Elvire Bestion

Dispersal response to climate change: scaling down to intraspecific variation

Range shift, a widespread response to climate change, will depend on species abilities to withstand warmer climates. However, these abilities may vary within species and such intraspecific variation can strongly impact species responses to climate change. Facing warmer climates, individuals should disperse according to their thermal optimum with consequences for species range shifts. Here we studied individual dispersal of a reptile in response to climate warming and preferred temperature using a semi-natural warming experiment. Individuals with low preferred temperatures dispersed more from warmer semi-natural habitats while individuals with higher preferred temperatures dispersed more from cooler habitats. These dispersal decisions partly matched phenotype-dependent survival rates in the different thermal habitats, suggesting adaptive dispersal. This process should result into a spatial segregation of thermal phenotypes along species moving ranges which should facilitate local adaptation to warming climates. We therefore call for range-shift models including intraspecific variation in thermal phenotype and dispersal decision.

Maternal exposure to predator scents: offspring phenotypic adjustment and dispersal

Predation is a strong selective pressure generating morphological, physiological and behavioural responses in organisms. As predation risk is often higher during juvenile stages, antipredator defences expressed early in life are paramount to survival. Maternal effects are an efficient pathway to produce such defences. We investigated whether maternal exposure to predator cues during gestation affected juvenile morphology, behaviour and dispersal in common lizards (Zootoca vivipara). We exposed 21 gravid females to saurophagous snake cues for one month while 21 females remained unexposed (i.e. control). We measured body size, preferred temperature and activity level for each neonate, and released them into semi-natural enclosures connected to corridors in order to measure dispersal. Offspring from exposed mothers grew longer tails, selected lower temperatures and dispersed thrice more than offspring from unexposed mothers. Because both tail autotomy and altered thermoregulatory behaviour are common antipredator tactics in lizards, these results suggest that mothers adjusted offspring phenotype to risky natal environments (tail length) or increased risk avoidance (dispersal). Although maternal effects can be passive consequences of maternal stress, our results strongly militate for them to be an adaptive antipredator response that may increase offspring survival prospects.

Habitat matching and spatial heterogeneity of phenotypes: implications for metapopulation and metacommunity functioning

Abstract Spatial heterogeneity in the distribution of phenotypes among populations is of major importance for species evolution and ecosystem functioning. Dispersal has long been assumed to homogenise populations in structured landscapes by generating maladapted gene flows, making spatial heterogeneity of phenotypes traditionally considered resulting from local adaptation or plasticity. However, there is accumulating evidence that individuals, instead of dispersing randomly in the landscapes, adjust their dispersal decisions according to their phenotype and the environmental conditions. Specifically, individuals might move in the landscape to find and settle in the environmental conditions that best match their phenotype, therefore maximizing their fitness, a hypothesis named habitat matching. Although habitat matching and associated non-random gene flows can produce spatial phenotypic heterogeneity, their potential consequences for metapopulation and metacommunity functioning are still poorly understood. Here, we discuss evidence for intra and interspecific drivers of habitat matching, and highlight the potential consequences of this process for metapopulation and metacommunity functioning. We conclude that habitat matching might deeply affect the eco-evolutionary dynamics of meta-systems, pointing out the need for further empirical and theoretical research on its incidence and implications for species and communities evolution under environmental changes.

Climate warming reduces gut microbiota diversity in a vertebrate ectotherm

Climate change is now considered to be the greatest threat to biodiversity and ecological networks, but its impacts on the bacterial communities associated with plants and animals remain largely unknown. Here, we studied the consequences of climate warming on the gut bacterial communities of an ectotherm, the common lizard (Zootoca vivipara), using a semi-natural experimental approach. We found that 2–3 °C warmer climates cause a 34% loss of populations’ microbiota diversity, with possible negative consequences for host survival.

Metabolic traits predict the effects of warming on phytoplankton competition

Abstract Understanding how changes in temperature affect interspecific competition is critical for predicting changes in ecological communities with global warming. Here, we develop a theoretical model that links interspecific differences in the temperature dependence of resource acquisition and growth to the outcome of pairwise competition in phytoplankton. We parameterised our model with these metabolic traits derived from six species of freshwater phytoplankton and tested its ability to predict the outcome of competition in all pairwise combinations of the species in a factorial experiment, manipulating temperature and nutrient availability. The model correctly predicted the outcome of competition in 72% of the pairwise experiments, with competitive advantage determined by difference in thermal sensitivity of growth rates of the two species. These results demonstrate that metabolic traits play a key role in determining how changes in temperature influence interspecific competition and lay the foundation for mechanistically predicting the effects of warming in complex, multi‐species communities.

