Biotic complexity, encompassing horizontal (within trophic levels) and vertical (among trophic levels) complexity, is crucial for ecosystem stability through various interactions. While plant diversity (horizontal complexity) is known to enhance ecosystem stability from both theory and experiments, the role of consumer diversity (vertical complexity) in these relationships remains underexplored. Over a decade-long grassland experiment, we investigated the effects of these dual complexity gradients on the temporal stability of primary producers by systematically manipulating number of plant species and the presence of heterotrophic consumers. A loss of plant diversity reduced plant community stability but increased the population-level stability of the remaining species. Reducing vertical complexity amplified the synchronization among species caused by plant diversity loss but did not affect either community- or population-level stability. These findings emphasize how consumer diversity loss potentially destabilizes plant communities by exacerbating synchronization and underscore the crucial role of trophic complexity in maintaining ecological equilibrium.

Context dependence impedes accurate prediction in ecology, including the extent and impact of invasion. Using a grassland experiment, we show that the interplay of limiting factors can explain why invasion trends vary with circumstance. By manipulating invader seed dose and physical disturbance and tracking cover of groups of fast and slow invaders in three communities over three years, we examined how seed-, resource- and growth rate-limitation affected the abundance and diversity impacts of invading plants. Evidence indicated that seeds primarily limited cover of resource-acquisitive fast invaders in early and mid successional communities, growth rate limited resource conservative slow invaders in early and mid succession, and resources limited invasion of both groups in late succession. Resident community diversity declined as invader cover increased, consistent with effects of resource limitation. A greater focus on limiting factors in invasion ecology will provide us with a structure for predicting invasion outcomes in different situations.