Glossary

William D. Bowman

University of Colorado

Sally D. Hacker

Oregon State University

Numbers in brackets refer to the chapter(s) where the term is introduced.

A

abiotic Of or referring to the physical or nonliving environment.

absolute population size The actual number of individuals in a population. Compare relative population size.

abundance The number of individuals of a species that are found in a given area; abundance is often measured by population size or population density.

acclimatization An organism's adjustment of its physiology, morphology, or behavior to lessen the effect of an environmental change and minimize the associated stress.

acid neutralizing capacity The ability of the chemical environment to counteract acidity, usually associated with concentrations of base cations, including Ca²⁺, Mg²⁺, and K⁺.

acidity A measure of the ability of a solution to behave as an acid, a compound that releases protons (H⁺) to the water in which it is dissolved. Compare alkalinity.

adaptation (1) A physiological, morphological, or behavioral trait with an underlying genetic basis that enhances the survival and reproduction of its bearers in their environment.

A process of evolutionary change in which traits that confer survival or reproductive advantages tend to increase in frequency in a population over time. adaptive evolution A process of evolutionary change in which traits that confer survival or reproductive advantages tend to increase in frequency in a population over time.

adaptive management A component of ecosystem management in which management actions are seen as experiments and future management decisions are determined by the outcome of present decisions.

adaptive radiation An event in which a group of organisms gives rise to many new species that expand into new habitats or new ecological roles in a relatively short time.

aerosols Solid or liquid particles suspended in the atmosphere.

age structure The proportion of individuals of a population in each age class.

albedo The amount of solar radiation reflected by a surface, usually expressed as a percentage of the incoming solar radiation.

alkalinity A measure of the ability of a solution to behave as a base, a compound that takes up protons (H⁺) or releases hydroxide ions (OH ). Compare acidity.

Allee effect A decrease in the population growth rate (r or λ) as the population density decreases.

allele One of two or more forms of a gene that result in the production of different versions of the protein that the gene encodes.

allelopathy A mechanism of competition in which individuals of one species release chemicals that harm individuals of other species.

allocation The relative amounts of energy or resources that an organism devotes to different functions.

allochthonous inputs Inputs produced outside the ecosystem.

alluvium Sediment deposited by flowing water.

alpha diversity Species diversity at the local or community scale. Compare beta diversity, gamma diversity.

alternation of generations A complex life cycle, found in many algae and all plants, in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte.

alternative stable states Different community development scenarios, or community states, that are possible at the same location under similar environmental conditions.

amensalism A species interaction in which individuals of one species are harmed while individuals of the other species do not benefit and are not harmed (-/0 relationship).

anisogamy Production of two types of gametes of different sizes. Compare isogamy.

anthropogenic Of, relating to, or caused by humans or their activities.

arbuscular mycorrhizae Mycorrhizae in which the fungal partner grows into the soil, extending some distance away from the plant root, and also grows between some root cells while penetrating others.

Arctic ozone dent An area of the stratosphere over the Arctic region where ozone concentrations are low but have not dropped below 220 Dobson units.

assimilation efficiency The proportion of ingested food that is assimilated by an organism.

atmospheric deposition The movement of particulate and dissolved matter from the atmosphere to Earth's surface by gravity or in precipitation.

atmospheric pressure The pressure exerted on a surface due to the mass of the atmosphere above it.

autochthonous energy Energy produced within the ecosystem.

autotroph An organism that converts energy from sunlight or from inorganic chemical compounds in the environment into chemical energy stored in the carbon-carbon bonds of organic compounds. Compare heterotroph.

avoidance A response to stressful environmental conditions that lessens their effect through some behavior or physiological activity that minimizes an organism's exposure to the stress. Compare tolerance.

behavioral ecology The study of the ecological and evolutionary basis of animal behavior.

benthic zone The bottom of a body of water, including the surface and shallow subsurface layers of sediment.

beta diversity The change in species diversity and composition, or turnover of species, from one community type to another across the landscape. Compare alpha diversity, gamma diversity.

bioaccumulation A progressive increase in the concentration of a substance in an organism's body over its lifetime.

biocrust A crust on the soil surface composed of a mix of species of cyanobacteria, lichens, and mosses; also called a biocrust.

biodiversity The diversity of important ecological entities that span multiple spatial scales, from genes to species to communities.

biogeochemistry The study of the physical, chemical, and biological factors that influence the movements and transformations of chemical elements.

biogeographic region A portion of Earth containing a distinct biota that differs markedly from the biotas of other biogeographic regions in its species composition and diversity.

biogeography The study of variation in species composition and diversity among geographic locations.

biological reserve An often small nature reserve established with the conservation of a single species or ecological community as the main conservation objective.

biological soil crust A crust on the soil surface composed of a mix of species of cyanobacteria, lichens, and mosses; also called a biocrust.

biomagnification A progressive increase in the tissue concentrations of a substance in animals at successively higher trophic levels that results as animals at each trophic level consume prey with higher concentrations of the substance due to bioaccumulation.

biomass The mass of living organisms, usually expressed per unit of area.

biome A large-scale terrestrial biological community shaped by the regional climate, soil, and disturbance patterns where it is found, usually classified by the growth form of the dominant plants.

biosphere The highest level of biological organization, consisting of all living organisms on Earth plus the environments in which they live; located between the lithosphere and the troposphere.

biotic Of or referring to the living components of an environment. Compare abiotic.

biotic resistance Interactions of the native species in a community with non­native species that exclude or slow the growth of those non-native species.

bottom-up control Limitation of the abundance of a population by nutrient supply or by the availability of food. Compare top-down control.

boundary layer A zone close to a surface where a flow of fluid, usually air, encounters resistance and becomes turbulent.

buffer zone A portion of a nature reserve surrounding a core natural area where controls on land use are less stringent than in the core natural area, yet land uses are at least partially compatible with many species' resource requirements.

