APEX PREDATORS

Research pinpoints predators' impact on ecosystems

Ecosystems and food chains are most often considered from the bottom up, said East Carolina University biology professor Dr. Michael McCoy, but just as important are the impacts from the top down of changes in the predator population.

McCoy, along with a team of researchers from Virginia Commonwealth University, Radford University and McMaster University, has received a grant from the National Science Foundation to further the development and testing of models that will help scientists understand and predict the effects of predator diversity on ecosystems.

“In ecology and how ecosystems function, plants garner the energy from the sun to produce new plant matter, which is consumed by herbivores, and food chains are fueled by this bottom-up process,” McCoy said. “But over the last couple of decades it has become more and more obvious that predators play a really important role in how ecosystems actually function, because they eat the things that eat the plants.”

Apex predators, because of their position at the top of the food chain, are often among the first species lost from a food web, whether it’s due to habitat destruction, climate change or the introduction of invasive species. Some large predators are also the most likely animals to have conflicts with humans – think sharks, lions and wolves.

The impact that the loss of a predator species or the introduction of a new predator species can have on the downstream functions of an ecosystem is hard to predict.

“One of the reasons that ecologists currently lack the ability to do that is that predators can interact with each other in ways that interfere with each other’s ability to catch prey, or they can change the behavior or other aspects of the prey, so some species actually change their body shape or physiology, or they spend more time hiding,” McCoy said.

All of those things can change the way an ecosystem functions either directly or indirectly.

“These are called emergent patterns because they’re things that we can’t directly measure,” McCoy said. “Our ability to predict how predator diversity affects lower-level processes is limited by our inability to detect these emergent properties.”

McCoy and his collaborators have been working to develop models designed to improve that predictive power.

“Dr. McCoy is noteworthy for his ability to bridge the gap between theory and data using well-designed experiments and sophisticated statistical analyses – and bring students along with him on a demanding but rewarding intellectual journey,” said Dr. Jeffrey McKinnon, chair of the biology department.

“As predator species go extinct and translocate in our region and around the world, this is an important but little understood issue,” he said. “Moreover, this grant will directly fund the training of students as well as providing insights that will help us better manage disrupted natural ecosystems.”

McCoy said the researchers have created a new framework that will allow them to predict how changes in the predator community in any general ecosystem will affect their primary function, the consumption of prey.

“We have a mathematical model that we can use to explore things really theoretically. But then we also have a statistical model that we’re building that allows us to put real biological data into the mathematical models and say something about the actual ecosystem that we’ve been studying,” he said.

The grant, which totals about $950,000, with $500,000 going to ECU as the lead institution, will allow the team to further develop those models, test them and create software to allow other scientists to use them.

The models will be tested using a series of experiments in riverine rock pools in and around Richmond, Virginia. The rock pools are found along the fall line of the eastern seaboard, where the granite bedrock is exposed, and where millions of years of flowing water has created hundreds of small pools.

“The reason we’re focusing our research on these is that each one of those is a little ecosystem; we know the communities that live in them. They consist of a single dominant grazing species, which is an herbivore, and up to 11 different kinds of predators,” McCoy said.

The researchers are using relatively small, self-contained ecosystems in riverine rock pools to test their models.

Each pool has its own ecosystem, which can be manipulated and observed, allowing the scientists to test their hypotheses and determine whether their models are capturing the changes. “If we remove a predator from these pools, do we get the right prediction about how those effects cascade through the ecosystem?” he said.

The primary herbivore in the system is a small freshwater snail, and predators include crayfish, flatworms, leeches, dragonfly nymphs, fish and water bugs.

“These are a model for any system,” McCoy said. “You could think of a coastal habitat like an oyster reef, where fishing pressure on top predators in those systems, things like blue crabs, might cascade down and affect oyster growth, health and survival, or important fishery species. … If our models work, we’ll be able to apply those predictions to more complicated systems.”

The grant will also help fund an education and outreach component of the research – a network of scientists who will help high school teachers and university professors incorporate their quantitative methods. Short movies about the rock pool ecology, geology and history, as well as web apps will be developed too.

“We want to make this all accessible to a general audience, including high school students,” McCoy said.