Contrasting functional responses of non-native invasive species along a tropical elevation gradient

ABSTRACT One hypothesized invasion strategy (“try-harder”) predicts that invaders exhibit functional traits that are better adjusted to the environment than native species. Alternatively, the “join-the-locals” hypothesis predicts trait convergence between invasive and native species due to environmental filtering with increasing resource limitation. We hypothesized that invasions strategies shift from “try-harder” to “join-the-locals” with increasing elevation. We used an elevational gradient to detect possible trait convergences between alien invaders and native plant species in Asteraceae, Fabaceae and Poaceae. We found a significant trait convergence with elevation only in Asteraceae, suggesting a species-specific pattern, but also an important phenotypic variability of the alien invader. This supports the idea that the more resource-limited the environment, the more it filters out traits substantially diverging from the locally-adapted native community, thereby entailing a shift from “try-harder” to “join-the-locals” strategies. The invasive grass was also more acquisitive but did not exhibit any relation to the native community, supporting the “try-harder” hypothesis. The size of the invasive Fabaceae species decreased with elevation, mirroring the native Fabaceae species, but not the overall native community. Including more replicates and a thorough quantification of environmental conditions, offers a promising avenue for improving the understanding the seemingly idiosyncrasies of invasion pathways.

摘要：有假说提出一类入侵策略——“竭力适配（try-harder）”，该假说认为外来入侵物种的功能性状相较于本地物种更能适配所处环境。另一“融入本地类群（join-the-locals）”假说则预测，随着资源限制程度加剧，环境过滤作用会驱使入侵物种与本地物种产生性状趋同。我们提出核心假说：随着海拔升高，植物入侵策略会从“竭力适配”转向“融入本地类群”。本研究依托海拔梯度，探究菊科（Asteraceae）、豆科（Fabaceae）与禾本科（Poaceae）中外来入侵物种与本地植物间的潜在性状趋同现象。研究结果显示，仅在菊科类群中发现性状随海拔升高出现显著趋同，这一模式既体现了物种特异性，也反映了外来入侵物种显著的表型变异。该结果支持下述观点：环境资源限制越强，越会筛选掉与本地适应群落性状差异显著的类群，进而推动入侵策略从“竭力适配”向“融入本地类群”转变。入侵禾本科物种的资源获取策略更为激进，但与本地整体群落无显著关联，这一结果支持了“竭力适配”假说。入侵豆科物种的个体大小随海拔升高而降低，该变化趋势与本地豆科物种一致，但与整体本地群落并不相符。未来可通过增加重复样本量并精准量化环境条件，为厘清入侵路径中看似独特的异质性特征提供更具前景的研究方向。