Diversity patterns, niches, and conservation: Herpetological case studies
Sigala Rodriguez, Jose Jesus
Understanding patterns of global diversity and their underlying causes has important implications for conservation. However, analyses at broad geographical scales with local natural history information are rarely undertaken, even when most conservation decisions are made at state or municipal levels. Here I cover three geographical scales and processes toward that end. Although latitudinal gradients of species richness have been explained in terms of water and energy, different groups respond differently to those variables. I describe patterns of species richness for 112 species of pitvipers throughout the Western Hemisphere and test five hypotheses that might explain those patterns, using geographical information systems and spatial statistics: area, water-energy, habitat heterogeneity, prey availability, and an index of phylogenetic diversity. The main explanatory factor was phylogenetic diversity, followed by prey diversity, then temperature, with other variables contributing only marginally. Next, I look at the factors that regulate patterns of species occurence at the Neotropic-Nearctic realms border as a way to understand distributional limits. I investigated potential limiting variables for two species of neotropical snakes as they reach the Nearctic realm by using ecological niche modeling. I identify limiting factors for the distribution of those species, the differential way they adapt to local conditions, and suggest marked niche separation for one species, but only moderate differences for the other. These results illustrate the need for intimate knowledge of the organisms to take full advantage of ecological niche modeling. Finally, I evaluate how humans impact the persistence of vertebrates at local and regional scales in central Mexico. By combining re-surveys with 50-year-old museum collections, field notes, and landscape photographs, I document an increase of species known for Aguascalientes and identify at least one species that might be eradicated. I also provide evidence for extensive habitat modification, and discuss the threat of local extinction at species? distributional limits has broader implications for regional biotas. My findings illustrate the conservation value of intensive small-scale studies, focused on the natural history of particular species and localities, as complements to large-scale biodiversity assessments.
Jesus Sigala's dissertation
Species richness; Patterns of biodiversity; Conservation; Ecological niche modeling; Paterns of distribution; amphibians and reptiles
dissertation or thesis