Environmental variables driving habitat differentiation in two sympatric pademelon (Thylogale) species in northeast NSW

Abstract

A pivotal question for community ecologists is whether assemblages are structured as a result of general rules that can be applied to any ecosystem. Trade-offs in species performance of ecological functions are a common theory behind the structure of communities and the co-occurrence of species. The phenomenon of sympatry was originally described as the co-occurrence of two or more forms in the same geographical region. Intraguild sympatry between ecologically similar species is fundamental in shaping the dynamics of community assembly. Temporal and spatial partitioning between comparable sympatric species can facilitate biodiversity and contribute to the structural complexity of mammalian community assemblies. My research aimed to describe the ecology of two sympatric forest wallabies, the red-legged pademelon, Thylogale stigmatica, and the red-necked pademelon, Thylogale thetis, in a rainforest-wet-sclerophyll forest in northeastern New South Wales. The diel activity pattern of both species was mapped using camera traps over a 16-month period. Structural vegetation components measured at each camera site were used to determine the variation in usage by the two pademelon species between two forest types in the study area, and which structural habitat variables correlated with their occurrence. Camera trap data revealed that both Thylogale species were strongly crepuscular, however, T. stigmatica was more active before dawn than during the evening, indicating some evidence of temporal partitioning. T. thetis spatiotemporally partitioned their habitat remaining under forest cover diurnally and travelling beyond the forest-pasture edge overnight. Detection data revealed that T. thetis were positively correlated with the density of multi-layered detection cover as well as disturbance variables, indicating an affiliation for fine-scale habitat attributes rather than a particular vegetation type. T. stigmatica was correlated negatively with disturbance related factors, indicating a preference for closed forest and multi-layered cover. T. stigmatica showed some plasticity in their activity budgets when sympatric with the ecologically similar species T. thetis, and likely exhibited temporal partitioning in response as a form of niche partitioning. T. stigmatica appear to narrow their preferred niche and become more specialised in the presence of T. thetis, consequently occurring in lower densities. The composition of the entire mammal community detected by camera traps was significantly affected by both habitat type and individual structural variables, indicating that fine-scale heterogeneity is important on an individual species scale as well as at a community level. In summary, this work shows that temporal and spatial niche partitioning allowed the ecologically similar T. stigmatica and T. thetis to co-occur in the same forest and contributed to the facilitation of high biodiversity in the wider mammal community.