Global Environmental changes and Metacommunities: Species interactions and spatial dynamics – GEMS

To apprehend this complexity, we will make use of a module composed of a few species in strong trophic association: a specialized herbivore (a myrmecophilous butterfly), its host plant and its host ant. The use of simplified systems made of a few species in strong interaction (modules) is promising to predict how biotic interactions at work in local communities and metacommunities would be affected by environmental changes. GEMS will particularly focus on the herbivore, investigating the cascade of changes in local populations resulting from the alteration of both local conditions, acting directly and indirectly through inter-specific interactions, and at the landscape scale through dispersal in the metapopulation.
In the field, local communities will be monitored along a gradient of elevation and a gradient of fragmentation to show how population dynamics change, how synchrony of critical life stages is affected, and how the strength of interspecific interactions change along these gradients.
Landscape genomics will be used to assess how landscape (including its fragmentation and its climate) affects dispersal of the three partners, and to identify putative tipping points for community functioning.
Community genomics will identify genomic regions affected by environmental conditions and the strength of species interactions.
Common-garden experiments will help discriminating between adaptive plasticity and adaptive evolution of key traits (involved either in dispersal or in species interactions).
All this information will then serve to build a model for the response of the metacommunity to (planned) environmental changes or its response to mitigation scenarios.

During the first 18 months, we have developed the protocols and collect the data. We also conducted theoretical work on central topics of GEMS, which resulted in 8 publications (5 already published,3 submitted).
In 2014, we selected thirty sites along a gradient of fragmentation and elevation.
We conducted genetic sampling of the 3 target species throughout these sites. The samples will then be genotyped for landscape genomics analysis. Plant and butterfly samples have been prepared for this analysis, ants undergo prior taxonomic verification.
During this season, we conducted the demographic characterization of populations of the three species. Populations of plants have also been the subject of phenotypic and phenological measurements.
The sites were also subjected to climatic analysis, showing a predominant effect of elevation on the conditions for the activity of ants, and no direct effect of fragmentation on climate. The landscapes were also the subject of a mapping that will be used for genetic analysis and modeling.
In order to achieve the common garden experiments, we have developed breeding conditions for all species. The conditions for germination and growth in greenhouse for the plant have been adjusted to seeds that we collected in the fall of 2014; ant colonies were installed at the lab in artificial nests, starting from individuals collected from a all sites, in order to integrate caterpillars to these breeding colonies. Common garden experiments began on ants to identify thermal preferential of individuals from climatically contrasting sites. Similar experiments will start this summer for the plants, and in 2016 for the butterfly.

The objectives for 2015 and early 2016 are to consolidate data acquisition, to complete the analysis of genetic and demographic data, to start experiments in a controlled environment, and to initiate the modeling part of GEMS. We will also continue our theoretical studies.

In terms of data collection, the field season 2015 will be to focus on demography for butterfly populations. For the plant, we will finish the demographic characterization of populations and also perform a further study of phenology. Monitoring of ant populations will be using the same protocol as in 2014.
We will analyze the impact of fragmentation and climate on gene flow. We will analyze the genetic relationships among the three partners species with community genomics tools .
We will continue the experiments on ants and define the protocols for butterflies experiments to complete during the summer of 2016.
We will begin the modeling part, building a habitat model for the plant and the butterfly. This part of the work will serve as a base for an extension to the project, to assess the impact of landscape history on demo-genetics of plant and butterfly populations.
We will continue our theoretical study, initiated a few weeks ago, on how climate and its changes affect the genetic diversity (and therefore adaptability) along food chains in communities, by performing a meta-analysis of literature review on this topic. This initiative was motivated by the lack of theoretical predictions and foundations currently available on this subject in direct line with GEMS.

1. Pavoine, S., Baguette, M., Stevens, V.M. et al. 2014. Life history traits, but not phylogeny, drive compositional patterns in a butterfly metacommunity. Ecology 95 (12), 3304-3313.
2. Stevens, VM. et al. (incl. M. Baguette) 2014. A comparative analysis of dispersal syndromes in terrestrial and semi-terrestrial animals. Ecology Letters 17 (8), 1039-1052.
3. Baguette, M., Stevens, V.M. & Clobert, J. 2014.The pros and cons of applying the movement ecology paradigm for studying animal dispersal. Movement Ecology, 2:13.
4. Legrand, D. et al. (incl. M. Baguette & V. Stevens). In press. Ranking the ecological causes of dispersal in a butterfly. Ecography, in press.
5. Coulon et al. (incl. M. Baguette & V. Stevens). In press. A stochastic movement simulator improves estimates of landscape connectivity. Ecology, in press.
6. Paz-Vinas, I. et al. (incl. V. Stevens). Evolutionary processes driving spatial patterns of intra-specific genetic diversity in river ecosystems. Under review as invited review for Molecular Ecology.
7. Villemey, A. et al. (incl. M. Baguette & V. Stevens). Butterfly dispersal in farmland: a multi-site landscape genetics study on the meadow brown butterfly (Maniola jurtina). Under review as classical paper in Molecular Ecology.
8. Baguette, M., Legrand, D. & Stevens, V.M. Genotype–phenotype interactions: an emergent, individual–centered evolutionary ecology framework. Presubmission inquiry sent to Trends in Ecology and Evolution.

To preserve the integrity of biodiversity functioning under the current global environmental changes (GEC) requires the availability of valuable tools to assess the efficiency of proposed management actions, which need to rely on a thorough knowledge of the relationship between the environmental conditions and the functioning of biodiversity at a variety of integration levels, from genes to ecosystems. These tools are currently mostly simulation platforms, whose efficiency strongly depends on their realism. Several over-simplifications however currently reduce this realism: GEC drivers like habitat fragmentation, climate change and so on, are considered separately from each other; species interactions are largely ignored; and evolutionary or plastic changes in key traits are not considered. The aim of GEMS is to clear these hurdles.

In GEMS, we will consider how habitat fragmentation and climate change, two main drivers of GEC in temperate regions that are currently considered in isolation, in combination affect the functioning of metacommnities. Rather than to focus on putative responses of disconnected populations, considered outside their network of inter-species interactions (competition, predation, etc.), we will consider explicitly these species interactions and the dispersal of individuals through fragmented landscapes. GEMS will thus consider local effects at the population level, indirect effects acting through species interactions at the community level, and landscape-scale effects acting through modified dispersal among local populations at the landscape level, that combined give rise to metacommunity functioning.

To that purpose, we will first identify along gradients of fragmentation and climate the modifications in key processes of metacommunity functioning (dispersal, phenology and population dynamics) for three species in strong interaction: a specialized herbivore, its host plant and its specialized parasitoid. The impact of landscape fragmentation and climate on dispersal will be addressed by landscape genetics, with the aim to identify tipping points in the responses of the three interacting species. In parallel, local phenology and dynamics will be recorded in populations of the three species along the two environmental clines, to see whether fragmentation and climate cause temporal mismatch of interacting species or modify their strength. Then, to highlight the processes behind the observed responses, we will manipulate the environment in controlled conditions. Using climate chambers and large-scale mesocosms (the Metatron), we will identify which of selection or phenotypic plasticity sustains the patterns of response, by which traits these changes in metacommunity functioning are mediated, and how the response at each trait is constrained by the other traits. Finally, we will integrate how the elemental responses observed combine by using a metacommunity model. With this model, we will also investigate what could be the response of this metacommunity to projected climate change, future landscape fragmentation, or mitigation scenarios, and their interactions.

Altogether, GEMS will thus provide both fundamentals insights on metacommunity functioning and have direct conservation applications by providing a realist tool to help decision-making in the conservation of biodiversity.