Context Spatial occupancy and local abundance of species often positively covary, but the mechanisms driving this widespread relationship are poorly understood. Resource dynamics and habitat changes have been suggested as potential drivers, but long-term studies relating them to abundance and occupancy are rare. In this 34-year study of acorn woodpeckers (Melanerpes formicivorus), a cooperatively breeding species, we observed a paradoxical response to changes in habitat composition: despite a reduction in the availability of high-quality breeding habitat, the population increased considerably.
Objectives We investigated the role of annual variation in food availability and long-term changes in habitat composition as predictors of population dynamics.
Methods Using model selection, we contrasted competing hypotheses on the effects of changing resource availability on occupancy and social group size across three spatial scales: territory, neighborhood, and landscape.
Results The increase in abundance was largely determined by the formation of new social groups, driven by a landscape-level expansion of canopy cover and its interaction with neighborhood-level acorn abundance, indicative of long-term increases in overall acorn productivity. Group size increased with neighborhood acorn crop two years earlier but groups were smaller in territories with more canopy cover.
Conclusions Our results indicate that scale-dependent processes can result in paradoxical relationships in systems with spatial and temporal resource heterogeneity. Moreover, the findings support the role of resources in driving changes in abundance and occupancy at a landscape scale, suggesting that colonization of marginal habitat drives the positive occupancy-abundance relationship in this cooperatively breeding species.
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© The Author(s) 2023
Article states: "The data used in the analysis are available in Data Dryad. Citizen science data from the Audubon Christmas Bird Count can be downloaded at https://netapp.audubon.org/cbcobservation/."
Original Publication Citation
Hagemeyer, N. D. G., Pesendorfer, M. B., Koenig, W. D., & Walters, E. L. (2023). Unraveling a paradox of habitat relationships: Scale-dependent drivers of temporal occupancy-abundance relationships in a cooperatively breeding bird. Landscape Ecology, 38(8),1955-1970. https://doi.org/10.1007/s10980-023-01668-0
Hagemeyer, Natasha D.G.; Pesendorfer, Mario B.; Koenig, Walter D.; and Walters, Eric L., "Unraveling a Paradox of Habitat Relationships: Scale-Dependent Drivers of Temporal Occupancy-Abundance Relationships in a Cooperatively Breeding Bird" (2023). Biological Sciences Faculty Publications. 560.
0000-0001-5368-4598 (Hagemeyer), 0000-0002-9414-5758 (Waters)