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Keywords:

  • Africa;
  • biodiversity;
  • climate change;
  • conservation;
  • deserts;
  • distribution;
  • diversification;
  • phylogeography;
  • Sahara;
  • Sahel

ABSTRACT

  1. Top of page
  2. ABSTRACT
  3. I. INTRODUCTION
  4. II. DISTRIBUTION OF BIODIVERSITY
  5. III. EVOLUTION OF BIODIVERSITY
  6. IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING
  7. V. RESEARCH NEEDS
  8. VI. CONCLUSIONS
  9. VII. ACKNOWLEDGEMENTS
  10. VIII. REFERENCES
  11. Supporting Information

Deserts and arid regions are generally perceived as bare and rather homogeneous areas of low diversity. The Sahara is the largest warm desert in the world and together with the arid Sahel displays high topographical and climatic heterogeneity, and has experienced recent and strong climatic oscillations that have greatly shifted biodiversity distribution and community composition. The large size, remoteness and long-term political instability of the Sahara-Sahel, have limited knowledge on its biodiversity. However, over the last decade, there have been an increasing number of published scientific studies based on modern geomatic and molecular tools, and broad sampling of taxa of these regions. This review tracks trends in knowledge about biodiversity patterns, processes and threats across the Sahara-Sahel, and anticipates needs for biodiversity research and conservation. Recent studies are changing completely the perception of regional biodiversity patterns. Instead of relatively low species diversity with distribution covering most of the region, studies now suggest a high rate of endemism and larger number of species, with much narrower and fragmented ranges, frequently limited to micro-hotspots of biodiversity. Molecular-based studies are also unravelling cryptic diversity associated with mountains, which together with recent distribution atlases, allows identifying integrative biogeographic patterns in biodiversity distribution. Mapping of multivariate environmental variation (at 1 km × 1 km resolution) of the region illustrates main biogeographical features of the Sahara-Sahel and supports recently hypothesised dispersal corridors and refugia. Micro-scale water-features present mostly in mountains have been associated with local biodiversity hotspots. However, the distribution of available data on vertebrates highlights current knowledge gaps that still apply to a large proportion of the Sahara-Sahel. Current research is providing insights into key evolutionary and ecological processes, including causes and timing of radiation and divergence for multiple taxa, and associating the onset of the Sahara with diversification processes for low-mobility vertebrates. Examples of phylogeographic patterns are showing the importance of allopatric speciation in the Sahara-Sahel, and this review presents a synthetic overview of the most commonly hypothesised diversification mechanisms. Studies are also stressing that biodiversity is threatened by increasing human activities in the region, including overhunting and natural resources prospection, and in the future by predicted global warming. A representation of areas of conflict, landmines, and natural resources extraction illustrates how human activities and regional insecurity are hampering biodiversity research and conservation. Although there are still numerous knowledge gaps for the optimised conservation of biodiversity in the region, a set of research priorities is provided to identify the framework data needed to support regional conservation planning.

I. INTRODUCTION

  1. Top of page
  2. ABSTRACT
  3. I. INTRODUCTION
  4. II. DISTRIBUTION OF BIODIVERSITY
  5. III. EVOLUTION OF BIODIVERSITY
  6. IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING
  7. V. RESEARCH NEEDS
  8. VI. CONCLUSIONS
  9. VII. ACKNOWLEDGEMENTS
  10. VIII. REFERENCES
  11. Supporting Information

Biodiversity is being eroded globally by habitat loss and climate change (Pimm, 2008). The challenges are to increase knowledge about species diversity and distribution (Whittaker et al., 2005) and to detect the ecological and evolutionary processes behind them (Crandall et al., 2000) in order to systematise biodiversity conservation planning (Margules & Pressey, 2000). Deserts [aridity index (average annual precipitation/potential evapo-transpiration) < 0.05; Ward, 2009] and arid regions (aridity index between 0.05 and 0.20) are generally perceived as bare and rather homogeneous areas of low diversity in comparison to other regions, thus attracting less scientific attention (Durant et al., 2012). However, they allow examining the effects of extreme environments on biodiversity patterns (Ward, 2009). Deserts and arid regions present patchily distributed species whose range limits are under strong climatic control, a relatively high rate of endemism due to adaptive processes of organisms to extreme environments, locally endangered micro-hotspots of biodiversity (Dumont, 1982; Davies et al., 2012; Murphy et al., 2012; Wilson & Pitts, 2012), and climatic extremes generating sharp ecological gradients (Schulz et al., 2009). Increasing human exploitation activities and progressive aridity conditions are negatively affecting desert biodiversity and also increasing poverty and the frequency of conflicts (McNeely, 2003; UNEP, 2006; Thorton et al., 2008; Trape, 2009). The magnitude and velocity of climate change in deserts are predicted to be strong and fast (Loarie et al., 2009), causing growing international awareness for desert biodiversity (McNeely, 2003; UNEP, 2006; Newby, 2007; Ward, 2009; Davies et al., 2012; Durant et al., 2012).

The Sahara desert and the neighbouring arid Sahel constitute two major ecoregions of the African continent (Olson et al., 2001) and exhibit features that distinguish them from other world deserts and arid regions (Fig. 1):

  1. The Sahara is the largest warm desert in the world with land coverage, including the Sahel, of about 11230000 km2 (larger than the Australian continent).
  2. There is high diversity of topographic features, from salt pans below sea level to high-altitude peaks (from −155 m at Lake Assal, Djibouti, to 3415 m at Emi Koussi, Chad) distributed along a system of ‘mountain-sky islands’ (UNEP, 2006).
  3. Climate is heterogeneous, resulting from considerable spatial variability in temperature (average annual temperature ranging from 9.4 to 30.8°C) and rainfall (average annual total precipitation up to 981 mm; both from www.worldclim.org).
  4. The limit between the Sahara and the Sahel constitutes the transition between the Palaearctic and Afro-Tropical biogeographic realms (Olson et al., 2001; Holt et al., 2013), resulting in latitudinal variation in species distribution and increased local biodiversity (Dumont, 1982; Le Houérou, 1992).
  5. The Sahara-Sahel spreads over ten countries, many rated as low development (UNDP, 2010) and characterised by long-term political instability (Ewi, 2010; Walther & Retaillé, 2010; Lohmann, 2011), making field surveys and trans-border research and conservation planning difficult.
  6. The onset of desert conditions in the Sahara was estimated as rather recently, at approximately 7 million years ago (Mya) in Chad (Schuster et al., 2006) or around 6 to 2.5 Mya in western areas (Swezey, 2009).
  7. Perhaps most importantly, the Sahara-Sahel experienced (and is still experiencing) strong climatic oscillations, with feedback mechanisms between rainfall reduction and vegetation cover (Wang et al., 2008; Claussen, 2009). Since the Pliocene (5.3 to 2.5 Mya), the Sahara-Sahel has experienced multiple dry-wet cycles (Le Houérou, 1997). The latest humid period occurred at the mid-Holocene, when the region was covered with extensive vegetation, lakes and wetlands (Gasse, 2000; Kröpelin et al., 2008). This wet period ended between 6 and 5000 years ago, when aridity greatly increased, mesic vegetation communities disappeared, and lake levels decreased (Foley et al., 2003; Holmes, 2008). Such climate and land-cover oscillations have greatly shifted the Sahara-Sahel limits, further regulating biodiversity patterns (Dumont, 1982; Le Houérou, 1992, 1997; Drake et al., 2011).
image

