2023 was the hottest year in history and the third driest summer in Spain since records began six decades ago. The lack of rain has particularly hit Catalonia, which ended the year with the worst drought on record, according to the Generalitat's Meteorological Service. People are increasingly familiar with the consequences: record low levels in reservoirs have led to supply cuts and restrictions on water consumption. In nature, the vegetation dries up and there are no longer any butterflies in parks and gardens. Although these insects have learned to regulate their body temperature, they are not free from the negative effects of heat, which increases their risk of disappearance.
The over 24,000 registered butterfly species are valued for their bright colors and their fluttering when the weather is nice. Their diversity goes beyond their hues: these butterfly insects use different strategies to adapt to the climate depending on where they live. This was demonstrated by an international study published in the Journal of Animal Ecology, which found that butterflies in Catalonia regulate their temperature more efficiently than species in the UK. However, warming caused by climate change increases the risk of extinction of Spanish butterflies. Eric Toro Delgado, from the CSIC Institute of Evolutionary Biology and author of the study, explains that this has an impact on their productivity, as they may spend time protecting themselves from the heat: “They cannot invest that time in reproduction.” or lay eggs, which “will negatively impact populations.”
Researchers have compared butterflies from these regions because they have different latitudes and temperature regimes. Additionally, Toro explains, “Knowing the conditions in the warmest region reflects to some extent what will be found in the coldest region in the future if climate change continues.”
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Scientists have found that both populations shift to heat avoidance behavior as temperatures rise. In Catalonia, butterflies vary their exposure to the sun by changing positions: “They open their wings more or less and change their orientation towards the sun's rays,” describes the environmental biologist. On the other hand, the population of the United Kingdom is “more dependent on finding suitable microclimates, that is, areas with slightly higher or lower temperatures and more or less wind exposure.”
For the research, scientists measured the body and air temperatures of nearly 800 adult butterflies from 23 different species. For ten of these, the researchers had comparable data between species from Catalonia and the United Kingdom. Despite the differences between the two populations, the researchers found that the difference between their body temperature and the ambient temperature decreased when they reached 22°C. This means that they have to heat up less or hardly at all. So if the temperatures rise too much, they too overheat and have to stop their activity to protect themselves. This change could initially benefit British butterflies, while Spanish butterflies will struggle to survive if they don't adapt quickly enough: “The UK will also end up overheating if global warming continues,” warns Toro . British species that rely primarily on shade to stay cool are at greater risk of population decline due to habitat loss.
One of the reasons why Spanish butterflies could regulate their temperature better could be that they have more thermal options at their disposal, the study authors point out. However, they are also looking for areas with lower temperatures and their displacement is becoming increasingly clear. The inappropriate and excessive use of fertilizers and pesticides or the introduction of non-native species are other threats faced by these pollinators. In Spain, 13 species are on the list of wild species subject to a special protection regime.
Butterflies are bioindicator species; This means that their behavior and development provide information about the state of the ecosystem in which they live. In addition, these butterflies respond quickly to changes, which is why they have been used to study the effects of climate change. Therefore, the fact that the number of butterflies is declining due to drought and heat may provide clues about the state of other insects such as bees or beetles and even vertebrates.
A better understanding of butterfly thermoregulation and temperature fluctuations is important for predicting which species are most at risk due to climate change. Different ecosystems offer these insects a greater variety of microclimates, which is why the authors highlight growing wildflowers and planting more trees as measures that could address habitat loss.
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