhibits JH expression.
    • When many young bees are added to the colony, the resident young bees will transition to forager bees and the JH gene is expressed.
  • Older bees inhibit the transition to forager in others by manufacturing a compound called ethyl oleate. Secreted by glands within the crop.
    • An Ultimate Explanation: to ensure that there are enough nurses and foragers within the colony to sustain the hive. An adaptive adjustment to the ratio of nurses and foragers.

Environmental Influences: 

  • Environmental Factors are critical for every element of gene expression within organisms.
  • The environment supplies the molecular building blocks (RNA bases, amino acids, etc.) that are essential for DNA translation.  Sources include food and the atmosphere.
  • Gene Expression → environmental factor → gene expression → environmental factor
  • The combination of a constantly changing internal and external environments of the organism that influence the expression of genes.

“DNA is both inherited and environmentally responsive” -Gene Robinson

“Tea for Cockatoos” by Rob and Stephanie Levy (CC BY 2.0)

Begging Calls and Contact Calls in Galah and Cockatoo:

  • Reciprocal swap test for hatchlings: the babies that were placed in opposite nests will continue to do the begging call of its species but will make the contact call of the species that raised it.
  • Genes constructing the learning system may be responsible for these differences-the environmental influence of the types of calls that these birds can make.
  • Most traits are an interactive relationship between several different genes: polygenic
    • Learning is a polygenic trait
    • Genes are responsive to important sensory stimuli

“Galahs” by Ed Dunens (CC BY 2.0)


  • The result of gene-environment interactions
  • Imprinting of baby geese on the first thing they see after hatching
  • Genes construct learning systems and genes are responsive to important sensory stimuli
  • Cross-fostering has different imprinting effects in two related species of songbirds.
    • Female Blue Tit fostered Great Tit hatchlings and vice versa.
      • GT fostered by BT pair with BT
      • BT fostered by GT pair with GT
    • Environmental differences: a Polistes wasps learn to recognize nestmates from odors and facial markings

“Eastern Garter Snake” by Fyn Kynd (CC BY 2.0)

  • Genetic Differences: cause behavioral differences among individuals.
    • A coastal Californian garter snake (Thamnophis elegans) has differences in their diets in different populations.
      • Inland populations eat fish and frogs
      • Coastal populations eat banana slugs – genetic adaptations to handle the slime of the slug?
      • Take hatchlings (naïve individuals) raised in the lab fed with generic food. Then give them slugs to determine if the baby snakes will consume slugs.
      • Data showed that inland baby snakes did not eat slugs regardless of lack of experience with other food. The coastal snakes did eat the slugs when they were introduced. -suggests genetic differences
      • Inland snakes tongue flicked at tadpole extract but not slug extract. Coastal snake tongue flicked at both extracts. ~ an evolutionary hypothesis: Inland ancestral non-slug eating population migrated towards the coast and alleles for slug eating become more abundant in the coastal regions because of the abundance of slugs as a prey source.

“Mouse” by Jason Bolonski (CC BY 2.0)

  • Sometimes a single gene can have a large influence on a behavior that is expressed. This is due to cascading events on the cellular level to activate/deactivate other genes.
    • For mice, a single gene affects maternal behavior. The gene fosB is responsible for maternal behavior. Those without this gene will be neglectful.
      • The environment still affects maternal behavior
      • Cascading effects on other genes into the phenotypic behavior that is observed.
      • Environmental cue causes this gene to be expressed. The olfactory stimulation from her pups activates the gene.



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The Mystery of the Fainting Goat

 “Faitning goats vs Exercise Ball” by Peahill Farm (Standard YouTube License)

Myotonic goats, or more commonly known as the fainting goat, are a popular pet becuase of their hilarious fainting behaviors. This is due to a genetic condition called myotonia congenita. Although they are called ‘fainting’ goats, they remian conscious during the experience [1]. This condition is also found in other livestock and sometimes in humans. It is a recessive genetic disorder that affects skeletal muscles in the organims by mutating the CLCN1 gene and inhibiting chloride channels [2].  This gene is responsible for muscle contractions and relaxations, and it is thought that mutations in the gene cause the muscles to become tense during the ‘Fight-or-Flight” response.  Whenever this goat becomes starled by something they tense up and fall to the side. This condition has the potential to cause harm if the goat is on top of a structure when this occurs.

