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This needs to be updated--hopefully soon. 1/8/05
Here are some descriptions of research that I am currently working on.
Process Based CO2 Modeling in a Desert Ecosystem (with
D. R. Bowling)
This was work I had completed this past summer (2003) in the University
of Utah Biology Department Bowling Lab . The
focus of that group is ecosystem ecology, and my task in particular was
to develop a model for belowground carbon dioxide cycling in a desert grassland
field site to the south of Canyonlands National Park. CO2 sensors installed
at 5 and 15 cm for the two dominant plant species showed a marked increase
in CO2 levels during rain events. The intuitive question is why? What
causes these concentrations to increase? In particular, are the increases
driven by physical or biological processes? This research
was an attempt to discover this.
What we found out was that when it rains, the CO2 concentrations increase
because the soil fills with water, effectively trapping the CO2 molecules
from diffusing out. As the soil dries, then diffusion returns as normal.
However soil microbes and root respiration also contribute CO2, as
the rain acts as a biological switch for activity for both. As a result,
using a process based model that incorporates biology can increase the accuracy
of models than just assuming source is of a particular form (such as constant
with increasing depth). What is unknown is the effect of plant roots
on the absorbtion of water-which might dry the soil quicker than what the
model would presume.
This work was presented at the fall meeting of the American Geophysical
to the poster.
Obnoxious Adolescents and Aggressive Adults: Consequences
of Age Structure in Biodiversity Models
This was independent work that I hade done for a class in Tropical Rain
Forest Ecology, specifically looking at current models of biodiversity
and asking the question: "Does incorporating age structure affect total
biodiversity between two species?"
There are two ways to look at biodiversity, and they are different sides
of the coin. One approach is the Null Model advocated by Stephen
P. Hubbel.  In such a model birth and death are all likely equal
processes, with interactions betweeen competing species all equal. The
advantage to such an approach is that one can generate a "fundamental biodiversity
number," allowing one to compare biodiversity
from habitat to habitat. The disadvantage to such an approach is that
it is mathematically dense and a discrete probabilistic model (ugh!)
On the other hand, one can use the principles of Competitive Exclusion
advocated initially by Lotka, and subsequentially by May, Horn and McArthur.
 In a sense, what this does is focus the "lens of biodiversity"
to interactions between competing species. As a result, biodiversity
is maintained by tradeoffs between species (such as one as a better colonizer
whereas the other is a better competitor for resources). The disadvantage
to such an approach is that it is hard to generalize to a range of species
over a habitat.
The compelling need to work on such models is that tropical rainforests
are vanishing rapidly as we speak. Estimates (dated of course), place
rain forests occupying less than 8 million square kilometers-a 70% reduction
in area! Thus understanding fragmented dynamics is important to understand
and maintain the biodiversity we have. Most models do not look at
age structure, which should be important because species age and mature and
the nature of their interactions changes.
This model asked what would happen if two species were competing for
resource as juveniles, with one species (call it alpha), is a better competitor
over the other species (call it beta). As adults, there is no competition.
To picture this, imagine the scenario for two tree species-while they
are still saplings, they compete for space or light (both examples of resources)
and one can displace the other while young. Yet once they mature,
each tree is established, so competition is not a factor. I was able
to show that the range of coexistence is considerably lessened under such
an approach (see the following graphs).
There are two immediate consequences one can gain from this. First:
biodiversity is much harder to maintain then previously thought. Second:
with an age structure approach, the amount of available resource left is
considerably greater, making the habitat more susceptible to invasion or
competition from other species. In the case of trees, it is invasive
species overtaking a habitat after clear-cutting.
 Hubbell, S. P. 2001. The Unified Neutral Theory of Biodiversity
and Biogeography. Princeton: Princeton University Press.
 Terborgh, J. 1992. Diversity and the Tropical Rain Forest. New York:
Scientific American Library.
 Connell, J.H. Diversity in Tropical Rain Forests and Coral Reefs.
 Sheil, D. and D. Burslem. Disturbing Hypotheses in Tropical Forests.
2003. TRENDS in Ecolocy and Evolution. 18:18-26.
 Molino, J. and D. Sabatier. Tree Diversity in Tropical Rain Forests:
A Validation of the Intermediate Disturbance Hypothesis. 2001. Science. 294:
 Chave, J. H. C. Muller-Landau, S. A. Levin. Comparing Classical Community
Models: Theoretical Consequences for Patterns of Diversity. 2002. The American
 Tilman, D. Competition and Biodiversity in Spatially Structured Habitats.
1994. Ecology. 75:2-16.
 Roberts, M.R. and F. S. Gilliam. Patterns and Mechanisms of Forest
Diversity in Forested Ecosystems: Implications for Forest Management. 1995.
Ecological Applications. 5(4):969-977.
 Edelstein-Keshet, L. 1988. Mathematical Models in Biology. New York:
 Armstrong, R. A. and R. McGehee. Competitive Exclusion. 1980. The
American Naturalist. 115(2):151-169.
 Adler, F.R. and J. Mosquera. Is Space Necessary? Interference Competition
and Limits to Biodiversity. 2000. Ecology. 81(11):3226-3232.