2023 has been the hottest year in history and the third driest summer in Spain since records began six decades ago. The lack of rain has especially affected Catalonia, which closed the year with the worst drought on record, according to the Meteorological Service of the Generalitat. People are increasingly familiar with the aftermath: Reservoirs at record lows have led to supply cuts and restrictions on water consumption. In the natural environment, vegetation is drying out and parks and gardens are running out of butterflies. 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 disappearing.
Appreciated for their bright colors and their fluttering that begins with good weather, there are more than 24,000 registered species of butterflies. Their diversity goes beyond their shades: these lepidopteran insects use different strategies to adapt to the climate depending on the place they live. This has been demonstrated by an international study, published in the Journal of Animal Ecology, which has found that butterflies in Catalonia are more efficient at regulating their temperature than species in the United Kingdom. However, warming due to climate change puts Spanish butterflies at greater risk of extinction. Eric Toro Delgado, from the Institute of Evolutionary Biology of the CSIC and author of the study, explains that there is an impact on their productivity, since it is possible that they spend time sheltering from the heat: “They cannot invest that time in reproducing or laying eggs, which “It will negatively affect the populations.”
Researchers have compared butterflies from these regions because they have different latitudes and temperature regimes. Furthermore, explains Toro, “knowing the conditions of the warmest region reflects to a certain extent what may be found in the future in the coldest region if climate change continues.”
Scientists have found that as temperatures rise, both populations shift to heat avoidance behavior. In Catalonia, butterflies vary their exposure to the sun with changes in position: “They open their wings more or less and change their orientation with respect to the sun's rays,” describes the environmental biologist. On the other hand, the populations of the United Kingdom “depend more on finding suitable microclimates, that is, areas with a somewhat higher or lower temperature, with more or less exposure to the wind.”
For the research, scientists measured the body and air temperatures of almost 800 adult butterflies from 23 different species. For ten of them, the researchers had comparable data between species from Catalonia and the United Kingdom. Despite the differences between both populations, the researchers observed that when they reached 22º, the difference between their body temperature and that of the environment was reduced. That is, they need to heat up less or almost not at all. Therefore, if temperatures rise too much, they will also overheat and must cease activity to protect themselves. This change could initially benefit British butterflies, while Spanish butterflies will face difficulties in surviving if they do not adapt quickly enough: “In the United Kingdom they will also end up overheating if global warming continues,” warns Toro. British species, which mainly depend on shade to stay cool, are at greater risk of population decline due to habitat loss.
One of the reasons Spanish butterflies are better at regulating their temperature could be because they have more thermal options available, the study authors point out. However, they also resort to searching for areas with lower temperatures and their displacement is increasingly evident. The inappropriate and excessive use of fertilizers and pesticides, or the introduction of non-native species, are other threats that these pollinators face. In Spain there are 13 species included in the List of Wild Species in Special Protection Regime.
Butterflies are bioindicator species; That is, their behavior and development provide information about the state of the ecosystem they inhabit. Furthermore, these lepidopterans react quickly to changes, which is why they have been used to study the effects of climate change. Therefore, the fact that butterflies decline due to drought and heat may provide clues to the status of other insects, such as bees or beetles, and even vertebrate animals.
A greater understanding of how butterflies thermoregulate, as well as understanding temperature variations, is essential to predict which species are most at risk due to climate change. Diverse ecosystems offer these insects a greater variety of microclimates, so the authors highlight growing wildflowers and planting more trees as some actions that could counteract habitat loss.
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