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

A

absolute population size: The actual abundance of a population or species. [8]
abundance: The number of individuals in a species that are found in a given area; abundance is often measured by population size or population density. [8]
acclimatization: An organism’s adjustment of its physiology, morphology, or behavior to lessen the effect of an environmental change and minimize the associated stress. [4]
acid neutralizing capacity: The ability of the chemical environment to counteract acidity, associated with concentrations of base cations, including Ca²⁺, Mg²⁺, and K⁺. [24]
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. [2]
adaptation: A physiological, morphological, or behavioral trait with an underlying genetic basis that enhances the survival and reproduction of its bearers in their environment. [1, 4, 6]
adaptive evolution: A process of evolutionary change in which adaptive traits tend to increase in frequency in a population over time. [6]
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. [23]
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. [6]
aerosols: Solid, liquid, or gaseous particles suspended in the atmosphere. [21]
age structure: The proportions of a population in each age class. [9]
albedo: The amount of solar radiation reflected by a surface, usually expressed as a percent of the incident solar radiation. [2]
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. [2]
Allee effect: A decrease in the population growth rate (r or λ) as the population density decreases. [10]
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. [6]
allelopathy: A form of interference competition in which individuals of one species release toxins that directly harm individuals of other species. [11]
allochthonous: The input of energy and nutrients from outside the ecosystem. Compare autochthonous. [20]
allometry: Differential growth of body parts that results in a change of shape or proportion with size. [7]
alpha diversity: Species diversity at the local or community scale. Compare beta diversity, gamma diversity. [17]
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. [7]
alternative stable states: Different community development scenarios that are possible at the same location under similar environmental conditions. [16]
anisogamy: Production of two types of gametes of different sizes. Compare isogamy. [7]
anoxic: Having a low oxygen concentration. [2]
anthropogenic: Of, relating to, or caused by humans or their activities. [24]
aposematic coloration: See warning coloration. [12]
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. Compare ectomycorrhizae. [14]
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. [24]
assimilation efficiency: The proportion of ingested food that is assimilated by an organism. [20]
atmospheric deposition: The movement of particulate and dissolved matter from the atmosphere into ecosystems by gravity or in precipitation. [21]
atmospheric pressure: The pressure the exerted on a surface due to the mass of the atmosphere above it. [2]
autochthonous: Energy and nutrients produced within the ecosystem. Compare allochthonous. [20]
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. [5]
avoidance: A response of an organism to stressful environmental conditions that lessens their effect through some behavior or physiological activity that minimizes exposure to the stress. Compare tolerance. [4]

B

balance of nature: The idea that natural systems tend to return to an original, preferred state after a disturbance. [1]
benthic: Of or relating to the bottom of a body of water. [3]
beta diversity: The change in species number and composition, or turnover of species, as one moves from one community to another. Compare alpha diversity, gamma diversity. [17]
bioaccumulation: The progressive concentration of a substance in an organism’s body over its lifetime. [20]
biodiversity: A term used to describe the diversity of important ecological entities that span multiple spatial scales, from genes to species to communities. [15]
biofuel: A liquid or gas fuel made from plant material (biomass). [18]
biogeochemistry: The study of the physical, chemical, and biological factors that influence the movements and transformations of chemical elements. [21]
biogeography: The study of variation in species composition and diversity among geographic locations. [17]
biological crust: A soil crust composed of a mix of species of cyanobacteria, lichens, and mosses; also called a cryptobiotic or cryptogamic crust. [21]
biological reserve: An often small nature reserve established with the conservation of a single species or ecological community as the main conservation objective. [23]
biomagnification: An increase in the tissue concentrations of a substance at higher trophic levels that results as animals at each trophic level consume prey with increasing concentrations of the substance. [20]
biome: A terrestrial biological community shaped by the regional climate, soil, and disturbance patterns where it is found, usually classified by the growth form of its most abundant plants. [3]
biosphere: The highest level of biological organization, consisting of all living organisms on Earth plus the environments in which they live; the biosphere is located between the lithosphere and the troposphere. [1, 3]
biotic resistance: Interactions of the native species in a community with non-native species that exclude or slow the growth of those non-native species. [18]
bottom-up control: Limitation of the abundance of a population by nutrient supply or by the availability of food. Compare top-down control. [10]
boundary layer: A zone close to a surface where a flow of fluid, usually air, encounters resistance and becomes turbulent. [4]
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. [23]