Figure 1. Environmental variability in North Africa derived by spatial principal components analysis (SPCA), approximate boundaries between ecoregions (Olson et al., 2001), and hypothesised dispersal corridors (1. Atlantic Sahara; 2. Nile River; 3. Red Sea Sahara) and refugia across the Sahara-Sahel (A, Adrar Atar-Kediet ej Jill; B: Tagant; C: Assaba; D: Afollé; E: Adrar des Ifoghas; F: Hoggar; G: Mouydir; H: Tassili n'Ajjer; I: Fezzan; J: Aïr; K: Tibesti-Dohone; L: Ennedi-Borkou; M: Marra; N: Uweinat-Gilf Kebir) (Dumont, 1982; Drake et al., 2011). Composite map of SPCA, where PC1 (44.0%): annual precipitation, precipitation of wettest month, and temperature annual range; PC2 (33.4%): altitude, annual mean temperature, and minimum temperature of coldest month; and PC3 (9.4%): topography roughness index. Environmental factors from Worldclim database (www.worldclim.org) at 2.5 arc-second resolution.

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The dynamic Sahara-Sahel region is highly appealing for biodiversity and evolutionary research, but its large size, remoteness, and long-term political instability contributed substantially to a generalised lack of knowledge during most of the 20th century. Temporal variation on Saharan biodiversity research, tracked by the number of scientific papers published on this topic in the last 140 years, highlights that research has been highly dependent on fluctuations in the political stability of the region (Fig. 2). The relatively peaceful period experienced in the decade 2001–2010 has translated into an impressive increase in the number of studies devoted to the region, for all taxonomic groups examined. These research efforts coupled molecular and geomatic (Global Navigation Satellite Systems and Geographical Information Systems) tools together with broad sampling of taxa. Such studies are starting to unravel micro-hotspots of biodiversity and cryptic diversity, and to provide information on the causes, timing and patterns of radiation and divergence for multiple taxa. These studies are also expanding tremendously our knowledge on biodiversity distribution and evolution, but also revealing gaps on these topics in urgent need of research effort for efficient planning of biodiversity conservation. Effective management policies are required as many large-sized vertebrates have been driven to regional extinction by hunting, including birds [e.g. Chlamydotis undulata (Goriup, 1997); Struthio camelus (Thiollay, 2006)] and mammals [e.g. Loxodonta africana (Barnes, 1999; Bouché et al., 2011); Acinonyx jubatus (Saleh, Helmy & Giegengack, 2001); Oryx dammah (Beudels et al., 2005); Panthera leo (Barnett et al., 2006)], or reduced to extremely low population sizes [e.g. Addax nasomaculatus and Gazella leptoceros (Manlius, 2000; Wacher et al., 2004; Beudels et al., 2005)]. The region is cyclically affected by disastrous droughts (Brooks, 2004) and, furthermore, it is predicted to experience the fastest velocities of climate change among world deserts (Loarie et al., 2009), which will increase vulnerability to extinction of the already fragile biodiversity (Davies et al., 2012).

image

Figure 2. Decadal evolution of the number of papers listed in Zoological Records since 1871 with the key word ‘Sahara’ and corresponding animal group. Historical events that shaped the temporal evolution of the number of papers are also identified. Until the early 20th century, the Sahara was kept off bounds to research. The first naturalists surveyed the area, following the military conquest of Saharan territories, until World War II. Afterwards, research effort fluctuated according to human conflicts in the region: there were significant research increases after the 1950s, and noticeable collapses after independence from European administration, and during a series of conflicts that erupted throughout many countries (e.g. Tuareg rebellion in the Central Sahara). The 21st century saw a burst of research that translates into an unprecedented number of published papers.

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The present review aims to track trends in the knowledge about biodiversity patterns and evolutionary processes across the Sahara-Sahel as well as to anticipate needs for biodiversity research and conservation. Focus is given to the most recent findings stemming from the use of molecular and geomatic tools. In particular, it aims to: (i) identify biogeographical patterns in the distribution of biodiversity as well as knowledge gaps on such diversity; (ii) emphasise the role of mountains as biodiversity refugia and of micro-scale water features as local biodiversity hotspots; (iii) relate palaeo-ecological events with diversification and speciation mechanisms and provide a synthetic overview of the most commonly hypothesised diversification mechanisms; (iv) identify present and future predicted threats to biodiversity; (v) evaluate gaps in biodiversity conservation targets and the main reasons for such gaps; and (vi) identify relevant actions for local biodiversity conservation. Finally, a set of research priorities is provided to identify the framework data needed to support regional conservation planning.

II. DISTRIBUTION OF BIODIVERSITY

  1. Top of page
  2. ABSTRACT
  3. I. INTRODUCTION
  4. II. DISTRIBUTION OF BIODIVERSITY
  5. III. EVOLUTION OF BIODIVERSITY
  6. IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING
  7. V. RESEARCH NEEDS
  8. VI. CONCLUSIONS
  9. VII. ACKNOWLEDGEMENTS
  10. VIII. REFERENCES
  11. Supporting Information

