Comparing Occupancy and Abundance Responses of Common Semi-arid Vertebrates

Occupancy and abundance are key population metrics used to demonstrate how environmental, and ecological processes influence wildlife populations. Given both metrics are strongly correlated, they are often used interchangeably to measure population response of species. Thus, studies that use occupancy as a surrogate for abundance are common. However, inherent sensitivity differences between these two metrics can indicate that their response to environmental or ecological processes, in common, can lead to metric specific responses. Key differences in the sensitivity of occupancy and abundance are likely to be observed because each metric's response could be influenced by different scales of ecological effect, resource granularities or species attributes. I used a multi-year study to assess whether occupancy and abundance responded differently (i.e., sensitivity) to variation in the spatial scale of coarse scale habitat attributes, fine-scale vegetation structures or due to implicit species-specific differences within the semi-arid landscape of Little Desert National Park. Occupancy and abundance displayed different response sensitivities, with abundance detecting responses to twice as many predictor covariates compared to occupancy. The key predictors that influenced the increased sensitivity of abundance relative to occupancy were related to measures testing habitat granularity, nor inherent species differences and not to the scale of effect nor inherent species differences. Thus, my study indicates the importance and specificity of vegetation measures for measuring species response, presenting possible predictors of uncoupling and variations among landscapes, and the need for continued research into other factors, aiding in understanding response patterns for management and conservation methods.