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Cascading impacts of predator biodiversity loss: development of a predictive framework

Final Report Summary - ECOPRED (Cascading impacts of predator biodiversity loss: development of a predictive framework)

With many ecosystems experiencing species losses, a key question is how such losses will affect the functioning of ecosystems and the services they provide human societies (e.g. climate regulation, shoreline protection, food security). Ecologists have traditionally focused on taxonomic measures of biodiversity; particularly the identity (what species) and number of species present in an ecosystem. Yet such measures are silent on the ecological interactions and roles of organisms, so a major scientific challenge is to incorporate information on the characteristics of organisms (i.e. so-called ‘functional traits’) into our measures of biodiversity. Despite a large research effort for terrestrial plants, however, functional traits and their variation among organisms (‘functional diversity’) remain poorly understood for other groups of organisms and ecosystems (e.g. marine systems), and in the context of interactions between herbivores and plants or predator and prey (i.e. multi-trophic ecosystems). Ecopred addressed these knowledge gaps, forwarding the general objectives to: 1) Quantify the functional diversity of organisms and its response to species loss in diverse systems; 2) Link the functional diversity of organisms to ecosystem functions and services across multiple ecosystems; 3) Investigate the roles of trophic interactions in structuring diverse ecosystems.

To address these objectives, the fellow performed experiments and observational studies in multiple ecosystem types enhancing his ability to evaluate the general applicability of functional traits. In rocky shore ecosystems, he characterised the functional diversity of marine macroalgae, providing the first quantitative, multiple trait assessment of functional diversity among these important primary producers (Objective 1). He found that experimental removals of macroalgal species led to a drop in functional diversity and a destabilisation of ecosystem properties (O2). Further, he experimentally demonstrated, for the first time, that functional diversity is a key driver of human interest in marine ecosystems (O2). In salt marsh ecosystems, he has shown that a crucial mutualistic interaction (i.e. mutually beneficial) between two functionally diverse and dominant species (a grass and a mussel) leads to high levels of a suite of ecosystem functions and creates small, dispersed, patches that are resistant to climatic (drought) stress; these patches then fuel post-drought recovery of the ecosystem (O2). Also in salt marshes, his work has provided insights into the functional consequences of trophic interactions. He showed that predatory crabs actually suppress plants because of the way they change their prey’s behaviour (counter to basic theory) (O3); he also used a meta-analysis to reveal the broad ecosystem function and service consequences of livestock grazing in salt marshes worldwide (O3). In a model natural enemy – aphid biocontrol system in the laboratory he has found inconsistent and non-linear effects of natural enemy functional diversity (O3). Overall, his work shows that species losses can drive functional diversity loss, which in turn has the potential to disrupt ecosystem functions and services. This work advances our understanding of functional diversity in systems beyond terrestrial plants, elucidates its distribution among organisms, and the effects of its loss on ecosystems. In doing so, Ecopred’s outputs promise to improve management and monitoring of biodiversity in diverse ecosystems.