The Challenge of Restoring Biodiversity's Outer Edge
For the rarest butterfly in North America, restoration efforts may have increased its food supply—but also its predators.
Nick Haddad at North Carolina State University has taken on one of the hardest jobs in conservation: studying and protecting the incredibly rare Saint Francis satyr butterfly. After 11 years of exploring the few hectares in eastern North Carolina where it is still found, no one on Haddad’s research team had even seen a caterpillar of the butterfly in the wild. A lucky break finally arrived in the summer of 2011 when a field technician serendipitously dropped his sunglasses near a sedge and noticed a caterpillar eating there. But as it turned out, Haddad’s work was just beginning.
Although saving a critically endangered species is never easy, the challenge is especially acute for a species like the Saint Francis satyr, which is severely limited in range. Such local species typically are neither well understood nor well monitored. They also have a low public profile and don’t attract advocacy efforts. At the same time, they are important components of Earth’s total biodiversity—hence the dogged work of Haddad and his team.
Once the researchers knew the specific sedges that the caterpillars ate, they set out to restore the wetlands that harbor the butterfly’s food plants. As a key part of that effort, Haddad’s team felled hardwoods and established dams on the area’s streams at Fort Bragg, North Carolina, in 2011. A focus on habitat for food plants is standard practice in restoration ecology. However, postdoc Erik Aschehoug realized that there were meager data on the effectiveness of that approach. “A lot of restoration programs focus on the vegetation layer, because that’s the base for the food web. But just having good plants doesn’t mean that the butterflies will do well,” he says.
Although the wetland restoration effort increased the sedge’s cover in the study area from about 5 percent to about 15 percent, the ecologists didn’t have the information to know whether this change had actually aided the endangered butterfly. “It occurred to us that by creating habitat for butterflies, we might also be creating habitat for predators,” Aschehoug says. The researchers in Haddad’s group decided to find out directly.
“The idea for the predation experiment came when we were measuring vegetation in the restoration plots, and we were struck by how many birds, dragonflies, and other insects were zipping around,” Aschehoug explains. Because they couldn’t set up an experiment that might affect predation on a critically endangered species, the team used a surrogate species of butterfly with similar food and habitat preferences to study survival through its juvenile life stages—egg, caterpillar, and pupa. They put a known number of eggs and caterpillars in the restoration area (the former for 48 hours, the latter until they pupated, 6 to 8 weeks). Some of the eggs and caterpillars were protected from predators by a fine mesh netting.
The results, recently published in the journal
, were sobering. The experiment on the surrogate species indicated that predation in the restoration areas could sharply reduce the survival rate to adulthood from about 20 percent to about 7 percent. If the restoration similarly reduced the survival rate of the Saint Francis satyr, it is an important lesson that habitat restoration is not automatically a benefit for an endangered species; the environmental changes must also be monitored for their effectiveness.
Haddad’s team won’t know for sure what the increased predation means for the Saint Francis satyr until the next stages of the study, when they will estimate the population growth for each life stage. At 100 feet by 100 feet, the restoration plots are small from the butterfly’s perspective, and Aschehoug says they would like to study larger areas. In the experiment, removing hardwood trees by cutting them down had a detrimental effect on caterpillars of the surrogate butterfly. But Aschehoug notes that the effects on predation could well be different if they had removed trees using fire. The researchers are hoping these tweaks to the restoration will maximize survival by increasing habitat without increasing predation.
Aschehoug remains optimistic about the ultimate success of the group’s conservation program: “We designed our experiments to be directly adjacent to historic populations of the St. Francis satyr. In two out of the four restoration sites, we saw natural colonization of Saint Francis satyrs, and we continue to see the butterflies in our restored habitats, which is really exciting. On the one hand, we’ve got a surrogate species study that says we should be really careful about how we restore habitat. But on the other hand, we have a whole bunch of observational data that suggest that the butterflies do like it, because they colonized it, and they continue to persist over time, even at low levels. That gives us hope that we’re at least on the right track.”
Still, the future of the Saint Francis satyr is far from certain—and that is for a species that has a dedicated research team working to save it. By the time researchers know that a rare species is endangered, it’s usually hard to obtain the kind of information that is crucial for protecting it. “Restoration programs come along at a bad time for the imperiled species,” Aschehoug says. “It’s very difficult to create habitat for something you don’t know much about.”
In the absence of good information, measures of success for conservation programs generally are loosely defined; funders typically favor doing something that seems like it should help over the trickier task of checking to see if the effort was fruitful. “I think restoration ecology as a field is working really hard to change that culture of fast actions without clear success guidelines. But it’s going to take time,” Aschehoug reflects.
Ideally, success should be measured as an increase in population numbers brought about by bolstering survival or reproduction. Such monitoring is possible only with adequate funding. For rare species such as the Saint Francis satyr, though, there are a lot of places to monitor, a lot of species to study, and not much money to go around. —
Katie L. Burke
Listen to an interview between Erik Aschehoug and Katie L. Burke.