Data from: Loss of animal seed dispersal increases extinction risk in a tropical tree species due to pervasive negative density dependence across life stages

Overhunting in tropical forests reduces populations of vertebrate seed
dispersers. If reduced seed dispersal has a negative impact on tree
population viability, overhunting could lead to altered forest structure
and dynamics, including decreased biodiversity. However, empirical data
showing decreased animal-dispersed tree abundance in overhunted forests
contradict demographic models which predict minimal sensitivity of tree
population growth rate to early life stages. One resolution to this
discrepancy is that seed dispersal determines spatial aggregation, which
could have demographic consequences for all life stages. We tested the
impact of dispersal loss on population viability of a tropical tree
species, Miliusa horsfieldii, currently dispersed by an intact community
of large mammals in a Thai forest. We evaluated the effect of spatial
aggregation for all tree life stages, from seeds to adult trees, and
constructed simulation models to compare population viability with and
without animal-mediated seed dispersal. In simulated populations,
disperser loss increased spatial aggregation by fourfold, leading to
increased negative density dependence across the life cycle and a 10-fold
increase in the probability of extinction. Given that the majority of tree
species in tropical forests are animal-dispersed, overhunting will
potentially result in forests that are fundamentally different from those
existing now.

热带森林中的过度捕猎行为会导致脊椎动物种子传播者（seed dispersers）的种群规模缩减。若种子传播能力的减弱对树木种群的生存力（population viability）产生负面影响，则过度捕猎可能会改变森林的结构与动态，其中包括生物多样性的下降。然而，现有实证数据显示，在遭受过度捕猎的森林中，依赖动物传播的树木丰度有所降低，这与种群动态模型（demographic models）的预测结果相悖——后者认为树木种群增长率对早期生活史阶段（life stages）的敏感性极低。解决这一矛盾的一种可行思路是：种子传播过程决定了种群的空间聚集（spatial aggregation）模式，而这一模式可能对所有生活史阶段的种群动态产生影响。我们针对热带树种五瓣瓜馥木（Miliusa horsfieldii）开展了相关实验，该树种目前在泰国的一片森林中，由完整的大型哺乳动物群落介导种子传播。我们评估了从种子到成年个体的所有树木生活史阶段的空间聚集效应，并构建了模拟模型，用以对比存在与缺失动物介导种子传播两种情境下的种群生存力。在模拟种群中，传播者的缺失会使空间聚集度提升四倍，进而导致整个生活周期内的负密度制约（negative density dependence）效应增强，并使种群灭绝概率提升10倍。鉴于热带森林中的绝大多数树木物种均依赖动物传播种子，过度捕猎或将彻底改变现存森林的固有面貌。