If you build it, will they come? Wildlife corridors need smarter design

The study was published in September in the journal Landscape Ecology.

"If we don't get these corridors right, our efforts at conservation will be wasted, and we could see more human-wildlife conflicts," said Jennifer Mullinax, an associate professor in the Department of Environmental Science and Technology at UMD, and senior author of the study. "In Florida, black bear populations were once threatened, but have been rebounding, and continue to spread. Better methods are urgently needed, because it takes a lot of time to do it right, and in the case of endangered or threatened species, we could build corridors and still not provide protections for those animals."

Creating corridors often means government agencies, municipalities, or non-profits purchase and protect expensive tracts of land or work with developers to conserve areas that might otherwise be developed. The tracts of land chosen for conservation are often determined by scientific modeling based on animal movements and landscape features. But the needs of different species in different locations are complex and not all corridors have the same goal. One may need to provide access to new habitats for an expanding population, and another may aim to improve genetic diversity by connecting populations that are separated by development.

In addition to these complexities, conserving wildlife corridors is expensive, and yet it remains unknown how different design methods influence their effectiveness, or how to evaluate if they are working for the intended purpose.

Mullinax and her team used three different mathematical models to create theoretical wildlife corridors for black bears in Florida and compared them to tracking data to determine how black bears actually move through the environment. They also compared their model corridors to the existing Florida Wildlife Corridor, a network of public and private conservation lands designated as a multi-species corridor across the state.

To develop potential corridors, the team combined information on bear habitats and where they are likely to live, with landscape features and information on how easy or difficult it is for bears to move through the environment. The study revealed how tricky it can be to define "easy movement" and then use it to develop corridor parameters. For example, traveling across open farm fields and roadways may be physically easier for a bear than traveling through dense woods, but that's not where you want bears to go. While an urban area could be considered more difficult for a bear to traverse, some bears will waltz right through town to find the local trash dump that offers lots of food. Mullinax and her team developed three different approaches to defining "difficult movement" and created three gridded maps of Florida, each with different levels of "resistance" built into the landscape.

The team used a program called Circuitscape to combine their resistance grids with bear habitat information and developed maps showing the most likely flow of bear movement in Florida. It can be thought of as a sort of road map that shows multiple bear "roads" and "highways" with more or less likely bear traffic.

They used those maps to create three different potential corridors and overlaid them with GPS tracking data on the real movements of 30 bears, each of which had been intensively tracked for an extended period of time. The results were mixed, and how well any corridor did changed depending on bear behaviors.

For example, the corridor that had the least overlap with bear movements, and scored the lowest in most evaluations, was the only corridor that included the movements of a single unique bear that had a mind of his own.

"That's what we call a dispersal movement, when an individual moves to a completely new location looking for a new home," Mullinax explained. "If one bear does it, others may too, and it's how animals establish themselves in new territories. That's what we want to capture, but the best overall models completely failed to capture that unique bear movement."

Additionally, what works for some animals may not work for all. The Florida Wildlife Corridor is considered a multi-species corridor that covers a large area, but it included fewer bears per square kilometer than the bear-specific model corridors the team designed.

The study challenges the often-raised idea that any wildlife corridor is always better than no corridor. According to Mullinax, it may be true that any conservation effort is better than none, but this work raises an urgent call for more research and more resources to ensure the expense and effort of building wildlife corridors does not go to waste, especially as we continue to experience shrinking wildlife habitats and a changing climate.