Community Ecology I
Sunday March 13:
8:30am-9:45am
Back to Concurrent Session
II
ABSTRACTS |
EFFECTS OF FOREST THINNING REGIMES
ON UNDERSTORY VEGETATION
Mooneyhan, R.E. and Vitt, D.H.
Southern Illinois University, Carbondale,
IL 62901
Bryophytes and lichens dominate the
ground layer in conifer-dominated forests. The dominant
lichens, Cladina mitis and C. rangiferina, form a
mosaic of extensive patches intermixed with the feather
mosses Pleurozium schreberi and Hylocomium splendens.
We studied lichen/moss responses to canopy opening
7 years post-thinning. Our questions were posed around
determining the responses to canopy opening of 1)
vegetation, 2) diversity, 3) diaspores, and 4) establishment.
Conclusions are that canopy opening has effected ground
layer vegetation, but has had little effect on overall
species richness. Both lichen and moss diaspores are
abundant. Moss vegetation has decreased, yet lichens
have not yet recolonized the resulting non-vegetated
space. We conclude that lichens are generalists and
with time are able to establish under a variety of
environmental conditions, however they are inhibited
by pre-existing substrates. Feather mosses are specialists
and they are limited by environmental conditions inhibiting
their establishment, except in local areas where pre-existing
substrates and canopy conditions have precluded lichen
establishment.
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HONEY, WHAT'S FOR DINNER? AN EXPLORATION
OF THE EFFECTS OF GARDEN PLANTS ON THE POLLINATION
AND REPRODUCTIVE SUCCESS OF NATIVE WILDFLOWERS
Smyth, K.N.1, Knight, T.M.2, and
Chase, J.M.2
1 Department of Biology, Saint Louis
University, Saint Louis, MO 63103
2 Department of Biology, Washington University, Saint
Louis, MO 63130
A better understanding of human influences
on natural systems is vital to conservation endeavors
in urban and suburban regions. Urban gardening with
cultivated plant species is very common, and usually
thought to be beneficial to native pollinators. However,
these cultivated plants could either compete with
or facilitate native plant species. In this study,
we examined how pollination and reproductive success
of a native plant species (Purple Coneflower, Echinacea
purpurea) is affected by the presence of a cultivated
showy, fragrant garden species (Butterfly Bush, Buddleia
davidii). Three possible relationships are: facilitation,
the garden plants attract pollinators and native plants
benefit from overflow; competition, pollinators are
limited and the garden plant is preferentially visited;
or no effect. We manipulated two experimental factors,
density of native plant (single vs. four) and presence
of garden plant (present vs. absent) to give us four
treatment combinations; we replicated each treatment
5 times for a total of 20 experimental plots. Pollinator
visitations were recorded for twenty minute periods
at least three times at each plot during the months
of June, July, and August. We also examined seed set
of Echinacea purpurea to determine differences in
reproduction between treatments. Our preliminary results
suggest that both density of flowers and the presence
of Buddleia davidii affect pollinator behavior and
Echinacea purpurea seed viability. High density plots
were visited by more pollinators overall and the presence
of Buddleia davidii attracted more butterfly visitors
to plots. In addition, there was a trend toward a
lower proportion of viable Echinacea purpurea seeds
per inflorescence in the presence of Buddleia davidii.
Keywords: Echinacea, plant-pollinator
interactions, urbanization, pollinators
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THE
EFFECTS OF EXOTIC ERODIUM CICUTARIUM ON AN ARID ECOSYSTEM
Schutzenhofer, M.R.
Department Of Biology, Saint Louis
University, St. Louis, MO 63103
One concern about exotic species is that
they can negatively affect native species and alter
ecosystem function. Erodium cicutarium was introduced
to the United States more than 300 years ago and is
found throughout western North America, but little is
known about how it affects native plant communities.
