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APES

Chapter 6
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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).