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The intra- and interspecific facets of biodiversity have traditionally been quantified and analysed separately, limiting our understanding of how evolution has shaped biodiversity, how biodiversity (as a whole) alters ecological dynamics, and hence eco-evolutionary feedbacks at the community scale. Here, we propose using candidate genes phylogenetically-conserved across species and sustaining functional traits as an inclusive biodiversity unit transcending the intra- and interspecific boundaries. This framework merges knowledge from functional genomics and functional ecology, and we first provide conceptual and technical guidelines for identifying phylogenetically-conserved candidate genes (PCCGs) within communities, and for measuring inclusive biodiversity from PCCGs. We then explain how biodiversity measured at PCCGs can be linked to ecosystem functions, which may unify recent observations that both intra- and interspecific biodiversity are important for ecosystem functions. We then highlight the eco-evolutionary processes shaping PCCGs diversity patterns, and argue that their respective role can be inferred from concepts derived from population genetics. Finally, we explain how PCCGs may shift the field of eco-evolutionary dynamics from a focal-species approach to a more realistic focal-community approach. This framework provides a novel perspective to investigate the global ecosystem consequences of diversity loss across biological scales, and how these ecological changes further alter biodiversity evolution.

Dispersal plasticity, when organisms adjust their dispersal decisions depending on their environment, can play a major role in ecological and evolutionary dynamics, but how it relates to fitness remains scarcely explored. Theory predicts that high dispersal plasticity should evolve when environmental gradients have a strong impact on fitness. Using microcosms, we tested in five species of the genus Tetrahymena whether dispersal plasticity relates to differences in fitness sensitivity along three environmental gradients. Dispersal plasticity was species- and environment-dependent. As expected, dispersal plasticity was generally related to fitness sensitivity, with higher dispersal plasticity when fitness is more affected by environmental gradients. Individuals often preferentially disperse out of low fitness environments, but leaving environments that should yield high fitness was also commonly observed. We provide empirical support for a fundamental, but largely untested, assumption in dispersal theory: the extent of dispersal plasticity correlates with fitness sensitivity to the environment.

According to theories on cave adaptation, cave organisms are expected to develop a lower metabolic rate compared to surface organisms as an adaptation to food scarcity in the subterranean environments. To test this hypothesis, we compared the oxygen consumption rates of the surface and subterranean populations of a surface‐dwelling species, the newt Calotriton asper, occasionally found in caves. In this study, we designed a new experimental setup in which animals with free movement were monitored for several days in a respirometer. First, we measured the metabolic rates of individuals from the surface and subterranean populations, both maintained for eight years in captivity in a natural cave. We then tested individuals from these populations immediately after they were caught and one year later while being maintained in the cave. We found that the surface individuals that acclimated to the cave significantly reduced their oxygen consumption, whereas individuals from the subterranean population maintained in the cave under a light/dark cycle did not significantly modify their metabolic rates. Second, we compared these metabolic rates to those of an obligate subterranean salamander (Proteus anguinus), a surface aquatic Urodel (Ambystoma mexicanum), and a fish species (Gobio occitaniae) as references for surface organisms from different phyla. As predicted, we found differences between the subterranean and surface species, and the metabolic rates of surface and subterranean C. asper populations were between those of the obligate subterranean and surface species. These results suggest that the plasticity of the metabolism observed in surface C. asper was neither directly due to food availability in our experiments nor the light/dark conditions, but due to static temperatures. Moreover, we suggest that this adjustment of the metabolic level at a temperature close to the thermal optimum may further allow individual species to cope with the food limitations of the subterranean environment., We showed evidence of a phenotypic plasticity at the metabolic level as a mechanism of cave colonization and adaptation in a european newt.

Dispersal is a key process for the dynamics and functioning of meta-communities and meta-ecosystems. Meta-ecosystem theory, however, does not fully integrate the possible effects of dispersal, largely assuming random diffusion of organisms and nutrients, contrasting with rising empirical evidence for intraspecific variability in dispersal strategies. Dispersal is often associated with a suite of phenotypic traits, forming dispersal syndromes. Since phenotypic variability is now acknowledged as a key factor mediating ecosystem dynamics, we argue that dispersal syndromes can link trait-based ecology and meta-ecosystem functioning together. We highlight that the dispersal of individuals can be associated with functional effect traits and can therefore alter trophic and nutrient-mediated interactions in ecosystems. We illustrate how the association between dispersal tendency and functional traits can modify the spatial heterogeneity of ecosystems.

