The causes and consequences of microbial community dynamics remain poorly understood. This is particularly true for host-associated microbiota, although such communities are commonly observed to change over time and contribute critical functions to their hosts. If community composition and functioning are coupled (as biodiversity-ecosystem function theory commonly posits), then ontogenetic or seasonal shifts in a host's microbiota may influence host performance or fitness. To test this hypothesis, I simultaneously tracked the dynamics of natural digestive communities from the carnivorous pitcher plant Darlingtonia californica and the rates of prey digestion and prey-derived nitrogen assimilation by the host plant. Furthermore, I ran additional experiments to test whether these temporal changes in host functioning could be caused by biodiversity-ecosystem function effects or by the host, independent of its microbiota.
Monitoring the yearlong development of independent microbial digestive communities in two pitcher plant populations revealed a number of trends in community succession matching theoretical predictions. These included mid-successional peaks in bacterial diversity and metabolic substrate use, predictable and parallel successional trajectories among microbial communities, and convergence giving way to divergence in community composition and substrate use. Bacterial composition, biomass, and diversity positively influenced the rate of prey decomposition in both laboratory and field settings, which was in turn positively associated with a host leaf’s nitrogen uptake efficiency. These patterns could not be explained by host leaf age alone, implicating an important role for microbial community dynamics in host nutrient acquisition. These results highlight links between community succession and ecosystem functioning and extend aspects of succession theory to host-associated microbial communities.