Dramatic Declines of Montane Frogs in a Central African Biodiversity Hotspot

Abstract

Amphibian populations are vanishing worldwide. Declines and extinctions of many populations have been attributed to chytridiomycosis, a disease induced by the pathogenic fungus Batrachochytrium dendrobatidis (Bd). 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 Bd in 2008, we screened additional recent field-collected samples and also pre-decline preserved museum specimens for the presence of Bd supporting emergence before 2008. When comparing the years before and after Bd detection, we found significantly diminished frog species richness and abundance on both mountains after Bd 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 Bd-induced declines in other regions. Not all species decreased; populations of some species remained constant, and others increased after the emergence of Bd. This variation might be explained by species-specific differences in infection probability. Increased habitat protection and Bd-mitigation strategies are needed for sustaining diverse amphibian communities such as those on Mt. Manengouba, which contains nearly half of Cameroon’s frog diversity.

Overview of chytrid emergence and impacts on amphibians

“…Bd is widespread in many of the highland regions [63], whereas tropical West African areas regions are reported to be clear of Bd [64]. Recent reports from Cameroon [65] found Bd present in several species, several of which had shown recent declines and they suggested Bd as a likely cause. One epidemic of chytridiomycosis has been reported from Africa, that of the Kihansi Gorge in Tanzania.…”

The Amphibians of Mount Oku, Cameroon: an updated species inventory and conservation review

“…It has also not been observed since 2010 despite monthly monitoring at Lake Oku and the Oku summit. It is also proposed that both Phrynobatrachus jimzimkusi Zimkus, Gvoždík & Gonwouo, 2013 and Phrynobatrachus steindachneri Nieden, 1910 be given a classification of Critically Endangered A2(a), A4(a), B1(b), B2(b) due to their limited range sizes and recent, substantial declines (Hirschfeld et al 2016). Phrynobatrachus jimzimkusi has been unobserved on Mt Oku since 2010, Phrynobatrachus steindachneri since 2009.…”

“…Phrynobatrachus jimzimkusi has been unobserved on Mt Oku since 2010, Phrynobatrachus steindachneri since 2009. Phrynobatrachus werneri , while observed in agricultural areas, has also become rare, from high sample success rate of several individuals in 2006 and 2009 to no individuals or rare occurrences of singletons at those same localities from 2010 onward (Hirschfeld et al 2016, TMD-B pers. obs.).…”

“…It is rarely found outside the forest and is likely a forest dependent species. It is one of the few montane endemic frog species to have not experienced a population crash as observed for other sympatric species on Mt Oku (Hirschfeld et al 2016). …”

“…Both species have been previously lumped under the name Phrynobatrachus steindachneri , which is currently listed as Vulnerable by the IUCN due to the threat from forest loss and degradation. As both species have sustained long term (since 2010) declines on Mt Oku (Hirschfeld et al 2016; TMD-B pers. ob.…”