Predator Strategies On Prey Populations PDF

Effect of predator strategies on prey populations Antoine OHC Leduc Ecology BIOL3005 SQU  Outline of predator strategies Predator strategy differ in … Energy used in getting food – High – Low The number of type of prey eaten – Many – Few ...

Effect of predator strategies on prey populations Antoine OHC Leduc Ecology BIOL3005 SQU  Outline of predator strategies Predator strategy differ in … Energy used in getting food – High – Low The number of type of prey eaten – Many – Few  Predator strategies Two major strategies exist for predators 1. Energy used in getting food Energy maximisers (= active hunters) Aim at catching food (prey) by actively hunting them Energy-expensive strategy: 1. Requires catching food frequently → to replenish the energy spent 2. Requires spending time carefully selecting the easiest prey to catch (such as weakest) E.g. wolfs  Predator strategies Two major strategies exist for predators 1. Energy used in getting food Time minimizers (= raptorial hunters) Inactive predator species that wait for their food to come to them Use little energy and so can survive with little food for long periods Have little choice over what they catch and so must be very adaptable in their food (non-selective) E.g. spider Stone fish  Predator strategies Two major strategies exist for predators 2. The number of prey eaten a) “Specialists” feed on a small number of prey (maybe only one species) This allows them to become very efficient at finding and catching that prey Examples of specialist predators are: Ant caught by antlion Snowshoe hare & Cheetah & baby gazelle Lynx  Antlions are insects that dig pits in sand specifically to catch ants that fall into the pit Note: these are raptorial predators Cheetahs feed almost entirely on gazelles Gazelles run fast But cheetah run even faster (but for only a few minutes before they exhaust their energy) They are active hunters Canadian lynx feed on snowshoe hares as an active hunter Key predators: Lynx controls the hare’s population… so the populations oscillate Prey population in turn controls the predator’s population Not key predator: Antlions have little effect on their prey abundance 2. Number of prey eaten b) “Generalists” feed on a large number of prey and their choice limited by: How much energy is used to catch prey Some prey are easier to catch than others How many calories they gain (size of prey) A cow feeds many humans Each human would need many mice You are not going to bother collecting ants for food ☺ Prey abundance: If one particular prey type becomes abundant The predator will concentrate on that prey and ignore the others Generalists have their population abundance controlled by factors other than prey abundance Owl population depends on the number of territories available Territory = tree holes Abundance of prey (mice and rats) is less important on their owl pop. size Serengeti lions are controlled by dry season survival: Abundance of prey during the wet season allows more cubs to be born But in a bad dry season the cubs will die from starvation Climatic factor controls population size Similarly prey population is not fully controlled by the predator because the predator will switch to a second prey species if the population of the first prey species is reduced too much Fluctuations in prey and predator populations Generalist predator Specialized predator Generalist Predator Population and its Prey Specialist Predator Populations and its Prey 3. Competition between predators (predator niches) Competition requires the predators to specialize so to reduce their niche This depends on their size (to prey size) and their behavior (how they hunt) Different hunting specialization allows coexistence of predators ▪Cheetahs use their high speed to catch gazelles ▪Most other prey are to big for them ▪ Lions hunt wildebeest, buffalo and zebra (all large animals → big meal) ▪ Leopards hunt at night in wooded areas rather than grassland ▪So catch baboons and impala ▪ Hunting dogs hunt large antelope such as zebra using their endurance ▪ Keep running until the prey collapses from exhaustion ▪Caracal (smaller cat) can catch birds in flight + also hunt rats  Prey strategies Prey have many strategies for reducing predation And maintaining their populations Examples include: Having highly developed sense organs (detect predators from safe distance) Escaping at high speed Hiding from predator Being poisonous (many insects and fish) Group living (herds of mammals, flocks of birds, shoals of fish)  Group living Has the disadvantages in intense competition for food but advantages of: A large group has many eyes watching for predators so an individual can feed safely (head down) while others watch Herds often include different species of prey animals: Zebra have excellent eyesight Wildebeest = good sense of smell Antelopes = good hearing Predator detection is more efficient in group  Group defense ▪ A group prey can chase away a predator Crows attack Hawk ▪ Flocks of small birds may attack a predator, such as hawks ▪ If attacked a herd will go in all directions ▪ Very confusing to a predator which tries to concentrate on a single prey ▪ Ends up catching nothing Being in the center of the herd is safer Individuals on the outside constantly move inwards leaving new ones exposed Reducing the risk for each individual Shoal of Fish