Robustness of alpine pollination networks: effects of network structure and consequences for endemic plants

Abstract

[eng] Global threats to plant-pollinator interactions are potentially serious in alpine ecosystems, which combine great diversity with particular fragility. We utilized tools from complex network theory to assess the robustness to species extinction of two Spanish alpine pollination networks. A comparison with ten additional alpine and subalpine pollination (ASP) networks allowed us to give our assessment a broader scope and provide a general view of ASP network robustness. We found a broad range of robustness among ASP networks. The two Spanish pollination networks ranked intermediate to high in robustness. This could be due to two of their structural features, connectance (proportion of potential interactions actually observed) and asymmetry (normalized difference between pollinator and plant richness), which showed a positive relationship with network robustness. A finer-scale focus on the two Spanish networks did not reveal differences between endemic and nonendemic plants in their functional role within the network but indicated that they differed in their robustness to pollinator extinction. Contrasting patterns across networks suggested that endemic robustness depends on community particularities. To improve the utility of robustness assessment as a conservation tool, we should increase our understanding on (1) the order in which network species will get extinct, (2) how species rewire once they have lost their partners, and (3) how much species depend on their mutualistic interaction.