Knowledge on biodiversity distribution across the Sahara-Sahel is scarce in relation to neighbouring areas (Fig. 3A). Large portions of northern-eastern Mauritania, northern Mali, western Algeria, southern Libya, and almost all mountain regions, are under-sampled. Current knowledge on species richness is particularly low in the Adrar des Ifoghas, Tibesti, Ennedi, and Marra mountains (for locations see Fig. 1), where there is scarce or non-existent sampling effort. Compilation and analysis of available species distribution data for Sahara-Sahel fauna (Dumont, 1982; Le Berre, 1989, 1990; Lévêque, 1990; Kingdon, 1997; Rödel, 2000; Denys, Granjon & Poulet, 2001; Crochet, Geniez & Ineich, 2003; Carranza et al., 2004, 2008; Geniez et al., 2004; Wilson & Reeder, 2005; Baha El Din, 2006; Geniez & Arnold, 2006; Johnson et al., 2006; Trape & Mané, 2006; Brito et al., 2008, 2010, 2011c; Sindaco & Jeremčenko, 2008; Arnold, Robinson & Carranza, 2009; Granjon & Duplantier, 2009; Hoath, 2009; Nicolas et al., 2009; Trape, 2009; Brahmi et al., 2010; African Chiroptera Report, 2011; Ferreira et al., 2011; Geniez, Padial & Crochet, 2011; Hekkala et al., 2011; Wagner et al., 2011; Trape, Chirio & Trape, 2012) indicates the presence of a total of 305 species of dragonflies, fishes, amphibians, reptiles and mammals, distributed mainly along a series of potential corridors and refugia (Table 1). The role of mountains in deserts and arid regions as refugia now is being emphasised, and supported by studies in several taxa, such as ferns (Anthelme, Mato & Maley, 2008; Anthelme, Abdoulkader & Viane, 2011), fishes (Trape, 2009), amphibians and reptiles (Geniez & Arnold, 2006; Tellería et al., 2008; Brito et al., 2011b,c; Vale et al., 2012b), birds (Tellería, 2009), and mammals (Busby et al., 2009; Brito et al., 2010; Vale, Álvares & Brito, 2012a). For instance, the Central Sahara mountains of Hoggar and Termit are major refugia for threatened large ungulates and carnivores [e.g. Ammotragus lervia, Nanger dama and Addax nasomaculatus (Wacher et al., 2004); Acinonyx jubatus and Panthera pardus (Busby et al., 2009)], most likely due to their relative inaccessibility to poachers and to generalised low human activity. Mountains host 41 Sahara-Sahel vertebrate endemics (51% of all endemics), with the Aïr (29% of all endemics), Adrar Atar (23%), and Hoggar (21%) particularly rich (see online Appendix S1), and contain isolated populations of 88 vertebrates of non-Saharan origin (45% of all non-Saharan). These isolated populations of species of non-Saharan origin persist in restricted habitats within oases and mountains of the Sahara-Sahel, suggesting temporal distribution shifts linked to Plio-Pleistocene climate fluctuations (Dumont, 1982; Le Houérou, 1992, 1997; Drake et al., 2011) and/or recent translocations (Brahmi et al., 2010). Although mountains are currently surrounded by sandy and rocky areas, they were probably connected by savannah-like habitats during past humid periods (Gasse, 2000; Kröpelin et al., 2008), forming a net of biodiversity corridors (Fig. 1). Those corridors have been hypothesised to follow a North-South axis (Dumont, 1982; Drake et al., 2011). Some seem to have persisted to the present, like the Atlantic and the Red Sea coastal areas, where high biodiversity levels (28 and 18 Sahara-Sahel vertebrate endemics and 33 and 23 vertebrates of non-Saharan origin, respectively) are related to the mild climate influenced by the proximity of the sea (Brito et al., 2009, 2011b). The Nile River is also a permanent corridor for biodiversity, holding 35 Sahara-Sahel vertebrate endemics (44% of all endemics) and 102 vertebrates of non-Saharan origin (53% of all non-Saharan) with distributions along the river and productive riverbanks (see online Appendix S1). Despite exhibiting overall low species richness, the vast empty-quarters (unpopulated areas) and dune massifs of the Sahara are crucial refugia for threatened birds, large ungulates, and carnivores that suffered extreme declines in other regions [e.g. Acinonyx jubatus (Saleh et al., 2001); Addax nasomaculatus (Beudels et al., 2005); Chlamydotis undulata (Chammem et al., 2012)].

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Figure 3. (A) Distribution data available for vertebrates in North Africa at the Global Biodiversity Information Facility (GBIF, 2012). (B) Examples of increasing knowledge on distribution and habitat suitability in the west Sahara-Sahel region for range-margin populations of Afro-tropical taxa (Echis leucogaster), local endemic taxa (Felovia vae) and Sahelian-endemic taxa (Vulpes pallida). Suitability maps are derived from ecological niche-based models and represent presence probability. Known occurrence localities are represented as data published mainly before the year 2000 (bibliography) and fieldwork data collected after the year 2000 to develop models (fieldwork). Distribution data and suitability maps for E. leucogaster, F. vae and V. pallida adapted from Brito et al. (2011b); Vale et al. (2012a), and Brito et al. (2009), respectively.

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Table 1. Species richness of endemic and relict taxa (combining dragonflies, fishes, amphibians, reptiles, and mammals) in hypothesised dispersal corridors and refugia of the Sahara-Sahel region
 Biogeographic range of species
AFTSHLSAHSASMEDTotal
  1. Location of corridors and refugia are indicated in Fig. 1. Richness is presented according to biogeographic range of species: Afro-tropical (AFT), Sahelian endemic (SHL), Saharan endemic (SAH), Saharo-Sindian (SAS), Mediterranean (MED). Values in parenthesis include species present in the Red Sea Sahara corridor that are distributed south of Gebel Elba, thus not entering the Sahara. Detailed data for each taxonomic group are provided as supporting information in online Appendix S1.

Corridors:      
Atlantic Sahara16919121874
Nile River108530187168
Red Sea Sahara23 (30)4 (3)14 (0)20 (3)3 (0)64 (36)
Refugia:      
Adrar Atar - Kediet ej Jill2061210149
Tagant32364045
Assaba25230030
Afollé11141017
Adrar des Ifoghas19675138
Hoggar1031415648
Mouydir10066123
Tassili n′Ajjer121139338
Fezzan41107426
Aïr39121111376
Tibesti - Dohone13466130
Ennedi-Borkou23553137
Marra17301021
Uweinat-Gilf Kebir4045013
Total numberof individual species16820603126305

