-P-- 



pandemic— Widespread throughout an area. 



panne— A depression among dunes kept 

 moist by capillary transport from the 

 water table. 



parasitism— A symbiotic relationship be- 

 tween two organisms in which one lives 

 in or on the body of its host and obtains 

 nutrition from the host tissue. This is 

 usually harmful or fatal to the host. 



parthenogenesis— The process by which an 

 egg undergoes development without fer- 

 tilization by sperm. 



peat— Fibrous, partly decayed fragments of 

 vascular plants which retain enough 

 structure so that the peat can be identi- 

 fied as originating from certain plants 

 (e.g., sphagnum peat or sedge peat). 



pelagic— All ocean waters covering the ben- 

 thic region. 



periphyton— Any organism attached or 

 clinging to stems, leaves or other surfaces 

 of plants under the water. See also 

 aufwuchs. 



phagotrophs— Macroconsumers, heterotro- 

 phic organisms chiefly animals which 

 ingest other organisms, or particulate 

 organic matter. 



phenotype— The outward expression of the 

 genotype, usually environmentally influ- 

 enced. 



philopatry— The tendancy to return to the 

 birthplace. 



photoperiod — Refers to the number of 

 hours of light or darkness in the day. 



photosynthesis— The manufacture of carbo- 

 hydrates from carbon dioxide and water 

 in the presence of chlorophyll using 

 sunlight as an energy source. 



phototrophism— A reaction or response to 

 light. 



phytocoenosis— The plant community. 



phytoplankton— Plant plankton. Members 

 of this group are in the ocean and are 

 important primary producers. 



pisciculture— The growing, or farming of 

 fish. 



plankter— A planktonic organism . 



plankton— Those organisms passively drift- 

 ing or weakly swimming in marine or 

 freshwater. 



plankton bloom— A sudden rapid increase 

 (usually geometric) to an enormous 

 number of individual plankters under 

 certain conditions. See also bloom. 



poly— A prefix referring to or of many. 



polymictic lake— A lake which is continu- 

 ally mixing or with very short stagnation 

 periods. 



polymorphism— The presence of two or 

 more forms (morphs) of the same species 

 (e.g., males and females which differ in 

 appearance). 



population growth forms — See growth 

 forms. 



potential, biotic— See biotic potential. 



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