3 Testing Models of Faunal Turnover with Neogene Mammals from Pakistan

mammalian faunas. This model is a modified form of Vrba’s turnover-pulse hypothesis, which posits that changes in the physical environment drive speciation, extinction, and local faunal turnover (Vrba 1995a). Model 2 emphasizes the dominance of species with large population sizes and large geographic ranges through intervals of environmental change. This model arises from the literature about macroecology and metapopulation dynamics (Hanski 1982, 1999, Maurer 1999). Although tests of these models here are preliminary, this analysis illustrates how amenable these models are to evaluation with data from the fossil record and allows us to assess the suitability of taxonomic, biostratigraphic, and paleoecological data from the Siwalik record for addressing general models in evolutionary ecology. Our results to date indicate that Model 1 is better supported by the late Miocene portion of the Siwalik record. The models evaluated here, while not fully mutually exclusive, emphasize different ecological and evolutionary responses of species to extrinsic environmental change. The environmental-forcing model assumes strict fidelity of species to their preferred habitats. The main responses are geographic-range shift or extinction. The demographic model stresses the ecological resilience of abundant species with large geographic ranges. The main responses are to remain in place and adapt to changing environmental conditions. Other models (e.g., null models, keystone-herbivore model) are beyond the scope of the present study. This paper is organized as follows. First, we briefly introduce the geology and paleontology of the Siwalik record of northern Pakistan to establish the context for this study. Salient aspects of the record of environmental change and mammalian faunal turnover in the late Miocene part of the record follow. Then, we describe the two models of faunal turnover and their specific predictions for the Siwalik record. Next, we analyze the biostratigraphic Introduction