Wainwright Claire E, Holt Robert D, Mayfield Margaret M
The Ecology Centre, School of Biological Sciences, The University of Queensland, St Lucia, QLD, Australia.
Exponent, Inc., Bellevue, WA, USA.
Oecologia. 2019 Aug;190(4):927-940. doi: 10.1007/s00442-019-04468-z. Epub 2019 Jul 12.
Exotic species are often predicted to successfully invade when their functional traits differ from species in recipient communities. Many studies have related trait differences among natives and invaders to competitive outcomes. Few studies, however, have tested whether functionally similar invaders have similar competitive impacts on natives. We investigated interactions in communities of a native annual forb Waitzia acuminata (Asteraceae) and two invasive annual grasses that are ecologically similar and co-occur in southwestern Australia. Using a combination of field and laboratory experiments and several performance measures, we assessed impacts of these grasses on W. acuminata. We also examined differences among species in their responses to intraspecific versus interspecific competition, including their frequency dependence. The two similar exotic grasses differed in interaction impacts, with one facilitating and the other suppressing the native. In general, intraspecific competition was stronger than interspecific competition for the native, while evidence of competition was weak for the exotics. These patterns may reflect that W. acuminata does well in these communities due to the combined impacts of stabilization and facilitation, whereas the exotics benefit from limited stabilization (mediated by their weak intraspecific competition) or weak interspecific competition with W. acuminata. We found divergent impacts of the exotic species despite their similar functional traits. We demonstrate that a native species may benefit from interactions with an exotic "benefactor" species, highlighting the potential importance of positive interactions in invaded communities. Our findings underscore the necessity of considering neutral and positive interactions in addition to competition in understanding invasion dynamics in real plant communities.
当外来物种的功能性状与接受群落中的物种不同时，通常预计它们会成功入侵。许多研究已将本地物种和入侵物种之间的性状差异与竞争结果联系起来。然而，很少有研究测试功能相似的入侵物种对本地物种是否具有相似的竞争影响。我们调查了澳大利亚西南部一年生本地草本植物尖叶维菊（菊科）与两种生态相似且共生的入侵一年生禾本科植物群落中的相互作用。通过结合田间和实验室实验以及多种性能指标，我们评估了这些禾本科植物对尖叶维菊的影响。我们还研究了物种在种内竞争与种间竞争反应上的差异，包括频率依赖性。这两种相似的外来禾本科植物在相互作用影响方面存在差异，一种对本地植物有促进作用，另一种则有抑制作用。总体而言，本地植物的种内竞争强于种间竞争，而外来植物的竞争证据较弱。这些模式可能反映出，由于稳定作用和促进作用的综合影响，尖叶维菊在这些群落中生长良好，而外来植物则受益于有限的稳定作用（由其较弱的种内竞争介导）或与尖叶维菊的弱种间竞争。尽管外来物种功能性状相似，但我们发现了不同的影响。我们证明本地物种可能受益于与外来“有益”物种的相互作用，突出了正向相互作用在入侵群落中的潜在重要性。我们的研究结果强调，在理解真实植物群落的入侵动态时，除了竞争之外，还需要考虑中性和正向相互作用。