Compare core natural area.

C

C₃ photosynthetic pathway A biochemical pathway involving the uptake of CO₂ by the enzyme ribulose 1,5 bisphosphate carboxylase/oxygenase (rubisco) and synthesis of sugars by the Calvin cycle.

C₄ photosynthetic pathway A biochemical pathway involving the daytime uptake of CO₂ by the enzyme phosphoenol pyruvate carboxylase (PEPcase) in mesophyll cells; the carbon is then transferred as a four-carbon acid to the bundle sheath cells, where CO₂ is released to the Calvin cycle for sugar synthesis. Compare C₃ photosynthetic pathway, crassulacean acid metabolism.

Calvin cycle The biochemical pathway used by photosynthetic and chemosynthetic organisms to fix carbon and synthesize sugars.

carnivore An animal predator that kills and consumes tissues or fluids of live animals.

carnivory A trophic species interaction in which the predator is an animal (carnivore) and the prey is an animal.

carrying capacity The maximum population size that can be supported indefinitely by the environment, represented by the term K in the logistic equation.

catchment The area in a terrestrial ecosystem that is drained by a single stream; a common unit of study in terrestrial ecosystem studies; also called a watershed.

cation exchange capacity A soil's ability to hold nutrient cations such as Ca²⁺, K⁺, and Mg²⁺ and exchange them with the soil solution, determined by the clay content of the soil.

character displacement A process in which competition causes the phenotypes of competing species to evolve to become more different over time, thereby easing competition.

cheater In a mutualism, an individual that increases its production of offspring by overexploiting its mutualistic partner.

chemical weathering The chemical breakdown of soil minerals leading to the release of soluble forms of nutrients and other elements. Compare mechanical weathering.

chemosynthesis The use of energy from inorganic chemical compounds to fix CO₂ and produce carbohydrates using the Calvin cycle; also called chemolithotrophy.

clay Fine soil particles (displacement A process in which the best competitor uses limiting resources that the weaker competitor requires ultimately causing a decline in the weaker competitor's population growth to the point of extinction.

competitive exclusion A process in which the best competitor uses limiting resources that the weaker competitor requires ultimately causing a decline in the weaker competitor's population growth to the point of extinction.

The principle that two species that use a limiting resource in the same way cannot coexist indefinitely.

competitive exclusion principle The principle that two species that use a limiting resource in the same way cannot coexist indefinitely.

competitive networks Sets of competitive interactions involving multiple species in which every species negatively interacts with every other species, thus promoting species coexistence.

competitive plants In Grime's triangular model, plants that are superior competitors under conditions of low stress and low disturbance. Compare ruderals, stress-tolerant plants.

complementarity hypothesis A hypothesis proposing that as the species richness of a community increases, there is a linear increase in the positive effects of those species on community function. Compare idiosyncratic hypothesis and redundancy hypothesis.

complex life cycle A life cycle in which there are at least two distinct stages that differ in their habitat, physiology, or morphology.

conduction The transfer of sensible heat through the exchange of kinetic energy between molecules due to a temperature gradient. Compare convection.

conservation biology The scientific study of phenomena that affect the maintenance, loss, and restoration of biodiversity.

consumer An organism that obtains its energy by eating other organisms or their remains. Compare producer.

consumption efficiency The proportion of the biomass available at one trophic level that is ingested by consumers at the next trophic level.

continental climate The climate typical of terrestrial areas in the middle of large continental land masses at high latitudes, characterized by high variation in seasonal temperatures. Compare maritime climate.

continental drift The slow movement of tectonic plates (sections of Earth's crust) across Earth's surface.

controlled experiment A standard scientific approach in which an experimental group (that has the factor being tested) is compared with a control group (that

lacks the factor being tested).

convection The transfer of sensible heat through the exchange of air and water molecules as they move from one area to another. Compare conduction.

convergence The evolution of similar growth forms among distantly related species in response to similar selection pressures.

core natural area A portion of a nature reserve where the conservation of biodiversity and ecological integrity takes precedence over other values or uses. Compare buffer zone.

Coriolis effect The apparent deflection of air or water currents when viewed from a rotating reference point such as Earth's surface.

crassulacean acid metabolism (CAM) A photosynthetic pathway in which CO₂ is fixed and stored as an organic acid at night, then released to the Calvin cycle during the day. Compare C₃ photosynthetic pathway, C₄ photosynthetic pathway.

crypsis A defense against predators in which prey species have a shape or coloration that provides camouflage and allows them to avoid detection.

D

decomposition The physical and chemical breakdown of detritus by detritivores, leading to the release of nutrients as simple, soluble organic and inorganic compounds that can be taken up by other organisms.

delayed density dependence A pattern of population growth in which delays in the effect of population density on population size can contribute to population fluctuations.

demographic stochasticity Chance events associated with whether individuals survive or reproduce.

denitrification A process by which certain bacteria convert nitrate (NO₃^-) into nitrogen gas (N₂) and nitrous oxide (N₂O) under hypoxic conditions.

density-dependent A factor that causes birth rates, death rates, or dispersal rates to change as the density of a population changes. Compare density-independent.

density-independent A factor whose effects on birth and death rates are independent of population density. Compare density-dependent.

desertification Degradation of formerly productive land in arid regions resulting in loss of plant cover and acceleration of soil erosion.

detritivore A heterotroph that consumes detritus.

detritus Freshly dead or partially decomposed remains of organisms.

dilution effect A phenomenon in which the chance that any particular member of a group is the one attacked (as by a predator) decreases as the number of individuals in the group increases.

direct development A simple life cycle that goes directly from fertilized egg to juvenile without passing through a free-living larval stage.

