Community Ecology: Predation and Herbivory (chapter 14)

Community Ecology

• A community is defined as a biological community consisting of interacting species living in a defined area.

  • It exists at the spatial scale between populations and ecosystems (biomes).

Species Interactions

• Species in a community interact constantly, affecting the fate of populations.

• Interactions can be assessed based on their fitness benefits:

  • Positive Interaction (+): Benefits one species without harming the other.

  • Negative Interaction (−): Harms one species while benefiting the other.

  • Neutral Interaction (0): No significant effect on either species.

Coevolution

• Coevolution occurs when two or more species evolve together due to their ecological interactions.

  • Example: Insects and flowering plants, where many plants rely on insects for pollination.

Types of Species Interactions

Short-Term & Long-Term Impacts:

• Short-Term:

  • Competition reduces population size of both species or leads to competitive exclusion.

  • Impact on prey populations depends on their density and defenses.

• Long-Term:

  • Coevolution leads to niche differentiation and adaptations in traits of both species involved.

Predation and Herbivory

• consumption is a +/− interaction where one individual consumes another for food.

  • Three primary types:

  1. Herbivory: Consumption of plant tissues by herbivores.

     • Grazers and Browsers: creatures that feed on herbaceous plants

  2. Parasitism: Consumption of small amounts of host tissues by a parasite.

     • Example: Trematode parasite Schistosoma mansoni.

     • does not kill its host

  3. Predation: Killing and consumption of another individual by a predator.

Characteristics of Predators and Parasites

• Predators:

  • Tend to kill and consume multiple prey individuals.

  • Often larger than prey.

• Parasites:

  • Typically do not kill the host; often smaller and consume less compared to predators.

• Micropredators:

  • (e.g., vampire bats) consume multiple hosts but do not kill them.

    • it doesnt kill the cow, and it isnt bigger than them

Effects of Predation

• Studies demonstrate significant influence of predators on prey populations, such as in lizard vs. spider studies.

• Effects of invasive species like the brown tree snake on island fauna are notable.

• Parasitoids further illustrate complex predator-prey dynamics by limiting prey abundance.

  • they ALWAYS kill their host

• introduced, exotic, or non-native species are introduced to a region of the world where they have not historically existed

  • invasive species are introduced species that spread rapidly and negatively affect other species

Mesopredators

• Mesopredators: relatively small carnivores that consume herbivores (e.g., coyotes,

  weasels, feral cats).

• Top predators: predators that typically consume both herbivores and predators

  (e.g., mountain lions, wolves, sharks).

  • Humans have reduced or eliminated the world’s top predators, which has allowed

Herbivory and its Impacts

• Herbivores can substantially influence plant community structure.

  • Example: Fencing has shown increased plant biomass when grazing is eliminated.

  • Changes in algal composition after sea urchin removal demonstrate herbivore impact.

Population Cycles

• Predator-prey relationships often exhibit synchronous population cycles.

  • Example: Snowshoe hares and Canada lynx have cycles of approximately 9-10 years.

  • prey pop increase → predator pop increase, followed by a subsequent decline in prey as predation pressure rises.

• Lotka-Volterra Model:

  • Describes predator-prey dynamics with equations detailing growth rates and interactions.

  • assumptions that are broken: does not take into account

    • responses by predator and prey populations to environmental changes, complex behaviors among species, or multi-species interactions that can significantly alter these dynamics.

Functional Responses

• Functional Response Types:

  1. Type I: Constant proportion taken until prey density does not increase.

     1. organism contonuously eats, no search time

  2. Type II: Slowing consumption at high prey densities due to handling time.

  3. Type III: Low consumption at low densities that increases with moderate to high densities.

     1. while doing that, im not reproduction

        • search image: a learned mental image that helps a predator locate and capture food

        • Predators may exhibit prey switching by changing their diet preferences to the more abundant prey.

        • Prey can easily find refuges to hide

numerical responses

• Numerical response: a change in the number of predators through population growth or population movement due to immigration or emigration.

  • Populations of predators usually grow slowly relative to populations of their prey, but the movement of mobile predators can occur rapidly when prey density increases

examples of adaptations

• Structural

  • Also called physical or morphological

  • It is a change in the physical or structural appearance of an organism.

• Physiological

  • It is a change in the production of either a noxious substance or an attractant

• Behavioral

  • A change in the behavior of an organism that aids its survival

Predator Hunting Strategies

• Predators that exhibit active hunting strategies spend most of their time moving around looking for prey (e.g., birds foraging on lawns for worms).

• Predators that exhibit ambush (sit and-wait) hunting strategies lie in wait for a prey to pass by (e.g., chameleons waiting for insect prey).

• Stalking is a combination of sit and wait and active hunting.

Defenses Against Predators

• Prey evolve various defenses such as camouflage, mimicry, physical defenses (armor, chemical), and behavioral strategies (fight back, group together)

  • Mimicry Types:

  • Müllerian: Harmful species resemble one another.

  • Batesian: Harmless species resemble harmful ones.

• apostomato: a type of mimicry where species with no protective attributes benefit by resembling harmful species, thus deterring predators.

Defense Costs

• Defensive traits can be costly, resulting in trade-offs in growth and reproduction.

  • Example: Coloration in ladybugs indicates taste and requires energy to produce.

Conclusions

• Predators and prey continuously evolve strategies and defenses leading to complex ecological dynamics.

• Conservation of predator populations is critical for maintaining natural ecological interactions and balances.

stocasticity

• = random

  • not every individual is the same

    • ex: some mothers are more fertile, some fathers are assholes (LOL)

  • you should take randomness into account when studying community dynamics, as variations can lead to different outcomes in predation and herbivory rates.

• meta population

  • subpopulations with large populations on a large scale

  • meta populations: