APES

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Chapter 6

community

(ecology) a group of interdependent organisms inhabiting the same region and interacting with each other

population ecology

The study of populations in relation to the environment, including environmental influences on population density and distribution, age structure, and variations in population size.

population size

The number of individuals in a population.

population density

Number of individuals in a specified portion of a habitat. (Refers to how many individuals are in an area, not how they are dispersed)

population distribution

Spatial arrangement of organisms within an area

sex ratio

Ratio of males to females

age structure

Percentage of the population (or number of people of each sex) at each age level in a population.

density-dependent factors

Limiting factors (such as competition, predation, parasitism, and disease) that are affected by the number of individuals in a given area

limiting resource

A particular natural resource that, when limited, determines the carrying capacity of an ecosystem for a particular species

carrying capacity

Largest number of individuals of a population that a environment can support

density-independent factors

A limiting factor whose effects on a population are constant regardless of population density.

growth rate

An expression of the increase in the size of an organism or population over a given period of time

intrinsic growth rate

the maximum potential for growth of a population under ideal conditions with unlimited resources

exponential growth model

a mathematical description of idealized, unregulated population growth

j-shaped

Curve with a shape similar to that of the letter J; can represent prolonged exponential growth. See exponential growth.

logistic growth model

A growth model that describes a population whose growth is initially exponential, but slows as the population approaches the carrying capacity of the environment.

s-shaped

Leveling off of an exponential, J-shaped curve when a rapidly growing population exceeds the carrying capacity of its environment and ceases to grow.

overshoot

The extent to which a population exceeds the carrying capacity of its environment

die-off

a rapid decline in population size when carrying capacity is exceeded and resources are limited

k-selected species

Species that produce a few, often fairly large offspring but invest a great deal of time and energy to ensure that most of those offspring reach reproductive age.

r-selected species

Species that reproduce early in their life span and produce large numbers of usually small and short-lived offspring in a short period.

survivorship curves

They show the likelihood of survival at different ages throughout the lifetime of the organism.

corridors

A strip of natural habitat that connects two adjacent nature preserves to allow migration of organisms from one place to another

metapopulation

A collection of populations that have regular or intermittent gene flow between geographically separate units

community ecology

The study of how interactions between species affect community structure and organization

competition

the struggle between two or more living things that depend on the same limited resource

competitive exclusion principle

Ecological rule that states that no two species can occupy the same exact niche in the same habitat at the same time

resource partitioning

The division of environmental resources by coexisting species such that the niche of each species differs by one or more significant factors from the niches of all coexisting species

predation

An interaction in which one organism captures and feeds on another organism

pathogens

Microbes that cause disease

mutualism

A relationship between two species in which both species benefit

commensalism

A relationship between two organisms of different species where one benefits and the other is neither harmed nor benefited

symbiotic

Mutualism

keystone species

A species that influences the survival of many other species in an ecosystem

predator-mediated competition

Competition in which a predator is instrumental in reducing the abundance of a superior competitor, allowing inferior competitors to persist.

ecosystem engineers

an organism that causes changes in the physical environment sufficient to influence the structure of landscapes, ecosystems, or communities.

ecological succession

(ecology) the gradual and orderly process of change in an ecosystem brought about by the progressive replacement of one community by another until a stable climax is established

primary succession

An ecological succession that begins in an area where no biotic community previously existed

secondary succession

Succession following a disturbance that destroys a community without destroying the soil

pioneer species

First species to populate an area during primary succession

theory of island biogeography

The number of species found on an island is determined by a balance between two factors: the immigration rate (of species new to the island) from other inhabited areas and the extinction rate (of species established on the island). The model predicts that at some point the rates of immigration and extinction will reach an equilibrium point that determines the island's average number of different species (species diversity).

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