Study Notes on Predator-Prey Interactions and Functional Responses

Types of Feeding Strategies:
- Carnivores: Organisms that consume animals.
- Herbivores: Organisms that consume plants.
- Omnivores: Organisms that consume both plants and animals.
Predators may be classified as:
- Specialists: Predators that specialize in certain types of prey.
- Generalists: Predators that consume a variety of prey.
- Even generalists usually have preferences, which can lead to phenomena such as prey switching.

Cost: Refers to energy and other resources spent to find, capture, and handle prey.
Benefit: Gained energy/resources from consuming prey.
Search Image: A behavioral selection mechanism that:
- Increases the efficiency of the search for prey.
- Specifies which abundant prey is worth capturing.
Factors affecting prey choice include:
- Abundance: How plentiful the prey is.
- Difficulty of Finding: How difficult it is to locate the prey.
- Difficulty of Capturing: How hard it is to catch the prey.
- Handling Time: The time required to consume the prey after capturing it.

Predators that consume prey with short handling times should behave as generalists.
Predators that consume prey with longer handling times are likely to be specialists.
Productive environments tend to favor specialists due to more reliable food sources.

Functional Response: Refers to the change in prey consumption rate of an individual predator in response to changes in prey density.
Types of Functional Responses:
- Type 1 Functional Response Curve: Exhibits a linear increase in prey consumption with density because the search and handling time are minimal.
- Type 2 Functional Response: Shows a decelerating increase in prey consumption as prey density increases due to handling time limits. Components include:
- Rate of successful search.
- Time available for hunting.
- Time spent handling prey after discovery.
- Hunger level of the predator.
- Type 3 Functional Response Curve: Exhibits low initial consumption rates that increase with higher prey densities as learning effects and prey switching occur.

Numerical Response: Refers to the increase in predator density in response to an increase in prey density due to increased reproduction and/or dispersal of predators into high-density areas.
Population dynamics of predation illustrates that:
- Predator-prey interactions can affect the abundances of both predator and prey populations.
- Predation results in prey mortality.
- Predation supplies resources that enable new predators to be produced.
- Predators may struggle to survive without adequate prey (food).
- However, the prey population dynamics may be minimally affected if:
- The prey killed is insignificant relative to the overall population.
- Predators are capable of utilizing alternative prey sources.

Case Study: Historical fluctuations in lynx and snowshoe hare populations show long-term cycles in population density.
- These cycles led ecologists to investigate the impact of predation on populations of various northern animals.

Lotka-Volterra Equations relate to predator-prey or parasite-host populations and are defined as follows:
- For prey or host population growth:
- $\frac{dN}{dt} = rN - pNn$
  - Where $N$ is the prey population size, $r$ is the exponential rate of increase for the host, $p$ is the predation rate per capita, and $n$ is the predator population size.
- For predator or parasite population growth:
- $\frac{dN}{dt} = cN - dP$
  - Where $c$ is the conversion rate of prey to predator offspring and $d$ is the predator death rate.

Predictions from these models:
- The examination of the model at equilibrium results in zero isoclines.
- Oscillations of prey and predator densities are expected.
Real Populations Behavior:
- Actual predator-prey interactions may behave according to the predictions
- Yes: Certain interactions support theoretical expectations.
- No: Some factors complicate predictions, including:
  - Lack of interaction of prey with food.
  - A linear relationship between predator and prey numbers.
  - Density-independent predator mortality rates.
  - Predator reproduction being functionally tied to the amount of prey consumed.

Population Fluctuations: Examined case studies such as:
- Azuki Bean Weevil and its larval parasite (braconid wasp).
- Tawny Owls and small rodents exhibit similar dynamics.
Importance of Prey Refuges: Lab studies emphasize:
- Environmental heterogeneity can support prey.
- Large prey populations can lead to predator satiation.
- Larger prey body sizes may also offer survival advantages against predation.