Butterflies and climate change: adapt or die

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“It’s not the smartest of the species that survives; nor the strongest; but one capable of adapting and adjusting best to the changing environment in which it finds itself”. This is surely one of Charles Darwin’s best-known quotes, although it is incorrectly attributed to him. It actually comes from an interpretation of Professor Leon C. Megginson in his article Lessons from Europe for American companies about the book The origin of species from Darwin. It is in any case this idea that led us to propose the main hypothesis of our latest work. The effects of climate change have been documented on many plants and animals, but one group of species in particular, butterflies, has been one of the best studied.

The high sensitivity and rapid response to environmental changes, along with their popularity in citizen science projects, have made butterflies a perfect study model.

The butterflies advance their flight

Phenology is the science that studies the relationship between climatic factors and the cycle of living things, such as the flowering of plants, the migration of birds and the flight period of butterflies. In a previous article, we described how many species of butterflies advance their emergence (that is, they begin to fly earlier) in response to rising temperatures.

But at the time, we knew little about how these responses related to trends in butterfly populations. In other words, what does it mean for butterflies to start flying earlier? What effect does this have on their populations? Do these phenological advances allow species to adapt to climate change, and therefore, will species that adjust their life cycle more closely to climate change have a better chance of surviving?

To try to answer these questions, we analyze the trends of 51 species of butterflies in Catalonia and Andorra thanks to data collected during 26 years of monitoring by the citizen science project of the Catalan butterfly monitoring program (CBMS).

The best-adapted species survive

Our results, recently published in Proceedings of the Royal Society B: Biological Sciencesdemonstrate once again the alarming decline of butterflies: more than half of the species have significantly decreased in abundance.

The most specialized species, those that live only in very specific habitats or whose larvae can only feed on a few plant species, have been the most affected. This result is linked to the vulnerability of specialist species to changes in land use and human activity. On the other hand, a more complex analysis shows that the evolution of populations is also determined by the phenological sensitivity of species to temperature.

Although 90% of species advance their flight in response to higher temperatures, some species do so more than others. The species whose flight period is most influenced by temperature, advancing or delaying their emergence more clearly depending on the climate, are those that have suffered the least in recent decades. In contrast, those with a lower phenological response to temperature experienced a greater decline.

All of this suggests that the ability of species to adjust their biological calendar to climate could be an adaptive trait that allows butterflies to be more in sync with the resources they feed on. For example, by advancing their appearance in warm years when plants advance their flowering, butterflies would be able to maintain synchronization between their maximum abundance and the maximum flowering of plants.

Species most at risk from climate change

Species that are less able to advance or retard their flight depending on the weather could be the most vulnerable and threatened by climate change due to loss of synchrony with the plants on which they depend.

Darwin’s apocryphal hypothesis could therefore be transposed in the context of trends in Mediterranean butterflies. Although at that time, when he raised his hypotheses to the scale of thousands of years, he surely did not imagine that a century and a half later we would live an experience in real time: climate change due to human activity and its effect on species.

Character font: Pau Colom / THE CONVERSATION

Reference article: https://theconversation.com/butterflies-and-climate-change-adapt-or-die-190605

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