Species size and survival under intra- and interspecific competition: implications for the coexistence of small and large plant species.
Schamp, Brandon*,1, Aarssen, Lonnie1, 1 Department of Biology, Kingston, Ontario, Canada
ABSTRACT- Plant species are believed to compete strongly within the community context, with experimental evidence suggesting that traits related to species size best predict the relative competitive ability of a given species. We postulated that the lack of a consistent relationship between species size/competitive ability and abundance patterns in natural communities may be explained by differences in proportional survival under intra- and interspecific competition. Specifically, we predicted that for large species, survival would be disproportionately lower in monoculture relative to mixture, and that survival in monocultures relative to mixtures would be a strong predictor of abundance rank in a local plant community. To test these predictions, we measured survival rates of ten commonly coexisting species competing in high density monocultures and mixtures in a greenhouse experiment. Study species vary in average and maximum biomass production, height, and also abundance in local old-fields. We found that, as predicted, larger species survived disproportionately less than small species in monocultures relative to mixtures. This suggests a demographic advantage to being small that may help explain why competitive ability, predicted by species size, does not successfully predict abundance in natural communities. While elements of size may predict pair wise competitive outcomes, they may not predict the range of outcomes possible when competitive conditions vary between monoculture and mixture. Neither species size, nor survival in monoculture relative to mixture was strong predictors of rank abundance in a local old-field.
Key words: interspecific competition, species size, relative abundance
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