Biology Unit 8 Ecology

population

A group of individuals of a single species living in the same general area.

density

The number of individuals per unit area or volume.

dispersion

The pattern of spacing among individuals within the boundaries of the population.

mark-recapture method

A sampling technique used to estimate the size of wildlife populations.

immigration

The influx of new individuals from other areas.

emigration

The movement of individuals out of a population and into other locations.

clumped

A pattern of dispersion in which individuals are aggregated in patches.

uniform

An evenly spaced pattern of dispersion.

territoriality

The defense of a bounded physical space against encroachment by other individuals.

random dispersion

Unpredictable spacing; the position of each individual in a population is independent of other individuals.

Demography

The study of the key characteristics of populations and how they change over time.

life table

A summary of the survival and reproductive rates of individuals in specific age-groups within a population.

cohort

A group of individuals of the same age.

survivorship curve

A plot of the proportion or numbers in a cohort still alive at each age.

exponential population growth

The growth of a population in an ideal, unlimited environment.

intrinsic rate of increase

The per capita rate at which an exponentially growing population increases in size at each instant in time.

carrying capacity

The maximum population size that a particular environment can sustain.

logistic population growth

A model where the per capita rate of population growth approaches zero as the population size nears the carrying capacity (K).

life history

The traits that affect an organism's schedule of reproduction and survival.

semelparity

A "one-shot" pattern of big-bang reproduction.

iteroparity

Repeated reproduction over an organism's lifetime.

K-selection

Selection for traits that are advantageous at high population densities.

r-selection

Selection for traits that maximize reproductive success in uncrowded environments (low densities).

density independent

A birth rate or death rate that does not change with population density.

density dependent

A death rate that increases with population density or a birth rate that falls with rising density.

population dynamics

Population fluctuations from year to year or place to place.

metapopulation

A number of local populations linked by immigration and emigration.

demographic transition

The movement from high birth and death rates toward low birth and death rates in human populations.

age structure

The relative number of individuals of each age in the population.

infant mortality

The number of infant deaths per 1,000 live births.

life expectancy at birth

The predicted average length of life at birth.

ecological footprint

The aggregate land and water area required by each person, city, or nation to produce all the resources it consumes and to absorb all the waste it generates.

community

A group of populations of different species living in close enough proximity to interact.

interspecific interactions

Ecological interactions between individuals of different species in a community.

competition

A -/- interaction that occurs when individuals of different species each use a resource that limits the survival and reproduction of both.

competitive exclusion

The local elimination of the inferior competitor due to two species competing for the same limiting resources.

ecological niche

The specific set of biotic and abiotic resources that an organism uses in its environment.

resource partitioning

The differentiation of niches that enables similar species to coexist in a community.

character displacement

The tendency for characteristics to diverge more in sympatric (overlapping) than in allopatric (geographically separate) populations of two species.

exploitation

Any type of +/- interaction in which individuals of one species benefit by feeding on (and thereby harming) individuals of the other species.

Predation

A +/- interaction in which an individual of one species (predator) kills and eats an individual of the other species (prey).

aposematic coloration

Warning coloration that warns predators that an animal has effective chemical defenses.

Cryptic coloration

Camouflage that makes prey difficult to see.

Batesian mimicry

When a palatable or harmless species mimics an unpalatable or harmful species to which it is not closely related.

Müllerian mimicry

When two or more unpalatable species resemble each other.

Herbivory

An exploitative (+/-) interaction in which an organism eats parts of a plant or alga.

Parasitism

A +/- exploitative interaction in which one organism derives its nourishment from another organism, which is harmed.

parasite

The organism that derives nourishment from its host in a +/- interaction.

host

The organism that is harmed in a parasitic interaction.

endoparasites

Parasites that live within the body of their host.

ectoparasites

Parasites that feed on the external surface of a host.

positive interactions

A +/+ or +/0 interaction between members of two species in which at least one individual benefits and neither is harmed.

