BIOL 203 Lecture 14: Predation and Herbivory

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Questions and Answers

How do predators typically affect prey populations?

They have no effect on prey populations.

They increase prey populations above carrying capacity.

They reduce prey populations below carrying capacity. (correct)

They stabilize prey populations at carrying capacity.

What is a mesopredator?

A relatively small carnivore that consumes herbivores. (correct)

A predator that consumes only herbivores.

A large predator that has no natural enemies.

A top predator that consumes both herbivores and mesopredators.

What can result from the overharvesting of top predators?

Increase in mesopredator populations and decline in prey species. (correct)

Stabilization of herbivore populations.

Decrease in mesopredator populations.

Increase in top predator diversity.

What is the consequence of introducing a predator to a new area?

It can lead to the establishment of invasive species. Signup and view all the answers

Why is understanding predator-prey interactions important?

It is crucial for managing crop pests, game populations, and endangered species. Signup and view all the answers

What role do herbivores play in their ecosystems?

They can have substantial impacts by controlling dominant species. Signup and view all the answers

How do sea urchins impact rocky shore communities?

They control algae populations and maintain biodiversity. Signup and view all the answers

What observed outcome occurred after introducing a new spider species to islands with no lizards?

Spider populations increased tenfold. Signup and view all the answers

What happens to prey populations when both mesopredators and top predators are removed?

Prey populations often increase rapidly. Signup and view all the answers

What effect can top predators have in an ecosystem?

They can suppress mesopredator populations and enhance prey diversity. Signup and view all the answers

What is the primary function of handling time in predators that exhibit a type I functional response?

To determine how efficiently they consume prey Signup and view all the answers

Which hunting strategy requires a predator to actively search for its prey?

Active hunting Signup and view all the answers

Which of the following is a common behavioral defense seen in prey species?

Alarm calling Signup and view all the answers

What best explains crypsis in prey species?

Camouflaging to blend into their environment Signup and view all the answers

What type of mimicry involves a palatable species resembling an unpalatable one?

Batesian mimicry Signup and view all the answers

What might be an energetic cost of mechanical defenses in prey species?

Decreased reproduction rates Signup and view all the answers

How do some plants respond to herbivory without evolving defensive traits?

By tolerating the damage and regrowing quickly Signup and view all the answers

Which of the following is an example of a chemical defense mechanism in plants?

Sticky resins Signup and view all the answers

What phenomenon occurs when the interactions between two species influence each other's evolution?

Coevolution Signup and view all the answers

Why might chemical defenses be costly for prey to produce?

They decrease reproductive output Signup and view all the answers

Which of these strategies is NOT a way prey can evolve to avoid predation?

Increased activity Signup and view all the answers

What is an example of a structural defense in prey species?

Spines on porcupines Signup and view all the answers

What effect can aposematic coloration have on prey species?

Deter herbivores without chemical defenses Signup and view all the answers

What defines a food web in ecological communities?

A complex and realistic representation of how species feed on each other. Signup and view all the answers

What role do primary consumers play in a food web?

They primarily eat producers. Signup and view all the answers

How can harmful interactions like predation affect a community?

They may trigger a trophic cascade effect. Signup and view all the answers

Which statement about trophic levels is true?

Consumers are always positioned above producers in a food web. Signup and view all the answers

What are detritivores primarily responsible for in an ecosystem?

Breaking down dead organic matter into smaller particles. Signup and view all the answers

What defines trait-mediated indirect effects in ecological systems?

Behavioral changes in prey due to predator presence. Signup and view all the answers

What is a common challenge when illustrating food webs?

The high number of species interactions makes it difficult to represent. Signup and view all the answers

Which group of consumers are classified as scavengers?

Organisms that consume dead organic matter. Signup and view all the answers

How do omnivores fit into trophic levels?

They can occupy multiple trophic levels depending on their diet. Signup and view all the answers

What can a trophic cascade result from?

Changes in predator density affecting prey populations. Signup and view all the answers

Which of these is a correct description of food chains?

They provide a linear and simplified view of feeding relationships. Signup and view all the answers

What is a characteristic of density-mediated indirect effects?

They depend on population density changes in intermediate species. Signup and view all the answers

What describes the role of decomposers in a food web?

They recycle nutrients back into the ecosystem by breaking down organic matter. Signup and view all the answers

What can be inferred about guilds within a trophic level?

