Ecology Terms Starting With H

Habitat fragmentation is the process by which a large, continuous area of habitat is divided into smaller, isolated patches separated by inhospitable terrain, reducing the total area available to species and limiting movement between patches.

Roads, agricultural fields, and urban development subdivide once-continuous habitat into isolated patches that may be too small to support viable populations of large-bodied or wide-ranging species. Fragmentation increases edge habitat and perimeter-to-area ratios, exposing interior specialists to harsh microclimate conditions, predation, and invasive species. Gene flow between isolated populations ceases, causing genetic drift and inbreeding that reduce fitness and adaptability even when patches are separated by short distances.

A forest patch must typically exceed 500 to 1,000 hectares to maintain viable populations of many birds and large mammals that require interior habitat conditions. Corridors connecting fragmented patches through continuous or semi-continuous vegetation allow animal movement and genetic exchange between isolated subpopulations.

Herbivory is the consumption of plant or algal material by an animal, representing a primary trophic interaction that transfers energy from producers to higher trophic levels.

Herbivory drives ecosystem dynamics by transferring energy from primary producers to higher trophic levels, with herbivores typically consuming only 10 to 20 percent of available plant biomass in most terrestrial ecosystems. Plant defenses against herbivory include physical structures like thorns and silica-reinforced leaf edges, as well as chemical compounds such as tannins, alkaloids, and glucosinolates that reduce digestibility or deter feeding. Different herbivores specialize on multiple plant parts: browsers consume leaves and shoots, grazers eat grasses, and granivores feed on seeds.

Large-scale herbivory can dramatically alter vegetation structure, as seen when white-tailed deer (Odocoileus virginianus) populations reach 30 animals per square kilometer, causing measurable declines in forest regeneration. African savannas demonstrate intensive herbivory where ungulates like zebras (Equus quagga) and wildebeest consume up to 66 percent of annual grass production during seasonal migrations.

Heterotroph is an organism that obtains energy and carbon by consuming organic molecules produced by other organisms, rather than synthesizing them from inorganic sources.

Heterotrophs obtain energy by consuming organic molecules synthesized by autotrophic producers, breaking down complex molecules through cellular respiration to release usable energy. Herbivores such as rabbits consume plant tissues directly, while carnivores such as eagles obtain energy by consuming other animals. Decomposers such as bacteria and fungi secrete enzymes into their substrate, breaking down dead organic matter externally before absorbing nutrient-rich solutions.

Parasitic heterotrophs such as tapeworms absorb pre-digested nutrients across their body surfaces while living inside host organisms. No heterotroph can synthesize organic molecules from inorganic materials alone, which means every heterotrophic organism ultimately depends on autotrophs to fix carbon into usable form.

Humus is the dark, chemically stable organic component of soil produced when microbial decomposition of plant and animal matter reaches a stage where the remaining compounds resist further rapid breakdown.

Humus represents the end product of decomposition, containing complex organic compounds that can persist in soil for hundreds to thousands of years. Comprising 2 to 10 percent of soil composition in temperate forests, humus improves soil structure by binding mineral particles into aggregates that enhance water retention and aeration. Formation of humus depends on climate, vegetation type, and microbial activity: cool temperate forests produce mor humus that accumulates in distinct layers, while tropical soils often contain minimal humus because warm, moist conditions accelerate decomposition faster than organic matter accumulates.

Humus holds nutrients like nitrogen and sulfur in organic forms, releasing them gradually through mineralization, and its dark coloration comes from humic acids and fulvic acids, complex polymers that also chelate metal ions and buffer soil pH. Carbon stored in humus represents a significant long-term reservoir, with some humic compounds persisting for over 1,000 years as measured by radiocarbon dating.