Ecology Terms Starting With N
Ecology Glossary: N
Jump to Ecology Term
Niche
/ NITCH / · French niche (recess in a wall)
Niche is the full set of biotic and abiotic conditions a species requires to survive and reproduce, including the resources it uses, the environmental tolerances it has, and its interactions with other organisms.
A species occupies a fundamental niche defined by all physical and chemical conditions it can tolerate, such as a temperature range of 5 to 35 degrees Celsius and a pH range of 6 to 8. Competition from other species, predation pressure, and parasitism typically restrict where the species actually survives, producing a realized niche that is smaller than the fundamental niche. G.
Evelyn Hutchinson formalized this distinction in 1957, describing the niche as an n-dimensional hypervolume in which each axis represents a different environmental variable. A pileated woodpecker’s (Dryocopus pileatus) niche includes foraging for wood-boring insects under loose bark, roosting in dead snags, and excavating nest cavities in dead wood, activities that shape forest structure for many other species.
The concept of competitive exclusion, formalized by Georgy Gause in 1934 using laboratory cultures of Paramecium, predicts that two species with identical niches cannot coexist indefinitely. One species will always outcompete the other, driving it locally extinct or forcing a shift in resource use.
Niche means only where an animal lives. Habitat is place, while niche is the species' role and requirements in that place.
The red-cockaded woodpecker (Leuconotopicus borealis) occupies a highly specialized niche in longleaf pine (Pinus palustris) forests of the southeastern United States, excavating nest cavities exclusively in living pines infected with red heart fungus. Colonies require territories of 80 to 200 hectares of mature pine forest, and their cavity trees are used by at least 27 other vertebrate species after the woodpeckers abandon them.
What Do Woodpeckers Eat? →Niche Overlap
/ NITCH OH-ver-lap / · French niche (recess) + Old English oferhleopan (to overlap)
Niche overlap is the degree to which two or more species share the same resources, environmental conditions, or habitat space within an ecosystem.
When two species exploit the same food types, feeding locations, or microhabitats, their niches overlap and interspecific competition intensifies as shared resources become limited. Robert MacArthur’s classic 1958 study of five warbler species in northeastern spruce forests showed that each species foraged in a distinct vertical zone within the same trees, reducing overlap and allowing coexistence. Coexistence despite niche overlap is possible when resource abundance exceeds total demand, when species differ along other niche dimensions, or when they partition resources temporally by feeding at different times of day.
Measuring niche overlap quantitatively, ecologists use indices such as Pianka’s index, which ranges from 0 (no overlap) to 1 (complete overlap).
Niche overlap and competitive exclusion are linked by the limiting similarity concept, which proposes that species can coexist only if their niches differ by at least a minimum amount. Theoretical and empirical work suggests that coexisting competitors typically differ by a factor of roughly 1.3 in the size of food items they consume, a ratio sometimes called Hutchinson's ratio.
Species with niche overlap cannot coexist in the same location. Overlapping species can coexist if resources are abundant, if they differ in other niche dimensions, or if they partition resources through space or time.
African lions (Panthera leo) and spotted hyenas (Crocuta crocuta) on the Serengeti overlap substantially in diet, both targeting wildebeest and zebra. Despite this overlap, stable coexistence persists because lions kill prey averaging about 230 kilograms while hyenas more frequently take prey in the 50 to 150 kilogram range, and the two species also differ in activity timing, with hyenas doing most hunting after dark.
Nitrogen Cycle
/ NY-troh-jen SY-kul / · Latin nitrum (niter) + Greek kyklos (circle)
Nitrogen Cycle is the biogeochemical pathway by which nitrogen moves and changes form among the atmosphere, soil, water, and living organisms.
Nitrogen fixation by bacteria such as Rhizobium and free-living Azotobacter converts atmospheric nitrogen gas into ammonium, making nitrogen biologically available for the first time in each cycle. Nitrification by Nitrosomonas and Nitrobacter bacteria then converts ammonium to nitrite and nitrate in soil and water, the forms most plants absorb through their roots. Animals obtain nitrogen by consuming plants or other organisms, and decomposers break down organic nitrogen in dead tissue back into ammonium through ammonification.
Denitrification by bacteria such as Pseudomonas returns nitrogen gas to the atmosphere, completing the cycle; globally, biological nitrogen fixation adds roughly 120 million metric tons of nitrogen to terrestrial ecosystems each year.
Industrial nitrogen fixation through the Haber-Bosch process, developed by Fritz Haber and Carl Bosch in the early twentieth century, now fixes more nitrogen annually than all natural biological fixation combined. This synthetic nitrogen feeds roughly half the world's human population through increased crop yields but has also driven widespread nitrogen pollution in rivers, coastal waters, and the atmosphere.
Plants use nitrogen gas directly from air the way they use carbon dioxide. Most plants require nitrogen in reduced forms such as ammonium or nitrate that bacteria or synthetic fertilizers provide.
Alder trees (Alnus species) form mutualistic root nodules with the nitrogen-fixing bacterium Frankia, allowing them to colonize nitrogen-poor soils such as glacial outwash and landslide scars. A single alder stand can add 50 to 100 kilograms of fixed nitrogen per hectare per year to the surrounding soil, accelerating forest succession by enriching conditions for other plant species.
Nutrient Cycling
/ NYOO-tree-ent SY-kling / · Latin nutrire (to nourish) + Greek kyklos (circle)
Nutrient cycling is the repeated movement of chemical elements such as carbon, nitrogen, phosphorus, and sulfur between living organisms and the nonliving environment through biogeochemical processes.
Decomposer organisms including bacteria, fungi, and soil invertebrates break down dead organic matter and release nutrients back into soil and water, where plant roots and microbes can reabsorb them. This recycling distinguishes nutrient dynamics from energy flow: matter cycles indefinitely through ecosystems, while energy enters as sunlight and exits as heat and cannot be reused. Phosphorus cycling illustrates how nutrients can become temporarily unavailable; phosphorus locked in deep ocean sediments or in mined rock takes millions of years to return to the surface through geological uplift, making it a limiting nutrient in many freshwater and terrestrial systems.
Mycorrhizal fungi accelerate nutrient cycling by extending the absorptive surface of plant roots and releasing enzymes that break down organic phosphorus and nitrogen compounds in soil.
Tropical rainforests cycle nutrients so rapidly that most of the ecosystem's nutrient capital resides in living biomass rather than in soil. When rainforest is cleared and burned, the nutrient pulse released by ash is exhausted within a few growing seasons, leaving soils that are often too poor to sustain agriculture without continuous fertilizer inputs.
Nutrients disappear after organisms use them and must be replaced. Chemical nutrients cycle repeatedly through living and nonliving ecosystem components, though they can become temporarily unavailable in certain compartments.
In a temperate deciduous forest, a single hectare of soil can contain more than a metric ton of fungal mycelium actively decomposing leaf litter and woody debris. White rot fungi such as Trametes versicolor break down lignin in fallen logs, releasing carbon, nitrogen, and phosphorus that tree roots and soil bacteria absorb within the same growing season.
Mycology →