Data from: Exploring the interaction of avian frugivory and plant spatial heterogeneity and its effect on seed dispersal kernels using a simulation model

Seed dispersal by avian frugivores is one of the key processes influencing plant spatial patterns, but may fail if there is disruption of plant-frugivore mutualisms, such as decline in abundance of dispersers, fragmentation of habitat, or isolation of individual trees. We used simulation model experiments to examine the interaction between frugivore density and behaviour and the spatial arrangement of fruiting plants and its effect on seed dispersal kernels. We focussed on two New Zealand canopy tree species that produce large fruits and are dispersed predominantly by one avian frugivore (Hemiphaga novaeseelandiae). Although the mean seed dispersal distance decreased when trees became more aggregated, there were more frugivore flights between tree clusters, consequently stretching the tails of the dispersal kernels. Conversely, when trees were less aggregated in the landscape, mean dispersal distances increased because seeds were deposited over larger areas, but the kernels had shorter tails. While there were no statistically meaningful changes in kernel parameters when frugivore density changed, decreases in density did cause a proportional reduction in the total number of dispersed seeds. However, birds were forced to move further when fruit availability and fruit ripening were low. Sensitivity analysis showed that dispersal kernels were primarily influenced by the model parameters relating to disperser behaviour, especially those determining attractiveness based on distance to candidate fruiting trees. Our results suggest that the spatial arrangement of plants plays an important role in seed dispersal processes – although tree aggregation curbed the mean seed dispersal distance, it was accompanied by occasional long distance events, and tree dispersion caused an increase in mean dispersal distance, both potentially increasing the probability of seeds finding suitable habitats for germination and growth. Even though low frugivore densities did not cause dispersal failure, there were negative effects on the quantity of seed dispersal because fewer seeds were dispersed.

鸟类食果动物（avian frugivores）介导的种子扩散是影响植物空间格局的核心过程之一，但当植物-食果动物共生关系（plant-frugivore mutualisms）遭到破坏时——例如扩散者种群丰度下降、生境破碎化或单株树木孤立化——这一过程可能失效。本研究通过模拟模型实验，探究食果动物密度与行为、结果实植物空间配置之间的交互作用，及其对种子扩散核（seed dispersal kernels）的影响。本研究聚焦于两种新西兰冠层树种：它们结有大型果实，且主要依赖一种鸟类食果动物——新西兰鸠（Hemiphaga novaeseelandiae）进行种子扩散。尽管当树木聚集度提升时，平均种子扩散距离会缩短，但树群间的食果动物飞行频次增加，进而拉长了扩散核的尾部（即提升了长距离扩散事件的占比）。反之，当景观中树木聚集度降低时，平均扩散距离则会增加——这是因为种子被散布至更大范围的区域，但扩散核的尾部更短。尽管食果动物密度变化并未对扩散核参数产生统计学上的显著影响，但密度下降确实会导致扩散种子总数成比例减少。不过，当果实可获得性低且成熟度不足时，鸟类会被迫飞行更远的距离。敏感性分析结果显示，扩散核主要受与扩散者行为相关的模型参数影响，尤其是那些基于候选结果树距离来判定吸引性的参数。本研究结果表明，植物的空间配置在种子扩散过程中发挥着重要作用：尽管树木聚集会压低平均种子扩散距离，但会伴随偶发的长距离扩散事件；而树木分散布局则会提升平均扩散距离，这两种情况均有可能提高种子找到适宜萌发与生长生境的概率。即便食果动物密度较低不会导致种子扩散完全失效，但其会因扩散种子数量减少而对种子扩散的数量效应产生负面影响。