Biodiversity as insurance: from concept to measurement and application

Abstract

Biological insurance theory predicts that, in a variable environment, aggregate ecosystem properties will vary less in more diverse communities because declines in the performance or abundance of some species or phenotypes will be offset, at least partly, by smoother declines or increases in others. During the past two decades, ecology has accumulated strong evidence for the stabilising effect of biodiversity on ecosystem functioning. As biological insurance is reaching the stage of a mature theory, it is critical to revisit and clarify its conceptual foundations to guide future developments, applications and measurements. In this review, we first clarify the connections between the insurance and portfolio concepts that have been used in ecology and the economic concepts that inspired them. Doing so points to gaps and mismatches between ecology and economics that could be filled profitably by new theoretical developments and new management applications. Second, we discuss some fundamental issues in biological insurance theory that have remained unnoticed so far and that emerge from some of its recent applications. In particular, we draw a clear distinction between the two effects embedded in biological insurance theory, i.e. the effects of biodiversity on the mean and variability of ecosystem properties. This distinction allows explicit consideration of trade-offs between the mean and stability of ecosystem processes and services. We also review applications of biological insurance theory in ecosystem management. Finally, we provide a synthetic conceptual framework that unifies the various approaches across disciplines, and we suggest new ways in which biological insurance theory could be extended to address new issues in ecology and ecosystem management. Exciting future challenges include linking the effects of biodiversity on ecosystem functioning and stability, incorporating multiple functions and feedbacks, developing new approaches to partition biodiversity effects across scales, extending biological insurance theory to complex interaction networks, and developing new applications to biodiversity and ecosystem management.

Biodiversity effects on seedling biomass growth are modulated by light environment across functional groups

“…Grassland species as well as mature trees show significant spatial and temporal insurance effects, which we did not detect on tree seedlings (Bunker et al, 2005; Isbell et al, 2018; and as reviewed in Loreau et al, 2021). This implies that although functional differences in mature trees might stabilise production through differential growth under heterogenous environments, these differences do not produce similar asynchrony in seedling communities.…”

Low‐intensity land‐use enhances soil microbial activity, biomass and fungal‐to‐bacterial ratio in current and future climates

“…Moreover, we hypothesized that (2b) a higher management intensity will have detrimental effects on soil microbial properties and decrease the proportion of fungal biomass in both land‐use types (de Vries & Thébault, 2013). It is recognized that low‐intensity management strengthens the resistance and resilience of ecosystems, due to positive biodiversity effects (Isbell et al., 2017; Loreau et al., 2021). Conversely, high‐intensity use stresses ecosystems, making them more vulnerable to further disturbances and environmental extremes.…”

Warming effects on grassland productivity depend on plant diversity

“…Warming-induced shifts in plant dominance may depend on species-specific responses to higher temperatures. Indeed, we cannot conclude if dominance-driven biomass responses in highdiversity communities could be entirely independent of shifts in species interactions, given that interspecific interactions can determine both overyielding and insurance effects (Loreau et al, 2021).…”