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. Compare C₄ photosynthetic pathway, crassulacean acid metabolism. [5]
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. [5]
Calvin cycle: The biochemical pathway used by photosynthetic and chemosynthetic organisms to fix CO₂ and synthesize sugars. [5]
carbon neutral: Of or relating to fuels that produce an amount of CO₂ when burned that is equal to or less than the amount taken up by the plants from which they are made. [18]
carrying capacity: The maximum population size that can be supported indefinitely by the environment; the concept of a carrying capacity is represented by the term K in the logistic equation (Equation 9.7). [9]
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. [21]
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. [21]
cavitation: A disruption of the water column in the xylem of a plant that can occur under dry conditions when high tension (negative pressure potential) on the water in the xylem pulls air into it, or following freezing of water in the xylem, and coalescence of air bubbles when the ice melts. [4]
character displacement: A process in which competition causes the forms of competing species to evolve to become more different over time, thereby causing species to become more different where they live together than where they live apart. [11]
cheater: In a mutualism, an individual that increases its production of offspring by overexploiting its mutualistic partner. [14]
chemical weathering: The chemical breakdown of soil minerals leading to the release of soluble forms of nutrients and other elements. Compare mechanical weathering. [21]
chemolithotrophy: See chemosynthesis.
chemosynthesis: The use of energy from inorganic chemical compounds to produce carbohydrates; also known as chemolithotrophy. [5]
clays: Fine soil particles (<2 μm) that have a semicrystalline structure and weak negative charges on their surfaces that can hold onto cations and exchange them with the soil solution. [21]
climate: The long-term description of weather, based on averages and variation measured over decades. Compare weather. [2]
climate change: Directional change in climate over a period of several decades or longer. [24]
climax stage: The final stage of succession, viewed as a stable end point that experiences little change. [16]
cline: A pattern of gradual change in a characteristic of an organism over a geographic region. [6]
clone: A genetically identical copy of an individual. [8]
clumped dispersion: A dispersion pattern in which individuals are grouped together. Compare random dispersion, regular dispersion. [8]
coarse-filter: Of or referring to an approach to conservation biology that focuses on habitats, landscapes, and ecosystems. Compare fine-filter. [22]
coevolution: The evolution of two interacting species, each in response to selection imposed by the other. [13]
cohort life table: A life table in which the fate of a group of individuals born during the same time period (a cohort) is followed from birth to death. [9]
commensalism: An interaction between two species in which individuals of one species benefit while individuals of the other species do not benefit and are not harmed. [14]
community: A group of interacting species that occur together at the same place and time. [1, 15]
community structure: The set of characteristics that shape a community, including the number, composition, and abundance of species. [15]
compensation: An adaptive growth response of plants to herbivory in which removal of plant tissues stimulates the plant to produce new tissues. [12]
competition: An interaction between two species in which individuals of both species are harmed when both species use a resource that limits their ability to grow and reproduce. [11]
competition coefficient: A constant used in the Lotka–Volterra competition model to describe the effect of one competing species on the other. [11]
competitive exclusion principle: The principle that two species that use a limiting resource in the same way cannot coexist indefinitely. [11]
competitive plants: In Grime’s plant life history model, plants that are superior competitors under conditions of low stress and low disturbance. Compare ruderals, stress-tolerant plants. [7]
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 redundancy hypothesis. [18]
complex life cycle: A life cycle in which there are at least two distinct stages that differ in their habitat, physiology, or morphology. [7]
conduction: The transfer of sensible heat through the exchange of kinetic energy by molecules in direct contact with one another. Compare convection. [2]
conservation biology: The scientific study of phenomena that affect the maintenance, loss, and restoration of biodiversity. [22]
consumer: An organism that obtains its energy by eating other organisms or their remains. Compare producer. [1]
consumption efficiency: The proportion of the biomass available in an ecosystem that is ingested. [20]
context-dependent: A view of species interactions as variable in strength and direction under different environmental conditions. [15]
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. [2]
continental drift: The slow movement of tectonic plates (sections of Earth’s crust) across Earth’s surface. [17]
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). [1]
convection: The transfer of sensible heat through the exchange of air and water molecules as they move from one area to another. Compare conduction. [2]
convergence: The evolution of similar growth forms among distantly related species in response to similar selection pressures. [3]
cooperative breeding: A behavioral pattern in which young animals postpone breeding and instead help their parents raise offspring. [8]
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. [23]
Coriolis effect: The influence of the frictional forces associated with the spinning of Earth on its axis on wind and ocean current direction. [2]
crassulacean acid metabolism (CAM): A photosynthetic pathway in which CO₂ is fixed and stored as an organic acid at night, and then released to the Calvin cycle during the day. Compare C₃ photosynthetic pathway, C₄ photosynthetic pathway. [5]
crypsis: A defense against predators in which prey species have a shape or coloration that provides camouflage and allows them to avoid detection. [12]
cryptobiotic crust: See biological crust.
cryptogamic crust: See biological crust.

