a lot of fruit consumers. None of these groups can
exist successfully outside of the tropics, since they are
so dependent on constant availability of nectar and/or
fruit.- Army ants are a unique resource in the Neotropics in
that their activity provides the food base for a complex
group sometimes called “professional antbirds,” species
that follow army ant swarms to feed on the arthropods
driven out by the ants (plate 9- 16). Many other bird
species, though not as specialized, nonetheless also
become active feeders on the arthropods at ant swarms. - Forest gaps also represent a resource. Gaps are a
characteristic of all forests, but tropical forest gaps may
present more opportunities to specialist species than
those outside of the tropics. Gaps occur frequently
in tropical lowland forests and their frequency alone
would serve to allow many species to become gap
specialists. Gap dynamics is discussed in greater detail
in chapter 7.
Do additional resources translate into ecological
specialization? Specialization occurs when a species
becomes uniquely adapted to a narrow resource
base. Ecologists say that specialist species have
narrow ecological foraging niches. (The word niche
in the parlance of ecology means in essence how a
species makes its living.) For example, the evolution
of specialization in the diet of the Black- and- white
Owl (Ciccaba nigrolineata; plate 9- 17) is rooted in the
abundance of Neotropical bats inhabiting rain forest.
This owl species, which ranges from southern Mexico
to northwestern Peru, is a bat specialist, feeding almost
entirely on the furry flying mammals. Another species,
the crepuscular Bat Falcon (Falco rufigularis; plate 9-
18), also specializes to a degree in bat capture, feeding
on the flying mammals at dawn and dusk. There are now
equivalents to these species outside of the tropics.
Bamboo stands, which are patchy resources
irregularly distributed throughout the Neotropics, allow
for specialization (plate 9- 19). Van Remsen and the late
Ted Parker surveyed Amazonian bamboo stands, in
which plants reach heights of up to 15 m (50 ft). These
stands supported as many as 21 bird species specialized
in some way to feed exclusively within bamboo stands.
Nine species specialized on eating bamboo seeds, and
12 were insect foragers. An additional 16 species of
insect- foraging birds were found mostly in bamboo but
also in other habitats.
Ephemeral Amazonian river islands of sandbar scrub
and young successional forests (chapter 12) provide
Plate 9- 19. Amazonian bamboo stands such as this are habitat
for several bird species that occur nowhere else. Photo by
John Kricher.Plate 9- 17. The Black- and-
white Owl forages heavily
on bats. Photo by Kevin
Zimmer.Plate 9- 18. The well- named
Bat Falcon, one of the smallest
of the world’s falcons, also
focuses its diet largely on bats.
Photo by James Adams.Plate 9- 20. This is a Ladder- tailed Nightjar (Hydropsalis
climacocerca) on its nest on a riverine sandbar in Ecuador. This
nocturnal species is not a “sandbar specialist,” but nonetheless it
uses sandbars for breeding real estate. Photo by John Kricher.chapter 9 why are there so many species? 145