Beetle Decline Increases Concern for Insect Ecosystems

A recent study shows that the populations of beetles are dwindling, and this could end up being just as problematic as the problems of bees and butterflies.

The research, published in the Journal of Applied Ecology, found that 3/4 of the beetle species examined had declined in number over the last 15 years. The abundance of half of these species had fallen at a rate equivalent to 30% per decade. Scientists warn that these declines, comparable to those seen in butterflies and moths over the same period, are of serious conservation concern.

The study focused on ground beetles or 'carabids'. Many of these species perform valuable tasks in their ecosystems that we'd miss if they disappeared. More work is needed to link the declines in different areas to environmental conditions to unravel exactly what's behind them. Yet, climate change and alterations to habitats that make the conditions within them less favorable to beetles are probably among the main culprits.

This is supported by clear differences between the trends in beetle populations in contrasting types of habitat. When averaged over ten year periods, mountain-dwelling carabid beetles suffered declines of 52 per cent, while beetles at the northern moorland and western pasture sites declined by 31 per cent and 28 per cent respectively. But the upland pasture sites had more balanced increases and decreases across species, and populations in woodlands and hedgerows were also mostly stable.

“Our ultimate objective is to guide policy aimed at conserving biodiversity and offsetting the effects of environmental change, particularly if this biodiversity provides us with important services,' says David Brooks, an invertebrate ecologist at Rothamsted Research and the study's lead author. 'But the interactions between different insect communities and their environment are complex, and we need more research to understand them.”

Brooks and his colleagues analyzed data on ground beetle populations at 11 ECN sites. These are generalist predators that play a variety of important roles both in natural ecosystems and on farmland; the beetles eat a lot of pests like slugs and aphids. Carabids also eat huge numbers of weed seeds, helping stop fields being overrun by unwanted plants.

Brook says it's only now becoming possible to draw firm conclusions from the ECN, which was set up in the early-90s. It's hard to pick up genuine long-term trends by studying periods shorter than 10-15 years.