Throughout the world, we are witnessing a decline in the numbers of insects as well as a drop in diversity. Several studies published in a special issue of Biology Letters discuss the causes of this decline and suggest potential ways to prevent further losses in the future.
According to the authors, the most common causes for the loss of biodiversity include increasing land use for agriculture, as well as climate change, and the spread of invasive animals as a result of human activities. “We learned that not just land-use intensification, global warming, and the escalating dispersal of invasive species are the main drivers of the global disappearance of insects, but also that these drivers interact with each other,” said Florian Menzel from the Institute of Organismic and Molecular Evolution at Johannes Gutenberg University Mainz (JGU) in Germany.
For example, areas damaged by humans are more likely to suffer the effects of climate change, which will inevitably have an impact on insect populations. In addition, invasive species can establish themselves in damaged habitats and displace native species, which will also affect insects. Native species decline or go extinct and invasive species increase, resulting in significant biodiversity loss.
“It looks as if it is the specialised insect species that suffer most, while the more generalised species tend to survive. This is why we are now finding more insects capable of living nearly anywhere while those species that need specific habitats are on the wane,” said Menzel. “Generally speaking, a decline in insect diversity threatens the stability of ecosystems. Fewer species means that there are fewer insects capable of pollinating plants and keeping pests in check. And, of course, this also means that there is less food available for insect-eating birds and other animals. Their continued existence can thus be placed at risk due to the decline in insect numbers.”
Menzel and others suggest ways to prevent any further damage. The authors emphasise the need to use standard techniques to monitor insect diversity across multiple habitats to ensure researchers can compare results and have a better picture of what’s happening. To limit biodiversity loss, the researchers suggest a network of interconnected nature reserves allowing species to move from one to the other. For example, temperature-sensitive insects could avoid areas where global warming is increasing temperature and move to cooler regions in the north. Finally, we need measures to reduce the spread of invasive species (both plants and animals). For example, the invasion of insectivorous fishes in Brazil has caused major declines in freshwater insects. “This is another problem that has become extremely serious in the last decades,” concluded Menzel.
Gossner M, Menzel F and Simons N (2023) Less overall, but more of the same: drivers of insect population trends lead to community homogenization. Biology Letters, https://doi.org/10.1098/rsbl.2023.0007