Mutualism

A +/+ interaction that benefits individuals of both of the interacting species.

commensalism

An interaction that benefits the individuals of one of the interacting species but neither harms nor helps the individuals of the other species (+/0).

species diversity

The variety of different kinds of organisms that make up the community.

species richness

The number of different species in a community.

relative abundance

The proportion each species represents of all individuals in the community.

Shannon diversity index (H)

An index of community diversity based on species richness and relative abundance.

biomass

The total mass of all organisms in a habitat.

introduced species

Organisms that humans have moved to regions outside of the species' native range.

trophic structure

The feeding relationships between organisms in a community.

food chain

The transfer of chemical energy from its source in plants and other autotrophs through herbivores to carnivores and eventually to decomposers.

trophic level

The position an organism occupies in a food chain.

food web

A group of food chains linked together to show complex trophic interactions.

energetic hypothesis

Suggests that the length of a food chain is limited by the inefficiency of energy transfer along the chain.

Foundation species

Species that have strong effects on their communities as a result of their large size or high abundance.

keystone species

Species that are not usually abundant but exert strong control on community structure by their pivotal ecological roles.

ecosystem engineers

Species that create or dramatically alter their environment.

bottom-up control

When the abundance of organisms at each trophic level is limited by nutrient supply or the availability of food at lower trophic levels.

top-down control

When the abundance of organisms at each trophic level is controlled by the abundance of consumers at higher trophic levels.

disturbance

An event, such as a storm, fire, or human activity, that changes a community by removing organisms from it or altering resource availability.

nonequilibrium model

Describes most communities as constantly changing after a disturbance, rather than being at a stable balance.

intermediate disturbance hypothesis

States that moderate levels of disturbance foster greater species diversity than do high or low levels of disturbance.

ecological succession

The gradual process by which the species composition of a community changes and develops over time after a disturbance.

primary succession

Ecological succession that begins in a virtually lifeless area where soil has not yet formed.

secondary succession

The recolonization of an area after a major disturbance has removed most but not all of the organisms in a community.

evapotranspiration

The evaporation of water from soil and plants; used as a measure of climate impacts on species richness.

species-area curve

The concept that, all other factors being equal, the larger the geographic area of a community, the more species it has.

pathogens

Disease-causing microorganisms, viruses, viroids, or prions.

zoonotic pathogens

Pathogens that are transferred to humans from other animals.

vector

An intermediate species, such as a tick or mosquito, that transfers a zoonotic pathogen to a host.

ecosystem

The sum of all the organisms living in a given area and the abiotic factors with which they interact.

law of conservation of mass

A physical law stating that matter, like energy, cannot be created or destroyed.

primary producers

The trophic level that ultimately supports all others; consists of autotrophs.

primary consumers

Herbivores, which eat plants and other primary producers.

secondary consumers

Carnivores that eat herbivores.

tertiary consumers

Carnivores that eat other carnivores.

decomposers

Heterotrophs (consumers) that get their energy from breaking down detritus.

detritus

Nonliving organic material, such as the remains of dead organisms, feces, and fallen leaves.

primary production

The amount of light energy converted to chemical energy by autotrophs during a given time period.

gross primary production (GPP)

Total primary production in an ecosystem.

Net primary production (NPP)

Gross primary production minus the energy used by the primary producers for their own cellular respiration.

net ecosystem production (NEP)

A measure of the total biomass accumulation by both producers and consumers during a given period.

limiting nutrient

The element that must be added for primary production to increase in an ecosystem.

eutrophication

A process by which nutrients, particularly phosphorus and nitrogen, become highly concentrated in a body of water, leading to increased growth of organisms such as algae.

secondary production

The amount of chemical energy in consumers' food that is converted to their own new biomass during a given period.

production efficiency

The percentage of energy stored in assimilated food that is used for growth and reproduction, not respiration.

trophic efficiency

The percentage of production transferred from one trophic level to the next (averaging about 10%).

biogeochemical cycles

Nutrient cycles that involve both biotic and abiotic components of ecosystems.

bioremediation

The use of organisms—usually prokaryotes, fungi, or plants—to detoxify polluted ecosystems.