This species is known from mid- to high-elevation sites (200–1,200 m Asl) in southwestern Cameroon, southeastern Nigeria and the island of Bioko, Equatorial Guinea. Once regarded as the rarest Bufonid in Africa (Grandison 1981), recent discoveries have greatly expanded the known distribution and confirmed persistence in historical localities. Its EOO is 12,743 km2. Didynamipus sjostedti has now been recorded from nine localities: 1) the Oban Hills Division of the Cross River National Park, Nigeria (Onadeko et al. 2010); 2) Pico de Basile National Park, Bioko, Equatorial Guinea (Boulenger 1905, “1906”; Mertens 1965, Weinberg 2008); and multiple localities within Cameroon: 3) Mt. Cameroon (Grandison 1981, Gartshore 1984), 4) the Kendonge and 5) Mokoko Forest Reserves (Grandison 1981), near the towns of 6) Baro and 7) Nguti (east of Korup National Park, Lawson 1993; Lawson unpublished, unpublished USNM specimens), 8) recently from the area between Korup and the Rumpi Hills Protected Area (Mukango area, Gonwouo et al. 2013), and 9) the area northwest of the Bakossi Mountains Wildlife Preserve (Talangaye area, Gonwouo et al. 2013).
The nine known localities can be grouped into approximately five threat-defined locations: 1) Bioko; in Cameroon 2) Mt. Cameroon and Kendonge Forest Reserve, 3) Mokoko Forest Reserve, 4) Baro road, Nguti, Mukango, Talangaye; in Nigeria 5) the Oban Hills.
An assessment of all available, georeferenced anuran collections from southwestern Cameroon and surrounding countries (n=1,656 from Cameroon alone) reveals a large gap in sampling effort within the predicted EOO. Notably the large Rumpi Hills and Banyang Mbo Protected Areas and the Bakossi Mountains Wildlife Reserve, areas with a documented dearth of herptelogical sampling (Gartshore 1984) and close proximity to recently documented subpopulations, have little evidence of herpetological effort. Recent herpetological exploration of a few highland sites at this southwestern edge of the Cameroon Volcanic Line illustrate how poorly known the fauna of this region is (Lawson 2001) with the discovery of numerous new species (Blackburn 2008, Blackburn et al. 2009, 2010). As further testament to the lack of knowledge of this area, these discoveries include not only the expected highland endemics restricted to a very small area (e.g. Leptodactylodon wildi Amiet and Dowsett-Lemaire 2000), but also widespread species categorized as Least Concern (Arthroleptis palava, Blackburn et al. 2010). Furthermore, the recent discovery of Didynamipus in the mid- to high-elevation regions of southeastern Nigeria associated with this Cameroon Volcanic Line, which is particularly poorly documented (Blackburn et al. 2010), and the large tracts of protected land in this area suggest the possibility of a much larger EOO in this region (e.g. Banyang Mbo, Bakossi, Rumpi Hills, Korup). These data support the findings of Amiet (1983) that collections of amphibians from Cameroon are sparse, only 16% of 20x20 km quadrants in the country have any records, and that additional records of D. sjostedti can be expected within and beyond the EOO as documented herein. (B. Noonan pers. comm. June 2013).
Habitat and Ecology
The species lives on forest edges and in clearings in moist forest from the lowlands to the submontane in the Cameroon Volcanic Belt. This species is frequently found in aggregations of as many as 40 individuals of mixed gender and life stage. They have been found in the leaf litter and frequently perched atop low-lying vegetation. In many instances individuals have been found in edge or disturbed areas, including secondary forest and farmland. Gartshore (1984) reported this preference for secondary or disturbed habitat and noted that this species may be less susceptible to anthropogenic habitat degradation, but also speculated that the species may not tolerate land use practices of the abundant palm oil plantations in the area. However, while not reporting D. sjostedti from these plantations specifically, Lawson (1993) did note that otherwise rare forest-dwelling amphibians achieved “uncharacteristically high densities in this habitat”, indicating that these land-use practices do not preclude anuran colonization.
Gartshore (1984) discovered individuals in the vicinity of gelatinous masses but was unable to verify these were anuran in origin. Gonwouo recently discovered an individual in the leaf litter next to a small clutch of 10 eggs, supporting hypotheses of terrestrial egg deposition and direct development (Gartshore 1984, Grandison 1981, Lawson 1993, Gonwouo et al. 2013).
This species has been observed in significant numbers as recently as February 2012 (Gonwouo et al. 2013) and subpopulations thought to have been extirpated (i.e. Bioko) have since been rediscovered (Weinberg 2008) and recorded again in September 2012 surveys in Pico Basile (Bioko) (P. McLaughlin pers. comm. November 2016). Recent accounts report the status of subpopulations to be “large and healthy” and “observed in abundance” (Weinberg 2008), “exceedingly abundant” (Lawson and Klemens 2001) or report the observation and collection of large numbers of individuals (Gartshore 1984, ~200 observations; Gonwouo et al. 2013, >45 observations). However, there is evidence of continuing decline in the area, extent and/or quality of habitat, primarily due to conversion of habitat for agricultural use, and the population overall is suspected to be decreasing.
The main threat to the species is habitat loss primarily due to agricultural expansion, in particular local and industrial palm plantations (Gonwouo pers. comm. May 2012), timber extraction, and human settlement. However, it is noted that this species seems to prefer disturbed edges of forest and may be less susceptible to disturbance than most anurans (Gartshore 1984, Lawson 1993).
This species is known from Cross River National Park (Nigeria), Pico de Basile National Park on the north end of Bioko Island (Equatorial Guinea), the Cameroonian Makoko and Kendonge Forest Reserves, and Mt. Cameroon National Park. Additionally this species has been discovered near the borders of Korup National Park, Rumpi Hills and Banyang Mbo Protected Areas and the Bakossi Mountains Wildlife Preserve and is likely to occur within those protected areas.
Despite its' tolerance to some habitat disturbance and occurrence in protected areas, the management of these protected areas requires improvement and much of its habitat still requires protection.
More information is needed on this species' taxonomy, distribution, population status, natural history. Finally, since the species seems to occur in palm plantations with certain types of management, it would be beneficial to study which kind of management promotes the survival of the species in modified habitats.
Red List Status
Listed as Vulnerable because its extent of occurrence (EOO) is 12,743 km2, it occurs in less than 10 threat-defined locations, and there is evidence of continuing decline in the area, extent and/or quality of habitat primarily due to conversion of habitat for agricultural use.
This is a monotypic species, believed to be closely related to the African endemic genus Nectophrynoides. This hypothesis is supported by the findings of Frost et al. (2006). Though the conclusions of relationship among those taxa closely related to D. sjostedti have come into question (compare Frost et al. 2006 to Van Bocxalaer et al. 2009), the identity and distinctiveness of this species is clear and uncontroversial.
IUCN SSC Amphibian Specialist Group 2017. Didynamipus sjostedti. The IUCN Red List of Threatened Species 2017: e.T54811A16272990. http://dx.doi.org/10.2305/IUCN.UK.2017-2.RLTS.T54811A16272990.en .Downloaded on 15 December 2018