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Wildlife Book (2003-5rd Ed)
Wildlife Biology - Predation (Chapter 9)
Updated 10 November 2009
some general ideas and concepts about predation--- predators have characteristics favoring the capture of prey – speed, sense of geometry in
determining angles of pursuit, strength, possess claws and teeth, keen senses of smell, vision
- several approaches to capturing prey-1. hide-and-pounce approach (e.g., owls, accipiter hawks, flycatchers, frogs, cats)
2. pursuit – chase prey and run them down- falcons, cheetahs
3. intermediate between swift pursuit and hide-and-pounce – wolves, coyotes, buteo hawks
- capture rate by predators is usually low (only 7% success rate of wolves on moose at Isle Royale)
- Predators - known to select individual prey animals that show some oddity in color, behavior,
location, etc.
- they think this may be the basis for the evolution of distraction displays, eg. female
bird with brood will feign a broken wing
- predation usually more successful when portion of prey population is forced outside of its normal
habitat (or outside its territory, home range)- thus only stronger individuals which can hold an area
under optimal living conditions will survive to pass on their genes (natural selection)
- many predators (especially felids, canids) are territorial- thus they are insured of a family hunting
territory
- in wolves (some other predators too, also non-predators, for that matter) only dominant female(s)
breed- better chance of getting food for young
Predation in Natural Communities
- Europe-antipredator sentiment -- same ideas brought to America
- William Hornaday (1913) - Director of New York Zoological Park- wrote book Our Vanishing
Wildlife - plea to protect wild animals, but he thought predators should be killed to “protect” other
species (read p. 154)
Theoretical Predator-Prey Systems
Lotka (1925) and Volterra (1926) - famous for developing equations (models) for predator-prey
relationships --in most books, called the Lotka-Volterra equations (see graphs and equations - p.
155 - Fig. 9-2, 9-3)
remember, equation for exponential growth is N = rN
t
2
Lotka-Volterra Predation Equations:
N1
t
= r1N1 - p1N1N2
where-N1 = prey population density
N2
t
= p2N1N2 - d2N2
N2 = predator population density
r1 = instantaneous rate of increase of prey population
(per head) (other books say innate capacity for increase)
p1, p2 = predation constants
(p1 is a constant measuring ability of prey to escape
predators)
(p2 is a constant measuring skill of predator in
catching prey)
d2 = death rate of predator population (per head)
-- see lynx and snowshoe hare cycles p. 155- some now question if this is really due to predation
Laboratory Studies of Predator-Prey Systems
Huffaker (1958) - study with mites on oranges
- see Fig. 9-4, p. 156
- predaceous mites would eat all of prey mites on oranges if no diversity on or
around oranges occurred -- prey population became extinct
- when orange habitat was diversified (different spacings of oranges, posts and
fan to aid dispersion, etc.)- prey could keep recolonizing different oranges ahead
of predator and did not go extinct
Field Observations of Predator-Prey Systems
Errington (1956, 1967) - studies of mink predation on muskrats
- during muskrat population high, more predation occurred, but usually was those muskrats which
were social outcasts and were already prone to death by starvation, disease
- found the mortality factors such as disease, predation, and starvation were compensatory rather
than additive
Holling (1959) - studied small mammal predation on pine sawfly larvae
- found density of prey influenced both feeding behavior of predators and numbers of predators
- functional response - is the tendency for predators to eat more of a prey species as the prey
becomes more abundant
- numerical response - the number of predators increases with an increase in the density of prey
animals available
see page 157 for graphs to demonstrate
- many studies give different results and it is often hard to tell if predators really limit their prey-
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Leopold (1933) - proposed you look at:
1.
density of prey population
2.
density of predator population
3.
characteristics of prey (eg., reactions to predators, nutritional condition)
4.
density and quality of alternate foods available to predator (buffer species!!)
5.
characteristics of predator (e.g., means of attack, food references)
Wolf-Moose interactions on Royale Isle Royale (island in Lake Superior)
- Mech has done lots of work; work started by Durvard Allen (from Purdue U.)
- most moose taken were either old or diseased; wolves usually “test” the moose first to see if it
will run or stay and fight- healthy ones usually face wolves to fight, weaker ones usually turned
tail and ran and were caught
- in years of unusually deep snow, moose congregated in certain areas and overbrowsed them weaker moose - more predation-- wolves increased-- then later wolf numbers decreased (some
wolves killed other wolves and also less moose for food) -- read p. 159-162
- Keith - studied cycles in snowshoe hares and predators - read p. 162
- hares overate their winter food supply - affected cycles- also affected predation rates and
numbers Field Experiments with Predator-Prey Systems (read 163-166)
- if predators are removed, deer sometimes increase in numbers-- but then deer usually get too dense
-- overbrowse and ruin their habitat—starvation, disease, etc. then usually bring the population
down anyway
- duck nesting success can increase by predator removal-- unless nest density gets too high and
attracts any remaining predators in the area (p. 163-165)
Wolf Control in Alaska – read pp. 166-168 –VERY controversial in Alaska right now
Deer-Predator Relationships: A Hard Look at the Literature – read p. 168
Predation on Domestic Animals
- coyotes and predation on sheep, other domestic animals -- this is a big deal in the western US read p. 168-177
- 4 main ways of coyote control -- trapping, den hunting (denning), shooting, poisoning (used to use
meat laced with strychnine- too dangerous- do not use it much
now); compound 1080 – (sodium monofluoracetate)
- Cain Report (around 1971-1972) - resulted in President Nixon banning use of all poisons for
predator control on federal lands and by federal agencies