Many species are finding it hard to adopt to a warming climate24 November 2020
The activities of countless species are timed to their environment, including usual temperatures throughout the year. “For plants to bloom when their pollinators are around, for birds to breed when there is food for their chicks — and then to leave before snow covers the ground — they must follow cues in their environment,” explains a team of experts the University of Helsinki in Finland.
The problem, they add, is that “the timing of these cues, like the accumulation of warm days, is rapidly shifting.” What that means to individual species depends on several variables, but generally the larger and faster changes in their environment are, the harder many species of flora and fauna will find it to adjust fast enough.
“One such cue relates to temperatures: in warm years, all types of events tend to occur early, and in cold years, they tend to occur late. How much events shift with shifts in temperature is described by something that we call a ‘reaction norm’,” says Professor Tomas Roslin, a scientist at the University of Helsinki who also works at the Swedish University of Agricultural Sciences.
Roslin is a lead author of a new study by a large group of researchers who are working on a large dataset of seasonal events to see how the timing of many species’ seasonal activities is failing to keep up with changing environmental cues owing to climate change.
Members of a given species are adapted to react to specific cues in their local environment and when a marked shift in such cues, including changes in temperature, takes place, they may respond differently. Roslin and his colleagues wanted to find out what this means when the changes occur on a large scale.
In looking for answers they relied on observations of hundreds of seasonal phenomena collected over decades at hundreds of sites throughout the former Soviet Union. The massive dataset has allowed them to explore climate change responses over a vast area and over a large time scale.
“We looked at events ranging from the first song of the great tit through the appearance of the common toad and the appearance of the first porcini mushroom to the end of birch leaf fall. What we saw was a general rigidity in species’ response to year-to-year variation in climate; i.e. the earlier the year, the more did the timing of the phenological event lag behind the timing of the cue from temperatures,” notes Maria Delgado, the other lead author of the study from the Oviedo University in Spain.
“On top of this, we saw large differences between seasons and sites. Differences in the reaction norms of different sites accentuated phenological responses in the spring and dampened them in the autumn,” Delgado adds. “As a result, among population variation in the timing of events is greater in the spring and less in the autumn than if all populations followed the same reaction norm. Overall, such patterns will affect species’ response to climate change in opposite ways in spring and autumn.”
While many of the changes are yet to play out, they will accelerate as the climate continues to warm in coming decades. Yet similar lines of research indicate that warming weather already means plenty of trouble for a large variety of species as changes in temperature can throw them off their habitual patterns of behavior.
As the climate warns, for instance, birds like great tits that depend for their survival on stable sources of food in spring might end up going hungry because those sources of food might not be readily available, scientists have just found.
Specifically, changes to when there is a large supply of larvae in spring can greatly affect great tits and other species of birds that need plenty of larvae to feed their newly hatched young. If the larvae supply peaks earlier than normal because of warmer weather, hatchlings might wind up with too little food during a critical stage in their lives.
If spring comes earlier than normal, trees begin to erupt in leaves earlier too, causing larvae that feed on these leaves to hatch earlier. “When the climate changes, the interactions between different species changes too,” explains Emily Simmonds, an associate professor at the Norwegian University of Science and Technology’s Department of Biology.
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