Dramatic Declines of Montane Frogs in a Central African Biodiversity Hotspot

<div><p>Amphibian populations are vanishing worldwide. Declines and extinctions of many populations have been attributed to chytridiomycosis, a disease induced by the pathogenic fungus <i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>). In Africa, however, changes in amphibian assemblages were typically attributed to habitat change. We conducted a retrospective study utilizing field surveys from 2004–2012 of the anuran faunas on two mountains in western Cameroon, a hotspot of African amphibian diversity. The number of species detected was negatively influenced by year, habitat degradation, and elevation, and we detected a decline of certain species. Because another study in this region revealed an emergence of <i>Bd</i> in 2008, we screened additional recent field-collected samples and also pre-decline preserved museum specimens for the presence of <i>Bd</i> supporting emergence before 2008. When comparing the years before and after <i>Bd</i> detection, we found significantly diminished frog species richness and abundance on both mountains after <i>Bd</i> emergence. Our analyses suggest that this may be the first disease-driven community-level decline in anuran biodiversity in Central Africa. The disappearance of several species known to tolerate habitat degradation, and a trend of stronger declines at higher elevations, are consistent with <i>Bd</i>-induced declines in other regions. Not all species decreased; populations of some species remained constant, and others increased after the emergence of <i>Bd</i>. This variation might be explained by species-specific differences in infection probability. Increased habitat protection and <i>Bd</i>-mitigation strategies are needed for sustaining diverse amphibian communities such as those on Mt. Manengouba, which contains nearly half of Cameroon’s frog diversity.</p></div

Frequency of detection of selected frog genera and species during all study years on Mt. Manengouba.

<p>Shown is the proportion of search events in which a genus (A-C) or a species (D-G) was present in a given year. The latter two bars show search events in which a genus or species was detected in all search events before and after the first recorded detection of <i>Bd</i> in the region (compare <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155129#pone.0155129.s005" target="_blank">S3 Table</a>). Bars showing events before the detection of <i>Bd</i> are colored white and those showing events after first detection of <i>Bd</i> are colored black. The number of search events was as follows: 2004 = 5; 2005 = 25; 2006 = 66; 2007 = 31; 2008 = 70; 2010 = 71; 2011 = 63; 2–12 = 35. Search events prior to detection of <i>Bd</i> = 366 and after detection of <i>Bd</i> = 98. For additional genus and species information, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155129#pone.0155129.s002" target="_blank">S2 Fig</a>.</p

Effects of habitat and study year on species sampling success.

<p>Effects of habitat and study year on species sampling success.</p

Map of the study region.

<p>Locations of the study sites, Mt. Manengouba and Mt. Oku, are marked with black triangles, additional localities surveyed for <i>Bd</i> are represented by black dots; map based on SRTM elevation model (light = low, dark = high elevations) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155129#pone.0155129.ref027" target="_blank">27</a>].</p

Differences in detected anuran species between search events conducted before and after <i>Bd</i>-positive records in these study regions.

<p>(A) Number of species per sampling event at Mt. Manengouba. (B) Sampling success (number of species recorded per person-hour for each search event at Mt. Manengouba. (C) Number of species per sampling event at Mt. Oku. (D) Sampling success at Mt. Oku. Boxplots depicting events before the detection of <i>Bd</i> in the region are shown as colored white, and those representing events after detection of <i>Bd</i> are shown as colored black. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0155129#pone.0155129.t002" target="_blank">Table 2</a> for statistical results and sample sizes</p

bi4africa dataset - open source

The bii4africa dataset is presented in a multi-spreadsheet .ods file. The raw data spreadsheet (‘Scores_Raw’) includes 31,313 individual expert estimates of the impact of a sub-Saharan African land use on a species response group of terrestrial vertebrates or vascular plants. Estimates are reported as intactness scores - the remaining proportion of an ‘intact’ reference (pre-industrial or contemporary wilderness area) population of a species response group in a land use, on a scale from 0 (no individuals remain) through 0.5 (half the individuals remain), to 1 (same as the reference population) and, in limited cases, to 2 (two or more times the reference population). For species that thrive in human-modified landscapes, scores could be greater than 1 but not exceeding 2 to avoid extremely large scores biasing aggregation exercises. Expert comments are included alongside respective estimates

bii4africa dataset

The bii4africa dataset is presented in a multi-spreadsheet .xlsx file. The raw data spreadsheet (‘Scores_Raw’) includes 31,313 individual expert estimates of the impact of a sub-Saharan African land use on a species response group of terrestrial vertebrates or vascular plants. Estimates are reported as intactness scores - the remaining proportion of an ‘intact’ reference (pre-industrial or contemporary wilderness area) population of a species response group in a land use, on a scale from 0 (no individuals remain) through 0.5 (half the individuals remain), to 1 (same as the reference population) and, in limited cases, to 2 (two or more times the reference population). For species that thrive in human-modified landscapes, scores could be greater than 1 but not exceeding 2 to avoid extremely large scores biasing aggregation exercises. Expert comments are included alongside respective estimates