This is a maladaptive trait that would lead to the goat becoming prey in natural environments. These goats have been bred as livestock for their meat since the late 1800’s and with the rise of the internet have become an entertaining spectacle. They are believed to have come to North America from Nova Scotia and are found  primarily in Tennessee. By the late 1900’s these goats had spread to Texas and were being bred for their size and reproductive rates. The larger goats weighing up to 175lbs are selected for as meat while smaller goats are bred as pets  [3]. Many people enjoy these goats as meals while other enjoy chasing them and the laughs that follow as they topple over.

“Tennessee Fainting Goat” by The She-Creature (CC by 2.0)


[1] Gibbens, Sarah. “Why ‘Fainting Goats’ Really Collapse in Fear.” National Geographic, National Geographic Society, 16 Feb. 2017,

[2] NIH. “Myotonia Congenita.” U.S National Library of Medicine , 11 Apr. 2018,

[3] Walker, Ryan. “Myotonic or Tennesse Fainting Goat.” The Livestock Conservancy,



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The Domestication of Cats

“Cat” by Fung0131 (CC BY-SA 2.0)

Cats come in all sizes, some have been domesticated while others are wild animals. The differances between wild and domestic cats could shed light on the evolutionary pathway that has led to cats as human companions. Typically untrainable, cats would not have been selected for in early agricultural communites like dogs and horses were. The inability to get a cat to follow commands makes them practically useless as helpers.

It is hypothesized that cats became integrated into human society as they exploited early civilaztions that often became overrun with prey species such as mice. Humans tolerated the presence of wild cats as they began to incorporate themselves into the human world. The process is described as one of natural selection in contrast to the artificial selection that has created the domesticated dog. Through time and evolutionary adapatations, the more docile and agreeable cats were then transplanted by humans across the globe.

Domestic cats, F. silvestris catus, are a subspecies of cats that evolved from wildcats that had chosen to live in and close to human settlements like in the Fertile Cresecent. Genotyping of domestic cats has shown that they are derived from five lineages and can be traced back to F. silvestris lybicaFossils and ancient art places the domestication of cats at around 11,000-4,000 B.P [1]. These data also suggest that there was a singular domestication event that began the process.

“Elly” by H. Schofield (CC by 2.0)

Mitochondiral DNA analysis of domesitcated cats suggests that divergence from the wild cats occured in sympatry. There is a marked phenotypic divergence in behavior of domestics and their less tame wild counterparts. Genes that made wild cats better suited to urban lifestyles were selected for geographically and concurrantly with humans.  The great diversity in housecats can be attributed to geographic dispersal along the Fertile Crescent and the thousands of years of evolution towards an increase in domestic genes in cat populations that integrated themselves into human settlements. The human preference for tameness provided an avenue for the translocation of tame cats to new settlements as human expansion continued. The adorable cats that we now snuggle in our homes are the result of wild cat’s exploitative behaviors that evolved into tamenss with increasing human contact.


[1] Driscoll, C. A., et al. “From Wild Animals to Domestic Pets, an Evolutionary View of Domestication.” Proceedings of the National Academy of Sciences, vol. 106, no. Supplement_1, 2009, pp. 9971–9978., doi:10.1073/pnas.0901586106.

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Progress Update #5

“Male #3 in the experimenal tank” by H. Schofield (CC by 2.0)

Data was collected on 4/5/18 and 4/8/18. The trials were completed and the averages of the trials were calculated. The fish were slightly more active the second. The female stayed close to the divider and interacted with the males often.