In recent years, field surveys using modern geomatic tools and alternative sampling strategies (photo-trapping and non-invasive genetics) began increasing knowledge on species composition and distribution, such as on bacteria (e.g. Prigent et al., 2005), ferns (e.g. Anthelme et al., 2008, 2011), invertebrates (e.g. Lourenço & Duhem, 2007; Patiny & Michez, 2007; Ferreira et al., 2011), fishes (Trape, 2009), amphibians and reptiles (e.g. Geniez & Arnold, 2006; Brito et al., 2008, 2011c; Ibrahim, 2008), birds (e.g. Selmi & Boulinier, 2003; Gaskell, 2005; Salewski, Schmaljohann & Herremans, 2005; Tellería, 2009), and mammals (e.g. Baziz et al., 2002; Wacher et al., 2002; Padial & Ibáñez, 2005; Londei, 2008; Tellería et al., 2008; Brito et al., 2010; Gaubert et al., 2012), as well as of migrant birds crossing the Sahara-Sahel (e.g. Meyburg et al., 2004; Salewski, Schmaljohann & Liechti, 2010; Ozarowska, Stepniewska & Ibrahim, 2011) and particularly of secretive fauna [e.g. Acinonyx jubatus (Saleh et al., 2001; Hamdine, Meftah & Sehki, 2003); Panthera pardus (Busby et al., 2009); bats (Rebelo & Brito, 2007)]. Phylogeographic studies using molecular markers are also uncovering cryptic diversity [e.g. Apis mellifera (El Niweiri & Moritz, 2008; Shaibi et al., 2009); Acanthodactylus spp. (Fonseca et al., 2008); Ptyodactylus spp. (Froufe et al., 2013)] and, in some cases, splitting previously considered wide-ranging species, including multiple invertebrates [e.g. Cataglyphis spp. (Knaden et al., 2005); Hottentotta spp. (Sousa et al., 2011)], reptiles [e.g. Chalcides spp. and Sphenops spp. (Carranza et al., 2008); Agama spp. (Geniez et al., 2011); Crocodylus spp. (Hekkala et al., 2011); Trapelus spp. (Wagner et al., 2011)], and mammals [e.g. Taterillus spp. (Dobigny et al., 2005); Acomys spp. (Volobouev et al., 2007; Frynta et al., 2010); Jaculus spp. (Ben Faleh et al., 2010, 2012; Boratyński, Brito & Mappes, 2012)]. Such studies are changing completely perceptions on regional biodiversity patterns. Instead of relatively low species diversity with distribution covering most of the region, broad taxa sampling and use of molecular tools suggest a larger number of species with much narrower ranges, frequently limited to micro-hotspots of biodiversity. At the same time, such studies are stressing that present knowledge on biodiversity distribution is incomplete. In fact, only a few comprehensive and recent distribution atlases are available, mostly biased towards amphibians and reptiles (e.g. Geniez et al., 2004; Trape & Mané, 2006; Trape et al., 2012), which hampers the identification of regional biodiversity hotspots. As such, observational data collected at high spatial resolution (less than 1 km) are forming the basis of ecological niche-based models (Fig. 3B) that allow estimation of habitat suitability for elusive species distributed across remote areas, such as canids and vipers (Brito et al., 2009, 2011b). Despite exhibiting wide extents of occurrence, from the Atlantic to the coasts of the Red Sea, fine-scaled ecological niche models suggest much smaller areas of occupancy, in rather fragmented distributions, and adaptation to particular habitats or environmental extremes [e.g. Vulpes rueppellii and V. zerda (Brito et al., 2009); Cerastes cerastes and C. vipera (Brito et al., 2011b)]. Ecological niche modelling of Sahel mountain endemics has also identified restricted and relatively fragmented suitable habitats for some of these species [e.g. Felovia vae (Vale et al., 2012a); Agama boulengeri (Vale et al., 2012b)]. Such models indicate that annual precipitation, precipitation of wettest month, and temperature annual range account for most of the environmental variation within the range of the Sahara-Sahel vertebrates (Fig. 1), and geographical variation in rainfall and temperature are major factors related to the biodiversity distribution of vegetation (El-Ghani, 1998), invertebrates (Patiny et al., 2009), reptiles (Brito et al., 2011b; Vale et al., 2012b), and mammals (Brito et al., 2009; Nyári, Peterson & Rathbun, 2010; Vale et al., 2012a), and human-related factors in threatened birds (Chammem et al., 2012).

Within the Sahara-Sahel, high concentrations of species are found around waterbodies (Rebelo & Brito, 2007; Trape, 2009; Brito et al., 2011c), giving these features the status of micro-hotspots of biodiversity. Oases in sand-seas are crucial for humans but also constitute refugia for multiple species (particularly to fishes and amphibians within vertebrates) around the most extreme arid areas of the Sahara (Le Berre, 1989, 1990; Saleh et al., 2001; Selmi & Boulinier, 2003; Brito et al., 2008). Recent studies in Mauritania are also emphasising the conservation importance of mountain lagoons (locally known as gueltas) that hold endemic fauna and range-margin populations (Fig. 4A). These pools are sparsely distributed in temporal riverbeds in mountains surrounded by sandy areas and allow the maintenance of rich communities, acting as refugia to relict populations and potential speciation drivers (Anthelme et al., 2008). Isolated populations of tropical and endemic species can be found in gueltas, including dragonflies [e.g. Ischnura saharensis, Trithemis annulata (Dumont, 1982; Ferreira et al., 2011)], fishes [e.g. Barbus macrops, Clarias anguillaris (Trape, 2009)], amphibians [e.g. Hoplobatrachus occipitalis, Amietophrynus xeros (Tellería, 2009)], reptiles [e.g. Crocodylus suchus, Ptyodactylus ragazzi, Python sebae, Varanus niloticus (Brito et al., 2011b)], birds [e.g. Burhinus senegalensis, Hieraaetus spilogaster (Tellería, 2009)], and mammals [e.g. Felovia vae, Procavia capensis, Papio papio (Brito et al., 2010).

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Figure 4. (A) Distribution of rock pools (gueltas) in the Sahara-Sahel. Gueltas are mostly concentrated in mountains. Coordinates of gueltas manually collected from fieldwork (Campos et al., 2012) and topographic maps (Institut Géographique National, Paris; 1:200,000 series). (B, C) Insights of heavily exploited and eutrophicated guelta El Khedia (B) and pristine guelta Metraoucha (C), Mauritania, both holding isolated crocodile populations (Brito et al., 2011c).

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The occurrence of crocodiles (Crocodylus suchus) in Saharan gueltas constitutes a spectacular example of the value of refugia for relict tropical fauna. Extirpated from Morocco and Algeria in the first half of the last century, a few relict populations were known to persist in Chad and Mauritania (Brito et al., 2011c). Field surveys conducted in Mauritania recently updated their distribution and habitat selection, finding that gueltas were the most frequent waterbody used by crocodiles and that most gueltas had less than five adults (Brito et al., 2011c). There is evidence of individual dispersal between some water localities (usually located at an average distance of less than 4 km) that may attenuate loss of genetic diversity in gueltas. Dispersal may occur during the rainy season, when raging water fills streams and partially connects gueltas and mountain lagoons, and occasionally mountains with the Senegal River. Remote sensing techniques quantifying hydrological features of central-southern Mauritania have detected distinct water availability patterns (Campos, Sillero & Brito, 2012) that may relate to dispersal events. Molecular markers are needed to quantify population sub-structuring and effective population size, and to detect the occurrence of gene flow.

III. EVOLUTION OF BIODIVERSITY

  1. Top of page
  2. ABSTRACT
  3. I. INTRODUCTION
  4. II. DISTRIBUTION OF BIODIVERSITY
  5. III. EVOLUTION OF BIODIVERSITY
  6. IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING
  7. V. RESEARCH NEEDS
  8. VI. CONCLUSIONS
  9. VII. ACKNOWLEDGEMENTS
  10. VIII. REFERENCES
  11. Supporting Information

Phylogeographic studies are revealing that diversification and speciation events that occurred in the Sahara-Sahel are most likely related to temporal and spatial variation of desert extent. The onset of the Sahara presumably acted mainly as a North-South vicariant feature, being associated with diversification processes for several species (Carranza et al., 2002, 2008; Carranza, Arnold & Pleguezuelos, 2006; Geniez & Arnold, 2006; Wagner et al., 2011; Metallinou et al., 2012) and to allopatric effects (Douady et al., 2003; Muwanika et al., 2003; Pook et al., 2009; Gonçalves et al., 2012). The palaeoclimatic oscillations following Sahara formation are estimated to have occurred at cycles of approximately 100000–20000 years during the last million years (Le Houérou, 1997), which greatly shaped the range of desert and savannah environments and constrained species distribution (Dumont, 1982; Le Houérou, 1992, 1997; Drake et al., 2011) and genetic structure (Fig. 5). For example, independent approaches using molecular markers and ecological niche-based modelling suggest vicariance as the major diversification force for the origin of the small mammal Elephantulus rozeti, which was linked to post-Pleistocene allopatry induced by increasing aridity in the Sahara (Douady et al., 2003; Nyári et al., 2010).

