Data from: Geographic shifts in the effects of habitat size on trophic structure and decomposition

Habitat size is known to affect community structure and ecosystem function, but few studies have examined the underlying mechanisms over sufficient size gradients or in enough geographic contexts to determine their generality. Our goal in this study was to determine if the relationship between habitat size and leaf decomposition varied across geographic sites, and which factors may be driving the differences.
We conducted replicated observations in a coastal forest in Brazil, and in rainforests in Costa Rica and Puerto Rico. We used leaf litter decomposition and macroinvertebrate composition in bromeliad phytotelmata of varying sizes to determine the relationships between habitat size, trophic structure and decomposition over a wide geographical range. We experimentally disentangled the effects of site and litter quality by quantifying invertebrate control of decomposition of a native and a transplanted litter type within one site.
We found that the relationship between bromeliad size and decomposition rates differed among study sites. In rainforests in Costa Rica and Puerto Rico, decomposition was strongly linked to macroinvertebrate trophic structure, which varies with bromeliad size, driving strong bromeliad size-decomposition relationships. However, in Brazil there was no relationship between bromeliad size and decomposition. Our manipulative experiment suggests that within coastal forest in Brazil, the poor quality of native litter resulted in little invertebrate control of decomposition. Furthermore, the key detritivore in this site builds a predator-resistant case, which likely prevented effects of bromeliad size on trophic structure from being transmitted to decomposition even when litter quality was increased.
We conclude that differences in both leaf litter quality and macroinvertebrate traits among sites determine the link between decomposition and macroinvertebrates, and consequently the decomposition-bromeliad size relationship. These results show that the response of decomposition to habitat size is context-dependent, and depends on which component of the food web is the main driver of the function.

已知生境大小会影响群落结构与生态系统功能，但鲜有研究在足够广泛的生境大小梯度下，或是在足够多的地理情境中探究其内在机制以验证其普适性。本研究旨在明确两点：其一，生境大小与叶片凋落物分解之间的关联是否会随地理样地而异；其二，哪些因素可能驱动了这类差异。

我们分别在巴西的海岸林、哥斯达黎加与波多黎各的热带雨林中开展了重复观测实验。我们借助不同大小的凤梨科植物积水贮水环境（bromeliad phytotelmata）中的叶片凋落物分解过程与大型无脊椎动物（macroinvertebrate）群落组成，在大范围地理尺度下探究生境大小、营养结构与分解过程之间的关联。此外，我们通过在单个样地内量化无脊椎动物对本土与移植凋落物分解过程的调控作用，实验性地分离了样地效应与凋落物质量的影响。

研究结果显示，凤梨科植物大小与分解速率之间的关联在不同样地间存在显著差异。在哥斯达黎加与波多黎各的热带雨林中，叶片凋落物分解过程与大型无脊椎动物营养结构紧密相关，而后者随凤梨科植物大小发生变化，进而形成了显著的凤梨大小-分解关联。但在巴西的样地中，凤梨大小与分解过程并未呈现出关联。我们的操控实验表明，在巴西的海岸林内，本土凋落物的劣质质量导致无脊椎动物对分解过程的调控作用极弱。此外，该样地中的关键食腐动物（detritivore）会构筑抵御捕食者的栖管，这使得即便提升了凋落物质量，凤梨科植物大小对营养结构的影响也无法传递至分解过程中。

综上，不同样地间的叶片凋落物质量与大型无脊椎动物性状差异，共同决定了分解过程与无脊椎动物之间的关联，进而决定了凤梨科植物大小-分解过程的关联模式。本研究结果证实，分解过程对生境大小的响应具有情境依赖性，其具体表现取决于食物网中的哪一组分是该生态功能的主要驱动者。