Predation PDF

Species Interactions: Predation Lesson Objectives Describe the different types of predation Know 4 key differences between carnivores and herbivores Describe adaptations for predators and prey in carnivorous relationships and herbivorous relationships Be able to use the Lotka-Volterr...

Species Interactions: Predation Lesson Objectives Describe the different types of predation Know 4 key differences between carnivores and herbivores Describe adaptations for predators and prey in carnivorous relationships and herbivorous relationships Be able to use the Lotka-Volterra model to estimate changes in predator and prey populations Understand how carnivory and herbivory can change entire communities of species Predation Definitions Trophic interaction in which an individual of one species (predator) consumes individuals of another species (prey) Includes: Carnivory (predator and prey are both animals) Omnivory (predator is an animal or plant and prey is animals and plants) Herbivory (predator is an animal and prey is a plant or alga) Parasitism (predator is a parasite and prey is a host) Key differences between carnivores and herbivores: 1. Carnivores invariably kill their prey while herbivores usually do not kill the plants they eat (at least not right away) Key differences between carnivores and herbivores: 1. Carnivores invariably kill their prey while herbivores usually do not kill the plants they eat (at least not right away) 2. Animal prey can usually move away or hide from predators, but most plant prey cannot (subject to herbivory) Key differences between carnivores and herbivores: 1. Carnivores invariably kill their prey while herbivores usually do not kill the plants they eat (at least not right away) 2. Animal prey can usually move away or hide from predators, but most plant prey cannot (subject to herbivory) 3. Even though plant prey are often more abundant, their body tissues have much lower nitrogen content, and thus are less nutritious, than animal prey Key differences between carnivores and herbivores: 4. Most carnivores are generalists and most herbivores are specialists Most predators eat prey in relation to their availability Most herbivores tend to feed on specific parts of their plants (usually where there is the most nutrition – seeds and/or leaves) and they feed on specific species of prey (largely just insects that feed on single plant species  Carnivory Eat or be eaten, that is the question…sort of https://vimeo.com/53914149 Carnivory: Eat Hunt prey Adaptations include stealth (owl), speed (cheetah, peregrine falcon), morphological alterations (snakes), venom (vipers), etc. Sit and wait for prey Adaptations include building traps (antlions), mimicry (scorpionfishes), etc. Carnivory: Avoid being eaten Large size (e.g., elephants) Speed (e.g., gazelle) Body armor (e.g., pangolin, armadillo, snail) Toxins (e.g., rough-skinned newt, monarch) Mimicry (e.g., monarch lookalikes, flatworm that looks like snake) Crypsis/camouflage (e.g., ground squirrel)  Herbivory Eat or be less eaten? Herbivory: how to be less eaten? Produce a lot of seeds, even if only rarely This lets a plant hide from seed-eating herbivores and then overwhelm them (masting) Can also time to release seeds when herbivores are scarce (think insects in winter) Compensation or the replacement of lost tissues If apical meristem is lost or shade is reduced, can stimulate foliage growth Inducible defenses such as increase spine growth following predation of cacti Secondary compounds which are chemical defenses (e.g. arugula) Herbivory: Eat Behavioral accommodations (e.g., Bursera beetle larva) Digestive tracts that accommodates secondary compounds or mechanical deterrents such as spines Etc. Predator-Prey Population Cycles Case Study: Snowshoe hare-lynx Predator-Prey Population Cycles Case Study: Snowshoe hare-lynx Predator-Prey Population Cycles How do we evaluate possible causes of population cycles? Lotka-Volterra predator-prey model: dN/dt = rN – aNP dP/dt = baNP – mP N = number of prey individuals P = number of predator individuals Predator-Prey Population Cycles Lotka-Volterra predator-prey model: dN/dt = rN – aNP dP/dt = baNP – mP N = number of prey individuals P = number of predator individuals **when predators are absent, we should see exponential growth of prey Predator-Prey Population Cycles Lotka-Volterra predator-prey model: dN/dt = rN – aNP dP/dt = baNP – mP N = number of prey individuals P = number of predator individuals **when predators are present, the rate at which they will increase depends in part on how frequently predators and prey encounter one another, which is expected to increase as N and P increase **the constant a refers to the efficiency with which predators can capture their prey (bigger the value, the more efficient predators are at catching prey) Predator-Prey Population Cycles Lotka-Volterra predator-prey model: dN/dt = rN – aNP dP/dt = baNP – mP N = number of prey individuals P = number of predator individuals **predators starve when there is no prey, so the number of predators will decrease exponentially if N = 0 with a mortality rate (m) Predator-Prey Population Cycles Lotka-Volterra predator-prey model: dN/dt = rN – aNP dP/dt = baNP – mP N = number of prey individuals P = number of predator individuals ** when prey are present, individuals are added to the predator population according to the number of prey that are killed (aNP) and the efficiency with which prey are converted into predator offspring (the constant b) Lotka-Volterra Model Effects of predation on communities Carnivores can alter the composition of species within a community Case study: Anolis lizards in the Bahamas Broad range of prey, including spiders Thomas Schoener and David Spiller (researchers) set up experiment to see community level effects of predation Selected 12 small islands 4 groups of 3, each similar in size and vegetation In each group, one island had lizards, one was without, and one had them introduced  Effects of predation on communities Do the data support the hypothesis that spider species diversity decreased because Anolis lizards predate spiders? A Yes B No Effects of predation on communities Herbivores can alter the composition of species within a community, too Case study: Lesser snow geese Migrate from US to salt marshes that border Canada’s Hudson Bay Graze on marsh grasses and sedges Although they remove plant matter, they add nitrogen to soil by defecating every few minutes!! Nitrogen is taken up by plants to help with compensatory growth  Effects of predation on communities Intermediate amounts of grazing are good, result in highest Net Primary Productivity (NPP) measured as new aboveground plant growth Effects of predation on communities However, around 1970, snow goose densities increased exponentially (superabundant crop foods likely the cause) Dramatic negative impact, turned salt marshes into mud flats