Mountains are home to 85% of the world’s amphibian, bird, and mammalian species, despite covering only 25% of the Earth’s surface. This makes them a highly diverse ecosystem and a key focus for conservation efforts.

In mountainous regions, species diversity—the measure of how many different species are present—can vary with elevation due to environmental factors like climatic conditions. However, a recent study from the Centre for Ecological Sciences (CES), Indian Institute of Science (IISc) has uncovered a different factor driving bird species diversity at mid-elevations: the presence of ants from the Oecophylla genus.

“In mountains, you often see hump-shaped patterns [of species diversity], and for a long time, people have been interested in why this happens. One of the mechanisms they did not think much about was biotic interactions like competition,” says Kartik Shanker, Professor at CES and co-author of the study published in Ecology Letters.

Oecophylla ants, known for their aggressive and dominant behavior, are voracious predators of insects at the bases of mountains found in the paleotropics, covering Africa, Asia and Oceania. The researchers decided to test how the ants’ presence affects the diversity of insect-eating birds, especially at lower elevations.

A previous study led by co-author Trevor D Price, Professor at the Department of Ecology and Evolution, University of Chicago, showed that the presence of Oecophylla ants at the base of the eastern Himalayas decreased the density of insects and might therefore have an effect on the presence of insect-eating birds. In the current study, the team wanted to see if this pattern was more widespread among other insect-eating species as well.

Led by Umesh Srinivasan, Assistant Professor at CES, the researchers used existing datasets with information about bird species observed at various elevations across different mountain ranges. They categorized the birds into dietary guilds—groups of species with similar dietary requirements, such as insectivores and omnivores.

“We looked at the ranges of these bird species. We noted what bird species [in each guild] occurred at 100 meters, then 200, 300 and so on, for every 100 meters,” explains Srinivasan. “We then classified mountain ranges with or without Oecophylla at the base, and looked at what species were present at different elevations.”

The researchers found patterns consistent with Oecophylla ants competing with insect-eating birds for food at lower elevations. This could then have ended up pushing these birds higher up in the mountains—the species diversity was highest at an elevation of about 960 meters. Other bird groups like nectar-eating and fruit-eating birds—which weren’t competing with Oecophylla ants—reduced in species diversity as the elevation increased.

The presence or absence of Oecophylla ants at the base of mountains, therefore, was a good predictor of why the diversity of insect-eating birds peaked at mid-elevations, the team found.

“With climate change, if the ants shift their ranges towards higher elevations, this might impact the bird species at higher elevations as well,” adds Srinivasan.

When dead animals are left lying around in nature, who takes advantage of the free feed—carnivores or herbivores? The answer may surprise you.

In Australia, people tend to think carnivores—such as dingoes, ravens, foxes and wedge-tailed eagles—lead the clean-up crew.

But our new research shows common brushtail possums—often thought to be herbivores—also dine on animal carcasses.

Understanding when and where brushtail possums scavenge is important. It can improve our knowledge of how carcasses are disposed of in nature, and how nutrients cycle through ecosystems.

Seeking a nutritious meal

Scavenging may provide specific essential nutrients otherwise lacking in herbivore diets.

Carcasses often contain much greater levels of crude protein than leafy greens do. Similarly, chewing on bones, may increase the intake of calcium and phosphorus, two key minerals essential for growth.

Scavenging on carrion may also help herbivores meet nutritional requirements in regions where typical food resources may be restricted during some seasons. Similarly, in times of drought, thirst may also drive herbivores to scavenge in an attempt to extract fluids from carcasses.

Though it may seem gruesome, scavenging is crucial to healthy ecosystems. Clearing carcasses from the landscape by feeding them back into food chains recycles nutrients into living systems.

Our previous research has found native marsupial herbivores feasting on the dead.

In alpine Australia, possums accounted for 61% of all recorded carcass scavenging—a proportion far surpassing species more typically considered carcass consumers.

In our latest research, we wanted to understand the factors that influence carrion consumption by brushtail possums in different ecosystems.

What we did

We monitored fresh eastern gray kangaroo carcasses across both alpine (Kosciuszko National Park) and temperate (Wolgan Valley, Greater Blue Mountains National Park) regions in New South Wales. We also compared sites in both open (grassland with no canopy cover) and closed (woodland) habitats, in cool and warm seasons.

At each carcass, we used a remote camera “trap” to record scavenging behaviors.

We found possums were one of the main scavengers, often feeding from carrion more than typical scavengers such as dingoes and ravens.

Possum scavenging rates varied by habitat and season. Regardless of region, possums scavenged exclusively in closed canopy habitats under the trees, probably for protection from predators and other scavengers such as dingoes, red foxes, and wedge-tailed eagles.

Out in the cold

Possum scavenging activity varied according to the season.

In temperate regions, possums scavenged only in winter when other food resources were limited.

In alpine areas, where food is scarce even in summer, possums scavenged year-round. But they still ate more from carcasses in cooler months. This may be necessary for possums to get the nutrition they need when other normal food resources—such as leaves, flowers and fruit—are limited.

Competition between scavengers may also change with the seasons. For example, in alpine regions, we saw fewer large scavengers such as dingoes in winter, possibly reducing competition and making it easier for possums to access carrion.

During warmer months, insect activity increases. These tiny scavengers often start eating a carcass within minutes of its death, accelerating its decomposition. It means animals such as possums have less time to feed on the carrion.

Flexible ‘herbivores’ around the world

Previous research has shown many herbivore diets are more flexible than previously thought. All over the world, certain plant-eaters have been found scavenging on animal remains—especially when other food sources are limited, such as during drought or after fire.

In Africa, hippopotamuses were found to have consumed flesh from the carcasses of other animals. In the United States, white-tailed deer fed on discarded fish.

Similarly, on a small island off Cape Town, introduced European fallow deer ate dead rabbits. On the Eurasian tundra (treeless plains), reindeer devoured lemming carcasses. In Italy, crested porcupine ate dead pigeons.

These are all still primarily herbivorous animals, they just happen to dip into carcass resources when they need to.

Improving our understanding of ‘bloody hungry’ herbivores

Our study found brushtail possums are an important scavenging species across several Australian ecosystems. It also highlights how scavenging can vary with a region, season and habitat.

Understanding the unusual foraging behavior of the common brushtail possum could also help inform more effective wildlife management. Specifically, understanding how carcasses can support possum populations during cooler months in places like New Zealand, where they are considered an invasive pest, may lead to more effective control measures.

Our methods could also help scientists understand herbivore scavenging in other environments. This may provide valuable insights into the complexities of food webs and how nutrients move through ecosystems.

This article is republished from The Conversation under a Creative Commons license. Read the original article.