Seed fates of four rainforest tree species in the fragmented forests of Anamalais in the southern Western Ghats, India

Seed predation is a key ecosystem process governing the plant population and community structure in forests. Forest fragmentation and habitat loss have been shown to affect seed predation, leading to altered tree recruitment. However, the effects of fragmentation and habitat loss on seed predation are highly variable and context-specific, with limited information from South Asia. For four rainforest tree species in a production landscape of tea and coffee, we examined the influence of forest type (benchmark, N = 3, and fragmented, N = 5, forests) and seed size on the proportion of seeds, 1) predated by vertebrate seed predators, 2) predated by invertebrate seed predators, and 3) removed by vertebrate seed predators. The seed fates were tracked by placing the seeds in four 1 × 1 m plots under the canopy of the tree (N ≥ 11 individuals per tree species and 48 trees overall), and camera traps were placed under a subset of trees (N = 29, trap nights = 712). Overall, we recorded nine species of seed predators, and the seed predator species composition differed for the four tree species. However, there was no significant difference in either seed predator species composition or their visitations across the forest types. The seeds were more likely to be predated (on average 6% higher predation) by vertebrate seed predators in the fragments than in the benchmark forests. Medium-seeded species were more likely to be predated by vertebrate seed predators than large-seeded species (on average 41% higher predation). Invertebrate seed predation and seed removal by vertebrate seed predators had a weak relationship with forest type, with higher invertebrate seed predation in the fragments and higher seed removal in the benchmark forests. With altered seed dispersal patterns resulting from habitat fragmentation and habitat loss, differential seed predation can alter regeneration patterns, thereby influencing adult tree communities in fragmented forests.

种子捕食是调控森林植物种群与群落结构的关键生态系统过程。森林破碎化与栖息地丧失已被证实会影响种子捕食过程，进而改变树木更新动态。然而，破碎化与栖息地丧失对种子捕食的影响具有极强的情境依赖性与变异性，目前南亚地区的相关研究数据仍较为匮乏。本研究针对茶-咖啡复合生产景观中的4种雨林乔木树种，探究了林型（基准林，样本量N=3；破碎化林，样本量N=5）与种子大小对种子占比的影响，具体包括：1）脊椎动物捕食的种子占比；2）无脊椎动物捕食的种子占比；3）脊椎动物移除的种子占比。研究通过在每株乔木冠层下布设4个1×1 m的样方放置种子（每个树种至少11株个体，总计48株乔木）以追踪种子命运，并在部分乔木冠层下布设红外相机陷阱（共29株，累计相机工作夜数712）。本次研究共记录到9种种子捕食者，且4种乔木对应的种子捕食者物种组成存在显著差异。但不同林型间的种子捕食者物种组成及其访见频次均无显著差异。相较于基准林，破碎化林中的种子更易受到脊椎动物捕食者的捕食（捕食率平均高出6%）。中等大小种子的树种相较于大种子树种，更易受到脊椎动物捕食者的捕食（捕食率平均高出41%）。无脊椎动物种子捕食率与脊椎动物介导的种子移除率仅与林型存在较弱的相关性：破碎化林中无脊椎动物种子捕食率更高，而基准林中种子移除率更高。由于栖息地破碎化与丧失会改变种子扩散模式，差异化的种子捕食过程可进一步改变树木更新模式，进而影响破碎化森林内的成年乔木群落结构。