direct interaction An interaction that occurs between two species, such as predation, competition, or a positive interaction. Compare indirect interaction.

directional selection Selection that favors individuals with one extreme of a heritable phenotypic trait. Compare disruptive selection, stabilizing selection.

dispersal The movement of organisms or propagules.

dispersal limitation A situation in which the limited capacity for dispersal of a species prevents it from reaching areas of suitable habitat.

dispersion The spatial arrangement of individuals within a population.

disruptive selection Selection that favors individuals with a phenotype at either extreme over those with an intermediate phenotype. Compare directional selection, stabilizing selection.

distribution The geographic area where individuals of a species are present.

disturbance An abiotic event that kills or damages some individuals and thereby creates opportunities for other individuals to grow and reproduce.

dormancy A state in which little or no metabolic activity occurs.

doubling time (t_d) The number of years it takes a population to double in size.

downwelling The sinking of deep ocean water from the surface.

dynamic equilibrium model An elaboration of the intermediate disturbance hypothesis proposing that species diversity is maximized when the level of disturbance and the rate of competitive displacement are roughly equivalent.

E

ecological footprint The total area of productive ecosystems required to support a population.

ecology The scientific study of interactions between organisms and their environment.

ecosystem All the organisms in a given area as well as the physical environment in which they live; an ecosystem can include one or more communities.

ecosystem management An approach to habitat management in which scientifically based policies and practices guide decisions on how best to meet an overarching goal of sustaining ecosystem structure and function for long periods.

ecosystem services Natural processes that sustain human life and that depend on the functional integrity of natural communities and ecosystems.

ecotype A population with adaptations to unique local environmental conditions. ectomycorrhizae Mycorrhizae in which the fungal partner typically grows between plant root cells and forms a mantle around the exterior of the root. Compare arbuscular mycorrhizae.

ectoparasite A parasite that lives on the surface of another organism. Compare endoparasite.

ectotherm An animal that regulates its body temperature primarily through energy exchange with its external environment. Compare endotherm.

edge effects Abiotic and biotic changes that are associated with an abrupt habitat boundary such as that created by habitat fragmentation.

effective population size The number of individuals in a population that can contribute offspring to the next generation.

El Nino Southern Oscillation (ENSO) An oscillation of pressure cells and sea surface temperatures in the equatorial Pacific Ocean that causes widespread climatic variation and changes in upwelling currents.

emigration The movement of individuals out of an existing population.

endemic A species that occurs in a particular geographic location and nowhere else on Earth.

endoparasite A parasite that lives inside the body of its host organism. Compare ectoparasite.

endotherm An animal that regulates its body temperature primarily through internal metabolic heat generation. Compare ectotherm.

environmental science An interdisciplinary field of study that incorporates concepts from the natural sciences (including ecology) and the social sciences (e.g., politics, economics, ethics), focused on how people affect the environment and how we can address environmental problems.

environmental Stochasticity Erratic or unpredictable changes in the environment.

epilimnion The warm surface layer of water in a lake, lying above the thermocline, that forms during the summer in some lakes of temperate and polar regions. Compare hypolimnion.

equilibrium theory of island biogeography A theory proposing that the number of species on an island or in an island-like habitat results from a dynamic balance between immigration rates and extinction rates.

eutrophic Nutrient-rich; characterized by high primary productivity. Compare oligotrophic, mesotrophic.

eutrophication A change in the nutrient status of an ecosystem from nutrient­poor to nutrient-rich; such changes occur naturally, but they may also be caused by nutrient inputs that result from human activities.

evapotranspiration The sum of water loss through evaporation and transpiration.

evolution (1) Change in allele frequencies in a population over time. (2) Descent with modification; the process by which organisms gradually accumulate differences from their ancestors.

evolutionary tree A branching diagram that represents the evolutionary history of a group of organisms.

exploitation competition An interaction in which species compete indirectly through their mutual effects on the availability of a shared resource. Compare interference competition.

exponential growth The change in the number of individuals within a population over time that is characterized by continuous birth and death at each instance in time. Compare geometric growth.

exponential growth rate (r) A constant whose value is determined by the per capita (or per individual) birth rate minus the per capita death rate at each instance in time; also called the intrinsic rate of increase. Compare geometric population growth rate.

extent In landscape ecology, the area or time period encompassed by a study; together with grain, extent characterizes the scale at which a landscape is studied. Compare grain.

extinction vortex A pattern in which a small population that drops below a certain size becomes even more vulnerable to the problems that threaten small populations and hence may decrease even further in size, perhaps spiraling toward extinction.

facilitation A trophic or non-trophic species interaction in which one or both species benefit and neither is harmed. See also mutualism, commensalism.

fecundity The average number of offspring produced by a female while she is of age x (denoted F_x in a life table).

Ferrell cell A large-scale, three-dimensional pattern of atmospheric circulation in each hemisphere, located at mid-latitudes between the Hadley and polar cells.

finite rate of increase A constant whose value is determined by the per capita (or per individual) birth rate minus the per capita death rate at each discrete time period; also called the finite rate of increase. Compare exponential growth rate.

fitness The genetic contribution of an organism's descendants to future generations.

fixation (1) The uptake of the gaseous form of a compound, including CO₂ in photosynthesis and N₂ in nitrogen fixation, by organisms for use in metabolic functions. (2) With respect to the genetic composition of a population, an allele frequency of 100%.

flagship species A charismatic species that may be emphasized in conservation efforts because it helps to garner public support for a conservation project.

focal species One of a group of species selected as a priority for conservation efforts, chosen because its ecological requirements differ from those of other species in the group, thereby helping to ensure that as many different species as possible receive protection.

food web A diagram showing the connections between organisms and the food they consume.

foundation species A species that has large, community-wide effects on the habitat or food of other species by virtue of its size or abundance.

fugitive species A species that can persist in an area only if disturbances occur regularly and must therefore disperse from one place to another as environmental conditions change.

functional group A subset of a community that includes species that function in similar ways, but do not necessarily use the same resources. Compare guild.

fundamental niche The full set of resources, along with other biotic and abiotic requirements, that are suitable for a species excluding the negative interactions with other species.

