EARTHWATCH INSTITUTE
FIELD REPORT
Section I: UNEP- WCMC Weblink Information
Project
Title:
Principal
Investigator: Lee Dyer
Position/Affiliations:
Professor,
E-mail
address: ldyer@tulane.edu
Research
Sites and Local Management Status:
Scientific
names of primary species being studied (if appropriate):
Lepidoptera,
Hymenoptera, Diptera, Angiosperms, Nemata
Key
Research Objectives (5-8 brief bullet points):
· Are tropical caterpillars more specialized than temperate caterpillars?
· What affects diversity and abundance of caterpillars and parasitoids in natural forests and adjacent agriculture (banana and alfalfa)?
· What parasitoids might be good candidates for biological control in banana plantations and alfalfa fields?
·
How do variation
in precipitation and temperature affect levels of parasitism (and subsequently
affect caterpillar densities)?
Date
this report was completed: 21 March,
2007
Data
Collection and Results
Diversity and caterpillar
specificity
For many animals, species richness is much
higher in tropical compared to temperate habitats. A major challenge in
community ecology and evolutionary biogeography is to determine what creates
these differences. For herbivorous insects, one such mechanism leading to an
increased number of species in a given locale could be increased ecological
specialization, resulting in a greater proportion of insect species with narrow
resource requirements within a community. We used data from all of our
Earthwatch sites along with collaborators’ data to test this hypothesis by
comparing host specialization in larval Lepidoptera (moths and butterflies) at
eight different
We found that diets of
tropical caterpillars are more specialized than their temperate forest
counterparts: tropical species on average feed on fewer plants species, fewer
plant genera, and fewer plant families than do temperate caterpillars (Figure
1). This contrasts recent studies (by V. Novotny) that suggest that tropical
herbivores are not more specialized and that conclude that there are fewer than
4 million species of animals in the world (compared to estimates of 30-80
million species made with the assumption that tropical herbivores are
specialized). The Novotny study used only 8 focal species of plants, which can
yield misleading results (Figure 1).
Table 1. Caterpillar rearing databases used for the
current study. Rearings include only those portions of the databases used for
analyses in this study. Sampling area was estimated for
|
Study Site |
Median Latitude |
Sampling Area (ha) |
Rearings |
Caterpillars (fam, gen, spp) |
Host Plants (fam, gen, spp) |
Effort (hours) |
Years |
|
47° 15’ N |
80,000,000 |
131,431 |
28, 280, 653 |
27, 59, 155 |
Unknown |
20 |
|
|
|
41° 30' N |
1,437,100 |
3,158 |
19, 166, 252 |
12, 13, 14 |
Unknown |
5 |
|
|
32° 13’ N |
1,000,000 |
7,601 |
20, 136, 184 |
50, 104, 161 |
9,000 |
10 |
|
|
31° 00’ N |
500,000 |
2,300 |
19, 98, 127 |
48, 77, 106 |
5,000 |
6 |
|
|
15° 56’ S |
10,000 |
5,614 |
43, 264, 565 |
44, 80, 109 |
8,000 |
12 |
|
|
10° 25' N |
2,400 |
22,348 |
29, 223, 509 |
72, 176, 281 |
52,000 |
15 |
|
|
9° 10’ N |
1,600 |
4,536 |
30, 384, 401 |
57, 139, 209 |
8,000 |
9 |
|
|
0°
25’ S |
30,000,000 |
24,413 |
13, 65, 192 |
53, 110, 177 |
72,000 |
6 |
|
|
Figure 1. Mean caterpillar diet breadth (± 95%
confidence intervals) for 1052 temperate caterpillar species (TEMP) from two
subtropical and two temperate sites and 1585 tropical caterpillar species
(TROP) from four sites in Central and South America. Diet breadth was
measured as the number of taxa (families, genera, species) of host plants per
caterpillar species. When eight focal host plant species were chosen randomly
from each site, to reflect previous diet breadth studies, the difference
between temperate (TEMP8) and tropical (TROP8) diet breadths are greatly
reduced. |
As a result of the increased specificity, there
is greater change in caterpillar species composition (greater b diversity) between tree
species in tropical faunas than in temperate faunas – this means that you are
more likely to find the same caterpillar species on different plants at the
We concluded that host plant specificity of
herbivorous insects is, on average, greater in the tropics than at higher
latitudes, and that a latitudinal gradient of dietary specialization is evident
from our data. The evidence from this study is consistent with the hypothesis
that ecological specialization is a factor in the origin and maintenance of
high biodiversity in the tropics. Our previous Earthwatch results have
indicated that this increased specialization in tropical herbivore communities
may be due to more intense parasitism from wasps and flies and more toxic host
plants – a specialized diet helps tropical caterpillars avoid these pressures.
