Post-doctoral Associates:
Todd Campbell (lizardman@utk.edu)
Carl-Gustaf
Thulin (carl-gustaf.thulin@ebc.uu.se)
Graduate Students:
Michael
Collins (mdcollins@utk.edu)
Tadashi
Fukami (tfukami@utk.edu)
Leah
Gibbons (lgibbon1@utk.edu)
Diego Vázquez (vazquez@utk.edu)
Betsy
Von Holle (vonholle@utk.edu)
Undergraduate Students:
Valerie K. McCammon-Creutzinger
(vmccamm1@utk.edu)
Chris Cattau (chriscattau@hotmail.com)
Our Academic
Interests:
Daniel
Simberloff
1. The patterns displayed by species introduced outside
their geographic ranges, the impacts such species have on the
communities they invade, and the means by which such invasions can be
managed.
2. The determinants of community composition (which
species can coexist in communities?) and community patterns that reflect
these determinants.
3. The ways in which species vary morphologically
depending on which other species are present.
Todd
Campbell
I study introduced species because they can be used for
answering questions about nearly any ecological or evolutionary
discipline. My interests range from basic to applied, and I seek
to bridge the wide gap between these genres of biological research. At
the IBI, my duties vary from office minutia to web site design to
literature database construction to local partnership efforts to some
really cool basic and applied research.
On the applied side, I recently won funding for a
baseline survey of exotic plants at the Big South Fork NRRA (with Joey
Shaw and Chris Fleming, UT Botany Dept.), and we are pursuing similar
surveys in other state and federal areas. Dan and I hope to assemble a
database of state-level exotic species program contacts in the United
States, which will hopefully assist in rapid response and basic
coordination efforts between agencies and private entities in managing
and eradicating introduced species. If possible, I hope to bring to the
same table some of the various "exotic species advocate groups" (e.g.,
pet and horticulture industries and animal rights groups) and exotic
species managers, so they might find and exploit their common principles
to effect positive ecological changes. I am also interested in the
utility of exotic species as surrogates for native species in
ecotoxicological studies. I just started a project with Kym Rouse
Campbell (my better half) and Joanna Burger (Rutgers) using exotic
lizards in Florida, and also intend to utilize Asian clams in this
regard. Finally, my research generally incorporates
the synergism between habitat alteration (destruction and fragmentation)
and introduced species; the #1 and #2 threats to the biodiversity of
this great planet.
On the basic side, I am currently interested in the
heritable (evolutionary) and non-genetic (plastic) morphological changes
that introduced species exhibit as they invade new lands. To study these
phenomena, I employ Caribbean Anolis lizards, one of the most
speciose genera of vertebrates (and arguably the most interesting
adaptive radiation of organisms on Earth). Anoles have been introduced
to many different islands and mainlands all over the planet, but with 10
species from 7 different Caribbean islands (as well as many other exotic
amphibians and reptiles), the novel assemblage of lizards in South
Florida is very interesting from a community (or guild) standpoint. I
have already done extensive research on the most widespread species, the
brown anole (Anolis sagrei). Brown anoles are likely the densest
and most biomassive terrestrial vertebrate in Florida - they can attain
densities of over 12,000 individuals per hectare and a biomass of over
50 kg per hectare in certain situations. Surely, this puts some level of
strain on the native systems they invade. More recently, I started
a project with Jonathan Losos (Washington University) that indicates
limb and body parameters of introduced brown anoles change very rapidly
depending on the type of habitat (i.e., perches) they occupy. This adds
an exotic species component to the elegant research of Jonathan and
others (e.g., Tom Schoener and David Spiller) on native populations of
brown anoles in the Bahamas. I am currently pursuing funding to study
morphological changes (plastic and evolutionary) that might occur in the
exotic anoles and other amphibians and reptiles of South Florida in
response to novel habitats and novel congeneric competitors. Back to the
applied side, morphological changes of invaders might represent "moving
targets" for managers and might influence the outcomes of their
interactions with native species.
Carl-Gustaf
Thulin
My research interests are colonisation history;
different modes of colonisation and their effect on genetic variation
and substructuring of populations. The role of the repeated glaciation
events for the diversification of the present flora and fauna and the
significance for speciation of reinforcement in secondary contact zones.
