Predation Great White Shark and Fur Seal
Specialists and Generalist Predators Advantages to being a specialist 1. Avoid interspecific competition 2. Allows evolution to overcome chemical defense 3. Allows evolution of cryptic coloration that matches prey - mostly for insects on plants 4. Increases chance of mate encounter Advantages of being a generalist 1. Flexibility in face of environmental uncertainty 2. Broad diet needed to get all necessary nutrients and vitamins 3. Avoid overdosing on any one toxin - mostly for animals grazing on chemically defended plants
Factors affecting predator behavior 1. Search time - the amount of time spent looking for food items 2. Handling time - the amount of time spent capturing prey once it is found, also includes time for consuming prey and time to digest before a predator can search for food again
Black-footed ferret – specialist – 90% of diet is prairie dogs
Food Preferences • A preference exists if the proportion of a type of food is higher in the animal’s diet than it is in its proportion in the environment • Ranked preference – predator preferentially eats prey which is most valuable (usually in terms of calories) • Balanced preference – predator eats prey items that provide integral parts of a balanced and mixed diet (usually in terms of nutrients and vitamins)
Preferences • Fixed preference – predator eats certain items regardless of what else is available – can be fixed in terms of species consumed or energy consumed
Search image – this image has dashes arranged as L, as T, and plus signs – can you find the Ts?
Effects on populations • Population regulation refers to the tendency of a population to decrease in size when above a particular level, and to increase in size when below that level. Population regulation can only occur as a result of one or more density dependent processes acting on birth or death rates. • Population abundance is determined by the combined effects of all factors and processes that influence population size, whether they are density dependent or density independent.
Arctic Ground Squirrel – Predator population is self-limited
Predator Switching Regulates Prey Population Bank vole Tawny Owl
Lynx Ruffed Grouse Snowshoe hare