ECOLOGICAL FACTORS IN SPECIATION

Abstract

All degrees of geographical isolation are known, resulting in a complete interruption or only slight reduction of gene flow between the isolated populations. The term microgeographical isolation may be used where only short distances are involved. The establishment of a new intraspecific population is usually associated with a shift in the ecological characteristics of such a population. All subspecies show ecological differences, and no 'ecological races' are known that are not also at least 'icrogeographical.' It is unproven and unlikely that reproductive isolation can develop between contiguous populations. Many of the assumptions made in the various hypotheses of sympatric speciation are erroneous. The evidence usually cited as proving sympatric speciation is fully consistent with the theory of geographic speciation. The concept of sympatric speciation creates many difficulties avoided by the concept of geographic speciation. Sympatric speciation, if it occurs at all, must be an exceptional process. The normal process of speciation in obligatorily sexual and cross fertilizing organisms is that of geographical speciation.