interspecific interactions

• predation: a member of one species kills and feeds on a member of another species

  • eg. wolf (predator) / caribou (prey)

• herbivory: the consumption of plant material by animals

  • eg. caribou (herbivore) / moss (plant)

• symbiosis: a relationship between two species that live in intimate contact — types are parasitism, commensalism, and mutualism.

• parasitism: a close relation between two species in which one benefits at the expense of the other but doesn’t necessarily kill it

  • eg. tapeworms (parasite) / wolf

• commensalism: a close relation between two species in which one benefits, and the other is neither helped nor harmed

  • eg. arctic fox eats polar bear’s leftovers

• mutualism: a close relation between two species in which they both benefit

  • eg. lichen — fungus (provides habitat) / algae (provides food)

• competition: a relationship between two organisms that struggle for the same resource

• resource: anything that an organism needs in order to survive or reproduce

  • eg. space, food, water, oxygen

• when a resource is used by one organism, it becomes unavailable to others → limited

  • interspecific competition: competition between individuals of different species

  • intraspecific competition: competition between individuals of the same species

*in this chart, “+” indicates a positive effect, “/” indicates a neutral effect, and “—” indicates a negative effect

competition

biological niches

• niche: a species’ functional role in an ecosystem, all the physical, chemical, and biological conditions in which it lives and reproduces

  • what it eats, where it nests, when it reproduces

  • not a habitat (where a population typically lives)

• principle of competitive exclusion: two species will not occupy the same niche, live in the same habitat, and compete for the same resources for very long

  • either one becomes extinct, or the species adapt/evolve to exploit different resources

• resource partitioning: the idea that over evolutionary time, species divide up scarce resources and reduce competition

• fitness: the ability of an individual to survive and produce offspring

  • a measure of reproductive success

types of species

tolerance limits

there are limits to the environmental conditions a living organism can endure

• tolerance limits: the minimums and maximums beyond which a species cannot survive for each environmental factor

• critical limiting factor: a single limiting factor which outweighs the rest in determining whether a species is present in an environment

types of species

• specialist: a species with a narrow niche

  • eg. koalas only eat eucalyptus

  • more susceptible to extinction

• generalist: a species with a broad niche

  • eg. raccoons are omnivores and eat nearly everything

  • less susceptible to extinction

• indicator species: a species whose presence, absence, or abundance in a certain location indicates something about the environmental conditions present there

  • eg. lichens are sensitive to air pollution; thus, their presence indicates the amount of nitrogen in the air

• native species: a species that naturally lives in a particular ecosystem

• immigrant species/alien species: a species that has migrated or has been introduced by humans to a certain area

  • sometimes become invasive species, which damage the ecosystem

• dominant species: the most abundant species in an ecosystem, or the one which has the greatest biomass in an ecosystem

  • are likely but not always important to the functions of an ecosystem due to their numbers

• keystone species: a species that plays a role in an ecosystem that affects many other organisms

  • effects far exceed the species’ abundance in an ecosystem

  • removal of a keystone species changes an ecosystem’s composition

  • term comes from architecture, the keystone which keeps pieces of an arch from falling apart