Scales of Effect for Urban Mammals Vary Among Species and Environmental Attributes

Abstract

Context. Cities are increasingly recognized for their biodiversity conservation potential. Incomplete understanding of urban species habitat requirements and of the areal extents over which species-habitat interactions occur (“scale of effect”), however, restricts such conservation.Objectives.Better-understanding scales of effect for urban species could improve urban conservation by identifying areal extents to target in management. We sought to identify scales of effect for urban mammals and if and how these scales differ among species and environmental covariates.Methods. We constructed Eastern fox squirrel (Sciurus niger), red fox (Vulpes vulpes), and Virginia opossum (Didelphis virginianus) occupancy models using data from trail cameras in Iowa City, Iowa, USA. We compared models constructed using environmental covariates estimated over different extents and identified appropriate scales of effect for each covariate based on model fit.Results. Scales of effect varied among species and covariates. Environmental covariates based on home ranges sometimes provided the best model fit; however, best-fit model covariates were often estimated over other extents. The best-fit fox squirrel model included covariates estimated at different, but relatively local scales (<250 m). Both opossum and red fox models included local to landscape-level covariates. Thus, scales of effect differed among species, possibly with body size, and environmental attributes, offering clear evidence that urban mammals exhibit a multi-scalar response to their environments.Conclusions. Our findings suggest that habitat models should include covariates estimated over a range of biologically-informed extents to more accurately identify habitat relationships. Such modeling will inform the choice of extent in urban habitat management.