1. Resident species can facilitate invading species (biotic assistance) or inhibit their expansion (biotic resistance). Species interactions are often context‐dependent and the relative importance of biotic assistance versus resistance could vary with abiotic conditions or the life stage of the invading species, as invader stress tolerances and resource requirements change with ontogeny. In northeast Florida salt marshes, the abundant dead litter (wrack) of the native marsh cordgrass, Spartina alterniflora, could influence the expansion success of the black mangrove, Avicennia germinans, a tropical species that is expanding its range northward.
2. We used two field experiments to examine how S. alterniflora wrack affects A. germinans success during (a) propagule establishment and (b) subsequent seedling survival. We also conducted laboratory feeding assays to identify propagule consumers and assess how wrack presence influences herbivory on mangrove propagules.
3. Spartina alterniflora wrack facilitated A. germinans establishment by promoting propagule recruitment, retention and rooting; the tidal regime influenced the magnitude of these effects. However, over time S. alterniflora wrack inhibited A. germinans seedling success by smothering seedlings and attracting herbivore consumers. Feeding assays identified rodents—which seek refuge in wrack—as consumers of A. germinans propagules.
4. Synthesis. Our results suggest that the deleterious effects of S. alterniflora wrack on A. germinans seedling survival counterbalance the initial beneficial effects of wrack on A. germinans seed establishment. Such seed‐seedling conflicts can arise when species stress tolerances and resource requirements change throughout development and vary with abiotic conditions. In concert with the tidal conditions, the relative importance of positive and negative interactions with wrack at each life stage can influence the rate of local and regional mangrove expansion. Because interaction strengths can change in direction and magnitude with ontogeny, it is essential to examine resident–invader interactions at multiple life stages and across environmental gradients to uncover the mechanisms of biotic assistance and resistance during invasion.

中文翻译：

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栖息物种的枯枝落叶首先促进然后抑制了范围扩大物种的连续生命阶段

1. 居住物种可以促进入侵物种（生物协助）或抑制其扩张（生物抗性）。物种之间的相互作用通常取决于环境，生物援助与抗药性的相对重要性可能会随着非生物条件或入侵物种生命周期的变化而变化，因为入侵者的耐受力和资源需求随个体发育而变化。在佛罗里达州东北部的盐沼中，原生沼泽冬草草（Spartina alterniflora）丰富的枯枝落叶（残骸）可能会影响黑红树林（Avicennia Germinans）的扩张成功，该物种是向北扩展其范围的热带物种。
2. 我们使用两个野外实验来检验互花米草残骸如何在（a）繁殖体建立和（b）随后的幼苗存活过程中影响A.菌种的成功。我们还进行了实验室喂养试验，以鉴定繁殖体的食用者并评估残骸的存在如何影响草食性对红树林繁殖体的影响。
3. 互花米草残骸通过促进繁殖体的繁殖，保留和生根而促进了A.菌种的建立。潮汐政权影响了这些影响的程度。然而，随着时间的推移互花米草藻抑制A. germinans通过扼杀幼苗，吸引食草动物消费者苗成功。饲养试验中鉴定的啮齿动物，它投靠灭亡，因为消费者的A. germinans繁殖。
4. 综合。我们的研究结果表明的有害影响互花米草藻对A. germinans苗木成活率平衡上漂流物的初始有利影响A. germinans种子建立。当物种的胁迫耐受性和资源需求在整个开发过程中发生变化并且随非生物条件而变化时，就会出现这种种子－种子冲突。与潮汐条件相一致，在每个生命阶段与残骸的正向和负向相互作用的相对重要性都可以影响本地和区域红树林的扩张速度。由于相互作用强度会随着个体发生而在方向和大小上发生变化，因此有必要在多个生命阶段和环境梯度之间研究居民与入侵者之间的相互作用，以发现入侵过程中生物协助和抵抗的机制。