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BIOdiversity, STAbility and sustainability in Spatial Ecological and social-ecological Systems

Periodic Reporting for period 3 - BIOSTASES (BIOdiversity, STAbility and sustainability in Spatial Ecological and social-ecological Systems)

Reporting period: 2018-09-01 to 2020-02-29

Biodiversity loss is one of the greatest environmental challenges of our time. There is growing evidence that biodiversity increases the stability of ecosystem functions and services, suggesting that it may be critical to the sustainability of ecosystems and human societies in the face of environmental changes. Classical ecological theory, however, has focused on measures of stability that cannot explain and predict these stabilizing effects, especially in spatial systems.

The goal of BIOSTASES is to develop a coherent body of new theory on the stability of ecosystems and coupled social–ecological systems and its relationships with biodiversity at multiple spatial scales that can better inform empirical research. BIOSTASES seeks to reach this goal through four complementary objectives. First, it aims to propose an integrative mathematical framework that connects different concepts and measures of stability used in ecology, and to clarify the merits and properties of temporal variability as an empirically relevant measure of stability (Work Package 1, WP1). Second, it uses dynamical metacommunity models to explore a wide range of novel questions related to ecosystem stability and diversity–stability relationships across scales (WP2). Third, it studies the stability of complex meta-ecosystems to provide new perspectives on the stability of food webs and on synergies and trade-offs between multiple ecosystem services across space (WP3). Fourth, it develops novel theory to study the long-term dynamics and sustainability of coupled social–ecological systems (WP4).

BIOSTASES proposes an ambitious innovative research programme that provides new perspectives on the functioning, stability, and sustainability of ecological and coupled social–ecological systems in the face of environmental changes. It contributes to bridging the gaps between theoretical and empirical ecology and between ecology and social sciences, and to developing new approaches in biodiversity conservation, landscape management, and sustainable development.
All four Work Packages have already delivered significant new results, but progress has been especially marked in WP1 and WP2.

Recent developments in WP1 have established the bases of an integrative mathematical framework that connects such different stability concepts as resilience, reactivity, variability, return rates, and structural stability. In particular, we showed that invariability — a stability measure that is often used in empirical studies — is more integrative than traditional theoretical stability measures such as asymptotic resilience and reactivity because they include information on the transient dynamics after a perturbation. Contrary to a widely held belief, asymptotic resilience is not representative of the recovery dynamics of ecosystems after a perturbation because it focuses on the very long-term recovery, which is both virtually impossible to observe empirically and almost entirely driven by rare species. In contrast, we have developed new stability measures that integrate the observable part of the recovery dynamics and that can be readily applied to empirical data. These include the median invariability and median return rate of ecosystems in response to the full set of possible perturbations.

Several studies performed in collaboration with colleagues from China and the USA have also tested theoretical predictions regarding the mechanisms underlying ecosystem stability in changing environments in temperate and semiarid grasslands. These studies have supported theory predicting that asynchrony between species plays a key role in ecosystem stability and that anthropogenic environmental changes such as nitrogen enrichment reduce ecosystem stability through decreased species asynchrony.

Work performed in WP2 has led to major advances regarding the spatial scaling of ecosystem functioning and stability and its relationships with the spatial scaling of biodiversity. We have developed several novel theoretical approaches to these issues. One approach uses the concepts of alpha, beta and gamma variability to propose a hierarchical conceptual and mathematical framework that connects ecosystem stability and biodiversity across a set of discrete spatial scales. A second approach uses an invariabilityarea relationship, which links ecological stability and the area observed, to predict variations in ecosystem stability over a continuous range of spatial scales. We have built new theory that predicts the shape of the invariabilityare relationship and its connections with the classical speciesarea relationship. We have applied this theory to empirical data, in particular on primary production from the plot to the global scale. We have also tested some of its predictions on the scale dependence of the diversitystability relationship in a temperate grassland experiment in China. A third approach uses an extended partition of biodiversity effects to quantify the insurance effects of biodiversity on ecosystem functioning across times and places. Its application to a temperate grassland experiment in the USA has showed that temporal insurance effects are quantitatively important even in small-scale controlled experiments.

Research in WP3 is already advanced in several promising directions but is less mature than in WP1 and WP2 because of the complexity of the topics addressed. We have developed a promising new approach to complex ecosystems in collaboration with a theoretical physicist from Israel. This approach considers ecosystems as disordered systems resulting from an assembly process, to which structure can be added to capture some key elements such as trophic levels or other well-defined functional groups. We have showed that many of the functional, dynamical and structural properties of the complex communities that emerge from the assembly process can be predicted analytically using a random model parameterised by only four statistical properties of the community. We are now using this approach to build ne
Most of the results described in the previous section represent progress beyond the state of the art, and we expect many more results until the end of the project.

In particular, BIOSTASES will focus on progress along the following directions during the second half of the project:

WP1: Build a synthetic, integrative mathematical framework that connects the various stability concepts used in ecology and other sciences. This integrative framework will be a major achievement that is likely to have a long-lasting influence on both theoretical and empirical ecology.

WP2: Provide a synthetic conceptual framework on the spatial scaling of the relationships between environmental factors, biodiversity and ecosystem functioning, stability and services, and develop new metacommunity models that turn this conceptual framework into testable theoretical predictions. These predictions should open up new avenues of research for empirical and theoretical studies in ecology.

WP3: Use the new approach to complex ecosystems we have developed to build new theory on the diversity and stability of complex food webs and meta-ecosystems. This is an area in which we hope to make significant breakthroughs during the second half of the project as it is a particularly complex and challenging area from both conceptual and technical viewpoints.

WP4: Expand our models to include spatial movements between multiple social-ecological systems, and use these models to study the dynamics and sustainability of spatial networks of coupled social-ecological systems. This is another area in which we expect significant breakthroughs during the second half of the project as there is virtually no formal theory on spatial networks of social-ecological systems currently.