D

damped oscillations: A pattern of population fluctuations where the extent to which the population rises and falls in abundance gradually become smaller over time. [10]
decomposition: The physical and chemical breakdown of detritus by detritivores for energy capture, leading to the release of nutrients as simple, soluble organic and inorganic compounds that can be taken up by other organisms. [21]
delayed density dependence: Delays in the effect of population density on population size that can contribute to population fluctuations. [10]
demographic stochasticity: Chance events associated with whether individuals survive or reproduce. [10]
denitrification: A process by which certain bacteria convert nitrate (NO₃^–) into nitrogen gas (N₂) and nitrous oxide (N₂O) under anoxic conditions. [21]
density-dependent: Of or referring to a factor that causes birth rates, death rates, or dispersal rates to change as the density of the population changes. Compare density-independent. [9]
density-independent: Of or referring to a factor whose effects on birth and death rates are independent of population density. Compare density-dependent. [9]
desertification: Degradation of formerly productive land in arid regions resulting in loss of plant cover and acceleration of soil erosion. [3, 24]
detritus: Freshly dead or partially decomposed remains of organisms. [8]
diapause: A state of suspended animation or dormancy in which an organism can survive unfavorable conditions. [7]
direct development: A simple life cycle that goes directly from fertilized egg to juvenile without passing through a free-living larval stage. [7]
direct interactions: Interactions between two species, including traditional relationships such as competition, predation, and positive interactions. Compare indirect interactions. [15]
directional selection: Selection that favors individuals with one extreme of a heritable phenotypic trait. Compare disruptive selection, stabilizing selection. [6]
dispersal limitation: A situation in which a species’ limited capability for dispersal prevents it from reaching areas of suitable habitat. [8]
dispersion: The spatial arrangement of individuals within a population. [8]
disruptive selection: Selection that favors individuals with a phenotype at either extreme over those with an intermediate phenotype. Compare directional selection, stabilizing selection. [6]
distribution: The geographic area where individuals of a species are present. [8]
disturbance: An abiotic event that kills or damages some organisms and thereby creates opportunities for other organisms to grow and reproduce. [7, 8, 16]
dominant species: A species that has large, community-wide effects by virtue of its size or abundance, its strong competitive ability, or its provision of habitat or food for other species, also called a foundation species. [15]
doubling time (t_d): The number of years it takes a population to double in size. [9]
driver and passenger hypothesis: A hypothesis proposing that the strengths of the effects of species’ ecological functions on their communities vary dramatically, such that “driver” species have a large effect on community function, while “passenger” species have a minimal effect. [18]
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. [18]

E

ecological footprint: The total area of productive ecosystems required to support a population. [9]
ecological niche: The physical and biological conditions that a species needs to grow, survive, and reproduce. [8]
ecology: The scientific study of interactions between organisms and their environment. [1]
ecosystem: A community of interacting organisms plus the physical environment in which they live. [1, 19]
ecosystem engineer: A dominant species that influences its community by creating, modifying, or maintaining physical habitat for itself and other species. [15]
ecosystem management: An approach to habitat management in which scientifically-based policies and practices guide management decisions on how best to meet an overarching goal of sustaining ecosystem structure and function for long periods of time. [23]
ecosystem services: Natural processes that sustain human life that depend on the functional integrity of natural communities and ecosystems. [22]
ecotype: A population with adaptations to a unique environment. [4]
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. [14]
ectoparasite: A parasite that lives on the surface of another organism. Compare endoparasite. [13]
ectotherm: An animal that regulates its body temperature primarily through energy exchange with its external environment. Compare endotherm. [4]
edge effects: Biotic and abiotic changes that are associated with an abrupt habitat boundary such as that created by habitat fragmentation. [17, 23]
El Niño Southern Oscillation (ENSO): A climatic oscillation in the Pacific Ocean causing widespread climate variation and changes in upwelling currents, characterized by a switch in the positions of high-pressure and low-pressure systems over the equatorial Pacific, leading to a weakening of the easterly trade winds that normally push warm water toward Southeast Asia. See also La Niña. [2]
endemic: Occurring in a particular geographic location and nowhere else on Earth. [17]
endoparasite: A parasite that lives inside the body of its host organism. Compare ectoparasite. [13]
endosperm: Nutrient-rich material in a seed that sustains the developing embryo and often the young seedling. [7]
endotherm: An animal that regulates its body temperature primarily through internal metabolic heat generation. Compare ectotherm. [4]
environmental science: An interdisciplinary field 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. [1]
environmental stochasticity: Erratic or unpredictable changes in the environment. [10]
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. [2]
equilibrium theory: A proposed explanation for the coexistence of species in a community that relies on relatively stable coexistence due to ecological and evolutionary “compromises” that result in resource partitioning. Compare nonequilibrium theory. [18]
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. [17]
eutrophic: Nutrient-rich; characterized by high primary productivity. Compare oligotrophic. [21]
eutrophication: A change in the nutrient status of an ecosystem from nutrient poor to nutrient rich; such a change may occur naturally in some lakes due to the accumulation of sediments, but it may also be caused by anthropogenic nutrient inputs. [21]
evapotranspiration: The sum of water loss through evaporation and transpiration . [2]
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. [1, 6]
evolutionarily significant unit: An appropriate target of management within a species (e.g., subspecies, populations) as determined by genetic analyses; also called a management unit. [22]
exploitation: A relationship in which one organism benefits by feeding on, and thus directly harming, another. [12]
exploitation competition: An interaction in which species compete indirectly through their mutual effects on the availability of a shared resource. Compare interference competition. [11]
exponential growth: Change in the size of a population of a species with continuous reproduction by a constant proportion at each instant in time. Compare geometric growth. [9]
exponential population growth rate (r): A constant proportion by which a population of a species with continuous reproduction changes in size at each instant in time; also called the intrinsic rate of increase. Compare geometric population growth rate. [9]
extent: In landscape ecology, the area or time period over which observations are collected for a region under study; together with grain, extent characterizes the scale at which a landscape is studied. Compare grain. [23]
extinction vortex: A pattern in which a small population that drops below a certain size may decrease even further in size, perhaps spiraling towards extinction; an extinction vortex results from the vulnerability of small populations to chance genetic, demographic, and environmental events. [22]

