Download Predator-Prey Relationships

Predator-Prey
Relationships
BIOL400
21 September 2015
Evidence Predators Can
Regulate Prey Abundance
 Achieved
via controlled prey-transplant or
predator-removal experiments
 Also strongly suggested by introduction of
new, exotic predators
Fig. 5.9 p. 73

Small mussels
eliminated by crabs
and starfish in Lough
Ine, but waves and
salinity limit predators
on open coast
 Large mussels
disappeared in SE
Lough, where they do
not occur due to large
crabs
Fig. 5.10 p. 74
Fig. 11.13 p. 200
Modelling
Predator-Prey
Interactions
Elton’s Oscillations (1924, 1942)
 Apparent
effect of prey density on predator
density in pelt data


Ups and downs in lynx seemed to come just
after ups and downs of their primary prey,
snowshoe hares, on a 9-10 year cycle
Ups and downs in prey base of hares are
probably also a part of this cycle
Fig. 11.19 p. 203
HANDOUT—Lynx and Hare Cycles
Fig. 11.2 p. 191

Assumptions of the
model:



Single predator
species/single prey
species
Simple relationship of
prey density to
predation rate (i.e.,
predator density)
Predator reproductive
rate is proportional to
prey density
Figs. 11.15a & 11.16 p. 201
Laboratory Attempts to
Generate Predator-Prey
Oscillations
Fig. 11.7a p. 195
Gause 1934
Fig. 11.7b p. 195
Gause 1934
Fig. 11.7c p. 195
Gause 1934
Huffaker’s Mites and Oranges
Experiments
 Eotetranychus,
a mite that feeds on
oranges
 Typhlodromus, a mite that feeds on
Eotetranychus
 Former disperses with threads of silk,
latter only disperses overland
Predator and Prey
on Single Orange
 Extinction
of prey
 Starvation and extinction of predator
Fig. 11.8 p. 195
Huffaker 1958
Multiple Oranges Adjacent
to One Another
 Prey
populations grew to 113-650 per
orange
 Prey extinct in 23-32 days
 Starvation and extinction of predator
Multiple Oranges,
Widely Dispersed
 Prey
populations grew to 2000-4000 per
orange
 Prey extinct in 36 days
 Starvation and extinction of predator
Vaseline Barriers,
Oranges Dispersed
 Four
oscillations generated over 14
months
Fig. 11.9 p. 196
Why it is Generally Not
That Simple in Nature





It's a food web, not a food chain
Prey may have refugia, and be less prone to
predation at low densities
Predators may have search images that switch
as prey become more abundant or less
abundant
Other environmental factors may influence prey
or predator density (e.g., salinity and
starfish/crabs)
Predator and prey constantly are selected by
one another in a co-evolutionary “arms race”
HANDOUT—Stenseth et al. 1997
Predator Responses
to Prey Density
Fig. 11.18 p. 202
Numerical Response
 Refers


to both…
…increases in predator N via reproduction
…aggregation of predators in prey-rich areas
HANDOUT—Bowman et al. 2006
Functional Response
 Change
in per-capita rate of prey
consumption



Type I—constant increase in per-capita rate
of consumption as prey density increases
Type II—predator satiation at high prey
densities plus the effect of handling time
Type III—satiation/handling time effect at high
prey densities, and, at low prey densities,
refugium saturation plus prey-switching
behavior
Fig. 11.14 p. 200
Fig. 11.15 p. 201
HANDOUT—Brown et al. 2010
Predator-Prey Model
Incorporating a
Functional Response
Panel a—Prey regulated near Kprey
Panel b—Prey regulated near Kprey
or at very low density (B is unstable point)
Panel c—Prey regulated well below Kprey
Panel d—Prey is driven to extinction
Indirect Effects
and Predation
Indirect Effects
and Predation
 An
effect expressed upon a species, A, via
an interaction between species B and C
 B, by preying on C, may benefit A

Exs: Keystone predators that limit strong
competitors
Fig. 19.17 p. 392
Paine 1974
Fig. 20.12 p. 413
Fig. 11.1 p. 189

Left: Competition between two predators
 Right: Apparent competition

If H1 increases, P1 increases, H2 decreases, and P2
decreases
• Last change not necessarily due to competition between
predators
Schmitt (1987)
 Experiments
with snails, clams, and their
major predators
• A lobster, an octopus, and a whelk
 Adding
either prey caused aggregative
numerical response of predators, leading
to reduced density of other prey
 “Apparent competition” between snails and
clams