Linking Species Diversity and Landscape Diversity

Abstract

Ecologists generally agree that species diversity is linked to landscape features (Pickett and White 1985, Glenn et al. 1992, Wiens et al. 1993, Rosenzweig 1995, Hoagland and Collins 1997, Ritchie and Olff 1999). We present a conceptual framework for connecting species diversity and landscapes by showing how changes in species assemblages and changes in landscape structure coincide. We focus on the dynamics of the mutual relationship between (1) the frequency of occurrence of the various landscape mosaic components (patches) and their properties in terms of abiotic conditions, resource availabilities, and structural features, and (2) the occurrence and abundance of the species of an assemblage within and among these components. Although we use examples of assemblages of annual plants in semiarid shrubland, we stress the generality of our approach and its applicability to many other groups of organisms and landscapes. Most ecologists would also agree that there are connections between the observations that (1) individuals and populations of organisms are affected by environmental heterogeneity in the landscape, (2) species assemblages (or communities) consist of populations (or parts of them), and (3) changes in the landscape affect species assemblages, and vice versa. In this chapter we explore this often intuitive relationship explicitly. Our basic premise is that species assemblages are collections of populations interacting with the heterogeneity of the landscape. We use the term “assemblage” to preclude assumptions about interactions and proximity or encounters among the organisms. Simple presence in the sampled landscape is the criterion for belonging to an assemblage; the landscape mosaic is an assemblage of patches, which, like species, may or may not interact. We assume that the landscape is heterogeneous, comprising a mosaic of distinct patches, which can be distinguished by some patch property. Our approach does not require a particular size or kind of landscape, but its scale and structure and the definition of patches have to be relevant for the distribution of the organisms whose diversity we study. In this chapter we discuss the functional connection between the dynamics of landscapes and of species assemblages.