motion an evolution of lek behavior such that lekking
is now more readily explained by phylogenetic history
than by any immediate selection pressures. Prum,
perhaps a bit tongue in cheek, writes, “For manakins
and a large majority of the lekking birds, the proximate
answer to the ‘paradox’ of why they breed in leks is
because their parents did; the ultimate answer lies in
the ancient past when these behaviors initially evolved.”
There are many areas in the Neotropics where you
can directly observe various manakin and cotinga
species at their leks, engaging in their sexual- selection-
driven behavior. Bearing witness to courting manakins,
bellbirds (chapter 15), and cock- of- the- rocks is one of
the outstanding opportunities awaiting the Neotropical
naturalist (plate 10- 24).Fish as Amazonian Seed Dispersers
Fish disperse seeds? That might seem impossible but
is far from it. It all has to do with the flood cycle, an
annual event throughout Amazonia.
Floodplain forests within the Amazon Basin cover
an area of approximately 150,000 km^2 (58,000 mi^2 ),
which is roughly equivalent to the size of the state
of Florida. Called várzea in Amazonia (chapter 12),
floodplain forests are inundated by the annual flood
cycle. Depending upon location, floodplain forests
may be submerged anywhere from two to 10 months
of the year. The Amazon forest itself (from Manaus
eastward), for example, is flooded for about six months,
whereas the upper Rio Madeira is in flood for only two
to five months annually.
Michael Goulding, a reigning expert on Neotropical
fish, estimated in the 1980s that there are more than
2,400 fish species inhabiting the waters of the Amazon
and its tributaries, and up to 800 additional species may
remain yet to be formally described. Approximately
40% of the species thus far described are members
of two groups, characins (family Characidae) and
catfish (order Siluriformes, numerous families), and
many among these multitudes include favorites of the
aquarist.
During the flood cycle, fish have direct access to
forest. Many become fruit and seed consumers and
some act as important seed dispersers. Goulding
estimates that approximately 200 species of fish
consume fruits and seeds in Amazonian waters, far
more species than do so in tropical Africa or Asia. Afrugivorous diet is facilitated by the flood cycle, which
enables fish to swim well within the gallery forest
and forage for dropped fruits, many of which float at
the surface, making them easy to find and consume.
There is a seasonal shift in diet among characin species
in which they move from an omnivorous diet that
includes zooplankton and various plants and algae to
essentially a diet of fruit when the forest is flooded.The Tambaqui
The Tambaqui (Colossoma macropomum) is an
inhabitant of blackwater rivers and igapo forests
(flooded forests on poor soil). This bass- like fish is
an important seed disperser, particularly for Hevea
spruceana, a rubber tree, and Astrocaryum jauari,
a palm species. Both of these tree species are widely
distributed, are relatively abundant, produce large
seed crops, and have fruits that are laden with fat and
protein but that are encased within hard nuts that many
animals are unable to break. The seeds of the rubber
tree are contained in large capsules that eventually
pop open and effectively toss their seeds as far as 20 m
(66 ft). The seeds float, and Tambaquis gather around
rubber trees where seeds are being released.
The Tambaqui is an oval- shaped characin, weighing
as much as 30 kg (66 lb), and has specialized, rounded,
molar- like teeth capable of crushing and grinding
very hard fruits. Tambaquis feed almost exclusively on
fruits for the first five months of the flooding season.
The fruits contain sufficient protein and fat that the
fish is able to survive during periods of low water from
fat stored during its flood cycle fruit consumption.Plate 10- 24. Wire- tailed Manakin male celebrating the family
tradition of display. Photo by Andrew Whittaker.chapter 10 tropical intimacy: mutualism and coevolution 169