Warming and Predation Alter Consumer Coexistence

Abstract Understanding how species coexist is a key question in ecology, with implications for conserving biodiversity. Species coexistence is affected by multiple factors, including climate warming and the presence of predators, yet most studies consider these ‘stressors’ in isolation. The interactive effects of warming and predation on species coexistence have not been explored. Here, we constructed simplified shallow lake food webs in 24 large mesocosm ponds and applied a crossed design to simulate warming (+4.5°C) and predation (by crucian carp Carassius auratus ). We monitored population responses of two common snails, Bellamya aeruginosa and Radix swinhoei over 200 days. We predicted that warming will alter the phenology of the snails, and that this will combine with predation to reduce their abundance. Warming advanced the reproduction of R. swinhoei by 21.5 days and reduced biomass and density of both snails. The advance in R. swinhoei phenology suppressed the slower growing B. aeruginosa population, reducing coexistence. Warming and predation combined in an additive manner to decrease the biomass of B. aeruginosa . In contrast, the two drivers synergistically decreased the biomass and density of R. swinhoe i because of enhanced pressure from the fish on their preferred snail prey under warming, due to rising metabolic demands. Therefore, snail coexistence was further reduced with fish presence under warming. In conclusion, future continuous warming and strong predation might undermine the coexistence of the gastropods, thereby changing food web structures in shallow freshwater ecosystems.