Presentation on theme: "Predation Competition (intra- and inter-) involve interactions between same trophic level Predation involves interactions between trophic levels One species."— Presentation transcript:
Predation Competition (intra- and inter-) involve interactions between same trophic level Predation involves interactions between trophic levels One species negatively effects the other Very important for management goals –Conservation –Control –Harvesting
Types of predation Herbivory –Animals prey on green plants –Death of plant not usual Parasitism –Usually don’t kill host Carnivory –Predator kills and eats prey Cannibalism –Predator and prey same species
Predator behavior and prey survival Herbivores gain nutrition from plants –Have to deal with plant defenses –chemical and physical Must also avoid predators –Protective shapes and coloration –Active defense –Alertness and swiftness –Protective cover –morphology Predators must catch prey –Speed, agility, claws, teeth, smell, vision, etc
Predation Many different techniques Normally involves large investment of time and effort per unit food Usually target physically weakened or in a vulnerable place Typically 4.5 to 10.8 % capture success e.g. 124 moose, 7% success rate by wolves
Predation Often select prey by oddity –Color –Behavior –Location
Predation Prey change behavior in absence of predators
Predation Conspicuousness and crypsis Prey change behavior in absence of predators Marginal habitat
Effect of predators on prey density CATEGORYLOCATIONDENSITY PER KM 2 PREDATORS ABSENTSlate islands4-8 Norway3-4 Newfoundland8-9 South Georgia2 MOUNTAIN-DWELLINGFinlayson0.15 (predator more intenseLittle Rancheria0.1 and frequent)Central Alaska0.2 FOREST-DWELLINGQuesnel Lake0.03 (predation high andOntario0.03 constant)Saskatchewan0.03
Effect of predators on prey density Predator numbers also correlated with prey numbers Based on correlations Are predators keeping prey below food supply, or killing only those that are malnourished? Need to understand the behavior of predators
The behavior of predators How do predators respond to: 1.Changes in prey density? 2.Changes in predator density? 3.Differences in the degree of clumping of prey?
Response to changes in prey density Response of predators to prey depends on: 1.Feeding behavior of individual predators Functional response 2.Response of the predator population through reproduction, immigration and emigration Numerical response
Functional response 1.Searches randomly for its prey 2.Has an unlimited appetite 3.Spends a constant amount of time searching –Then the number of prey found will increase in direct proportion to prey density –Type I response Prey Density Number of Prey Eaten Per Predator Prey Density Percent of Prey Population Eaten
Functional Response Assumptions are usually unrealistic Some predators show an approximation of a type 1 function response –Reindeer feeding on lichens No animal has an unlimited appetite. Constant search time unlikely Handling time – more prey eaten per unit time, more time is taken up with handling and less for searching.
Functional response N a = (aT t N) / (1 + ahN) Type II response Number eaten per time increases to an asymptote as prey density increases Prey Density Number of Prey Eaten Per Predator Prey Density Percent of Prey Population Eaten
Functional response Type III response Prey switching Prey Density Number of Prey Eaten Per Predator Prey Density Percent of Prey Population Eaten
Functional response Success at catching depends on prey density Predators react to individuals of own species by dispersing –Territoriality –Eviction Interference Interference reduces the searching efficiency of the predator as predator density increases Interference stabilizes predator numbers
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 thereby have a regulating effect on prey numbers
Numerical response Trend of predator numbers against prey numbers Predators increase as prey density increases Due to 1.Increased rate of predator reproduction when prey are abundant Numerical response 2.Attraction of predators to prey aggregations Aggregational response
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
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
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 predators 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 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 Unlikely predation is cause of synchrony, but likely intensifies it.
Conservation and management Predator and prey populations usually coexist –Prey at low density by regulation –Prey at high density by intraspecific competition for food with predation depensatory 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 Which situation occurs depends on –Ability of predator to catch prey –Ability of prey to escape predation –Reproduction