Data from: Biotic-drivers of seedling establishment in Neotropical savannas: selective granivory and seedling herbivory by leaf-cutter ants as an ecological filter

1. Herbivory has been shown to have prominent top-down effects on vegetation in Paleotropical savannas, where consumers of early stages of life-history act as demographic bottlenecks. Such impact has been largely ignored in Neotropical savannas, however, despite insect consumption being linked to reduced recruitment of woody species. 2. We hypothesize that Atta leaf-cutter ants – the prevalent herbivores in the Neotropics – alter the establishment of woody plant seedlings in the Brazilian Cerrado by reducing seed availability and seedling survival. We also hypothesize that the demographic effects will be species-specific. 3. To test these hypotheses we experimentally (1) compared seed removal in areas with and without Atta foraging and (2) compared the survivorship of seedlings exposed to or protected from Atta foraging. Both experiments were performed with the same common Cerrado species which allowed us to evaluate the potential net effects of consumers at the population and community levels. 4. Overall seed removal rates in sites with Atta foraging were greater than those where ants were absent (59.2% and 39.2% of seeds removed, respectively). There were differences in removal for ten of the twelve tested species, with per-species removal 1.1-3.8 fold greater in areas with Atta foraging. On transplanted plants, 45% of seedlings exposed to Atta were attacked, resulting in a survival 7.6% lower than that of protected seedlings. Seedling survival was 11.8-31.5% lower in five species, with the largest differences in survival between treatments during the dry season. 6. Taken together these results support the hypothesis that consumers can lead to demographic bottlenecks in Neotropical savanna plant species, with effects varying among life-history stages and between species. 7. Synthesis: Granivory by ants has been linked to reduced seedling recruitment of woody species in the Brazilian Cerrado. Our results shown that leaf-cutter ants may largely limit early seedling establishment of woody species by reducing seed availability and seedling survival with differential species-specific effects. Atta ants may therefore be acting as an ecological filter, which coupled with potential selectivity in foraging on reproductive life-history stages, may ultimately influence the relative abundance of different species and hence the structure and composition of Cerrado vegetation.1. 已有研究表明，植食作用（Herbivory）对古热带稀树草原（Paleotropical savannas）的植被具有显著的下行调控效应，该生态系统中生活史早期阶段的生物消费者会成为植物的种群瓶颈（demographic bottlenecks）。然而，尽管已有研究将昆虫取食与木本物种的种群补充率降低相关联，但新热带稀树草原（Neotropical savannas）中的这类植食影响却长期被忽视。 2. 本研究提出假说：作为新热带区优势植食类群的Atta切叶蚁（Atta leaf-cutter ants），会通过降低种子可获得性与幼苗存活率，影响巴西塞拉多（Brazilian Cerrado）地区木本植物幼苗的定植过程；同时推测该种群调控效应具有物种特异性。 3. 为验证上述假说，本研究开展了两项受控实验：（1）对比存在与不存在Atta切叶蚁觅食活动的区域内的种子移除率；（2）对比暴露于Atta切叶蚁觅食活动与免受其干扰的幼苗存活率。两项实验均采用同一批塞拉多地区常见物种作为研究材料，以便评估消费者在种群与群落尺度上的潜在净效应。 4. 整体而言，存在Atta切叶蚁觅食活动的样地内种子移除率显著高于无蚁样地（分别为59.2%与39.2%的种子被移除）。12个受试物种中有10个物种的种子移除率存在显著差异，存在切叶蚁觅食的区域内单物种种子移除率可达无蚁区域的1.1~3.8倍。在移栽植株上，45%暴露于切叶蚁的幼苗受到取食，其存活率较受保护的幼苗低7.6%。其中5个物种的幼苗存活率降低了11.8%~31.5%，且不同处理组间的存活率差异在旱季最为显著。 6. 综合以上研究结果，本研究验证了"生物消费者可导致新热带稀树草原植物种群出现种群瓶颈"的假说，且该效应会因生活史阶段与物种的不同而存在差异。 7. 综合讨论：蚂蚁的食籽作用（Granivory）已被证实与巴西塞拉多地区木本物种的幼苗种群补充率降低相关。本研究结果表明，切叶蚁可通过降低种子可获得性与幼苗存活率，显著限制木本植物早期幼苗的定植过程，且该效应具有物种特异性。综上，Atta切叶蚁可作为一种生态过滤因子，结合其在生殖生活史阶段觅食的潜在选择性，最终会影响不同物种的相对丰度，进而塑造塞拉多植被的群落结构与组成。