Ecology Terms Starting With B

Bioaccumulation is the buildup of a substance, typically a toxin or pollutant, within an individual organism over time because the rate of intake exceeds the rate of elimination.

Bioaccumulation occurs when a chemical enters an organism through food, water, or direct contact faster than the organism can metabolize or excrete it. Long-lived organisms such as bowhead whales (Balaena mysticetus), lake sturgeon, and predatory fish accumulate higher total toxin loads because they have more years to absorb pollutants from food and water. Methylmercury, the organic form of mercury, is particularly prone to bioaccumulation because it binds tightly to proteins in muscle tissue and organisms lack efficient pathways to break it down.

A 50-year-old swordfish (Xiphias gladius) can carry mercury concentrations hundreds of times higher than the surrounding seawater, reflecting decades of dietary exposure.

Biodiversity is the variety of life in a given area, encompassing genetic variation within populations, the number and relative abundance of species, and the range of ecosystem types present.

Biodiversity encompasses genetic diversity within populations, species diversity measured by richness and evenness across communities, and ecosystem diversity reflecting habitat heterogeneity and ecological function. Ecosystems with high biodiversity show greater resistance to disturbance because functionally redundant species compensate when some populations decline, while low-diversity systems dominated by few species show larger productivity fluctuations. Tropical rainforests contain approximately 50 percent of Earth’s species despite covering only 7 percent of its land area, supporting 10 to 100 times higher species density than temperate forests at the same spatial scale.

A landmark 1994 study by David Tilman and colleagues at Cedar Creek, Minnesota, demonstrated experimentally that grassland plots with more plant species maintained more stable biomass production across years with variable rainfall.

Biogeography is the scientific study of the geographic distributions of species and the evolutionary, geological, and climatic processes that produced those distributions.

Biogeography integrates evolutionary biology, plate tectonics, climate science, and dispersal ecology to explain why species occur where they do across continents and islands. Vicariance events such as continental drift and mountain formation create barriers that isolate populations and drive independent evolution, as occurred with marsupials in Australia after it separated from Antarctica roughly 45 million years ago. Dispersal routes across ocean currents, land bridges like the Isthmus of Panama, and through human transport determine which species reach new regions.

Climate zones constrain where species can survive based on physiological tolerances for temperature, precipitation, and seasonality, which is why cacti dominate North American deserts but are absent from the Sahara despite similar aridity.

Biomagnification is the progressive increase in concentration of a persistent toxic substance at successively higher trophic levels of a food chain.

Persistent organic pollutants like DDT and heavy metals such as mercury accumulate in fatty tissues and are not easily broken down or excreted by organisms. As predators consume contaminated prey, the concentration of these substances increases at each trophic level because the predator ingests all the toxins from many prey organisms. A top predator may accumulate toxin levels 10,000 times higher than concentrations measured in the surrounding water.

These chemicals are lipophilic, meaning they dissolve in fat rather than water and resist excretion through urine, so each meal adds to a growing body burden rather than flushing the toxin out.

Biome is a large geographic region characterized by a specific climate, soil type, and distinctive communities of plants and animals adapted to those conditions.

Biomes are defined by characteristic climate patterns, including temperature and precipitation ranges, which select for particular plant functional types such as evergreen trees, deciduous trees, grasses, or shrubs that structure entire communities. The tropical rainforest biome experiences warm temperatures and high rainfall year-round, supporting continuous growth and rapid decomposition, while the taiga or boreal forest endures 6 to 8 months of temperatures below freezing, limiting productivity despite receiving moderate precipitation. Each biome occupies specific latitude and altitude ranges where climate conditions are similar, so the same biome type appears independently on different continents, each supporting different species but similar ecological structures.

Biosphere is the zone of Earth that supports life, encompassing all terrestrial surfaces, aquatic environments, and the lower atmosphere where organisms live and interact.

The biosphere extends from approximately 11,000 meters depth at the deepest ocean trenches to roughly 15,000 meters altitude in the upper atmosphere, with the densest concentration of life between 200 meters below sea level and 6,000 meters altitude. Life persists in extreme environments including hot springs at 80 to 90 degrees Celsius, frozen soils at minus 40 degrees Celsius, subsurface aquifers kilometers below the land surface, and anoxic mud layers, demonstrating that the biosphere reaches wherever liquid water and an energy source permit metabolism. Collectively, the biosphere contains approximately 8.7 million eukaryotic species and an unknown number of microbial species, with total biomass dominated by plants, which comprise roughly 82 percent of all biosphere carbon.

Biotic describes all living organisms present in an ecosystem and the interactions among them, including predation, competition, mutualism, parasitism, and decomposition.

Biotic factors encompass every organism in an ecosystem and the ways those organisms affect one another. Predators regulate prey populations by consuming roughly 5 to 30 percent of annual prey production depending on predator-prey ratios, while decomposers such as bacteria and fungi break down dead organic matter and release nutrients back into soil at rates of 10 to 20 percent annual mass loss. Plants compete for light, water, and nutrients, with taller species shading and excluding shorter competitors, restructuring entire communities over time.

Mycorrhizal fungi form symbiotic associations with plant roots, increasing nutrient uptake by 100 to 1,000 times compared with uncolonized roots, illustrating how one biotic factor can determine the productivity of another.