G

gamma diversity Species diversity at the regional scale; the regional species pool. Compare alpha diversity, beta diversity.

gene flow The transfer of alleles from one population to another via the movement of individuals or gametes.

generation time (G) The average age of the parents of all the offspring produced within the cohort.

genet A genetic individual, resulting from a single fertilization event; in organisms that can reproduce asexually, a genet may consist of multiple, genetically identical parts, each of which has the potential to function as an independent physiological unit. Compare ramet.

genetic drift A process in which chance events determine which alleles are passed from one generation to the next, thereby causing allele frequencies to

fluctuate randomly over time; the effects of genetic drift are most pronounced in small populations.

genotype The genetic makeup of an individual.

geographic range The entire geographic region over which a species is found.

geometric growth The change in the number of individuals within a population over time that is characterized by birth and death from one discrete time period to the next. Compare exponential growth.

geometric population growth rate (λ) A constant whose value is determined by the per capita (or per individual) birth rate minus the per capita death rate at each discrete time period; also called the finite rate of increase. Compare exponential growth rate.

grain In landscape ecology, the size of the smallest homogeneous unit of study (such as a pixel in a digital image), which determines the resolution at which a landscape is observed; together with extent, grain characterizes the scale at which a landscape is studied. Compare extent.

gravitational potential The energy associated with gravity.

greenhouse effect The warming of Earth by gases in the atmosphere that absorb and reradiate infrared energy emitted by Earth's surface.

greenhouse gases Atmospheric gases that absorb and reradiate the infrared radiation emitted by Earth's surface, including water vapor (H₂O), carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O).

gross primary production (GPP) The amount of energy that autotrophs capture by photosynthesis and chemosynthesis per unit of time. Compare net primary

production.

guild A subset of a community that includes species that use the same resources, whether or not they are taxonomically related. Compare functional group.

H

habitat corridor A relatively narrow patch that connects blocks of habitat and often facilitates the movement of species between those blocks.

habitat degradation Anthropogenic change that reduces the quality of habitat for many, but not all, species.

habitat fragmentation The breaking up of once continuous habitat into a complex pattern of spatially isolated habitat patches.

habitat loss The outright conversion of an ecosystem to another use by human activities.

habitat mutualism A mutualism in which one partner provides the other with shelter, a place to live, or favorable habitat.

Hadley cell A large-scale, three-dimensional pattern of atmospheric circulation in each hemisphere in which air is uplifted at the equator and subsides at about 30°N and S.

heat capacity The amount of energy required to raise the temperature of a substance.

herbivore An animal predator that consumes, or partially consumes, the tissues or internal fluids of living plants or algae.

herbivory A trophic species interaction in which the predator is an animal

(herbivore) and the prey is a plant or alga.

heterotroph An organism that obtains energy by consuming energy-rich organic compounds made by other organisms. Compare autotroph.

hibernation Torpor lasting several weeks during the winter; a strategy that is possible only for animals that have access to enough food and can store enough energy reserves.

horizons Layers of soil distinguished by their color, texture, and permeability.

horizontal interactions Non-trophic interactions, such as competition and some positive interactions, that occur within a trophic level.

host An organism on or within which an herbivore, parasite, or mutualist lives and feeds.

hypolimnion The densest, coldest water layer in a lake, lying below the thermocline. Compare epilimnion.

hyporheic zone The portion of the substrate below and adjacent to a stream bed where water movement still occurs, either from the stream or from groundwater moving into the stream.

hypothesis A possible answer to a question developed using previous knowledge or intuition.

An iterative and self-correcting process by which scientists learn about the natural world, consisting of four steps: (1) observe nature and ask a question about those observations; (2) develop possible answers to that question (hypotheses); (3) evaluate competing hypotheses with experiments, observations, or quantitative models; (4) use the results of those experiments, observations, or models to modify the hypotheses, pose new questions, or draw

conclusions.

hypoxic Of or relating to a condition of oxygen depletion, usually below a level that can sustain most animals.

hysteresis The inability of a community that has undergone change to shift back to the original community type, even when the original conditions are restored.

I

idiosyncratic hypothesis A hypothesis proposing that as the species richness of a community increases, community function will vary idiosyncratically as the result of some species having stronger effects on the community than others. Compare complementarity hypothesis and redundancy hypothesis.

immigration The movement of individuals into an existing population.

inbreeding Mating between related individuals; inbreeding tends to increase the frequency of homozygotes, including those that have two copies of a harmful allele.

indirect interaction An interaction in which the relationship between two species is mediated by a third (or more) species. Compare direct interaction.

induced defense In plant-herbivore interaction, a defense against herbivory, such as production of a secondary compound, that is stimulated by herbivore attack.

interaction strength A measure of the effect of one species (the interactor) on the abundance of another species (the target species).

interaction web A concept that describes both the trophic (vertical) and non- trophic (horizontal) interactions among the species in a traditional food web.

interference competition An interaction in which species compete directly by performing antagonistic actions that interfere with the ability of their competitors to use a resource that both require, such as food or space. Compare exploitation competition.

intermediate disturbance hypothesis A hypothesis proposing that species diversity in communities should be greatest at intermediate levels of disturbance (or stress or predation) because competitive exclusion at low levels of disturbance and mortality at high levels of disturbance should reduce species diversity.

interspecific competition An interaction in which individuals of different species are harmed by their shared use of a resource that limits their ability to grow, reproduce, or survive (-/- relationship). Compare intraspecific competition.

intertidal Referring to the portion of the shoreline that is affected by the rise and fall of the tides.

