Waterton Joseph, Cleland Elsa E
Ecology, Behavior and Evolution Section University of California San Diego La Jolla CA USA.
Ecol Evol. 2016 Nov 30;6(24):8942-8953. doi: 10.1002/ece3.2610. eCollection 2016 Dec.
Ecological trade-offs are fundamental to theory in community ecology; critical for understanding species coexistence in diverse plant communities, as well as the evolution of diverse life-history strategies. Invasions by exotic species can provide insights into the importance of trade-offs in community assembly, because the ecological strategies of invading species often differ from those present in the native species pool. Exotic annual species have invaded many Mediterranean-climate areas around the globe, and often germinate and emerge earlier in the growing season than native species. Early-season growth can enable exotic annual species to preempt space and resources, competitively suppressing later-emerging native species; however, early-emerging individuals may also be more apparent to herbivores. This suggests a potential trade-off between seasonal phenology and susceptibility to herbivory. To evaluate this hypothesis, we monitored the emergence and growth of 12 focal species (six each native and exotic) in monoculture and polyculture, while experimentally excluding generalist herbivores both early and later in the growing season. Consistent with past studies, the exotic species emerged earlier than native species. Regardless of species origin, earlier-emerging species achieved greater biomass by the end of the experiment, but were more negatively impacted by herbivory, particularly in the early part of the growing season. This greater impact of early-season herbivory on early-active species led to a reduction in the competitive advantage of exotic species growing in polyculture, and improved the performance of later-emerging natives. Such a trade-off between early growth and susceptibility to herbivores could be an important force in community assembly in seasonal herbaceous-dominated ecosystems. These results also show how herbivore exclusion favors early-active exotic species in this system, with important implications for management in many areas invaded by early-active exotic species.
生态权衡是群落生态学理论的基础；对于理解不同植物群落中的物种共存以及多样生活史策略的演化至关重要。外来物种的入侵能够为权衡在群落构建中的重要性提供见解，因为入侵物种的生态策略往往与本地物种库中的物种不同。外来一年生植物物种已经侵入了全球许多地中海气候地区，并且通常比本地物种在生长季节更早发芽和出苗。早期生长能够使外来一年生植物物种抢占空间和资源，从而竞争性地抑制晚出苗的本地物种；然而，早期出苗的个体可能也更容易被食草动物发现。这表明在季节性物候和对食草动物的易感性之间存在潜在的权衡。为了评估这一假设，我们监测了12个重点物种（本地和外来各6种）在单作和混作中的出苗和生长情况，同时在生长季节早期和晚期通过实验排除广食性食草动物。与过去的研究一致，外来物种比本地物种出苗更早。无论物种来源如何，早期出苗的物种在实验结束时获得了更大的生物量，但受到食草动物的负面影响更大，尤其是在生长季节早期。生长季节早期食草动物对早期活跃物种的这种更大影响导致了混作中外来物种竞争优势的降低，并提高了晚出苗本地物种的表现。在早期生长和对食草动物的易感性之间的这种权衡可能是季节性草本植物主导生态系统群落构建中的一种重要力量。这些结果还表明了食草动物排除如何在这个系统中有利于早期活跃的外来物种，这对许多被早期活跃外来物种入侵地区的管理具有重要意义。
