Understanding community and food web dynamics in the moss-microarthropod model ecological system: temporal variability and combined experimental habitat fragmentation and climate change

Abstract

There is a clear crisis in the maintenance of global biodiversity worldwide. Climate change and widespread habitat loss, degradation and fragmentation are exerting strong, landscape-scale pressures on biodiversity. Negative impacts of these stressors are seen at all levels of biological organization, but studies at the level of community and food webs are relatively rare. This is in large part due to the large spatial and temporal scales at which food webs operate. Natural microcosms (food webs operating at small spatial scales) have been used to experimentally approach complex theoretical and applied questions in ecology, and have provided many important insights to date. In particular, moss micro-arthropod communities have been used extensively for the study of the effects of habitat fragmentation. Here, we used this ecosystem in a replicated, manipulative experiment to study the combined effects of warming and habitat fragmentation on community and food web structure. In order to do this, we developed tools to estimate diet of Oribatid mites, which were one of the most abundant and diverse taxa in the food web. Stable isotope techniques and analysis of mouthpart morphology allowed us to describe a food web for a moss-microarthropod ecosystem from south eastern Australia. The food web comprised over 100 taxa organized into a suite of feeding guilds: herbivores, fungivores, detritivores, lichenivores and predators. The speciose nature of the system is a strength, and the challenge of dealing with the taxonomy, data storage and food web analysis was met by development of a publicly available taxonomy database/tool, and a food web analysis package. We described temporal variation in a suite of food web attributes across one summer and winter. We found marked differences in food web structure between sampling occasions, with patterns suggestive of temperature- and humidity-driven changes in resource availability. To test the generality of food web structure in our system as compared to other ecosystems, food web attributes were compared to those of a large compilation of food webs from around the world. Comparison revealed similarities in food web structure to other communities across a range of spatial scales and ecosystems. Dissimilarities were also found and discussed. We concluded that the moss-microarthropod system provides an adequate model for achieving a deeper understanding of processes in community ecology. Our experiments assess the assembly of moss-microarthropod communities after an extreme high-temperature event, against a back-drop of altered climate, and in the context of habitat fragmentation. Data provide initial indications that isolated habitats may be more susceptible to negative impacts of warming than less isolated habitats. Variability of responses among replicate landscapes was considerable, with some being relatively resilient. Future understanding of the underpinnings of this resilience could point to management options for resisting rapid environmental change. Our results highlight the value of dispersal in disturbed landscapes and of disturbance-buffered communities in the face of climate change. Given the importance of synergies between disturbances as drivers of biodiversity loss, and considering the paucity of data assessing the combined impacts of climate change and habitat fragmentation on food webs, further research must be carried out in this area. This could build and draw on the model system we have validated for that purpose, enabled by the suite of new tools generated here.