POPULATION-LEVEL EFFECTS OF

PREDATIONPREDATION

I. THE ROLE OF PREY DENSITY

A. Functional Response of Predators

Deer Mice and Pine Sawflies

Coccoon Density (103/acre)

0 200 400 600 800 1000 1200

Co

cc

oo

ns

Op

en

ed

0

50

100

150

200

250

Type III

Source: Caughley and Sinclair (1994, Wildlife ecology and management)

I. THE ROLE OF PREY DENSITY

B. Numerical Response of Predators

Prey Density

Pre

da

tor

de

ns

ity Numerical Response Curve

I. THE ROLE OF PREY DENSITY

C. Total Response of Predators

Prey Density

Vit

al

Ra

te (

%)

K

A

B

Recruitment

Mortality (+)

Mortality (-)

II. DO MAMMALIAN PREDATORS REGULATE PREY POPULATIONS?

A. Predators of Waterfowl

II. DO MAMMALIAN PREDATORS REGULATE PREY POPULATIONS?

A. Predators of Waterfowl

II. DO MAMMALIAN PREDATORS II. DO MAMMALIAN PREDATORS REGULATE PREY POPULATIONS?REGULATE PREY POPULATIONS?

II. DO MAMMALIAN PREDATORS REGULATE PREY POPULATIONS?

B. Wolves and Ungulates– Declining

caribou, moose, Dall sheep populations in Yukon

– Experimental reduction of wolves over 5 years

Photo © Stephen Loring

www.frankoberle.com

www.oklahoma.net

II. DO MAMMALIAN PREDATORS REGULATE PREY POPULATIONS?

B. Wolves and Ungulates– Declining caribou, moose, Dall sheep

populations in Yukon– Experimental reduction of wolves over 5 yrs– Wolf predation was

» reducing recruitment of caribou & moose calves» reducing adult survival of moose

II. DO MAMMALIAN PREDATORS II. DO MAMMALIAN PREDATORS REGULATE PREY POPULATIONS?REGULATE PREY POPULATIONS?

C. WeaselsC. Weasels– and voles in western USAand voles in western USA

– and voles in Russian crop ricks

II. DO MAMMALIAN PREDATORS REGULATE PREY POPULATIONS?

D. Overview

III. INTERACTION OF PREDATION AND COMPETITION

A. Lynx and Hares– During peak hare year:

III. INTERACTION OF PREDATION AND COMPETITION

B. Wildebeest and Lions-Hyenas1. Predation-sensitive food hypothesis

(PSFH)

2. Predator regulation hypothesis (PRH)

3. Surplus prey hypothesis (SPH)

III. INTERACTION OF PREDATION AND COMPETITION

Prey Density

Vit

al R

ate

(%)

K

PRH

PSFH

Recruitment

SPH

Mortality

IV. INDIRECT EFFECTS OF PREDATORS ON PREY

Indirect effect:

– Effect of one species on another is mediated through a third

IV. INDIRECT EFFECTS OF PREDATORS ON PREY

Example: Iberian lynx

Egyptian mongoose

European rabbit Rabbits preyed upon: 5-10 fold increase in

absence of lynx Rabbit density: 2-4 fold lower in areas

without lynx

V. THE CONCEPT OF COMPENSATORY EFFECTS

Compensatory Mortality– Substitution of mortality agents

V. THE CONCEPT OF COMPENSATORY EFFECTS

Compensatory Mortality– Substitution of mortality agents

– Example: deer in predator-removal area

V. THE CONCEPT OF COMPENSATORY EFFECTS

Compensatory Mortality– Substitution of mortality agents– Example: woodchucks in Pennsylvania

V. THE CONCEPT OF COMPENSATORY EFFECTS

Other Types of Compensation– Example: woodchucks on a hunted site

»increased survival of juveniles

»reduced emigration of juveniles

»increased fertility of yearling females