Spatial pattern and scale influence invader demographic response to simulated precipitation change in an annual grassland community

Authors: Skaer Thomason, Meghan; RICE, KEVIN - University Of California

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2016
Publication Date: 1/3/2017
Citation: Skaer Thomason, M.J., Rice, K.J. 2017. Spatial pattern and scale influence invader demographic response to simulated climate change in an annual grassland community. PLoS One. 12(1):e0169328. doi:10.1371/journal.pone.0169328.

Interpretive Summary: Climate change is expected to have major impacts on ecosystems worldwide, and will likely interact with other drivers of change, such as biological invasions. California, with its diverse geography and climate, is host to an incredible range of diversity. However, because of factors such as climate change and biological invasions, it is considered to be at high risk for species loss. Therefore, studying the response of invasive species to climate change is a critical first step in mitigating these biodiversity losses. California’s heavily invaded grasslands are particularly vulnerable to further degradation, particularly in light of more recent invasions by species like barb goatgrass, Aegilops triuncialis. This vulnerability is compounded by the state’s uncertain climate future (up to 25% more or less total annual rainfall). We evaluated the response of this more recent invader to both simulated changes in climate (altered rainfall) and local invasion pattern and density. By manipulating these factors, we aimed to understand the potential for further invasion and spread of barb goatgrass under California’s predicted climate scenarios. We found that invasion pattern and scale of observation were both very important in the response of barb goatgrass to altered rainfall. Unexpectedly, denser plantings of barb goatgrass lead to greater seed output. Furthermore, our results suggest the high-density, patchy plantings were better able to maintain steady seed production in the face of annual climate variability. These results will help land managers prioritize weed control efforts over the long term, especially as California’s climate begins to shift.

Technical Abstract: It is important to predict which invasive species will benefit from future changes in climate, and thereby identify those invaders that need particular attention and prioritization of management efforts. Because establishment, persistence, and spread determine invasion success, this prediction requires detailed demographic information. Explicit study of the impact of pattern on demographic response is particularly important for species that are naturally patchy, such as the invasive grass, Aegilops triuncialis. In the northern California Coast Range, where climate change may increase or decrease mean annual rainfall, we conducted a field experiment to understand the interaction of climate change and local-scale patterning on the demography of A. triuncialis. We manipulated rainfall (reduced, ambient, or augmented), seed density, and seeding pattern. Demographic and environmental data were collected for three years following initial seeding. Pattern and scale figure prominently in the demographic response of A. triuncialis to rainfall manipulation. Pattern interacts with rainfall and seeding density in its influence on per-plant seed output. Although per-plot seed production was highest when seeds were not aggregated, per-plant seed output was higher in aggregated patches. Results suggest aggregation of invasive A. triuncialis reduces the detrimental impact of interspecific competition in its invaded community, and that interspecific competition per se has a stronger impact than intraspecific competition.