How Soil and Elevation Shape Local Plant Biodiversity in a Mediterranean Hotspot

Biodivers Conserv (2016) 25:1133–1149 DOI 10.1007/s10531-016-1113-y ORIGINAL PAPER How soil and elevation shape local plant biodiversity in a Mediterranean hotspot 1,2 1 Rafael Molina-Venegas • Abelardo Aparicio • 3 1 Se´bastien Lavergne • Juan Arroyo Received: 16 November 2015 / Revised: 5 April 2016 / Accepted: 16 April 2016 / Published online: 26 April 2016 Ó Springer Science+Business Media Dordrecht 2016 Abstract Elucidating how evolutionary and ecological factors drive the assemblage of communities in biodiversity hotspots remains an important challenge. This currently impedes our ability to predict the responses of communities to the ongoing global changes in these major world’s biodiversity reservoirs. Here, we focus on the Sierra Nevada mountain range, a core region of the Baetic-Rifan biodiversity hotspot in the western Mediterranean, and explore the relative importance of soil properties and elevation in shaping phylogenetic and functional diversity of shrub communities. We recorded the total number of each species in community transects across elevation gradients and contrasting soil conditions, and measured some ecologically relevant functional traits (specific leaf area, leaf carbon:nitrogen ratio, plant height and blooming duration). Phylogenetic dis- tances among species were inferred from a genus-level time-calibrated molecular phy- logeny. Elevation was the main factor predicting phylogenetic and functional alpha diversity of plant communities. Species in high-elevation communities were phylogenet- ically distant but functionally similar, being relatively smaller and having relatively short blooming durations, whilst species in low-elevation communities showed the opposite pattern. Beta diversity in SLA and leaf C:N ratio based on species incidences were pos- itively correlated with a soil pH and micronutrient gradient. Specifically, communities that Communicated by Daniel Sanchez Mata. Electronic supplementary material The online version of this article (doi:10.1007/s10531-016-1113-y) contains supplementary material, which is available to authorized users. & Rafael Molina-Venegas [email protected] 1 Departamento de Biologıá Vegetal y Ecologıá, Universidad de Sevilla, Apartado 1095, 41080 Seville, Spain 2 Present Address: Departmento de Ciencias de la Vida, Universidad de Alcala´, Alcala´ de Henares, Madrid, Spain 3 Laboratoire d’E´ cologie Alpine, CNRS Universite´ Grenoble Alpes, BP 53, 38041 Grenoble Cedex 9, France 123 1134 Biodivers Conserv (2016) 25:1133–1149 develop on soils of high pH and low micronutrient concentrations showed low SLA values and high leaf C:N ratios, whilst communities on soils of lower pH and high micronutrient concentrations showed the opposite pattern. We conclude that soil properties and elevation simultaneously shape the structure of Mediterranean shrub communities by differentially acting on the different dimensions of the species niches. Elevation seems to filter plant height and phenology-related traits whereas nutrient-related functional traits are more related to soil properties. Our study illustrates the primary role of environmental heterogeneity for the maintenance of diversity in Mediterranean mountain ecosystems. Keywords Alpha and beta diversity Á Baetic-Rifan range Á Community ecology Á Environmental filtering Á Functional diversity Á Phylogenetic structure Introduction Despite the ‘renaissance’ of community ecology that occurred over the past decade (Mouquet et al. 2012), elucidating how evolutionary and ecological factors drive the assemblage of communities in biodiversity hotspots remains an important challenge (Mason and de Bello 2013). Much of the work focused on elucidating causes of high diversity in the hotspots has been achieved at regional scales, whereas community level studies are less frequent (but see Kembel and Hubbell 2006; Comita et al. 2010). Importantly, many ecological and evolutionary processes that ultimately shape biodiversity occur at the community scale (McIntire and Fajardo 2014; Valiente-Banuet et al. 2015), and therefore community-level studies are of paramount relevance for applied conserva- tion. Further, understanding the mechanisms driving the assemblage of communities in biodiversity hotspots is critical if we are to predict their response to ongoing global changes (Ho´dar et al. 2011; Matıás et al. 2012). The incorporation of phylogenetic information into community assembly studies has permitted the evaluation of the effect of the ancestor–descendant relationship on the present distribution of species in communities (Webb et al. 2002). Besides shedding light on the drivers of community assembly, phylogenetic data may also be highly valuable for con- servation (Mouquet et al. 2012; Tucker et al. 2016), particularly