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中物种互作的功能结局的研究兴趣日益浓厚。对于包括传粉网络与种子扩散网络在内的多数互利共生网络（mutualistic networks），研究者通常通过记录动物对植物的觅食访视行为来采样其互作关系。然而，即便这些访视行为往往是研究关注的核心生态过程，它们未必能真实反映传粉或种子扩散事件本身。
2. 食果动物可通过两种方式作用于植物：一是吞食完整果实并扩散种子，从而充当种子扩散者；二是啄食果实以获取果肉或种子，进而成为果肉啄食者或种子捕食者（seed predators）。这两类互作对植物繁殖成功的影响截然相反。因此，若将访视行为直接等同于种子扩散事件，可能会对种子扩散互利共生关系的生态学、演化与保护研究产生有偏推断。
3. 本研究借助基于物种两两互作功能结局的自然历史信息，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-食果动物访视网络的结构变化。基于学界对互利共生网络与拮抗网络（antagonistic networks）结构差异的已有认知，我们提出了一系列互作移除后的结构变化假说，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%，占总互作频率的6%~24%。移除非互利互作后，网络水平指标（network-level metrics）如连接度（connectance）与嵌套性均出现显著升高，而鲁棒性（robustness）则有所下降。这些变化整体幅度较小、分布均匀，且主要由网络规模缩小驱动。与之相对，物种水平指标（species-level metrics）的变化则更为多变，部分变化幅度较大：植物节点度（plant degree）、互作频率、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（species strength）则显著升高。
5. 访视数据可能会高估植物-食果动物网络中种子扩散服务的实际发生频率。本研究表明，整合基于物种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行的生态过程与功能。我们的分类式研究方法（categorical approach）为未来研究量化互作功能结局沿互利-拮抗连续体（mutualism–antagonism continuum）的变化奠定了基础——正如其他食果动物区系（frugivore faunas）研究中所记录的那样。