Dominance, Biomass and Extinction Resistance Determine the Consequences of Biodiversity Loss for Multiple Coastal Ecosystem Processes

Thomas W Davies,Stuart R Jenkins,Stephen J Hawkins,Joseph Kenworthy,Jan G Hiddink,Rachel Kingham,Tamara Natasha Romanuk

doi:10.1371/journal.pone.0028362

Thomas W Davies, Stuart R Jenkins + Show 5 more

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https://doi.org/10.1371/journal.pone.0028362

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Abstract

Key ecosystem processes such as carbon and nutrient cycling could be deteriorating as a result of biodiversity loss. However, currently we lack the ability to predict the consequences of realistic species loss on ecosystem processes. The aim of this study was to test whether species contributions to community biomass can be used as surrogate measures of their contribution to ecosystem processes. These were gross community productivity in a salt marsh plant assemblage and an intertidal macroalgae assemblage; community clearance of microalgae in sessile suspension feeding invertebrate assemblage; and nutrient uptake in an intertidal macroalgae assemblage. We conducted a series of biodiversity manipulations that represented realistic species extinction sequences in each of the three contrasting assemblages. Species were removed in a subtractive fashion so that biomass was allowed to vary with each species removal, and key ecosystem processes were measured at each stage of community disassembly. The functional contribution of species was directly proportional to their contribution to community biomass in a 1∶1 ratio, a relationship that was consistent across three contrasting marine ecosystems and three ecosystem processes. This suggests that the biomass contributed by a species to an assemblage can be used to approximately predict the proportional decline in an ecosystem process when that species is lost. Such predictions represent “worst case scenarios” because, over time, extinction resilient species can offset the loss of biomass associated with the extinction of competitors. We also modelled a “best case scenario” that accounts for compensatory responses by the extant species with the highest per capita contribution to ecosystem processes. These worst and best case scenarios could be used to predict the minimum and maximum species required to sustain threshold values of ecosystem processes in the future.

Highlights

It is expected that biodiversity will continue to decline in the 21st century in terrestrial, marine and freshwater ecosystems [1]
In the sessile invertebrate assemblage community clearance rates of micro algae declined in an asymptotic curve with species loss (Figure 1B, Table 2), indicating that species which contributed most to clearance rates were most resistant to extinction
This relationship appeared heavily influenced by the 0 species treatment because the dominant species (Balanus crenatus) which contributed to 71% of community biomass was the most resistant to hypoxic disturbance, and the removal of more extinction susceptible species had little detectable impact on community clearance rates

Summary

Introduction

It is expected that biodiversity will continue to decline in the 21st century in terrestrial, marine and freshwater ecosystems [1]. Two decades of research into the role of biodiversity in ecosystem functioning has demonstrated that species and functional diversity can have a positive effect on a variety of key ecosystem processes such as carbon and nutrient cycling [2,3,4]. Understanding how such processes deteriorate as species are lost from ecosystems is necessary to enable predictions of the decline in ecosystem processes during extinction events. The resulting assemblages do not reflect reality where species loss in unlikely to be random [9,10] and extinction resistant species do not always compensate for biodiversity loss [11,12]

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