Gradients in plant-herbivore interactions involving tropical systems
Organized by:
 Robert Marquis, Dept. Biology, University of Missouri-St. Louis
 Karina Boege, Universidad Nacional Autónoma de México, Instituto de Ecología
The goal of this symposium is to provide an overview of the current available
information regarding patterns in plant herbivore interactions, and their interactions with
the natural enemies, among tropical habitat types and biomes, and across latitudinal
gradients that include tropical systems. In so doing, our aim is to present, and when
possible test hypotheses about what factors control populations of tropical insect
herbivores and their species richness, and the resulting impact of those herbivores on host
plant populations and plant communities. Although these questions have addressed at
individual locations, few cross location studies have been performed. Thus, we have only
limited information about how habitat type, successional stage, annual rainfall, soil
nutrient status, elevation, and latitude contribute to what happens locally. Comparative
studies are becoming sufficiently numerous to allow such comparisons. By bringing
together researchers who are making such comparisons our intention is to gain insight
through comparison, discussion, and meaningful synthesis of current results, and to
inspire future research using this approach.
Herbivores and herbivory across two soil types in a Borneo rain forest
Markus P. Eichhorn1
1
University of Nottingham.
email: markus.eichhorn@nottingham.ac.uk
The role of herbivory in segregating species between soil types within rain forests is
poorly understood and theoretical predictions are often conflicting. The Biological
Interactions in Tropical Rain Forests (BITRF) project planted five species of dipterocarp
tree seedlings in experimental plots on two soil types in both gaps and understorey.
Seedlings on sandstone soils had greater concentrations of foliar phenolics and lower
nitrogen than on alluvial soils, but insect herbivores were apparently unable to distinguish
between leaves from plants grown in sandstone and alluvial soils in trials. Insect
herbivores on the seedlings had reduced abundance and species richness on sandstone
soils. Nevertheless, herbivory rates on the two soil types were equivalent over two years,
with no evidence of differential impacts on growth or mortality.
keywords: Herbivory; insect; dipterocarp; soil type; specialisation
Leaf herbivore richness and diversity on plant species in burned and
unburned plots in the Brazilian Cerrado
Ivone R. Diniz, John D. Hay, Helena C. Morais, Cintia L. Gonçalves, Bárbara F.
Higgins
Universidade de Brasilia
Email: jhay@unb.br
This study examines the effect of fire frequency and time of year on Lepidopteran larvae
on species of host plants in the Cerrado. The following questions were raised: Is
abundance and species richness higher in burned areas? Does species composition vary
among areas? The study was done in central Brazil with following treatments: 1)
occasional fires (intervals of 7 and 11 years), 2) biennial fire in August (mid dry season),
and 3) biennial fire in September (end dry season). For both biennial sites, the fire regime
started in 1992. At the occasional fire site, two species of Erythroxylum
(Erythroxylaceae) were studied using 1000 individuals of each species. At the biennial
sites we studied Byrsonima coccolobifolia (Malpighiaceae) using 900 individuals in each
area. Results were compared with nearby protected sites. At the occasional fire site larval
abundance was 2X higher in the burned site but the proportion of parasitism was similar;
species richness was higher in the burned area (37) versus protected (29); three species of
Gelechiidae were the most abundant and were found on both plant species in both areas.
For the biennial fire sites larval abundance in the unburned area was 3.5X (August) to 5X
(September) higher than in the burned sites; larval species richness in the unburned area
(36 spp) was 1.5X and 2.6X higher than in the burned areas; the fauna varied between
areas with predominance of rare species and Elachistidae in the unburned area and
predominance of Noctuidae and Elachistidae (Stenoma salome) in both burned areas. The
results indicate that frequent fires drastically reduce the abundance and richness of larvae,
especially in late dry season fires, while occasional fires may be a positive factor for
renewing and maintaining Lepidoptera diversity in the Cerrado.
Keywords: Lepidoptera, fire, disturbance
Ant-plant-herbivore interactions and the divergence in the defensive
ecology of Inga between two Neotropical sites
Tania Brenes-Arguedas 1, Phyllis D. Coley 2 and Thomas A. Kursar 2
1
Smithsonian Tropical Research Institute
2
University of Utah
Email: taniabrenes@gmail.com
Plants have evolved a diverse array of defensive adaptations which can vary widely
among populations due to differences in the environment. It has been hypothesized that
seasonality correlates inversely with pest pressure and thus plant defensive investment.
We provide evidence that differences in ant and herbivore abundance between two
communities influence the divergence and types of defensive strategies in 18 species of
the genus Inga (Fabaceae: Mimosoideae). We compared chemical and ant defenses in
Inga at two sites: the aseasonal Amazonian forest of Yasuni, Ecuador and the seasonal
forest of Barro Colorado Island (BCI), Panama. Because ant abundance was 2.5 times
higher at Yasuni, Yasuni Ingas relied more on ant defenses and leaf extracts were on
average 50% less bioactive than at BCI. Bioactivity of Yasuni Ingas varied widely among
species and was negatively correlated with ant visitation. In contrast, due to low ant
abundance, most species at BCI had low ant visitation and high bioactivity. Reciprocal
transplants with I. spectabilis suggest that Ingas experience higher herbivore pressure at
Yasuni. However, leaf damage was similar both between sites and among most species,
indicating that different defensive strategies were equally effective. These results suggest
that ant abundance, potentially linked to seasonality, drives the defensive strategies
expressed by Inga species and promotes defense diversity within the genus.
