Functional landscape connectivity for a select few: Linkages do not consistently predict wildlife movement or occupancy

Landscape-level connectivity models developed in geographic information systems (GIS) produce hypothetical objects proposed to connect areas of habitat in fragmented landscapes, hereafter called "linkages". Assuming they are used by organisms in nature, linkages could be an important tool for the maintenance of viable wildlife populations and biodiversity conservation. We evaluated five California linkage models (four statewide and one desert specific) for use by common California mammal, reptile and amphibian species in two ways using >180,000 wildlife detections over 20 years. If species are using linkages more often than surrounding areas, we expect to find evidence of their occurrence within linkages significantly more than outside linkages. First, we focused on wildlife-vehicle collision (WVC) data as a proxy for wildlife movement across landscapes and tested whether linkages were an important predictor for the presence of WVCs. Second, we used occupancy modeling with inferred non-detections to assess whether linkages were important predictors of species presence on the landscape. We found that the linkage areas were not consistent predictors of WVCs, with the exception of certain large-bodied mammals by individual models. Linkage areas were also not important predictors for the probability of landscape occupancy for most species. These results show that, lacking validation, hypothetical landscape linkages alone will not support functional connectivity for general biodiversity conservation. Therefore, caution should be exercised when using linkages in land and transportation-based conservation planning. In urban environments, modeled linkages may reflect the critical last places for wildlife to move and should be reserved. However, in mixed-use landscapes where wildlife may move more easily, connectivity as a gradient across the landscape should be the target of conservation, including in land-use and transportation planning.