EEB324 Module 2

What is competition?

An interaction where two species require the same resources leading to a lowering in both of their fitness’s

What is exploitative competition?

When two organisms are using the same resource, one uses the resource up faster than the other

What is interference competition?

When individuals physically prevent others from accessing a resource

What is pre-emptive competition?

Occurs when an early-arriving species monopolizes a resource and/or space

How can competition be studied?

Pairwise competition where species are studied in pairs or diffuse competition where all species in a community are studied

What are stabilizing differences?

Species that coexist stably occupying different niches

What is the effect of stabilizing differences on intra vs. inter specific competition?

These differences can result in intraspecific competition having fewer fitness costs than interspecific competition

What is a competition coefficient and what does it represent?

This describes the effects of species 2 on species 1, relative to the effects of species 1 on itself

How do you solve a Lotka-Volterra competition equation

Multiple the number of individuals in species 2 by by the competition by the coefficient of species 2 on species 1. Subtract that by the carry capacity for species 1 by the number of individuals of species 1. The result of that equation is divided by the number of individuals in species 1. Separately multiply the growth rate for species 1 by the number of individuals of species 1. Multiply those results together to get the change in population growth over time.

What is character displacement, and how does it differ from disruptive selection?

It is a pattern where populations of two species are more dissimilar when coexisting (sympatric) than when in different regions (allopatric). Unlike disruptive selection that looks at traits in the same species, character displacement compares a trait between two species

Give two reasons why can character displacement be difficult to confidently identify in nature

Trait divergence could have happened before coexistence and its hard to rule out environmental factors causing the changes

What are the six characteristics for defining character displacement?

Phenotypic differences between the populations should have a genetic basis, the pattern should be replicated across multiple populations, the greater differences in sympatry should be due to evolution that occurred in sympatry not environmental filtering that occurred during colonization, trait differences must reflect difference in resource use, sites of sympatry and allopatry should be otherwise similar, individuals with similar phenotypes must be demonstrated to compete

Given one of the six “requirements” for diagnosing character displacement, describe the data or experiment you might use to test that requirement

If you are using a species arrival to test character displacement, setting up an experiment where an experiment runs for a few generations in the respective environments then bring them out and observing their offspring could help identify if the traits being observed have a genetic basis.

Under the theory of island biogeography, what are our predictions for large vs. small islands, and near vs. far islands, and why?

The smaller an island is the more likely it is to face extinction as stochastic fluctuations will likely affect the islands smaller population more. Further islands are also more likely to face extinction as there is a lower rate of immigration

Why is predation important in evolutionary ecology?

It’s a major source of natural selection for predator and prey and predators affect the rate of increase* of the prey population (and vice versa)

Explain in general terms why predators and prey may undergo population size cycles

The two are very intertwined where the growth of one population leads to the decrease of the other. However this decrease leads to the other population to also reduce in size causing an increase in the others population

Given the Lotke-Volterra prey equation, explain what each term encompasses

For prey the equation is the exponential population growth subtracted by the total number of prey consumed per unit time. The exponential population growth is solved by multiplying the number of prey by the population growth rate. The total number of prey consumed is measured by multiplying the attack rate by the number of predator by the number of prey

Given the Lotke-Volterra predator equation, explain what each term encompasses

Fore predators the equation is the total amount of prey converted to predator biomass per unit time subtracted by the predator death rate. The prey to predator biomass is found by multiplying the conversion coefficent (how well prey is converted into predator biomass) by the attack rate by the number of predators by the number of prey

List some predator and prey traits that might experience selection in predator-prey interactions and explain their relevance

Traits that may be under selection in predators are ones used in catching prey such as sensory organs to better detect prey, speed to pursue prey, or claws/strength to catch prey. Meanwhile selected traits for prey focus on avoiding predators like blending into the background, mimicing toxic animals to deter predators, or speed to allow them to escape.

What differs parasitism from other types of interactions?

There is no obligate relationship between individuals as the parasite has a negative affect on the host with no vice versa

How parasite-host interactions can influence the genetic diversity of populations

Hosts adapt to have genetic variation to avoid these parasites while parasite evolve to have genetic diversity to overcome the host’s defense mechanisms

What is niche conservatism?

The retention of similar niches (and niche-related traits) over time within a species or among related species.

What does it mean for a community to be phylogenetically clustered vs. phylogenetically overdispersed

Phylogenetically clustered communities are part of a cluster of species that live in a similar habitat based on niche conservatism. Phylogenetically communities have a representative from each cluster in a different habitat

What does this graph represent?

A community that’s phylogenetically clustered

What does this graph represent?

A community that’s phylogenetically overdispersed

What are the other terms for niche conservatism vs niche liability

Phylogenetically clustered and phylogenetically overdispersed

If we assume abiotic conditions are the main factor affecting species occurrence, what can we infer about niche conservatism vs. lability from phylogenetic relationships within communities?

When traits are conserved across phylogeny as seen in niche conservatism, the species in the habitat will have similar trait values. However in niche lability, the traits then clustering will be variable.

Assuming traits are conserved, what is the expected effect of biotic filtering on phylogenetic relatedness in communities?

The harsher the environment, the stronger the environmental filtering making species more clustered and related

What observation sparked the Janzen-Connell hypothesis, and what explanations did researchers come up with to explain that pattern?

The observation was that trees make a lot of seeds but don’t disperse them far. Researchers came up with the idea that antagonists like predators and pathogen may be closer to adult trees meaning seedlings that grow near them are more likely to be attacked and not survive. Since antagonists are more abundant in areas with high victim density, areas where seedlings are most abundant may experience the most biotic pressure

What is facultative mutualism?

A relationship that is not needed or specific and can easily change to an antagonistic relationship

What is obligate mutualism?

Symbiosis or where the interactions are essential for survival

What is specialist mutualism?

Where species interact exclusively with each other

What is generalist mutualism?

Interactions are not exclusive with one species

Draw a diagram of a community that’s phylogenetically clustered

This is what it looks like

Draw a diagram of a community that’s phylogenetically overdispersed

This is what it looks like

Draw a graph of trait distributions/means in sympatry that suggest character displacement

This is what it looks like

Draw a graph of trait distributions/means in allopatry that suggest character displacement

This is what it looks like