Are Nested Networks More Robust to Disturbance? A Test Using Epiphyte-Tree, Comensalistic Networks

Recent research on ecological networks suggests that mutualistic networks are more nested than antagonistic ones and, as a result, they are more robust against chains of extinctions caused by disturbances. We evaluate whether mutualistic networks are more nested than comensalistic and antagonistic networks, and whether highly nested, host-epiphyte comensalistic networks fit the prediction of high robustness against disturbance. A review of 59 networks including mutualistic, antagonistic and comensalistic relationships showed that comensalistic networks are significantly more nested than antagonistic and mutualistic networks, which did not differ between themselves. Epiphyte-host networks from old-growth forests differed from those from disturbed forest in several topological parameters based on both qualitative and quantitative matrices. Network robustness increased with network size, but the slope of this relationship varied with nestedness and connectance. Our results indicate that interaction networks show complex responses to disturbances, which influence their topology and indirectly affect their robustness against species extinctions.近年来针对生态网络的研究显示，互利共生网络（mutualistic networks）的嵌套性（nestedness）高于拮抗网络（antagonistic networks），因此其抵御干扰引发的物种灭绝级联的鲁棒性（robustness）更强。本研究旨在验证两个科学假设：其一，互利共生网络的嵌套性是否高于偏利共生网络（comensalistic networks）与拮抗网络；其二，高嵌套性的宿主-附生植物（host-epiphyte）偏利共生网络是否符合“对干扰具备高鲁棒性”的理论预测。通过对包含互利、拮抗、偏利共生关系的59个生态网络的综合分析，本研究发现：偏利共生网络的嵌套性显著高于拮抗网络与互利共生网络，而后两者的嵌套水平并无显著差异。基于定性与定量矩阵的分析结果显示，原始老龄林（old-growth forests）中的宿主-附生植物网络与受干扰森林中的同类网络，在多项拓扑参数（topological parameters）上存在显著差异。生态网络的鲁棒性随网络规模扩大而提升，但该相关性的斜率会随嵌套性与连接度（connectance）的变化而发生改变。本研究结果表明，物种互作网络对干扰会产生复杂响应，这类响应会影响网络拓扑结构，并间接改变其抵御物种灭绝的鲁棒性。