Species richness — the number of different species present in an ecosystem — is one of the key drivers of how that ecosystem functions, performs, and persists over time. In general, ecological research shows that higher species richness tends to strengthen an ecosystem in several interrelated ways, though the relationship is not perfectly linear and depends on context.
Productivity and resource use. Ecosystems with more species often make fuller use of available resources (light, nutrients, water, space) because different species occupy slightly different niches. This "niche complementarity" can increase total biomass production and nutrient cycling efficiency compared to species-poor systems.
Stability and resilience. Greater richness is frequently linked to more stable ecosystem functioning over time, an idea known as the insurance hypothesis. If one species declines due to disease, drought, or predation, others with overlapping roles can help maintain overall function — a form of ecological redundancy. This can buffer the ecosystem against environmental disturbances and reduce the risk of collapse.
Resistance to invasion and disease. Species-rich communities are sometimes more resistant to invasive species and pathogen outbreaks, since available niches are already filled, leaving fewer opportunities for outsiders to establish.
Food web complexity. More species generally means more complex food webs, with more predator-prey and mutualistic links. This complexity can dampen the effects of losing any single species but can also make the network more vulnerable to certain kinds of cascading failures, depending on which species and interactions are affected.
Ecosystem services. Richness supports services humans rely on, including pollination, water purification, soil fertility, carbon storage, and pest control.
Important caveats: the effect of richness depends heavily on which species are present (functional traits matter as much as raw counts), some ecosystems function well with relatively few species, and extremely high richness doesn't always translate to proportionally higher stability or productivity — the relationship often shows diminishing returns. Ecologists continue to debate the precise mechanisms and generality of these patterns across different ecosystem types.