Further, the population genetic effects of translocations of species by
humans, such as genetic bottle-necks, admixture and “founder flush”.
Also, the effects of translocated species on the native fauna,
especially interactions such as competition and hybridisation with
native congenerics.
Cytonuclear compatibility; empirical investigations of
mtDNA/nDNA interactions, their role in the establishment, reinforcement
and preservation of reproductive barriers and the implications for
utility of mtDNA as a genetic marker, especially for systematic
purposes. Selection on mtDNA variants and mtDNA adaptations to the nDNA
background, with emphases on metabolism and fitness characters, such as
growth rate, morphological asymmetry and immuno-defense.
Michael
Collins
I am generally interested in issues related to theoretical and
community ecology. I am currently conducting a worldwide investigation
for evidence of competition in the genus Accipiter (true hawks).
In particular, I am looking for character displacement and limiting
similarity. Species in the genus Accipiter exhibit very
pronounced reverse size dimorphism (females are larger than males). I am
treating each sex of each species as a morphospecies. As the suite of
coexisting species changes over space (through either the addition or
loss of a species), I am examining whether tarsus morphology changes
predictably.
Tadashi
Fukami
I am interested in using experimental and theoretical
approaches to ecology, particularly in the context of community
assembly. Community assembly refers to the construction of local
communities through stochastic, sequential arrivals of species.
For my dissertation, I am studying how community assembly may interact
with regional species pool, nutrient availability, and disturbance
regime to influence species diversity at different spatial scales.
I am using computer simulations and microcosm experiments to develop and
test specific hypotheses.
Other questions that I have worked on or am working
on include the following: implications of community similarity for
ecosystem functions, effects of disturbance history on community
structure, mutually facilitated invasions by predators and prey, and
applications of self-organized criticality theory to community
ecology. I have also been involved in field studies with various
organisms, including competition and predation in spiders, ideal free
distribution in birds, and foraging behavior of aquatic insects.
For my post-doctoral research, I am most interested
in incorporating ecosystem functions into my assembly models and testing
resulting predictions with field experiments using, for example, soil
food webs.
Leah
Gibbons
Because competitive superiority is one
of the mechanisms of invasion success for introduced species and because
competition is important in structuring ant communities, I studied
competition between native ant genera and the hybrid imported fire ant,
Solenopsis invicta x S. richteri, in two habitats in
southeast Tennessee. (Results were similar for both habitats)
Species abundance and diversity can be
an indicator of competition. In habitats invaded by hybrid imported fire
ants, species abundance and diversity was significantly lower than in
areas not invaded by fire ants. These study sites were similar in all
ways except for the presence or absence of fire ants. These findings
indicate that fire ants are causing, either directly or indirectly, a
decrease in native ant abundance and diversity. Further more, the total
number of ants was 6.75 times greater in the invaded areas, and fire
ants accounted for 93% of all individuals collected. Clearly, fire ants
are altering the dynamics of these ant communities, and probably
communities of other organisms, in these areas. Some native genera
(Monomorium, Solenopsis (Diplorhoptrum)) seemed unaffected
by the presence of fire ants.
To directly observe competition between
native ants and hybrid imported fire ants, I observed interactions
between ants at baits in areas invaded by the hybrid imported fire ant.
I quantified three measures of competitive ability: number of baits
discovered first, recruited to first, and control (numerical control) by
ant genera. Fire ants discovered first significantly more baits than
native ants, recruited first to significantly more baits, and controlled
significantly more baits. Clearly, fire ants are superior competitors in
these ant communities.
