Contributions to Zoology, 86 (4) – 2017Samuel G. Penny; Angelica Crottini; Franco Andreone; Adriana Bellati; Lovasoa M.S. Rakotozafy; Marc W. Holderied; Christoph Schwitzer; Gonçalo M. Rosa: Combining old and new evidence to increase the known biodiversity value of the Sahamalaza Peninsula, Northwest Madagascar

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Introduction

Madagascar ranks amongst the richest countries in the world for the diversity of its herpetofauna, harbouring about 400 described species of non-avian reptiles (from here onward, we will use the traditional term ‘reptiles’ for species included in the Sauropsida excluding birds) and about 320 described species of amphibians (Glaw and Vences, 2007; Perl et al., 2014; AmphibiaWeb, 2017). The uniqueness of present-day Madagascan biota can be partially explained by the biogeographic isolation of the island. Indeed, much of Madagascar’s extant fauna is the result of succesful colonizations around the K-T boundary at ca. 60-70 mya (Crottini et al., 2012; Samonds et al., 2012). The Madagascan herpetofauna shows remarkably high levels of endemism, with 92% of non-marine reptile species and all but one of the native amphibian species found nowhere else (Glaw and Vences, 2007).

Over the last few years, large-scale taxonomic inventories, using a combination of molecular tools, bioacoustics and morphological methods have led to a rapid increase in species descriptions and in the identification of a large number of candidate species that await description (Vieites et al., 2009; Nagy et al., 2012; Rosa et al., 2012; Perl et al., 2014). Many of the newly identified taxa are easily diagnosable, while many other species that were thought to be relatively widespread across Madagascar represent complexes of several species. This resulted in several taxonomic revisions (mostly at the genus level) and in a remarkable number of new or resurrected amphibian and reptile species [e.g. Aglyptodactylus (Köhler et al., 2015), Boophis (Glaw et al., 2010), Blommersia (Andreone et al., 2010), Gephyromantis (Vences et al., 2017), Guibemantis (Lehtinen et al., 2011), Mantidactylus (Bora et al., 2011), Scaphiophryne (Raselimanana et al., 2014), Anodontyla (Vences et al., 2010a), Cophyla (Rakotoarison et al., 2015), Platypelis (Rosa et al., 2014), Rhombophryne (Scherz et al., 2016); Stumpffia (Rakotoarison et al., 2017), Brookesia (Glaw et al., 2012), Furcifer (Florio et al., 2012), Calumma (Gehring et al., 2011), Chalarodon (Miralles et al., 2015), Zonosaurus (Raselimanana et al., 2006), Madascincus (Miralles et al., 2011), Paracontias (Miralles et al., 2016), Paragehyra (Crottini et al., 2015), Uroplatus (Ratsoavina et al., 2011), Phelsuma (Crottini et al., 2011), Liopholidophis (Glaw et al., 2014)].

Amphibians are experiencing an unprecedented worldwide decline, 41% of the described species are threatened with extinction (Monastersky, 2014) and species loss is occurring at more than 200 times the average background extinction rate (Roelants et al., 2007). Many reptile species are also in decline. In a representative sample of 1500 species nearly one fifth were found to be threatened (Böhm et al., 2013). The leading causative factors are the destruction, alteration, and fragmentation of habitats (Stuart et al., 2004; Andreone et al., 2005; Sodhi et al., 2008; Irwin et al., 2010; Jenkins et al., 2014). Having lost one third of its primary forest since the 1970s, Madagascar is no exception, and it continues to lose around 8600 km2 (0.5%) of primary forest per year (FAO 2015). This loss will have a tremendous impact on all unique biodiversity of Madagascar, including amphibian and reptile species due to their specific habitat requirements coupled with a high dependency on the stability and quality of their habitats (Andreone et al., 2005; Sinervo et al., 2010; Riemann et al., 2015), and most probably also on human communities.

Climatic change is likely to intensify the effects of Madagascar’s habitat loss (Raxworthy et al., 2008; Huey et al., 2009; Walls et al., 2013), as will the recent discovery of potentially emergent infectious pathogens (Bletz et al., 2015a, 2015b; Kolby et al., 2015), and the introduction of invasive species (Andreone et al., 2014; Crottini et al., 2014; Kolby et al., 2014; Vences et al., 2017).

A large proportion of Madagascar’s amphibian and reptile diversity is limited to the island’s northern and eastern rainforest slopes, which are known to host a high number of endemic species (e.g. Rosa et al., 2012; Heinermann et al., 2015; Brown et al., 2016). In recent years, high levels of species diversity have also been described from the west of the island (e.g. D’Cruze et al., 2006; Mercurio et al., 2008; Bora et al., 2010). Many reptile and amphibian species are known exclusively from western dry forests, such as several species of Gerrhosauridae (Raselimanana, 2003), Opluridae (Raselimanana et al., 2000) and tree frogs (Penny et al., 2014), most of which have narrow ranges. Dry forests, in particular those in the sub-arid regions of Madagascar, are poorly understood in terms of flora and fauna (Sussman and Rakotozafy, 1994). Malagasy deciduous dry forests declined in primary forest cover from 12.5% in 1950 to 2.8% in 1990 (Smith, 1997) and, due to their susceptibility to fire and conversion to agricultural land, are among one the most threatened habitats in the country (Janzen, 1988; Pons et al., 2003; Elmqvist et al., 2007). Forest destruction was further exacerbated by a political coup in 2009, which led to a weakening in government enforcement (Schuurman and Andreone, 2010; Andreone et al., 2012; Schwitzer et al., 2014). Despite acquiring formal protection in 2007, the Sahamalaza Peninsula, in western Madagascar, still experiences high levels of anthropogenic pressure on its terrestrial, freshwater and marine ecosystems (Schwitzer et al., 2007; Seiler et al., 2012; Penny et al., 2014). No large intact areas of primary forest remain, with forest consigned to a matrix of small isolated fragments, all of which show some degree of anthropogenic disturbance and/or edge effects (Schwitzer et al., 2007). The human communities living in the periphery of the protected area depend on subsistence agriculture (through ‘slash-and-burn’) and fishing for their livelihoods, which traditionally occurred in the core zones of the park.

A total of 14 species of amphibians and 32 species of reptiles were previously documented from the Sahamalaza Peninsula (Andreone et al., 2001; Raselimanana, 2008). The conservation importance of this community is high, due to the presence of several microendemic and threatened species. Species with spatially narrow niches are often more sensitive to the microhabitat changes associated with disturbance, thus it is particularly important to collect further ecological and distributional data on them (Glos et al., 2008; Irwin et al., 2010). To implement an effective conservation plan for Sahamalaza’s herpetofauna it is crucial to increase our knowledge on the distribution and ecology of the species that occur here (Penny et al., 2016), particularly for the local endemics that were discovered before much of the recent habitat destruction had occurred. Using an integrative taxonomic approach to species identification, we here provide an update on the presence and distribution of amphibian and reptile species found on the Sahamalaza Peninsula.