By Stephen Beech via SWNS
The most common insects are dying off – and invasive species are taking over, warns a new study.
Worrying declines in insect numbers are largely being driven by losses of the more abundant species, say scientists, who discovered similar trends around the world.
Researchers analyzed long-term trends of land-based insects – such as beetles, butterflies and grasshoppers.
They found that decreases in the number of the formerly most common species have contributed most to local insect declines.
Common or abundant insect species are the ones that are locally found in the highest numbers, but which species these are differ among locations.
The findings of the study, published in the journal Nature, challenge the idea that changes in insect biodiversity result from rarer species disappearing.
The research follows the recent sounding of alarm bells about insect loss, as researchers note dramatic declines in the total number of insects in many parts of the world.
But little was known about the general trends among locally rare and abundant species over long periods.
Study lead author Doctor Roel van Klink, senior scientist at the German Centre for Integrative Biodiversity Research (iDiv), said: “It was obvious this needed exploring.
“We had to know whether observations about declines in total abundances of insects differed among common and rare species, and how this translated into changes in the overall insect diversity.”
Dr. van Klink and his colleagues set out to better understand trends in insect numbers by diving into previous studies.
The team compiled a database on insect communities using data collected over periods between nine and 64 years as part of 106 different studies. For example, one Dutch study on ground beetles was started in 1959 and continues today.
With the updated database, the research team confirmed that despite variation among the data, on the whole, land-based insects from these long-term surveys are declining by 1.5 percent each year.
To better understand that pattern, the team compared trends of species in different abundance categories and found that the ones that were the most abundant at the start of the time series showed the strongest average decline – around eight percent annually – while rarer species declined less.
But the losses of previously dominant species were not compensated for by rises in other species, which the team says has far-reaching implications as abundant species are a “staple” food for birds and other insect-eating animals, making them essential for ecosystems.
Dr. van Klink said: “Food webs must already be rewiring substantially in response to the decline of the most common species.
“These species are super important for all kinds of other organisms and for the overall functioning of the ecosystem”.
He said the analysis clearly shows that the formerly abundant species are consistently losing the most individuals compared to the less abundant insect species.
But less abundant and rare species are also taking losses, driving declines in local species numbers.
The study found a small decrease in the overall number of species of just under 0.3 percent annually.
The researchers say the decline indicates that as well as significant losses of common insects, some rare species are going locally extinct.
Coming out on top are new arrivals who managed to successfully establish themselves, according to the findings.
Dr. van Link says most of the new arrivals stay locally rare and replace other formerly rare insects, but occasionally they become very abundant.
One example is the invasive Asian Ladybeetle (Harmonia axyridis), which is now common throughout Europe, the Americas and South Africa.
The team says further research is needed to determine the underlying causes of the trends.
Although the study didn’t explicitly investigate possible causes, the researchers believe that the declines are likely linked to recent human-related impacts, such as climate change and urbanization, which are considered major drivers of biodiversity loss.
Study senior author Professor Jonathan Chase, of iDiv, said: “Insects seem to be taking a heavier hit than many other species as humans continue to dominate the planet.
“Other studies, including those our team has worked on, have not found such diversity declines at local scales from many other groups of animals and plants”.
Chase added: “The patterns we observed might be a best-case scenario for quantifying the real impact of people on insects.
“These declines were observed in long-term data from areas that have remained largely intact, sort of like a lifeboat, rather than in areas where massive conversion of natural areas into human-dominated landscapes has occurred, such as malls and parking lots.”
