1.4 Species and 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

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

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

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 \n