Estimating biodiversity changes in the Camargue wetlands: An expert knowledge approach.

Sara Fraixedas,Sofia Ribeiro-Lopes,Jacques Blondel,Anthony Olivier,Hugo Fontès,Ilse R Geijzendorffer,Delphine Nicolas,Thomas Galewski,Patrick Grillas,Philippe Lambret,Jonathan Loh

doi:10.1371/journal.pone.0224235

Abstract

Mediterranean wetlands are critical strongholds for biodiversity and the provision of ecosystem functions and services; yet, they are being severely degraded by a number of socio-economic drivers and pressures, including climate change. Moreover, we still lack comprehensive understanding of the extent to which biodiversity loss in Mediterranean wetlands will accelerate change in ecosystem processes. Here, we evaluate how changes in biodiversity can alter the ecosystem of the Camargue (southern France). We collected data on species presence/absence, trends and abundance over a 40-year period by combining observations from the scholarly literature with insights derived from expert knowledge. In total, we gathered more than 1500 estimates of presence/absence, over 1400 estimates of species abundance, and about 1400 estimates of species trends for eight taxonomic groups, i.e. amphibians, reptiles, breeding birds, fish, mammals, dragonflies (odonates), orthopterans and vascular plants. Furthermore, we used information on recently arrived species and invasive species to identify compositional changes across multiple taxa. Complementing targeted literature searches with expert knowledge allowed filling important gaps regarding the status and trends of biodiversity in the Camargue. Species trend data revealed sharp population declines in amphibians, odonates and orthopterans, while birds and plants experienced an average increase in abundance between the 1970s and the 2010s. The general increasing trends of novel and invasive species is suggested as an explanation for the changing abundance of birds and plants. While the observed declines in certain taxa reflect the relative failure of the protection measures established in the Camargue, the increasing exposure to novel and invasive species reveal major changes in the community structure of the different taxonomic groups. This study is the first attempt to assess changes in biodiversity in the Camargue using an expert knowledge approach, and can help manage the uncertainties and complexities associated with rapid social-ecological change in other Mediterranean wetlands.

Highlights

There is well-established evidence that Mediterranean wetlands are critical strongholds for biodiversity in the face of global change [1,2,3,4]
This is partially the case for amphibians and odonates, which are closely linked to freshwater wetlands, and orthopterans, where many species are associated with grasslands
It is likely that the severe degradation of the conservation status of these three taxonomic groups is related to the loss of those habitats

Summary

Introduction

There is well-established evidence that Mediterranean wetlands are critical strongholds for biodiversity in the face of global change [1,2,3,4]. Due to the increasing pressure from human activities such as drainage, pollution and agricultural intensification, Mediterranean wetlands are being severely degraded and biodiversity is being lost at alarming rates [5,6,7,8]. The Camargue is an excellent example of the co-evolutionary dynamics of nature-culture interactions and a good case study of the state of biodiversity that is applicable to similar Mediterranean wetlands. In these habitats, the arrival of new species (some of them considered as invasive) and the extinction of native species have largely unknown consequences on species communities and ecosystem functioning [11,12,13,14]

Methods

Results

Conclusion