A recent study found that dung beetle species experienced significant diversity and population declines in human-modified tropical Brazilian ecosystems in the aftermath of droughts and fires exacerbated after the 2015-2016 El Niño climate event.

Forests that burned during the El Niño lost, on average, 64% of their dung beetle species while those affected only by drought showed an average decline of 20%. Dung beetles provide vital ecoservices, processing waste and dispersing seeds and soil nutrients.

For roughly the past three years, entomologists have been sounding alarms over a possible global collapse of insect abundance. In the tropics, climate change, habitat destruction and pesticide use are having clear impacts on insect abundance and diversity. However, a lack of funds and institutional interest is holding back urgently needed research.

Imagine if your local trash collectors stopped showing up for work. Garbage would immediately pile up and the waste management system would eventually fail, causing the entire community to suffer. It appears something similar is happening in parts of the Amazon rainforest, where a recent study showed that one of nature’s most important waste management systems — the humble dung beetle — is becoming far scarcer in ecosystems stressed by climate change-driven drought, fire and human disturbances.

Filipe França, associate researcher at Lancaster University and Embrapa Amazônia Oriental, recently led researchers in a study published in Biotropica examining the effect of stronger El Niños and human activity on dung beetles populations. The results are alarming

Scientists found that dung beetle species experienced significant diversity and population declines in human-modified tropical Brazilian ecosystems in the aftermath of droughts and fires exacerbated by the intense 2015-2016 El Niño climate event — El Niño is a periodic warming of Pacific Ocean currents off of Peru that result in disruptive extreme weather around the planet, a phenomena that appears to be intensifying due to climate change.





Loss of ecosystem services

The new study, conducted in the Brazilian state of Pará also showed these insects’ ability to provide vital ecological services including nutrient cycling, seed dispersal and soil fertilization was also negatively impacted.

“It may seem like dung beetles are just strange insects that run around eating poop, but they’re actually hard-working insects that are critical for bringing ecological balance,” França said. “We consider [dung beetles] to be a very good indicator for how healthy or how disturbed a forest is because their health is connected to the health of other plants and mammal species.” In turn, a higher number of dung beetle species helps assure a correspondingly higher number of bio-recycling services provided in the forest.

There are three main types of dung beetles — rollers, tunnellers and dwellers — and the more diversity found among these variously employed species, the more “ecological services” they can deliver. A beetle that is a dung roller, for example, may provide its particular ecological service by tumbling animal feces along the forest floor, thereby dispersing seeds and nutrients deposited within, and moving them from where they aren’t so much needed, to where they are required, helping forests recover from drought or logging.

The study examined both the impacts of El Niño-intensified drought and human activities on the scavenger insect populations. While drought alone caused a significant decrease in dung beetles in pristine, undisturbed forest, the greatest losses were observed in previously logged or burned forests. Forests that burned during the El Niño lost, on average, 64% of the dung beetle species while those affected only by drought showed an average decline of 20%.

Dung beetle “species richness, abundance, biomass, compositional similarity to pre‐El Niño condition, and rates of dung removal and seed dispersal declined after the 2015–16 El Niño, but the greatest immediate losses were observed within fire‐affected forests,” the study found.

França noted that while the new study did not investigate the direct impacts of climate change on the Amazon forest, he pointed to other studies that suggest climate change may be bringing more intense, frequent, longer dry seasons and deepening drought conditions to the Amazon region.

“Climate change is increasing frequency and intensity of droughts in the Amazon, making fires more likely to spread. This problem affects both pristine and human-modified forests,” França explained. “The combination of stronger droughts and anthropogenic disturbance is driving drastic biodiversity loss in the Amazon.” Importantly, nearly all fires in the Amazon are set by people clearing land for cattle or crops, but such fires are intensified by drought.

Dung beetles just one indicator of ecosystem stress

The interaction between climate change, deforestation and human-caused fires may hold dire implications not only for dung beetles and the ecosystem services they provide, but also for biodiversity and forest carbon storage.

Climatologist Carlos Nobre and conservation biologist Thomas Lovejoy warn that the combination of climate change, rampant agribusiness-linked deforestation and tropical fires are already impacting vast swaths of Brazilian rainforest, threatening to turn tropical forest into degraded shrubland.

A recent study published in Science Advances found that escalating climate-related forest fires in the southern Amazon could likely turn the world’s largest rainforest from a carbon storehouse into a source of carbon emissions before 2030, unless action is immediately taken to limit Amazon deforestation and to curb greenhouse gas emissions.

Global insect collapse in the tropics?

For roughly the past three years, entomologists have been sounding loud alarms over a possible global collapse of insect abundance based on initial major studies in Germany and Puerto Rico, and meta-reviews of scores of studies on insect populations around the globe.

In the tropics, entomologists say that climate change, habitat destruction and pesticide use are having clear impacts on insect abundance and diversity. However, a lack of funds and institutional interest is holding back urgently needed research.

Based on the rapidly growing risk posed by human activities to insect populations, a group of 70 scientists from 21 countries published a global “roadmap to recovery” in January for achieving insect conservation and recovery. Jason Tylianakis, professor of Terrestrial Ecology at the University of Canterbury, took part in creating a plan that calls for immediate action, including the phasing out of toxic pesticide use, increasing landscape diversity in agriculture, and performing large-scale assessments of the conservation status of insect groups to define priority species.

It’s unclear, Tylianakis said, whether overall insect population declines are more or less substantial in the tropics. But he warned that scientists have found some evidence of that possibility. “Bees, for example, are more sensitive to agriculture in South America than in Europe.” Bee species are being especially hard hit in Brazil, where pesticide use is among the highest in the world.

In January, 2020, Nature published a study by Danielle Salcido, a PhD student at the University of Nevada, documenting declines of caterpillar and parasitoid richness and diversity in protected tropical forest sites in Costa Rica based on 22 years of data collection from 1997 to 2018.

Salcido believes the steep Amazonian dung beetle declines in the Amazon are important because those population drops show how changes in climate can interact with other drivers, such as fire and deforestation, to impact ecosystem functioning and services.

“If we knew more about the direct or indirect effects of the observed dung beetle declines on other organisms, we could get a better handle on the cascading effects of these losses. The story may appear more grim if this was revealed,” Salcido concluded. “But that gets at another conversation on the need for long-term research on insects and species interactions in the tropics.”

Citation:

França, FM, Ferreira, J, Vaz‐de‐Mello, FZ, et al. El Niño impacts on human‐modified tropical forests: Consequences for dung beetle diversity and associated ecological processes. Biotropica. 2020; 00: 1– 11. https://doi.org/10.1111/btp.12756.

Banner image caption: Coprophanaeus lancifer, the largest tunneling species of dung beetle photographed in the Brazilian Amazon near Monte Dourado in Pará state, Brazil. Image by Hannah Griffiths.

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