It is clear from the abundance and diversity data that I
collected that hybrid imported fire ants occur in much higher densities
than native ants in invaded areas. Fire ants’ competitive superiority
could be due largely to these extremely high population densities. To
assess the role that fire ants’ population density plays in competition,
I poisoned half of the fire ant mounds in a one-hectare area. One week
later, I again collected data from observations at baits and quantified
competitive interactions between fire ants and native ant genera. After
poisoning, native ants performed much better (and significantly so) on
all measures of competition (number of baits discovered first, recruited
to first, controlled) than they did before poisoning. Also, fire ant
performance on these measures, except for number of baits controlled,
decreased significantly. Native ant genera discovered first and
recruited first to significantly more baits than fire ants after fire
ants population density was reduced. However, after poisoning, native
ants and fire ants controlled statistically equal numbers of baits at
the end of the three-hour observation period. Fire ants foraged longer
than native ants thus maintained individuals at baits for longer periods
of time than native ants. Clearly, fire ant population density plays an
important role in their competitive superiority and invasion
success.
Diego
Vázquez
I am interested in how changes in ecosystems affect
community structure and species interactions, both from basic and
applied points of view. I am currently working with plant-pollinator
systems in the temperate forests of the southern Andes, trying to
understand how introduced ungulates alter the community structure of
plants and pollinators, and their patterns of interaction.
I am addressing two different, but related questions.
The first one is whether there is a relationship between the degree of
ecological specialization and the response of species to disturbance.
Common sense, some theory, and some data suggest that we should expect
that specialists tend to lose with disturbance. I tested this hypothesis
with my data on plant-pollinator interactions.
The second question has to do with the indirect effects
of introduced herbivores on plants. Plants can be affected by introduced
herbivores not only directly through trampling or browsing, but also
indirectly, through a modification of the frequency of interaction
between plants and pollinators. Since population density of some plant
species can change, this modified density can result in changes in the
frequency of interaction with pollinators and in the quality of
pollination. This, in turn, can affect plant reproduction. My
preliminary results show that this effect can occur in the amancay,
Alstoemeria aurea, one of the most common insect-pollinated
plants in the forest understory during the summer.
Betsy Von
Holle
Studies detailing
the mechanisms of ecological resistance are vital to maintain the
integrity of frequently invaded communities. Although there have been studies
of the various types of ecological resistance, no quantitative studies
have examined the relative importance of these. The study described here
is unique in testing simultaneously all three components of ecological
resistance; all prior studies have compared only two factors at a
time.
Identifying the relevant components of ecological resistance will
guide future resistance research.
Understanding mechanisms that govern the addition and deletion of
species is important for the understanding ecological community
structure. Additionally,
this study links complex environmental and biotic factors that can be
extended to understand landscape-level interactions such as riverine
influence on native biodiversity and invasion.
My objective is to rank the components of ecological resistance
to biological invaders and explore levels of resistance within the
different components. My
hypotheses are: that
ecological resistance will comprise environmental, demographic and
biotic resistance, ranked in that order. The probability of successful
invasion will increase with decreasing species richness of the recipient
community. Invaders are less likely to survive in sites with high
flooding intensity. There is a
greater probability of invasion success with higher propagule
pressure.
I monitored the condition (dead,
alive) of invaders 2 weeks after seeding into the treatment plots. In a multiple regression
analysis, I found a negative relationship between survivorship of the
800 transplanted invaders with the density of the recipient plot
(partial correlation coefficient = -0.037), and a positive correlation
with plot diversity (partial correlation coefficient = 0.0425). The
relationship nine months later (after the first season of flooding) was
much the same with invader survivorship positively related to diversity
and negatively related to density of the recipient plot. Native invaders had
significantly less mortality than exotics (p<0.0001, Chi-square =
39.847, n=700). The
mortality of exotic invaders in flooded sites (58.8%) was higher than in
non-flooded sites (47.4%), and there was no significant difference
between the growth of plants of different origins and the flooding
treatment (p=0.61, F=0.495, n=442). These results were most likely
due to the severe winter drought of 1999-2000, in southwestern
VA.
I measured various
environmental variables in the summer of 2001 and initiated a new
experiment, testing the influence of the shrub dominant, Rhododendron
maximum, on the invasion of species into riparian habitat. I am in the process of analyzing
these data and ranking the components of ecological resistance to
biological invasion.
In 2002, I will monitor all of the introduced and tagged plants
and make further environmental measurements. I will be monitoring this
experiment in the future, as I will use the experimental set-up to
assess the impact of the newly invading species, the Hemlock Wooly
Adelgid on vegetation dynamics.
This page was last updated on
11/09/2004
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