Environmental changes induced by the activities of organisms, such as soil enrichment by colonizing legumes are also significant as they influence vegetation structure (Vitousek et al. 1987). Mortality factors like predation and parasitism are also obvious, for they result in immediate death or readily measured debilitation. Competition, strictly defined to exclude processes such as facultative predation and changes to the environment (Walter and Paterson 1995), may also influence local ecology, although its impact is undoubtedly more sporadic than other ecological variables, in part because it is subject to subtle contextual intrusions as well (e.g., Andrewartha and Birch 1954, Buss 1990). Competition cannot, therefore, provide a sound basis for developing generalizations in evolution and ecology (Walter 1988a, 1995, 2008).