Data from: Moving from frugivory to seed dispersal: incorporating the functional outcomes of interactions in plant-frugivore networks

1.There is growing interest in understanding the functional outcomes of species interactions in ecological networks. For many mutualistic networks, including pollination and seed dispersal networks, interactions are generally sampled by recording animal foraging visits to plants. However, these visits may not reflect actual pollination or seed dispersal events, despite these typically being the ecological processes of interest.

2.Frugivorous animals can act as seed dispersers, by swallowing entire fruits and dispersing their seeds, or as pulp peckers or seed predators, by pecking fruits to consume pieces of pulp or seeds. These processes have opposing consequences for plant reproductive success. Therefore, equating visitation with seed dispersal could lead to biased inferences about the ecology, evolution and conservation of seed dispersal mutualisms.

3.Here we use natural history information on the functional outcomes of pairwise bird‐plant interactions to examine changes in the structure of seven European plant‐frugivore visitation networks after non‐mutualistic interactions (pulp‐pecking and seed predation) have been removed. Following existing knowledge of the contrasting structures of mutualistic and antagonistic networks, we hypothesised a number of changes following interaction removal, such as increased nestedness and lower specialisation.

4.Non‐mutualistic interactions with pulp peckers and seed predators occurred in all seven networks, accounting for 21–48% of all interactions and 6–24% of total interaction frequency. When non‐mutualistic interactions were removed, there were significant increases in network‐level metrics such as connectance and nestedness, while robustness decreased. These changes were generally small, homogenous and driven by decreases in network size. Conversely, changes in species‐level metrics were more variable and sometimes large, with significant decreases in plant degree, interaction frequency, specialisation and resilience to animal extinctions, and significant increases in frugivore species strength.

5.Visitation data can overestimate the actual frequency of seed dispersal services in plant‐frugivore networks. We show here that incorporating natural history information on the functions of species interactions can bring us closer to understanding the processes and functions operating in ecological communities. Our categorical approach lays the foundation for future work quantifying functional interaction outcomes along a mutualism–antagonism continuum, as documented in other frugivore faunas.

1. 当前学界对解析生态网络（ecological networks）中物种种间互作的功能效应愈发关注。在诸多互利共生网络（mutualistic networks）中，包括传粉（pollination）与种子传播（seed dispersal）网络，研究人员通常通过记录动物对植物的觅食访问来采样互作数据。然而，尽管这些互作通常正是研究关注的核心生态过程，但此类访问记录未必能反映真实的传粉或种子传播事件。
2. 食果动物可通过两种方式参与植物互作：一是吞食完整果实并传播种子，扮演种子传播者；二是啄食果实以获取果肉或种子，成为果肉啄食者或种子捕食者（seed predators）。这两类过程对植物的繁殖成功会产生截然相反的影响。因此，若将访问记录直接等同于种子传播事件，可能会对种子传播互利共生关系的生态学、演化与保护研究产生有偏推断。
3. 本研究借助鸟类-植物两两互作的功能效应相关自然历史信息，探究了移除非互利互作（即果肉啄食与种子捕食）后，7个欧洲植物-食果动物访问网络的结构变化。基于学界已知的互利网络与拮抗网络（antagonistic networks）结构差异，我们提出了若干互作移除后的变化假设，例如嵌套性（nestedness）升高、特化程度（specialisation）降低等。
4. 7个网络中均存在与果肉啄食者、种子捕食者的非互利互作，这类互作占总互作数量的21%~48%，占总互作频次的6%~24%。移除非互利互作后，网络层面的连接度（connectance）、嵌套性等指标显著升高，而鲁棒性（robustness）则有所下降。这类变化整体幅度较小且较为均质，其驱动因素为网络规模的缩减。与之相反，物种层面的指标变化则更具变数，部分变化幅度较大：植物节点度（plant degree）、互作频次、特化程度以及对动物灭绝的恢复力（resilience）均显著下降，而食果动物的物种强度则显著升高。
5. 在植物-食果动物网络中，访问记录可能会高估种子传播服务的实际频次。本研究表明，纳入物种种间互作功能的自然历史信息，有助于我们更深入地理解生态群落中运作的生态过程与功能。我们的分类框架为未来量化互利-拮抗连续体（mutualism–antagonism continuum）上的功能互作效应奠定了基础，这一思路亦可推广至其他食果动物类群的相关研究中。