Plant diversity stabilizes communities by enhancing food web compartmentalization
The network structure of trophic interactions can determine the sensitivity of consumer communities to perturbations. Highly compartmentalized food webs that are composed of clusters of interacting species can resist disturbance by preventing the proliferation of extinctions. Despite the important ecological consequences of compartmentalization, its causes remain poorly understood. Here we examine compartmentalization of food webs composed of over 1000 invertebrate species sampled in The Jena Experiment, a long-term grassland biodiversity experiment located in Jena, Germany. We test the hypotheses that 1) plant species richness enhances food web compartmentalization; 2) compartmentalization increases with experimental duration; 3) aboveground food webs are more compartmentalized than belowground food webs.
We find that plant species richness has a positive linear relationship with food web compartmentalization, but a saturating, asymptotic relationship with consumer species richness. The divergent patterns of these two metrics reveal that loss of plant species has detrimental effects on consumer community stability even when consumer species richness is not affected. Despite some inter-annual variation, the positive relationship between plant species richness and compartmentalization grew stronger through time. Surprisingly, belowground food webs were more compartmentalized than aboveground food webs, not less as we predicted. Although, belowground food web compartmentalization was not sensitive to changes in plant species richness. Network approaches, which examine food web structure, expose cryptic sources of community stability that are more sensitive to alterations in plant diversity than invertebrate species richness would suggest. Considered together, these results show that older, more diverse communities should be less sensitive to disturbance and they emphasize the importance of linkages between aboveground and belowground communities as a key factor stabilizing consumer communities.