2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Caddis flies Hydropsyche pellucidula. The caddis flies are the fastest disappearing order of insects. Now it has a declining population of 68 percent of the species.
Scientists conducted a meta-analysis of articles on insect dynamics and found that total insect biomass is declining by 2.5 percent per year. The researchers estimate that 41 percent of insect species are now declining, a figure that will grow by one percent each year, says Biological Conservation.
We already know about the extinction and decline of many vertebrates. Quite a lot of research has been published on this topic over the past decades. Many researchers believe that we have witnessed (and the main cause) of the sixth mass extinction, which began about 12 thousand years ago. However, scientists have only recently begun to pay attention to the dynamics of the number of invertebrates, in particular insects. Thus, ecologists have found that the number of insects in nature conservation areas in Germany for 27 years has decreased by 76 percent. In the tropics of Puerto Rico, insect biomass has declined 78 to 98 percent in 36 years. The fall in the number of insects led to the extinction of birds, frogs and lizards that fed on them. It seems that the number of insects is decreasing even faster than the number of birds or plants.
Australian environmentalists Francisco Sánchez-Bayo of the University of Sydney and Kris A. G. Wyckhuys of the University of Queensland decided to investigate the situation and understand how serious it is. They conducted a meta-analysis of articles over the past 40 years that examined insect dynamics. Scientists selected those of them in which the abundance of many species of insects (family or order) was analyzed in the area of an entire country or several countries. Or works that were carried out in a smaller area, but for 10 years or longer. In total, the authors found 73 such studies.
As a result, it turned out that the number of insect species is now decreasing (for comparison, the number of vertebrate species, whose number is declining, is almost half that, 22 percent). Each year, one percent of the species is added to this list, and the total insect biomass falls by 2.5 percent each year. At the same time, representatives of some families and orders are dying out faster than average. Thus, in the Mediterranean, more than 60 percent of the species of dung beetles (Geotrupidae) are falling; and in Europe - 71 percent of the species of Lepidoptera (Lepidóptera - butterflies, moths and moths). In general, the number of Lepidoptera is falling faster than average, with 53 percent of species declining. But the number of insects from the order of caddis flies (Trichoptera) is falling the fastest - 68 percent of the species. The most alarming, according to the authors, is that not only the number of insects-"specialists", which live in a narrow ecological niche or depend on a certain plant species, is decreasing, but also widespread species that are found in several countries. In addition, scientists note that the picture is incomplete - most of the studies were carried out in Europe and the United States, so the authors could not adequately assess the dynamics of the number of tropical insects.
Reduction of species of terrestrial insects (by families or orders). Blue shows a decrease in numbers of less than 30 percent, orange - a decrease in numbers of more than 50 percent, yellow - endangered species (decrease in numbers by 75 percent or more), gray - extinct species.
Countless endangered species are being replaced by a few insects that can survive in different ecosystems or are less sensitive to pollution, such as Putnam's metalloid (Plusia putnami) or the changeable ladybird (Hippodamia variegata). Perhaps they can to some extent be able to replace other species, but it is not clear how such a change will affect the ecosystem as a whole. For example, whether vertebrates that feed on insects will be able to adapt to a different diet.
Almost half of the analyzed studies (49.7 percent) cite habitat change or disappearance as the main cause of insect extinction. Therefore, the number of mammals and birds is also decreasing. The next most important factors are pollution, pesticides and insecticides (they are mentioned in 28.5 percent of studies), biological causes such as diseases and parasites, as well as invasive species (17.6 percent of studies) and climate change (6.9 percent of studies) …
The authors come to a disappointing conclusion. In their opinion, if the ways of food production do not change, almost all insects could disappear in the next few decades. Perhaps this can be avoided by restoring insect habitats and reducing the amount of chemical fertilizers and pesticides.
Biologists previously estimated that at the current rate of extinction of mammals, it would take three to five million years for biodiversity to recover. Even if extinction stops right now and no other species disappears, it will take about 500 thousand years to restore biodiversity.