Ecological communities along gradients of environmental stress are thought to be structured by trade-offs between resisting biotic interactions in physically benign habitats and successfully exploiting physically stressful habitats. However, these trade-offs are likely to be affected by the predictability of abiotic stressors, and variation in the strength of biotic interactions. I investigated community assembly and food web interactions in ponds across an unpredictable gradient of water inundation (pond permanence) in Canterbury, New Zealand. Pond community composition and species richness were strongly influenced by pond permanence. However, species in temporary ponds were a nested subset of generalists that were also found in permanent ponds, rather than a unique assemblage of temporary pond specialists. Subsequent experiments indicated predator impact decreased with pond permanence, partially due to the foraging suppression of predatory invertebrates in permanent ponds by fish. Weak predation in permanent ponds combined with unpredictable drying regimes likely selected for generalist traits, and resulted in community assembly being driven by a gradient of drying stress rather than trade-offs between biotic interactions and drying. Furthermore, predator impact increased over time in temporary ponds. In predictable snow-melt ponds in the Colorado Rocky Mountains, seasonal windows of weak predation were exploited by vulnerable species, leading to increased diversity within habitats. However in unpredictable systems like Canterbury, temporal increases in predation risk that depend on drying history are likely to increase variability in the spatial arrangement of suitable habitats for particular species. This should further favour the evolution of generalist traits and reduce the importance of trade-offs between predation and drying in the assembly of communities. Considering the predictability of disturbance regimes and the spatial and temporal variation in biotic interactions will greatly enhance understanding and management of communities in heterogeneous landscapes.

Ecological communities along gradients of environmental stress are thought to be structured by trade-offs between resisting biotic interactions in physically benign habitats and successfully exploiting physically stressful habitats. However, these trade-offs are likely to be affected by the predictability of abiotic stressors, and variation in the strength of biotic interactions. I investigated community assembly and food web interactions in ponds across an unpredictable gradient of water inundation (pond permanence) in Canterbury, New Zealand. Pond community composition and species richness were strongly influenced by pond permanence. However, species in temporary ponds were a nested subset of generalists that were also found in permanent ponds, rather than a unique assemblage of temporary pond specialists. Subsequent experiments indicated predator impact decreased with pond permanence, partially due to the foraging suppression of predatory invertebrates in permanent ponds by fish. Weak predation in permanent ponds combined with unpredictable drying regimes likely selected for generalist traits, and resulted in community assembly being driven by a gradient of drying stress rather than trade-offs between biotic interactions and drying. Furthermore, predator impact increased over time in temporary ponds. In predictable snow-melt ponds in the Colorado Rocky Mountains, seasonal windows of weak predation were exploited by vulnerable species, leading to increased diversity within habitats. However in unpredictable systems like Canterbury, temporal increases in predation risk that depend on drying history are likely to increase variability in the spatial arrangement of suitable habitats for particular species. This should further favour the evolution of generalist traits and reduce the importance of trade-offs between predation and drying in the assembly of communities. Considering the predictability of disturbance regimes and the spatial and temporal variation in biotic interactions will greatly enhance understanding and management of communities in heterogeneous landscapes.

En combinant des approches empiriques et expérimentales, nous avons évalué les effets de trois composantes du changement climatique sur la biodiversité aquatique alpine: le recouvrement glaciaire, le gradient altitudinal et la température de l'eau. Nous avons montré que: 1) Les niveaux intermédiaires de recouvrement glaciaire génèrent une hétérogénéité environnementale élevée associée à une plus grande diversité locale du zooplancton. 13% de la diversité régionale est limitée aux tourbières aux bassins fortement englacés, et pourrait être amenée à disparaître avec le réchauffement. 2) Les filtres environnementaux et spatiaux impactent fortement la structuration des communautés de zooplancton, avec une influence probable des évènements stochastiques (sécheresse, inondation). 3) La température de l'eau n'a que peu d'influence sur les interactions prédateurs (Anax imperator)- proies (Daphnia magna), la probabilité de capture des proies semblant dépendre principalement de la précision du prédateur. Ce travail suggère une structuration multiéchelle des potentiels effets du changement climatique sur la biodiversité aquatique alpine. / Using empirical and experimental approaches, we assessed the effects of three components of climate change on alpine aquatic diversity: glacier’ influence, elevation, and temperature. We found that: 1) intermediate levels of glacial influence on peatland’s catchment resulted in a high environmental heterogeneity and high local zooplankton diversity. Thirteen percent of the total regional aquatic diversity was restricted to peatlands with a high percentage of glacial influence. This diversity might be lost in a context of glacial retreat and a future increasing warming. 2) environmental and spatial filters contributed significantly to the zooplankton community structure at higher spatial scales and the important role of the environmental filter at small spatial scale, likely influenced by disturbance events (e.g. droughts and floods) 3) water temperature did not influence on the prey-predation interaction between Anax imperator and Daphnia magna, and the predator’s capture probability mainly depended on the precision of the predator in capturing the prey. This work suggests that there is a multi-scale structure of the potential effects of climate change on alpine aquatic diversity.