species interactions: predation

(+/-) interactions

predation:

• carnivory

herbivory

parasitism

predations

• a trophic interaction in which one organism kills and consumes another

  • predators consume many prey items in the course of their life

  • carnivory: both predator and prey animals

herbivory

• consumptions of primary producers (plant or algae) by primary consumers (often animals)

parasitism

• pne organism, parasite, lives in symbiosis with another organism, host, and consumes nutrients from it resulting in decreased host fitness

  • often does not result in host death

predation vs herbivory

• carnivores kill prey, herbivores dont kill plants

• animal prey can move away or hide from predators, plants can’t

• plants are more abundant but less nutrtitious than animals

• optimal foraging theory tells us diestay specialization depends on:

  • encounter rate: ease of searching and finding prey

  • handling time: time it takes to subdue/ consume/ digest/ detoxify prey

based on encounter rates and handling times of animals vs plants as food, would you expect predators or herbivores to be more generalist or specilist int heri diet?

• herbivores will be specialist because abundance and encounter rate

• predators generalist less likely to encounter the prey they want

carnivores tend to have broad diets

• most carnivores are generalists they eat prey in relation to their availbility without showing a preference for any particular prey

• exceptions:

  • lynx and coyotes eat more hares than would be expected even at low abundance

  • prey switching

prey switching

• when predators concentrate on whatever prey is most abundant, guppies eat fruit flies vs worms

• at fifty

herbivores as specialists

• plant part and plant species

• most herbovores eat leaves (abundant relatively nutritious)

• others specialize on roots phloems seeds bark

• reduce survival growth reproduction of plants

• most herbivores insects specialize on particular plant species

• exceptions:

  • large herbivores like cows will just everything above ground

  • grasshoppers are generalists

  • apple snail

adaptations of plants against herbivory/ seed predation

avoidance

• masting: producing large numbrs of seeds in some years and few/ no seeds in other years

tolerance

• compensations: removal of plant tissue stimulates new growth

defense

• structural defenses: tough leaves, spines, thorns, rough edges, hairs

• secondary compounds: toxic chemicals to reduce herbivory or compounds that attract predators or parasitouds to attack the herbivores

• induced defense: stimulated by herbivor attack vs constitutive

adaptaitons in herbivores

• evolutionary “arms race”

• some herbivores can tolerate plant structural defenses

• some herbivores can tolerate plant toxins

  • monarch caterpillars can sequester the toxic cardenolides in milkweed to make themselves toxic

why is the earth green?

• top down control of herbivores by predators og hospital

• plant defenses “green desert”

  • need entire community to have a nutritious land

lynx and hare, get more of an explanation

• 200 years of Hudson’s bay company records document populations cycles of lynx and snowshoe hares

• populations peak about every 10 years, hare populatiosn rise and fall in synchrony acorss boad regions of canada

• belived it was stress?