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Beyond Evolutionary Fitness, Mammals Are Ecosystem Engineers

Photo: A beaver, depicted on the Canadian Parliament Building, by D. Gordon E. Robertson, CC BY-SA 3.0 , via Wikimedia Commons.

Scientists are increasingly noticing the role of mammals in maintaining healthy ecosystems. This means that their roles extend far beyond their own fitness needs. We’ve looked at bacteria as “ecosystem engineers” in the past, but larger creatures deserve the title as well. When animals give back more than they take, does that fit the model of selfishness that Darwinism promoted?

Those Dam Beavers

Long celebrated for the ability to increase biodiversity through their engineering prowess, beavers are now being esteemed for their work in reviving wetlands. Writing for the BBC, Navin Singh Khadka says that beavers are “keystone” mammals for our time:

We are losing wetlands three times faster than forests, according to the Ramsar Convention on Wetlands. When it comes to restoring them to their natural state there is one hero with remarkable powers — the beaver.

Wetlands store water, act as a carbon sink, and are a source of food. The Ramsar Convention on Wetlands says they do more for humanity than all other terrestrial ecosystems — and yet they are disappearing at an alarming rate. [Emphasis added.]

With their strong teeth, muscle, and determination, these furry ecosystem engineers hold the secret to halting the effects of drought and climate change, this article claims.

The main problems are agricultural and urban expansion, as well as droughts and higher temperatures brought about by climate change.

But if you have a river and a beaver it may be possible to halt this process.

Efforts in the last fifty years to restore beavers after hunters nearly wiped them out have had beneficial side effects. Khadka tells how Finnish researchers found that the beavers’ shallow, wood-cluttered ponds are much more productive than other ponds. “Basically, beavers excel at creating complex wetland habitats that we’d never match,” comments Nigel Willby, professor of freshwater science at University of Stirling.

On a side note, wetland depletion — while serious — is not as catastrophic as claimed in earlier studies. Stanford scientists report that the global decline is more like 21-35 percent since 1700, not 50-87 percent as previous studies estimated. They call wetlands “biodiversity superheroes” for their roles in purifying our water, preventing flooding, and expanding habitats for plants and animals. In other words, superheroes among mammals create superheroes among ecosystems.

Are beavers acting selfishly for their own fitness, or is there a larger master plan that foresaw the need for creatures equipped to actively preserve healthy habitats for other species?

Thoughtful Elephants

Not many years ago, elephants were blamed for destroying some African forests by yanking down tree limbs with their powerful tusks and trunks and leaving a mess. That opinion has changed. The elephants had a method to their madness. They were trying to save the planet, writes Jacob Born at Saint Louis University. How could that be? It turns out, as research at the university shows, that elephants selectively prune forests to increase carbon storage.

Elephants play multiple roles in protecting the global environment. Within the forest, some trees have light wood (low carbon density trees) while others make heavy wood (high carbon density trees). Low carbon density trees grow quickly, rising above other plants and trees to get to the sunlight. Meanwhile, high carbon density trees grow slowly, needing less sunlight and able to grow in shade. Elephants and other megaherbivores affect the abundance of these trees by feeding more heavily on the low carbon density trees, which are more palatable and nutritious than the high carbon density species. This “thins” the forest, much like a forester would do to promote growth of their preferred species. This thinning reduces competition among trees and provides more light, space and soil nutrients to help the high carbon trees to flourish.

Are the elephants “thinking” about this? Are they acting altruistically or in pure self-interest? Or does the effect point to a higher purpose that can actively maintain healthy habitat for the benefit of many other animals, and even mitigate global climate change?

A Lion in the Sand

Many think of deserts as inhospitable wastelands, the dropouts of productive ecosystems. Wrong, says ecology expert Sarah Curtis at Trent Nottingham University: Topped by a photo of a lion walking on a desert dune in Namibia, her headline proclaims, “Deserts are brimming with life but remain one of the most poorly-understood ecosystems — here’s why that needs to change.”

When most people think of deserts, the word that often comes to mind is sand – and a lot of it. Deserts cover almost a quarter of the earth, yet it’s hard to imagine life thriving in such hostile environments, regulated by how much water and food is available….

Although to the naked eye deserts appear barren, there is actually a surprising amount of life to be found. Deserts are one of the top three richest biomes for terrestrial vertebrates, with a quarter of species, totalling almost 7000, found there. Three percent of these species are only found in desert environments — many of which have developed various adaptations to help them survive in environments where rainfall may be mere millimetres per year.

Some of the mammals in Curtis’s article include carnivores like lions and hyenas and herbivores like the oryx, which is “incredibly well adapted to desert life.” With its striking face markings and long horns, this grazer looks out of place in desert sand, but it is wise enough to change “its foraging behaviour during periods of drought, alongside grazing more at night when the water content of many grass species increases.”

And yes, there actually are lions in the sand. Like every other desert creature, the desert lion has a role to play for the greater good.

Even at low densities large carnivores play a key role in the functioning of desertskeeping herbivore populations at a density where sufficient vegetation to support multiple levels in the food chain is still able to persist. Desert-living carnivores are likely to exhibit unique behaviour and dietary habits compared to their temperate-region counterparts, while interactions between carnivores in deserts are likely to be more intense due to the lack of resources available.

The Bipedal Engineer

As usual, these articles accuse humans of bad stewardship in each of these ecosystems. It is man that destroys wetlands. It is man that poaches elephants. It is man that expands desertification through global warming, reduces habitat for native species with roads and towns, and makes the lions walk farther to find food. And yet humans are the consummate engineers in all the world.

Certainly, we humans have been bad actors in a variety of ecosystems. Many species have gone extinct on our watch. But thinking evolutionarily for a moment, shouldn’t humans do what comes naturally by acting selfishly for their own fitness? Or, like the misunderstood elephants, are we part of a higher plan for the good of all?

If so, humans are the only mammals with choice. We can decide to promote healthy ecosystems or to act selfishly and grab all we can get for our own pleasures. When we play the latter role and destroy things, would we not be acting in a Darwinian manner? Wouldn’t our selfish genes drive us to act for immediate gratification as an instinctual behavior?

It takes foresight to achieve beneficial relationships between numerous diverse actors. All other mammals achieve working relationships by instinct. If the human role is stewardship of the environment, we can choose to do a better job of it, for sure. These articles place a moral imperative on us through shaming. But if we learn to do better, we will succeed not by acting in a Darwinian manner. We will succeed by reasoning, convincing one another, and collectively choosing to act beyond our self-interests. We will become the world’s premiere ecosystem engineers by employing intelligent design with foresight, wisdom, and high values. Many feel that was our intended role in the first place.