well over 100 at any given time in some places, are
exposed to predation as they cling to an embankment,
but their repeated presence suggests that they are
somehow enhancing their fitness by acquiring a
necessary chemical from ingesting the soil. A total of
28 bird species were observed, all ingesting soil, at one
clay lick— a dirt cliff 500 m (1,640 ft) long and 25– 30
m (80– 98 ft) high— studied by Donald Brightsmith
and his colleagues in southeastern Peru. Up to 1,700
parrots of 17 species visited daily. Research has shown
that, in comparison with soils from other areas, the soil
of clay licks:- has a greater percentage of clay,
- a higher cation exchange capacity (CEC),
- greater quinine binding (quinine is an alkaloid used
to test for absorption of toxins), - greater sodium content,
- lower sand percentage.
Use of collpas correlated closely with the soil’s clay
percentage, CEC, sodium, and quinine binding.
The study showed that sodium was nearly 40 times
more concentrated in the collpa soil, compared with
surrounding soils. Parrots feed on plant material,
particularly seeds and fruits, vegetation that is
poor in sodium content. Clay lick soil had sodium
concentrations of greater than 245 parts per million,
about six times the sodium available in the parrots’
natural foods. That fact alone may go a long way in
explaining why parrots, and perhaps other species,
utilize collpas.
The Ecological Importance of
TermitesTermites are pantropical social insects occurring in great
abundance. Termites are essential to biogeochemical
cycling in the tropics. Like ants and certain bees,
termites are complex social insects that have distinct
castes (workers, soldiers, king, queen). They resemble
ants but are easily differentiated by the termites’ lack
of a sharp constriction between the thorax and the
abdomen. Another important difference is that termites
do not undergo a complete metamorphosis— larvae,
pupae, adult— as hymenopterans (bees, ants, wasps), as
well as many other insect groups, do (fig. 6- 2).
There are about 2,650 species of termites, and the
majority of them occur within tropical and subtropical
latitudes. Termites represent the ancient insect orderIsoptera; their closest relatives are cockroaches and
mantises (also abundant in the tropics). Unlike other
social insects, such as bees and ants, termites are
not haplodiploid (females diploid, males haploid).
All termite individuals, like most other animals, are
diploid. This tells us that termites evolved their complex
societal structure independently of other social insect
groups. Termites occur in all habitats, from rain forest
to grassland, savanna, and mangrove forest.
No one can visit the Neotropics without seeing
termite nests and/or mounds. Basketball- size termite
nests are typically attached to tree trunks and branches
(plates 6- 16– 17). From the rounded, blackish- brown
nests radiate termite- constructed tunnels in which
the workers pass to and from the colony. In addition,
especially in grassland, dry forest, and savannas, cone-
shaped termite mounds, some rising to heights of 2 m
(6.5 ft) or more, erupt directly from the ground (plate
6- 18). Many termite species also nest undergroundFigure 6– 2. The basic life cycle of termites. If you look carefully
at termites around a nest, you will easily see workers and
soldiers and, at various times, winged termites. Termites have
a complex life cycle in which all reproduction is accomplished
by a queen. The queen is always well hidden within the nest.
Reprinted with permission from Kricher, John. Tropical Ecology.
Princeton, NJ: Princeton University Press, 2011.chapter 6 essential dirt: soils and cycling 91