Data Collection: The Completion of the Trials 

Side A: Focal Fish Side B: Bystander Avg. Gill Flares Avg. Tail Beats
Male #2 Nothing-self trial 40.33 15.33
Male #2 Male betta 13.167 4.417
Male #2 Female betta 1.33 5
Male #3 Nothing- self trial 26 8.667
Male #3 Male betta 7 2
Male #3 Female betta 6.667 11.667
Male #4 Nothing- self trial 8.33 3.33
Make #4 Male betta 15.889 3.778
Male #4 Female betta 8.33 9.33
Male #5 Nothing- self trial 3 1
Male #5 Male betta 11.22 3.778
Male #5 Female betta 1.33 6.667

Table 1: Averages from the self trials and crossed trials.. 

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Progress Update #4

“Male #3 gill flaring to the Female Betta splendens” by H. Schofield (CC by 2.0)

This data was collected 4/3/18 and 4/4/18. More male/male trials were completed and most of the male/female trials were completed. Each pair was tested 3 times for a total of 15 minutes under inspection. The experimental tank was used for all of these trials. Experiment side A housed the focal male and contained the mirror. Experiment side B housed the bystander. The pebbles at the bottom of the experiment tank were removed due to interference with the divider.

The female fish was placed on experiment side B for Male #2, #3, and #5. There appears to be a possible reversal in the behavior that the male preferentially displays. There were low levels of activity in all fish during both days of these trials. The female attempted to interact with each male that she was placed with. she displayed her tail fin and swam the length of the divider often. She faced toward the divider and often followed the male if he swam along the divider of the tank. When Male #3 was in experiment side A and the female in experiment side B, when he gill flared at her, she responded with a gill flare. Although it was not as impressive, she was able to extend her gills partially to puff them out.

Data Collection: The Introduction of the Female Betta splendens 

Trial # Experiment Side A Experiment Side B Gill Flares Tail Beats
1 Male #2 Male #3 31 5
2 Male #2 Male #3 35 10
3 Male #2 Male #3 37 5
Average: 34.33 6.66
1 Male #2 Male #4 3 0
2 Male #2 Male #4 12 5
3 Male #2 Male #4 7 4
Average: 7.33 3
1 Male #2 Male #5 6 2
2 Male #2 Male #5 13 4
3 Male #2 Male #5 10 3
Average: 9.667 3
1 Male #2 Female 1 4
2 Male #2 Female 1 5
3 Male #2 Female 2 6
Average: 1.33 5
1 Male #3 Female 6 10
2 Male #3 Female 5 13
3 Male #3 Female 9 12
Average: 6.66 11.66
1 Male #4 Male #5 14 1
2 Male #4 Male #5 21 2
3 Male #4 Male #5 16 1
Average: 17 1.33
1 Male #5 Female 1 5
2 Male #5 Female 2 8
3 Male #5 Female 1 7
Average: 1.33 6.66

Table 1: Crossed Trials with Betta splendens. Counts of gill flares and tail beats per five minute trial. Averages of each pair were calculated. 

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Proximate and Ultimate Causation

“Astronomy Evolution 2” by Giuseppe Donatiello (CC0 1.0)

  • Physiological adaptations and evolutionary history of the species.

Proximate Causation: a nervous system component to create a preference.  For exmaple, taste bud receptor create a preference for sugary foods due to the carbohydrate energies that they provide. Send neorons to the brain to induce a preference (neoronal). Short term, physiological explanations for behaviors.

  • Genetic Components-developmental mechanisms influence the assembly of an animal and its internal components, including the nervous/endocrine systems.
  • Neuronal Components-hormonal mechanisms develop within an individual within a lifetime. Influences behavior.

Ultimate Causation: long term, evolutionary adaptations as it is affected by descent with modification from ancestral species.

  • Adaptive Value: a behavioral trait as affected by the process of evolution by natural selection.
  • Example: mate guarding to ensure that all of a females offspring will be sired by the male.

