Variation of small mammal richness with land use: A case study from Digya NP, West Africa

Background/Question/Methods

West Africa is experiencing rapid environmental change due to growth of economies through exploitation of natural resources, increasing habitat degradation, and human expansion.  Protected areas (or parks) are presumed to be refuges that shield wildlife from these growing anthropogenic pressures, thereby maintaining species diversity and ecological function within park boundaries.  To determine whether species richness, composition, or community structure differed between sites located inside and outside a park, we conducted a survey of small mammals in and around Digya National Park, Ghana.  Digya NP is the second largest protected area in Ghana (3,743 km²), and is located in a transitional zone between forest and savanna, amidst a matrix of variable land use that includes agriculture, charcoal production, and timber extraction.

Five paired grids (4,200 m²per grid) were established for four trap-nights each.  Each pair consisted of one trap grid inside Digya NP and one grid > 300 m outside the park boundary.  Each grid consisted of 49 Sherman traps, arranged in 7 x 7 configuration, and 9 Tomahawk traps distributed within the grid.  We collected morphometric measurements and a tissue sample from each captured individual for species identification, which was later confirmed by sequencing their mitochondrial cytochrome b genes. 

Results/Conclusions

We captured 62 individuals across 12 species within 1,905 trap-nights.  A comparable number of species were captured inside and outside Digya NP; 8 species were captured inside the park (n = 29), and 8 species were captured outside the park (n = 33).  Although species richness was similar, the composition of small mammals inside and outside Digya NP differed.  For example, Praomys daltoni, an omnivorous savanna-dwelling mouse, was the most common species inside the park (48.3% of inside captures, n = 14).  In contrast, the most common species outside the park was Mastomys erythroleucus (36.6% of outside captures, n = 12), a commensal species in association with human habitation.

Our results inform natural history for small mammals in a data-deficient West African region.  There is a critical need to identify small mammal species in Ghana not only to produce accurate inventories, but also because many questions relevant to disease transmission, human livelihood, and conservation biology depend on our knowledge of these species and their distributions.