F

facultative CAM: The ability to switch from C₃ to CAM photosynthesis when water availability decreases. [5]
fecundity: The average number of offspring produced by a female while she is of age x (denoted F_x in a life table). [9]
Ferrell cell: A large-scale, three-dimensional pattern of atmospheric circulation in each hemisphere, located at mid-latitudes between the Hadley and polar cells. [2]
fine-filter: Of or referring to an approach to conservation biology that focuses on genes, populations, and species. Compare coarse-filter. [22]
finite rate of increase: See geometric population growth rate. [9]
fixation: (1) With respect to the genetic composition of a population, an allele frequency of 100%. [6] (2) 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. [5]
flagship species: A charismatic species that may be emphasized in conservation efforts because it helps to garner public support for a conservation project. [22]
focal species: One of a group of species selected as a priority for conservation efforts and chosen because its ecological requirements differ from other species in the group, thereby helping to ensure that as many different species as possible receive protection. [22]
food web: A diagram showing the connections between organisms and the food they consume. [20]
foundation species: See dominant species.
fugitive species: A species whose persistence depends on its being able to disperse from one place to another as environmental conditions change. [11]
functional group: A subset of the species in a community that function in similar ways, but do not necessarily use the same resources. Compare guild. [15]

G

gametophyte: A multicellular haploid life cycle stage, found in many algae and all plants, that produces haploid gametes. Compare sporophyte, alternation of generations. [7]
gamma diversity: Species diversity at the regional scale; the regional species pool. Compare beta diversity, alpha diversity. [17]
gene flow: The transfer of alleles from one population to another via the movement of individuals or gametes. [6]
gene-for-gene interaction: A specific defensive response that makes particular plant genotypes resistant to particular parasite genotypes. [13]
genet: In plants and animals that reproduce asexually, the entire genetic individual; a genet may consist of multiple, genetically-identical parts, each of which has the potential to function as an independent physiological unit. Compare ramet. [8]
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. [6, 10]
genotype: The genetic makeup of an individual. [6]
geographic range: The entire geographic region over which a species is found. [4, 8]
geometric growth: Change in the size of a population of a species with discrete reproduction by a constant proportion from one discrete time period to the next. Compare exponential growth. [9]
geometric population growth rate (λ): A constant proportion by which a population of a species with discrete reproduction changes in size from one discrete time period to the next; also called the finite rate of increase. Compare exponential population growth rate. [9]
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. [23]
gravitational potential: The energy associated with gravity. [4]
greenhouse effect: The warming of Earth by gases in the atmosphere that absorb and reradiate infrared energy emitted by Earth’s surface. [24]
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). [2]
gross primary production (GPP): The amount of energy that autotrophs capture by photosynthesis and chemosynthesis. [19]
guild: A subset of the species in a community that use the same resources, whether or not they are taxonomically related. Compare functional group. [15]

H

habitat corridor: A relatively narrow patch that connects blocks of habitat and often facilitates the movement of species between those blocks. [23]
habitat degradation: Anthropogenic changes that reduce the quality of habitat for many, but not all, species. [22]
habitat fragmentation: The breaking up of once continuous habitat into a complex matrix of spatially isolated habitat patches amid a human-dominated landscape. [10, 22]
habitat loss: The outright conversion of an ecosystem to another use by human activities. [22]
habitat mutualism: A mutualism in which one partner provides the other with shelter, a place to live, or favorable habitat. [14]
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. [2]
heat capacity: The amount of energy required to raise the temperature of a substance. [2]
herbivore: An organism that eats the tissues or internal fluids of living plants or algae. [12]
heterogeneity: The quality or state of consisting of dissimilar elements. [23]
heterotroph: An organism that obtains energy by consuming energy-rich organic compounds from other organisms. Compare autotroph. [5]
horizons: Layers of soil distinguished by their color, texture, and permeability. [21]
horizontal interactions: Non-trophic interactions, such as competition and some positive interactions, that occur within a trophic level. [15]
host: An organism on or within which a parasite or other symbiont lives. Compare symbiont, symbiosis. [13]
hypolimnion: The densest, coldest water layer in a lake, lying below the thermocline. Compare epilimnion. [2]
hyporheic zone: The portion of the substratum below and adjacent to a stream bed where water movement still occurs, either from the stream or from groundwater moving into the stream. [3]
hypothesis: A possible answer to a question developed using previous knowledge or intuition. See scientific method. [1]
hysteresis: An inability to shift back to the original community type, even when the original conditions are restored. [16]

I

inbreeding: Mating between related individuals. [10]
indirect interactions: Interactions in which the relationship between two species is mediated by a third (or more) species. Compare direct interactions. [15]
induced defense: In plant–herbivore interactions, a defense against herbivory, such as production of a secondary compound, that is stimulated by herbivore attack. [12]
interaction strength: A measure of the effect of one species’ population on the size of another species’ population. [15, 20]
interaction web: A concept that has been introduced to describe both the trophic (vertical) and non-trophic (horizontal) interactions in a traditional food web. [15]
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. [11]
intermediate disturbance hypothesis: A hypothesis proposing that species diversity in communities should be greatest at intermediate levels of disturbance because competitive exclusion at low levels of disturbance and mortality at high levels of disturbance should reduce species diversity. [18]
interspecific competition: Competition between members of different species. Compare intraspecific competition. [11]
Intertropical Convergence Zone (ITCZ): The zone of maximum solar radiation, atmospheric uplift, and precipitation within the tropical zone. [2]
intraspecific competition: Competition between individuals of a single species. Compare interspecific competition. [11]
intrinsic rate of increase: See exponential population growth rate. [9]
invasive species: Introduced species that survive and reproduce in their new environment, sustain a growing population, and have large effects on the native community. [22]
island biogeography: See equilibrium theory of island biogeography.
isogamy: The production of equal-sized gametes. Compare anisogamy. [7]
isolation by distance: A pattern in which patches located far away from occupied patches are less likely to be colonized than are nearby patches. [10]
iteroparous: Having the capacity to reproduce multiple times in a lifetime. Compare semelparous. [7]

