Global changes threaten functional and taxonomic diversity of insular species worldwide

Camille Leclerc,Céline Bellard,Clara Marino,Sébastien Villéger,Enrico Di Minin

doi:10.1111/ddi.13024

Abstract

AbstractAimThe assessment of biodiversity patterns under global changes is currently biased towards taxonomic diversity, thus overlooking the ecological and functional aspects of species. Here, we characterized both taxonomic and functional diversity of insular biodiversity threatened by multiple threats.LocationWorldwide islands (n = 4,348).MethodsWe analysed the relative importance of eleven major threats, including biological invasions or climate change, on 2,756 insular endemic mammals and birds. Species were functionally described using five ecological traits related to diet, habitat and body mass. We computed complementary taxonomic and functional diversity indices (richness, specialization, originality and vulnerability) of species pools affected by each threatening process to investigate relationships between diversity dimensions and threats. We also determined whether species‐specific traits are associated with specific threats.ResultsOn average, 8% of insular endemic species at risk of extinction are impacted by threats, while 20% of their functional richness is affected. However, a marked disparity in functional richness values associated with each threat can be highlighted. In particular, cultivation and wildlife exploitation are the greatest threats to insular endemic species. Moreover, each threat may contribute to the loss of at least 10% of functional diversity, because it affects threatened species that support unique and extreme functions. Finally, we found complex patterns of species‐specific traits associated with particular threats that is not explain by the threatening processes (directly affecting survival or modifying habitat). For instance, cultivation threatens very large mammals, while urbanization threatens very small mammals.Main conclusionsThese findings reinforce the importance of exploring the vulnerability of biodiversity facets in the face of multiple threats. Anthropogenic pressures may result in a loss of unique functions within insular ecosystems, which provides important insights into the understanding of threatening processes at a global scale.

Highlights

Worldwide biota is subject to an unprecedented level of rapid biodiversity loss because of human activities such as overexploitation, land modifications and pollution (Ceballos, Ehrlich, & Dirzo, 2017)
We focused on the following questions: (a) What is the functional diversity harboured by insular endemic species at risk of extinction due to each threat, and how is it related to the number of species? Overexploitation and cultivation are known to be major threats to the taxonomic diversity of insular endemic species (Leclerc et al, 2018)
This study adds to our understanding of how global changes threaten functional and taxonomic diversity on islands, providing insights for conservation purposes

Summary

Introduction

Worldwide biota is subject to an unprecedented level of rapid biodiversity loss because of human activities such as overexploitation, land modifications and pollution (Ceballos, Ehrlich, & Dirzo, 2017). 72% of IUCN-threatened or -near-threatened species are being overexploited (Maxwell, Fuller, Brooks, & Watson, 2016), and invasive predators have contributed to 58% of the contemporary extinctions of all birds, mammals and reptiles (Doherty, Glen, Nimmo, Ritchie, & Dickman, 2016). Most biodiversity assessments at the global scale consider only taxonomic diversity. These assessments focusing only on species diversity assume that all species are equivalent entities, even though they are a product of complex ecological and evolutionary processes (May, 1990; Vane-Wright, Humphries, & Williams, 1991). There has been a growing effort over the last two decades to assess other facets of biodiversity, and functional diversity (e.g., Brum et al, 2017; Devictor et al, 2010)

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