ABSTRACT
Organisms are a vital component of geoecosystems. Individually, even the largest of them occupy very little space. As a whole, they form an almost continuous film over the land surface and in the edaphosphere. Single organisms are basic units in the genealogical and societary hierarchies. In the genealogical hierarchy, they are storehouses of genetic informationgenomes; in the societary hierarchy, they are members of local populations. From an evolutionary point of view, these twofold aspects of organisms should be treated together (Eldredge 1985). Changes in the genealogical hierarchy supply the means by which organisms, expressed as phenotypes, can adapt over generations to evolving biotic and abiotic environmental circumstances, including changing climatic fields. As members of populations, individual organisms are part of societies or communities that, over time, evolve to suit the environmental fields in which they are engulfed, providing that these fields stay constant long enough for adaptation to occur. In this chapter, the ways in which the present climatic fields influence the distribution of species and communities will be explored.