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Figure 5. (A) Distribution and (B) phylogenetic relationships of North African Agama lizard species. Detailed biogeographic patterns of mountain endemic lineages of (C) A. tassiliensis in Central Sahara and of (D) A. boulengeri in West Sahara-Sahel (colour scale on maps indicates elevation). Colours identify species and lineages within species; polygons in A delimit approximate distributions of lineages; in C and D question marks show genetically undefined populations and dots represent sequenced specimens. Shaded horizontal bars in the phylogenetic tree correspond to estimates of diversification times (with confidence intervals) for Agama lineages, with a scale bar denoting millions of years ago (Mya).

Data adapted from Gonçalves et al. (2012).

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Assuming a neutral scenario (without adaptation processes) as the main driver of speciation in the Sahara-Sahel, divergence within species occurred through vicariant events, where allopatric effects induced the interruption of gene flow and led to evolutionarily independent lineages or new species. The time and nature of vicariant events have variable effects on taxa according to their habitat requirements (Fig. 6). Xeric species likely experienced diversification processes during humid periods [e.g. Tarentola spp., Chalcides spp. and Sphenops spp. (Carranza et al., 2002, 2008); Jaculus spp. (Boratyński et al., 2012); Stenodactylus spp. (Metallinou et al., 2012)]. Conversely, population contraction and diversification events under hyper-arid conditions likely occurred in multiple mesic vertebrates, adapted to arid conditions but still requiring some moisture [e.g. Taterillus spp. (Dobigny et al., 2005); Malpolon spp. and Hemorrhois hippocrepis (Carranza et al., 2006); Pristurus spp. (Geniez & Arnold, 2006); Psammophis spp. (Rato et al., 2007); Galerida spp. (Guillaumet, Crochet & Pons, 2008); Acomys spp. (Nicolas et al., 2009); Rhabdomys dilectus (Castiglia et al., 2012); Agama spp. (Gonçalves et al., 2012); Gazella spp. (Godinho et al., 2012)]. The ancestors of these species most likely entered the region during wet periods and diversified during the arid phases of the Plio-Pleistocene. During these arid periods, mesic species suffered range fragmentation in wetter and milder areas, such as rocky massifs and mountain ranges. Recent population expansions have been observed for mesic taxa during humid periods (Froufe, Brito & Harris, 2009). Divergence events occurred during hyper-arid periods particularly for water-dependent species: during wet periods, these species occur continuously along permanent or temporary rivers, and become extinct or isolated in small waterbodies (oases and gueltas) during dry periods [e.g. Mastomys huberti (Mouline et al., 2008); Astatotilapia desfontainii (Genner & Haesler, 2010); Apis mellifera (Shaibi & Moritz, 2010)]. Similar vicariant patterns are suggested for taxa that show divergence processes by isolation into savannah patches during Plio-Pleistocene climatic shifts, with recent demographic expansions occurring during arid phases since the Holocene [e.g. Mastomys erythroleucus (Brouat et al., 2009)]. Climatic fluctuations also led to changes in hydrological networks that affected major river courses and might prompt vicariant processes, as suggested in Lake Chad and in the Nile River (Dobigny et al., 2005; Hassanin et al., 2007; Brouat et al., 2009; Pook et al., 2009). Existing molecular studies have mostly focused on non-volant small vertebrates with relatively low dispersal capacity and for which barrier effects may be more pronounced. The few studies available on highly mobile vertebrate species show little geographic genetic structure in all North Africa [e.g. Gazella dorcas (Lerp et al., 2011); Canis spp. (Gaubert et al., 2012).

image

Figure 6. Summary of hypothetical diversification mechanisms through allopatric processes expected for three types of Saharan-adapted species: xeric (circles), mesic (squares) and water-dependent species (diamonds). A time series of climatic cycles is shown from top to bottom. Wet periods associated with a cooler climate lead to expansion of semiarid environments (Sahel) while dry periods, associated with a warmer climate, lead to wider arid environments (Sahara). Cycles of range expansion-contraction lead to the formation of new lineages (colours) and subsequent contact zones between lineages (black lines).

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The cycles of population expansion during favourable climatic conditions and population contraction with harsh climate translated into opposing patterns: (i) dispersal along the geographical corridors that facilitated gene flow during suitable climatic periods [e.g. Canis spp. (Gaubert et al., 2012)]; (ii) divergence without gene flow in refugia and promotion of speciation [e.g. Taterillus spp. (Dobigny et al., 2005)] and morphological evolution [e.g. Galerida spp. (Guillaumet et al., 2008)] during unsuitable climatic periods. Mountains play a key role in diversification patterns across the Sahara-Sahel by acting as refugia for many species and facilitating gene flow during favourable climatic conditions. Thus, harsh climatic conditions allowed divergence of multiple taxa in mountains, possibly resulting in long-term allopatric isolation and speciation [e.g. Agama tassiliensis (Geniez et al., 2011; Gonçalves et al., 2012]. On the other hand, mountain populations have likely been at the origin of several episodes of expansion, promoting gene flow events between isolated populations [e.g. Olea spp. (Besnard, Rubio de Casas & Vargas, 2007); Myrtus spp. (Migliore et al., 2012)]. For instance, Central Saharan mountains harbour a variety of Mediterranean-origin plant species that have been able to survive long-distance colonisation episodes and now constitute relict populations of great conservation interest [e.g. Senecio spp. (Coleman et al., 2003); Atriplex spp. (Ortíz-Dorba et al., 2005); Myrtus spp. (Migliore et al., 2012)]. Ecological adaptation and morphological convergence have been reported in contact zones of lizards [e.g. Acanthodactylus (Crochet et al., 2003)], but molecular studies are needed to understand patterns of gene flow dynamics.

