Quantifying the effects of global change on invasive species and invaded habitats

Background/Question/Methods

   Range shifts are expected to be the most common response of species to global change and it has become clear that native species and the environments they inhabit will be vulnerable to these often non-aggressive invaders. However, the extent to which the native community in the invaded habitat plays a role in modifying habitat response to global change and colonizing organisms is unknown. We isolated two stages of a range shift (introduction and establishment) to investigate whether the effects of increased temperature and nitrogen influence the way in which invaders affect their new habitat and what role, if any, the native community plays in modifying these effects.
    The experiment was conducted in a xeric old-field in northern Florida in which soil nitrogen, temperature, plant invader addition (as a seed or an adult) and native plant community biomass were all manipulated in a randomized complete block, split-plot design. Each treatment block was replicated 5 times, for a total of 120, 4 m² plots. A range of habitat variables, including: vegetation richness, percent invasive species, availability of understory light, soil chemistry (pH, chemical composition, and percentage organic matter), and soil moisture were compared between treatment plots and analyzed with an ANOVA.

Results/Conclusions

    The seed addition treatment did not result in any detectable changes in any habitat characteristics measured. The addition of adult colonizers increased ambient plant species richness and the presence of invasive species across experimental plots. However, these effects were significantly smaller in plots exposed to the native plant community biomass reduction treatment. Moreover, the interactive effects of adult colonizers and global change treatment factors (increased soil nitrogen and warming) resulted in a stronger, non-additive effect on both native community characteristics (richness and percent invasive species), as well as soil characteristics (percent organic material and availability of soil surface light) than for either treatment alone. These results are evidence for the interactive effects of established colonizers and factors of global change on habitat level characteristics. Furthermore, the native plant community was found to clearly play a role in modifying these interactive effects.  Results of this work will be useful for understanding habitat level modifications likely to be initiated by global change.