absent from Reserva Ducke, presumably because of the
poor soil conditions at that particular site.
The similarities among these four geographically
separated forest sites are as compelling as the differences.
The dozen most well represented plant families were
essentially the same in each of the sites. The legume
family (Fabaceae), for instance, had the most species
richness of any family at BCI, Cocha Cashu, and Ducke,
and was the fifth most species- rich family at La Selva. Of
the total of 153 vascular plant families represented in at
least one of the four sites, 66 (43%) were represented at
all four sites, a high overlap. What this suggests is that
essentially the same array of plant families has speciated
throughout the vast area of the Neotropics.
Animals Also Exhibit High Species
Richness
The prodigious number of plant species is rivaled by
the amazing species richness of many animal groups.
Insects, spiders, birds, toads, frogs, tree frogs, and
mammals exhibit amazingly high species richness in
the Neotropics.
Colombia is estimated to contain nearly 1,900 bird
species, while Ecuador has approximately 1,600, and
Peru has 1,800. In comparison, there are approximately
800 bird species found in all of North America north
of Mexico. At Cocha Cashu Biological Station in
Amazonian Peru, an area of approximately 5,000
ha (12,355 ac), the total bird species list tops 550. At
La Selva Biological Station in Costa Rica, an area of
approximately 1,500 ha (3,700 ac), 410 species of birds
have been found. Yes, you read that correctly. At La
Selva the total bird list equals about half the number
of species found in all of North America. Observers
at Explorer’s Inn Reserve in southern Peru have seen
about 575 bird species within an area of approximately
5,500 ha (13,590 ac). This area may contain more
species of birds per hectare than any other in the world.
Why do more bird species occupy the Neotropics
than the temperate zone? The general answer is rain
forest. In a study done by Eliot Tramer in 1974 that
looked at bird species richness within grids of equal
sizes that covered North America, Central America,
and northern South America, it was obvious that bird
species richness took a major jump when the grid
contained rain forest. Simple as that. Want birds? Visit
rain forest (plate 9- 2).
Amphibians are represented in the Neotropics
mostly by anurans, the toads, frogs, and tree frogs,
and there are lots of species (plate 9- 3). At one site in
the Ecuadorian Amazon, William Duellman found 81
species of frogs. That is exactly how many species occur
in all of the United States. Indeed, Duellman collected
56 different species on a single night of sampling and
reported that it is routine to find 40 or more species in
areas of rain forest as small as 2 km^2 (0.75 mi^2 ).
Insect species richness in the Neotropics is staggering
(plates 9- 4– 5). For Costa Rica, not a large country, Philip
DeVries describes nearly 550 butterfly species. At La
Selva alone, 204 butterfly species have been identified.
At BCI in Panama 136 species have been documented.
At Explorer’s Inn Reserve in southern Peru, a staggering
1,234 butterfly species have been identified from an area
about 2 km^2 (0.75 mi^2 ) within the reserve.
In an oft- cited study from 1987, Edward O. Wilson
reported collecting 40 genera and 135 species of ants
from four forest types at Tambopata Reserve in the
Peruvian Amazon. Wilson noted that 43 species of ants
were found in one tree, a total approximately equal to
all ant species occurring in the British Isles.
In Panama in the early 1980s, Terry Erwin famously
used a fogging technique to extract insects from the forestPlate 9- 2 The Jocotoco Antpitta (Grallaria ridgelyi) was
discovered only in 1997. Its range is restricted to a few areas
in southeastern Ecuador and Peru. A fairly specialized species,
it inhabits wet forests at elevations between 2,250 and 2,700
m (7,380– 8,860 ft). At some of these places naturalist- guides
have acclimated these birds to come for earthworms, so
ecotourists and birders can glimpse this unique species. Look
carefully at the photo and notice the earthworms used to coax
the normally secretive bird into the open. Photo by Edison
Buenaño.136 chapter 9 why are there so many species?