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A new study has shed light on the poten­tial of birds to sur­vive in the face of cli­mate change. In the analy­sis, based on more than fifty years’ detailed study of a pop­u­la­tion of great tits near Oxford, UK, a team of sci­en­tists were able to make pre­dic­tions about how the birds could cope with a chang­ing cli­mate in the future. They found that for small, short-​lived birds like the great tit, evo­lu­tion can work fast enough for genetic adap­ta­tion to keep pace with a chang­ing envi­ron­ment. How­ever, even for such fast-​evolving species, evo­lu­tion on its own is not enough.

Biol­o­gists typ­i­cally use the cli­matic con­di­tions in which species cur­rently live to project the like­li­hood that those cli­mates will be avail­able fol­low­ing a period of cli­mate change, and these almost always pre­dict dra­mat­i­cally high rates of species extinc­tions and bio­di­ver­sity loss in future cli­mates. In many instances, such pre­dic­tions are war­ranted, and recently shown in the pub­li­ca­tion about evo­lu­tion being too slow to keep up with cli­mate change. Polar bears (Ursus mar­itimus), for exam­ple, are pro­jected to be at high extinc­tion risk as a result of the global warming-​induced loss of arc­tic sea ice on which they depend for hunt­ing their prey. For other species, how­ever, the effect of cli­mate change on extinc­tion risk is less obvi­ous. Because species can adapt to chang­ing envi­ron­ments through both phe­no­typic plas­tic­ity (changes in behav­iour, phys­i­ol­ogy, and/​or mor­phol­ogy) and micro-​evolutionary adap­ta­tion, many can per­sist and even thrive in the face of chang­ing climates.

By study­ing indi­vid­ual birds over mul­ti­ple years, the team of sci­en­tist from the Uni­ver­sity of Oxford was able to show that indi­vid­ual birds have a built-​in flex­i­bil­ity that enables them to adjust their behav­iour rapidly in response to short-​term changes in the envi­ron­ment. This flex­i­bil­ity — known as phe­no­typic plas­tic­ity — greatly increases the chances that a pop­u­la­tion can sur­vive in spite of short-​term changes, but that pos­si­bil­ity depends on how closely they can track the key aspects of their envi­ron­ment, such as the avail­abil­ity of food. This has also been addressed in a study with a slightly dif­fer­ent approach when researchers showed that high pop­u­la­tion den­sity of great tits was only buy­ing them some time to sur­vive, but evo­lu­tion­ary adap­ta­tion would be needed for ‘real’ sur­vival. As species become longer-​lived, and thus slower to repro­duce, evo­lu­tion­ary adap­ta­tion is far slower and can’t on its own save such species from cli­mate change-​induced extinction.

The study con­ducted by the Oxford team and pub­lished on 9 July in the jour­nal PLoS Biol­ogy, uses the birds as a model sys­tem for under­stand­ing responses to cli­mate change, since they rely on a spring peak in cater­pil­lar num­bers to feed their young. The team com­bined their inten­sive study of the birds with data on how this key cater­pil­lar food source has changed over time, allow­ing them to pre­dict how well the birds can track the change in the envi­ron­ment through its effects on the cater­pil­lar pop­u­la­tion. The data were gath­ered from the same study site over decades of fieldwork.

The sci­en­tists looked at when the birds lay their eggs rel­a­tive to spring tem­per­a­tures, and how they have tracked the shifts in peak cater­pil­lar num­bers caused by the changes in tem­per­a­ture. They found that the birds are now lay­ing their eggs two weeks ear­lier (on aver­age) than they did 50 years ago, pri­mar­ily as a result of this phe­no­typic plas­tic­ity. The authors’ pre­dic­tions show that this mech­a­nism could allow the birds to sur­vive warm­ing of 0.5°C per year, eas­ily out­pac­ing the cur­rent worst-​case sce­nario of 0.03°C from cli­mate mod­els. In the absence of plas­tic­ity, how­ever, there’s a 60% chance that they would become extinct.

“The key to this study was long-​term field work,” said lead author Ben Shel­don. “Indi­vid­u­als were iden­ti­fied and tracked over their whole lives, which enabled direct mea­sure­ment of nat­ural selec­tion, inher­i­tance and phe­no­typic plasticity.”

Pre­vi­ous work on the effects of cli­mate change has over­looked the way that pop­u­la­tions can change to match chang­ing envi­ron­ments. “The main rea­son for this has been the lack of very detailed data to pre­dict how the pop­u­la­tions can respond to such cir­cum­stances,” said Sheldon.

“Our results show us under what con­di­tions we can expect species to be able to cope with a chang­ing envi­ron­ment, and under what con­di­tions we should be more pes­simistic,” he said. “We should be par­tic­u­larly con­cerned about slow-​reproducing species, for which the need to show just the right response to the envi­ron­ment is par­tic­u­larly cru­cial. A key area for future work is to under­stand why some species respond by the right amount, and oth­ers show the wrong response.”

The above news item is reprinted from mate­ri­als avail­able at PLoS Biol­ogy via Sci­enceDaily. Orig­i­nal text is edited for con­tent and length.
(Source: PLoS Biol­ogy, Quan­ti­ta­tive Assess­ment of the Impor­tance of Phe­no­typic Plas­tic­ity in Adap­ta­tion to Cli­mate Change in Wild Bird Pop­u­la­tions, 09.07.2013; PLoS Biol­ogy, Adapt­ing to Change, 09.07.2013)