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||An American movement in the field of painting that began in the late
forties and emphasized a nonrepresentational style. The movement broke into two branches:
action painting and color field painting.
||Any genetically controlled structural, physiological, or behavioral
characteristic that helps an organism survive and reproduce under a given set of
environmental conditions. It usually results from a beneficial mutation. See biological
evolution, differential reproduction, mutation, natural selection.
||Process in which numerous new species evolve to fill vacant and new
ecological niches in changed environments, usually after a mass extinction or mass
depletion. Typically, this takes millions of years.
||Slightly different molecular form found in a particular gene.
||Height above sea level. Compare latitude.
||See old-growth forest.
||Pertaining to water. Compare terrestrial.
|aquatic life zone
||Marine and freshwater portions of the biosphere. Examples include
freshwater life zones (such as lakes and streams) and ocean or marine life zones (such as
estuaries, coastlines, coral reefs, and the deep ocean).
||Dry. A desert or other area with an arid climate that has little
||Process by which humans select one or more desirable genetic traits in
the population of a plant or animal and then use selective breeding to end up with
populations of the species containing large numbers of individuals with the desired
traits. Compare genetic engineering, natural selection.
||Reproduction in which a mother cell divides to produce two identical
daughter cells that are clones of the mother cell. This type of reproduction is common in
single-celled organisms. Compare sexual reproduction.
||Normal extinction of various species as a result of changes in local
environmental conditions. Compare mass depletion, mass extinction.
||Change in the genetic makeup of a population of a species in successive
generations. If continued long enough, it can lead to the formation of a new species. Note
that populations--not individuals--evolve. See also adaptation, differential
reproduction, natural selection, theory of evolution.
||Terrestrial regions inhabited by certain types of life, especially
vegetation. Examples are various types of deserts, grasslands, and forests.
||Maximum rate at which the population of a given species can increase
when there are no limits on its rate of growth. See environmental resistance.
|broadleaf deciduous plants
||Plants such as oak and maple trees that survive drought and cold by
shedding their leaves and becoming dormant. Compare broadleaf evergreen plants, coniferous
|broadleaf evergreen plants
||Plants that keep most of their broad leaves year round. Examples are
the trees found in the canopies of tropical rain forests. Compare broadleaf deciduous
plants, coniferous evergreen plants.
|carrying capacity (K)
||Maximum population of a particular species that a given habitat can
support over a given period of time. See dieback.
||Formation of the earth and its early crust and atmosphere, evolution of
the biological molecules necessary for life, and evolution of systems of chemical
reactions needed to produce the first living cells. These processes are believed to have
occurred about 1 billion years before biological evolution. Compare biological
||Physical properties of the troposphere of an area based on analysis of
its weather records over a long period (at least 30 years). The two main factors
determining an area's climate are temperature, with its seasonal variations, and the
amount and distribution of precipitation. Compare weather.
||Land along a coastline, extending inland from an estuary, that is
covered with salt water all or part of the year. Examples are marshes, bays, lagoons,
tidal flats, and mangrove swamps. Compare inland wetland.
||Warm, nutrient-rich, shallow part of the ocean that extends from the
high-tide mark on land to the edge of a shelflike extension of continental land masses
known as the continental shelf. Compare open sea.
||Evolution in which two or more species interact and exert selective
pressures on each other that can lead each species to undergo various adaptations. See evolution,
|coniferous evergreen plants
||Cone-bearing plants (such as spruces, pines, and firs) that keep some
of their narrow, pointed leaves (needles) all year. Compare broadleaf deciduous plants,
broadleaf evergreen plants.
||Cone-bearing trees, mostly evergreens, that have needle-shaped or
scalelike leaves. They produce wood known commercially as softwood. Compare deciduous
||Ability of a living system, such as a population, to maintain a certain
size. See homeostasis. Compare inertia, resilience.
||Formation produced by massive colonies containing billions of tiny
coral animals, called polyps, that secrete a stony substance (calcium carbonate) around
themselves for protection. When the corals die, their empty outer skeletons form layers
and cause the reef to grow. They are found in the coastal zones of warm tropical and
||Trees, such as oaks and maples, and other plants that survive during
dry seasons or cold seasons by shedding their leaves. Compare coniferous trees, succulent
||Biome in which evaporation exceeds precipitation and the average amount
of precipitation is less than 25 centimeters (10 inches) a year. Such areas have little
vegetation or have widely spaced, mostly low vegetation. Compare forest, grassland.
||Sharp reduction in the population of a species when its numbers exceed
the carrying capacity of its habitat. See carrying capacity.
||Phenomenon in which individuals with adaptive genetic traits produce
more living offspring than do individuals without such traits. See natural selection.
||Time it takes (usually in years) for the quantity of something growing
exponentially to double. It can be calculated by dividing the annual percentage growth
rate into 70. See rule of 70.
