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The Mediterranean region under climate change

 | 
Jean-Paul Moatti
, 
Stéphane Thiébault

Part 2. Vulnerability and impacts

Sub-chapter 2.4.4. Using the past to predict the future

The case of French Mediterranean orchids

Bertrand Schatz, Hélène Vogt-Schilb, François Munoz, Philippe Geniez, Laetitia Hugot, Roger Pradel et Franck Richard

Texte intégral

The time has come to document patterns of biodiversity variation in the Mediterranean

1A major issue in ecology is understanding the drivers of temporal changes in the spatial distribution patterns of species. Species are distributed in space in response to a restricted range of compatible conditions defined by their ecological niche (Chase and Leibold, 2003), but also in response to long-term environmental changes (Blondel et al. 2010). Given the currently accelerating global environmental change, we need to understand and predict the influence of ongoing global changes on biodiversity to rank priorities for conservation planning (Margules and Pressey, 2000; Bottrill et al. 2008). Several studies have pinpointed the effect of global changes on biodiversity showing latitudinal/altitudinal displacements, reductions in species ranges and local or global extinctions (Hughes et al., 2000; Parmesan and Yohe, 2003; Vogt-Schilb et al. 2015; 2016; Bose et al. 2016). Measuring the amplitude, and understanding the mechanisms underlying biodiversity shifts in space and over time has become a central issue in conservation biology. Species will be impacted differently across their distribution range, with the biggest changes in areas prone to the greatest environmental shifts (e.g. climate, land use; Underwood et al. 2009). For this reason, one can predict that species with a narrow niche, a localized distribution area and/or low dispersal ability will be more impacted by environmental shifts and less prone to respond (Thuiller et al. 2005; Devictor et al. 2008; Zhu et al. 2012).

2The nature and amplitude of past and current environmental changes vary considerably depending on the regions concerned, their historical legacies, and their environmental characteristics (Walther et al. 2002; Reidsma et al. 2006; Hansen et al. 2015). Like species, regions differ in their vulnerability to environmental changes. Therefore, geographical concentrations of biodiversity are also often hot-spots of threats to biodiversity (Myers et al., 2000). Such areas include the western part of the Mediterranean basin, where current landscape dynamics are greatly affecting biodiversity patterns, notably as a consequence of the marked decline of agro-pastoral practices and encroachment since the Second World War (Underwood et al. 2009; Blondel et al. 2010; Sirami et al. 2010). This region now faces major climate change including increasingly frequent dry periods (Schleussner et al. 2016). Observations at large geographical scales are needed to investigate the current dynamics of species distribution in the face of global environmental change. Data on several regions/countries should cover broad environmental gradients in order to address species’ responses under different regimes of environmental change (Pearson and Dawson, 2003). To date, studies of changes in distribution in vulnerable ecosystems at large spatial scales are rare (Settele et al. 2014).

The time has come to develop methods for the quantification of biodiversity changes

3Measuring shifts in biodiversity patterns requires appropriate and specific methods (Vogt-Schilb et al. 2016). The satisfactory quality and quantity of information (species identification, accurate localization, period of observation, etc.) are primary prerequisites. Unfortunately, most historical data do not satisfy these requirements, for instance because observers had a wide variety of motives, including naturalism, and only paid attention to the quality of the records. Diachronic analyses are appropriate ways to explore variations in biodiversity over time. The main methodological requirement is using identical methods (sampling design, timing and locations) to allow comparisons between past and present data (Kéry et al. 2006; Vogt-Schilb et al. 2016). In other words, the format (in terms of method, choice of sites, period of visits, and recorded species) used for the collection of past data will determine the research conducted in the present.

4Once the past and present data have been acquired, the next methodological challenge is to establish inter-annual variations in the presence of species in the past and in the present and to distinguish them from the true variation in species presence between the two periods of observation in order to determine biodiversity loss or gain. For instance, inter-annual variations in species presence, as well notable differences in detectability among species (Kéry et al. 2006; Archaux et al. 2009; MacKenzie et al. 2009; Vogt et al. 2013; Iknayan et al. 2014) have to be taken into account by sampling in several consecutive years. A second challenge in ecology is designing adequate statistical procedures to assess the diversity of ecological drivers of species’ distributions from local to regional scale and to predict their response to environmental changes (Thuiller et al. 2008; Munoz, 2010). In other words, it is essential to design statistical tests that acknowledge the structure of regional species pools case by case (Lessard et al. 2012), depending on their different functional (de Bello et al. 2012) and biogeographical properties (Carstensen et al. 2013).

