Quantifying biodiversity: a phenotypic perspective

With recently derived algorithms, it is possible to calculate the relative phylogenetic distinctiveness of taxa with respect to patterns of phylogenet ic branching. We extended this approach by exploring the relative extent to which taxa represent phenotypic biodiversity. We devised a method, based o n the use of independent contrasts, that measures the amount of phenotypic change that occurs when lineages diverge. We use this method to quantify th e extent to which a taxon represents the phenotypic diversification that ha s occurred in the past. We applied our method to an analysis of variation i n clutch size across 133 avian families. All families did not contribute eq ually to representing clutch size diversification. The top 10 avian familie s in terms of representing clutch size diversification were the mesites (Me sitornithidae), cranes (Gruidae), bustards (Otidae), new world quail (Odont ophoridae), seriemas (Cariamidae), finfoots ( Heliornithidae), swallows (Hi rundinidae), megapodes (Megapodiae), and guans (Cracidae). The 217 species in these 10 families (2.3% of all bird species, 7.5% of families) represent ed 19.3% of diversification in clutch size. Seventeen percent of overall cl utch size diversification was represented by taxa threatened with extinctio n. The 10 families that represent the greatest proportion of overall clutch size diversification threatened by extinction were the mesites (Mesitornit hidae), kagu (Rhynochetidae), cranes (Gruidae), kiwis (Apterygidae), new wo rld quail (Odontophoridae), megapodes (Megapodiae), cassowaries (Casuariida e), finfoots (Heliornithidae), guans (Cracidae), and logrunners (Orthonychi dae). The 42 threatened species (0.5% of all bird species, 3.8% of all thre atened bird species) in these 10 families encompassed 53% of the clutch siz e diversification whose representation was threatened with extinction. Our results suggest that this type of analysis could potentially help prioritiz e species-based conservation efforts by identifying those taxa that contrib ute most toward representing the evolutionary processes that lead to curren t phenotypic biodiversity.