Abstract
While it is crucial to understand the factors that determine the biodiversity of primary producer communities, the relative importance of bottom-up and top-down control factors is still poorly understood. Using freshwater benthic algal communities in the laboratory as a model system, we find an unimodal relationship between nutrient availability and producer diversity, and that increasing number of consumer species increases producer diversity, but overall grazing decreases algal biodiversity. Interestingly, these two factors interact strongly in determining producer diversity, as an increase in nutrient supply diminishes the positive effect of consumer species richness on producer biodiversity. This novel and thus-far overlooked interaction of bottom-up and top-down control mechanisms of biodiversity may have a pronounced impact on ecosystem functioning and thus have repercussions for the fields of biodiversity conservation and restoration.
Highlights
While it is crucial to understand the factors that determine the biodiversity of primary producer communities, the relative importance of bottom-up and top-down control factors is still poorly understood
Still no study has to our knowledge investigated the effect of nutrient enrichment and consumer species richness on the biodiversity of primary producers simultaneously, their potential interactions have remained elusive
The impact of consumer species richness might not be strong enough to counteract competitive exclusion among primary producers. This could result in a strong interaction of both bottom-up and top-down control mechanisms on primary producer biodiversity
Summary
While it is crucial to understand the factors that determine the biodiversity of primary producer communities, the relative importance of bottom-up and top-down control factors is still poorly understood. Using freshwater benthic algal communities in the laboratory as a model system, we find an unimodal relationship between nutrient availability and producer diversity, and that increasing number of consumer species increases producer diversity, but overall grazing decreases algal biodiversity. These two factors interact strongly in determining producer diversity, as an increase in nutrient supply diminishes the positive effect of consumer species richness on producer biodiversity. The impact of consumer species richness might not be strong enough to counteract competitive exclusion among primary producers This could result in a strong interaction of both bottom-up (nutrient supply) and top-down (consumer species richness) control mechanisms on primary producer biodiversity.
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