Disparity in the distribution of suitable habitat as a metric for capturing responses to contrasting land-use types.

Global species observations from community science platforms offer an unprecedented opportunity to analyze large-scale patterns of biodiversity. This holds great promise for developing data-driven metrics to measure species' responses to landscape-level environmental changes, essential for ameliorating the ongoing biodiversity crisis. A primary cause of declines in local populations of native species is the expansion and intensification of anthropogenic land uses, foremost urbanization. While species' responses to urbanization can remain consistent across spatial and temporal scales, city-specific factors, such as land-use dynamics or local biotic interactions, can profoundly influence populations and shift responses. This underscores the importance of measuring responses to urbanized landscapes at the local population level and the need for a quantitative method to track changing responses as they occur. For this purpose, I propose applying the receiver operating characteristic (ROC) and its associated area under the curve (AUC), a well-established continuous summary metric. Specifically, the novel habitat disparity (HD) metric quantifies variation in the spatial distribution of suitable habitat between two contrasting land-use types. Applying it here to a highly urbanized landscape, HDURBAN quantifies the urban affinity of 1023 species using geographic predictions of their environmental niches. Additionally, modeling virtual species for each urban response type introduced in Blair's seminal 1996 study provides place-based, expected HDURBAN values for urban avoiders, urban utilizers, and urban dwellers. Validation efforts demonstrate accurate predictions of expected urban responses of real species in three scenarios. First, following a route-of-introduction hypothesis, non-native species exhibit significantly higher HDURBAN than native species. Second, assessing the consistency of urban responses in space and time, HDURBAN is significantly correlated with the urban responses of the same 38 bird species from Blair's study, conducted 450 km apart and 25 years earlier. Third, testing for sensitivity to temporal shifts within species, HDURBAN decreases significantly in a species displaced from urban areas due to negative interactions with a recently introduced, congeneric species. In summary, HD is a versatile metric that provides a quantitative way to compare local population-level responses, supporting future research into the patterns and processes underlying spatial and temporal variation in response to contrasting land-use types.