J

jump dispersal: A long-distance dispersal event by which a species colonizes a new geographic region. [10]

K

K: See carrying capacity. [7]
K-selection: In the r- and K-selection approach to classifying life history strategies, the selection pressures faced by organisms that live in environments where population densities are high (at or near the carrying capacity, K). Compare r-selection. [7]
keystone species: A strongly interacting species that has a large effect on energy flow and on community structure and composition disproportionate to its abundance or biomass. [15, 20]

L

La Niña: A stage of the El Niño Southern Oscillation consisting of a stronger-than-average phase of the normal climatic pattern, with high atmospheric pressure off the coast of South America and low pressure in the western Pacific. [2]
land use change: The conversion of land from natural to human-disturbed communities for resource extraction, such as agriculture or pastoral land use. [3]
landscape: An area that is spatially heterogeneous either in its elements (such as the vegetative cover types found at different locations) or in how those elements are arranged. [23]
landscape composition: In landscape ecology, the kinds of elements or patches comprised by a landscape and how much of each kind is present. [23]
landscape ecology: The study of landscape patterns and the effects of those patterns on ecological processes. [23]
landscape structure: In landscape ecology, the physical configuration of the different compositional elements of a landscape. [23]
lapse rate: The rate at which atmospheric temperature decreases with increasing distance from the ground. [2]
latent heat flux: Heat transfer associated with the phase change of water, such as evaporation, sublimation, or condensation. [2]
latent period: A period in which an individual is infected with a disease but cannot spread the disease. [13]
leaf area index: The area of leaves per unit of ground area (a dimensionless number, since it is an area divided by an area). [19]
lentic: Of or referring to still water. Compare lotic. [3]
life history: A record of major events relating to an organism’s growth, development, reproduction, and survival. [7]
life history strategy: The overall pattern in the timing and nature of life history events, averaged across all the individuals of a species. [7]
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 are often based on the size or life history stage of individuals. [9]
lignin: A structural compound that strengthens plant tissues. [21]
lithosphere: Earth’s surface crust and upper mantle; the layer of Earth that includes the tectonic plates. [3]
litter: Fresh, undecomposed organic matter. [21]
littoral zone: The nearshore zone of a lake where the photic zone reaches to the bottom. [3]
local scale: A spatial scale that is essentially equivalent to a community. [17]
loess: Thick layers of sediment deposited by wind. [21]
logistic growth: Change in the size of a population that is rapid at first, then decreases as the population approaches the carrying capacity of its environment. [9]
lotic: Of or relating to flowing water. Compare lentic. [3]
Lotka–Volterra competition model: A modified form of the logistic equation used to model competition (see Equation 11.1). [11]
lottery model: A nonequilibrium 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. [18]
lower critical temperature: The environmental temperature at which the heat loss of an endotherm is greater than its basal metabolic heat production, so that its body temperature begins to drop, triggering an increase in metabolic heat generation. [4]

M

macroparasites: Relatively large parasite species, such as arthropods and worms. Compare microparasites. [13]
macrophyte: A rooted aquatic plant. [3]
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. [5]
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. [2]
mark–recapture: An approach to estimating population size in which a subset of the individuals in a population are captured, marked, and released; after a suitable period of time, individuals are then captured again, and the proportion of marked individuals found in the second capture is used to estimate the population size. [8]
mass extinction: An event in which a large proportion of Earth’s species are driven to extinction worldwide in a relatively short time. [6]
matric potential: The energy associated with attractive forces on the surfaces of large molecules inside cells or on the surfaces of soil particles. [4]
mean residence time: The amount of time an average molecule of an element spends in a pool, such as a plant or the soil, before leaving it. [21]
mechanical weathering: The physical breakdown of rocks into progressively smaller particles without a chemical change. Compare chemical weathering. [21]
mesotrophic: Having a nutrient status that is intermediate between oligotrophic and eutrophic, usually used in reference to lakes. [21]
metamorphosis: An abrupt transition in form from the larval to the juvenile life cycle stage that is sometimes accompanied by a change in habitat. [7]
metapopulation: A set of spatially isolated populations linked to one another by dispersal. [10]
microparasites: Parasite species too small to be seen with the naked eye, such as bacteria, protozoans, and fungi. Compare macroparasites. [13]
Milankovitch cycles: Cycles of regular change over thousands of years in the shape of Earth’s orbit, in the angle of tilt of its axis, and in its orientation toward other celestial bodies that change the intensity of solar radiation primarily at high latitudes. [2]
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. [12]
mineralization: The chemical conversion of organic matter into inorganic nutrients. [21]
morphs: Discrete phenotypes with few or no intermediate forms. [7]
mosaic: A composite of heterogeneous elements. [23]
mutation: Change in the DNA of a gene. [6]
mutualism: A mutually beneficial interaction between individuals of two species (a +/+ relationship). [14]
mycorrhizae: Symbiotic associations between plant roots and various types of fungi that are usually mutualistic. [14]

