Biology Reference
In-Depth Information
for example, have corrugated, straight-boled trunks and skull-sized seedpods that accu-
mulate around them. I knew each of these majestic “canopy-emergents” along several
miles of trails, like familiar commuters on a bus route—attentiveness no doubt inspired
by fear of falling “monkey pots” and curiosity about why frogs don't use their rain-filled
husks for breeding ponds, as happens with a related Brazilian species. Without con-
sciously counting individuals of this species, I was impressed by their scarcity and real-
ized, because I'd been told most tropical trees are likewise rare, that the total number
of kinds in the forest must be great indeed.
Of course, species richness is most obvious for familiar organisms, and La Selva
bustled with herpetological treasures. During a morning I'd see dozens of strawberry
dart-poison frogs, and the leaf litter buzzed with their territorial calls. Occasionally a
North American wood frog look-alike careened across the trail; with the jumper in hand,
squirming red-and-yellow spotted legs confirmed it was Rana warzewitschii. I'd snatch
little brown frogs, and each time careful inspection disclosed yet another species of
Eleutherodactylus 3 —one with black mask, another with dark flank bars, while a third
was warty and filled my palm. I'd dive on a shiny black snake basking in a sunspot, then
palpate a juvenile smoky jungle frog and an adult narrow-mouthed toad from its stom-
ach. Later, as we greedily drained canteens before heading back for lunch, someone
would say with amazement that almost every frog we'd found was a different species.
Studying all of the roughly 115 species of vertebrate predators at La Selva proved
impossible, but our findings, coupled with previous work, elucidated some details of
their natural history and contradicted prevailing wisdom. 4 Ecologists at the time be-
lieved that more species coexisted in the tropics by having narrower, often unique
niches—and indeed, ocelots do mainly eat rats, harpy eagles mostly sloths and monkeys,
while vampire bats subsist entirely on blood, and some snakes specialize on slugs. We
were surprised, though, by the number of dietary generalists. Eyelash palm-pitvipers
prey on frogs, lizards, birds, mouse opossums, bats, and rodents, while crane-hawks
methodically search nooks and crannies of tree trunks and epiphytic plants, taking
everything from caterpillars and katydids to baby birds. Jaguars consume animals ran-
ging in size from small lizards and armadillos to deer and tapirs.
As in the simpler Chilean predator assemblages, we also discovered unexpected diet
overlap. Jaguars eat sloths, perhaps catching them thanks to the inverted creatures'
puzzling habit of descending from the canopy to defecate, as well as green iguanas that
come down to nest—and because brown vinesnakes and double-toothed kites prey upon
the baby lizards as well, those two-hundred-pound cats might compete with a quarter-
pound serpent and a small hawk for food. Each species thus faces diverse enemies in
an intricate food web, enforcing a perilous uncertainty on rainforest lifestyles. Plants
and animals have evolutionarily responded to these challenges with spectacular adapta-
tions—some katydids, for example, have fake herbivore damage on their leaflike wings.
In fact, our fascination with camouflage, chemical defenses, and other protective mech-
anisms traces to pioneering tropical biologists like Alfred Russel Wallace and his friend
Henry Bates, who discovered mimicry while collecting Amazonian butterflies.
Annoying, even painful incidents inevitably punctuate fieldwork, reminding us not to
take nature for granted. Each trip I slipped on a muddy trail, grasped wildly to break my
fall, and learned anew that some plants come armed with shockingly effective spines.
Fungi grew on camera lenses and beneath my beard, and a nematode under the skin of
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