Dung beetles remove faeces from wild animals in forests and thus inhibit the spread of parasites. They work the dung into the soil and thus supply nutrients to plants. They fulfil this task both in European commercial forests and in the Amazon. However, rising temperatures could lead to a decline in species diversity and population sizes of dung beetles.

In a study in the Amazon region of Peru, researchers from the Universities of Würzburg and Bremen have discovered that temperature is the decisive factor for the beetles' tolerable living conditions. Other conditions such as soil moisture and food supply only played a minor role in the diversity of species and the number of dung beetles.

"We studied the populations at altitudes of 250 to 3,500 metres above sea level and found that diversity and dung beetle abundance were highest at an altitude of 500 metres," says Dr. Kim Holzmann, research associate at the Chair of Animal Ecology and Tropical Biology at the Biocenter of Julius-Maximilians-Universität Würzburg (JMU). Unexpectedly for the researchers, the number of dung beetle species fell rapidly between 500 and 250 metres above sea level.

The reason for this observation: at an altitude of 500 metres, the temperatures are in a range that is ideal for the beetles, while the higher temperatures in the lowlands lead to heat stress. In turn, diversity fell at the higher, colder altitudes. In total, the research team collected almost 5,000 dung beetles in pitfall traps, which they loaded with dung, fruit and carrion as bait. The researchers collected their data in 2022 and 2023.

Many insect species in the Amazon could reach their heat threshold

The survey was part of a larger study by the team, which shows that up to half of the insects in the Amazon lowlands could reach their heat threshold as a result of climate change. "Around 70 per cent of the insects described worldwide are found in the tropics. We have observed that insects at higher altitudes can adapt their heat tolerance in the short term. However, many lowland species do not have this ability and are therefore endangered," explains Dr. Marcell Peters, animal ecologist at the University of Bremen.

With the study on the effects of rising temperatures on dung beetles at different altitudes, the research team provided evidence of the overall trend already observed. "The effects of climate change are clearly recognisable in this case," says Holzmann. According to the JMU scientist, if dung beetles are at risk, this is probably also true for other insect groups in the Amazon lowlands.