N

natural catastrophe: An extreme environmental event such as a flood, severe windstorm, or outbreak of disease that can eliminate or drastically reduce the sizes of populations. [10]
natural selection: The process by which individuals with certain heritable characteristics tend to survive and reproduce more successfully than individuals with other heritable characteristics. [1, 6]
nekton: Swimming organisms capable of overcoming water currents. Compare plankton. [3]
net ecosystem exchange: See net ecosystem production. [19]
net ecosystem production: The combined ecosystem fluxes of CO₂, including net primary production and heterotrophic respiration. [19]
net primary production (NPP): The amount of energy (per unit time) that autotrophs capture by photosynthesis and chemosynthesis, minus the amount used in cellular respiration. [1, 19]
net reproductive rate (R₀): The mean number of offspring produced by an individual in a population during its lifetime. [9]
net secondary production: The balance between energy gain through ingestion, and energy losses by cellular respiration and egestion in heterotrophs. [19]
niche model: A predictive tool that models the ecological niche occupied by a species based on the conditions at localities the species is known to occupy. [8]
nitrification: A process by which certain chemoautotrophic bacteria, known as nitrifying bacteria, convert ammonia (NH₃) and ammonium (NH₄⁺) to nitrate (NO₃^–) under aerobic conditions. [21]
nitrogen fixation: The process of taking up nitrogen gas (N₂) and converting it into chemical forms that are more chemically available to organisms. [21]
nitrogenase: A nitrogen-fixing enzyme found only in certain bacteria. [21]
nonequilibrium theory: A proposed explanation for the coexistence of species in a community that relies on fluctuating conditions that maintain their coexistence by keeping dominant species from monopolizing resources. Compare equilibrium theory. [18]
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 eastern coast of North America. [2]
nurse plant: An adult plant that provides shade or other protection allowing plants of its own or other species to germinate and survive. [14]
nutrient: A chemical element required by an organism for its metabolism and growth. [21]
nutrient cycling: The cyclic movement of nutrients between organisms and the physical environment. [1, 21]

O

occlusion: A process by which soluble phosphorus combines with iron, calcium, and aluminum to form insoluble compounds that are unavailable as nutrients. [21]
oligotrophic: Nutrient-poor, characterized by low primary productivity. Compare eutrophic. [21]
omnivore: An organism that feeds on more than one trophic level and/or feeds on both plants and animals. [15]
ontogenetic niche: A size- or life cycle stage-specific ecological role. [7]
optimal: Resulting in the maximization of fitness. [7]
optimal foraging: A theory proposing that animals will maximize the amount of energy acquired per unit of time, energy, and risk involved in finding food. [5]
osmotic adjustment: An acclimatization response to changing water availability in terrestrial and aquatic environments that involves changing the solute concentration, and thus the osmotic potential, of the cell. [4]
osmotic potential: The energy associated with dissolved solutes. [4]
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. [24]

P

Pacific Decadal Oscillation (PDO): A long-term oscillation in sea surface temperatures and atmospheric pressures in the North Pacific Ocean that affects climates primarily in northwestern North America. [2]
paedomorphic: Resulting from a delay of a developmental event relative to sexual maturation. [7]
parasite: An organism that lives in or on a host organism and feeds on its tissues or body fluids. [12, 13]
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. [12]
parent material: The rock or mineral material broken down by weathering to form a soil; usually the bedrock underlying the soil. [21]
pathogen: A parasite that causes disease. [13]
pelagic zone: The open water zone of a lake or ocean at some distance from the shore. [3]
permafrost: A subsurface soil layer that remains frozen year-round for at least 3 years. [3]
phenotype: The observable characteristics of an organism. [6]
phenotypic plasticity: The ability of a single genotype to produce different phenotypes under different environmental conditions. [7]
photic zone: The surface layer of a lake or ocean where enough light penetrates to allow photosynthesis. [3]
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. [5]
photosynthesis: A process that uses sunlight to provide the energy needed to take up CO₂ and synthesize sugars. [5]
physical factor: A feature of the environment that affects organism function and population growth rates but is not consumed or depleted. Compare resource. [11]
phytoplankton: Photosynthetic plankton. Compare zooplankton. [3]
pioneer stage: The first stage of primary succession. [16]
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. [3]
polar cell: A large-scale, three-dimensional pattern of atmospheric circulation in which air subsides at the poles and moves toward the equator when it reaches Earth’s surface, and is replaced by air moving through the upper atmosphere from lower latitudes. [2]
polar zone: The major climatic zone above 60° N and S. [2]
polyphenism: A type of phenotypic plasticity in which a single genotype produces multiple, discrete morphological forms. [7]
pool: (1) The total amount of a nutrient or other element found within a component of an ecosystem. [21] (2) A relatively deep and slowly flowing portion of a stream. Compare riffle. [3]
population: A group of individuals of the same species that live within a particular area and interact with one another. [1, 8]
population cycles: A pattern of population fluctuations in which alternating periods of high and low abundance occur after nearly constant intervals of time. [10]
population density: The number of individuals per unit of area. [8]
population fluctuations: The most common pattern of population growth, in which population size rises and falls over time. [10]
population outbreak: An extremely rapid increase in the number of individuals in a population. [10]
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. [9]
population size: The number of individuals in a population. [8]
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. [22]
positive interactions: Interactions between species in which one or both species benefit and neither is harmed. [14]
predator: An organism that kills and eats other organisms, referred to as its prey. [12]
pressure potential: The energy associated with the exertion of pressure. [4]
primary producer: See producer.
primary production: The chemical energy in an ecosystem generated by autotrophs, derived from the fixation of carbon during photosynthesis and chemosynthesis. See also gross primary production, net primary production. [19]
primary succession: Succession that involves the colonization of habitats devoid of life. Compare secondary succession. [16]
producer: An organism that can produce its own food by photosynthesis or chemosynthesis; also called a primary producer or autotroph. Compare consumer. [1]
production efficiency: The proportion of assimilated food that is used to produce new consumer biomass. [20]
pubescence: The presence of hairs on the surface of an organism. [4]

