Do fine-scale factors shape the use of riparian galleries by carnivores in a Mediterranean agro-forested environment?

The Mediterraneanbasin is considered to be a biodiversity hotspot (Médail and Quézel 1999), being a mosaic of natural and culturalaltered-landscapes, resulting from the long coexistence of human civilization and wild nature (Cuttelod et al. 2008). 

These landscapes have been shaped by human activities for millennia (Naveh and Vernet 1991; Lavorel et al. 1998), yet, more recently, they have been subject to increasing anthropogenic pressures and disturbances which have led to drastic changesatthe landscapelevel(Myers et al. 2000). Men actions, such as deforestation, cattle breeding, conversion of natural systems in agro or planted forest systems, intensification of agricultural practices and road construction, have shaped and transformed Mediterranean landscapes (e.g. Lepart and Debussche 1992; De Aranzabal et al. 2008; Geri et al. 2010), leading tothe decline ofmany species ofboth thefloral and faunal communities, and its replacement for a smaller number ofexotic and expanding ones, a process known as biotic homogenization (e.g. McKinney and Lockwood 1999). This anthropogenization of the landscape has shown negative impacts on biodiversity, especially important in areas where the management is not adequate, and does not equally affect all landscape components.

 Agriculture, lodging, fire and livestock grazing are the main drivers of deforestation and forest degradation (e.g. Hosonoma et al. 2012), impacting a significant part of the land’s surface, but other side effects are also reported. This is the case of riparian galleries, which are unique and key structural elements in the landscape, maintaining regional biodiversity (e.g. Naiman et al. 1993, Ferreira et al. 2005). Established normally along river margins, forming dense patches of vegetation adapted to water and soil fluctuation dynamics (Naiman and Décamps 1997), they serve multiple roles, including the regulation of temperature and light regimes (Naiman and Décamps 1997), water provision (Malanson 1993; Naiman and Décamps 1997), nutrient retention (Jacobs et al. 2007), refuge for species (Sabo et al. 2005), provision of food and conditions for the reproduction of many animal species (Matos et al. 2009; Pereira and Rodriguez 2010), acting also as movement and dispersal corridors (Machtans et al. 1996; Burbrink et al. 1998), providing connectivity between isolated habitat fragments (Beier and Noss 1998; Santos et al. 2011). In regions of semi-arid climate, as some found in the Mediterranean, riparian galleriesare the only habitat that remains less human intervened atthelarge scale (Virgós 2001a; Matos et al. 2009; Santos et al. 2011),holdinghigh biodiversity levels (Sabo et al. 2005) considering their small land area (Naiman and Décamps 1997). 

The response of wildlife to riparian corridors has been investigated by many authors, in different environmental contexts and for diverse animal taxa, from invertebrates (e.g. Da Silva et al. 2011), to amphibians and reptiles (e.g. Suazo-Ortuño et al. 2011), birds (e.g. Bennett et al. 2014)andmammals (e.g. Sullivan et al. 2014). 

The conservation value of these linear habitats for carnivores in human-altered landscapes has also been highlighted (Virgós 2001b; Santos-Reis et al. 2004; Maiorano et al. 2006; Matos et al. 2009; Pereira and Rodriguez 2010), having been demonstrated that species richness and abundance is quite higher in riparian corridors, compared to an intervened matrix (Virgós 2001a; Matos et al. 2009), being also higher in conserved galleries than in degraded ones (Hilty and Merenlender 2004).

 Although mammalian carnivores can persist in several habitat types, they are particularly sensitive to anthropogenic impacts, due to their vast spatial requirements and low population densities (Sunquist and Sunquist 2001). This makes them particularly vulnerable to human persecution and susceptible to changes in the structure and dynamics of their habitats (Schonewald-Cox et al. 1991; Hargis et al. 1999), being largely affected by habitat destruction and fragmentation (Schaller 1996). Their position at the top of the food chain, and impact on different human activities such as agriculture, hunting and livestock raising (Reynolds and Tapper 1996; Treves and Karanth 2003, Baker 2008), make conservation and management actions especially important. 

Climate change projections for the Mediterranean, indicating a heat stress intensification (e.g. Diffenbaugh et al. 2007), makes riparian zones the only places where water and water-dependent resources can be found and therefore key landscape elements for carnivores (Virgós 2001a; Matos et al. 2009). Their association with these habitats is further explained by the inherent patchiness of the landscape (Schonewald-Cox et al. 1991; Hargis et al. 1999) and its seasonally variable resources (Rosalino et al. 2005; Loureiro et al. 2009). 

Considering the importance of these habitats for carnivores (Pereboom et al. 2008; Pereira and Rodriguez 2010), and assuming that some of the ecological processes that affect more significantly populations and communities operate at local spatial scales (Huston 1999; Soto and Palomares 2015), species richness and abundance can vary depending on the availability of local resources, vegetation structure and size of the habitat patch (Wiens 1989; Dunning et al. 1992). For conservation purposes, it is therefore important to fully understand the factors driving carnivores’ use of riparian ecosystems. The importance of riparian quality at landscape (Malanson 1993; Virgós 2001a) and regional (Naiman et al. 1993) scales have been demonstrated but, to our knowledge, carnivore response to variation in quality at the stream level was never investigated.

 Considering that riparian galleries can have different ecological quality, A. Munné and collaborators (Munné et al. 2003) developed an index of riparian quality(QBR- ‘Qualitat del Bosc de Ribera’in Spanish), to evaluate, in a expedite way, the quality of these habitats, regarding their physical and biological characteristics, namely the vegetation composition. However, the construction of this index and the derived management recommendations for riparian galleries, have been focusing on the importance of maintaining these systems at landscape level, not having yet analysed their importance and management needs at local level (Hilty and Merenlender 2004; Matos et al. 2009). Their foliage is supported by the high availability of water, and therefore man-made actions resulting in irregularities in the flow have negative impacts, for both riparian habitat (Salinas et al. 2000), as for its associated biota, including mammalian carnivores (Matos et al. 2009). 

In this study we compared riparian ecological quality variation with the use made by carnivores, predicting that species occurrence and intensity of use is related to its fine-scale quality. We further tested if the QBR index developed by Munné et al. (2003 – hereafter termed as original QBR), and an adaptation of the same based on carnivore ecological requirements, may be used as prompt indicators of the occurrence of carnivores, serving as a guide for land managers and conservation practitioners.