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Predator-Prey Predator-Prey RelationshipsRelationships
BIOL400BIOL40021 September 201521 September 2015
Evidence Predators Can Evidence Predators Can Regulate Prey Abundance Regulate Prey Abundance
Achieved via controlled prey-transplant or Achieved via controlled prey-transplant or predator-removal experimentspredator-removal experiments
Also strongly suggested by introduction of Also strongly suggested by introduction of new, exotic predatorsnew, exotic predators
Fig. 5.9 p. 73Fig. 5.9 p. 73 Small mussels Small mussels
eliminated by crabs eliminated by crabs and starfish in Lough and starfish in Lough Ine, but waves and Ine, but waves and salinity limit predators salinity limit predators on open coaston open coast
Large mussels Large mussels disappeared in SE disappeared in SE Lough, where they do Lough, where they do not occur due to large not occur due to large crabscrabs
Fig. 5.10 p. 74Fig. 5.10 p. 74
Fig. 11.13 p. 200Fig. 11.13 p. 200
Modelling Modelling Predator-Prey Predator-Prey
InteractionsInteractions
Elton’s Oscillations (1924, 1942)Elton’s Oscillations (1924, 1942)
Apparent effect of prey density on predator Apparent effect of prey density on predator density in pelt datadensity in pelt data Ups and downs in lynx seemed to come just Ups and downs in lynx seemed to come just
after ups and downs of their primary prey, after ups and downs of their primary prey, snowshoe hares, on a 9-10 year cyclesnowshoe hares, on a 9-10 year cycle
Ups and downs in prey base of hares are Ups and downs in prey base of hares are probably also a part of this cycle probably also a part of this cycle
Fig. 11.19 p. 203Fig. 11.19 p. 203
HANDOUT—Lynx and Hare CyclesHANDOUT—Lynx and Hare Cycles
Fig. 11.2 p. 191Fig. 11.2 p. 191 Assumptions of the Assumptions of the
model:model: Single predator Single predator
species/single prey species/single prey speciesspecies
Simple relationship of Simple relationship of prey density to prey density to predation rate (i.e., predation rate (i.e., predator density)predator density)
Predator reproductive Predator reproductive rate is proportional to rate is proportional to prey densityprey density
Figs. 11.15a & 11.16 p. 201Figs. 11.15a & 11.16 p. 201
Laboratory Attempts to Laboratory Attempts to Generate Predator-Prey Generate Predator-Prey
OscillationsOscillations
Fig. 11.7a p. 195Fig. 11.7a p. 195Gause 1934Gause 1934
Fig. 11.7b p. 195Fig. 11.7b p. 195 Gause 1934Gause 1934
Fig. 11.7c p. 195Fig. 11.7c p. 195 Gause 1934Gause 1934
Huffaker’s Mites and Oranges Huffaker’s Mites and Oranges ExperimentsExperiments
EotetranychusEotetranychus, a mite that feeds on , a mite that feeds on orangesoranges
TyphlodromusTyphlodromus, a mite that feeds on , a mite that feeds on EotetranychusEotetranychus
Former disperses with threads of silk, Former disperses with threads of silk, latter only disperses overlandlatter only disperses overland
Predator and Prey Predator and Prey on Single Orangeon Single Orange
Extinction of preyExtinction of prey Starvation and extinction of predatorStarvation and extinction of predator
Fig. 11.8 p. 195Fig. 11.8 p. 195Huffaker 1958Huffaker 1958
Multiple Oranges AdjacentMultiple Oranges Adjacent to One Another to One Another
Prey populations grew to 113-650 per Prey populations grew to 113-650 per orangeorange
Prey extinct in 23-32 daysPrey extinct in 23-32 days Starvation and extinction of predatorStarvation and extinction of predator
Multiple Oranges, Multiple Oranges, Widely Dispersed Widely Dispersed
Prey populations grew to 2000-4000 per Prey populations grew to 2000-4000 per orangeorange
Prey extinct in 36 daysPrey extinct in 36 days Starvation and extinction of predatorStarvation and extinction of predator
Vaseline Barriers, Vaseline Barriers, Oranges Dispersed Oranges Dispersed
Four oscillations generated over 14 Four oscillations generated over 14 months months
Fig. 11.9 p. 196Fig. 11.9 p. 196
Why it is Generally Why it is Generally NotNot That Simple in Nature That Simple in Nature