Keywords: Inga, herbivory, ant defenses, chemical defenses, trade-offs
Is seasonality a driver of herbivory and defense?: A comparison
between tropical dry and rain forests
Karina Boege1 and Rodolfo Dirzo2
1
Instituto de Ecología. Universidad Nacional Autónoma de México
2
Stanford University
Email: kboege@servidor.unam.mx
Herbivores can have a significant impact on plant fitness and thus represent a selective
force for the evolution of plant defenses. However, plant phenology can influence such
impacts by determining the availability of foliage for herbivores and the risk of herbivore
attack. We developed a conceptual model to predict how rainfall seasonality, and as a
consequence leaf phenology of tropical rain forest (TRF) and tropical dry forest (TDF)
plants bring about contrasting patterns of herbivory and defense in these two tropical
ecosystems. We predicted that higher constancy of foliage, implying greater risk and
impact of herbivory in aseasonal TRF plants, may lead to a greater evolutionary history
of herbivory selecting for increased defense and lower herbivory than in plants of TDF
with a marked rainfall seasonality. The predicted patterns were evident when we
controlled for interspecific heterogeneity in herbivory and defense within both TRF (due
to contrasts in life history and growth) and TDF (due to contrasts in phenology).
Analyzing the available data in the literature and from our own ongoing work, we found
that damage of TDF deciduous species was two-fold greater than that of slow-growth
TRF species. The leaves of slow-growth TRF had twice the concentration of total
phenolics and were 10-times tougher than leaves of deciduous species from TDF. In
addition, the expected patterns were mirrored using controlled intra-site (dry forest)
comparisons looking at plants of contrasting phenologies. We found that TDF deciduous
species had 2.8 times greater herbivory than evergreen species. We also found that the
later had 60% greater concentration of total phenolics and their leaves were two-fold
tougher than the former. In consistency with our conceptual model and predictions, we
found that leaf phenology, as affected by rainfall seasonality, can produce contrasting
ecological and evolutionary outcomes of the interaction between plants and their
herbivores.
Keywords: Herbivory, defenses, seasonality
Role of latitude and phylogeny for plant defense traits in broad-leaved
tree species
Robert J. Marquis1, Robert E. Ricklefs1 and Luis Abdala-Roberts2
1
University of Missouri-St. Louis
2
Universidad Autonoma de Yucatan
Email: robert_marquis@umsl.edu
An often-stated hypothesis is that year-round herbivore attack in the tropics should result
in the evolution of greater defense investment in tropical and than in temperate habitats.
Previous literature surveys demonstrate that plant defense traits are higher in tropical
broad-leaved trees than in their temperate counterparts. However, this conclusion is
potentially biased by lack of control for the effect of host plant phylogeny. We tested for
the effect of latitude while controlling for the effect of phylogeny: we compared a variety
of leaf traits from different tree species of the same family, sampled in Panama (9°
latitude, 31 species) and Missouri (39°latitude, 16 species). We hypothesized that there
would be higher defenses (both physical and chemical) and lower nutrients in leaves of
Panamanian trees than those of Missouri trees. As predicted, physical defenses and
nutritional values were lower in Panama than Missouri: toughness and fiber (both aciddetergent and neutraldetergent) content were greater, and nitrogen lower. However,
neither condensed nor hydrolysable tannins differed between locations, contrary to
expectation. Our results show some support for the idea that herbivore attack throughout
the year results in reduced leaf quality, but mainly through changes in physical characters
and nutrition. Future studies should include sites at multiple latitudes, all while
controlling for phylogeny, to determine whether there is a gradient or in contrast, an
abrupt shifts in leaf quality with changing latitude.
Keywords: herbivory, plant defenses, leaf traits, latitudinal gradients, phylogeny
Latitudinal and climatic gradients in tritrophic interactions
Lee Dyer
Tulane University
Email: orugas@hotmail.com
Tritrophic interactions are expected to be different in tropical communities simply
because of the increased diversity for most taxa at all trophic levels. However, many of
the assumptions about how tropical communities are different from their temperate
counterparts are not well tested and could be incorrect. Utilizing data from large
caterpillar rearing projects around the world and meta analyses from published studies, I
tested the following prominent assumptions for tropical communities: 1) chemical
defenses are more abundant and toxic in the tropics, 2) herbivore specialization decreases
with latitude, 3) predation is more intense in the tropics, and 4) multitrophic mutualisms
are more important for tropical communities. Plant chemical defense, dietary
specialization, and strength of trophic cascades all decreased significantly with latitude.
Gradients in climatic variability and rainfall were the best predictors of parasitism and
other trophic interaction variables that did not vary with latitude. Understanding
mechanisms underlying these gradients will contribute to clarifying issues
about climate change, resiliency of tropical ecosystems, and the origin and maintenance
of high tropicaldiversity.
Keywords: tritrophic, gradients, caterpillars, specialization, parasitism