Intertropical Convergence Zone (ITCZ) The zone of maximum solar radiation, atmospheric uplift, and precipitation within the tropical zone.

intraspecific competition An interaction in which individuals of the same species are harmed by their shared use of a resource that limits their ability to grow, reproduce, or survive (-/- relationship). Compare interspecific competition.

intrinsic rate of increase A constant whose value is determined by the per capita (or per individual) birth rate minus the per capita death rate at each instance in time; also called the intrinsic rate of increase. Compare geometric population growth rate.

invasive species An introduced species that survives and reproduces in its new environment, sustains a growing population, and has large effects on the native community.

isocline The set of abundances for which the population growth rate (dN/dt) of one of the species involved in a species interaction is zero.

isogamy The production of equal-sized gametes. Compare anisogamy.

isolation by distance A metapopulation pattern in which habitat patches located far from occupied patches are less likely to be colonized than are nearby patches.

iteroparous Having the capacity to reproduce multiple times in a lifetime. Compare semelparous.

K

Ê-selection In the r-K continuum used for classifying life history strategies, the selection pressure for slower rates of increase faced by organisms that live in environments where population densities are high (at or near the carrying capacity, K). Compare r-selection.

keystone species A strong interactor species that has an effect on energy flow and community structure that is disproportionate to its small size, abundance, or biomass.

L

land use change The alteration of terrestrial surface, including vegetation and landforms, by human activities such as agriculture, forestry, or mining.

landscape An area that is spatially heterogeneous in one or more features of the environment, such as the number or arrangement of different habitat types; a landscape typically includes multiple ecosystems.

landscape composition In landscape ecology, the kinds of elements or patches comprised by a landscape and how much of each kind is present. Compare landscape structure.

landscape ecology The study of landscape patterns and the effects of those patterns on ecological processes.

landscape structure In landscape ecology, the physical configuration of the different compositional elements of a landscape. Compare landscape composition.

lapse rate The rate at which atmospheric temperature decreases with increasing distance from the ground.

latent heat flux Heat transfer associated with the phase change of water, such as evaporation, sublimation, or condensation.

leaching The vertical movement of dissolved matter and fine mineral particles from upper to lower layers of soil.

leaf area index The area of leaves per unit of ground area (a dimensionless number, since it is an area divided by an area).

lentic Of or referring to still water. Compare lotic.

life history The major events relating to an organism's growth, development, reproduction, and survival; these events include the age and size of first reproduction, the amount and timing of reproduction, and longevity.

life history strategy The overall pattern in the timing and nature of life history events, averaged across all the individuals of a species.

life table A summary of how survival and reproductive rates in a population vary with the age of individuals; in species for which age is not informative or is difficult to measure, life tables may be based on the size or life cycle stage of individuals.

lignin A structural compound that strengthens plant tissues.

line transect A straight line from which an observer can count the number of individuals and estimate their abundance per unit of area.

litter Fresh, undecomposed organic matter on the soil surface.

littoral zone The nearshore zone of a lake where the photic zone reaches to the bottom.

local scale A spatial scale that is essentially equivalent to a community.

loess Sediment deposited by wind.

logistic growth The change in the number of individuals within a population over time that is rapid at first, then decreases as the population approaches the carrying capacity of its environment.

lotic Of or relating to flowing water. Compare lentic.

Lotka-Volterra competition model A modified form of the logistic equation used to model interspecific competition.

Lotka-Volterra predator-prey model A modified form of the logistic equation used to model predator-prey interaction cycles.

lottery model A hypothesis proposing that species diversity in communities is maintained by a “lottery” in which resources made available by the effects of disturbance, stress, or predation are captured at random by recruits from a larger pool of potential colonists.

lower critical temperature The environmental temperature at which the heat loss of an endotherm triggers an increase in metabolic heat generation.

M

macroparasites Relatively large parasite species, such as arthropods and worms. Compare microparasites.

macrophyte A rooted or floating aquatic vascular plant.

marginal value theorem A conceptual optimal foraging model proposing that an animal should stay in a food patch until the rate of energy gain in that patch has declined to the average rate for the habitat, then depart for another patch.

maritime climate The climate typical of coastal terrestrial regions that are influenced by an adjacent ocean, characterized by low daily and seasonal variation in temperature. Compare continental climate.

mass extinction An event in which a large proportion of Earth's species are driven to extinction worldwide in a relatively short time.

mating system The number of mating partners that males or females have and the pattern of parental care in which they engage.

matric potential The energy associated with attractive forces on the surfaces of large molecules inside cells or on the surfaces of soil particles.

mean residence time The amount of time an average molecule of an element spends in a pool before leaving it.

mechanical weathering The physical breakdown of rocks into progressively smaller particles without chemical change. Compare chemical weathering.

mesotrophic Having a nutrient status that is intermediate between oligotrophic and eutrophic, usually used in reference to lakes. Compare eutrophic, oligotrophic.

metamorphosis An abrupt transition from a larval to a juvenile life cycle stage that is sometimes accompanied by a change in habitat.

metapopulation A set of spatially isolated populations linked to one another by dispersal.

microparasites Parasite species too small to be seen with the naked eye, such as bacteria, protists, and fungi. Compare macroparasites.

migration The round-trip movement of an entire population.

mimicry A defense against predators in which prey species resemble less palatable organisms or physical features of their environment, causing potential predators to mistake them for something less desirable to eat.

mineralization The chemical conversion of organic matter into inorganic compounds.

morphs Discrete phenotypes with few or no intermediate forms.

mosaic The composite or pattern of the heterogeneous features of the environment in a landscape.

mutation Change in the DNA of a gene.

mutualism A mutually beneficial interaction between individuals of two or more species (+/+ relationship).

mycorrhizae Symbiotic associations between plant roots and various types of fungi that are usually mutualistic.