At the same time, organisms inhabiting the Sahara-Sahel have developed unique adaptive features to cope with the harsh environmental conditions, including unpredictable and limited water and food resources, and extreme temperatures and solar radiation. Most desert-dwellers avoid exposure or activity during the hottest parts of the day (mid-day) and year (dry season). Some evolved larger body size to avoid over-heating by increased thermal inertia (when evaporative cooling is not possible) that allows activity during daylight [e.g. Psammomys obesus (Haim, Alma & Neuman, 2006)]. An elongated body, wedge-shaped head and limb reduction evolved multiple times in ‘grass swimmers’ and ‘sand burrowers’ [e.g. Chalcides spp. and Sphenops spp. (Carranza et al., 2008); Scincus scincus (Maladen et al., 2009)]; these are examples of complex and unique adaptations to dry habitats that increase mobility under sand and grass in savannah and desert conditions. Two other important physiological adaptations are connected with limited food and water resources. Reduced resting metabolic rate evolved multiple times (e.g. Acomys russatus, Lepus capensis, Bedouin goat) in response to selective pressures, allowing more efficient conservation of energy and water (Choshniak et al., 1996; Kronfeld & Shkolnik, 1996). Reduction of overall energy turnover, as well as lower metabolic rate, is connected with another physiologically adaptive mechanism: long retention time of fluid in the gastrointestinal tract. Such water-saving mechanisms allowed species to survive and persist even in an environment without permanent, or indeed any, water resources, such as the vast empty quarters of the Sahara desert [e.g. Addax nasomaculatus (Hummel et al., 2008); Lepus capensis (Kronfeld & Shkolnik, 1996)].

IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING

  1. Top of page
  2. ABSTRACT
  3. I. INTRODUCTION
  4. II. DISTRIBUTION OF BIODIVERSITY
  5. III. EVOLUTION OF BIODIVERSITY
  6. IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING
  7. V. RESEARCH NEEDS
  8. VI. CONCLUSIONS
  9. VII. ACKNOWLEDGEMENTS
  10. VIII. REFERENCES
  11. Supporting Information

Biodiversity in the Sahara-Sahel is presently under threat as a direct result of the synergistic effects of climate change, habitat alteration and most notably, the effect of other multiple human pressures. The spreading of four-wheel-drive vehicles and firearms from the beginning of the 20th century increased dramatically the extent and impact of hunting activities (Valverde, 1957; Newby, 1980), resulting in local extinction of large mammals [e.g. Giraffa camelopardalis (Ciofolo, 1995); Acinonyx jubatus (Saleh et al., 2001); Oryx dammah (Beudels et al., 2005); Panthera leo (Barnett et al., 2006)] and birds [e.g. Chlamydotis undulata (Goriup, 1997); Struthio camelus (Ostrowski, Massalatchi & Mamane, 2001; Thiollay, 2006)]. Conflicts related to water accessibility have resulted in the extinction of relict crocodile populations throughout the Sahara-Sahel (Brito et al., 2011a,c). Overgrazing, wood collection and conversion of natural habitats into pastures and agricultural fields have also affected large portions of the Sahel by fragmentation and destruction of savannah-like micro-habitats (ECOWAS & SWAC-OCDE, 2006). More recently, the extraction of natural resources (oil, gas and mining) has become widespread over the Sahara (Fig. 7), and prospection for new oil sources has increased over the last decade, endangering the last known viable addax (Addax nasomaculatus) populations in Niger (Rabeil, 2011). The escalating conflict observed in the Sahel since 2012 is also prompting disastrous declines in endangered ungulates across the Sahara-Sahel (Zedany & Al-Kich, 2013) and is likely threatening the northernmost population of elephants (Loxodonta africana) in Africa, located in the Sahel of Mali and Burkina-Faso (Wall et al., 2013).

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Figure 7. Human activities in the Sahara-Sahel. Interpolated distribution of human population density in North Africa (adapted from CIESIN-FAO-CIAT, 2005), areas of insecurity including attacks on people and infrastructures and kidnapping for ransom since 2003, regions of long-standing conflict, and regions with landmine occurrence (updated from Ewi, 2010; Walther & Retaillé, 2010; www.sahara-overland.com; and www.desert-info.ch/desert-info-forum/viewtopic.php?t=1927), areas of exploration of natural resources including gas, oil, and mining (adapted from multiple internet-based sources; e.g. Rabeil, 2011), major roads and tracks (updated from ESRI, 1996), protected areas (adapted from IUCN and UNEP, 2009), and hypothesised biodiversity refugia in the Sahara-Sahel region.

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Mountain lagoons are important for humans, providing water for both human and cattle consumption (Fig. 4B). Water overexploitation produces several conservation problems, including shortage during the dry season, faecal contamination, excessive eutrophication, and increased activities for excavating pools or pumping water (Tellería et al., 2008; Brito et al., 2011c). Moreover, documented reductions in water-dependent species diversity and population sizes (Jödicke et al., 2004; Trape, 2009; Brito et al., 2011c) as a direct consequence of the dramatic droughts in the 1970s (Brooks, 2004) suggest a major threat for biodiversity at gueltas under predicted global warming scenarios.

New threats for biodiversity are forecasted with global climate warming at an unprecedented rate in the last 1000 years (IPCC, 2007). North Africa is a land of extremes, being traditionally affected by climate fluctuations (Foley et al., 2003; Claussen, 2009). During the 20th century, Africa warmed by 0.5°C (Hulme et al., 2001) and predictions of human-induced climate change for the continent suggest that this warming will continue, especially in desert biomes, where the predicted rate of temperature increase is highest (Hulme et al., 2001; Loarie et al., 2009). Future climate warming is likely to affect the phenology, physiology and distribution of many species and the synergistic combination with other human-induced habitat fragmentation and loss will likely increase range contraction and species extinction (Pimm, 2008). Ecological niche-based models are forming the basis for simulating future distributions under climate-change scenarios. Predictions for migrant passerines and breeding birds indicate extensive range contractions and species loss across the Sahel and the northern margin of the Sahara, respectively (Barbet-Massin et al., 2009; Barbet-Massin, Thuiller & Jiguet, 2010). Protected areas located in deserts and xeric shrublands are expected to suffer dramatic losses of suitable climates for African mammals; for instance, the Tassili n'Ajjer National Park of Algeria is predicted to lose about 50% of current mammal richness with only about 10% species gain (Thuiller et al., 2006). Quantifications of species range shifts and population trends in the region are mostly absent, but the few studies available reported negative population trends and range shifts constrained by the ecophysiological traits of species. Examples come from multiple taxonomic levels, such as woody vegetation (Wezel, 2005; González, Tucker & Sy, 2012), fishes (Trape, 2009), reptiles (Brito et al., 2011c), and small mammals (Thiam, Bâ & Duplantier, 2008). By contrast, invasion of alien species profiting from agricultural expansion associated with human settlements has been reported (Bachir et al., 2011). Regional red-listing is mostly unavailable for all taxonomic groups and countries within the Sahara-Sahel, with the exception of Morocco where 31 and 14% of amphibians and reptiles, respectively, were identified as threatened mostly related to small species range and habitat specialisation (Pleguezuelos et al., 2010). Area prioritisation for biodiversity conservation is mostly unavailable, with the exception of African dragonflies (Simaka et al., 2013) and the amphibians and reptiles of Morocco (de Pous et al., 2011). Both works suggest the expansion of the present conservation area network to Sahara environments to ensure species persistence, even if considering low representation of species distributions across protected areas.