Resident-disperser differences and genetic variability affect communities in microcosms

Dispersal is a key process mediating ecological and evolutionary dynamics. Its effects on metapopulations dynamics, population genetics or species range distribution can depend on phenotypic differences between dispersing and non-dispersing individuals (i.e., dispersal syndromes). However, scaling up to the importance of dispersal syndromes for meta-ecosystems have rarely been considered, despite intraspecific phenotypic variability is now recognised as an important factor mediating ecosystem functioning. In this study, we characterised the intraspecific variability of dispersal syndromes in twenty isolated genotypes of the ciliateTetrahymena thermophilato test their consequences for biomass productivity in communities composed of fiveTetrahymenaspecies. To do so, dispersers and residents of each genotype were introduced, each separately, in ciliate communities composed of four other competing species of the genusTetrahymenato investigate the effects of dispersal syndromes. We found that introducing dispersers led to a lower biomass compared to introducing residents. This effect was highly consistent across the twentyT. thermophilagenotypes despite their marked differences of dispersal syndromes. Finally, we found a strong genotypic effect on biomass production, confirming that intraspecific variability in general affected ecosystem functions in our system. Our study shows that intraspecific variability and the existence of dispersal syndromes can impact the functioning of spatially structured ecosystems in a consistent and therefore predictable way.

International audience; Intraspecific trophic variability has important ecological and evolutionary implications, and is driven by multiple interacting factors. Functional traits and environmental conditions are important in mediating the trophic niche of individuals because they determine their ability to consume certain prey, their energetic requirements, and resource availability. In this study, we aimed at investigating the interacting effects of functional traits and environmental conditions on several attributes of trophic niche in natural populations. Here, we quantified intraspecific variability in the trophic niche of 12 riverine populations of European minnow (Phoxinus phoxinus) using stable isotope analyses. Functional traits (i.e. morpho‐anatomical traits) and environmental conditions (i.e. upstream–downstream gradient, forest cover) were quantified to identify the determinants of (1) trophic position and resource origin, (2) trophic niche size, and (3) trophic differentiation (β‐diversity) among populations. We demonstrated that trophic position and resource origin covaried with functional traits related to body size and locomotion performance, and that the strength and shape of these relationships varied according to local environmental conditions. The trophic niche size also differed among populations, although no determinant was identified. Finally, trophic β‐diversity was correlated to environmental differentiation among sites. Overall, the determinants of intraspecific variability in trophic niche appeared highly context‐dependent, and related to the interactions between functional traits and environmental conditions. Because populations are currently facing important environmental changes, understanding this context‐dependency is important for predicting food web structure and ecosystem dynamics in a changing world.

Loss in intraspecific diversity can alter ecosystem functions, but the underlying mechanisms are still elusive, and intraspecific biodiversity–ecosystem function (iBEF) relationships have been restrained to primary producers. Here, we manipulated genetic and functional richness of a fish consumer (Phoxinus phoxinus) to test whether iBEF relationships exist in consumer species and whether they are more likely sustained by genetic or functional richness. We found that both genotypic and functional richness affected ecosystem functioning, either independently or interactively. Loss in genotypic richness reduced benthic invertebrate diversity consistently across functional richness treatments, whereas it reduced zooplankton diversity only when functional richness was high. Finally, losses in genotypic and functional richness altered functions (decomposition) through trophic cascades. We concluded that iBEF relationships lead to substantial top-down effects on entire food chains. The loss of genotypic richness impacted ecological properties as much as the loss of functional richness, probably because it sustains “cryptic” functional diversity., Global change is expected to generate a loss of intraspecific diversity worldwide. This mesocosm study explores whether loss of genetic and functional diversity in a predator species affects community and ecosystem functioning of lower trophic levels in pond ecosystems, revealing that diversity loss in a single consumer species can impact an entire ecosystem, reducing its functionality.

