Use of the abundance spectrum and relative-abundance distributions to analyze assemblage change in massively altered landscapes

Fragmentation of natural landscapes is a pervasive process in the world. Common models predict coherent change in assemblages, with less numerous species becoming locally extinct first, then species of intermediate abundance, and so forth. Relative-abundance distributions should change systematically in landscapes characterized by greater change. Such a predictable sequence of change is not evident in the avifaunas of landscapes of central Victoria, Australia, where relative-abundance patterns in more affected landscapes bear little resemblance to reference distributions. I provide two sets of analyses of relative-abundance distributions: ( 1) analyses that do not depend on the identity of individual species and ( 2) abundance spectra, which use ordered lists of species ranked by species' commonness in reference systems. While abundance spectra change dramatically in smaller remnants, relative-abundance distributions change little, suggesting that the reorganization of abundances occurs over ecological time frames. The dispersal-limited multinomial is a flexible distribution that may fit many data sets yet be unrelated to assumptions ( species neutrality) and processes ( fixed total numbers of individuals) of the unified neutral theory. A more complete understanding of human impacts at landscape scales must include capacities to predict those species that will be advantaged by change, as well as those that will be disadvantaged.