Data from: Plant connectivity underlies plant-pollinator-exploiter distributions in Ficus petiolaris and associated pollinating and non-pollinating fig wasps

Mutualism is ubiquitous in nature, and nursery pollination mutualisms provide a system well suited to quantifying the benefits and costs of symbiotic interactions. In nursery pollination mutualisms, pollinators reproduce within the inflorescence they pollinate, with benefits and costs being measured in the numbers of pollinator offspring and seeds produced. This type of mutualism is also typically exploited by seed-consuming non-pollinators that obtain resources from plants without providing pollination services. Theory predicts that the rate at which pollen-bearing “foundresses” visit a plant will strongly affect the plant's production of pollinator offspring, non-pollinator offspring, and seeds. Spatially aggregated plants are predicted to have high rates of foundress visitation, increasing pollinator and seed production, and decreasing non-pollinator production; very high foundress visitation may also decrease seed production indirectly through the production of pollinators. Working with a nursery mutualism comprised of the Sonoran Desert rock fig, Ficus petiolaris, and host-specific pollinating and non-pollinating fig wasps, we use linear models to evaluate four hypotheses linking species interactions to benefits and costs: 1) foundress density increases with host-tree connectivity, 2) pollinator production increases with foundress density, and 3) non-pollinator production and 4) seed production decrease with pollinator production. We also directly test how tree connectivity affects non-pollinator production. We find strong support for our four hypotheses, and we conclude that tree connectivity is a key driver of foundress visitation, thereby strongly affecting spatial distributions in the F. petiolaris community. We also find that foundress visitation decreases at the northernmost edge of the F. petiolaris range. Finally, we find species-specific effects of tree connectivity on non-pollinators to be strongly correlated with previously estimated non-pollinator dispersal abilities. We conclude that plant connectivity is highly important for predicting plant-pollinator-exploiter dynamics, and discuss the implications of our results for species coexistence and adaptation.

互利共生在自然界中广泛存在，传粉抚育型互利共生（nursery pollination mutualisms）则为量化共生相互作用的收益与成本提供了理想的研究体系。在该类互利共生关系中，传粉者会在其授粉的花序内繁殖，其收益与成本可通过传粉者后代数量与植物结实量进行衡量。此类互利共生通常还会被食籽非传粉者所利用：这类生物从植物中获取资源，却不提供传粉服务。理论预测，携带花粉的建群雌蜂（foundresses）造访植株的频率，会对植物产生的传粉者后代、非传粉者后代以及种子产量产生显著影响。空间聚集生长的植物被预测拥有更高的建群雌蜂造访率，这会提升传粉者与种子的产量，同时降低非传粉者的种群产出；极高的建群雌蜂造访率甚至可能通过增加传粉者后代的产生，间接降低植物的种子产量。本研究以索诺兰沙漠岩榕（Sonoran Desert rock fig，Ficus petiolaris）与其宿主特异性传粉、非传粉榕小蜂构成的抚育型互利共生系统为研究对象，通过线性模型（linear models）验证四项将物种相互作用与收益、成本相关联的假说：1）建群雌蜂密度随宿主树连通性的提升而增加；2）传粉者产量随建群雌蜂密度的升高而增加；3）非传粉者产量随传粉者产量的提升而降低；4）种子产量随传粉者产量的提升而降低。此外，我们还直接检验了树体连通性对非传粉者产量的影响。研究结果为上述四项假说提供了强有力的支持，我们据此认为树体连通性是调控建群雌蜂造访率的关键驱动因子，进而显著影响柄叶榕（Ficus petiolaris）群落的空间分布格局。同时我们发现，在建群雌蜂分布范围的最北端，其造访率会出现下降。最后，我们发现树体连通性对非传粉者产生的物种特异性效应，与此前估算的非传粉者扩散能力存在显著相关性。我们的研究表明，植物连通性对于预测植物-传粉者-剥削者动态具有极高的重要性，并就本研究结果对物种共存与适应性演化的启示进行了讨论。