Understanding the relationships between biodiversity and ecosystem functioning has major implications. Biodiversity-ecosystem functioning relationships are generally investigated at the interspecific level, although intraspecific diversity (i.e. within-species diversity) is increasingly perceived as an important ecological facet of biodiversity. Here, we provide a quantitative and integrative synthesis testing, across diverse plant and animal species, whether intraspecific diversity is a major driver of community dynamics and ecosystem functioning. We specifically tested (i) whether the number of genotypes/phenotypes (i.e. intraspecific richness) or the specific identity of genotypes/phenotypes (i.e. intraspecific variation) in populations modulate the structure of communities and the functioning of ecosystems, (ii) whether the ecological effects of intraspecific richness and variation are strong in magnitude, and (iii) whether these effects vary among taxonomic groups and ecological responses. We found a non-linear relationship between intraspecific richness and community and ecosystem dynamics that follows a saturating curve shape, as observed for biodiversity-function relationships measured at the interspecific level. Importantly, intraspecific richness modulated ecological dynamics with a magnitude that was equal to that previously reported for interspecific richness. Our results further confirm, based on a database containing more than 50 species, that intraspecific variation also has substantial effects on ecological dynamics. We demonstrated that the effects of intraspecific variation are twice as high as expected by chance, and that they might have been underestimated previously. Finally, we found that the ecological effects of intraspecific variation are not homogeneous and are actually stronger when intraspecific variation is manipulated in primary producers than in consumer species, and when they are measured at the ecosystem rather than at the community level. Overall, we demonstrated that the two facets of intraspecific diversity (richness and variation) can both strongly affect community and ecosystem dynamics, which reveals the pivotal role of within-species biodiversity for understanding ecological dynamics.

International audience; The adaptive value of correlations among phenotypic traits depends on the prevailing environmental conditions. Differences in selection pressures during species range expansions may therefore shape phenotypic integration. In this study, we assessed variation in behavioral and morphological traits, as well as their covariations, in replicated southern and northern European populations of the northward expanding dragonfly Crocothemis erythraea. Larvae from northern populations were, on average, darker in color, and therefore, better camouflaged than larvae from southern populations. However, there was no difference in activity level. Darkness and activity were positively correlated in larvae from northern populations, whereas this trait covariation was missing in southern populations. These findings indicate the emergence of alternative strategies in time-limited northern populations, a higher activity level that required better camouflage through darker coloration, while less active larvae benefited from an energy-saving strategy by reducing the investment in costly traits, such as body darkness. We further found that larger larvae emerged into larger adults, with a higher investment in flight morphology. Our findings imply that phenotypic integration is associated with the northward range shift, potentially differentially shaping fitness consequences, and ecological interactions in southern versus northern populations.

Theory predicts that biodiversity is causally linked to key ecological functions such as biomass productivity, and that loss in functional traits both among- and within-species can reduce the efficiency of ecosystem functions. There has been ample empirical and experimental demonstration that species loss indeed reduces the efficiency of ecosystem functions, with tremendous impacts on services provided by biodiversity. Nonetheless, and despite the fact that within-species diversity is strongly altered by human activities, there have been little attempts to empirically test (i) whether intraspecific genetic diversity actually promotes productivity and stability in wild populations, and, (ii) if so, to quantify its relative importance compared to other determinants. Capitalizing on 20-year demographic surveys in wild fish populations, we show that genetic diversity does not increase mean biomass production in local populations, but strongly and consistently stabilizes biomass production over time. Genetic diversity accounts for about 20% of explained variance in biomass stability across species, an important contribution about half that of environment and demography (about 40% each). Populations having suffered from demographic bottlenecks in the recent past harbored lower levels of genetic diversity and showed less stability in biomass production over the last 20 years. Our study demonstrates that the loss of intraspecific genetic diversity can destabilize biomass productivity in natural vertebrate populations in just a few generations, strengthening the importance for human societies to adopt prominent environmental policies to favor all facets of biodiversity.

International audience; Functional traits can covary to form “functional syndromes.” Describing and understanding functional syndromes is an important prerequisite for predicting the effects of organisms on ecosystem functioning. At the intraspecific level, functional syndromes have recently been described, but very little is known about their variability among populations and—if they vary—what the ecological and evolutionary drivers of this variation are. Here, we quantified and compared the variability in four functional traits (body mass, metabolic rate, excretion rate, and boldness), their covariations and the subsequent syndromes among thirteen populations of a common freshwater fish (the European minnow, Phoxinus phoxinus). We then tested whether functional traits and their covariations, as well as the subsequent syndromes, were underpinned by the phylogenetic relatedness among populations (historical effects) or the local environment (i.e., temperature and predation pressure), and whether adaptive (selection or plasticity) or nonadaptive (genetic drift) processes sustained among‐population variability. We found substantial among‐population variability in functional traits and trait covariations, and in the emerging syndromes. We further found that adaptive mechanisms (plasticity and/or selection) related to water temperature and predation pressure modulated the covariation between body mass and metabolic rate. Other trait covariations were more likely driven by genetic drift, suggesting that nonadaptive processes can also lead to substantial differences in trait covariations among populations. Overall, we concluded that functional syndromes are population‐specific, and that both adaptive and nonadaptive processes are shaping functional traits. Given the pivotal role of functional traits, differences in functional syndromes within species provide interesting perspectives regarding the role of intraspecific diversity for ecosystem functioning.

