Summary

The effects of anthropogenic impacts on biodiversity are varied and complex. The challenge of our age is to understand, predict, and mitigate the consequences of different components of global change on biodiversity, community dynamics and ecosystem functioning. Here, biotic interactions are key. Thanks to all the advances in the study of species interaction networks over the last fifteen years we are now in a unique position to tackle this challenge. But also, there are fundamental gaps that must be filled. I suggest a broad, ambitious, and novel research agenda that comprises the development of new theoretical frameworks, the compilation of new databases and the experimental manipulation in the short, mid, and long term. I briefly outline my main research lines and then I focus on one of them in which I try to understand and predict the combined effects of climate change and habitat fragmentation on biodiversity, community dynamics and ecosystem functioning.

Motivation and Research Vision

The largest challenge to understand and predict the consequences of different components of global change on biodiversity and ecosystems is to include the role of biotic interactions. Recent studies both on climate change impacts on biodiversity, which is expected to be the major future global change threat, and on biodiversity-ecosystem functioning relationships suggest that the greatest advances would arise from including biotic interactions, both as determinants of global change impacts and as affected by them. If biotic interactions are not explicitly included in the research agenda, the interpretation of many of our observations and predictions may not be valid.

Over the last fifteen years a revolution happened on the study of species interaction networks, both antagonistic (e.g. predator-prey, host-parasitoid) and mutualistic (e.g. plant-pollinators, plant-furgivores). Several universal patterns have been reported regarding the way biodiversity is organized into these complex interaction networks. Most species, for instance, are diet specialists while only a few are generalists. Specialized species tend to interact with generalist ones, and species tend to interact more strongly within compartments. Some of these patterns have challenged prevailing wisdom on the outcome of evolution and co-evolution based on isolated pairwise interactions, offering a new view on how biodiversity is generated and organized, and on how disturbances propagate throughout the entire ecological network.

Thanks to all these advances in the study of species interaction networks we are now in a unique position to investigate the effects of global change on complex ecosystems. We know what interaction patterns to look for, which conceptual and theoretical models to use, which data analyses to perform, and which experiments to design. But also we know what the big gaps in the study of ecological networks are and must be filled in coming decades.

Main Research Lines

1. Multiple stressors effects on communities and ecosystems.

In particular, I am interested on the combined effects of cliatic warming and fragmentation on biodiversity, community dynamics, and ecosystem functioning. This is the central topic of my ongoing ERC Consolidator Grant FRAGCLIM.

My overarching goal is to determine the role of climatic warming and habitat fragmentation on biodiversity, community dynamics and ecosystem functioning in multitrophic communities. To this end, I aim at developing a novel integrative and predictive theory to be tested with a unique experimental set-up. My project is organized around five workpackages in order to maximize feedbacks between new theoretical developments and experimental work:

WP1. Warming effects on non-fragmented ecosystems. How does the temperature dependence of metabolism, growth rates, and biotic interactions determine the effects of warming on biodiversity, food web structure, community dynamics and stability, and ecosystem functioning?

WP2. Habitat fragmentation effects on ecosystems. How does fragmentation and isolation affect dispersal limitation across several trophic levels, and how this in turn alters biodiversity, trophic dynamics, community structure and stability, and ecosystem functioning?

WP3. Combined effects of warming and fragmentation on meta-ecosystems. What are the interactive effects of changing temperatures and increasing isolation and dispersal limitation in the previous community and ecosystem properties over time?

WP4. Evolutionary thermal adaptation to warming: causes and ecosystem consequences. Does thermal adaptation occur in multitrophic communities subject to environmental warming, and how does isolation due to fragmentation modulate thermal adaptation? If so, what are the consequences for community dynamics and ecosystem functioning?

WP5. Mitigation measures for the combined effects of warming and fragmentation. Which theoretically and empirically sound environmental policies and restoration practices should be adopted to mitigate the combined effects of warming and fragmentation?

I use an integrative approach that combines the development of new theoretical models in close dialogue with a unique whole-ecosystem aquatic mesocosm experiment complemented by laboratory manipulations. All the models and the mesocosm experiment will be developed to explore the dynamics of two interacting trophic levels with several species within each level. Model predictions will be tested in AQUATIC METATRON experimental facility at Moulis. This new facility provides a unique opportunity to explore the effects of climatic warming and fragmentation in freshwater systems, by independently controlling ambient temperature and dispersal in highly replicated yet relatively large and species-rich multitrophic systems.

2. Towards an integration of ecological networks and biogeography.

Species interaction network studies and biogeography have evolved independently from each other. Prevailing wisdom is that biotic interactions rule in local-scale networks while large spatial scales are the province of climate. This and other cross-disciplinary boundaries are artificial. I suggest much progress can be made through the adoption of both a biogeographical perspective in networks and a network perspective in biogeography. In particular, we are trying to answer 2 main questions:

(1) Does network structure and community dynamics change across biogeographical gradients?

(2) Are there any universal patterns in the way networks change as we increase area- in other words, can we characterise network-area relationships, as we characterize species-area relationships?

 We continue developing theory, as in Galiana et al. (2018), but our focus now will be on empirical tests of the patterns.

3. The multidimensionality of ecological stability.

Ecological stability is key to both the maintenance of biodiversity and the sustainability of human societies as fluctuations of ecosystem services often have detrimental effects. Stability has been defined in many different ways that have been kept separate so far, preventing a coherent and operational research agenda on ecological stability and the effects of perturbations on ecological systems. I suggest we should adopt a multidimensional approach to stability and disturbances. In particular, we are trying to answer:

(1) What is the expected relationship between different stability metrics (i.e., resilience, variability, resistance)?

(2) How different stability metrics respond to different global change components, in particular habitat loss and fragmentation, climate change, and biodiversity loss?

(3) What is the evidence for the existence of thresholds and tipping points on ecosystems?

4. Structure, dynamics and functioning of host-microbiome systems.

We continue using community ecology perspective in order to understand the assembly, dynamics and functioning of complex host-associated microbiomes. I am focusing on marine sponges and their associated diverse and complex bacterial communities, asking the following questions:

(1) What is the structure of the global sponge microbiome networks, and what are the main ecological and evolutionary drivers?

(2) How dynamic are host-microbiome systems, and how can we identify core symbionts?

(3) What are the main mechanisms of symbiont transmission that give raise to the observed patterns?

I continue working on the large sponge microbiome database, gathering additional data for the evidence for vertical and horizontal transmission of microbiomes. But also, I am developing a theory to understand host-microbiome assembly and evolution.