||Total way of life or role of a species in an ecosystem. It includes all
physical, chemical, and biological conditions a species needs to live and reproduce in an
ecosystem. See fundamental niche, realized niche.
|ecological population density
||Number of individuals of a population per unit area of habitat. Compare
||Transitional zone in which one type of ecosystem tends to merge with
another ecosystem. See edge effect.
||Existence of a greater number of species and a higher population
density in a transition zone (ecotone) between two ecosystems than in either adjacent
ecosystem. See ecotone.
||All the limiting factors that act together to limit the growth of a
population. See biotic potential, limiting factor.
||Partially enclosed coastal area at the mouth of a river where its fresh
water, carrying fertile silt and runoff from the land, mixes with salty seawater.
||Upper layer of a body of water through which sunlight can penetrate and
||Lake with a large or excessive supply of plant nutrients, mostly
nitrates and phosphates. Compare mesotrophic lake, oligotrophic lake.
||Plants that keep some of their leaves or needles throughout the year.
Examples are ferns and cone-bearing trees (conifers) such as firs, spruces, pines,
redwoods, and sequoias. Compare deciduous plants, succulent plants.
||See biological evolution.
||Growth in which some quantity, such as population size or economic
output, increases by a fixed percentage of the whole in a given time period; when the
increase in quantity over time is plotted, this type of growth yields a curve shaped like
the letter J. Compare linear growth.
||Complete disappearance of a species from the earth. This happens when a
species cannot adapt and successfully reproduce under new environmental conditions or when
it evolves into one or more new species. See also endangered species, mass
depletion, mass extinction, threatened species. Compare speciation.
||Biome with enough average annual precipitation (at least 76
centimeters, or 30 inches) to support growth of various tree species and smaller forms of
vegetation. Compare desert, grassland.
|freshwater life zones
||Aquatic systems where water with a dissolved salt concentration of less
than 1% by volume accumulates on or flows through the surfaces of terrestrial biomes.
Examples are (1) standing (lentic) bodies of fresh water such as lakes, ponds, and inland
wetlands and (2) flowing (lotic) systems such as streams and rivers. Compare biome.
||The full potential range of the physical, chemical, and biological
factors a species can use if there is no competition from other species. See ecological
niche. Compare realized niche.
||Movement of genes between populations, which can lead to changes in the
genetic composition of local populations.
||Sum total of all genes found in the individuals of the population of a
||Species with a broad ecological niche. They can live in many different
places, eat a variety of foods, and tolerate a wide range of environmental conditions.
Examples are flies, cockroaches, mice, rats, and human beings. Compare specialist
||Changes in the genetic makeup of organisms of a species that allow the
species to reproduce and gain a competitive advantage under changed environmental
conditions. See differential reproduction, evolution, mutation, natural
||Complete set of genetic information for an organism.
||Separation of populations of a species for long times into different
||Biome found in regions where moderate annual average precipitation
(25-76 centimeters, or 10-30 inches) is enough to support the growth of grass and small
plants but not enough to support large stands of trees. Compare desert, forest.
||Place or type of place where an organism or population of organisms
lives. Compare ecological niche.
||Ability of a living system to resist being disturbed or altered.
Compare constancy, resilience.
||Land away from the coast, such as a swamp, marsh, or bog, that is
covered all or part of the time with fresh water. Compare coastal wetland.
||Area of shoreline between low and high tides.
|intrinsic rate of increase (r)
||Rate at which a population could grow if it had unlimited resources.
Compare environmental resistance.
||Animals that have no backbones. Compare vertebrates.
||Species that produce a few, often fairly large offspring but invest a
great deal of time and energy to ensure that most of those offspring reach reproductive
age. Compare r-selected species.
||See K-selected species.
||Large natural body of standing fresh water formed when water from
precipitation, land runoff, or groundwater flow fills a depression in the earth created by
(1) glaciation, (2) earth movement, (3) volcanic activity, or (4) a giant meteorite. See eutrophic
lake, mesotrophic lake, oligotrophic lake.
||Distance from the equator. Compare altitude.
||Growth in which a quantity increases by some fixed amount during each
unit of time. Compare exponential growth.
||Pattern in which exponential population growth occurs when the
population is small, and population growth decreases steadily with time as the population
approaches the carrying capacity. See S-shaped curve. Compare J-shaped curve.
||Long-term, large-scale evolutionary changes among groups of species.
||Swamps found on the coastlines in warm tropical climates. They are
dominated by mangrove trees, any of about 55 species of trees and shrubs that can live
partly submerged in the salty environment of coastal swamps.
||Period of species loss in which extinction rates are much higher than
normal but not high enough to classify as a mass extinction. Compare background, extinction,
||Catastrophic, widespread, often global event in which major groups of
species are wiped out over a short time compared with normal (background) extinctions.
