What Is Driving Declines of Montane Endemic Amphibians? New Insights from Mount Bamboutos, Cameroon
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What is driving declines of montane endemic amphibians? New insights from Mount Bamboutos, Cameroon A. M. TCHASSEM F., T. M. DOHERTY-B ONE,M.M.KAMENI N. W. P. TAPONDJOU N.,J.L.TAMESSE and L . N . G ONWOUO Abstract Amphibians on African mountains are threatened Preserving a network of connected forest patches is there- by habitat loss and fragmentation, pollution, disease and fore critical to save the endemic amphibians of Mount climate change. In particular, there have been recent reports Bamboutos. of declines of montane endemic frogs in Cameroon. Mount Keywords Africa, amphibians, anurans, Cameroon, caeci- Bamboutos, although home to numerous species of endemic lians, endemic species, forest degradation, mountains amphibians, has no official protection and its amphibian populations have so far not been studied quantitatively. Supplementary material for this article is available at We surveyed frog assemblages on this mountain along a https://doi.org/./S gradient of forest modification over a -year period. Through visual encounter surveys stratified across forest and farm- land, we found that threatened montane amphibian species Introduction are closely associated with forested areas, particularly the Critically Endangered Leptodactylodon axillaris and mphibians are threatened globally, with over one-third Endangered Leptodactylodon perreti, Astylosternus ranoides Aof all known species at risk of extinction and half show- and Cardioglossa oreas. Using the updated inventory of ing population declines (Stuart et al., ; IUCN, ). amphibians, which includes species with broader ranges Threats include habitat alteration, loss and fragmenta- across Africa, we found % of amphibian species on tion, pollution, overexploitation, disease, invasive species, Mount Bamboutos to be threatened. We did not record climate change and combinations of these factors (Beebee several species present in historical records, which suggests & Griffiths, ). Habitat loss, degradation and fragmen- they may have disappeared from this mountain, includ- tation, such as through conversion to and intensification ing Cardioglossa pulchra, Phrynobatrachus steindachneri, of agriculture (Stuart et al., ), can leave amphibians Phrynobatrachus werneri, Sclerophrys villiersi, Werneria vulnerable to predation and desiccation and thus are im- bambutensis and Wolterstorffina mirei. The pattern of portant drivers of amphibian declines (Cushman, ). change detected in the amphibian community is consistent Conversion to agriculture is also often accompanied by use with declines on other mountains in the country, with a of agrochemicals and other pollutants that have the potential loss of Phrynobatrachus, Werneria and Cardioglossa spp., to negatively affect amphibians (Mann et al., ). but persistence of Astylosternus, Arthroleptis and Leptodact- Responses of African amphibians to habitat change y-lodon. The observed relationships of land-use patterns are poorly understood because of a paucity of studies and amphibian diversity suggest that ongoing land-use across the continent, especially in forested areas (Lawson & changes could extirpate the remaining montane endem- Klemens, ; Gardner et al., a;Brito,). However, ic frog species, particularly L. axillaris and L. perreti. some studies have been carried out across the continent, showing that amphibian diversity and abundance differ between primary forest, selectively logged forests and A. M. TCHASSEM F.* (Corresponding author), M. M. KAMENI N.* and L. N. forestry plantations in Côte d’Ivoire, Madagascar and Ghana GONWOUO* Laboratory of Zoology, Faculty of Sciences, University of Yaoundé I, P.O. Box 812, Yaoundé, Cameroon (Ernst et al., ; Hillers et al., ; Ofori-Boateng et al., E-mail [email protected] ; Riemann et al., ), and between natural wooded T. M. DOHERTY-BONE Conservation Research & Action for Amphibians of savannah and areas converted for agriculture in East Cameroon, Royal Zoological Society of Scotland, Edinburgh, UK Africa (Gardner et al., b). Some African amphibian W. P. TAPONDJOU N.