First population estimates of two Critically Endangered frogs from an isolated forest plateau in Madagascar
I ZABELA M. BARAT A ,J AR Y H. RAZAFINDRAI BE,ROJO NAD R I AN IN A RAV E L O J A O N A E TIE NNE RAL O VAR ISO A,KAT H E R I N E E. MULLIN MICHAEL A. HUDSON and J EFF DAWS O N
Abstract In the largely deforested areas of Madagascar, small forest fragments remain as last refuges for amphibian diversity. Isolated populations of the Critically Endangered Anodonthyla vallani and Anilany helenae persist in the fragmented forest of Ambohitantely but little information is available to inform their management and any conser- vation interventions. We generated estimates of population size and occupancy for both species in the largest fragment of Ambohitantely Special Reserve using acoustic survey data collected from 84 sites along 12 transects in December 2018. We used a single-season occupancy model to estimate de- tection and occupancy and a Royal–Nichols model to esti- mate abundance and population size. Anilany helenae and A. vallani had high occupancy rates (80 and 93%, respec- tively) whereas their detection rates differed (34 and 55%, respectively). Abundance and occupancy were best ex- plained by vegetation structure whereas detection was in- fluenced by time of survey and rainfall. For our sampled sites the estimated population sizes of males were 855 for A. vallani, with an estimated density of 52 individuals/ha, and 388 for A. helenae, with an estimated population density of 23 individuals/ha. Given their relatively low densities, small population sizes and restricted ranges, any further habitat loss could have drastic consequences for these pop- ulations. Our results provide guidance for future species- focused studies, and can inform conservation management at the local scale. Our work will help to improve species monitoring in Madagascar and elsewhere, especially for range-restricted non-charismatic amphibians.
Keywords Acoustic monitoring, amphibian conservation, Anilany helenae, Anodonthyla vallani, hotspot, population management, small population size
Supplementary material for this article is available at
doi.org/10.1017/S0030605321001034
Introduction
their high levels of species richness and increasing threats (Myers et al., 2000). The fauna and flora of Madagascar have a unique evolutionary history as a result of the separa- tion of Madagascar from Africa and India 165 and 88 mil- lion years ago, respectively (Ali & Aitchison, 2008). Multiple processes have shaped the current endemism rates of many taxa, resulting in a large number of restricted-range species (Goodman & Benstead, 2005; Pearson & Raxworthy, 2009). Approximately 9% of species in Madagascar have been driven to extinction by deforestation between 1950 and 2000 (Allnutt et al., 2008). Estimates show that 44% of natural forest cover of Madagascar has been lost over 6 decades (1953–2014) and c. half of the remaining forest is within 100 m of the forest edge (Vieilledent et al., 2018). As deforestation accelerates inmany areas ofMadagascar
T IZABELA M. BARATA (Corresponding author,
orcid.org/0000-0002-8955-2607,
izabela.barata@
durrell.org), MICHAEL A. HUDSON*(
orcid.org/0000-0002- 7640-1885) and JEFF DAWSON (
orcid.org/0000-0002-1563-9849) Durrell
Wildlife Conservation Trust, Les Augrès Manor, Trinity, Jersey, JE3 5BP, Channel Islands
JARY H. RAZAFINDRAIBE,ROJO NADRIANINA RAVELOJAONA and ETIENNE RALOVARISOA University of Antananarivo, Antananarivo, Madagascar
KATHERINE E. MULLIN (
orcid.org/0000-0002-7816-3083) Cardiff School of Biosciences, Cardiff University, Cardiff, UK
*Also at: Institute of Zoology, Zoological Society of London, Regent’s Park, London, UK
Received 18 February 2021. Revision requested 27 May 2021. Accepted 27 July 2021. First published online 29 September 2022.
(Allnutt et al., 2008; Vieilledent et al., 2018), small fragments remain as last refuges for biodiversity (Andreone et al., 2008a). Comprising .40 fragments of multiple sizes, Ambohitantely Special Reserve contains some of the last re- maining forest in the central plateau of Madagascar and is considered the last refuge for multiple range-restricted en- demic frogs. Despite high levels of amphibian richness and endemicity (Goodman & Benstead, 2005; Andreone et al., 2007), no extinctions ofMalagasy amphibians have been de- tected (Andreone et al., 2008a). However, amphibian diver- sity is probably underestimated (Vieites et al., 2009)and species losses could occur before species are discovered. Species occurring in small fragments are under heavy an- thropogenic pressure (Vallan, 2000b; Lehtinen & Ramana- manjato, 2006) and the mid- to long-term stability of these amphibian communities is uncertain (Andreone et al., 2007). Additionally, little information is available on the biology and
This is an Open Access article, distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike licence (
http://creativecommons.org/licenses/by-nc-sa/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the same Creative Commons licence is included and the original work is properly cited. The written permission of Cambridge University Press must be obtained for commercial re-use. 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
he tropical forests of Madagascar are one of the highest- priority areas for biodiversity conservation because of
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