The Footsteps of Large Animals Fill Landscapes with Life

Candice Gaukel Andrews October 29, 2019 0

As elephants walk, they leave heavy footprints behind them—sometimes as much as 12 inches deep. They then fill with water, creating microhabitats for other forms of life. ©Francisco Di Poi

When you weigh anywhere from 1,000 to 14,000 pounds, you tend to leave huge, deep footprints wherever you walk. But more than just evidence of your passing through, those footprints, it turns out, can be habitats for dozens of other beings.

Much like beavers, elephants have widely been recognized as “ecosystem engineers.” They extensively modify the vegetation where they live through browsing, knocking down branches and trees—which opens gaps in the forest canopy, creating a natural shelter for other wildlife, such as small lizards and mammals—dispersing seeds, trampling, and converting large amounts of plant biomass into dung that is a food for a diversity of beetles and an important nutrient input for aquatic and terrestrial systems.

But in a recent study published in the African Journal of Ecology, researchers in Kibale National Park in Uganda found that when elephant footprints fill up with water, they also play an important ecological role: they become small, foot-shaped microhabitats for at least 61 different microinvertebrates from nine different scientific orders. Those species include beetles, gastropods, mayflies, midges, mites and tadpoles. For these creatures, such pools are vital, especially in the dry season.

They may even serve as corridors for distributing those pool-dwelling animals across vast and otherwise parched distances. In other words, they are frog stepping-stones, connecting populations.

Research shows that elephant footprints may have a place within the life cycles of several species and within the food web itself. ©amanderson2, flickr

African elephant tracks mean biodiversity abundance

Although some previous research had linked elephant footprints to mosquito breeding sites, this abundance of diversity had never been observed before.

The researchers, from Germany’s University of Koblenz-Landau and other institutions, did more than just discover this microcommunity. In order to ascertain just how much these tiny occupants relied on elephant footprints, they measured the age of each imprint, the temperature and pH of the water inside, and its distance to other footprints and natural bodies of water.

They found that the oldest footprints held the highest levels of biodiversity due to the added level of dead leaves that had fallen into the prints, as well as new vegetation that had started to grow. The oldest prints were also the only ones that contained tadpoles. The medium-aged prints had the lowest biodiversity levels.

The findings, however, also point to a troubling question: if African elephants are so unexpectedly important for aquatic species and the pachyderms continue to be poached and slaughtered, what will become of the ecosystems to which we now know they are so essential?

It’s likely that some species—such as some dragonflies—would have a very hard time finding suitable breeding habitats and might disappear locally.

This screeching frog is found in Uganda and could be one of the beneficiaries of African elephant tracks. ©Bernard DUPONT, flickr

Asian elephant tracks support tadpole continuance

Meanwhile, another, more recent study found that frogs in Myanmar also depend on elephants. Flooded elephant tracks are amphibian pathways, predator-free breeding grounds and “condos.”

Publishing in the journal Mammalia, researchers found that tracks of Asian elephants were brimming with frog egg masses and tadpoles. The tracks can persist for a year or more and provide temporary habitat and—until now—underappreciated sanctuaries for laying eggs during the dry season when alternate sites are unavailable. Importantly, the tracks aren’t big enough to host fish, which prey on frog eggs and tadpoles.

The scientists involved in the study visited Myanmar’s Htamanthi Wildlife Sanctuary in the dry-season month of March in 2016 and again in 2017 to learn more about the Asian elephant’s impact on the landscape. This sanctuary features a seasonally flooded wetland surrounded by an evergreen forest. The sanctuary gets really wet during the rainy season from June to September (great for frogs), but it’s dry from March to June.

Tracks of Asian elephants, such as these in India’s Bandipur National Park, are virtual condominiums for frogs. ©Mike Prince, flickr

The researchers documented hundreds of elephant tracks during their two visits, many of which appeared to be older than 60 days. Most of the tracks had no water, but some did—the result of groundwater seepage. Of those tracks, 20 were found to contain batches of frog eggs or tadpoles (no adult frogs were found in any of the footprints). In one case, a single trackway contained seven, water-filled prints, suggesting the important contribution of a single elephant.

Sadly, Asian elephants are considered endangered by the International Union for Conservation of Nature (IUCN) due to habitat loss, poaching and retribution for crop raiding and elephant/human conflict.

Moose move mud—and thus nutrients, such as nitrogen and phosphorus—into northern waters, enhancing the growth of algae and aquatic plants, and providing food and habitat for fish, shellfish and smaller organisms. ©Candice Gaukel Andrews

Moose tracks equal more nutrients

It’s a bit mind-boggling to think of creatures so big that their very footprints can support life. And, the phenomenon isn’t restricted to Africa: in the wake of moose, foraging for aquatic plants, great mounds of mud—and nutrients—are kicked by their great feet into the waters of the northern hemisphere.

In a study published in Oikos, a monthly, peer-reviewed scientific journal covering research in the field of ecology, researchers quantified those mounds. Where moose fed, water concentrations of phosphorus were 42 times higher than in undisturbed waters. Nitrogen levels nearly tripled.

As stated in the study, in some bodies of water, moose foraging most likely accounts for a large portion of those nutrients, which are foundational to food webs and ripple outwards into many other species. Exactly how much life all that phosphorus and nitrogen produces remains to be studied, but the researchers raise the possibility of “lake-level ecological consequences.”

Unfortunately, as with the elephants, moose populations are also declining, though not as precipitously.

Pixabay

Sadly, Asian elephants are considered endangered, and African elephants continue to be slaughtered. Will their ecosystems unravel when they are gone?

Unabridged ecosystems epitomize the wild

These three studies show us that megaherbivores shape their habitats in ways we are just beginning to fully appreciate and understand. When you save the elephants, you just might be saving the frogs—a connection between species that’s not immediately obvious. Such scientific endeavors underscore life’s interdependence.

And that’s the beauty of intact ecosystems, with their full complement of wild things.

Here’s to finding your true places and natural habitats,

Candy

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