Q

quadrat: A sampling area (or volume) of any size or shape. [8]

R

r-selection: In the r- and K-selection approach to classifying life history strategies, the selection pressures faced by organisms that live in environments where population densities are usually low. Compare K-selection. [7]
radiatively active gases: See greenhouse gases. [2]
rain-shadow effect: The effect a mountain range has on 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. [2]
ramet: An actually or potentially physiologically independent member of a genet that may compete with other members for resources. Compare genet. [8]
random dispersion: A dispersion pattern that is similar to what would occur if individuals were positioned at locations selected at random. Compare clumped dispersion, regular dispersion. [8]
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. [15]
redundancy hypothesis: A hypothesis that assumes an upper limit on the positive effect of species richness on community function because once species richness reaches some threshold, the functions of species in the community will overlap. Compare complementarity hypothesis. [18]
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 their dispersal capabilities. [17]
regional species pool: All the species contained within a region; sometimes called gamma diversity. [17]
regular dispersion: A dispersion pattern in which individuals are relatively evenly spaced throughout their habitat. Compare clumped dispersion, random dispersion. [8]
relative population size: An estimate of population size based on data that are related in an unknown way to the absolute population size, but can be compared from one time period or place to another. [8]
replicate: To perform each treatment of a controlled experiment, including the control, more than once. [1]
reproductive effort: The quantity of energy and resources an organism devotes to reproduction. [7]
rescue effect: A tendency for high rates of immigration to protect a population from extinction. [10]
resilience: The rate of recovery after a disturbance. [18]
resistance: The influence of a barrier on the movement of compounds such as water or CO₂. [4]
resource: A feature of the environment that is required for growth, survival, or reproduction and which can be consumed or otherwise used to the point of depletion. Compare physical factor. [11]
resource partitioning: The use of limiting resources by different species in a community in different ways. [11, 18]
resource ratio hypothesis: A hypothesis that posits that species can coexist in a community by using resources the same resources but in different proportions. [18]
riffle: A fast-moving portion of a stream. Compare pool. [3]
ruderals: In Grime’s plant life history model, plants that are adapted to environments with high levels of disturbance and low levels of stress. Compare competitive plants, stress-tolerant plants. [7]

S

salinity: The concentration of dissolved salts in water. [2]
salinization: A process by which high rates of evapotranspiration in arid regions result in a progressive buildup of salts at the soil surface. [2]
sand: The coarsest soil particles (0.05–2 mm). [21]
savanna: A type of community dominated by grasses with intermixed trees and shrubs. [3]
scale: The spatial or temporal dimension at which ecological observations are collected. [1]
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. [1]
secondary compound: One of a wide variety of chemicals produced by plants and used in functions such as defense against herbivory, protection from harmful radiation, and soil nutrient cycling; secondary compounds are so-named because they are synthesized on side branches off of the primary metabolic pathways that produce the carbohydrates, amino acids, lipids, and other compounds common to all organisms. [12]
secondary production: Energy in an ecosystem that is derived from the consumption of organic compounds produced by other organisms. Compare primary production. [19]
secondary succession: Succession that involves the reestablishment of a community in which most, but not all, of the organisms have been destroyed. Compare primary succession. [16]
semelparous: Reproducing only once in a lifetime. Compare iteroparous. [7]
senescence: A decline in the fitness of an organism with age as a result of physiological deterioration. [7]
sensible heat flux: The transfer of heat through the exchange of energy by conduction or convection. [2]
sequential hemaphroditism: A change or changes in the sex of an organism during the course of its life cycle. [7]
service mutualism: A mutualism in which one partner performs an ecological service for the other. [14]
Shannon index: The index most commonly used to describe species diversity quantitatively. [15]
sit-and-wait predator: A predator that hunts by remaining in one place and attacking prey that move within striking distance. [12]
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. [21]
speciation: The process by which one species splits into two or more species. [6]
species: A population or group of populations whose members have similar characteristics and can interbreed with one another, but not with members of other such groups. [6]
species accumulation curve: A graph that plots species richness as a function of the total number of individuals that have accumulated with each additional sample. [15]
species–area relationship: The relationship between species richness and area sampled. [17]
species composition: The identity of the species present in a community. [15]
species diversity: A measure that combines both the number of species (species richness) in a community and their relative abundances compared with one another (species evenness). [15]
species evenness: The relative abundances of species in a community compared with one another. [15]
species richness: The number of species in a community. [15]
sporophyte: A multicellular diploid life cycle stage, found in many algae and all plants, that produces haploid spores. Compare gametophyte, alternation of generations. [7]
stability: The tendency of a community to remain the same in structure and function. [18]
stabilizing selection: Selection that favors individuals with an intermediate phenotype. Compare directional selection, disruptive selection. [6]
stable: Returning to the original state after some perturbation. [16]
stable age distribution: A population age structure that does not change from one year to the next. [9]
stable limit cycle: A pattern of population fluctuations in which abundance cycles indefinitely. [10]
static life table: A life table that records the survival and reproduction of individuals of different ages during a single time period. [9]
stomate: A pore in plant tissues, usually leaves, surrounded by specialized guard cells that control its opening and closing. [4]
stratification: The layering of water in oceans and lakes due to differences in water density and temperature with depth. [2]
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 survival, growth, or reproduction. [4, 7, 16]
stress-tolerant plants: In Grime’s plant life history model, plants that are adapted to conditions of high stress and low disturbance. Compare competitive plants, ruderals. [7]
subsidence: In meteorology, a sinking (downward) motion in the atmosphere, usually over a broad area, leading to the development of a high pressure cell. Compare uplift. [2]
succession: The change in species composition over time as a result of abiotic and biotic agents of change. [16]
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. [22]
survival rate: The proportion of individuals of age x that survive to be age x + 1 (denoted S_x in a life table). [9]
survivorship: The proportion of individuals that survive from birth (age 0) to age x (denoted l_x in a life table). [9]
survivorship curve: A graph that is based on survivorship data (l_x) and that plots the number of individuals from a hypothetical cohort (typically, of 1,000 individuals) that will survive to reach different ages. [9]
symbiont: As the smaller member of a symbiosis, an organism that lives in or on an organism of another species, its host. Compare host, symbiosis. [13]
symbiosis: A relationship in which two species live in close physiological contact with each other. Compare host, symbiont. [14]

