In the southeastern United
States, burrows dug by gopher tortoises are used for shelter by no fewer than
200 other species of animals, from owls to rabbits and rattlesnakes. Gopher
tortoises are exceptional in this regard, but hardly unique: many reptiles dig
holes used by other species. Yet they’re rarely regarded as ecosystem engineers
— an oversight that’s repeated often when it comes to reptiles, and limits our
vision of just how ecologically important they’ve been and how important they
might yet be again.
“The vision of reptiles as
unimportant, simplistic, peripheral and expendable proto-animals remains
strongly rooted in society,” writes ecologist Everton de Miranda of Brazil’s
Federal University of Mato Grosso in the
journal Frontiers in Ecology and Evolution. “Because reptiles are
rarely as noisy as birds or conspicuous as large animals, they often pass
unnoticed as ecosystem players.” It’s time, writes de Miranda, for a “paradigm
shift.”
Since the end of the last Ice
Age, human activity has driven extinct scores of reptilians, with 53
extinctions taking place in just the last century. Many more have been
extirpated, and at least 19 percent of all remaining reptiles are now
considered threatened — a loss to be understood not just in the usual terms of
vanished biological heritage, but the myriad ecological roles they play.
Many reptiles consume fruit and
disperse seeds across landscapes, helping those plants to spread and preventing
populations from becoming isolated. Animals often go along for the ride too,
particularly on marine reptiles: a sea turtle’s shell might host communities
containing hundreds of species of plants and invertebrates, forming what de
Miranda calls a “miniature reef” colonized by yet more animals.
He describes aquatic reptiles as
“ecosystem linkers,” transporting nutrients between water and land, providing
prey for terrestrial predators. In the neotropics, for example, crocodilians
can comprise up to 70% of jaguar diets. Elsewhere reptiles once were — or, as
with remaining large crocodile species, still are — apex predators, shaping
ecosystems with their habits. Other species engineer ecosystems by grazing
vegetation or, as with gopher tortoises, digging burrows.
As reptiles, especially
large-bodied reptiles, continue to decline, ecosystems and their services
contract. Some plants, such as baobab trees in Madagascar that rely on
tortoises to spread their seeds, may vanish. Less nutrients are transported
onto land; in the case of sea turtles, that means less fertilizer for beachside
plants and a subsequent erosion of coastal dunes. Fewer burrows means fewer
homes for other creatures. On and on the connections go. “Remove a highly
interactive species from an ecosystem and other species tend to suffer,” says
de Miranda.
The first step in de Miranda’s
paradigm shift is appreciating the wealth and complexity of these interactions.
Next up: doing something about it. Beyond protecting the reptiles who remain,
de Miranda thinks they should be a focus of rewilding and reintroduction
programs, particularly in tropical regions where the losses are most acute. One
rewilding candidate is the Cuban crocodile, once an apex predator of Caribbean
landscapes and now restricted to two tiny, insular populations; people might
also, says de Miranda, keep an open mind to the value of reptiles now living
outside their historic ranges.
Though some conservation programs
do include reptiles, they’re usually an afterthought. Rarely are these efforts
framed in larger ecological terms. “Lost and current ecological processes
performed by large reptiles may be orders of magnitude higher than what is
currently perceived,” writes de Miranda. Unless we appreciate and act on that,
“the astonishing biodiversity related to them can vanish, too.”
Source: de Miranda, Everton. “The
Plight of Reptiles as Ecological Actors in the Tropics.”
Frontiers in Ecology and Evolution, 2017.
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