Questions: Functional Response: Types and Predation Efficiency

Question 1

A prey population crashes to very low density. Under which type of functional response would predation pose the greatest additional threat to prey recovery?

• A. Type I, because the linear response means predators always consume prey in proportion to density
• B. Type II, because handling time limits cause predators to consume a disproportionately high *proportion* of the remaining prey at low density
• C. Type III, because the sigmoidal curve accelerates rapidly through its inflection point at low densities
• D. All types are equally threatening at low prey density since predation rate only reflects absolute numbers

Answer: (B)

Type II is the most destabilizing at low prey density. As prey become scarce, the time predators spend searching shrinks, but handling time per prey item remains constant — so each encountered prey is still worth pursuing. This means predators consume a *higher proportion* of a low-density prey population than of a high-density one, creating a positive feedback loop that can drive prey to extinction. Type III is actually *stabilizing* at low density: predators switch to other prey when the focal prey is rare, creating a low-density refuge.

Question 2

A generalist predator that hunts rabbits and voles shifts almost entirely to voles when rabbit numbers drop sharply one winter. This behavior is the mechanism that produces which functional response type?

• A. Type I, because the predator is still consuming prey linearly relative to total prey available
• B. Type II, because prey switching is equivalent to prey handling in terms of time costs
• C. Type III, because prey switching (or learning/search image formation) creates low predation rates on rare prey and accelerates consumption once prey become common
• D. Type II and Type III are identical; the distinction is only mathematical

Answer: (C)

Prey switching is the behavioral mechanism that generates a Type III (sigmoidal) functional response. When a prey species is rare, the predator focuses on more abundant alternatives, producing low predation rates at low prey density. As the focal prey becomes more common, the predator switches its attention, and consumption accelerates through an inflection point before eventually saturating (like Type II). This switching creates a low-density refuge — the crucial stabilizing feature that Type II lacks.

Question 3

A Type II functional response is destabilizing primarily because predators eat more prey per individual as prey become more abundant, overwhelming prey reproductive capacity.

• T. True
• F. False

Answer: False

This statement inverts the key dynamic. Type II is destabilizing at *low* prey density, not high density. The destabilizing feature is that at low prey density, predators consume a *higher proportion* of the prey population because handling time dominates total time (search time is already short). At high density, the Type II response saturates — predators are handling-time limited, so the proportion consumed actually drops. The danger for prey populations is not predator saturation at high density but disproportionate predation when prey are already struggling.

Question 4

The difference between Type II and Type III functional responses has real consequences for whether prey populations can recover from low numbers — Type III provides a stability mechanism that Type II does not.

• T. True
• F. False

Answer: True

This is the core ecological insight of functional response theory. Type II creates a destabilizing 'predator pit' at low prey density — once prey decline past a threshold, proportional predation can accelerate the decline toward extinction. Type III provides a low-density refuge: as prey become rare, predator attention shifts to alternative prey, relieving pressure and allowing the focal prey to recover. This difference in low-density behavior is why functional response type profoundly affects whether predator-prey systems exhibit stable coexistence or boom-bust cycles and extinction.

Question 5

Why does prey handling time create an upper bound on predation rate in a Type II functional response, and what does this saturation mean for the proportion of a prey population consumed at very low versus very high prey densities?

Model answer: Handling time — the time spent chasing, capturing, killing, eating, and digesting each prey item — is independent of how abundant prey are. As prey density increases, a predator spends less time searching (prey are easy to find) but must still spend the same handling time per prey caught. Eventually, search time approaches zero and handling time alone limits intake, creating a ceiling on consumption rate. At high prey density, the predator is handling-time limited and consumes a *smaller proportion* of the prey population. At low prey density, search time is long but each prey encountered is still handled — the predator continues eating a *higher proportion* of the sparse prey, which is the destabilizing feature of Type II.

The mathematical origin is Holling's disc equation: consumption rate = (attack rate × prey density) / (1 + attack rate × handling time × prey density). As prey density grows, the denominator grows faster than the numerator, producing saturation. The ecological consequence — disproportionate predation at low density — follows directly from this formula and explains why Type II can destabilize prey populations already at low numbers.