A new research paper from the Department of Zoology at the University of Oxford examines the potential impacts of climate change on great tits:
We apply structured population models to a well‐characterised great tit‐caterpillar model system and identify thresholds of temporal asynchrony, beyond which the predator population will rapidly go extinct. Our model suggests that phenotypic plasticity in predator breeding timing initially maintains temporal synchrony in the face of environmental change. However, under projections of climate change, predator plasticity was insufficient to keep pace with prey phenology. Directional evolution then accelerated, but could not prevent mismatch. Once predator phenology lagged behind prey by more than 24 days, rapid extinction was inevitable, despite previously stable population dynamics. Our projections suggest that current population stability could be masking a route to population collapse, if high greenhouse gas emissions continue.
According to this research, even a stable population of great tits could face rapid extinction if their food sources — in this case, largely caterpillars — suddenly disappeared. This scenario becomes more and more likely as climate change causes the spring climate to begin earlier in the year, which in turn causes caterpillars to hatch earlier, which makes them asynchronous to great tit breeding schedules.
"This new model is exciting because it lets us look at the mechanisms behind the change in timing as well as the result," said lead researcher Dr. Emily Simmonds in a statement. "It tracks both evolutionary change and flexible changes in behaviour."
"What I find most interesting is the idea that populations that seem stable could suddenly go extinct. That matching with a food source can act as a threshold, before a certain point things are ok and then quite suddenly they are not."
Dr. Simmonds added:
While some extinctions of simulated populations occurred in all scenarios of climate change, in models running a high emissions scenario the species went extinct 17% of the time, compared to under 5% when using low or medium emissions scenarios. Therefore, reducing climate change seems to be a route to mitigate some of the risk to the population. It could allow more time for evolution to occur as well, as this was shown to be slow in our model.
There are also some elements that this model does not include, which could help prevent extinction. Great tits could reduce their risk of extinction by switching to a different food source or the caterpillars could increase in numbers. But we should also be cautious that changes in climate could be impacting populations that we don't currently think of as at risk.
Poor great tits!
Phenological asynchrony: a ticking time‐bomb for seemingly stable populations? [Emily G. Simmonds, Ella F. Cole, Ben C. Sheldon, Tim Coulson / Ecological Letters]
Climate change and mistiming: modelling phenology in great tits [Dr Emily Grace Simmonds / University of Oxford Department of Zoology]
Image: a great tit nest by nottsexminer/Wikimedia Commons (CC 2.0)
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