Lecture 10: Predation and Predator Management II

Question 1

Explain the three types of functional response curves with respect to predation.

Answer 1

The three types of functional response curves with respect to predation are:

Type I – Linear Response: Predation rate increases linearly with prey density. Each additional prey adds a constant increase to the predation rate.
Type II – Decelerating Response: Predation rate initially increases with prey density but at a decreasing rate, eventually reaching a plateau. This indicates a satiation point where predators cannot consume prey any faster.
Type III – S-shaped Response: Predation rate is low at very low prey densities, then accelerates as prey density increases before eventually plateauing at high densities. This suggests an initial difficulty in locating or capturing prey which is overcome as prey becomes more abundant.
These curves illustrate how predator consumption rates vary with prey density, influencing predator-prey dynamics and ecosystem stability.

Question 2

Explain why the functional response curves take the shape that they do.

Answer 2

The functional response curves take their specific shapes due to the interaction between predator and prey, influenced by factors like prey density, predator hunting efficiency, and prey defense mechanisms:

• Type I (Linear Response): Predators consume more prey as prey density increases in a linear fashion, reflecting a constant success rate in predation without saturation.
• Type II (Decelerating Response): Initially, predation rate increases with prey density but then plateaus due to factors like satiation, increased handling time, or difficulty in processing additional prey.
• Type III (S-shaped Response): Predation rate is low at very low prey densities due to inexperience or lack of interest, increases rapidly as predators specialize or learn, and eventually plateaus at high prey densities due to similar reasons as Type II.

These shapes reflect the dynamics of predation under varying environmental and biological conditions, capturing the complexity of predator-prey interactions.

Question 3

Describe an example from class showcasing evidence of how predators control the
population size of:
○ small game
○ waterfowl
○ ungulates

Answer 3

Small Game: Not explicitly mentioned in the provided text.
Waterfowl: In the Prairie Pothole Region, changes in habitat and predator community composition have led to up to 90% nest loss in ducks due to predators, influenced by habitat loss and increased predator populations from abandoned farms providing more food and shelter.
Ungulates: A case study by Kie et al. involved fencing 391 ha of habitat to exclude predators, demonstrating that without predators, prey populations can grow too high, leading to starvation and disease. This illustrates that predators help keep prey populations healthy.

Question 4

Explain the two broad classes of approaches to managing predators, and explain why one
approach might be favoured over the other.

Answer 4

The two broad classes of approaches to managing predators are:

Active Approach: This involves directly attempting to limit predator numbers through methods such as trapping or shooting. It can be effective but may have unknown ecological consequences, be expensive, and politically challenging.
Passive Approach: Focuses on managing habitat to limit the effects of predators, such as changing farming methods or protecting habitats. This approach is less direct, potentially avoiding some of the ecological and political issues associated with actively removing predators.
One approach might be favored over the other based on factors like cost, ecological impact, political feasibility, and the specific goals of the management program.