Download Predation

PREDATION
• One of the least well developed areas of
ecological theory
• Management problems occur with a lack
of information
– Biological data on predators and prey
– Explanation of the Ecosystem
PREDATORS
• Change in feeding behavior of individual
predators to different prey densities
– Functional Response
• Response of predator population through
reproduction, immigration, and emigration
– Numerical Response
Functional Responses
Predator Density
Predator Density
Predator Density
Prey Density
Type lll
Type ll
Type l
Prey Density
prey
switching
Prey Density
DEFINITIONS
• PREY SWITCHING
– Changing preference toward the more
abundant prey.
– Ignoring rare prey
– Concentrating search in more rewarding
areas
– Any of these behaviors result in:
Type III Functional Response
PREDATION
• Population Models are uniquely related to
predator-prey dynamics
– ½ equation
– Density Dependence
• Place where prey are most vulnerable to
predation, predators have the least effect.
– At K
– Low population density prey are in good
condition and more dispersed.
– Predators have have greatest effect, but prey
are least vulnerable in body condition.
Population Model of Prey
Size of “hump” above no growth line
Potential to be resilient to
offtake by a predator
Nt+1
Recruitment Rate
Steepness of the line
Population Size (N)
Nt
Predator Pits
No Predators in System
K
Nt+1
Equilibrium
N
Losses to predators
Equilibrium
Nt
Functional response
• Prey live in small patches of high density
and low density in between
• Clumped distribution
• Predators concentrate on areas of high
density
• Predators may have a regulating effect on
prey numbers
Numerical response
•
Trend of predator numbers against prey
numbers
Predators increase as prey density increases
Increased rate of predator reproduction when
prey are abundant
•
•
•
•
Numerical response
Attraction of predators to prey aggregations
•
•
Aggregational response (short term)
immigration
Numerical response
• Reproduction and mortality rate of predators
depends on predation rate
• More prey, more energy
• Predator numbers increase to an asymptote
– determined by interference
• Interference such as territoriality can cause
reduction or stabilization of predators.
– High density: 20% adult wolves, 50% juveniles
disperse
Total response
• Total number eaten = number eaten by one
predator multiplied by number of predators
• Can be plotted as Total response curves
• Need to also incorporate recruitment rate of
prey
• Different types of curves indicate different
types of relationships
– Predators regulate prey population
– Prey regulated by intraspecific competition for
food
– Multiple stable states
Population Cycles
•
•
•
•
•
Strongest representation at high latitude
Specialist predator
Lynx - hare cycle
Weasel – microtine cycle
Red grouse – possibly gut nematodes.
POPULATION CYCLES
 Mid-16th century, Archbishop of Uppsala, Sweden published 2
reports on cyclic fluctuations of northern small rodents.
 In early 1900s, wildlife biologists analyzed the fur trading records
of the Hudson’s Bay Company, including those for the Canadian
lynx.
•Period is amount of time it takes population to go through complete cycle.
•Amplitude can be defined as difference between maximum population size and
population size at midpoint, but some researchers refer to peak-to-trough
amplitudes.
•In general, periods tend to be fairly consistent for a particular cyclic population,
whereas amplitudes are more variable.
Population Cycles
Behavior of prey
• How does the behavior of the prey
influence predation?
• Migration
• Herding and spacing
• Birth synchrony
Migration
If a prey species can migrate beyond the range of its
predators the population can escape predator
regulation
Predators have slow growing
young and are restricted to a
small area to breed
Ungulates have precocial
young that can move within a
few hours
Thus prey follow food resource,
predators cannot
Herding and spacing
• Animals reduce risk of predation by forming
groups
– Group size predicted to increase with increasing
predator densities
– Group size increases with distance from cover
– More animals in group, more vigilance of groups, less
per individual.
• Can also leave group when most vulnerable
– Leave group when give birth as predators are
concentrated around herds
Birth synchrony
• Synchronize births to reduce predation
rate
• Predator swamping
• Also influenced by seasonal availability of
resources
Conservation and management
• Predator and prey populations usually coexist
– Prey at low density by regulation
– Prey at high density by intraspecific competition for
food.
• Both systems can operate in one area
– Type III functional response or density-dependent
numerical response
– Disturbance moves from one state to other
– Explains outbreaks of pest species, decline of hunted
species
Conservation and management
• Prey population can become extinct
– Type II response with no prey refuge, no alternative
prey
– Important in management where there are habitat
changes
– Small populations or exotics
• Which situation occurs depends on
– Ability of predator to catch prey
– Ability of prey to escape predation
– Reproduction