6 Stefan A. Schnitzer and Walter P. Carson
ANIMAL COMMUNITY ECOLOGY
AND TROPHIC INTERACTIONS
Although community-level theories in tropical
ecology are most commonly tested with plants,
they can also be addressed using animals. For
instance, in this section, Dyer (Chapter 16)
explores the complexity of tritrophic interac-
tions and argues compellingly that the empiri-
cal basis for much conventional wisdom within
tropical community ecology remains “largely
untested.”This includes such standards as tropical
consumers are more specialized and that
predation is more intense in tropical habitats.
Dyer reviews the diversity of trophic cascades
and identifies the shortcomings of previous stud-
ies. He provides a clear roadmap to how future
research will need to integrate solid natural his-
tory, phylogenetics, modeling, and experimental
approaches.
Theimer and Gehring (Chapter 17) examine
the tritrophic interaction among terrestrial
vertebrates, tree seedlings, and mycorrhizal
fungi using a vertebrate exclusion experiment
in an Australian tropical forest. They report
that after nearly 5 years, vertebrates reduced
seedling species richness via increased rates
of density-independent mortality, and concomi-
tantly increased arbuscular mycorrhizal fungi
richness via spore dispersal. The authors propose
a conceptual model to address how these complex
opposing but interrelated effects can alter forest
community dynamics and diversity.
Terborgh and Feeley (Chapter 18) exploit
an excellent model system of predator-free
fragmented forests on small islands in Venezuela
to explore the role of complex trophic
cascades among plants, herbivores, and their
predators. Their results “strongly supported the
hypothesis of Hairston, Smith, and Slobodkin,”
which posits that regulation by predators prevents
herbivores from decimating plant populations.
Nevertheless, Terborgh and Feeley ultimately
conclude that trophic cascades are “far more com-
plex than implied by simple [tritrophic] models”
and that “plant composition is established and
maintained by...numerous interaction links...
between plants and animals.”
Adler (Chapter 19) also examines forest frag-
ments on small islands to evaluate top-down
versus bottom-u pforces in central Panama. Adler
finds that when predators are absent, herbivores
(spiny rats) can be resource limited, even in times
of resource abundance. He argues that fragmen-
tation will increase conditions where predators
are absent, leading to strong trophic cascades. His
take-home message: “attempts to categorize her-
bivore populations as being limited solely by either
top-down or bottom-up processes are likely to fail”
because both processes operate, but their relative
strengths vary seasonally.
Why are arboreal ants the most dominant
arthropods of tropical forest canopies in terms
of abundance and biomass? Davidson and Cook
(Chapter 20) address this and other sizeable ques-
tions using the unique approach of ecological
stoichiometry, which is the elemental balances
(and imbalances) between an organism and its
food. The authors use this framework, combined
with knowledge of ant digestive anatomy and
function, to examine interactions among different
ant functional groups and between ants, plants,
and trophobionts.
Utilizing an extensive neotropical dataset, Peres
(Chapter 21) provides one of the first large-scale
tests of the theory that mammalian biomass is
directly correlated with soil fertility, which drives
plant productivity and food quality (Janzen 1974).
Peres’s data support this theory and he provides a
predictive model for estimating primate biomass,
abundance, and diversity along gradients of soil
fertility. He then extends the model to other conti-
nental vertebrate communities, urging ecologists
to continue to link “soil processes to vertebrate
populations...at large spatial scales.”SECONDARY FOREST
SUCCESSION, DYNAMICS, AND
INVASION
In this section, Peterson and Carson (Chapter 22)
review and identify the major constraints on
woody species colonization into pastures and call
for studies that test broad general hypotheses of
species turnover. They find that most temperate
models of succession fail to apply in tropical