N

natural catastrophe An extreme environmental event such as a flood, severe windstorm, or outbreak of disease that can eliminate or drastically reduce population size.

natural selection The process by which individuals with certain heritable characteristics tend to survive and reproduce more successfully than other individuals because of those characteristics.

nekton Swimming organisms capable of overcoming water currents. Compare plankton.

net ecosystem exchange (NEE) The combined fluxes of CO₂ into and out of an ecosystem principally by net primary production and autotrophic and heterotrophic respiration.

net primary production (NPP) The amount of energy per unit of time that producers capture by photosynthesis and chemosynthesis, minus the amount they use in cellular respiration. Compare gross primary production.

net reproductive rate (R₀) The mean number of offspring produced by an individual in a population during its lifetime.

net secondary production The balance between heterotroph energy gains through ingestion and heterotroph energy losses by cellular respiration and egestion.

neutral model A hypothesis proposing that species diversity in communities is maintained by a “lottery” in which resources made available by the effects of disturbance, stress, or predation are captured at random by recruits from a larger pool of potential colonists.

niche partitioning The use of limiting resources by different species in a community in different ways.

nitrification A process by which certain chemoautotrophic bacteria, known as nitrifying bacteria, convert ammonia (NH₃) and ammonium (NH₄⁺) into nitrate (NO₃^-) under aerobic conditions.

nitrogen fixation The process of taking up nitrogen gas (N₂) and converting it into chemical forms that are more chemically available to organisms.

North Atlantic Oscillation An oscillation in atmospheric pressures and ocean currents in the North Atlantic Ocean that affects climatic variation in Europe, in northern Asia, and on the east coast of North America.

non-trophic A species interaction that does not involve feeding such as competition and facilitation.

nutrient A chemical element required by an organism for its metabolism and growth.

nutrient cycle The cyclic movement of nutrients between organisms and the physical environment.

O

occlusion A process by which soluble phosphorus combines with iron, calcium, and aluminum to form insoluble compounds (secondary minerals) that are

unavailable to organisms as nutrients.

oligotrophic Nutrient-poor, characterized by low primary productivity. Compare eutrophic, mesotrophic.

omnivore (1) An organism that feeds on both plants and animals. (2) In trophic studies, an organism that feeds on more than one trophic level.

optimal foraging A theory proposing that animals will maximize the amount of energy acquired per unit of feeding time.

osmotic adjustment An acclimatization response to changing water availability or salinity in terrestrial and aquatic environments that involves changing the solute concentration, and thus the osmotic potential, of the cell.

osmotic potential The energy associated with dissolved solutes.

outbreak An extremely rapid increase in the number of individuals in a population.

ozone hole An area of the stratosphere with an ozone concentration of less than 220 Dobson units (= 2.7 ? 10¹⁶ molecules of ozone) per square centimeter; found primarily over the Antarctic region.

P

Pacific Decadal Oscillation (PDO) A long-term oscillation in sea surface temperatures and atmospheric pressures in the North Pacific Ocean that has widespread climatic effects.

paedomorphic Resulting from a delay of a developmental event relative to sexual maturation.

parasite An organism that lives in or on a host organism and feeds on its tissues or body fluids.

parasitism A trophic species interaction in which a predator (parasite) lives and feeds on or in its prey (host) without necessarily killing it.

parasitoid An insect that lays one or a few eggs on or in a host organism (itself usually an insect), which the resulting larvae remain with, eat, and almost always kill.

parent material The rock or sediments that are broken down by weathering to form mineral particles in soil.

pathogen A parasite that causes disease.

pelagic zone The open water column of a lake or ocean.

permafrost A subsurface soil layer that remains frozen year-round for at least 3 years.

phenotype The observable characteristics of an organism.

phenotypic plasticity The ability of a single genotype to produce different phenotypes under different environmental conditions.

photic zone The surface layer of a lake or ocean where enough light penetrates to allow photosynthesis.

photorespiration A chemical reaction in photosynthetic organisms in which the enzyme rubisco takes up O₂, leading to the breakdown of sugars, the release of CO₂, and a net loss of energy.

photosynthesis A process that uses sunlight to provide the energy needed to take up CO₂ and synthesize sugars.

physiological ecology The study of the interactions between organisms and the physical environment that influence their survival and persistence.

phytoplankton Photosynthetic plankton. Compare zooplankton.

pioneer stage The first stage of primary succession.

plankton Small, often microscopic organisms that live suspended in water; although many plankton are mobile, none can swim strongly enough to overcome water currents. Compare nekton.

polar cell A large-scale, three-dimensional pattern of atmospheric circulation in which air subsides at the poles, moves toward the equator when it reaches Earth's surface, and is replaced by air moving through the upper atmosphere from lower latitudes.

polar zone The major climatic zone above 60°N and S.

pool The total amount of a nutrient or other element found within a component of an ecosystem.

population A group of individuals of the same species that live within a particular area and interact with one another.

population cycles A pattern of population fluctuations in which alternating periods of high and low abundance occur after nearly constant intervals of time.

population density The number of individuals per unit of area.

population fluctuations The most common pattern of population growth, in which population size rises and falls over time.

population growth The change in the number of individuals within a population over time.

population regulation A pattern of population growth in which one or more density-dependent factors increase population size when numbers are low and decrease population size when numbers are high.

population size The number of individuals in a population.

population viability analysis (PVA) Projection of the potential future status of a population through use of demographic models; a PVA approach is often used to estimate the likelihood that a population will persist for a certain amount of time in different habitats or under different management scenarios.

positive interaction A trophic or non-trophic species interaction in which one or both species benefit and neither is harmed.