Orchids as an ecological model to evaluate biodiversity shifts

5Here, we investigate the temporal shifts in the distribution patterns of orchids in contrasted environmental contexts (continental France vs. Corsica) in the Mediterranean region. Orchids are a particularly relevant group for documenting changes in the presence and distribution of species, for the three following reasons. First, orchids are a species rich and ecologically diversified group, particularly in the Mediterranean region (Schatz et al. 2014); some species are widely distributed, whereas others are more or less narrowly endemic (Bournerias and Prat, 2005). Second, orchid niches are segregated over broad abiotic environmental gradients (continental, oceanic and Mediterranean climatic regions, Munoz, 2010) in Europe. Third, orchids are particularly vulnerable to changes in climate and land cover (Wotavova et al. 2004; Pfeifer et al. 2006) due to their dependence on both pollinators and fungal symbionts (Selosse et al. 2006). In the last decade, the decline of many orchid species has been reported in Europe (Jacquemyn et al.

62005; Kull and Hutchings, 2006; Schatz et al. 2014), as well as in Australia and North America (Whigham and Willems, 2003; Duncan et al. 2011) but, surprisingly, no trend has been reported for the orchid rich Mediterranean region. To record orchid occurrence, a single visit by the observer is generally not sufficient to identify all species present at one site. In the Mediterranean region, an average of around 80% of orchid species are detected during a single visit (Vogt-Schilb et al. 2013). Three sampling years are necessary to provide an exhaustive view of the community, including rare or inconspicuous species or barely visible (detectable) ones (Kéry et al. 2006; Vogt-Schilb et al. 2013).

7We recently conducted two studies on the diachronic variations of orchids in Mediterranean France, and designed and applied an appropriate method to compare changes in the composition of communities. In the first analysis, we characterized the recent dynamics of orchid distribution in Western Europe, with regards to climate and land cover changes but also the habitat requirements of species (Vogt-Schilb et al. 2015). We used surveys made by the French Orchid Society on 134 orchid species in France, Belgium and Luxembourg over a 20 year period (1985-2005) (Vogt-Schilb et al. 2015). In the context of a large-scale biogeographical and ecological gradient of orchid richness from the Mediterranean to Northern temperate areas (Schatz et al. 2014), we expected that the significance of extinction or colonization patterns would depend on the number of species likely to be locally present. In order to identify the significance of recorded changes (disappearance/appearance) within each administrative unit and for each orchid species, we applied a statistical procedure (called ‘null models’) that acknowledges variations in orchid richness in space and the overall distribution of orchid species.

8We found sharp declines in most orchids in northern France, Belgium and Luxembourg, and many new appearances in the Mediterranean region (Figure 1). We found more declining species among heliophilous (shade-intolerant) orchids than among sciaphilous (shade-requiring) ones. This is due to the loss of open natural habitat in the highly urbanized regions in the northern part of the study area. No significant differences in appearance or disappearance were detected between Mediterranean and Euro-Siberian species. Changes in land cover were found to be the primary driver of orchid distribution dynamics, with a significant role of urbanization (Duncan et al. 2011), reduction in open habitats (Sirami et al. 2010) and the destruction of wetlands (Hartig et al. 1997). Concerning the link between conservation policies and orchid dynamics, our study revealed a major decline in species of orchids in metropolitan France considered as threatened by IUCN et al. (2010) and those that are nationally protected (Bournérias & Prat, 2005). This suggests an urgent need for complementary conservation measures and updated tools (Schatz et al. 2014). When considering the contrasted decline between the northern and southern parts of the study area, one may argue that the ongoing change will exacerbate the existing unbalanced geography of species richness, and that the high number of species in the Mediterranean is well conserved. The historical dataset analyzed here was provided by a network of amateur naturalists (3,000 observers belonging to the French Orchid Society) who fruitfully collaborated with researchers and enabled updating of the recent changes in orchid distributions and their drivers (Schatz et al. 2014; Vogt-Schilb et al. 2015).

Figure 1
Number of orchid species (A) and patterns of orchid disappearance (B) and appearance (C) across administrative units in France, Belgium and Luxembourg. In (B) and (C), a positive value indicates that there were more changes than would be expected by chance, while a negative value indicates that there were fewer changes than would be expected by chance. From Vogt et al. 2015.

9In the second analysis, we evaluated the effect of an increase in forest cover on the local dynamics of orchids using data from two field surveys conducted 27 years apart (1982-1984 vs. 2009-2011) at a set of 45 sites in Corsica (Vogt-Schilb et al. 2016). This effect has already been investigated in northern Europe (Jacquemyn et al., 2005; Kull and Hutchings, 2006), but never in the Mediterranean region. We applied a Bayesian multispecies site-occupancy model to each of the 36 orchid species recorded at these sites to estimate their probability of detection. The analysis showed that the probability of detection of orchids is significantly and positively correlated with the density of their population and the size (height) of their individuals (Vogt-Schilb et al. 2016). We then took species related under detection biases into account in estimating their temporal dynamics. The woody plant cover in the study area increased from 43.3 + 3.5% to 61.2 + 3.4% (+18% on average). During the same period, orchid communities underwent a marked changed in composition at the local scale (Fig. 2), with no effect on species richness at the regional scale (Vogt-Schilb et al. 2016). However, the abundance of heliophilous species decreased more sharply than that of sciaphilous species. As a result, conserving landscape mosaics could increase species richness at the local scale by providing a wide range of suitable habitats for orchids of different ecologies and limit species turnover (Vogt-Schilb et al. 2016). However, similar observations conducted in two continental and Mediterranean French regions, where the observed increase in woody plant cover was at least twice as high (more than 30%) during the same period (see also Debussche et al. 1999; Sirami et al. 2010; Titeux et al. 2016), revealed a marked decline in the abundance of orchid species at both local and regional scale (Schatz et al. in prep).

