The resilience of pollination interactions: Importance of temporal phases

AimsThe loss of species that engage in close ecological interactions, suchas pollination, has been shown to lead to secondary extinctions,ultimately threatening the overall ecosystem stability and functioning.Pollination studies are currently flourishing at all possible levelsof interaction organization (i.e., species, guild, group and network),and different methodological protocols aimed to define the resilienceof pollination interactions have been proposed. However,the temporal dimension of the resilience of pollination interactionshas been often overlooked. In the light of these considerations, weaddressed the following questions: does a temporal approach helpto reveal critical moments during the flowering season, when pollinationinteractions are less resilient to perturbations? Do pollinationinteractions evaluated at species, guild, group and network levelshow different patterns when assessed through time?MethodsWe monitored contacts between plant and pollinator species in drygrassland communities every 15 days during the overall communityflowering season (12 surveys). For each survey, we built a quantitativeplant-pollinator interaction matrix and we calculated two sets ofmetrics characterizing, respectively, the diversity and the distributionof interactions across hierarchical levels. To describe the diversity ofinteractions, we calculated partner diversity (PD) at the species level,vulnerability/generality (V/G) at the guild level, and interaction diversityand evenness at the network level. The distribution of interactionswas characterized by calculating selectiveness at the species and thenetwork level, and modularity at the group level. We assessed thetemporal variation of PD, V/G at the level of plants and pollinators,and species selectiveness, by means of Linear Mixed Models (LMMs).To investigate the temporal variation of indexes calculated at groupand network level, we applied simple linear and quadratic regressionsafter checking for temporal autocorrelation in residuals.Important FindingsWhen taking into account the temporal dimension of interactions,the diversity of interactions showed different patterns at differentlevels of organization. At the species level, no relationship was disclosedbetween PD and time, when assessing the temporal trend ofV/G separately for the guild of plants and pollinators we observedan asymmetric structure of interactions. Pollination interactionsshowed to be asymmetric throughout the flowering season; however,evenness of interactions and network selectiveness showedsignificant positive relationships with time, revealing a poorer networkof interactions during the end of the flowering season. Thetemporal analysis of pollination interactions revealed a stronger riskof secondary extinctions at the end of the flowering season, due toa lower degree of redundancy and thus of resilience of the overallnetwork of interactions.