Interactive effects of global change and invasion on biotic response across organizational levels in an old-field plant community

Background/Question/Methods

Global change will have significant and pervasive effects across the planet. It is therefore crucial that we develop an understanding of the extent and mechanisms involved with the way in which organisms will respond to global change. Many studies of global change effects across time and spatial scales have documented changes in effect size (differences between ecological responses to the presence and absence of global change factors) or even a reversal in the direction of effects across levels. The complexity of patterns of biotic response is likely to increase when non-climatic factors, such as invasion, interact with global change across organizational scales. However, despite the widespread occurrence of interactions between invasion and factors of global change, the effect of this relationship on biotic response across organizational levels has not been studied.

Over a period of three years, I measured a suite of responses associated with plant species invasion in experimental plots exposed to two factors associated with global change in an old-field in north Florida. The global change treatments included warming by stand-alone open top chambers, and increased soil nitrogen, in plots with and without a native invader.  I investigated how the interaction among global change treatments and invasion differentially affected leaf-level, plant-level, and community-level characteristics to assess global change effects across scales.

Results/Conclusions

The effect sizes of elevated temperature and soil nitrogen on leaf (leaf toughness, and relative water content) and plant (biomass, and number of flowers) level response variables were significantly larger than the effect sizes of the same global change treatments on community (diversity and percent invasives) level response variables. Moreover, the presence of the invasion treatment appeared to increase the effect size overall, while dampening the pattern of decreasing effect size across organizational levels. This data builds on previous work by quantifying how invasion might interact with factors of global change to modify trends of dissimilarity among ecological responses at different levels of organization. Understanding how effect size of factors of global change and invasion are modified by scale of observation can be useful for determining local vs. global mitigation of global change impacts.