Phenotypic or genotypic variation within species affects ecological processes, from populations to ecosystems. However, whether the ecological imprint of intraspecific variation is substantial compared to key environmental drivers, and persistent enough to carry over to next generations is still questioned. Here, we experimentally showed that intraspecific variation manipulated in a freshwater fish (the European minnow,Phoxinus phoxinus) led to ecological and transgenerational carry-over effects that were as strong as those of varying temperature by 2°C. Specifically, variation in fish body mass, growth rate and activity altered the size and abundance of prey, which ultimately affected traits and survival of the next fish generation. Temperature variation modulated other ecosystem functions (e.g. litter decomposition) that were also associated to transgenerational carry-over effects. Our results demonstrate that shifting genotypes or phenotypes in wild populations can have substantial and persistent consequences on ecosystems with a similar intensity than climatic variation.

Understanding the relationships between biodiversity and ecosystem functioning has major implications. Biodiversity–ecosystem functioning relationships are generally investigated at the interspecific level, although intraspecific diversity (i.e. within-species diversity) is increasingly perceived as an important ecological facet of biodiversity. Here, we provide a quantitative and integrative synthesis testing, across diverse plant and animal species, whether intraspecific diversity is a major driver of community dynamics and ecosystem functioning. We specifically tested (i) whether the number of genotypes/phenotypes (i.e. intraspecific richness) or the specific identity of genotypes/phenotypes (i.e. intraspecific variation) in populations modulate the structure of communities and the functioning of ecosystems, (ii) whether the ecological effects of intraspecific richness and variation are strong in magnitude, and (iii) whether these effects vary among taxonomic groups and ecological responses. We found a non-linear relationship between intraspecific richness and community and ecosystem dynamics that follows a saturating curve shape, as observed for biodiversity–function relationships measured at the interspecific level. Importantly, intraspecific richness modulated ecological dynamics with a magnitude that was equal to that previously reported for interspecific richness. Our results further confirm, based on a database containing more than 50 species, that intraspecific variation also has substantial effects on ecological dynamics. We demonstrated that the effects of intraspecific variation are twice as high as expected by chance, and that they might have been underestimated previously. Finally, we found that the ecological effects of intraspecific variation are not homogeneous and are actually stronger when intraspecific variation is manipulated in primary producers than in consumer species, and when they are measured at the ecosystem rather than at the community level. Overall, we demonstrated that the two facets of intraspecific diversity (richness and variation) can both strongly affect community and ecosystem dynamics, which reveals the pivotal role of within-species biodiversity for understanding ecological dynamics.

International audience; Although intraspecific differences between the phenotypes of organisms are an important driver of ecological dynamics (Des Roches et al. 2018), research to help integrate phenotypic variation and its drivers with ecosystem management has been limited. For this reason, the novel conceptual framework proposed by Palkovacs et al. (2018) – which helps to clarify the ecological implications of harvest‐driven trait changes – is timely.

Phenotypic variability is increasingly assessed through functional response and effect traits, which provide a mechanistic framework for investigating how an organism responds to varying ecological factors and how these responses affect ecosystem functioning. Covariation between response and effect traits has been poorly examined at the intraspecific level, thus hampering progress in understanding how phenotypic variability alters the role of organisms in ecosystems. Using a multi-trait approach and a nine-month longitudinal monitoring of individual red-swamp crayfish ( Procambarus clarkii ), we demonstrated that most of the measured response and effect traits were partially stable during the ontogeny of individuals. Suites of response and effect traits were associated with a response syndrome and an effect syndrome, respectively, which were correlated to form a functional syndrome. Using a bioenergetic model, we predicted that differences in the response syndrome composition of hypothetical populations had important ecological effects on a key ecosystem process (i.e. whole-lake litter decomposition) to a level similar to those induced by doubling population size. Demonstrating the existence of a functional syndrome is likely to improve our understanding of the ecological impacts of phenotypic variation among individuals in wild populations across levels of biological organization, and the linkage between ecosystem and evolutionary ecology.