Plant survival and keystone pollinator species in stochastic coextinction models: role of intrinsic dependence on animal-pollination

Coextinction models are useful to understand community robustness to species loss and resilience to disturbances. We simulated pollinator extinctions in pollination networks by using a hybrid model that combined a recently developed stochastic coextinction model (SCM) for plant extinctions and a topological model (TCM) for animal extinctions. Our model accounted for variation in interaction strengths and included empirical estimates of plant dependence on pollinators to set seeds. The stochastic nature of such model allowed us determining plant survival to single (and multiple) extinction events, and identifying which pollinators (keystone species) were more likely to trigger secondary extinctions. Consistently across three different pollinator removal sequences, plant robustness was lower than in a pure TCM, and plant survival was more determined by dependence on the mutualism than by interaction strength. As expected, highly connected and dependent plants were the most sensitive to pollinator loss and collapsed faster in extinction cascades. We predict that the relationship between dependence and plant connectivity is crucial to determine network robustness to interaction loss. Finally, we showed that honeybees and several beetles were keystone species in our communities. This information is of great value to foresee consequences of pollinator losses facing current global change and to identify target species for effective conservation.

共同灭绝模型有助于理解群落对物种丧失的稳健性及对扰动的恢复力。我们通过混合模型模拟传粉网络中的传粉者灭绝事件，该模型结合了近期开发的用于植物灭绝的随机共同灭绝模型（SCM）与用于动物灭绝的拓扑模型（TCM）。我们的模型考虑了互作强度的变异，并纳入了植物依赖传粉者结实的实证估计。该模型的随机性使我们能够确定植物在单次（及多次）灭绝事件中的存活情况，以及识别出哪些传粉者（关键物种，keystone species）更可能引发次生灭绝。在三种不同的传粉者移除序列中，植物稳健性始终低于纯拓扑模型（TCM）的结果，且植物存活更多由对互利共生的依赖而非互作强度决定。正如预期，高连接度且依赖传粉的植物对传粉者丧失最为敏感，在灭绝级联中崩溃速度更快。我们预测，依赖度与植物连接度之间的关系是决定网络对互作丧失稳健性的关键因素。最后，我们发现蜜蜂及若干甲虫是群落中的关键物种。这些信息对于预见当前全球变化下传粉者丧失的后果，以及识别有效保护的目标物种具有重要价值。