902 I. M. Barata et al.
requirement for the observer to be at the site at the same time as the species, enabling data collection on much larger spatial and temporal scales and improving the robustness of any inferences made, although both tools require significant technical expertise. Overall, occupancy and abundance were strongly asso-
ciated with vegetation structure. Anilany helenae is terres- trial and has been recorded in the leaf litter of riparian forests, with its breeding behaviour possibly involving ground nests (Vallan, 2000a; IUCN SSC Amphibian Specialist Group, 2016). Pandanus leaf axils and bamboo leaves on the forest floor could influence species presence by creating hiding places and benefitting the behaviour of this cryptic species. Anodonthyla vallani is active at night, with males calling from tree trunks at heights of 2–3 m. It is presumed to reproduce through larval development in water-filled tree holes (Vences et al., 2010; IUCN SSC Amphibian Specialist Group, 2020). Given this requirement for trees and tree holes, the negative relationship between abundance and canopy cover could be explained by the pro- portion of such habitat available. Given this narrow habitat requirement, any further habitat degradation could have drastic consequences for the studied populations. Our findings indicate that a mosaic of vegetation cover is
an important feature for the persistence of these species, and probably many others, providing a diversity of habitats that regulates ecological processes and population sizes. However, wildfires (caused by human activity outside the Reserve) are a continuing threat to the forest in Ambohitantely Special Reserve and these forest-dependent species. In Ambohitantely Special Reserve forest fragmen- tation decreases amphibian population sizes and increases species vulnerability to local extinction by reducing hetero- geneity in microhabitats (Vallan, 2000b). Positively en- gaging and working with local communities to address the pressures leading to habitat degradation are key conserva- tion actions required. For example, management authorities often work with communities in protected areas in Mada- gascar to establish and maintain firebreaks (J. Dawson, pers. obs., 2020) and this is already being done in Ambohi- tantely. Similarly, to reduce forest exploitation at the nearby Ankafobe Private Reserve, plantations have been established outside the Reserve for people to use for firewood and char- coal in return for protecting the forest (K.E. Mullin, pers. obs., 2020). As the annual deforestation rate increases in Madagascar (Vieilledent et al., 2018), persistent isolation is becoming a threat to amphibian species that are rare, habitat specialists and/or intolerant of matrix habitats, making them particu- larly prone to local extinction (Lehtinen &Ramanamanjato, 2006). Although A. helenae occurs elsewhere in the sur- rounding landscape (Mullin et al., 2021a), the status of both target species in other fragments is largely unknown and the forest fragment we surveyed is probably a key
refugium of the species. Studies of amphibian population connectivity and viability in isolated fragments in the central plateau ofMadagascar are essential, contributing to our un- derstanding of the effects of fragmentation and providing evidence to support future land-use planning. Anodonthyla vallani and A. helenae are both categorized as Critically Endangered based on criteria B1ab(iii) because of their re- duced extent of occurrence (B1), severe fragmentation (a) and the continued decline (b) in the quality of their habitat (iii) (IUCN SSC Amphibian Specialist Group, 2016, 2020). Anilany helenae was assessed in 2016 and would benefit froman update to its assessment.Our findings do not contra- dict the current assessment but provide a baseline fromwhich to assess any potential future changes in population size (IUCN Red List criterion A) or continuing declines (IUCN Red List criteria C). Despite Madagascar currently having 370 described frog species (AmphibiaWeb, 2021), population and/or abundance baselines are only available for a few charismatic species (e.g. Mantella spp.). Research is needed to increase this knowledge as these are keymetrics for asses- sing the impacts of threats as well as conservation actions, especially for range-restricted species. Highly threatened frogs with small population sizes could be close to extinction, highlighting the need to preserve remaining forest fragments if we are to conserve the high number of range-restricted species that have so far survived deforestation in Madagascar.
Acknowledgements Wethank the Malagasy authorities for permit- ting this research and the Director of Ambohitantely Special Reserve, Hery Lala Ravelomanantsoa, for facilitating our work; Tovo Raditra for being our forest guide and the other Madagascar National Parks staff at Ambohitantely Special Reserve for providing support; Steve Buckland for advice on developing this project; Serge Ndriantsoa and Tsanta Rakotonanahary for logistical support in organizing fieldwork and securing permissions; and the staff at Durrell Madagascar’s head office in Tana for logistical support, especially our drivers Bruno and Franckly. Funding was provided through a Mohammed bin Zayed Conservation Fund grant to Durrell Wildlife Conservation Trust.
Author contributions Study design: JD, JHR; fieldwork: JHR, RNR, ER; data analysis: IMB, with input from MAH; writing: IMB, with equal contributions from all other authors.
Conflicts of interest None.
Ethical standards This research abided by Oryx guidelines on eth- ical standards. Surveys were undertaken under a research permit issued by the Ministry of Environment, Ecology and Forests (now Ministry of Environment and Sustainable Development) and with permission from Madagascar National Parks (permit number 259/19/MEEF/SG/ DGF/DSAP/SCB).
References
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Oryx, 2022, 56(6), 897–903 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321001034
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