Seed size variation and coexistence: testing a novel hypothesis

植物在养分、水分和光照方面相互竞争，但竞争能力不同。生态学理论预测，优势竞争对手应该将劣势竞争对手推向局部灭绝（即最优秀的战斗者获胜！）然而，植物群落包含许多具有不同竞争能力的物种，因此生态学的一个核心问题是：竞争物种如何在自然界中共存？例如，共生植物物种在种子大小上差异很大，大种子物种通常是更好的竞争对手，有时也比小种子物种更能忍受压力条件。考虑到这些不平等，种子大小的变化是如何维持的？一种主流理论认为，小种子物种比大种子物种有更好的传播能力，使它们能够到达没有大种子物种的地方。然而，这一理论忽略了一个事实，即大种子物种的种子通常比小种子物种的种子被啮齿动物吃掉的要多得多。因此，本研究将通过实验验证大种子物种和小种子物种共存的新观点，因为啮齿动物的种子捕食者优先以大种子物种为食，从而抵消了这些物种之间基于种子大小的竞争能力不平衡。这项研究将使人们对促进共存的机制有更深入的了解，并对决定群落中物种相对丰度和多样性的生态力量有更全面的认识。这项工作还将用于增加公众对草地生态学的了解，并增强对植物群落如何组织的认识，这对有效管理这些栖息地至关重要。种子大小和数量长期以来被认为是共存策略的核心，但表明这些性状如何由特定共存机制形成的经验证据仍然很少。在试验点内，将18种共生草本植物（9种小种子，9种大种子）的种子添加到有和没有束草竞争对手的试验点中，以测试物种在竞争耐受性方面的差异。在12个生产力和其他非生物因素不同的地点，将同一焦点物种的种子以不同的密度添加到不同的地块中，以控制来自本地优势束草和啮齿动物种子捕食的竞争。这将允许评估竞争，种子捕食和处理压力非生物条件的能力如何影响具有不同种子大小的物种的招募功能。它还将有助于探索种子大小是否是一系列相关性状的一部分，这些性状形成“综合征”，预测在不同的生物和/或非生物条件下的人口表现。

Plant species compete for nutrients, water and light, yet differ in competitive ability. Ecological theory predicts that the superior competitor should drive inferior competitors to local extinction (i.e. the best fighter wins!) Yet, plant communities contain many species with varying competitive abilities, so a central question in ecology is: How do competing species coexist in nature? For example, co-occurring plant species differ dramatically in seed size, and larger seeded species are often better competitors and also sometimes better at tolerating stressful conditions than smaller seeded species. Given these inequalities, how is seed size variation maintained? A leading theory is that small-seeded species have better dispersal abilities than large-seeded species, enabling them to reach local sites where large-seeded species are absent. This theory, however, ignores the fact that large-seeded species often have substantially more of their seeds eaten by rodents than do small-seeded species. Thus, this research will experimentally test the novel idea that large and small-seeded species coexist because rodent seed predators preferentially feed on large seeded species, thereby countering the imbalance in competitive ability among these species based on their seed size. This research will generate a deeper understanding of the mechanisms that promote coexistence and a fuller appreciation for the ecological forces that determine the relative abundance and diversity of species in communities. This work will also be used to increase public understanding of grassland ecology and enhance knowledge of how plant communities are organized, which is essential for effectively managing these habitats. Seed size and number have long been considered central to coexistence strategies, yet empirical evidence showing how these traits are shaped by specific coexistence mechanisms remains scarce. Within sites, seeds of 18 co-occurring forb species (9 small-seeded, 9 large-seeded) will be added to plots with and without resident bunchgrass competitors to test how species vary in competitive tolerance. Across 12 sites that vary in productivity and other abiotic factors, seeds of the same focal species will be added to plots at different densities where competition from resident dominant bunchgrasses and rodent seed predation are manipulated. This will allow an evaluation of how competition, seed predation, and ability to handle stressful abiotic conditions influences recruitment functions of species with different seed sizes. It will also enable an exploration of whether seed size is part of a suite of correlated traits that form "syndromes" that predict demographic performance under distinct biotic and/or abiotic conditions.