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