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
Discussion

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Species composition of the Sahamalaza Peninsula

Although surveys always depend on contingency, it is likely that a significant proportion of Sahamalaza’s amphibian and reptile fauna have been detected, when considering all herpetological survey work of the area. The detection of three new taxa (Boophis ankarafensis, Stumpffia sp. aff. pygmaea Ca “Sahamalaza”, Geckolepis humbolti) unnoticed during the previous surveys, highlights the efficiency of using an integrative approach to species identification. The detection of several species (almost 20%) in the final few weeks of the wet season, together with the detection of species missed during a previous survey by Andreone et al. (2001), highlights the necessity of conducting herpetological surveys over extended periods for areas with strong seasonal differences.

The presence of species representative of the drier biomes of West Madagascar (e.g. Aglyptodactylus securifer, Blommersia sp. Ca05 (UCS), Heterixalus luteostriatus, H. tricolor, Laliostoma labrosum, Blaesodactylus ambonihazo, Oplurus cuvieri, Madascincus stumpffi and Zonosaurus laticaudatus concurrent with species representative of the rainforests of Sambirano region to the north (e.g. Boophis brachychir, B. jaegeri, B. tephraeomystax, Gephyromantis pseudosasper, Mantella ebenaui, Mantidactylus ulcerosus, Stumpffia gimmeli, Alluaudina bellyi, Brookesia stumpffi, B. minima, Ebenavia inunguis, Ithycyphus perineti, Phelsuma laticauda, P. vanheygeni, Paroedura oviceps, P. stumpffi, Uroplatus henkeli and U. ebenaui) confirms that Sahamalaza’s intermediate climate supports a transitional fauna between these two biomes.

The two forests of Anabohazo and Ankarafa show broadly similar species compositions with a few notable differences (Table 2). Four amphibian and ten reptile species were recorded in Anabohazo Forest but not in Ankarafa, while two amphibian and eight reptile species were found in Ankarafa but not in Anabohazo. It is likely that some of these differences only reflect bias in survey effort between the two locations. For example, several of the Gekkonidae detected from Ankarafa and not in Anabohazo: Blaesodactylus ambonihazo, E. inunguis, Phelsuma sp. aff. quadriocellata and P. vanheygeni, were likely missed due to the shorter time spent surveying this area, coupled with their infrequent to rare encounter rates. On the other hand, the species recorded in Anabohazo but not in Ankarafa are prone to have been missed, due to the positive bias in the sampling period in Ankarafa. However, the two forests fragments differ in size, habitat quality and geography and so some differences in species composition might be due to this. The two fragments are separated from one another by around 20 km of savannah and scrubland, potentially isolating many of the forest-dependent species. The far-ranging calls of G. pseudoasper were extremely conspicuous throughout Anabohazo yet entirely absent from Ankarafa. This difference cannot be attributed to season as surveys in Ankarafa took place immediately before and after the sampling period in Anabohazo. Anabohazo marks the most southerly extent of this species range (Glaw and Vences, 2007) and it is possible that the climate or geography of Ankarafa make it unsuitable for G. pseudoasper. The recently described Boophis ankarafensis was only found along perennial lotic streams in Ankarafa, a hydrological feature that is entirely absent within Anabohazo, which may explain its potential absence from here. This factor likely accounts for the non record of the helmeted turtle Pelomedusa subrufa.