Dead litter of resident species first facilitates and then inhibits sequential life stages of range-expanding species

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 1) propagule establishment and 2) subsequent seedling survival. We also conducted laboratory feeding assays to identify propagule consumers and assess how wrack presence influences herbivory on mangrove propagules. 3. S. alterniflora wr...1. 本土物种可对入侵物种发挥双重作用：一是生物促进（biotic assistance），助力其成功入侵；二是生物抵抗（biotic resistance），抑制其扩张进程。物种间的相互作用通常具有情境依赖性，生物促进与生物抵抗的相对重要性可能随非生物环境或入侵物种的生活阶段发生变化，因入侵物种的胁迫耐受性与资源需求会随个体发育（ontogeny）而改变。在佛罗里达东北部的盐沼生境中，本土盐沼植物互花米草（Spartina alterniflora）的大量枯落漂积物（wrack），可能会影响热带物种黑皮红树（Avicennia germinans）的扩张成功率——该物种正逐步向北扩张其分布范围。 2. 我们通过两项野外实验（field experiments），分别探究了互花米草枯落物在1）繁殖体（propagule）定殖阶段、2）后续幼苗存活阶段对黑皮红树存活状况的影响。此外，我们还开展了室内取食实验（laboratory feeding assays），以明确繁殖体的取食类群，并评估枯落物存在与否对红树林繁殖体植食作用（herbivory）的影响。 3. 互花米草（S. alterniflora）的枯落漂积物（wrack）……