Neutral Stability

Vectors spiralinwards

Functional response = rate at which individualpredators capture and eat more prey per unittime as prey density increases

Numerical response = increased prey density raises the predator’spopulation size and a greater number of predators consume An increased number of prey

Moderately efficient predatorNeutral stability — Vectors form a closed ellipse. Amplitude of oscillations remains constant.

Unstable — extremely efficient predatorVectors spiral outwards until a Limit Cycle is reached

Damped Oscillations — inefficient predatorVectors spiral inwards to stable equilibrium point

“Prudent” Predation and Optimal Yield Feeding territories Consequence of senescence

Industrial Melanism Numbers of Typical and Melanic Marked Moths (Biston betularia) Released and Recaptured in a Polluted Woods Near Birmingham

and an Unpolluted Woods Near Dorset*__________________________________________________________

Polluted Woods Unpolluted Woods__________________________________________________________ Numbers of marked moths released

Typical 64 496Melanic 154 473

Number of moths recapturedTypical 16 (25%) 62 (12.5%)Melanic 82 (53%) 30 (6.3%)

__________________________________________________________* The wild population in the polluted woods was 87% melanic. Source: From data of Kettlewell (1956).

Predator Escape TacticsAspect DiversityCryptic coloration (countershading)Disruptive colorationFlash colorationEyespots, head mimicryWarning (aposematic) coloration Alarm signalsHawk alarm callsSelfish callersPlant secondary chemicals

Selfish caller Hypotheses1. Full up “I see you”2. Mass pandemonium3. Keep on moving4. Mixed species flocks, fake alarm calls

Predator Escape TacticsAspect DiversityCryptic coloration (countershading)Disruptive colorationFlash colorationEyespots, head mimicryWarning (aposematic) coloration Alarm signalsHawk alarm callsSelfish callersPlant secondary chemicals

1. Physiological dependence on host most parasites are highly specialized many have complex life cycles with intermediate and final hosts challenge: how to infect new hosts?

2. Higher reproductive potential than host (high fecundity necessary for dispersal)

3. Parasites can kill highly infected hosts but typically do not — allow host to live

4. Infection produces an overdispersed distribution of parasites among hosts

Parasite ExamplesAssassin bugs (Triatoma)MalariaTapeworms (Cestodes)Cholera (Shigella) transmission via dysenteryToilet seats, elevator buttons, shopping carts...Molecular mimicry“eclipsed antigens” resemble host antigenshence do not elicit formation of host antibodiesMajor Histocompatibility ComplexTrypanosoma shed coats, change antigensFilariasis Elephantiasis (blocked lymph nodes,nematode worms carried by mosquitos)