A mutually beneficial interaction between individuals of two or more species (+/+ relationship).

A species interaction in which individuals of one species benefit while individuals of the other species do not benefit and are not harmed (+/0 relationship).

predation A trophic interaction in which an individual of one species, a predator, consumes individuals (or parts of individuals) of another species, its prey.

predator An organism that consumes other organisms (or parts of organisms), referred to as its prey.

prey An organism eaten by a predator.

pressure (or turgor) potential The energy associated with the exertion of pressure; has a positive value if pressure is exerted on the system and a negative value if the system is under tension.

primary production The rate at which chemical energy in an ecosystem is generated by autotrophs, derived from the fixation of carbon during photosynthesis and chemosynthesis. Compare secondary production.

The amount of energy that autotrophs capture by photosynthesis and chemosynthesis per unit of time. Compare net primary production.

The amount of energy per unit of time that producers capture by photosynthesis and chemosynthesis, minus the amount they use in cellular respiration. Compare gross primary production.

primary succession Succession that involves the colonization of habitats devoid of life. Compare secondary succession.

producer An organism that can produce its own food by photosynthesis or chemosynthesis; also called a primary producer or autotroph. Compare consumer.

production efficiency The proportion of assimilated food that is used to produce new consumer biomass.

proximate cause An immediate, underlying cause that is based on internal features of an organism and can be used to explain how a behavior (or other characteristic of the organism) occurs. Compare ultimate cause.

pubescence The presence of hairs on the surface of an organism.

R

r-selection In the r-K continuum used for classifying life history strategies, the selection pressure for high population growth rates faced by organisms that live in environments where population densities are usually low. Compare K- selection.

rain-shadow effect The effect a mountain range has on regional climate by forcing moving air upward, causing it to cool and release precipitation on the windward slopes, resulting in lower levels of precipitation and soil moisture on the leeward slope.

ramet An actual or potential physiologically independent member of a genet that may compete with other members for resources. Compare genet.

random dispersion A dispersion pattern in which individuals are positioned at random. Compare clumped dispersion, regular dispersion.

rank abundance curve A graph that plots the proportional abundance of each species in a community relative to the others in rank order, from most abundant to least abundant.

realized niche The part of a fundamental niche that a species occupies as a result of species interactions. Compare fundamental niche.

recombination Rearrangements of genetic material during sexual reproduction that result in the production of offspring that have combinations of alleles that differ from those in either of their parents.

redundant A species that may have the same function in the community as other species within a larger functional group.

regional scale A spatial scale that encompasses a geographic area where the climate is roughly uniform, and the species contained therein are often restricted to that region by dispersal limitation.

regional species pool All the species contained within a region; sometimes

called gamma diversity.

regular dispersion A dispersion pattern in which individuals are relatively evenly spaced throughout their habitat. Compare clumped dispersion, random dispersion.

relative population size An estimate of population size based on data that are related to the absolute population size, but which can be compared from one time period or place to another. Compare absolute population size.

replication The performance of each treatment of a controlled experiment, including the control, more than once.

rescue effect A metapopulation pattern in which high rates of immigration protect a population from extinction.

resistance Any force that impedes the movement of compounds such as water or gases such as carbon dioxide along an energy or concentration gradient; its inverse is conductance.

resource A feature of the environment, such as food, water, light, and space, that is required for growth, reproduction, or survival.

resource partitioning The use of limiting resources by different species in a community in different ways.

resource ratio hypothesis A hypothesis proposing that species can coexist in a community by using the same resources, but in differing proportions.

ruderals In Grime's triangular model, plants that are adapted to environments with high levels of disturbance and low levels of stress. Compare competitive plants, stress-tolerant plants.

salinity The concentration of dissolved salts in water.

salinization A process by which high rates of evapotranspiration in arid regions result in a progressive buildup of salts at the soil surface.

sand The coarsest soil particles (0.05-2 mm).

savanna A vegetation type dominated by grasses with intermixed trees and shrubs.

scale The spatial or temporal dimension at which ecological observations are collected.

scientific method An iterative and self-correcting process by which scientists learn about the natural world, consisting of four steps: (1) observe nature and ask a question about those observations; (2) develop possible answers to that question (hypotheses); (3) evaluate competing hypotheses with experiments, observations, or quantitative models; (4) use the results of those experiments, observations, or models to modify the hypotheses, pose new questions, or draw conclusions.

secondary compound A chemical compound in plants not used directly in growth, and often used in such functions as defense against herbivores or protection from harmful radiation.

secondary production Energy in an ecosystem that is derived from the consumption of organic compounds produced by other organisms. Compare primary production.

secondary succession Succession that involves the reestablishment of a community in which some, but not all, of the organisms have been destroyed.

Compare primary succession.

semelparous Reproducing only once in a lifetime. Compare iteroparous.

sensible heat flux The transfer of heat through the exchange of energy by conduction or convection.

sequential hermaphroditism A change or changes in the sex of an organism during the course of its life cycle.

sexual selection A process in which individuals with certain characteristics have an advantage over others of the same sex solely with respect to mating success.

