The atmosphere is getting hotter, and the conditions for plants and animals worldwide are changing. It’s a challenge that slaps a big question mark on our future: Can we save biodiversity from climate change?
That’s the issue we tackled at IonE’s Frontiers in the Environment talk October 21. Jessica Hellmann, who serves as director of the Institute on the Environment and a professor in the College of Biological Sciences, studies just that. Here’s what she had to say:
- Earth is warming fast. It’s not news that our planet is heating up, but what really matters is how much. If we fail to reduce greenhouse gas emissions, by the time this century is over Earth could be 5 to 6 °C hotter than in the recent past.
- Climate change means colossal change for life on Earth. Today’s changes are big for plants and animals. Every species has its geographic range, and climate change fundamentally reorganizes those distributions. Hellmann pointed out that last time there was as much carbon dioxide in the air as we’ll likely get within the next few decades, relatives of alligators lived near the poles.
- Glance at the flip side, and you’ll recall that we have a name for the last time Earth was 6°C cooler than it is now: the Ice Age. During that most recent glacial period (really one of many ice ages over the eons), Minnesota was covered by a mile of ice. In California’s Death Valley, today punishingly hot and dry, an evergreen forest spanned the landscape. It gave shelter to an entirely different crop of species, one that held none of the plants or animals now dwelling there. Modern climate change could bring a similar degree of warming over a much shorter time.
- Organisms react to climate change in four ways. When the climate changes, life takes the heat. In response to a shifting climate, biological organisms do one of a few things: deal with it, evolve, move or die. Some plants and animals have genes that act differently under different environmental conditions, a phenomenon called phenotypic plasticity. Others can evolve over generations to fit a new climate, an approach that only works when the change isn’t too fast. Those strategies aside, organisms have two paths: move or die. If a population can migrate — say, northward, to keep the kind of habitat it needs—it might survive. If a species can’t move, or it can’t most fast enough, it’ll likely go extinct.
- Biodiversity is about more than species. Biodiversity is seemingly simple, though deceivingly so. It’s not just about preserving individual species. Seen properly, conservation isn’t some video game with the sole goal of saving species after species until we rack up enough points to move to the next level. Instead, Hellmann explained, biodiversity is a complex concept encompassing not only species diversity, but also genetic diversity, and diversity of ecosystem function and ecosystem services.
- Populations within a species can react differently to change. When pondering climate change, asking only how a species’ geographic range will shift misses the point that populations within one species might differ. As an example, Hellmann discussed her work on the Karner blue butterfly. The two distinct populations of this endangered insect, a western form and an eastern form, live in different climates. Since evolution has equipped each population to withstand different pressures, the two will respond differently to climate change. When modeling how climate change will shift species ranges, Hellmann and her colleagues treated the two forms as separate entities. If scientists treat distinct subpopulations as one, they’ll get entirely different—and probably wrong—results, hindering conservation planning.
- Adaptation matters. “I had worked on this word [adaptation] for a long time, and then someone—the entire discipline of climate science—came along and they stole it,” Hellmann joked. “So now it has two meanings.” Biologists talk about adaptation as how organisms evolve over time in response to their surrounding. Climate researchers talk about adaptation as management: humans adjust to improve our lot in a new situation. Smart climate adaptation on the part of humans considers adaptive evolution. We need both uses of the term to turn biodiversity loss around.
- Conservation should work to build adaptive capacity in species and ecosystems. An example that entails both meanings of adaptation is the notion of adaptive capacity. Species have a fundamental adaptive capacity, a theoretical limit to what they can adjust to. they also have a realized adaptive capacity: The areas and conditions they could actually fit, given ecological constraints not considered by fundamental capacity, such as interactions with other organisms. Fundamental adaptive capacity sets a hard limit to adaptation; realized adaptive capacity is where a species is at right now. Hellmann says that to effectively manage biodiversity under climate change, we should expand adaptive capacity as close to its theoretical, fundamental limit as possible. Strategies include breeding organisms to bolster genetic diversity and connecting habitats to enlarge living space.
- Managed relocation holds promise, mystery — and complexity. Managed relocation, or assisted migration, involves helping organisms disperse to a new location. If humans actively help other species move to areas that suit them better as the climate changes, we can save species that might otherwise go extinct. Potential problems concern some researchers, though, including opportunity cost, endangering source populations, and the chance that transplanting organisms to new areas could unleash devastating invasive species on those places. Some of Hellmann’s work on the issue seems to show that the risk of new pests from managed relocation is low. Hellmann also talked about her research showing that, while managed relocation is often seen as a point of divisive controversy, expert opinions are more middling, with few scientists loving the idea, but few scientists hating it. Hellmann’s conclusion: Context matters, so relocation decisions should be made on a case-by-case basis.
- Can we save biodiversity from climate change? Hellmann’s answer: No — and yes. On one side, we don’t have a deep understanding of ecological predictions and adaptive capacity. We also don’t have much money, and we’re running out of time. On the other side, scientists are open to new methods, researchers do have some understanding of adaptive capacity, and managed relocation holds promise. That said, adaptation, while important, can’t fix everything. Hellmann contends that mitigating climate change by reducing greenhouse gas emissions is cheaper and easier. “We will come back to mitigation,” Hellmann said. “If we really think our way through adaptation, we will come back to mitigation. They are two sides to the same coin.”