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Pair bonding. The forming of a pair for breeding.
 
Paleoecology. The application of ecological concepts to fossil communities.
 
Palustrine. Pertaining to wet or marshy habitats.
 
Palynology. The study of living and fossil pollen and spores.
 
Parasite. An organism that is intimately associated with and metabolically dependent on another living organism (the host) for completion of its life cycle, and which is typically detrimental to the host.
 
Passerine. Of or relating to the largest order (Passeriformes) of birds, which includes more than half of all living birds and consists primarily of perching songbirds, whose young are hatched in an immature and helpless condition.
 
Patch dynamics. The idea that communities are a mosaic of different areas (patches) within which nonbiological disturbances (such as climate) and biological interactions proceed.
 
Pathogen. A specific causative agent of a disease, such as a bacterium or a virus.
 
Patterned ground. An assemblage of small, geometric features (circles, polygons, nets, steps) at the surface of nonconsolidated, weathered rock, resulting from disturbance by frost action such as cracking, heaving, and mass movement.
 
Pelagic. Referring to or occurring in the open sea.
 
Percent cover. In descriptions of plant communities, the proportion of ground, expressed as a percentage, that is occupied by the perpendicular projection down onto it of the aerial parts of individuals of the species under consideration.
 
Perennial. A plant that normally lives for more than two seasons and which, often after an initial period, produces flowers annually.
 
Permafrost. A permanently frozen layer of soil at variable depth below the surface in frigid regions of a planet. It may be discontinuous, that is, it may be interspersed with areas that are free of permafrost.
 
pH. A measure of acidity and alkalinity of a solution, taken by measuring the relative concentration of hydrogen ions in the solution.
 
Phenology. The study of the relationship between climate and the timing of periodic natural phenomena such as migration of birds, bud bursting, or flowering of plants.
 
Phenotype. The observable manifestation of a specific genetic makeup; those observable properties of structure and function of an organism as modified by genetic structure in conjunction with the environment.
 
Piscivores. Fish-eaters; those organisms that subsist exclusively or primarily on fish.
 
Photic zone. The surface zone of the sea or a lake having sufficient light penetration for photosynthesis.
 
Photoperiod. The length of time an organism is daily exposed to light, especially with regard to how that exposure affects growth and development.
 
Phreatophyte. A plant that absorbs ground-water from the permanent watertable.
 
Phylogenetic. Pertaining to the evolutionary history of a group or lineage, or the evolutionary relationships within and between taxonomic levels; the relationships of groups of organisms as reflected by their evolutionary history.
 
Physiognomy. The physical features of something. For example, the physiognomy of a landscape includes its topography and vegetation.
 
Physiographic province. A region of the landscape with distinctive geographical features.
 
Physiography. Landform; physical geography.
 
Phytoplankton. One of two groups into which plankton are divided, the other being zooplankton. Phytoplankton comprise all the freely floating photosynthetic forms in the oceans.
 
Pingo. A low hill or mound forced up by hydrostatic pressure in an area underlain by permafrost and consisting of an outer layer of soil covering a core of solid ice. Pingos range from 2 to 50 meters in height.
 
Pinniped. Any of a suborder of aquatic carnivorous mammals with all four limbs modified into flippers; includes seals, sea lions, and walruses.
 
Pioneer. The first species or community to colonize or recolonize a barren or disturbed area, thereby commencing a new biological succession.
 
Placer mining. The removal of ore from placers, which are glacial or alluvial deposits of sand or gravel containing valuable minerals.
 
Plankton. One of three major ecological groups into which marine organisms are divided, the other two being the nekton and the benthos. Plankton are small aquatic organisms (animals and plants) that, generally having no locomotive organs, drift with the currents. The animals in this category include protozoans, small crustaceans, and the larval stages of larger organisms, while plant forms are mainly diatoms.
 
Playa. A nearly level area at the bottom of an undrained desert basin, sometimes temporarily covered with water during wet periods. Playas are barren and usually saline.
 
Pleistocene. The earlier epoch of the Quaternary period or the corresponding system of rocks; 1.6 million-10,000 years ago; the "Ice Age."
 
Plutonic. Of or relating to conditions of rock formation from magma within the crust of the Earth.
 
Pluvial. Characterized by abundant rain.
 
Pocosin. A swamp or marsh in an upland coastal region. The term is chiefly used in the South Atlantic states of Virginia, Maryland, Delaware, and the Carolinas.
 
Polychaetes. Any of a class (Polychaeta) of chiefly marine annelid worms (such as clam worms), usually with paired segmental appendages, separate sexes, and a free-swimming trochophore larva.
 
Polychlorinated biphenyls (PCB's). A group of toxic, carcinogenic organic compounds containing more than one chlorine atom. PCB's were used in the manufacture of plastics and as insulating fluids in electrical transformers and capacitors. They behave much like DDT in the environment in that they are very stable compounds and are also fat-soluble; therefore, they accumulate in ever-higher concentrations as they move up the food chain. The use of PCB's was banned in the United States in 1979.
 
Population. A group of organisms, all of the same species, which occupies a particular area. Also, the total number of individuals of a species within an ecosystem, or of any group of similar individuals.
 
Primary producer. An organism capable of using the energy derived from light or a chemical substance in order to manufacture energy-rich organic compounds, mainly green plants.
 
Primary productivity. The rate at which biomass is produced by organisms which synthesize complex organic substances from simple inorganic substrates, such as in photosynthesis and chemosynthesis.
 
Primary production. The biomass produced through photosynthesis and chemosynthesis in a community or group of communities.
 
Progradation. The outward building of a sedimentary deposit, such as the seaward advance of a delta or shoreline, or the outbuilding of an alluvial fan.
 
Province. An area of land, less extensive than a region, having a characteristic plant and animal population.
 
Purse seine. A large seine net designed to be set by two boats around a school of fish and so arranged that after the ends have been brought together, the bottom can be closed.
 
Pyroclastic. Formed by or involving fragmentation as a result of volcanic or igneous action.
 
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