2.1 Individuals, populations, communities, and ecosystems

Population

group of individuals of the same species, living in the same area, interbreeding

Community

all populations of different species living and interacting in an area

Ecosystem

a community of interacting organisms and the abiotic (physical/chemical) environment they interact with

Habitat

the environment in which a species normally lives

Niche

the role and position a species occupies in its environment, including how it obtains resources, interacts with other species, and its tolerance range for abiotic factors

Fundamental niche

full range of conditions/resources a species could theoretically occupy

Realized niche

actual niche occupied by a species, limited by competition/biotic interactions

Carrying capacity

maximum population size an environment can sustainably support

Limiting factor

a factor that restricts population growth, can be density-dependent (e.g. food, competition, disease) or density-independent (e.g. natural disasters, climate)

Survivorship curve (Type I)

high survival early/mid-life, high mortality in old age (e.g., humans, large mammals)

Survivorship curve (Type II)

constant mortality rate throughout life (e.g., some birds, small mammals)

Survivorship curve (Type III)

high mortality early in life, few survive to adulthood (e.g., most fish, insects)

Competition

interaction where organisms compete for shared limited resources; intraspecific (same species) or interspecific (different species)

Predation

one organism (predator) kills and consumes another (prey)

Parasitism

a species interaction where the parasite benefits and the host is harmed (not usually killed)

Mutualism

a species interaction where both species benefit

Commensalism

a species interaction where one species benefits and the other is unaffected

Zone of tolerance

the range of an abiotic factor within which an organism can survive, including an optimum range and zones of intolerance at the extremes

Eurytopic

describes a species with a wide tolerance range for an abiotic factor

Stenotopic

describes a species with a narrow tolerance range for an abiotic factor