Compare background extinction, mass depletion.
||Lake with a moderate supply of plant nutrients. Compare eutrophic
lake, oligotrophic lake.
||Small genetic changes a population undergoes. Compare macroevolution.
|minimum dynamic area (MDA)
||Minimum area of suitable habitat needed to maintain the minimum viable
population. See minimum viable population.
|minimum viable population (MVP)
||Estimate of the smallest number of individuals necessary to ensure the
survival of a population in a region for a specified time period, typically ranging from
decades to 100 years.
||Chemical or form of radiation that causes inheritable changes
(mutations) in the DNA molecules in the genes found in chromosomes. See carcinogen,
||Random change in DNA molecules making up genes that can yield changes
in anatomy, physiology, or behavior in offspring. See mutagen.
|natural rate of extinction
||See background extinction.
||Process by which a particular beneficial gene (or set of genes) is
reproduced in succeeding generations more than other genes. The result of natural
selection is a population that contains a greater proportion of organisms better adapted
to certain environmental conditions. See adaptation, biological evolution, differential
||Strongly swimming organisms found in aquatic systems. Compare benthos,
||See ecological niche.
||Virgin and old, second-growth forests containing trees that are often
hundreds, sometimes thousands of years old. Examples include forests of Douglas fir,
western hemlock, giant sequoia, and coastal redwoods in the western United States. Compare
second-growth forest, tree plantation.
||Lake with a low supply of plant nutrients. Compare eutrophic lake,
||Part of an ocean that is beyond the continental shelf. Compare coastal
||Small plant organisms (phytoplankton) and animal organisms
(zooplankton) that float in aquatic ecosystems.
||Number of organisms in a particular population found in a specified
area or volume.
||General pattern in which the members of a population are arranged
throughout its habitat.
||Variation of population density over a particular geographic area. For
example, a country has a high population density in its urban areas and a much lower
population density in rural areas.
||Major abiotic and biotic factors that tend to increase or decrease the
population size and age and sex composition of a species.
||Number of individuals making up a population's gene pool.
|population viability analysis (PVA)
||Use of mathematical models to estimate a population's risk of
extinction. See minimum viable population.
||Species that reproduce early in their life span and produce large
numbers of usually small and short-lived offspring in a short period of time. Compare K-selected
||See r-selected species.
||Parts of the fundamental niche of a species that are actually used by
that species. See ecological niche, fundamental niche.
||Production of offspring by one or more parents.
||Long-term geographic separation of members of a particular sexually
||See biotic potential.
||Ability of a living system to restore itself to original condition
after being exposed to an outside disturbance that is not too drastic. See constancy,
||Fresh water from precipitation and melting ice that flows on the
earth's surface into nearby streams, lakes, wetlands, and reservoirs. See reliable
runoff, surface runoff, surface water. Compare groundwater.
||Leveling off of an exponential, J-shaped curve when a rapidly growing
population exceeds the carrying capacity of its environment and ceases to grow.
||Reproduction in organisms that produce offspring by combining sex
cells, or gametes (such as ovum and sperm), from both parents. This produces offspring
that have combinations of traits from their parents. Compare asexual reproduction.
||Species with a narrow ecological niche. They may be able to (1) live in
only one type of habitat, (2) tolerate only a narrow range of climatic and other
environmental conditions, or (3) use only one type or a few types of food. Compare generalist
||Formation of two species from one species because of divergent natural
selection in response to changes in environmental conditions; usually takes thousands of
years. Compare extinction.
|species equilibrium model
||See theory of island biogeography.
||Plants, such as desert cacti, that survive in dry climates by having no
leaves, thus reducing the loss of scarce water. They store water and use sunlight to
produce the food they need in the thick, fleshy tissue of their green stems and branches.
Compare deciduous plants, evergreen plants.
||Precipitation that does not infiltrate the ground or return to the
atmosphere by evaporation or transpiration. See runoff. Compare groundwater.
||Graph showing the number of survivors in different age groups for a
||Pertaining to land. Compare aquatic.
||Process in which organisms patrol or mark an area around their home,
nesting, or major feeding site and defend it against members of their own species.
|theory of evolution
||Widely accepted scientific idea that all life-forms developed from
earlier life-forms. Although this theory conflicts with the creation stories of many
religions, it is the way biologists explain how life has changed over the past 3.6-3.8
billion years and why it is so diverse today.
|theory of island biogeography
||The number of species found on an island is determined by a balance
between two factors: the (1) immigration rate (of species new to the island) from other
inhabited areas and (2) extinction rate (of species established on the island). The model
predicts that at some point the rates of immigration and extinction will reach an
equilibrium point that determines the island's average number of different species
||See tree plantation.
||Animals that have backbones. Compare invertebrates.
||Land area that delivers water, sediment, and dissolved substances via
small streams to a major stream (river).