To examine the effect of E. cicutarium on native annual
plants, we first examined patterns of abundance of E.
cicutarium and native annuals at 2 spatial scales 1)
on 24 – 0.5 ha experimental plots and 2) on 0.5m2
quadrat communities. We found significant negative correlations
between the abundance of E. cicutarium and natives at
both scales, suggesting a competitive interaction. To
study this further, we conducted a field experiment
in southeastern Arizona that consisted of 40 –
0.25m2 quadrats from which E. cicutarium was removed
and 40 control quadrats. We found that E. cicutarium
removal quadrats contained significantly higher richness
of annual plants but the experimental quadrats did not
differ in abundance of natives. However, control plots
contained significantly higher abundance due to the
presence of E. cicutarium. Thus while E. cicutarium
appears to suppress the diversity of natives, it increases
community productivity.
Keywords: Exotic, Richness, Productivity
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FOOD
WEB DYNAMICS OF THE INQUILINE COMMUNITY IN THE NORTHERN
PITCHER PLANT, Sarracenia purpurea: THE EFFECT
OF LATITUDE.
Hoekman, D. S.
Department of Biological Sciences,
University of Notre Dame,
Galvin Life Science Center, Notre Dame IN 46556
Ecologists have tried to quantify the
strengths and relative importance of resource (bottom-up)
and predator (top-down) effects in food webs. The aquatic
food web found within the leaves of the northern pitcher
plant, Sarracenia purpurea, is a model system
well suited to asking questions about the factors controlling
food web structure and dynamics. A number of aquatic
organisms coexist in a food web fueled by invertebrates
drowned in the pitfall trap of the pitcher plant. In
the summer and fall of 2004, I conducted two 4x4 factorial
press experiments using pitcher plant communities, one
in the upper peninsula of Michigan (MI) and the other
in the Apalachicola National Forest, Florida (FL). Treatments
included 4 levels of resource input and top-predator
density. Though these experiments were conducted over
1000 miles apart (1830 km), at quite different temperatures
(average daily mean temperature C: MI 14.6, FL 24.7)
and in different ecosystems (MI: ombrotrophic bog, FL:
longleaf pine savanna), the community wide effects of
top-down and bottom-up forces were remarkably similar.
Both bottom-up and top-down treatments had significant
effects on some populations within the inquiline food
web, and produced similar trends at both sites. For
example, resource addition had positive effects on bacteria
density in both MI and FL (p<0.0001). Top-predator
density had a negative effect on protozoa biomass and
richness as well as rotifer abundance at both sites
(p<0.05). Clearly, both top-down and bottom-up effects
are important in this food web at both locations. The
main difference between the two experiments is that
top-predator density had a negative effect on bacteria
populations in FL (p=0.02), but not in MI (p=0.54).
One explanation is that the top-predator is more omnivorous
at higher temperatures in FL, or that bacteria densities
are lower in FL than in MI and are therefore more susceptible
to top-down control.
Keywords: top-down, bottom-up, food-web,
pitcher plant
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A
COMPARISON OF BEE COMMUNITY COMPOSITION IN NATURAL AND
LOGGED CLEARINGS ON HORSE MOUNTAIN, TRINITY COUNTY,
CA
Watrous, K.M.
Department of Biological Sciences,
Humboldt State University, Arcata, CA 95521
Disturbance can have substantial community-level
effects. Bee communities are dependent on both floral
resources and nesting substrate availability for suitable
habitat. Changes in either habitat parameter, through
disturbance, can greatly impact nearby bee communities.
Because bees provide a valuable ecological service as
pollinators of the surrounding plant community, understanding
the effects of logging on bee community composition
can be useful in conservation and restoration of natural
habitats. I compared bee community composition in three
logged and three natural clearings. I documented plant
community composition and relative species cover at
each site using line-intercept transects. I also recorded
flowering individuals and calculated floral richness
and relative cover at each site. There was no significant
difference in bee species richness, abundance or evenness
between the two treatments. Bee community diversity
between treatments was marginally significant (p=0.04),
possibly due to additive effects of both species richness
and evenness. Bee abundance was significantly correlated
with relative floral cover and plant species richness
(p=0.039 and 0.0337, respectively). Plant species richness
and bee community diversity were also significantly
correlated (p=0.043), but all of these correlations
had low R2 values. Logging therefore did not appear
to have a significant impact on bee community composition,
but other factors such as plant community composition,
slope or aspect may be important.
Keywords: bee community, logging
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II
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