Abstract Detail



Ecology

Braasch, Joseph [1], Johnson, Maria, A. [2], Dlugosch, Katrina [3].

Climate driven community change is attributable to introduced species in a California grassland.

Considerable effort has been spent in attempts to identify traits which explain the ability of invading species to establish and compete in novel habitats. Rarely are consistent patterns found which can be applied broadly within taxonomic groups. Comparisons of introduced and native species responses to environmental change are not often examined at a community scale and represent an underappreciated trait dimension that could delineate these groups. Climate change is also expected to advantage introduced species by disrupting niche relationships among native species and creating open niche space.
We tested for different responses of native and introduced species to climate change using a long-term data set collected in a California grassland from 2006 to 2016. These communities exist on two distinct soil types; stressful serpentine soils which are generally resilient to most invading species, and non-serpentine soils which harbor a large compliment of noxious weeds. Reductions in species richness have been documented on both soil types, although the effect has been much larger on non-serpentine soils. This loss of richness can primarily be attributed to reductions in plot-scale occupancy for rare native forbs. We therefore expected to find changes in the composition of native plant communities on both soils, with little change in the assemblage of exotic species. 
We tested for directional changes in community composition on serpentine and nonserpentine soils using non-metric dimensional scaling and overlaying a vector for sampling year. We found significant, directional change in invaded nonserpentine sites only, while native dominated serpentine sites were stable. We then split nonserpentine communities in to native and exotic species assemblages and repeated this analysis. We found no signal of directional change in the community of native plants on nonserpentine soils, while the patterns of change in introduced plants recapitulated patterns of change. We then used gradient boosted machine learning to identify the species most important for describing patterns of compositional change in nonserpentine communities. These models identified three invading grasses which showed differing demographic patterns over the sampling period. These analyses, in conjunction with previous work, paint a picture of a relatively stable community of native plants for which the rarest species are becoming more so. In contrast, we see an assemblage of exotic species exhibiting strong responses to changes in climate over the past decade.


1 - University Of Arizona, Ecology And Evolutionary Biology, 1041 E. Lowell St., Tucson, AZ, 85721, United States
2 - University Of Arizona, School of Natural Resources and the Environment, Environment and Natural Resources 2, 1064 East Lowell Street, Tucson, AZ, 85721, USA
3 - University Of Arizona, ECOL AND EVOL BIOLOGY, P.O. Box 210088, Tucson, AZ, 85721, United States

Keywords:
community ecology
Invasion
Grasslands
multivariate statistics
climate change.

Presentation Type: Oral Paper
Number: 0001
Abstract ID:844
Candidate for Awards:Ecological Section Best Graduate Student Paper


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