Data from: Reduced hornbill abundance associated with low seed arrival and altered recruitment in a hunted and logged tropical forest

Logging and hunting are two key direct threats to the survival of wildlife in the tropics, and also disrupt important ecosystem processes. We investigated the impacts of these two factors on the different stages of the seed dispersal cycle, including abundance of plants and their dispersers and dispersal of seeds and recruitment, in a tropical forest in north-east India. We focused on hornbills, which are important seed dispersers in these forests, and their food tree species. We compared abundances of hornbill food tree species in a site with high logging and hunting pressures (heavily disturbed) with a site that had no logging and relatively low levels of hunting (less disturbed) to understand logging impacts on hornbill food tree abundance. We compared hornbill abundances across these two sites. We, then, compared the scatter-dispersed seed arrival of five large-seeded tree species and the recruitment of four of those species. Abundances of hornbill food trees that are preferentially targeted by logging were two times higher in the less disturbed site as compared to the heavily disturbed site while that of hornbills was 22 times higher. The arrival of scatter-dispersed seeds was seven times higher in the less disturbed site. Abundances of recruits of two tree species were significantly higher in the less disturbed site. For another species, abundances of younger recruits were significantly lower while that of older recruits were higher in the heavily disturbed site. Our findings suggest that logging reduces food plant abundance for an important frugivore-seed disperser group, while hunting diminishes disperser abundances, with an associated reduction in seed arrival and altered recruitment of animal-dispersed tree species in the disturbed site. Based on our results, we present a conceptual model depicting the relationships and pathways between vertebrate-dispersed trees, their dispersers, and the impacts of hunting and logging on these pathways.

盗伐与狩猎是热带地区野生动物存续面临的两大核心直接威胁，同时也会破坏重要的生态系统过程。本研究于印度东北部的一处热带森林中，探究了这两类干扰因素对种子扩散循环各阶段的影响，涵盖植物及其扩散者的种群丰度、种子扩散与种群补充过程。研究以该类森林中的重要种子扩散者——犀鸟及其食源树种为对象：首先选取盗伐与狩猎压力较高的重度干扰样地，以及无盗伐且狩猎压力相对较低的轻度干扰样地，对比两地犀鸟食源树种的丰度，以明晰盗伐对犀鸟食源树种丰度的影响；同时对比了两地犀鸟的种群丰度。随后，我们对比了5种大粒树种的分散扩散种子到达量，以及其中4个树种的种群补充情况。结果显示，优先作为盗伐目标的犀鸟食源树种，在轻度干扰样地中的丰度为重度干扰样地的2倍；而犀鸟的种群丰度则为后者的22倍。分散扩散种子的到达量在轻度干扰样地中是重度干扰样地的7倍。2个树种的幼株补充丰度在轻度干扰样地中显著更高；对于另一个树种，重度干扰样地中的幼龄补充个体丰度显著更低，而成龄补充个体丰度则显著更高。本研究结果表明，盗伐会减少一类重要的食果-种子扩散者类群的食源植物丰度；而狩猎则会降低扩散者的种群丰度，进而导致干扰样地中种子到达量下降，以及动物扩散树种的种群补充过程发生改变。基于本研究结果，我们构建了一个概念模型，用以阐释脊椎动物扩散树种、其扩散者之间的关联与作用路径，以及盗伐与狩猎对这些路径的影响。