California Snow Changes May Lead to ‘Starved Predators’

Climate change-driven shifts in the snowpack in the Sierra Nevada mountains may have knock-on effects that could cause certain species to go hungry.

Due to increasing global temperatures, lower snowfall levels in the Sierras are expected to become the norm, which will also lead to snowmelt streams forming earlier in the year.

These changes to the timings of stream formation may subsequently lead to shifts in the timings of animals emerging, which could leave predators at the top of the food chain without dinner, a new paper in the journal Proceedings of the National Academy of Sciences reveals.

As the planet warms, the Sierra Nevada mountains are expected to see less snowfall, leading to smaller snowpacks that melt earlier in the year than they do now. By 2100, the Sierra mountain streams are expected to predicted to run out—reaching “low-flow” conditions—an average of six weeks earlier than they do currently.

In the paper, researchers from the University of California, Berkeley describe how they simulated Sierra Nevada snowmelt stream environments under a variety of potential conditions in order to investigate the impacts these scenarios would have on local ecosystems.

They monitored the populations of organisms from all walks of life, from algae and insects to birds and mammals, and found that the shifting of the timing of the streams also shifted the life cycles of many of the organisms.

Climate change can disrupt the delicate balance of ecosystems, leading to mismatches in emergence times in food webs. Altered seasonal patterns can lead to shifts in the timing of key events such as flowering, leafing, and hatching—for example, warmer temperatures can cause insects to emerge earlier in the year.

However, the organisms that depend on these insects for food may not adjust their emergence times accordingly, leading to a mismatch in timing. This can echo up the food web, affecting predators at the very top.

“Climate warming has changed the timing of key life history events such as hatching, migration, mating, blooming, and death in a wide variety of plants and animals. These changes may benefit individual species via extended growing seasons and resource pulses; or harm them via stress, habitat contraction, and spatio-temporal mismatches between energy needs and food availability,” the authors wrote in the paper.

The researchers found that midges nearly doubled in population, going through metamorphosis earlier, but decreased in body size. They also found that Brewer’s blackbirds, which feed on midges, increased in numbers, thriving as their food source suddenly became plentiful.

“It is remarkable that despite the stability at the broad ecosystem level, even slight changes can be consequential,” paper co-author Albert Ruhi, an associate professor of environmental science, policy and management at UC Berkeley, said in a statement.

“We did not expect that early snowmelt would control the abundance of stream insects metamorphosing, leading to earlier, more abundant pulses of flying bugs that in turn attracted riparian birds. This type of cross-ecosystem linkage is something we just had not envisioned, and we would have never captured in a laboratory setting. It underlines that timing is everything.”

Changes to these streams in real life could, therefore, have knock-on effects on species ranging from birds and bats to lizards and other predators. They could also lead to mismatches in food webs, resulting in predator species going hungry.

“Ecologists often think of climate change leading to predator-prey mismatches, because predators and their prey shift their life cycles at different rates, or even in different directions, resulting in starved predators,” study author Kyle Leathers, a graduate student in Ruhi’s Lab at UC Berkeley, said in the statement.

The researchers also determined that species were capable of adjusting to these shifts in emergence times, meaning that stream ecosystems may be resilient to these climate-driven changes in the future. Some species may even thrive, as this paper found the Brewer’s blackbird to do in the case of increased numbers of midges.

“We were surprised to see such a clear example of how biodiversity can stabilize ecosystems,” Leathers said. “It’s similar to having a balanced financial portfolio — because different species respond in different ways to warming, the more species a river has, the more likely it is that warming will not drastically impact an ecosystem process that is key for the broader food web.”

“The notion of novel matches may be underappreciated, but important.”

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