Biology Reference
In-Depth Information
to reach the tasty inner bark and kill them, rapidly converting a silk cotton tree savanna to a
grassland.
So, in a forest still stocked by its Pleistocene herbivores, only the saplings that are unpal-
atable to the giant browsers will ever reach the canopy. For the invertebrate species, such as
sucking bugs and beetles, that can eat the trees unpalatable to the large mammals, the more
favorable ratio is a blessing. For other browsing herbivores that eat the same plants as rhinos
do, the trampling behavior of the pachyderms leaves more browse potentially available in
the layer they can reach. In short, an Asian forest minus rhinos and elephants will barely re-
semble one where they are the dominant browsers. Once-in-a-century monsoon deluges may
reset the ecological clock on the floodplain. But between the flood events, it is truly the big
beasts, through their manuring of seeds and intense pruning, that influence the structure and
composition of the riverine forests and savannas.
Beyond Asia and its rhinos, rare vertebrates serving as ecosystem engineers are evident in
many environments. Besides the fruiteating birds of paradise in New Guinea and hornbills
in Asia, the large frugivorous birds in Amazonian forests and fruit-eating monkeys have an
important impact, as we saw in Peru. In the habitat of the Kirtland's warbler, beavers, even at
low abundance, create habitat with their damming of streams. Studies suggest that prehistor-
ic mammals, such as woolly rhinos, created the productive Pleistocene high-latitude steppe
through their intense grazing and trampling, just as the greater one-horned rhino and white
rhino maintain what one biologist has termed “grazing lawns,” where the close cropping of
grassy areas by giant herbivores with prehensile lips keeps a low sward at a height that bene-
fits many smaller herbivores in their search for nutritious grasses. In the boreal forest zone,
the giant today is the moose, but this browser eats mostly twigs. How different would the
boreal forests look if they still had their full complement of mammoths and rhinos?
Although rhino numbers were increasing in Chitwan while we were there, Hemanta Mishra
knew that an epidemic, a severe outbreak of poaching, or a catastrophic flood could decimate
Nepal's only population. In the 1980s, translocations of endangered rare mammals to rees-
tablish extirpated populations had become a centerpiece of conservation efforts around the
globe. The more populations were spread across their historical range, the theory goes, the
greater was the likelihood for the species to adapt to new or changing conditions. Creating
a second and even a third rhino population within their former range could be an important
hedge against local extinction. As a rule of thumb, conservation biologists advocate that at
least ten populations of an endangered mammal species be established initially, with at least
100 founders in each, to reduce the threat of extinction. More than two hundred years ago,
rhinos roamed across the Bardia and Suklaphanta reserves in the far western part of Nepal's
