Ecology Terms Starting With P

Parasitism is a symbiotic relationship in which one organism, the parasite, benefits by obtaining resources from a host organism that is harmed but usually not immediately killed by the interaction.

Parasites are extraordinarily diverse, encompassing viruses, bacteria, fungi, protozoa, helminths, arthropods, and parasitic plants, and collectively they may represent the majority of all species on Earth when all forms are counted. Unlike predators, parasites typically do not kill their hosts immediately, instead exploiting them as living resources over extended periods, and many have coevolved diverse mechanisms to evade host immune systems. Parasitism drives much of the diversity of immune systems and life history traits across animals and plants, making it one of the most powerful selective forces in evolution.

Permafrost is ground that stays frozen at or below 0 degrees C for at least two consecutive years, covering about a quarter of all land in the Northern Hemisphere and storing enormous amounts of frozen carbon from ancient plant material.

Permafrost underlies much of Siberia, Canada, and Alaska, as well as high-altitude mountain areas worldwide. While the surface layer thaws each summer, the ground below stays frozen year-round. Permafrost stores carbon like a giant freezer for dead plant material that has accumulated for thousands of years, when it thaws, bacteria break down this material and release carbon dioxide and methane, both greenhouse gases.

Persistent organic pollutants, commonly abbreviated POPs, are toxic human-made chemicals that do not break down in the environment for many years, build up in the fat of animals and humans, and become more concentrated the higher up the food chain they go.

POPs include pesticides like DDT, industrial chemicals like PCBs, and unwanted by-products like dioxins. Because they are fat-soluble and very stable, they dissolve into the fat of small animals, plankton, insects, small fish. When larger animals eat many of these smaller ones, the chemicals accumulate further in their fat.

Phosphorus Cycle phosphorus cycle is the continuous movement of phosphorus from rocks and soil into plants and animals, through food chains, back to the soil through decomposition, and eventually into water systems and ocean sediments.

Phosphorus enters ecosystems through weathering of phosphate-rich rocks at rates of 0.1 to 10 milligrams per square meter per year depending on rock type and climate. Plants absorb dissolved phosphate ions from soil water through their root systems, and animals obtain phosphorus by consuming plants or other animals. Decomposition releases phosphorus back to soil, while water transport carries phosphate to lakes and oceans where it settles into sediments.

Unlike carbon and nitrogen, phosphorus lacks a significant atmospheric gaseous phase under normal Earth conditions.

Population density is the number of individuals of a species that live within a specific area or volume, such as the count of deer per square mile in a forest.

Population density measured as individuals per unit area affects resource availability, disease transmission rates, and mating opportunities for individuals in a population. High-density mussel beds experience intense competition for space with individual mussels reducing growth rates as available attachment substrate becomes limited. Disease spread increases exponentially with population density in crowded populations, allowing pathogens to transmit rapidly between nearby hosts.

Predation intensity often increases with prey density as predators locate food more efficiently in crowded populations.

Population dynamics is the study of how and why the size and structure of a population change over time.

Births, deaths, immigration, and emigration directly change population size through mathematical relationships described by the equation Nt+1 equals Nt plus births plus immigration minus deaths minus emigration. Population size affects intraspecific competition for food and space, which then influences survival and reproduction rates. Density-dependent factors like disease and resource availability can cause populations to cycle, crash, or stabilize rather than grow indefinitely.

Environmental variation drives populations to fluctuate unpredictably in some species while others show stable cycles.

Predator Prey predator-prey relationship is the interaction between a predator, the hunting animal, and its prey, the animal it hunts and eats, a relationship that shapes the population sizes of both species in linked cycles over time.

Predator and prey populations cycle through predictable phases with a time lag between peaks. When prey like snowshoe hares are abundant, predator lynx have abundant food, reproduction increases, and lynx population surges after about one year. The larger lynx population then overhunts hares, causing hare numbers to crash.

With insufficient food, lynx reproduction declines and population falls, allowing hare recovery and restarting the cycle. These linked oscillations occur in many predator-prey systems including wolves and moose.

Primary Producer primary producer is an organism that makes organic food from simple substances, usually by photosynthesis.

Primary producers capture light or chemical energy and convert it into organic molecules through photosynthesis or chemosynthesis. Plants fix carbon dioxide into glucose using chlorophyll and solar energy at efficiency rates between 0.5 and 3 percent. Cyanobacteria and chemosynthetic bacteria oxidize hydrogen sulfide or methane to generate energy in deep ocean vents and other anoxic environments.

These organic molecules flow up food chains as herbivores consume producers and carnivores consume herbivores.

Primary production is the process by which plants, algae, and some bacteria convert sunlight or chemical energy into organic matter, forming the energetic foundation of nearly all food chains.

Gross primary production is the total amount of organic matter made by photosynthesis. Net primary production is what remains after producers use some of that energy for respiration, and it represents the energy available to animals and other consumers. On land, tropical rainforests have the highest net primary production; at sea, coastal waters and upwelling zones are among the most productive.

Primary succession is the development of a community in a place where soil and an earlier community are absent.

Primary succession begins on unvegetated surfaces like new lava flows, bare rock, or sand dunes where no soil or previously established biological community exists. Lichens and mosses colonize bare substrate first because they require minimal soil and can fix nitrogen from the air. These early colonists weather rock surfaces and accumulate organic matter that gradually builds soil depth measured in millimeters per year.

Grasses and shrubs establish once soil development supports their deeper root systems, eventually allowing trees to dominate decades or centuries later.