This week the RSPB has launched a new report showing the effects climate change is already having on Europe's wildlife. This is the first in a series of guest blogs over the next five days showing how those effects are playing out. Today's blog comes from Matthew Carroll, RSPB Conservation Scientist and one of the authors of the new report.
Thanks to the work of scientists across the world, we know a great deal about how climate change is affecting wildlife. As shown in a recent report produced by the RSPB Centre for Conservation Science, rising temperatures and changing rainfall patterns have already caused substantial impacts on European wildlife. Worryingly, the impacts are likely to get bigger still, making climate change a key concern for conservationists. Whilst we can observe what is happening to wildlife populations, if conservation actions are going to help species adapt, we need to understand the mechanisms behind the observed patterns.
Some mechanisms could be ‘direct’. For example, winter temperatures might rise, meaning that a species can survive further north. Alternatively, even if a species isn’t directly affected by climatic conditions, its predators, prey or competitors might be, meaning the impacts could be ‘indirect’. So, for example, a predator might survive better under warmer winter conditions, meaning their prey face a greater predation risk.
Recent reviews of the scientific literature suggest that changing species interactions are the single most important mechanism behind climate change impacts. This means it is very important to understand how species interactions are changing, and what the impacts are. Three examples from the recent report show just what these ‘indirect’ impacts could mean for wildlife.
Shifting springtime?
In Dutch woodlands, great tits and pied flycatchers feed on caterpillars in spring. As temperatures have risen, the tree leaves that caterpillars feed on have started to emerge earlier. The caterpillars have responded to this by emerging earlier themselves. And the birds have responded to earlier caterpillar availability by breeding earlier.
However, these timing shifts have all been by slightly different amounts: the tightly-coupled system is becoming mismatched. For the birds, this could be a substantial challenge: bird populations grew more, and more chicks were fledged, when the timings were better matched. So, it seems that the birds are being affected by rising temperatures not directly, but via caterpillars and leaves.
Too dry for flies?
In UK peat bogs, golden plovers feed heavily on craneflies during the breeding season. Chick survival is higher when there are more craneflies to eat.
Cranefly larvae, sometimes known as leatherjackets, live in the upper layers of peat, and need conditions there to remain very damp. If the peat becomes too dry, especially during summer, the larvae can die. Summer temperatures and rainfall therefore strongly influence cranefly abundance the following spring, when the birds feed on them.
Statistical models suggest that warmer, drier summers could drive down cranefly abundances. Falling availability of craneflies could golden plover populations decline, restricting them to the wettest areas, and even causing local extinctions. Increasing droughts could therefore threaten golden plovers via availability of their cranefly prey.
Marine food webs all at sea?
The UK kittiwake population has declined by around 70% since the mid 1980s. This has been linked to big declines in breeding success – the number of chicks a pair can successfully raise – and adult survival. Studies have shown that these declines could be linked to two key things, both of which are linked to sandeels, small fish that kittiwakes feed on during the breeding season.
First, sandeel fisheries in sensitive foraging areas reduce kittiwake breeding success. This seems straightforward – humans fishing for these small fish reduces the amount of food available for the birds.
Second, changing ocean conditions, in particular rising sea temperatures, are also associated with lower breeding success. This seems less straightforward, but is once again likely to be linked ot sandeels. Higher temperatures could reduce sandeel abundances, make sandeel body sizes smaller, and maybe even cause sandeels to emerge too early for the birds. Rising temperatures under climate change could therefore be harming kittiwake populations through sandeels.
Tangled food webs
Although these ‘indirect’ impacts can seem complex and challenging, conservation actions can help. If changing timings are a problem, maintaining habitats with a range of microclimates – small-scale patches where conditions differ from those in the wider area – might provide variation and flexibility in the timing of events, reducing the risk of mismatches. If droughts threaten prey populations, site hydrology can be managed to increase moisture levels. And at sea, appropriate marine protection could ensure that important prey populations are safe from damaging human activities, giving them a fighting chance as the climate changes.
Changing species interactions are likely to be a major component of climate change impacts. However, by studying them now, we can put in place appropriate conservation measures and, hopefully, prevent some of the most damaging effects of climate change.
Matt Williams, Assistant Warden, RSPB Snape.