Biodiv Sci ›› 1995, Vol. 03 ›› Issue (Suppl.): 12-21.

### Spatial Patterns of Species Richness: A Hierarchical Perspective

JIANGUO WU, WEI GAO

1. Biological Sciences Center, Desert Research Institute University of Neveda System, Reno, NV 89506-0220, USA
• Received:1994-11-19 Online:1995-12-20 Published:1995-12-20

Abstract:

This paper examines several major geographic patterns of species richness and related hypotheses of mechanisms. These species patterns include latitudinal gradient, elevation gradient, aridity gradient, species-area relationship, and microenvironmental pattern. Hypotheses and mechanisms to be examinedinclude time hypothesis, origination-extinction dynamics hypothesis, available energy/productivity hypothesis, habitat heterogeneity hypothesis, moderate disturbance/ stress hypothesis, and niche theory/species interaction hypothesis. There has been a lack of conceptual frameworks to integrate biodiversity studies carried out at different spatial, temporal and organizational scales. We believe that such frameworks must take a hierarchical and scale perspec- tive and explicitly consider the multiplicity of processes and mechanisms. In a rather concise fashion, we propose a hierarchical structure for relating both the patterns and hypotheses of species richness with spatial scales. This hierarchical framework helps to understand patterns, hypotheses and their relationship in terms of spatial scales and related processes. For example, patterns of species richness and responsible processes are usually scale-dependent. At continental and global scales, available energy in the environment seems to be the ultimate determinant of the number of species. However, other hypotheses must be invoked in order to satisfactorily explain the largescale patterns of species richness. Spatial heterogeneity and disturbance are significant at landscape or regional scales, whereas species interactions, disturbances, and microenvironmental factors operate most importantly on local scales.