Answer:
Diversity-Stability Theory
Theoretical models suggest that there could be multiple relationships between diversity and stability, depending on how we define stability (reviewed by Ives & Carpenter 2007). Stability can be defined at the ecosystem level — for example, a rancher might be interested in the ability of a grassland ecosystem to maintain primary production for cattle forage across several years that may vary in their average temperature and precipitation. Figure 1 shows how having multiple species present in a plant community can stabilize ecosystem processes if species vary in their responses to environmental fluctuations such that an increased abundance of one species can compensate for the decreased abundance of another. Biologically diverse communities are also more likely to contain species that confer resilience to that ecosystem because as a community accumulates species, there is a higher chance of any one of them having traits that enable them to adapt to a changing environment. Such species could buffer the system against the loss of other species. Scientists have proposed the insurance hypothesis to explain this phenomenon (Yachi & Loreau 1999). In this situation, species identity — and particular species traits — are the driving force stabilizing the system rather than species richness per se (see Figure 2).
