Multiple scale analysis of species filtering processes and their determinants
Lior Blank, Yohay Carmel
Understanding the factors regulating the diversity of ecological communities is one of the greatest challenges of community ecology. Scale is a crucial component of any ecological system, and the processes generating the observed patterns of species diversity can be conceptualized as a series of hierarchical ‘filters’ that determine the manner by which local-scale species assemblages are derived from the species pools of larger scales. While this ‘filtering’ concept has been used extensively as a conceptual framework for understanding the organization of ecological communities, empirical applications of this concept in natural communities have usually been limited to only two scales: a ‘local community’ and a ‘regional species pool’. The distinction between these two scales is usually arbitrary, and is not derived from ecological considerations. Moreover, while data on the relationship between species richness of local vs. regional communities have been obtained for a wide spectrum of organisms and environments, the identity and relative importance of the ‘filters’ responsible for the observed relationships were usually left unknown. Thus, even for arbitrary two-level hierarchies of local-regional systems, the processes generating the observed relationships of species diversity are rarely understood.
In this project we shall apply a multi-scale approach for analyzing patterns of species diversity along a rainfall gradient in Israel. Our main working hypotheses are that (a) the number and identity of species occurring at any spatial scale reflect the result of filtering processes operating at larger spatial scales, (b) that the relative importance of different filters varies in a predictable manner from larger to smaller scales, and (c) that different taxa respond differentially to the same filters, depending on their ecological requirements and dispersal ability. We shall test these and other hypotheses by analyzing patterns of species diversity of vascular plants, several invertebrate taxa, and passerine birds, over spatial scales ranging from a small scale of 10-1 – 104 m2 (depending on the group) up to a large scale of>108 m2. The observed patterns of species diversity will be analyzed with respect to several environmental factors, operating differentially at different scales (in order of increasing scale): the woody vegetation structure, soil, topography, and climate. We believe that such a spatially hierarchical, multi-factor analysis of patterns of species diversity will contribute significantly to our understanding of the role of scale in determining the organization of ecological communities.