Patterns of species richness and turnover in endemic amphibians of the Guineo-Congolian rainforest

Aim: The African Guineo-Congolian (GC) region is a global biodiversity
hotspot with high species endemism, bioclimatic heterogeneity, complex
landscape features, and multiple biogeographic barriers. Bioclimatic and
geographic variables influence global patterns of species richness and
endemism, but their relative importance varies across taxa and regions and
is poorly understood for many faunas. We characterized patterns of
richness and turnover in endemic amphibians of the GC biodiversity hotspot
and evaluated the relative roles of geographic distance and bioclimatic
variables in predicting turnover.  Location: West and
Central Africa.  Major taxa studied: Amphibians Methods:
We compiled species-occurrence records via field sampling, online
databases, and taxonomic literature. Our study used 1205 unique
georeferenced records of 222 amphibian species endemic to the GC region.
Patterns of species richness were mapped onto a grid with a spatial
resolution of 0.5° × 0.5°. We estimated weighted endemism and tested
whether endemism was higher than the expected species richness
(randomization test). We quantified species turnover using generalized
dissimilarity modelling to evaluate the processes underlying observed
patterns of species richness in GC endemic amphibians. We explored
bioregionalization using agglomerative hierarchical clustering based on
the unweighted pair group method with arithmetic averages. 
Results: We identified six areas within the lower GC region – forests in
Southern Nigeria, Cameroon, Equatorial Guinea, Gabon, Republic of Congo,
and Democratic Republic of Congo – as having high species richness of
endemic amphibians. The randomization test returned four major areas of
significant weighted endemism: Nigeria-Cameroon mountains, forest regions
of the Democratic Republic of Congo, Cote d’Ivoire, and Ghana. Our
analysis revealed five bioregions for amphibian endemism, four of which
were located within the lower Guineo-Congolian forest. Species turnover
was strongly related to the geographic distance between grid cells;
contributing bioclimatic variables included precipitation of the warmest
quarter, mean temperature of the wettest quarter, and mean diurnal
temperature range.   Main conclusions: Our results
indicate that geographic distance between grid cells is the primary
determinant of turnover in GC endemic amphibians, with secondary but
significant effects of rainfall- and temperature-related variables. Our
results identify key areas of endemic amphibian richness that could be
prioritized for conservation actions.