Adaptations to climate change

In Paris as elsewhere, cherry trees are adapting to current climate change by flowering earlier

In response to global climate warming, two main types of adaptation are expected and observed, in both animals and plants [1], which can be seen as two dimensions, ecological and geographical (or spatial), of species adaptation:

• Phenotypic adjustment and/or genetic adaptation of the ecological niche of individuals and populations to new local conditions. That is to say: partial adjustment of the life cycle (phenology) and other biological characteristics (morphology, physiology) of individuals and populations confronted with new local climatic and ecological conditions (seasonal cycle, nycthemeral cycle), exploration and use of local micro-habitats and micro-climates, exploitation of new  local preys, confrontation and defences against new predators and competitors, etc.
• Shift of the distribution area of populations towards more favourable climatic conditions, i.e. mainly towards the poles or at higher altitudes, with a variable speed.

Biodiversity monitoring over the last twenty years has largely documented these two main types of response, both from species and communities. Locally, most plants flower and fruit earlier in spring in temperate and boreal regions, with a general phase shift in the “greening” of plant communities observed by satellite, at the scale of habitats, landscapes and regions [2].

Insects respond to this phase shift by progressively adjusting their life cycle, via their ‘r’ strategy and/or their behavioural plasticity, to that of the plants they feed on. This adjustment is easier for generalist species such as lemon butterflies (Gonepteryx rhamni) and bees (Figure 1)… as long as the plants are not sprayed with pesticides! In addition, the wing colour of butterflies, dragonflies and other insects in Europe is gradually lightening on a regional scale in response to increasing summer temperatures [3]. Natural selection in favour of a paler livery, absorbing less solar radiation, indeed applies for all dark insect species exposed to hyperthermia in a warmer climate. Thus, the populations of dark species are becoming scarcer in southern Europe, but they are also evolving (paler) through the selection and reproduction of the palest individuals.

Mammals, birds and reptiles adapt locally more or less well, according to their behavioural plasticity and their demogenetic strategy, to the new life cycles of their preys and other ecological partners: shifting of migration or hibernation dates, of the reproduction calendar, use of new resources, etc

As for movements, at the European scale, plant, butterfly and bird communities monitored for more than 20 years have been expanding their range northwards, at varying rates depending on the groups and countries considered [4].

However, these responses to climate change can only be partially adaptive [5], [6], [7]. In particular, they seem insufficient to reverse the decline of ‘K’ type specialists (i.e. long-lived and not very fecund species), which are more sensitive to the massive transformation and fragmentation of their habitats, for several reasons:

• the lack of synchronization between species, especially according to their trophic level, partially disorganizes the ecological networks, especially to the detriment of specialist, long-lived and low fertility species (type ‘K’);
• given the shape of the biosphere, the continents and the relief, the surface area of habitats with a potentially favourable climate decreases towards the poles and at altitude, limiting the number of ‘climatic refugee’ species (type ‘r’ or ‘K’) that will be able to establish themselves there; moreover, the accessibility of these habitats is not guaranteed, especially for the large specialist ‘K’ species that will have to cross unfavourable and/or anthropised habitats;

• 

  all these responses cannot protect populations of ‘K’ species from the devastating effects of extreme climatic events such as prolonged droughts, forest fires, storms and floods (even typhoons and tsunamis, in tropical regions), the frequency of which is currently increasing with the intensity of climate change.

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Notes and references

Cover image. Cherry trees in bloom. [Source: Koudkeu, CC BY-SA 4.0, via Wikimedia Commons]

[1] Moritz C. & R. Agudo, 2013. The future of species under climate change: Resilience or decline? Science 341:504-508.

[2] Bellard C., C. Bertelsmeier, P. Leadley, W. Thuillier & F. Courchamp, 2012. Impacts of climate change on the future of biodiversity. Ecol. Lett. 15:365-377.

[3] Zeuss D., R. Brandl et al. 2014. Global warming favours light-coloured insects in Europe. Nature Communications 5, 3874.

[4] Devictor V., C. van Swayy et al., 2012. Differences in the climatic debts of birds and butterflies at a continental scale. Nature Climate Change 2:121-124.

[5] Biesmeijer J.C., Roberts S.P.M., Reemer, M. et al. 2006. Parallel declines in pollinators and insect-pollinated plants in Britain and the Netherlands. Science 313:351-354.

[6] Sanchez-Bayo F. & Kris A.G. Wyckhuys, 2019. Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation 232: 8-27.

[7] Bellard C., C. Bertelsmeier, P. Leadley, W. Thuillier & F. Courchamp, 2012. Impacts of climate change on the future of biodiversity. Ecol. Lett. 15:365-377.