Invasive species may act as a functional filter on native communities by differentially affecting species with different trait values. Across environments, invasive plants typically display traits associated with high resource acquisition and fast growth. Conversely, native plants, especially those in water-limited environments, tend to adopt one of two functional strategies: fast growth during high resource availability to avoid stress (resource-acquisitive), or slow growth during resource-poor conditions to tolerate stress (resource-conservative). While invasive competition can be a strong filter on these groups, many invaders also alter the structure of native communities through their accumulation of litter. How fast-growing invaders with litter shift native functional communities remains unknown. To elucidate these functional shifts, I manipulated invasive annual grasses and their litter in an annual grassland and followed the demographic rates of six native annual forb species that varied in their functional strategy. Live grass competition alone decreased per capita growth rates of resource-acquisitive natives and had no effect on resource-conservative natives. The presence of litter, however, decreased growth rates in both functional types of natives, with stronger declines in resource-acquisitive species through differential effects on seed set and germination. Invaders in this system thus create an unfavorable environment for natives through litter, limiting the capacity of both resource-acquisitive and resource-conservative native forbs to maintain high population growth. These findings suggest that grass invasions have the potential to dramatically shift the functional composition of native communities through the time-lagged effects of their litter.

入侵物种可以通过不同地影响具有不同特征值的物种来充当本地群落的功能过滤器。在整个环境中，入侵植物通常表现出与高资源获取和快速生长相关的特征。相反，本地植物，尤其是在缺水环境中的植物，倾向于采用两种功能策略之一：在高资源可用性期间快速生长以避免压力（资源获取），或在资源贫乏条件下缓慢生长以承受压力（资源获取） -保守的）。虽然侵入性竞争可以成为这些群体的强大过滤器，但许多入侵者也通过垃圾堆积改变了当地社区的结构。垃圾如何快速增长的入侵者如何改变本地功能社区仍然未知。为了阐明这些功能转变，我在一年生草原上操纵了入侵的一年生草及其凋落物，并跟踪了六种本地一年生杂草的人口统计率，这些物种的功能策略各不相同。仅活草竞争就降低了资源获取型本地人的人均增长率，并且对资源节约型本地人没有影响。然而，凋落物的存在降低了两种功能类型本地人的增长率，通过对种子结实和发芽的不同影响，资源获取性物种的下降幅度更大。因此，该系统中的入侵者通过乱扔垃圾为当地人创造了不利的环境，限制了资源获取型和资源节约型本土杂物维持高人口增长的能力。