| dc.description.abstract | The invasive Chinese Tallow tree (Triadica sebifera or Sapium sebiferum) was
heavily introduced to the southern United States from Asia at the turn of the 20th
Century. A Tallow invasion can reduce richness within the plant community by direct
competition and can decrease density of consumer communities by limiting basal food
resources. Additionally, tallow leaches rapidly into aquatic systems, where a sharp
increase in aerobic microbial decomposition can simultaneously drop dissolved oxygen
and pH levels, thus causing mortality in macroorganisms. I predicted an input of solely
Tallow leaves into mesocosms (artificial streams) would temporarily increase N & P
concentration, algae concentration, invertebrate density, and fishes because of increased
rates of rapid decomposition, but would fail to sustain long-term and overall growth for
that same reason. In contrast, sycamore leaves would provide a more sustained, long-term
allochthonous subsidy to the mesocosms, thus resulting in increased growth of fishes and
other response variables relative to that of tallow leaf treatments. Cellulose paper was
used as a no-leaf control to account carbon input. Bullhead minnows (Pimephales
vigilax) were stocked in half of our experimental stream mesocosms, where benthic
algae, invertebrate density, and nutrient content were sampled for 16 weeks. After 16
weeks, 50% of the original Sycamore leaves remained, whereas less than 10% of the
cellulose paper (control) and Tallow remained. The concentration of benthic algae was
highly dependent on time as values increased significantly after week 6, and tended to be
higher in treatments with no-fish and cellulose/tallow. Invertebrate density generally
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remained higher in no-fish treatments; densities were highest in tallow treatments before
the experimental halfway point, and were highest in sycamore treatments past the
halfway point. Nitrogen and phosphorous concentrations fluctuated highly throughout the
experimental runtime, and showed no significant interactions among treatment groups.
Fish were largest in mesocosms with the Sycamore leaves where either the
undecomposed leaves provided additional surface area for food resources, or growth was
higher relative to tallow treatments because of possible physiological inhibition. Tallow
treatment fish growth was significantly smaller than sycamore, and relatively equal to
cellulose. Herein, we discuss the reasons for the decreased fish growth in the presence of
tallow leaves such as: (1) rapid decomposition providing a short-term nutrient pulse that
moved through the food web quickly, and (2) physiological inhibition from the chemical
composition of tallow leaves. | |