T

taxonomic homogenization: A 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. [22]
temperate zone: The major climatic zone between 30° and 60° N and S. [2]
thermocline: The zone of rapid temperature change in a lake beneath the epilimnion and above the hypolimnion. [2]
thermoneutral zone: The range of environmental temperatures over which endotherms maintain a constant resting metabolic rate. [4]
threshold density: The number of individuals in a population susceptible to a disease at (or above) which the disease will become established and spread. [13]
tides: Patterns of rising and falling ocean water generated by the gravitational attraction between Earth and the moon and sun. [3]
till: Thick layers of sediment deposited by glaciers. [21]
tolerance: The ability to survive stressful environmental conditions. Compare avoidance. [4]
top-down control: Limitation of the abundance of a population by consumers. Compare bottom-up control. [10]
torpor: A state of dormancy in which endotherms drop their lower critical temperature and associated metabolic rate. [4]
trade-off: An organism’s allocation of its limited energy or other resources to one structure or function at the expense of another. [7]
transpiration: The evaporation of water from the inside of a plant, typically through stomatal pores. [2]
trophic cascade: A change in the rate of consumption at one trophic level that results in a series of changes in species abundances and species compositions at lower trophic levels. [15, 20]
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. [20]
trophic facilitation: An interaction in which a consumer is indirectly facilitated by a positive interaction between its prey and another species. [15]
trophic level: A group of species in a community that obtain energy in similar ways, classified by the number of feeding steps by which the group is removed from auto-trophs, which are the first trophic level. [15, 20]
trophic mutualism: A mutualism in which one or both of the mutualists receives energy or nutrients from its partner. [14]
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. [20]
tropical zone: The major climatic zone between 25° N and S, encompassing the equator. [2]
turgor pressure: Hydrostatic pressure that develops in a plant cell when water moves into it, following a gradient in water potential. [4]
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] (2) The replacement of one species with another over time or space. [17]
turnover rate: See mean residence time. [21]
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. [9]
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. [9]
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. [9]

U

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 which is easy to count. [22]
uplift: (meteorology) The rising of warm, less dense air in the atmospheredue to surface heating. Compare subsidence. [2]
upwelling: The rising of deep ocean waters to the surface where prevailing wind patterns cause surface waters to flow away from a coast. [2]

V

variability: The range of abiotic conditions in an environment. [2]
vertical transmission: The spread of a disease from mother to newborn. [13]
vicariance: An approach to biogeography that explains the geographic distribution of species in terms of events such as continental drift that result in the geographic isolation of populations that once were connected to one another. [17]

W

warning coloration: A defense against predators in which prey species that contain powerful toxins advertise those toxins with bright coloration; also referred to as aposematic coloration. [12]
water potential: The overall energy status of water in a system; the sum of osmotic potential, gravitational potential, and matric potential. [4]
watershed: See catchment. [21]
weather: The current temperature, humidity, precipitation, wind, and cloudiness. Compare climate. [2]
weathering: The physical and chemical processes by which rock minerals are broken down, eventually releasing soluble nutrients and other elements. [21]

Z

zero population growth isoclines: Lines derived from the Lotka–Volterra competition model marking the variables at which population does not increase or decrease in size. [11]
zooplankton: Nonphotosynthetic plankton. Compare phytoplankton. [3]