Anthropogenic-based regional-scale factors most consistently explain plot-level exotic diversity in grasslands

Authors: MACDOUGALL, ANDREW - University Of Guelph; BENNETT, JOSEPH - University Of Queensland; FIRN, JENNIFER - Queensland University Of Technology; SEABLOOM, ERIC - University Of Minnesota; BORER, ELIZABETH - University Of Minnesota; LIND, ERIC - University Of Minnesota; ORROCK, JOHN - University Of Wisconsin; HARPOLE, W. STANLEY - Iowa State University; HAUTIER, YANN - University Of Zurich; ADLER, PETER - Utah State University; CLELAND, ELSA - University Of California; DAVIES, KENDI - University Of Colorado; MELBOURNE, BRETT - University Of Colorado; PROBER, SUZANNE - Commonwealth Scientific And Industrial Research Organisation (CSIRO); BAKKER, JONATHAN - University Of Washington; Fay, Philip; Jin, Virginia; KENDIG, AMY - University Of Minnesota; LA PIERRE, KIMBERLY - Yale University; MOORE, JOSLIN - University Of Melbourne; MORGAN, JOHN - La Trobe University; STEVENS, CARLY - Lancaster University

Submitted to: Global Ecology and Biogeography
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2014
Publication Date: 3/14/2014
Publication URL: http://handle.nal.usda.gov/10113/59400
Citation: MacDougall, A.S., Bennett, J.R., Firn, J., Seabloom, E.W., Borer, E.T., Lind, E.M., Orrock, J.L., Harpole, W., Hautier, Y., Adler, P.B., Cleland, E., Davies, K., Melbourne, B., Prober, S.M., Bakker, J.D., Fay, P.A., Jin, V.L., Kendig, A., La Pierre, K.J., Moore, J., Morgan, J., Stevens, C.J. 2014. Anthropogenic-based regional-scale factors most consistently explain plot-level exotic diversity in grasslands. Global Ecology and Biogeorgraphy. 23:802-810.

Interpretive Summary: Human activities have resulted in extensive loss of native plant populations and introductions of non-native species that often are highly aggressive and may out-compete native species, often with negative aesthetic, recreational and agricultural consequences. This paper examines the relationships between losses of native species and gains in non-native species for over 30 globally-distributed grasslands. The sites were subjected to identical experimental studies and protocols, avoiding problems of many previous studies of native vs. non-native plant diversity. The study finds that the replacement of natives by non-natives is related to numerous indicators of human activity, with higher occurrence of non-native plant species with indicators of nearby urban economic activity and human population density. This study helps clarify the linkages between human activity and the spread of non-native plant species, which will enable better prediction and management of future non-native species encroachment.

Technical Abstract: Invasion is viewed as a dominant threat to Earth’s biological diversity, but evidence linking the accumulation of exotic species to the simultaneous suppression of native diversity is equivocal, relying heavily on data from studies using different methods and designs. Fine-scale studies often describe negative associations between native and exotic diversity via competitive interactions, while regional studies often report habitat-mediated positive associations between the two species groups. Using standardized multi-scale data from 32 grasslands on two continents, we show that regional-scale anthropogenic factors relating to urbanization, landscape, and climate suitability can create the negative fine-scale relationship between native and exotic diversity that has often been attributed to fine-scale competitive interactions. Native diversity was positively correlated with biotic resistance in some cases but typically in regions with less prevalent urbanization. The strongest predictors of plot-level diversity were regional drivers that had divergent effects on exotic and native species, with indicators of urban-based economic activity associated with high exotic:native diversity ratios while climate- and landscape-based indicators of lower human population density were associated with low exotic:native ratios. These findings help explain the long-standing difficulty in resolving drivers of exotic establishment using single-factor mechanisms, instead pointing to multiple processes associated with human activity as key contributors to invasions.