DELMARVA ALMANAC

Delmarva’s Apex Predators

by Dave Wilson

Hear naturalist Dave Wilson and his guest Dr. Aaron Hogue tell us about apex predators here on Delmarva.

Dave Wilson:
My guest today is Dr. Aaron Hogue who is a biology professor at Salisbury University where he has worked for the past 11 years. He holds a PhD in Evolutionary Biology from Northwestern University in Chicago. His specialties are in mammalogy and evolution and he has done extensive research studying the nexus between human activities, terrestrial habitat destruction, and species declines. Today we're going to discuss biodiversity on the peninsula and how the loss of apex predators and other mammals has affected the shore's biota and what we might do about it. Dr. Hogue, good morning.

Dr. Aaron Hogue:
"Good morning."

Dave Wilson:
Let's begin with what we've lost. What apex predators used to be here that are no longer on the shore?

Dr. Aaron Hogue:
"In terms of mammalian carnivores as a whole we did an extensive survey of the archaeological and historical literature and were able to document 10 species as being native to the peninsula. Of those I would say four could qualify as apex predators. Those would be cougar, bobcat, wolves (and we can talk about which species of wolves) and black bear. The other predators that are native would be gray fox, raccoon, long-tailed weasel, mink, river otter, and skunk."

Dave Wilson:
How many of those have we lost or are no longer on the peninsula?

Dr. Aaron Hogue:
"All the species I would say could qualify as apex predators are gone. Cougar were probably the first to go. Wolves and black bears were heavily persecuted as were bobcats. The last record I could document of wolves was in 1768. And the last evidence of black bear was in the Great Cypress Swamp in Southern Delaware in 1906. For bobcats it's a little less clear when they disappeared. I have evidence from as recently as the 1980s but beyond that they seem to have disappeared."

Dave Wilson:
How has the loss, in general, of apex predators, particularly on the shore, affected biodiversity?

Dr. Aaron Hogue:
"There isn't really any research locally, in part because most of those species disappeared well before people cared to investigate them. So I can only go based on the work that's been done elsewhere. The role of top predators and has been pretty extensively analyzed in many parts of the world including the United States and consistently we find top predators exert a top-down effect on the ecosystem."

"The typical term applied to that role is trophic cascades and they influence all aspects of the ecosystems either through their predation on herbivores, or really any species in general, as well as their effect on midsize predators called mesopredators. There's even a term to describe their effect on mesopredators and that's "mesopredator release." Their role in suppressing mesopredators, in turn has ripple effects throughout the ecosystem as does their impact on herbivores."

"The classic study from the United States would be on gray wolves and their impact on the ecosystem in Yellowstone. They were removed from Yellowstone many decades ago and because wolves were federally listed as an endangered species under the Endangered Species Act they were reintroduced into the Yellowstone ecosystem. Decades of research looking at their impact on not only other vertebrates but also on vegetation from the Yellowstone ecosystem found that they not only exerted an impact on large herbivores like elk and deer and moose but the downstream effect on many aspects of the ecosystem were pretty extensive."

"For example, with the absence of gray wolves in the ecosystems the large herbivores could go anywhere they wanted to and they could aggregate along stream edges and eat most of the vegetation eliminating tree seedlings as well as low-lying vegetation like shrubs and herbaceous plants. That denuded most of those stream edges of vegetation which then affected the hydrology of the area and eliminated potential streamside habitat for a lot of the birds and small vertebrates in those areas. So their presence profoundly altered those ecosystems in favor of greater diversity. What that would mean locally is not completely clear but it's reasonable to assume that comparable impacts would be present on Delmarva so the loss of those large predators probably results in lower biodiversity and distribution of many small vertebrates."

Dave Wilson:
Are there any species here now that are comparable to gray wolves or bobcat that are having an impact of the ecosystem similar to what those species would have had?

Dr. Aaron Hogue:
"On the Eastern Shore the closest would be coyote. Depending on where they're found they can play a role as a mesopredator or they can play a role as a top predator. Given the absence of all the top carnivores on the Eastern Shore they have the potential to fill that role at least partially and to exert impact on those mesopredators like fox in particular, cats, etc."

"Research in other parts of the country, for example, in California found that in the areas they're present they actually control some of these midsize predators including domesticated cats and that has profound impacts on a lot of small vertebrates including a lot of breeding birds. So their presence here presumably would prevent a similar impact on the local ecosystems by controlling cat populations and controlling some of the fox populations including red fox which are technically not native either and that would presumably benefit many of the breeding birds in the area especially songbirds and other small birds."

Dave Wilson:
I want to talk a little bit more about coyotes when we have you in the studio next week but for now we've been talking to Dr. Aaron Hogue of Salisbury University. He has done extensive work on apex predators and they're relation to humans and human involvement in their extirpation so thank you Dr. Hogue for visiting us today.

Dr. Aaron Hogue:
"Thank you for having me."

References:


Part II - Coyotes On Delmarva
Delmarva Almanac

Aaron Hogue
Salisbury University Faculty Biography

Apex Predator
Wikipedia

Coyotes in Maryland
Maryland DNR

Delaware’s Wildlife Species Of Greatest Conservation Need - Chapter 1 (PDF)
Delaware DNREC