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GLOSSARY 



community that receives the full impact of the en- 

 vironment and more or less alters it to affect the habi- 

 tat of its associates; dominants generally are plants 

 on land and in shallow water and are animals below 

 100 feet in water. 



dormancy the apparently spontaneous arrested activity or 

 development in any stage in the life history of an or- 

 ganism. 



dorsal the back of an animal, upper surface of a plant, or 

 comparable part of other organisms. 



dorsoventral from back to belly or upper to lower surface. 



drift rocks of any sort after they have been moved and 

 deposited in another place by glaciers or streams; 

 glacial drift is till. 



drumlin a smooth, oval hill of glacial origin, generally of 

 clay but also of particles up to gravel size. 



dystrophic pertaining to bodies of water with fewer than 

 normal organisms and often with brown, acid water; 

 often associated with peat bogs. 



earthquake an abrupt shock (snapping) or many vibra- 

 tions (rolling) of the earth, probably due to disturb- 

 ance of the equilibrium of rocks at or beneath the sur- 

 face; perhaps due mostly to displacement along a fault. 



ecesis the establishment of invading organisms within 

 the ecosystem of an area. 



ecliptic the great celestial circle upon the plane con- 

 taining the sun and all points on the earth's path about 

 the sun; roughly, the earth's orbital plane; hence, the 

 apparent annual path of the sun through other stars. 



ecological amplitude the inherent capability of an or- 

 ganism to tolerate a range of total environmental con- 

 ditions, exclusive of competition with other organisms. 



ecological factor any biological or physical feature in an 

 organism's surroundings; anything contributing to an 

 organism's environment. 



ecology the study of the interrelationships between or- 

 ganisms and their total environment, physical and 

 biological. 



ecosystem a community and its physical environment, 

 plus the dynamic relationships existing within and 

 between the two components, all operating as an 

 integrated unit. 



ecotone a mixed community or transition area formed 

 by the overlays of two adjacent communities and 

 having characteristics of both components plus char- 

 acteristics of its own. 



ectoderm the outer layer of cells, perhaps tissue, of the 

 gastrula or embryo stages of most animals; often ap- 

 plied to any tissue formed from this layer. 



ectotherm any organism (but usually restricted to ani- 

 mals) whose primary source of body heat is the sun. 



edaphic pertaining to soil. 



eelgrass any marine member of the Zosteraceae, the 

 pondweeds, a family of mostly fresh-water and 



strictly aquatic, perennial, herbaceous vascular 

 plants. 



egestlon the process of discharging unusable and un- 

 digested materials from the digestive tract. 



element (I) chemical, one of about 100 natural or man- 

 made, distinct kinds of matter that singly or in com- 

 bination, are the components of all substances; the 

 smallest representative unit of an element is an atom; 

 (2) biogeographical, the organisms typical or char- 

 acteristic of a particular ecological unit; floral and 

 faunal units can be recognized separately and can be 

 of any size; one element might be part of a larger 

 element. 



embryo generally, any development stage starting from 

 a fertilized egg; often restricted in plants to develop- 

 mental stages within a seed and, in animals, to stages 

 prior to birth or hatching. 



embryo sac the female gametophyte of a flowering plant, 

 a typically eight-celled structure found in the ovule, 

 which in turn is in the ovary of a flower's pistil. 



embryology the study of the formation and development 

 of embryos. 



emigration the desertion of its home by an organism. 



encystment the formation by any life-cycle stage of a 

 protective outer covering or cyst. 



endemic a taxon of any size having a relatively restricted 

 geographic distribution. 



endoderm the innermost layer of cells (perhaps tissue) of 

 the gastrula or any embryo stage of most animals; 

 often applied to any tissue formed from this layer. 



endodermis the single tissue layer of roots and some 

 stems found between the outer cortex and the inner 

 veins. 



endoskeleton an internal framework or similar structure 

 providmg support from within an organism. 



endosperm the triploid nutritive tissue surrounding a 

 flowering plant embryo and within an ovule. 



endotherm an organism that both produces and regulates 

 its body heat by means of self-regulating body func- 

 tions; specifically, birds and mammals. 



enterocoel a coelom that originates by formation and 

 separation of a series of pouches from the embryonic 

 gut; the basis for defining the Enterocoela, the 

 Echinodermata, Hemichordata, Pogonophora, Chor- 

 data, and (perhaps) Chaetognatha. 



environmental resistance the restriction of the total en- 

 vironment upon biotic potential; a factor determining 

 carrying capacity. 



Eon any of the two or three most inclusive subdivisions of 

 geological time; the more recent Phanerozoic Eon of 

 about the last 600 million years is diagnosed by a 

 relative abundance of fossils; the older Cryptozoic 

 Eon is represented by few fossils; the time before 

 the origin of life, the "Azoic Era," also may be 

 recognized as a third Eon, the Azoic. j 