* Department of Ecology and Evolutionary Biology, species are threatened because their sole habitat is subject to University of Kansas, Lawrence, USA development, such as Nimbaphrynoides occidentalis, which J. L. TAMESSE Department of Biological Science, Higher Teacher Training College, Yaoundé, Cameroon is under threat from mining activities (Sandberger-Loua et al., ). The impact of agrochemicals and other pollu- *Also at: Cameron Herpetology—Conservation Biology Foundation, Yaoundé, Cameroon tants, another major threat besides habitat loss, has been Received June . Revision requested August . rarely studied in Africa (Schiesari et al., ), with some Accepted November . First published online December . exceptions in Nigeria (Akani et al., ). This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, Downloadeddistribution, from https://www.cambridge.org/core and reproduction in any medium,. IP address: provided 170.106.35.234 the original work, on is 01 properly Oct 2021 cited. at 20:24:09, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/termsOryx, 2021, 55(1), 23–33 © 2019. https://doi.org/10.1017/S0030605318001448 Fauna & Flora International doi:10.1017/S0030605318001448 24 A. M. Tchassem F. et al. A significant number of African amphibians endemic and Oku (Gountié Dedzo et al., ). The climate of to individual mountains or mountain ranges are threat- Mount Bamboutos is characterized by dry (November– ened with extinction because of their small range sizes March) and wet (April–October) seasons. Mean annual (Poynton et al., ; Largen & Spawls, ). For example, rainfall is , mm and mean temperature is . °C at an % of Cameroonian amphibians categorized as Vulner- altitude of , m (Kengni et al., ). The natural vege- able, Endangered or Critically Endangered on the IUCN tation is montane forest and grassland, much of which has Red List are restricted to highland areas (IUCN, ). been replaced by crop fields, Eucalyptus plantations or pas- Threats to Afromontane endemic amphibians have rarely ture. Human communities living on the mountain include been quantified, although such studies are required urgently Fulani (sometimes referred to as Mbororo) and Mbouda as these regions are undergoing both rapid development and peoples. climate change (Beniston et al., ; Burgess et al., ). In addition to the threats posed by habitat loss and pollution, less understood factors such as pathogens are correlated Methods with the recently reported declines of amphibians in Cameroonian mountain ranges (Hirschfeld et al., ). Field surveys Research into the status of and threats to African montane amphibians is therefore urgently needed. To obtain an updated assessment of the amphibian species The amphibian fauna of Cameroon is relatively well- composition, status and habitat requirements on Mount studied (Perret, ; Amiet, ), and species have Bamboutos, we conducted field surveys every months dur- been assessed as threatened with extinction (.%; IUCN, ing March –May , with a total of surveys across ). Many of these occur in the country’s highlands, and all seasons. Surveys were stratified between forest, grassland the majority are montane endemics (Gartshore, ; Bergl and cultivated areas. We designated six discrete plots per et al., ). Detailed inventories have been compiled and land-use type, with a minimum distance of m between updated for several Cameroonian mountains in the past them, which we revisited during each survey period. We decades (Amiet, , ; Herrmann et al., , ; chose sample sites at an altitude of ,–, m, to Doherty-Bone & Gvoždík, ), but not for the more focus on land-use effects and minimize variation caused severely deforested mountains in the Bamenda High- by altitude. Because the landscape on Mount Bamboutos lands, particularly Mount Bamboutos. This mountain is fragmented, we could not locate plots of a homogenous hosts several threatened amphibian species endemic to the land-use type that were large enough to allow for a m Cameroon Volcanic Line, most notably the Critically buffer from the plot boundary to eliminate possible edge Endangered egg frog Leptodactylodon axillaris. The species effects (sensu Gardner et al., a). We thus interpreted is possibly endemic to this particular mountain (Amiet, survey data with caution, notably treating single occurrences ); although specimens suspected to be L. axillaris have of a species as potential vagrants (Barlow et al., ). At been found on nearby Mount Oku, their identity has yet each survey we recorded number of surveyors, search to be confirmed (Doherty-Bone & Gvoždík, ). Other time, elevation, species and number of individuals of each rare species recorded from this mountain include the species observed. Endangered Werneria bambutensis and Wolterstorffina We conducted day and night-time surveys in the desig- mirei (Perret, ; Gartshore, ). Despite harbouring nated sample sites using visual and acoustic encounter amphibian species of conservation concern, Mount Bam- surveys. This involved searching of microhabitats, such as boutos is not officially protected (Bergl et al., ). The lifting rocks and logs, peeling bark from trees, moving objectives of our study were to () update the amphibian in- fallen debris and inspecting tree stems during the day ventory of this mountain, () assess the trend of remaining (.–.)