10In summary, the first study in three different countries revealed a good conservation status of orchids in the Mediterranean region in terms of species appearances or disappearances across administrative units (Vogt-Schilb et al. 2015). Conversely, studies in three Mediterranean regions revealed detailed variations in the conservation status, including a high turnover of orchids in Corsica but a decline in species in the continental regions due to a bigger increase in woody plant cover. Recent urbanization and variations in woody plant cover are thus two important drivers of rapid reduction in the presence of orchids, beyond the effects of the ongoing climate change.

Outlook for the investigation of biodiversity changes in a context of global change

11Similar data concerning diachronic variations are available for other taxonomic groups, including butterflies (Ekross et al. 2010), birds (Devictor et al. 2008; LeViol et al. 2012) and fungi (Gange et al. 2007; Kauserud et al. 2008). The diversity of responses in each of them (a northward shift or a shift in altitude for the two first and a shift in their phenology in fungi) and the variability of species-specific response within each taxonomic group underline the complexity of the impacts of global changes. Observations from the past are important for the reconstruction of earlier conditions, and they offer unique opportunities to assess the ecological plasticity of species assemblages. In this context, historical records belonging to naturalists, museum and herbaria collections are extremely valuable for scientific studies of changes in biodiversity (Lavoie, 2013; Vogt-Schilb et al. 2016). Beyond the diachronic variation in species presence and distribution, we also need to recognize interactions with other organisms that determine survival and reproduction. In Great Britain and the Netherlands, wild bees and hoverflies have declined in parallel with insect-pollinated plants, whereas wind-pollinated plants have increased (Biesmeijer et al., 2006). This illustrates how biotic homogenization of assemblages at the local scale (loss of rare or specialized species) and the key role of biotic interactions determine biodiversity loss (Ekross et al. 2010; LeViol et al. 2012; Vogt-Schilb et al. 2015, 2016). It is therefore desirable that researchers in ecology and conservation biology continue their observations in different compartments of biodiversity worldwide so that they can be used as background data in the future.

Figure 2
Extinction and colonization probability (in %) of the most abundant orchid species sampled in Corsica, illustrated by photos of the two extreme species Photos: P. Geniez.

Acknowledgments

12This work was funded by a CIFRE convention (N° 187/2011), by the National Botanical Conservatory of Corsica and the Corsican Environment Office (n° 082037) and by the OSU-OREME (long-term orchid survey). We express our gratitude to all observers and members of the SFO (Société Française d’Orchidophilie) for the transfer of databases. We also thank the BioDivMeX program (CNRS, Mistrals) for helpful discussions.

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Table des illustrations

Légende Figure 1Number of orchid species (A) and patterns of orchid disappearance (B) and appearance (C) across administrative units in France, Belgium and Luxembourg. In (B) and (C), a positive value indicates that there were more changes than would be expected by chance, while a negative value indicates that there were fewer changes than would be expected by chance. From Vogt et al. 2015.
URL http://books.openedition.org/irdeditions/docannexe/image/23667/img-1.jpg
Fichier image/jpeg, 267k
Légende Figure 2Extinction and colonization probability (in %) of the most abundant orchid species sampled in Corsica, illustrated by photos of the two extreme species Photos: P. Geniez.
URL http://books.openedition.org/irdeditions/docannexe/image/23667/img-2.jpg
Fichier image/jpeg, 212k

Auteurs

CEFE, Biotope, France, University of South Bohemia, Czech Republic
Ecologist, CEFE, UMR 5175, CNRS, Montpellier University, EPHE, France/Biotope, Mèze, France/Faculty of Science, University of South Bohemia, Czech Republic
helene.vogtschilb@gmail.com

French Institute of Pondicherry, India
Community and conservation ecologist, French Institute of Pondicherry, India
francois.munoz@cirad.fr

CEFE, France
Taxonomist and ecologist, CEFE, UMR 5175, CNRS, Montpellier University, EPHE, France
philippe.geniez@cefe.cnrs.fr

National Botanic Conservatory of Corsica, France
Botanist and conservation ecologist, Conservatoire Botanique National de Corse, Corte, Corsica France
hugot@oec.fr

CEFE, France
Biostatistician, CEFE, UMR 5175, CNRS, Montpellier University, EPHE, France
roger.pradel@cefe.cnrs.fr

CEFE, France
Ecology of plant-fungi interactions, CEFE, UMR 5175, CNRS, Montpellier University, EPHE, France
franck.richard@cefe.cnrs.fr

© IRD Éditions, 2016

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