All of the above components influence regional climate.

Mutualism benefits both species; for example, a pollinator obtains nectar while transferring pollen between flowers. Commensalism benefits one species without measurably affecting the other. Competition reduces access to resources for both participants. In parasitism and predation, one species benefits at the expense of the other.

Allopatric speciation occurs when geographic isolation separates populations that later become reproductively isolated. Sympatric speciation occurs without geographic separation.

Nitrifying microbes oxidize ammonium (NH₄⁺) to nitrite (NO₂⁻) or nitrite to nitrate (NO₃⁻). Denitrification reduces nitrate to gaseous nitrogen products, including N₂. Nitrogen fixation converts N₂ to ammonia (NH₃).

In the classical model, r-selected life histories favor rapid population increase, early reproduction, and many small offspring, often in disturbed or unpredictable environments. K-selected life histories typically involve fewer offspring, later reproduction, and greater parental investment in populations near carrying capacity. These strategies form a continuum.

Secondary consumers eat primary consumers. A wolf feeding on a herbivore acts as a secondary consumer. Deer, cows, and grasshoppers typically consume plants and are primary consumers. Plants are producers.

All four listed features are typical of Arctic tundra. Permafrost is persistently frozen ground beneath a surface layer that can thaw in summer. The biome has low precipitation, long cold winters, short cool summers, and low-growing vegetation.

Analogous features perform similar functions but evolved independently, as in vertebrate wings and insect wings. Homologous features share an evolutionary origin and may have similar or different functions. The forelimbs of bats, cats, horses, and whales are homologous.

Biotic factors and abiotic factors are components of ecosystems and a biosphere contains ecosystems.

With 10% transfer at each step, herbivores receive 10% of producer energy, and primary carnivores receive 10% of that amount: 0.10 × 0.10 = 0.01, or 1%. Actual transfer efficiencies vary.

Imprinting is learning during an early sensitive period that can establish a lasting recognition or attachment response. A duckling learning to follow its mother is a classic example.

The ecological hierarchy is biosphere → ecosystem → community → population → organism. A population consists of individuals of one species in a particular area; a species can include multiple populations.

All four statements describe rain shadows. Rising air cools and loses moisture as precipitation on a mountain’s windward side. Descending air warms on the leeward side, producing drier conditions. Death Valley lies in the rain shadows of several mountain ranges.

Habituation is a decrease in response to a repeated, harmless stimulus. Imprinting occurs during a sensitive period. A fixed action pattern is an innate, stereotyped behavior. Spatial learning involves remembering locations, while associative learning links stimuli or links behavior with its consequences.

Freshwater bony fish gain water by osmosis and excrete abundant dilute urine while taking up ions through their gills. Marine bony fish lose water by osmosis, drink seawater, and excrete excess salts through their gills and kidneys.

Natural selection changes the frequencies of existing heritable variants through differences in survival and reproduction. It does not create the variation on which it acts. Evolution is a change in a population’s genetic composition over generations; natural selection is one mechanism of evolution.

A climax community is the classical term for a relatively stable, late-successional community. Real communities can continue to change because of disturbance and environmental change. Pioneer species colonize newly available habitat; secondary succession begins where soil remains. A keystone species has an effect on its community that is large relative to its abundance.

Tertiary consumers are secondary carnivores, which eat primary carnivores.

Taiga, or boreal forest, is dominated by cold-adapted conifers. Savannas are tropical grasslands with scattered trees, and tundra supports low-growing vegetation rather than forests.

Jean-Baptiste Lamarck proposed inheritance of acquired characteristics and the effects of use and disuse. Darwin developed the theory of evolution by natural selection. Linnaeus established binomial nomenclature, Cuvier advanced paleontology and catastrophism, and Lyell promoted geological uniformitarianism.

Cryptic coloration provides camouflage that reduces detection by predators. In Batesian mimicry, a harmless species resembles a harmful or unpalatable species. In Müllerian mimicry, defended species resemble one another. Aposematic coloration warns predators of defenses such as toxicity or unpalatability.

Poikilothermy means that body temperature varies substantially. Many reptiles and amphibians are poikilothermic ectotherms, but variability in body temperature and the source of body heat are distinct concepts. Homeothermy means maintaining a relatively stable body temperature.

A niche includes the resources a species uses, the conditions it tolerates, and its interactions with other organisms. A habitat is where an organism lives. Competition occurs when organisms use the same limited resources. An ecosystem includes a community and its abiotic environment.

A biological species comprises natural populations that actually or potentially interbreed and are reproductively isolated from other such groups. A population consists of individuals of one species in a particular area. A community includes interacting populations of different species.

Photosynthetic producers, including plants and phytoplankton, convert light energy into chemical energy stored in organic compounds. Herbivores obtain that chemical energy by consuming producers.

During spring and fall turnover, surface and deeper waters mix as temperature and density differences diminish. Mixing redistributes oxygen and nutrients. Strong thermal stratification inhibits this mixing.

Biotic factors are living components of an ecosystem, such as bacteria, plants, fungi, and rabbits. Abiotic factors are nonliving physical or chemical components, such as sunlight, wind, and water.

Natural selection, gene flow, and genetic drift can change allele frequencies. Bottleneck and founder effects are forms of genetic drift. Therefore, all four listed processes can alter a population’s genetic composition.

Operant conditioning changes behavior through its consequences, such as reward or punishment. Learning to press a lever for food and trial-and-error learning are examples. Learning that a bell predicts food is classical conditioning, which associates two stimuli.

The hadal zone occupies the deepest ocean trenches, generally below 6,000 m. Littoral, photic, aphotic, and limnetic zones occur in freshwater systems, although not every lake contains every zone.

Deserts receive little precipitation and generally have sparse vegetation. Many desert organisms conserve water, and some plants store it in succulent tissues. Deserts occur on several continents and can be hot or cold.

Stabilizing selection favors intermediate phenotypes over both extremes. Directional selection favors one extreme, while disruptive selection favors both extremes. These are patterns of natural selection.

Homologous structures share an evolutionary origin, even when they serve different functions. Adaptive radiation produces multiple species adapted to different ecological roles from a common ancestor. Convergent evolution independently produces similar features; analogous structures share a function without the same evolutionary origin.

Photoautotrophs, such as most plants, many algae, and cyanobacteria, use light for energy and CO₂ as a carbon source. Chemoautotrophs obtain energy by oxidizing inorganic substances and use inorganic carbon to build organic compounds.

Tropical rainforests have high species diversity, warm temperatures, and abundant rainfall. Their canopies are generally evergreen, with leaves replaced throughout the year; this does not mean that every tree species is evergreen. Widespread seasonal canopy leaf loss is more typical of seasonally dry or temperate deciduous forests.

The epipelagic, or sunlit, zone extends from the surface to roughly 200 m, although light penetration varies. The mesopelagic zone receives dim light that is generally insufficient for photosynthesis. Deeper bathypelagic and abyssal waters lack sunlight. The limnetic zone refers to open water in a lake.