Cornell ecologists and colleagues have developed a new model that captures the abundance of wildlife species in a region and offers new insights into animals’ interactions with each other – information that will aid wildlife management and conservation.

The model was tested on coyotes, fishers and American martens in northern New York but can be used on any wildlife system, including mammals, birds, fish and even insects.

“Abundance-Mediated Species Interactions” published Dec. 5 in the journal Ecology. First author is Joshua Twining, a former postdoctoral researcher in the Department of Natural Resources and Environment (DNRE) and now an assistant professor in the Department of Fisheries, Wildlife, and Conservation Sciences at Oregon State University.

It was co-authored by Angela Fuller, leader of the New York Cooperative Fish and Wildlife Research Unit and professor in DNRE in the College of Agriculture and Life Sciences.

“Most current models for species interactions are based on co-occurrence – whether two species occur at a site or not,” Twining said. “And that’s important to know, but it’s a very coarse measurement that misses a huge amount of information that’s critical for understanding when and how species are actually interacting.”

Species interactions – including competition, predation and disease – depend on the abundance of the species involved, he said. The new statistical model uses detection data from repeat surveys, such as a multi-year camera trap survey carried out by the New York State Department of Environmental Conservation in the Adirondacks and Tug Hill region of northern New York.

Fishers and martens are members of the weasel family, and both species are recovering from severe historical declines in the region. Fishers weigh 3 to 13 pounds, while American marten weigh 1 ½ to 3 pounds. Coyotes are the apex predators in the region, forming family groups and hunting large prey such as deer and beaver, while mesopredators like fishers and American martens rely on carrion as a key part of their winter diets.

Previous research has suggested that coyotes might be limiting fisher populations and, thus, indirectly helping martens, but “we found almost the complete opposite,” Twining said. Areas with larger numbers of coyotes had higher populations of fishers but lower populations of martens.

The reasons for these dynamics are uncertain, Twining said. It may be that the smaller martens are killed by coyotes more often when feeding at carrion sites than the larger fishers, or that some unknown ecosystem factor is benefiting both coyotes and fishers but not martens, he said.

Marten populations declined rapidly in the late 1800s and early 1900s because of habitat loss and unregulated trapping. DEC closed marten trapping from 1936-78 to allow populations to recover. Marten trapping today is closely monitored; trappers must get a permit and abide by a season bag limit. Despite a carefully managed harvest in New York state, climate change may threaten the species’ populations in the Northeast, because martens thrive in areas with deeper snow, as compared to fishers, Fuller said.

“Martens have survived in the region in part because of this niche separation, where they persist in areas of high snow depth where fishers don’t do as well. But with climate change, we’re going to see reductions in that snow depth and these snowy refuges,” Twining said. “We certainly should be monitoring these populations very carefully and planning for their future.”

Fuller emphasized that the model can help elucidate wildlife interactions and inform wildlife management strategies across a host of species and habitats.

“We are now applying this model to study interactions among moose, deer and parasites, particularly to test hypotheses about parasite-mediated competition,” she said. “It will provide valuable insights to inform wildlife management strategies amid emerging challenges like disease dynamics.”

Also contributing to the study were colleagues from the U.S. Geological Survey in Montana and Maryland.

Krisy Gashler is a writer for the College of Agriculture and Life Sciences.