It's a food web, not a food chainIt's a food web, not a food chain Prey may have refugia, and be less prone to Prey may have refugia, and be less prone to
predation at low densitiespredation at low densities Predators may have search images that switch as Predators may have search images that switch as
prey become more abundant or less abundantprey become more abundant or less abundant Other environmental factors may influence prey or Other environmental factors may influence prey or
predator density (e.g., salinity and starfish/crabs)predator density (e.g., salinity and starfish/crabs) Predator and prey constantly are selected by one Predator and prey constantly are selected by one
another in a co-evolutionary “arms race” another in a co-evolutionary “arms race”
HANDOUT—Stenseth et al. 1997HANDOUT—Stenseth et al. 1997
Predator Responses Predator Responses to Prey Densityto Prey Density
Fig. 11.18 p. 202Fig. 11.18 p. 202
Numerical ResponseNumerical Response
Refers to both…Refers to both… ……increases in predator N via reproductionincreases in predator N via reproduction ……aggregation of predators in prey-rich areas aggregation of predators in prey-rich areas
HANDOUT—Bowman et al. 2006HANDOUT—Bowman et al. 2006
Functional ResponseFunctional Response
Change in per-capita rate of prey Change in per-capita rate of prey consumptionconsumption Type I—constant increase in per-capita rate Type I—constant increase in per-capita rate
of consumption as prey density increasesof consumption as prey density increases Type II—predator satiation at high prey Type II—predator satiation at high prey
densities plus the effect of handling timedensities plus the effect of handling time Type III—satiation/handling time effect at high Type III—satiation/handling time effect at high
prey densities, and, at low prey densities, prey densities, and, at low prey densities, refugium saturation plus prey-switching refugium saturation plus prey-switching behaviorbehavior
Fig. 11.14 p. 200Fig. 11.14 p. 200
Fig. 11.15 p. 201Fig. 11.15 p. 201
HANDOUT—Brown et al. 2010HANDOUT—Brown et al. 2010
Predator-Prey Model Predator-Prey Model Incorporating a Incorporating a
Functional ResponseFunctional Response
Panel a—Prey regulated near KPanel a—Prey regulated near Kpreyprey
Panel b—Prey regulated near KPanel b—Prey regulated near Kpreyprey or at very low density (B is unstable point)or at very low density (B is unstable point)
Panel c—Prey regulated well below KPanel c—Prey regulated well below Kpreyprey
Panel d—Prey is driven to extinctionPanel d—Prey is driven to extinction
Indirect Effects Indirect Effects and Predationand Predation
Indirect Effects Indirect Effects and Predationand Predation
An effect expressed upon a species, A, via An effect expressed upon a species, A, via an interaction between species B and Can interaction between species B and C
B, by preying on C, may benefit AB, by preying on C, may benefit A ExsExs: Keystone predators that limit strong : Keystone predators that limit strong
competitorscompetitors
Fig. 19.17 p. 392Fig. 19.17 p. 392Paine 1974Paine 1974
Fig. 20.12 p. 413Fig. 20.12 p. 413
Fig. 11.1 p. 189Fig. 11.1 p. 189
Left: Competition between two predatorsLeft: Competition between two predators Right: Apparent competitionRight: Apparent competition
If HIf H11 increases, P increases, P11 increases, H increases, H22 decreases, and P decreases, and P22 decreasesdecreases
• Last change not necessarily due to competition between Last change not necessarily due to competition between predatorspredators
Schmitt (1987)Schmitt (1987)
Experiments with snails, clams, and their Experiments with snails, clams, and their major predatorsmajor predators
• A lobster, an octopus, and a whelk A lobster, an octopus, and a whelk Adding either prey caused aggregative Adding either prey caused aggregative
numerical response of predators, leading numerical response of predators, leading to reduced density of other preyto reduced density of other prey
““Apparent competition” between snails and Apparent competition” between snails and clamsclams