The underlying mechanisms for differences in specialization by latitude, and
perhaps by longitude, will continue to be a focus of our Earthwatch research.
While it is clear that a significant proportion of tropical animal diversity is
a product of a higher number of plant species, our results also imply that
greater ecological specialization contributes to the great diversity of
herbivores in rainforests and lends support to higher estimates of the total
number of species on earth.
|
|
Figure 2. Diversity (β) of herbivores between
plants for two temperate ( |
Significance/Benefits of Research
Diversity
and natural history
Our most
significant accomplishment in 2006 is the compilation of natural history data
related to approximately 3200 species of caterpillars, plants, and parasitoids.
We share this natural history information with locals and scientists alike,
including talks in Spanish to Costa Rican and Ecuadorian students, naturalists,
and local workers; the local talks have increased awareness and respect for
insect diversity. Many of the naturalist guides at our research sites use our
data and images and find caterpillars during their tourist walks to discuss the
role they play in the forest. We also share these data with anyone who has
internet access by publishing it on caterpillar web pages at www.caterpillars.org. The web pages are constantly
undergoing improvements and should be a very useful tool for managing and
studying biodiversity for many years to come. In addition, our basic research
on diversity relationships between trophic levels will contribute to a growing
understanding of how parasitoids and other natural enemies affect entire biotic
communities.
Sustainable
agriculture
Managers of
banana plantations, alfalfa fields, and other agricultural systems who are
attempting to control pests without using pesticides will benefit from
increased knowledge of the parasitoid community. First, we discovered at least 35
new species of parasitoids in the families Braconidae and Tachinidae, all of
which are potentially important biological control agents. Second, our modeling
approach is being used to identify the most important biological control agents
in tropical agriculture under different pesticide management, which allows
plantation owners to manage for caterpillar pests without resorting to harmful
insecticides.
Sustainable
employment in the rainforest
Although it is not a direct benefit from the research, our
Earthwatch project benefits the local communities by supporting the research
stations and by continuing collaborations with local naturalists and
scientists. Field stations generally benefit the communities by providing
excellent employment opportunities that are not destructive to the forest and
by boosting the economy. At the
Environmental
education
Finally, our work has directly benefited the educational community
because many volunteers have been school teachers and have incorporated ideas
learned from this project into their classes. In collaboration with volunteers
on the
Dissemination
of Results (all publications
below are available in pdf format at: http://www.tulane.edu/~ldyer/papers.htm)
Peer reviewed articles and book chapters
Dyer, L.A.,
M.S. Singer, J.T. Lill, J.O. Stireman III, G.L. Gentry, R.J. Marquis, R.E.
Ricklefs, H.F. Greeney, D.L. Wagner, H.C. Morais, I.R. Diniz, T.A. Kursar, and
P.D. Coley. Revised, in review. Host
specificity of Lepidoptera in tropical and temperate forests. Nature.
Dyer,
Dyer,
Dyer,
Presentations
University
of
Organization
for Tropical Studies, 2007
Section II: Volunteers
Earthwatch
will send Section II to the volunteers who worked on your project. It will not be used on the UNEP-WCMC web site.
Cover Letter to Volunteers (please see next page)
March 1, 2007
Dear Volunteers,
I am writing this letter from my office in
uptown
I have been impressed with the amount of
high quality data that Earthwatch volunteers have collected with us over the
past 10 years. I am sure that I will continue leading this research for at
least 20 more years, and I hope to keep discovering new species and new
associations. Perhaps the most important paper that we have completed from
these data is our paper that is currently in review to the journal Nature. We found that diets of tropical
caterpillars are more specialized than their temperate forest counterparts. We
hope that this paper helps resolve issues about how diversity is maintained and
debates about how many species of animals are on earth. We have also been
making improvements to the webpage (caterpillars.org), including extensive
plant species pages for
If you are wondering about the rest of the
team of plant/caterpillar/enemy investigators, feel free to send an email
asking for their addresses. The Ecuadorian gusaneros, Maria, Rafael, and Wilmer
are all still working on the project, collecting and rearing amazing numbers of
caterpillars. Beto, Gerardo, Grant, Genoveva, Angela, Tara, Clark, Michael, and
Mark are still working full-time with me on various projects, including the
caterpillar work. Mike Singer is still
in
I would like to thank all of you for your
hard work. As an extended team, we have a strong database and positive memories
of great people. My collaborators and I have enjoyed working with the
volunteers, and our project would not be successful without your help. We also
want to thank all of you for sending us great emails, cards, pictures, slides,
and other thoughtful items. We definitely appreciate this correspondence.
Please feel free to keep in touch and we will do our best to respond. Hopefully
we'll see you again in the field.
