The shifting balance of facilitation and competition affects the outcome of intra- and interspecific interactions over the life history of California grassland annuals |
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Authors: | Elizabeth A Leger Erin K Espeland |
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Institution: | (1) Department of Natural Resources and Environmental Science, University of Nevada, Reno, Mail Stop 186, 1000 Valley Road, Reno, NV 89512, USA;(2) USDA ARS Pest Management Research Unit, 1500 N. Central Ave, Sidney, MT 59270, USA |
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Abstract: | Trait-based resource competition in plants, wherein more similar plants compete more strongly for resources, is a foundation
of niche-based explanations for the maintenance of diversity in plant communities. Alternatively, neutral theory predicts
that community diversity can be maintained despite equivalent resource requirements among species. We examined interactions
at three life history stages (germination, survival, and juvenile-adult growth) for three native and three exotic California
annual species in a glasshouse experiment. We varied plant density and species composition in small pots, with pots planted
with either intraspecific seeds or in a three species mix of intra- and interspecific neighbors. We saw a range of facilitative,
neutral, and competitive interactions that varied significantly by species, rather than by native or exotic status. There
were more competitive interactions at the emergence and juvenile-adult growth stages and more facilitative interactions for
survival. Consequently, the relative strength of competition in intraspecific versus mixed-species communities depended on
whether we considered only the juvenile-adult growth stage or the entire life history of the interacting plants. Using traditional
analysis of juvenile-adult growth only, all species showed negative density-dependent interactions for final biomass production.
However, when the net effect of plant interactions from seed to adult was considered, which is a prediction of population
growth, two native species ceased to show negative density dependence, and the difference between intraspecific and mixed-species
competition was only significant for one exotic species. Results were consistent with predictions of neutral, rather than
niche, theory for five of six species. |
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