LECTURE 13 CH 15 DYNAMICS OF PREDATION
BEFORE LECTURE, READ 18-19; DIGEST FIG. 1.15
MAJOR CONCEPTS
1) Predators have adaptations for capturing their prey.
2) Prey have adaptations for escaping their predators.
3) Predators influence the distribution and population size of prey (top-down control).
4) A change in prey density changes catch rate by individual predator (3 types of
functional responses).
5) A change in prey density changes predator population size by growth or immigration.
6) Predator and prey populations often increase and decrease in regular cycles.
7) Predator cycle lags behind cycle of prey.
8) Several factors act as stabilizing forces that reduce cycles.
9) Prey can persist in presence of predator if have refuge or exist in spatially complex
habitat.
I. Predator adaptations to capture prey
II. Prey deterrents to predation
Group living and early detection of predator
Induced structural defense
Chemical defense (active warfare) 14.5
Cryptic coloration (crypsis) 17.2
Aposematism (warning coloration) by toxic prey 17.3
III.Evidence that predators control prey abundance (impose ‘top-down’ control) 15.3
ICA 1,2,3
Human harvests of predator and prey (marine system) 18-19; 1.15
Removal experiments; e.g. insecticide experiments 15.3
Introduction (invasions) of predators
Islands with and without predators
If predators remove the strongest competitor among prey species 
decrease in species number of prey when predator removed
IV. Functional response of individual predator 15.21 ICA 4
Change in prey density changes rate of prey capture by individual predator
Type I: Capture directly proportional (linear) to prey density
Type II: Capture levels off at high prey density (predator satiation)
Type III: as in Type II, but also low at low prey density because:
Heterogeneous habitat hiding places
Lack of learned search behavior
Switch to alternative prey
V. Numerical response of predator population to prey density 15.22, 15.23 ICA 5,6,7,
Predator response is in population size via population growth or immigration
Cycles out of phase: predator lags behind prey population
VI. Populations of predator/prey fluctuate for many reasons; many without cycles
Abiotic factors
Biotic factors
Some predator-prey populations increase and decrease in synchronized cycles 15.2
Predators lag prey ICA 8
VII. What controls cyles?
A. Stabilizing forces that reduce oscillations 15.7
Predator inefficiency
D-D limitation of either predator or prey
Alternative food sources for predator
Refuges from predation at low prey densities
Reduced time delays in predator responses to changes in prey abundance
B. Time delays destabilize and push toward cycles
Development period and time to reproduce
Time required for numerical response by predator
Time for immune response and induced response
C. If destabilizing forces outweigh stabilizing forces  cycles
Development of host immunity influences pathogen population cycles 15.9
Habitat structure can affect population cycles (e.g. edges of fragments) 15.10
VIIILaboratory studies of predator-prey populations
A. Gause: Paramecium (prey) and Didinium (predator) p. 309
Refuge for prey needed to maintain prey
Regular immigration can yield stable cycles
B. Huffaker: oranges (habitats) and predator mite and prey mite 15.11, 15.12
ICA 9, 10, 11
Oranges clumped extinction
Oranges random  predators slow to find prey  survive longer
Spatial heterogeneity in habitats brings stability to cycles
Need complex environment for prey to hide; reduces ease of predator dispersal
Summary 1-5, 10-13