Whereas the Sahara-Sahel harbours several endemics, relict populations, and cryptic diversity, and supplies important ecosystem services, its conservation has been mostly neglected (UNEP, 2006; Davies et al., 2012; Durant et al., 2012). In fact, a small number of studies have been devoted to Sahara-Sahel biodiversity compared to other regions (Durant et al., 2012), resulting in a lack of knowledge on biodiversity distribution. As such, protected area coverage in the region (7.4%; Fig. 7) is below the 10% target of the Convention on Biological Diversity (Secretariat of the Convention on Biological Diversity, 2010). The paucity of conservation actions derives from inefficiency in attracting conservation funds, probably caused by: (i) funding priority been given to global biodiversity hotspots (Durant et al., 2012); (ii) generalised lack of knowledge on biodiversity distribution deriving from the remoteness of the region, regional widespread conflicts (Fig. 7), or persistent regional insecurity (Ewi, 2010; Walther & Retaillé, 2010; Lohmann, 2011); and (iii) chronic poverty with some countries ranking low on the human development rating (UNDP, 2010). Such limitations have resulted in conflicts between biodiversity conservation and poverty reduction (Adams et al., 2004; Davies et al., 2012).

The future of Sahara-Sahel biodiversity is highly dependent on the development of human societies. In this context, greater regional investment, both in human development and biodiversity conservation is needed. Resource allocation via major international funding institutions, such as the World Bank (www.worldbank.org) or the Global Environmental Fund (www.globalenvironmentfund.com), is paramount. In parallel and at smaller scales, non-governmental organisations and international cooperation agencies are developing biodiversity surveys and promoting the establishment of local protected areas (e.g. Cooper et al., 2006). Several organisations, such as the Sahara Conservation Fund (SCF, www.saharaconservation.org), are promoting reintroductions and population monitoring of endangered ungulates (Oryx dammah, Addax nasomaculatus, and Nanger dama mhorr) in Algeria, Chad, Niger, Senegal and Tunisia (e.g. Abáigar et al., 1997), and in 2012 the SCF promoted the creation of the largest African protected area in the Termit and Tin-Toumma of Niger. Other relevant local protected areas recently established include the reintroduction facilities for ungulates of Safia (Morocco), which are vital for maintaining overall genetic diversity of endangered ungulates (Godinho et al., 2012). By contrast, the subspecies Giraffa camelopardalis peralta needs urgent inclusion in captive breeding programmes as it is known only from a small wild population of less than 200 individuals in Niger (Hassanin et al., 2007). Community-based natural resources management policies are needed to assure human welfare with coexisting biodiversity, similarly to other successful experiences across Africa (e.g. Virtanen, 2003). Local practices and beliefs towards large vertebrates dictate levels of human persecution, and have major implications in local extinctions or in the acceptance of in-situ conservation efforts (Ostrowski et al., 2001; Beudels et al., 2005; Brito et al., 2011a). Local communities have an accurate perception of surrounding biodiversity (Hammiche & Maiza, 2006), revealing traditional knowledge as a useful conservation tool to determine the distribution, status and biological traits of elusive and rare species living in remote areas (Burbidge et al., 1988; Kowalski & Kowalska, 1991; Brito et al., 2011a). As such, the declaration of the Gabbou hydrological network of Mauritania as a Ramsar site (Tellería, 2009) is especially relevant, as it could generate alternative income sources for local human populations linked to birdwatching and to the presence of relict crocodile populations (Brito et al., 2011c). Eco-tourism programmes established in protected areas, combining wildlife observation and discovery of human cultural heritage and rock art, may also be of direct benefit locally (UNEP, 2006).

V. RESEARCH NEEDS

  1. Top of page
  2. ABSTRACT
  3. I. INTRODUCTION
  4. II. DISTRIBUTION OF BIODIVERSITY
  5. III. EVOLUTION OF BIODIVERSITY
  6. IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING
  7. V. RESEARCH NEEDS
  8. VI. CONCLUSIONS
  9. VII. ACKNOWLEDGEMENTS
  10. VIII. REFERENCES
  11. Supporting Information

Current research is allowing us to unravel the patterns and processes behind Sahara-Sahel biodiversity, but many questions remain unanswered, hampering regional conservation planning. The main issues in need of addressing are:

  1. Raw distribution data with GPS resolution is being collected (e.g. Brito et al., 2008, 2010; Ferreira et al., 2011) and high-resolution maps of suitable habitats are being produced for some taxonomic groups and regions (e.g. El-Ghani, 1998; Brito et al., 2009, 2011b; Vale et al., 2012a,b). However, there are still huge information gaps on local species richness and individual species' ranges at all taxonomic levels, and biodiversity mapping needs to be extended to many taxa, with priority given to endangered species, mountain-endemic fauna, and relict populations of non-Saharan origin. Accurate distribution data are paramount for developing atlases of biodiversity distribution. Assessments are needed in remote and hard-to-sample mountain areas, which most likely still hold undescribed endemic diversity. Environmental factors have been related to ranges of multiple vertebrates, but vulnerability and potential adaptation to climate change is still poorly understood. Remote sensing can provide environmental data appropriate to derive ecological models with high spatial and temporal resolution (e.g. Campos et al., 2012).
  2. Cryptic diversity and geographic structuring in genetic diversity have been observed in widespread species (e.g. Boratyński et al., 2012; Gaubert et al., 2012; Gonçalves et al., 2012), but the systematic status of these genetic demes and the evolutionary drivers of such diversity are mostly unknown. Molecular studies will likely continue to reveal biodiversity and genetic analysis of museum specimens will provide essential material from regions where sampling is currently nearly impossible due to political instability.
  3. Geological and palaeoclimatic events are thought to be major drivers of biodiversity (e.g. Carranza et al., 2002, 2006; Geniez & Arnold, 2006; Wagner et al., 2011; Metallinou et al., 2012). Although the climate-driven speciation hypothesis has been suggested to explain the evolutionary patterns at interspecific and intraspecific levels in the Sahara-Sahel (e.g. Carranza et al., 2002, 2008; Boratyński et al., 2012; Gonçalves et al., 2012), it still requires detailed verification. Integrative studies of historical biogeography, combining ecological niche modelling (e.g. Nyári et al., 2010), genetic analyses and functional experiments, are needed to estimate ecophysiological (and adaptive) limits of species/clades to reconstruct and predict evolutionary trajectories, as well as to test if diversification patterns match past wide-impact events. Also, parapatric and sympatric speciation mechanisms are rarely considered and their ecological components, like character displacement hypotheses (interspecific competition), need exploration.
  4. Mountains are being emphasised as biodiversity hotspots (e.g. Trape, 2009; Brito et al., 2010, 2011b,c; Geniez et al., 2011), but they remain largely unexplored. The development of phylogenetic, phylogeographic and population genetic studies will most likely unravel a unique situation where the combination of long-term persistent populations with distinct origins by long-distance colonisation processes was at the origin of peculiar and unexpectedly rich biological assemblies.
  5. Biodiversity corridors have been proposed for coastal regions, central mountains, and the Nile river (Dumont, 1982; Drake et al., 2011), but studies incorporating modern phylogenetic/phylogeographic analyses are needed to test biogeographic hypotheses and to date diversification events and phylogeographic splits. It is also necessary to investigate diversity in low- and high-dispersal taxa along putative corridors.
  6. Metapopulation systems of biodiversity hotspots associated with micro-scale humid habitats have been detected (e.g. Trape, 2009; Brito et al., 2011c; Campos et al., 2012), but it is unknown how landscape features link to gene flow and connectivity, and how climate change may affect such dynamics. Monitoring of climate-change effects should be prioritised in sensitive areas by focusing on water-restricted fauna.
  7. Ecological adaptation and possible hybridisation in contact zones between full species has been suggested (Crochet et al., 2003), but the role of climate and landscape features in defining the extent of ranges, connectivity and gene flow are unknown. Integrative landscape models are needed to understand contact-zone and gene-flow dynamics in desert environments and to strengthen knowledge on evolutionary and adaptation mechanisms to extreme arid conditions.
  8. Present regional red-listing of biodiversity is very limited [amphibians and reptiles of Morocco (Pleguezuelos et al., 2010)] and is urgently needed to be extended to other taxonomic groups and countries to identify threatened biodiversity and define conservation priorities.
  9. Assessments of genetic diversity in captive and semi-captive threatened ungulates have stressed the importance of using molecular markers for optimising management options (e.g. Godinho et al., 2012), but such assessments are now needed for wild populations, particularly for the identification of management units and effective population sizes and their trends (Crandall et al., 2000). Non-invasive genetic sampling techniques should be prioritised given their usefulness in studying secretive or hard-to-sample species.
  10. Optimised conservation solutions for the Sahara-Sahel biodiversity are lacking. Reserve design solutions targeting biodiversity representativeness and persistence together with human development, are needed. Special emphasis should be given to mitigate expected negative impacts of climate change, incorporating evolutionary processes in conservation solutions, and identifying potential corridors among conservation areas.

