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 Type lll Type ll Type l Predator Density Predator Density Predator Density prey switching Prey Density Prey Density 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 Steepness of the line Potential to be resilient to offtake by a predator Recruitment Rate Nt+1 Nt Population Size (N)
No Predators in System K Equilibrium Losses to predators Equilibrium Predator Pits N Nt+1 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.
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