Saludos,
Lee Dyer, gusanero, ldyer@tulane.edu
Volunteer Tasks and Accomplishments
In
our 10th year of funding by Earthwatch, we were fortunate to have
the help of 49 volunteers. These volunteers helped us bring our rearing total
up to approximately 2100 species of butterflies and moths (35,000 individuals),
over 400 species of parasitoids, and 750 plant species. The 10 teams participated in
all aspects of our Forest Caterpillars project. Team members searched for and
collected caterpillars, noted possible morphological or behavioral characters,
and took care of the larvae. At La Selva, Tirimbina, and Yanayacu they also
assisted with experiments on the understory pepper plants, Piper spp.
and helped with encapsulation experiments. In
The 10 teams logged over 2000 total person
hours in the field, searching for and recording data on caterpillars and
working on related experiments. At La Selva and Tirimbina, they found over 1400
caterpillars belonging to 85 butterfly and moth species in 24 families; at
least 12 of those were new species. From these caterpillars they reared over 20
species of parasitoid wasps and flies. At the Southwest Research Station,
volunteers collected 400 individual caterpillars for a total of 40 species in 15
families. At least 12 species of parasitoids were reared. The teams in Ecuador
contributed to our NSF funded biotic survey and inventory of the eastern slope
of the Andes, collecting 2200 caterpillars, including 90 species in 19
families, and a couple dozen new species. The site will continue to yield many
new species of caterpillars and parasitoids (Figure 3). The host plant data at
our 4 Earthwatch sites were used in our important new finding that tropical
caterpillars are more specialized than temperate caterpillars.
|
|
Figure 3a. Two
potentially new species in the family Sphingidae. These rare caterpillars
were parasitized, so unless we find them again, they will not receive a scientific
name. Yanayacu Biological |
|
|
Figure 3b. Cryptic geometrid
caterpillars from the Southwest Research Station, |
|
|
|
Figure 4. This new
species of tachinid fly, Hyphantrophaga
sp., emerged from an unknown skipper
(Hesperiidae) caterpillar that it had parasitized. More information on
this species is published on caterpillars.org, under the |
Project Development
The data we have collected thus far at all sites support our hypotheses that the dynamics in these strikingly different habitats (Arizona, Ecuador, Costa Rica, Louisiana) are very similar, but the actors are different — species composition of the caterpillars and their parasitoids show very little overlap. The larvae that we studied exhibited a wide array of defenses, and we continued a focus on two specific defenses: frass-throwing and encapsulation. Several more years of data will allow us to make conclusions about how these defenses function against different types of parasitoids. For all sites, we will continue to focus on collecting new species (Figure 4), but we will also focus more on altitudinal gradients in parasitism, similar to the precipitation gradient that we’ve tested.
Educational Opportunities
Educational opportunities were provided to:
- Local communities.
We employed six local naturalists and gave talks to local residents at all
of the research sties.
- Students. Nine graduate
students in Dyer’s laboratory participated in the projects, either
directly or by analysing data and working on papers. Seven undergraduates were also involved
with the Earthwatch research. One PhD dissertation was completed with help
from the Earthwatch funded work.
- Early career
scientists. One post doctoral researcher (Gentry) and three Assistant
Professors (Walla, Stireman, Singer) helped run Earthwatch teams.
Our Earthwatch project has
united workers from
Acknowledgements
Research assistants:
Costa
Rican paraecologists: Gerardo Vega, Humberto Garcia, Maylin Paniagua
Ecuadorian paraecologists: Rafael Maitio, Wilmer Simbana,
Maria de los Angeles
Graduate
students: Angela Smilanich, Malia Fincher, Michael Olson, Clark Pearson, Tara Massad,
Genoveva Rodriguez, Kathleen Burke, Heidi Connahs, Rebecca Hazen
Collaborators:
Dr.
John Stireman,
Dr.
Mike Singer,
Dr.
Grant Gentry,
Dr.
Craig Dodson,
Dr.
Thomas Walla,
Dr.
Daniel Janzen,
Dr.
Deborah Letourneau,
Harold
Greeney, Yanayacu Biological Station
John
Lill,
Robert
Marquis,
Robert
Ricklefs,
David
Wagner,
Helena
Morais,
Ivone
Diniz,
Phyllis
Coley, Smithsonian Tropical Research Institute
Tom
Kursar, Smithsonian Tropical Research Institute
Jim
Whitfield,
Scott
Shaw,
Phil
DeVries,
Cooperating Institutions:
Organization
for Tropical Studies
Grants from additional funding
sources:
National
Science Foundation – Ecology
National
Science Foundation – Biotic Surveys and Inventories
National
Geographic
United
States Department of Energy, National Institute for Climate Change Research