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Coping With Climate Change

Coping with climate change swallow

This summer, temperatures climbed above 40˚C in the UK for the first time since records began. With the country experiencing eight of its ten warmest years since 1990, this is part of an ongoing global trend of rising temperatures, a result of greenhouse gas emissions. But how is the natural world adapting, if at all, to a warming planet? And will these adaptations be enough to survive?

Stress-Induced Senescence

Following this summer’s heatwave in the UK, there were lots of references in the news to evidence of a so-called ‘false autumn’ where leaves change colour and fall prematurely. This was a result of stress-related senescence, or aging, in some of our trees. In a normal autumn, deciduous trees conserve valuable energy and nutrients by slowing down the production of the green pigment chlorophyll. To further retain moisture and energy, the trees then shed their leaves and concentrate all their efforts in their central systems for the winter. When they undergo stress, such as drought or extreme heat, this process is brought forward in order to retain as much water and use as little energy as possible. Trees can use this survival strategy to survive in the short term. However, they may not be able to cope with repeated periods of stress.

Autumn leaves
Some deciduous trees shed their leaves early this year

Another way that trees might cope with periods of stress, including higher temperatures, is to focus on the next generation, rather than their own individual survival. Producing higher seed yields involves vast amounts of energy. So it might seem counter-intuitive for a tree to put valuable energy into producing more seeds after a heatwave instead of just surviving. However, because the ultimate biological aim is to pass on genes for the next generation, there is a certain logic to cutting one’s losses and putting all your efforts into ensuring you produce viable offspring. This could lead to high bumper yields of seeds and fruit next year.

Breeding Behaviour

Every year, the exact timing of the breeding season for birds needs to coincide with the emergence of their food. If not, they risk being unable to find enough to feed their chicks. As temperatures rise, some species of caterpillar and other invertebrates are emerging earlier in the spring. The same applies to flowering plants. Researchers have discovered that some birds are now laying their eggs up to a month earlier than 100 years ago to keep pace with these changes. In the US, species that have managed to bring their egg-laying earlier include blue jays and brown-headed cowbirds. In the UK, some of the famous Wytham Woods great tits are laying their eggs 3 weeks earlier than at the start of the 75-year-old study.

Blue tit
Blue tits are nesting earlier than they used to

The situation is not completely straightforward, however. Scientists are concerned that by altering the timing of their breeding cycles, the intricate balance that exists between multiple species in an ecosystem may be upset. And those species that are unable to adapt quickly enough will lose out. By nesting at the same time they always nest, they may find that they have missed the height of insect or seed availability for their chicks and not be able to breed successfully.

Migration

Closely related to breeding is migration, and it seems some organisms have changed their migratory behaviour as temperatures rise. Marine biologists have found that narwhals are delaying their annual migration from coastal to deeper waters by approximately 17 days as Arctic waters stay ice-free for longer each autumn. Conversely, many bird species are migrating to their breeding grounds earlier each year. In Europe birds like swallows and pied flycatchers are arriving approximately a day earlier for each degree of temperature rise. Earlier migration enables birds to breed earlier and take advantage of the earlier emergence of food sources. There are concerns, though, that longer distance migrants are not adapting as quickly and so may miss out on these food sources by the time they reach their summer grounds.

Pied flycatcher
Pied flycatchers are migrating earlier as temperatures rise

Some migratory species, however, are choosing not to bother migrating at the end of the breeding season at all. As winters become warmer, there is less reason for species to leave for milder locations as food remains available throughout the year. White storks are less likely to migrate to Africa from Europe in warmer years, although their offspring are genetically programmed to head off once they are old enough. Likewise, in the last few years, increasing numbers of chiffchaffs and swallows have been spending the winter in the UK rather than flying south.

Chiffchaff
Increasing numbers of chiffchaffs winter in the UK rather than migrate

Range Changes

A number of different organisms are adapting to climate change by expanding or shifting their ranges. As UK temperatures rise, we are seeing some new arrivals that would have previously found this country too cold. Birds are some of the most visible examples of this phenomenon. Little, great white and cattle egrets are now all breeding regularly in the UK. In the last few years, black-winged stilts and bee-eaters have also bred here on more than one occasion. All these species prefer warmer conditions and have taken advantage of our now more favourable conditions.

Great white egret
Great white egrets now breed in large numbers on the Somerset Levels

Less obvious to some are the insects visiting us more often from further south. Southern migrant hawker dragonflies are a Mediterranean species but have bred in England since 2010. Migrant influxes of the species are increasing each year. And unprecedented numbers of migrant moths have been recorded in the UK over the last few years, including convolvulus and striped hawkmoths and crimson speckled moths.

Holly blue
Holly blues are extending their range into Scotland

Some of our native species are expanding their ranges further north as well. Nuthatches have expanded into Scotland partly due to milder winters, although increased garden feeding may also have helped. In the insect world, comma and holly blue butterflies are now seen increasingly in Scotland, as revealed by the results of this year’s Big Butterfly Count. Moths such as the Jersey tiger are also spreading north. Range changes don’t always equate to bigger populations, though, so can disguise other issues such as habitat loss and pollution. In addition, those organisms that can only tolerate a narrow temperature range may be able to move north but not survive in the southern part of their range as temperatures rise too high. And of course, those species that are adapted to colder climates, including the rare twinflower and birds like ptarmigan and dotterel, may run out of places with low enough temperatures completely.

Physical Changes

Finally, some organisms seem to be adapting to cope with climate change with physical changes. Banded snails, common in the UK, are extremely variable in colour. A study of the species in the Netherlands found that urban individuals, subject to the urban heat island effect, were much more likely to be yellow than pink or brown. This could be because the yellow reflects heat more, allowing yellow snails to survive higher temperatures than their counterparts. As temperatures rise, rural snails may start to show this tendency as well.

Banded snail coping with climate change
Banded snails are less likely to be brown in warmer areas

Various studies have found that some birds and animals are changing their body shapes to help them regulate body temperature, in line with Allen’s rule. This states that generally, organisms in colder climes have shorter limbs and appendages to conserve heat. Those in warmer areas have bigger ones to help them lose heat. Overseas, various parrot species are evolving bigger bills to help them thermoregulate. Likewise, rabbits in Europe are growing bigger ears for the same reason.

Winners and Losers

Various organisms seem so far to be able to adapt to the rising temperatures resulting from climate change. This may be through changing their behaviour, such as altering the timing of breeding, migration or leaf-shedding. Many are expanding or changing their ranges. Some are evolving different physical attributes. However, there are many species that are already being outpaced by climate change and ultimately they face severely reduced populations or extinction. Those who can’t move any further north, or further quick enough, will run out of suitable habitat. Some species that change colour seasonally to stay camouflaged, such as the ptarmigan, may not be able to stop this process. If their remaining habitats no longer see any snow in the winter and they stay white, predators will see them much easier. Some species, like the puffin, are finding that their preferred food is no longer present where they are. For all the joy that new species to the UK like the bee-eater bring, the worry is that there will be many more losers than winners as our world heats up.