Humans may find ways to cope, but is this true of the natural world, asks S.Ananthanarayanan.

Climate disasters in the past wiped out vast numbers of species, but there was time for many to adapt and live through to better times. A question is whether the current trend of global warming is giving the natural world the same space.

Lead author Victoriia Radchuk and sixty others from Germany, Ireland, France, The Netherlands, UK, Czech Republic, Belgium, Sweden, Canada, Spain, USA, Japan, Finland, Norway, Switzerland and Poland, attempt an answer in their paper, in the journal, Nature Communications. Based on a review of 10,090 abstracts and data from 71 studies, reported in 58 relevant publications, they assess whether changes in the physical features of animals are coming about as a means of adapting to climate change. The results of the study are that although many species make a good showing, most seem to be losing the race.

Climate change, the study says, can affect the ability of species to survive, and extinctions reduce the mutually supporting mix of species in ecosystems. Species could maintain numbers if they responded with physical changes or changes in behaviour which matched or lessened the effect of climate change. This could come about by physical adaptation, like changes in digestive secretions when there is a change in diet, or by minute evolutionary steps, or by migration to other regions. Even the physical adaptation, like when mountaineers, who pause to acclimatise before they venture into higher altitude, must take time. Evolutionary changes, which occur by the environment favouring strains within a species, need several generations. Detecting and quantifying just how far the observed changes in species, over the last few decades, are evolutionary responses to climate change is hence important in forecasting species numbers and to plan interventions, the paper says.

An example of adaptation is the timing of breeding or egg laying according to when sources of food to feed the young are most abundant. The authors cite a study where the mean egg laying date of a species of birds in the UK has advanced by 14 days over a 47-year period of observation. This is a case where "individual adjustment of behavior in response to the environment has enabled the population to track a rapidly changing environment very closely," the study says.

Another study, a case of mal-adaptation, is the response to climate change, by a bird species that breeds during the Arctic summer, which leads to low fitness when individuals migrate to the tropics for the winter. The summer-time adaptation is that chicks are born with smaller bodies, to lose heat more efficiently in the warmer conditions. But the smaller birds have shorter beaks, which proves a disadvantage when they migrate, in the winter, to places where the best feeding is buried a little deeper.

Herbivores, such as the caribou, have evolved to have offspring at the best plant-growing season. This timing is maintained by linking migration and breeding behaviour to the length of the day, while the plant-growing season is linked to the local temperature. With climate change, however, this timing falls out of step and one study reports that birth rates have fallen four-fold, with higher mortality.

While there are changes of form and behaviour in species, over a period, the objective of the study was to identify changes that were instances of adaptation to climate change. This would be the case, the paper says, if three things are true. The first is that there has been climate change. The second, that it is climate change, and not some other cause, that has brought about the change in the physical features of an animal. And the last, that the change arises from selection of traits that help the animal cope with stress of climate change.

Testing the third condition, the authors say, requires data that has been collected over multiple generations in single populations. The large team of researchers carried out an extensive search of investigations of how change in temperature or precipitation, or both, affects the physical form or timing of life events in different animal species. And from the large data available, they found useful sets that were in respect of birds. This would be because of the relative ease of collection of data, of nesting, egg laying and hatching, and movement, of birds, over a period.

Most earlier studies of how species respond to climate change, the paper says, have focused on changes in the distribution and abundance of species. Changes in their behaviour, dimensions or physiology have been studied much less and models to simulate distribution and populations have not considered the possibility of species to adapt. The present "study thus makes an important contribution by focusing on the temporal dimension of species responses to changing environments", the authors say. "We demonstrate that some bird species analysed here seem to respond to warming temperatures by adaptive advancement of timing their life events, emphasizing the possibility of species tracking their thermal niches in situ, which can occur with or without shifts in geographic ranges. However, we did not find evidence for adaptive change in all species, and even populations undergoing adaptive change may do so at a pace that does not guarantee their persistence."

The authors add that the species studied are common and abundant species, for which data is more easily collected. "We fear that the forecasts of population persistence for rare and endangered species will be more pessimistic," they say.

The conclusion, that a great many animal species are likely to go extinct by the end of the century, is alarming. There are many who consider that biotechnology would be the key to getting through the 21 century. True, the above study does not include plant species. But plants are also affected by climate change and there is close dependence of vegetation on animal species. The results of the study may not be far from true in the case of bacteria and microorganisms. Massive decline of animal biodiversity would hence be mirrored in the botanical world and this would not bode well for the role of plants that we are counting on in the coming decades

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