Assessing prey competition in fossil carnivore communities — a scenario for prey competition and its evolutionary consequences for tigers in Pleistocene Java

We assess prey competition between various carnivore species that overlapped in time and geographic range during the Early to Late Pleistocene of Java, using a three step procedure. Our sample encompasses 5 carnivore species–two pantherines (Panthera tigris, P. pardus); a single hyaenid (Hyaena brevirostris); and two canid species (Cuon alpinus, Cuon (Mececyon) trinilensis)–each of which occurs in one or more faunal levels (Ci Saat, Trinil HK, Kedung Brubus, Ngandong, and Punung) in the well-documented Stegodon–Homo erectus Fauna. The tiger is the only carnivore that occurs in all faunal levels studied here. Since changing body mass can lessen competition, monitoring tiger body mass through the chronological sequence–as other species enter or leave the fossil record–provides an opportunity to assess the effects of competition. First, we estimate body mass of each individual in these species using regression equations based on measurement of skeletal elements. Second step, from these estimates of individual body mass we derive prey focus masses (PFM) and prey mass spectra (PMS). Third, we examine pairwise PMS overlap of coexisting carnivore species, deriving a quantitative Competition Index (CI) that expresses the degree to which a specific carnivore is affected by the presence of another carnivore species. The CI provides a measure of the consequences of changes in the carnivore communities upon each species and also allows us to evaluate the impact of different hunting strategies on competition. We suggest the significant increase in body mass of tigers in the Ngandong faunal level reflects unusually intense competition among carnivores in the preceding Kedung Brubus level.