The New Neotropical Companion

for one individual to defend the resource, excluding

all others. Therefore it is not surprising to encounter

flocks of tanagers, parrots, or toucans. Fruit- eating

mammals also tend toward sociality. Pacas, coatis, and

peccaries are organized in bands and herds.

Because fruits are generally easy to locate and require

virtually no “capturing” time and effort, frugivorous

birds tend to have much free time. The male Bearded

Bellbird (Procnias averano), a South American species

that is entirely frugivorous, spends an average of 87%

of its time on a perch in the forest subcanopy or canopy

calling females to mate (see “Fruits: The Evolutionary

Stimulus for Sexual Selection,” below). Another South

American frugivorous bird, the male White- bearded

Manakin (Manacus manacus; plate 10- 9), spends 90%

of its day courting females!

The Abundance of Frugivores

Frugivorous birds are more abundant per species

compared with insectivorous species because fruit

biomass is typically high and therefore supports high

populations of fruit- consuming species. Insects, on the

other hand, are widely dispersed, often difficult to find

and capture, and represent far less overall biomass, so

insectivorous populations are smaller. In one area of

rain forest in Trinidad, David Snow netted 471 Golden-

headed Manakins (Ceratopipra erythrocephala) and

246 White- bearded Manakins, a total of 717 birds.

In this same area he caught 11 species of tyrant

flycatchers (most of which are strongly if not entirely

insectivorous), but their combined abundance did not

equal that of the two frugivorous manakins. Flycatchers

must focus on a more narrow resource spectrum that

requires them to search, locate, and capture their prey.

But not all flycatchers catch flies. A study by Barbara

Snow and David Snow of the Ochre- bellied Flycatcher

(Mionectes oleagineus; plate 10- 10) on Trinidad showed

that the species is undergoing a major evolutionary

diet shift. Though it is a tyrant flycatcher, it now feeds

almost exclusively on fruit. The Ochre- bellied is the

most abundant forest flycatcher in Trinidad, and its

numerical success is attributed to its diet of fruit. The

Snows hypothesized that as the resource base for the

Ochre- bellied Flycatcher expanded, its population

increased.

Studies throughout the tropics confirm the high

biomass of frugivorous bird and mammal species in

lowland humid forest. This is not surprising. Theodore

H. Fleming and colleagues determined that between

50 and 90% of tropical trees and shrubs (depending on

the site) have seeds primarily dispersed by frugivorous

vertebrates. True, there are fewer frugivorous species

overall than insectivorous species, but nonetheless

somewhere between 80 and 100 species of primarily

frugivorous primates, bats, and birds typically occur in

forest sites ranging from Central America to Amazonia.

Plate 10- 9. The White- bearded Manakin spends the majority

of its time courting females. This one appears to be awaiting a

female to court. Photo by John Kricher.

Plate 10- 10. The Ochre- bellied Flycatcher, here part of a bird

banding study in Belize, is unusually abundant, presumably

because it has shifted to a diet primarily of fruit. Photo by

John Kricher.

chapter 10 tropical intimacy: mutualism and coevolution 159