Role of carbon allocation efficiency in the temperature dependence of autotroph growth rates

Significance To predict how plant growth rate will respond to temperature requires understanding how temperature drives the underlying metabolic rates. Although past studies have considered the temperature dependences of photosynthesis and respiration rates underlying growth, they have largely overlooked the temperature dependence of carbon allocation efficiency. By combining a mathematical model that links exponential growth rate of a population of photosynthetic cells to photosynthesis, respiration, and carbon allocation; to an experiment on a freshwater alga; and to a database covering a wide range of taxa, we show that allocation efficiency is crucial for predicting how growth rates will respond to temperature change across aquatic and terrestrial autotrophs, at both short and long (evolutionary) timescales. Relating the temperature dependence of photosynthetic biomass production to underlying metabolic rates in autotrophs is crucial for predicting the effects of climatic temperature fluctuations on the carbon balance of ecosystems. We present a mathematical model that links thermal performance curves (TPCs) of photosynthesis, respiration, and carbon allocation efficiency to the exponential growth rate of a population of photosynthetic autotroph cells. Using experiments with the green alga, Chlorella vulgaris, we apply the model to show that the temperature dependence of carbon allocation efficiency is key to understanding responses of growth rates to warming at both ecological and longer-term evolutionary timescales. Finally, we assemble a dataset of multiple terrestrial and aquatic autotroph species to show that the effects of temperature-dependent carbon allocation efficiency on potential growth rate TPCs are expected to be consistent across taxa. In particular, both the thermal sensitivity and the optimal temperature of growth rates are expected to change significantly due to temperature dependence of carbon allocation efficiency alone. Our study provides a foundation for understanding how the temperature dependence of carbon allocation determines how population growth rates respond to temperature.

Changes in temperature alter the relationship between biodiversity and ecosystem functioning

Significance Empirical evidence for the response of ecosystem functioning to the combined effects of warming and biodiversity loss is scarce. We show that warming and biodiversity loss interact synergistically, impairing the functioning of microbial communities. We found that as temperatures departed from ambient conditions more species were required to maintain ecosystem functioning. Our results suggest interspecific complementarity increased under thermal stress and high-diversity communities that seemed functionally redundant at ambient temperature became more functionally unique as temperatures changed. Biodiversity may therefore be even more important than previously anticipated when considering the impacts of multiple facets of environmental change. Global warming and the loss of biodiversity through human activities (e.g., land-use change, pollution, invasive species) are two of the most profound threats to the functional integrity of the Earth’s ecosystems. These factors are, however, most frequently investigated separately, ignoring the potential for synergistic effects of biodiversity loss and environmental warming on ecosystem functioning. Here we use high-throughput experiments with microbial communities to investigate how changes in temperature affect the relationship between biodiversity and ecosystem functioning. We found that changes in temperature systematically altered the relationship between biodiversity and ecosystem functioning. As temperatures departed from ambient conditions the exponent of the diversity-functioning relationship increased, meaning that more species were required to maintain ecosystem functioning under thermal stress. This key result was driven by two processes linked to variability in the thermal tolerance curves of taxa. First, more diverse communities had a greater chance of including species with thermal traits that enabled them to maintain productivity as temperatures shifted from ambient conditions. Second, we found a pronounced increase in the contribution of complementarity to the net biodiversity effect at high and low temperatures, indicating that changes in species interactions played a critical role in mediating the impacts of temperature change on the relationship between biodiversity and ecosystem functioning. Our results highlight that if biodiversity loss occurs independently of species’ thermal tolerance traits, then the additional impacts of environmental warming will result in sharp declines in ecosystem function.

Species Responses to Climate Change: Integrating Individual-Based Ecology Into Community and Ecosystem Studies

Studies on climate change responses have often been carried at the species level, without considering the potential inter-individual variation within species in responses to climate and without taking into account the biotic and abiotic environment of the focal species. However, to really understand consequences of climate change, it is necessary to work at all levels of biological organization, from the individual and intraspecific level to the population, community, and ecosystem. Here, we review evidence on the importance of integrating every biological level into studies of climate change consequences, with a particular focus for the importance of intraspecific variation. In this review, we propose a synthetic approach to the study of climate change responses and illustrate our stance with a case study on a model ectotherm species, the common lizard ( Zootoca vivipara ). We advocate that this approach may allow unraveling potential feedbacks between biological levels and their nonadditive effects on biodiversity response to climate. Controlled mesocosm studies such as the one in this case study can allow a better understanding of these complex dynamics through a fine-tuned balance between ecological realism and the necessity to control ecological parameters.