Evaluating relative species competitive strength is a central question in community ecology, with strong implications for invasion ecology. Models assessing invader success consider three components: distribution, abundance and per-capita impact. However, relative strength and interactions among these factors remain unclear when applying to specific invasion scenarios. We hypothesized that performance of native and non-native species will vary as a function of direct and indirect effects at different abundances and scales. We conducted a replacement experiment between two dominant grasses in subtropical grasslands (the native Axonopus fissifolius and the non-native Paspalum notatum) in central Florida, USA. Thirty fenced plots (1 m x 3 m each) representing a gradient (15 levels) of increasing non-native groundcover and decreasing native groundcover were set up in November 2017. We transplanted individuals of these two species in subplots (12 subplots and 36 transplants per plot; 1080 plants in total) in a 2*2 factorial design (mixed /single focal species * 2/4 transplants per subplot). Leaf length/number and plant biomass were evaluated at the beginning and end of the experiment along with plot species composition and soil nutrients. Over 92% of transplants of each grass species survived until harvest (11 months). There were significant differences in leaf length, leaf number and plant biomass between conspecific/allospecific subplots. Both P. notatum and A. fissifolius performed better when transplanted in non-native P. notatum subplots. There were also interactions between conspecific/allospecific subplot treatment (direct effects) and the gradient of increasing Paspalum notatum /decreasing Axonopus fissifolius groundcover (indirect effects) treatments. Increasing P. notatum in the whole plot made environments more favorable for both grass species. Effects were consistent for leaf length/number and biomass of the two focal species. More comprehensive evaluation on indirect effects need to be considered when examining competition between non-native species and native species.
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Master of Science (M.S.)
College of Sciences
Length of Campus-only Access
Masters Thesis (Open Access)
Li, Haoyu, "Do Per-capita Impact or Abundance Dominate the Impact of an Invader? Interactions Among Neighboring Species in Context-dependent Competition" (2019). Electronic Theses and Dissertations. 6278.