Malcolm L. “Mac” Hunter, Jr., is a professor of wildlife ecology at the University of Maine and a member of the science committee advising OSI’s Northeast Resilient Landscapes Initiative. Hunter’s research has focused mainly on forest ecosystems and the maintenance of their biological diversity. He spoke recently with OSI’s Abby Weinberg about species adaptation, habitat connectivity and resiliency.
How do species adapt to change in general?
At a fundamental level, evolution is an adaptation to change. We have sex to rearrange our genes, which allows each new generation to adapt to change.
The natural follow-up question is to ask whether sex is the solution to climate change.
Sex can, if given enough time, allow a species to respond to almost any external environmental change. The problem is time. Most species require multiple years for each generation. But to some extent we have underestimated short-term evolution. Insects have adapted to pesticides and viruses have adapted to antibiotics more quickly than anticipated. We have documented that many species are not able to keep pace with the changes in climate that we are witnessing.
The main long-term strategy for species adapting to climate change is a shift in geographic range, and it’s particularly obvious at higher altitudes and latitudes. There are dozens and dozens of studies out now showing species that are starting to shift geographic ranges. There are probably even more studies that show a shifting of timing—flowers that bloom earlier in the spring, birds that migrate earlier.
Given that this shift in location is the preferred approach for biodiversity adapting to climate change, what can a land conservation organization do to help counteract the effects of climate change?
There are a couple of ways that species shift geographic range. We tend to think first about latitude, simply going toward or away from the poles. It would be northward in cases of warming climates in the northern hemisphere. This broad north-to-south movement is probably the best historically documented response by paleoecologists looking at pollen records. We know that that pattern is quite clear.
But on the smaller scale, you can also go upward in altitude. About 100 meters of altitude is equal to 100 kilometers of latitude. Obviously going upward is moving toward a cooler climate, but even shifting from the south side of a mountain range to the north side will cause a difference in climate because of the orientation toward the sun. So, it has happened at different scales, from the very large movements north to south, to simply going up the side of a mountain. The problem of course comes at the top of the mountain, because those species that are already on the top of the mountain can’t go any higher.
Also remember we are mostly talking about an evolutionary process over multiple generations. It’s not about individuals, like, for instance, if one particular moose decides to move north. Most individuals don’t shift their range as adults. It’s more a matter of the moose’s offspring as they disperse away from where they were born and that the ones that go north might be more successful than the ones that move south. But all of this assumes a certain level of ecological connectivity, and as we fragment landscapes more and more with roads and power lines, we make it more difficult for species to move their range. The land trust is critical to retaining that ecological connectivity.
Here’s another example. Let’s say you’ve got an oak tree that has grown to maturity and is 100 years old. That oak tree is not going to shift its geographic range to the other side of the mountain, but it’s producing acorns and those acorns get dispersed in many different directions and the acorns that end up on the cooler north side of the mountain are more likely to be successful than the ones that end up in a place that is too hot and dry for them to grow to adulthood.
What does that mean for local and regional land trusts, many of which are relatively small and not necessarily equipped to tackle something global like climate change?
One strategy is to try to contribute to ecological connectivity at the regional scale. The riparian zones along rivers are wonderful examples. Rivers are long, linear features and we have lots of good reasons to protect their shorelines anyway—for recreation and water quality—but they can also represent important ecological connectivity. You’ll hear the term “wildlife corridors.” I don’t actually like that term because it makes me think of narrow strips of vegetation which is often not sufficient. It’s better to think about how connected the landscape is, and how easy is it to move across it.
Just step back and look at the map and see places where connectivity could be restored or maintained. In a lot of settings, ridge tops have the same sort of connectivity function. Mountains are often organized into ridges and if those ridges are protected they provide long, intact corridors for movement. Not every land trust is going to have this opportunity, but for those in places where there are significant altitudinal gradients, protecting land at the top of the mountain down to the bottom of the valley is a good thing to do. We have done a pretty good job of protecting mountaintops, so nobody is going to put a shopping mall on the top of a mountain. We’ve done less of a good job protecting the valleys, and protecting the whole altitudinal range.
And then, it is also important to protect both the north face and a south face of a mountain range to offer the sort of climate diversity that is important for species that are trying to adapt to climate change at the top.
Can you talk a little about this new resilience science and how it may play a role in informing adaptation strategies?
Let me back up a little and talk in terms of the perspective of a local land trust. One thing that is important is that they be prepared to accept change. I recall a meeting of The Nature Conservancy (TNC) Board of Trustees for the state of Maine, which I serve on. We had a lecture on climate change, and at the end of it one of the board members was quite discouraged. He said, “Gosh, you know, climate change is going to eradicate all the good work we’ve done. We’ve protected all this habitat for pine martens and Canada lynx and they’re all just going to retreat to Canada and we’ve wasted our time.”
And I said, “Well, no, that’s not the case. The places that we’ve protected in the interest of moose, martens, and Canada lynx will be good habitat in the future for bobcats and whitetail deer and fisher and other species.”
We need to embrace or at least accept change. We should not be concerned about the particular suite of species that happen to be there; we should be concerned with protecting the environment that they inhabit over time.
Mark [Anderson, science director for TNC’s Eastern U.S. Division] has shown, through a very sophisticated analysis, how that could play out in northeastern North America by looking at some of the enduring features of the environment, things like altitudinal gradients and diversity of bedrock and soil types and hydrology. Those fundamental underpinnings of ecological diversity that lie within the physical environment can be great predictors of where biological diversity can find refuge. Thinking about the soils, the water and topography can sometimes be a bit of a challenge for people to get their heads around. But we need to get to the place where we can say, “We’re interested in protecting the physical diversity out there as home for a changing array of species.” We’re protecting the stage. Don’t worry so much about what actors are out there at the moment.
So that’s the fundamental principle of Mark’s work, and it plays out in a number of ways. One example is that he’s learned that there’s a certain bedrock type associated with calcareous materials that are important to a lot of species and are underrepresented in conservation areas. So, if we care about biodiversity in the long term, we should think about protecting those kinds of places. Even though the particular set of species sitting on this particular area of calcareous materials may change over time in response to the climate. But we know with some confidence that having that calcareous area will always be important to some species, so we have to make an effort to protect those places.
So, returning to your first point, if we protect the ecological stage, does it lessen the importance of sex?
Even with a strong ecological stage protected—and we are far from being finished with that work—species will still be experiencing many unprecedented challenges. Genetic diversity and sex will play an important role as well.