Shannon index The index most commonly used to describe species diversity quantitatively.

silt Intermediate-sized soil particles, often ranging in size between 0.05 and 0.002 mm.

soil A mix of mineral particles, detritus, dissolved organic matter, water containing dissolved minerals and gases (the soil solution), and organisms that develops in terrestrial ecosystems.

speciation The process by which one species splits into two or more species.

species accumulation curve A graph that plots species richness as a function of the total number of individuals that are present with each additional sample.

species-area relationship The relationship between species richness and area sampled.

species composition The identity of the species present in a community.

species distribution model A tool that predicts the geographic distribution of a species based on the environmental conditions at locations where the species is known to occupy.

species diversity A measure that combines the number of species (species richness) in a community and their relative abundances compared with one another (species evenness).

species evenness The relative abundances of different species compared to one another in a community.

species richness The number of species in a community.

stability When a community retains, or returns to, its original structure and function after some perturbation.

stabilizing selection Selection that favors individuals with an intermediate phenotype. Compare directional selection, disruptive selection.

static life table A life table that records the survival and reproduction of individuals of different ages during a single time period.

stomate A pore in plant tissues, usually leaves, surrounded by specialized guard cells that control its opening and closing.

stratification The layering of water in oceans and lakes due to differences in water temperature and density with depth.

stress An abiotic factor that results in a decrease in the rate of an important physiological process, thereby lowering the potential for an organism's growth, reproduction, or survival; the condition caused by such a factor.

stress-tolerant plants In Grime's triangular model, plants that are adapted to conditions of high stress and low disturbance. Compare competitive plants,

ruderals.

subsidence A sinking (downward) movement of air in the atmosphere, usually over a broad area, leading to the development of a high-pressure cell. Compare uplift.

succession The process of change in the species composition of a community over time as a result of abiotic and biotic agents of change.

surrogate species A species selected as a priority for conservation with the assumption that its conservation will serve to protect many other species with overlapping habitat requirements.

survival rate The proportion of individuals that survive over time.

survivorship (l_x) The proportion of individuals that survive from birth (age 0) to age x (denoted l_x in a life table).

survivorship curve A graph based on survivorship data (l_x) that plots the numbers of individuals from a hypothetical cohort (typically, of 1,000 individuals) that will survive to reach different ages.

symbiosis A relationship in which two species live in close physical and/or physiological contact with each other.

An organism on or within which an herbivore, parasite, or mutualist lives and feeds.

T

taxonomic homogenization The worldwide reduction of biodiversity resulting from the spread of non-native and native generalists coupled with declining abundances and distributions of native specialists and endemics.

temperate zone The major climatic zone between 30° and 60°N and S.

territory An area that an animal defends against intruders.

thermocline The zone of rapid temperature change in a lake beneath the epilimnion and above the hypolimnion.

thermoneutral zone The range of environmental temperatures over which endotherms maintain a constant basal metabolic rate.

threshold density The minimum number of individuals susceptible to a disease that must be present in a population for the disease to become established and spread.

tides Patterns of rising and falling of ocean water generated by the gravitational attraction between Earth and the moon and sun.

till Layers of sediment deposited by glaciers.

tolerance The ability to survive stressful environmental conditions. Compare avoidance.

top-down control Limitation of the abundance of a population by consumers. Compare bottom-up control.

torpor A state of dormancy in which endotherms drop their lower critical temperature and associated metabolic rate.

trade-off An organism's allocation of its limited energy or other resources to one structure or function at the expense of another.

trophic A species interaction that involves feeding such as carnivory, herbivory, parasitism, and facilitation.

trophic cascade A change in the rate of consumption at one trophic level that results in a series of changes in species abundance or composition at lower trophic levels.

trophic efficiency A measure of the transfer of energy between trophic levels, consisting of the amount of energy at one trophic level divided by the amount of energy at the trophic level immediately below it.

trophic facilitation An interaction in which a consumer is indirectly facilitated by a positive interaction between its prey or food plant and another species.

trophic interaction An interaction in which a predator consumes a prey.

trophic level A group of species that obtain energy in similar ways, classified by the number of feeding steps by which the group is removed from primary producers, which are the first trophic level.

trophic mutualism A mutualism in which one or both of the mutualists receives energy or nutrients from its partner.

trophic pyramid A common approach to conceptualizing trophic relationships in an ecosystem in which a stack of rectangles is constructed, each of which represents the amount of energy or biomass within one trophic level.

tropical zone The major climatic zone between 25°N and S, encompassing the equator; also called the tropics.

tropics The major climatic zone between 25°N and S, encompassing the equator; also called the tropics.

turgor pressure Pressure that develops in a plant cell when water moves into it, following a gradient in water potential.

turnover (1) The mixing of the entire water column in a stratified lake when all the layers of water reach the same temperature and density. (2) The change in species diversity and composition from one community type to another across the landscape;

The change in species diversity and composition, or turnover of species, from one community type to another across the landscape. Compare alpha diversity, gamma diversity.

type I survivorship curve A survivorship curve in which newborns, juveniles, and young adults all have high survival rates and death rates do not begin to increase greatly until old age.

type II survivorship curve A survivorship curve in which individuals experience a constant chance of surviving from one age to the next throughout their lives.

type III survivorship curve A survivorship curve in which individuals die at very high rates when they are young, but those that reach adulthood survive well later in life.

U

ultimate cause The underlying evolutionary or historical reason for a particular behavior (or other characteristic of an organism). Compare proximate cause.

umbrella species A surrogate species selected with the assumption that protection of its habitat will serve as an “umbrella” to protect many other species; often a species with large or specialized habitat requirements or one that is easy to count.

uplift The rising of warm, less dense air in the atmosphere due to heating of

Earth's surface. Compare subsidence.

upwelling The rising of deep ocean waters to the surface.

V

vicariance The evolutionary separation of species due to a barrier that results in the geographic isolation of species that once were connected to one another.

W

warning coloration A defense against predators in which prey species that contain powerful toxins advertise those toxins with bright coloration; also called aposematic coloration.

water potential The overall energy status of water in a system; the sum of osmotic potential, gravitational potential, turgor pressure, and matric potential.

weather The temperature, humidity, precipitation, wind, and cloud cover at a particular time and place. Compare climate.

weathering The physical and chemical processes by which rock minerals are broken down, eventually releasing soluble nutrients and other elements.

Z

zooplankton Nonphotosynthetic plankton. Compare phytoplankton.