Understanding the relationships between biodiversity and ecosystem functioning stands as a cornerstone in ecological research. Extensive evidence now underscores the profound impact of species loss on the stability and dynamics of ecosystem functions. However, it remains unclear whether the loss of genetic diversity within key species yields similar consequences. Here, we delve into the intricate relationship between species diversity, genetic diversity, and ecosystem functions across three trophic levels - primary producers, primary consumers, and secondary consumers - in natural aquatic ecosystems. Our investigation involves estimating species diversity and genome-wide diversity - gauged within three pivotal species - within each trophic level, evaluating seven key ecosystem functions, and analyzing the magnitude of the relationships between biodiversity and ecosystem functions (BEFs). We found that, overall, the absolute effect size of genetic diversity on ecosystem functions mirrors that of species diversity in natural ecosystems. We nonetheless unveil a striking dichotomy: while genetic diversity was positively correlated with various ecosystem functions, species diversity displays a negative correlation with these functions. These intriguing antagonist effects of species and genetic diversity persist across the three trophic levels (underscoring its systemic nature), but were apparent only when BEFs were assessed within trophic levels rather than across them. This study reveals the complexity of predicting the consequences of genetic and species diversity loss under natural conditions, and emphasizes the need for further mechanistic models integrating these two facets of biodiversity.
Keywords: Alnus; Gammarus; Phoxinus; crustaceans; ecology; fish; riparian trees.
When we speak about the loss of biodiversity, we often think of the loss of different species from an ecosystem. However, when ecosystems start to lose biodiversity, often, the first thing lost is diversity within species. This is, individuals of the same species become more like one another, leading to a loss of variety within a species. This can cause issues at the species level as a lack of variation means that the species as a whole is less able to adapt to new environmental challenges, which can potentially lead to extinction. Humans are driving a loss of biodiversity worldwide, but it is unclear how the loss of diversity within a species affects ecosystems. To answer this question, Fargeot et al. analyzed a complete food chain in an aquatic ecosystem in the wild, quantifying species diversity and using genetic tools to quantify within-species diversity. The researchers also quantified seven ecosystem functions associated with the ecosystem's productivity (how much biomass the ecosystem produces) and its ability to degrade dead organic matter. Fargeot et al. found that the effects of losing within-species diversity in the ecosystem were as impactful as losing species diversity. The scientists also discovered that the relative impact of within- and between-species diversity on ecosystems were opposite. Losing species surprisingly increased the rate of ecosystem function, which also increased the amount of biomass produced and the amount of degraded organic matter. Conversely, losing diversity within species slowed down these ecosystem functions and thus decreased the services they can provide to humans. These findings imply that measuring the loss of both within-species and between-species diversity is necessary to fully understand the effects of biodiversity loss. This will inform both conservation and agricultural efforts, where within-species diversity is often ignored.
© 2024, Fargeot et al.