Biology Reference
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in front of her in 10 minutes. On a second trial a few weeks later, she ate 300 fruits in 50
minutes. Each time, we waited for the seeds to come out the other end.
Kali let us collect her dung each day, and Vishnu, Kancha Lama, and I painstakingly
picked through hundreds and hundreds of kilograms of bright green rhino dung to extract the
shiny black Trewia seeds. The first seeds appeared within 46 hours after ingestion, and the
peak occurred between 60 and 84 hours after Kali ate them. The last whole seed to emerge
took its grand time, appearing 172 hours after intake. Because we knew there are approxim-
ately 3.2 seeds per Trewia fruit, we estimated that about 60 percent of seeds ingested made it
through Kali in the two feeding trials.
Being eaten by a rhino, then, was not a dead end for Trewia seeds, which is a good thing,
given that during the fruiting season as much as 10 percent of the rhino's diet can be Trewia
fruit. It also gave the seeds a brighter future. It turned out that gut treatment and manuring
of seeds had no effect on seed germination. But being encased in giant pillows of dung gave
young seedlings a huge boost over seeds planted in soil.
And where rhinos defecate really matters. Like the rain forest tree seedlings in the Peruvian
Amazon, Trewia sprouts do poorly under the parent tree in the dense forest; they belong to the
caste of seedlings that biologists call shade intolerant. To prosper, they need to be manured
into grasslands exposed to intense sunlight. By planting seeds and seedlings under various
conditions and moving latrines from shade to sun and vice versa, we were able to establish
that rhinos are essential to the survival of Trewia . Clearly, the latrines were a significant phe-
nomenon, not only as a landscape feature but also as a beachhead for woody plants in a sea
of grass.
Giant herbivores shape their world in other ways as well. In the winter months, the rhinos
in Chitwan, for example, shifted from grazing grasses to browsing tender shoots and leaves in
the riparian forest next to the wild cane. During December, the sound of rhinos walking over
saplings of wild avocado trees filled the damp night air. By the end of February, when the
rhinos switched back to grazing, the riverine forest resembled a war zone of flattened wild
avocado trees. Yet rather than dying off, the trees adapted to this abuse. They grew horizont-
ally and sent out new shoots snaking in all directions, like a woody medusa.
What might a rhino-less forest look like? Given the decline of rhinos in so many places,
this wasn't an idle question. We constructed stockades sturdy enough to exclude rhinos. After
three years of protection, we compared tree growth inside the stockades with that in paired
plots where rhinos had enjoyed free access. The results were striking, even to the uneducated
eye. Where the wild avocados were protected, their stems grew straight to the sky; where rhi-
nos worked them over, trees remained stunted. Rhinos do the same to wild rosewood and a
tree genus called Mallotus . In a similar way, elephants suppress silk cotton trees, Asia's ana-
logue of the baobab. If left unattended in a silk cotton grove, elephants will girdle the trees
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