VI. CONCLUSIONS

  1. Top of page
  2. ABSTRACT
  3. I. INTRODUCTION
  4. II. DISTRIBUTION OF BIODIVERSITY
  5. III. EVOLUTION OF BIODIVERSITY
  6. IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING
  7. V. RESEARCH NEEDS
  8. VI. CONCLUSIONS
  9. VII. ACKNOWLEDGEMENTS
  10. VIII. REFERENCES
  11. Supporting Information
  1. The Sahara-Sahel system is a good model to investigate the effects of extreme climate shifts on biodiversity dynamics. The region is environmentally heterogeneous and has been subjected to profound climatic oscillations that have shaped biodiversity distribution. Biodiversity hotspots and cryptic diversity have been found in restricted and small-sized water-features located in mountains. The system of mountains surrounded by sand seas provides isolated areas to assess responses of species to climatic oscillations. It is an ideal laboratory to study phenology, physiology, tolerance and adaptation to climate change. Patterns currently observed may provide indications on potential outcomes of global warming and increasing aridity that are of particular relevance for neighbouring global biodiversity hotspots, such as the Mediterranean Basin and the West African Forests.
  2. Increasing scientific studies based on modern geomatic and molecular tools, and broad sampling of taxa in these regions, are allowing insights on patterns of biodiversity distribution and evolution. The steep increase in taxonomic research on vertebrates during the last decade suggest that the Sahara-Sahel still harbours cryptic biodiversity in urgent need of research and that biodiversity conservation targets are far from being achieved.
  3. The onset of the Sahara has been associated with diversification processes, mostly for low-mobility vertebrates. Phylogeographic patterns highlight the importance of allopatric divergence in the Sahara-Sahel.
  4. Regional insecurity is growing and the escalating conflict in the Sahel, apart from the associated local human tragedy, is hampering biodiversity research and conservation. The trend of research effort increase experienced in the last decade is thus uncertain for the future. Research priorities and conservation policies can only be achieved fully with the complementary advanced training of local human resources, technology transfer, and improvement of social conditions. Such developments will clearly contribute to the stabilisation of the region and ultimately to conserving biodiversity.

VII. ACKNOWLEDGEMENTS

  1. Top of page
  2. ABSTRACT
  3. I. INTRODUCTION
  4. II. DISTRIBUTION OF BIODIVERSITY
  5. III. EVOLUTION OF BIODIVERSITY
  6. IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING
  7. V. RESEARCH NEEDS
  8. VI. CONCLUSIONS
  9. VII. ACKNOWLEDGEMENTS
  10. VIII. REFERENCES
  11. Supporting Information

This study was partially supported by grants from the National Geographic Society (Commission on Research and Exploration, grants 7629-04 and 8412-08), from Mohammed bin Zayed Species Conservation Fund (projects 11052709, 11052707, and 11052499), from SYNTHESIS programs (BE-TAF-1796 and AT-TAF-1665), and by Fundação para a Ciência e Tecnologia (PTDC/BIA-BEC/099934/2008) through EU Programme COMPETE. Logistic support for fieldwork was given by Pedro Santos Lda (Trimble GPS), Off Road Power Shop, P. N. Banc d'Arguin (Mauritania), and Ministère Délégué auprès du Premier Ministre Chargé de l'Environnement et du Développement durable of Mauritania.

VIII. REFERENCES

  1. Top of page
  2. ABSTRACT
  3. I. INTRODUCTION
  4. II. DISTRIBUTION OF BIODIVERSITY
  5. III. EVOLUTION OF BIODIVERSITY
  6. IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING
  7. V. RESEARCH NEEDS
  8. VI. CONCLUSIONS
  9. VII. ACKNOWLEDGEMENTS
  10. VIII. REFERENCES
  11. Supporting Information
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Supporting Information

  1. Top of page
  2. ABSTRACT
  3. I. INTRODUCTION
  4. II. DISTRIBUTION OF BIODIVERSITY
  5. III. EVOLUTION OF BIODIVERSITY
  6. IV. THREATS TO BIODIVERSITY AND CONSERVATION PLANNING
  7. V. RESEARCH NEEDS
  8. VI. CONCLUSIONS
  9. VII. ACKNOWLEDGEMENTS
  10. VIII. REFERENCES
  11. Supporting Information
FilenameFormatSizeDescription
brv12049-sup-0001-Appendix S1.docxapplication/unknown19KAppendix S1. Distribution of species richness of endemic and relict taxa of dragonflies, fishes, amphibians, reptiles, and mammals in hypothesised dispersal corridors and refugia of the Sahara-Sahel region.

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