If you build it, will they come?
I often find myself asking this question as I’m reading through the latest work on corridor modeling or planning for connectivity conservation. Although methods to predict corridor locations and movement pathways for animals and plants have developed rapidly over the last decade, research has tended to focus on analyses and outcomes with relevance to a single species occupying a terrestrial environment. Here, the principal assumption is that ‘they’ (the focal species) will use the corridor(s) or pathway(s) identified by a research effort. However, in the question I offer above, ‘they’ also can refer to multiple species and sometimes an unknown number of species.
From my perspective, the science of multispecies connectivity has progressed somewhat slowly. Perhaps this is not surprising – efforts to precisely identify areas that facilitate connectivity for multiple species can be hindered by, for example, a lack of suitable empirical data on multiple focal species and compounding model uncertainty. Nevertheless, the conservation community seems ready to consider multispecies approaches in the placement of corridors. Given the pace of environmental changes, this is understandable.
So, if we’re tasked with finding ways to conserve the simultaneous movement of multiple species or taxa, are reasonable approaches to modeling connectivity and corridor mapping available to move society toward appropriate planning and implementation steps? Few empirically driven analyses of multispecies connectivity are available to address this question.
In a recent paper by Brodie and colleagues (full disclosure: I’m one of them), the efficacy of single versus multispecies connectivity scenarios was evaluated for five threatened mammals in rainforests of Malaysian Borneo. Briefly, they used estimates of local abundance generated from camera trap data and remotely sensed environmental variables to map the cost (and flow) of movement for each species among a network of protected areas. These individual results were then overlaid to produce corridor maps for combinations of species that could be compared to the original maps derived for each species.
Results suggested that multispecies connectivity scenarios are not always more likely to facilitate movement and dispersal of the focal species than a single species scenario, though multispecies connectivity scenarios based on ecologically similar species (in this case, carnivores or herbivores) could be more effective than a single species scenario. Moreover, the authors concluded from their results “umbrella species approaches may fail to conserve community connectivity for threatened species.”
To derive their connectivity scenarios and corridor maps, Brodie and colleagues leveraged data obtained for a relatively small set of focal species. Although the methods are contemporary, the empirical data required to build and test their models were not easy to come by. Of course, a variety of data collection and combination methods could be used to predict connectivity and the locations of potential habitat corridors in almost any geography.
But can we also be comfortable with the assumptions and uncertainties that might underlie estimates of multispecies connectivity and any resultant corridor maps?
I would argue that reasonable concepts and tools are available to advance the science of multispecies connectivity. In the context of rapid climate and land cover changes, we have little choice but to move forward.
Brodie, J. F., A. J. Giordano, B. Dickson, M. Hebblewhite, H. Bernard, J. Mohd-Azlan, J. Anderson, and L. Ambu. 2015. Evaluating multispecies landscape connectivity in a threatened tropical mammal community. Conservation Biology 29:122-132.
Brás, R., J. O. Cerdeira, D. Alagador, and M. B. Araújo. 2013. Linking habitats for multiple species. Environmental Modelling and Software 40:336–339.
Koen, E. L., J. Bowman, C. Sadowski, and A. A. Walpole. 2014. Landscape connectivity for wildlife: development and validation of multispecies linkage maps. Methods in Ecology and Evolution 5:626–633.
Lawler, J. J., A. S. Ruesch, J. D. Olden, and B. H. McRae. 2013. Projected climate-driven faunal movement routes. Ecology Letters 16:1014-1022. (Predicting the future movement routes of 3000 species)
Theobald, D. M., S. E. Reed, K. Fields, and M. Soule. 2012. Connecting natural landscapes using a landscape permeability model to prioritize conservation activities in the United States. Conservation Letters 5:123–133. (Connectivity across the United States)
Urban, D. L., E. S. Minor, E. A. Treml, and RS Schick. 2009. Graph models of habitat mosaics. Ecology Letters 12:260–273.