For or against: the importance of variation in growth rate for testing the EICA hypothesis |
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Authors: | Xiao-Yun Pan Xin Jia Jia-Kuan Chen Bo Li |
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Institution: | (1) Coastal Ecosystems Research Station of Yangtze River Estuary, Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Institute of Biodiversity Science, Fudan University, 200433 Shanghai, China; |
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Abstract: | The evolution of increased competitive ability (EICA) hypothesis proposes that invasive species evolve decreased defense and
increased competitive ability following natural enemy release. Previous studies have found evidence both for and against EICA.
The resource-enemy release hypothesis (R-ERH) suggests that fast-growing species may experience stronger enemy release than
slow-growing species. On the basis of R-ERH, the prediction of EICA will be held true for slow-growing genotypes, i.e., the
slow-growing genotypes from the introduced range will be less resistant to herbivory and grow faster than those from the home
range; while the EICA will not be held for fast-growing genotypes, i.e., there will be no significant differences in growth
and defense traits between the introduced and native fast-growing genotypes. We tested these predictions preliminarily using
five populations of the invasive plant Alternanthera philoxeroides. This species has two varieties in its home range, which showed a distinct growth-defense strategy: the northern A. p. var. acutifolia (Apa) had higher growth rate but lower resistance, while the southern A. p. var. obtusifolia (Apo) had lower growth rate but higher resistance level. Our results suggest that the EICA hypothesis is consistent with
the slow-growing Apo, but not with the fast-growing Apa. We suggest that evolutionary changes in growth or resistance following
enemy release are influenced by variation in growth rate within an invasive alien plant. These findings have important implications
for the EICA hypothesis, and may partially explain why previous studies have found evidence both for and against EICA. |
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