Biodiversity Generation, Overview

Abstract

Biodiversity involves at least two components: (1) phylogenetic biodiversity, which might be summarized crudely as the number of species, and (2) character state biodiversity. To understand the generation of biodiversity one must understand both components. A description of the generation of phylogenetic biodiversity can only be properly achieved if there is a good fossil record. In the absence of a fossil record, molecular phylogenies can often be reconstructed to show when pairs of species last shared common ancestors in relative or absolute time. It is possible to analyze the structure of such phylogenies to estimate historical speciation and extinction rates, and to detect changes in speciation and extinction rates. The causes of variation in rates of speciation are becoming better understood through the analysis of possible key innovations that allow taxa to exploit more niches, with the associated methodology of sister taxon analysis. Reasons for character state diversity, such as variation in morphology, behavior, or life history, can be determined by using modern comparative methods. Since species inherit characters from their ancestors, closely related species are more similar than distantly related species, and species do not provide independent points for statistical analysis. Instead, independent evolutionary origins of character states are sought. For continuously varying characters, such as body size, independent contrast analysis often provides a useful approach. The results of such analyses reveal that there are far fewer causal factors than character states, so that the same character complexes have evolved on many occasions, thereby simplifying a complex database. The consequence is that understanding the reasons for the generation of biodiversity becomes a manageable task.