Researchers have long known about climate dipoles: a synchronized seesaw in patterns of temperature and precipitation across vast distances. El Niño years, for example, tend to bring rainy weather to the southern United States and drought in the Pacific Northwest. Now, researchers believe that there are ecological dipoles as well: contrasting effects of climate dipoles on populations of plants or animals separated by thousands of kilometers.
In a new study, published in Trends in Ecology and Evolution, researchers suggest that ecologists can use tools from climate science to study how climate variability manifests as ecological signals at continental scales.
“Climate scientists have a whole suite of tools by which they’re able to look at things like variability and changes over space and time, and now we can take those same approaches and think about how we can capture those dynamics for ecological responses,” said Benjamin Zuckerberg, an associate professor at the University of Wisconsin—Madison and lead author on the new study. “It’s basically treating the biological observations of, say, birds and plants in the same way that climatologists treat observations of temperature and rainfall.”
Ecologists have long known that plants and animals respond to regional changes in climate—even climate shifts that correspond with climate dipoles. Scientists tracking migratory songbirds, for example, have found that when a positive North Atlantic Oscillation brings warmer weather to the United States, migrants arrive earlier in the spring.
Some of the strongest evidence so far that climate dipoles correlate with ecological ones comes from marine species, according to the study authors. The phase of the Indian Ocean Dipole (IOD), a shift in sea surface temperatures nicknamed the “Indian Niño” that impacts the position of the northern boundary of cold, Antarctic waters, correlates with the breeding success of king penguins, for example. Penguin populations tend to fall when warm water associated with a positive IOD pushes the boundary (where penguins’ prey tends to congregate) away from their colonies, forcing penguins to travel farther and deeper for food.
The Rise of Citizen Science
Until recently, however, ecologists couldn’t always see what was happening at the other end of the climate seesaw. That’s because, historically, ecological data have been collected and analyzed at smaller spatial scales than climate and weather data, according to Zuckerberg.
“We tend to collect data for a few species, on a few acres of land, over a few years to answer very specific questions in ecology,” he said. “But we’re opening up now, in the sense that we’re able to collect ecological data at a scale that now rivals what meteorologists and climatologists have been working with for the last 50 years or more.”
Zuckerberg credits citizen scientists with providing ecologists with the troves of data necessary to study the connections between climate variability and populations at continental scales. He points to platforms such as the USA National Phenology Network, which tracks seasonal changes in plants and animals with help from thousands of amateur naturalists, and Cornell University’s eBird platform, one of the largest citizen science projects in the world. The platform has collected more than half a billion bird observations by birdwatchers from around the world, which the Cornell Lab of Ornithology used to create migration maps for more than 600 species of birds in the Western Hemisphere. Both platforms make all the data collected available to researchers, resource managers, educators, and, of course, the public.
Now that researchers can tap into that data and use tools that have been honed by climate researchers, Zuckerberg said, they can begin to think about ecological synchronicity in populations that are separated by thousands of kilometers.
Climate Change Complicates Forecasts
“The key advancement here is a conceptual one: this idea of ecological dipoles,” said Kevin Rose, an assistant professor at the Rensselaer Polytechnic Institute in Troy, N.Y., who was not involved in the study. “This paper sets the stage: Here’s what an ecological dipole is; here’s how we quantify it.”
That’s what Zuckerberg and his colleagues plan to do next: test their hypothesis in future studies by looking at the relationships between bird migration, seed production, and climate variability.
Forecasting ecological dipoles, or the lack thereof, is a critical tool for conservationists and resource managers. If distant populations are synchronized, entire species may be vulnerable to disease outbreaks, pests, or extreme weather such as flooding or drought. If they’re not synchronized, managers can focus resources on the populations at the vulnerable end of the dipole. Understanding how populations will respond to shifts in climate is all the more important in the era of climate change.
Take the king penguins: As ocean waters have warmed over the past few decades, some 900,000 king penguins have disappeared from Île aux Cochons, a volcanic island sitting between Antarctica and Madagascar that’s home to the largest aggregation of the birds. Researchers predict that if the warming trend continues, the king penguin population could be cut in half by the end of the century.
Climate change is also influencing the magnitude, predictability, and even the location of climate dipoles. “A warming world will definitely alter these climate dipoles in the future. Some of these fairly regular and predictable changes in the climate system, like El Niño and the North Atlantic Oscillation, are becoming more variable, strengthening in their magnitude, and in some cases, are shifting,” Zuckerberg said. “Thinking about how species are going to respond to that shifting variability is one of the big challenges that we have going forward.”
—Kate Wheeling (@katewheeling), Science Writer