Examples of causation:

“Prairie Voles” by theNerdPatrol (CC by 2.0)

Monogamy of Prairie Voles: neural stimulation through vasopressin is induced when the male spends time with a female- he receives positive neural rewards.

  • Proximate cause: avpr1a gene codes for V1a protein receptor– the expression of the gene influences the male to spend more time with the female, more vasopressin is then released.
  • Flow Chart:
    • The History of the Vole
    • The Internal Changes

Previous evolutionary history in the lineage leading to the prairie vole  –>  the spread of adaptations by natural selection in previous generations of the vole –> the genes that have survived to the present prairie voles –> Developmental system of young voles –> physiological system of adults, including the brain –> Behaviors including mating behaviors are influenced            –> contribution of genes to the next generation, the reproductive success of individuals  –> ev olution by natural selection continues.

“White-Crowned Sparrow” by Irene (CC0 1.0)

White-crowned Sparrows of the same species develop different dialects in different populations.

  • Causes?..
    • Possible genetic differences may affect the neural mechanisms
    • Environmental differences in Alaska and Washington may affect the experience and learning in the young males to influence their singing behaviors/dialects.
  • Research that was done:
    • Raised white crowned sparrows in the lab from the Marin and Berkeley populations.
      • Some raised in isolation- they only twittered
      • Some listened to tapes of adult male songs at 10-50 days:
        • Started singing at 150 days
        • Full song by 200 days
        • Sang the dialect that they heard, regardless of which nest they came from.
      • The data supported the idea that the young males were learning the songs through their environmental surrounding.
      • Other experiments showed that:
        • Deaf birds that could not hear themselves sing, did not mimic the song correctly. Shows the importance of hearing oneself sing.
        • Lab raised, isolated white crown sparrows will not sing songs of another species. Will only twitter.
          • Genetic composition within sparrows construct the learning system, are responsible for physiology.
        • Young white crowned sparrow can selectively store white crowned acoustical information while ignoring the songs of other species.
        • Male birds have larger song system nucleus than the female birds. The song system is called the RA and is a region in the brain that has measurable amounts of aldehyde dehydrogenase.
          • When birds listen to longer songs, there tends to be an increase in the RA size of that bird.
          • Social learning is powerful.
        • Proximate mechanisms include neurophysiology and genetic activity:
          • Part of the brain where song memories are stored
          • Part of the brain that controls sound production
          • Neural mechanisms involved in song matching
          • Flow Chart:

Key sensory (environmental) inputs –>  gene activity  –>  changes in biochemistry  –> alters neurophysiological mechanisms (song control system) –>  learning.

“Parrot” by D Coetzee (CC0 1.0)

Song Learning in Birds:Two phylogenies of song learning in birds: hummingbirds and parrots/passerine songbirds.

  • If all three of these groups were derived from a common ancester: they would have similar song control systems. Studies showed that the three groups are very similar in the RA suggesting a song learning common ancester that was lost in other groups of birds. Is more likely than convergent evolution.
  • “Hummingbird” by C Watts (CC by 2.0)

    Disadvantages to learning to sing: learning  a dialect and multiple songs is a time and energy investment.

  • Develop adaptive dialects that can be recognized easily by conspecifics so as to be more effective in a particular habitat.
    • There are differneces in Great Tit birds singing in dense forrests and open woodlands.
  • Song Matching to a Social Environment: repertoire matching allows neighbor recognition and variation in communication. The territorial success of a male depends on how many different song types he shares. The response to the focal bird will influence the future interactions between the birds.
  • Males that learn songs of particular dialects may be more attractive to females.
    • Females get information about his developmental history and suitability to a particular habitat.
      • It was found that females chose males who could copy their tutor more often than males who could not.
    • Nutritional stress in the early stages of life will affect the song learning ability of male swamp sparrows.

“Black-Crested Titmouse” by Andy Morffew (CC by 2.0)

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