Guilds consist of species that feed on similar items, regardless of relation. Signup and view all the answers

Study Notes

Lecture 14: Predation and Herbivory

Lecture pertains to BIOL 203 on November 20, 2024.
Learning objectives include explaining food webs, demonstrating predator/herbivore population limitation, illustrating consumer/consumed population fluctuation, describing predator/herbivore responses to food availability, and explaining how predation and herbivory drive defensive evolution.
Communities are organized into food webs, categorizing species by who eats whom.
Food chains are linear representations of feeding relationships.
Food webs are complex and realistic representations of species feeding relationships in a community, including producers, consumers, detritivores, scavengers, and decomposers.

Trophic Levels

Trophic levels are broad categories in a food web/food chain.
Organisms within a trophic level gain energy in a similar way.
Producers are autotrophs that create their own energy through photosynthesis or chemosynthesis (plants, phytoplankton).
Consumers are heterotrophs, gaining energy by consuming other organisms.
Consumers are categorized into primary, secondary, and tertiary consumers based on their feeding level.
Omnivores, like crayfish, can occupy multiple trophic levels.
Guilds group species that feed on similar items within a trophic level (leaf eaters, stem borers).

Direct vs. Indirect Effects

Species can affect each other's abundance via direct effects (predation, parasitism, competition, mutualism).
In interconnected food webs, direct effects can have ripple effects through the community.
Indirect effects involve interactions with intermediate species.
Trophic cascades are indirect effects initiated by predators.

Density-mediated Indirect Effects

Density changes in intermediate species (e.g., increased sea stars) can cause a decline in other species (e.g., mussels) and open up more ecological space for other species (e.g., barnacles).

Trait-mediated Indirect Effects

Indirect effects are caused by changes in traits of an intermediate species.
These effects occur when a predator causes prey to change its feeding behavior.
Example: wolves in Yellowstone.

Predator-prey Interactions

Predators often reduce prey populations below carrying capacity.
Example: spider and lizard populations on Caribbean islands.
Predator-prey interactions can lead to cyclical population fluctuations, as seen in the Canadian lynx and snowshoe hare system.
Studies in the lab have demonstrated these cycles. Prey dispersing and predators' ability to locate prey impact the strength of the cycles.

Mesopredators

Mesopredators are relatively small carnivores consuming herbivores (example: coyotes).
Top predators are larger predators consuming herbivores and mesopredators (example: wolves).
Human activities have led to a ~60% increase in mesopredator range in North America. Over-harvesting prey species can have unintended consequences.

Herbivore-producer Interactions

Herbivores can significantly impact prey populations.
Many herbivores specialize in consuming specific producer species (example: sea urchins in rocky shore communities).

Numerical Responses

A numerical response is a change in the number of predators due to immigration and emigration in response to changing prey densities.
Example: predator populations increase during prey outbreaks.

Predator-prey Cycles

Predator-prey models often show cyclical dynamics.
Predator-prey co-exist if prey have a dispersal advantage. Predator can’t quickly find dispersed prey.
Mathematical models (Lotka-Volterra) describe these cycles.

Functional Responses/Handling Times

Functional responses describe how a predator's consumption rate changes with prey density, impacting predator cycles.
Predators can quickly switch prey species (prey switching) when the preferred prey is rare or unavailable.
Three kinds of functional responses are described—Type I, II, and III. Type I is linear, Type II incorporates handling time (amount of time for capture), and Type III occurs with slow prey consumption initially, but rapidly increases with high prey densities.
Predators learning their prey species helps regulate populations.

Defences against Predators and Herbivores

Predators have hunting strategies, and prey have evolved defenses (behavioral, structural, chemical).
Examples of defenses:
- Behavioral adaptations (alarm calls, spatial avoidance, reduced activity)
- Structural adaptations (spines, quills, camouflage - crypsis)
- Chemical adaptations (toxins, warning coloration - aposematism).
Camouflage and mimicry help prey avoid predation.
Counter-adaptations, such as adaptation to handle chemical defenses, demonstrate coevolutionary arms races.

Tolerance to Herbivory

Some plants tolerate herbivory instead of developing defenses.
Compensatory growth mechanisms maintain appropriate fitness levels.

Costs of Defenses

Defenses often have associated costs, such as reduced growth or reproduction even if the prey isn't being consumed.
Chemical defenses can have costs to produce.

Next Class

Next week's seminar will cover changes in communities.
Students will present posters on this topic.
Posters should be emailed at least 24 hours in advance of the seminar.

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Description

This quiz covers essential concepts from Lecture 14 of BIOL 203, focusing on predation and herbivory. It delves into the structure and dynamics of food webs, the roles of different trophic levels, and how these interactions shape ecological communities. Understanding these principles is key to comprehending ecological balance and evolution.