in preserving the evolutionary potential of floras in biodiversity hotspots (Forest et al. 2007) and predicting ecosystem functioning (Srivastava et al. 2012). However, despite the advantages of incor- porating phylogenetic information, there is evidence that phylogenies may be unable to capture all aspects of community structure (Carboni et al. 2013) given the varied evolutionary trajectories of the species’ niches (Ackerly and Cornwell 2007; Devictor et al. 2010). A solution to this problem consists in analyzing functional trait distributions within and among communities and along varied environmental gradients (de Bello et al. 2013; Mason et al. 2013). Thus, understanding the drivers of community structure requires quantifying species’ ecological differences based on either functional traits and phylogenetic information (Chalmandrier et al. 2013, 2015; de Bello et al. 2013), and studying community patterns along varied environmental gradients (Bernard-Verdier et al. 2012; Gross et al. 2013). Plant assemblages in the Mediterranean are characterized by a high turnover of narrow- ranging species and vegetation types along sharp environmental gradients (Thompson 2005; Molina-Venegas et al. 2013; Jimeńez-Alfaro et al. 2014). At regional scales, glacial refugia have played an important role in structuring the exceptional concentration of biodiversity in these ecosystems (Me´dail and Diadema 2009), allowing the long-term 123 Biodivers Conserv (2016) 25:1133–1149 1135 persistence of extant representatives of the flora that once existed under past climatic conditions (Herrera 1992; Postigo-Mijarra et al. 2009). At local scales, the enormous spatial heterogeneity that characterize Mediterranean ecosystems is a key factor for understanding the distribution of biodiversity in these species-rich biomes (Thompson 2005). Specifically, elevation gradients have been shown to be an important factor in structuring Mediterranean plant assemblages (Fontaine et al. 2007; Loidi et al. 2015; Molina-Venegas et al. 2015). However, less attention has been paid to the effects that soil properties have on the functional and phylogenetic structure of Mediterranean plant communities (but see Ojeda et al. 2010; Escudero et al. 2015). Mediterranean landscapes show a high incidence of stressful substrates that characterize the spatial heterogeneity of the region (Mota et al. 2008, 2011;Pe´rez Latorre et al. 2013). This lithological heterogeneity could be acting as local environmental filters that ultimately would lead to ‘clustered’ local trait variation compared to that of the surrounding habitats (Diamond 1975; de Bello et al. 2012). As well, strong phylogenetic clustering may be observed in such stressful environments due to deep phylogenetic signal in species niches (Kraft and Ackerly 2014; Molina-Venegas et al. 2015; Chalmandrier et al. 2015). However, because species do not coexist in isolation from one other, the resulting local species pool and observed composition of communities will be the result of both environmental filters and biotic interactions (Webb et al. 2002). Incidence-based functional composition of communities may mainly inform about environmental filters selecting species based on their physiological tolerance, whereas the abundance-weighted functional composition could be more related to the effect of biotic interactions (Chalmandrier et al. 2015). Thus, considered in tandem, diversity indices based on species’ incidence-only and abundance can provide evidence for different processes of community assembly. Moreover, the mosaic-like pattern of Mediterranean plant landscapes suggests a high diversity turnover in communities, and thus the decomposition of diversity into within-community (alpha diversity) and among-community (beta diversity) components should tease apart processes driving species coexistence within local sites and species distributions along environmental gradients (Hardy and Senterre 2007). In this study, we analyzed patterns of species incidence and abundance in vegetation surveys, along with multiple traits and phylogenetic information in order to assess the relative importance of soil properties and elevation gradients in shaping phylogenetic and functional diversity of Mediterranean shrub communities. We focused on the Sierra Nevada, a core range of the Baetic-Rifan biodiversity hotspot located between the southern part of the Iberian Peninsula (mostly in Andalusia) and northwest Africa (north Morocco) (Me´dail and Que´zel 1997; 1999) in the western Mediterranean. The Sierra Nevada pro- vides an ideal eco-historical setting for assessing the role of elevation and soil properties in shaping shrub communities in Mediterranean mountain ecosystems. Indeed, this mountain range is one of the highest ranges in the

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