The influence of land use patterns on diversity and abundance of rodents in Gachoka division of Mbeere district, Kenya

Abstract

Abstract This study was conducted in Gachoka division of Mbeere district Kenya, between the months of September and December 2001. The aim of the study was to establish how patterns of land use influences the diversity, distribution and abundance of small mammals in various habitats types under varying human influence and assess which of the measured habitat parameters strongly influence diversity of rodents, information which is hitherto not well documented in Gachoka division of Mbeere district. The study also sought to determine how land use practice influences habitat conditions with a view of identifying possible indicator species for the site. Various habitat factors, such as plant species composition, percentage vegetation cover, plant density and diversity, burrows, and mounds, all of which influence diversity, distrib~tion and abundance of small mammals were determined in various land use types in the semi-arid region of Mbeere district. Data on rodent abundance was collected through rodent captures on square grids of 64 live traps, set out over an area of 70m ~7E)m in four land use types, namely cultivated, grazing, fallow and bushy sites. All rodents sampled were identified to species level. Data on vegetation parameters was obtained through a habitat survey conducted using transects. The number and composition of woody plant species, number of burrows and mounds were estimated in each transect. Grass species composition, percentage cover and soil depth were measured in 1m by 1m quadrants placed at 10 meter intervals along the transect line. The area sampled for habitat parameters corresponded with trapping points of small mammals. A total of 213 specimens comprising of five species of Murids were recorded. Three species, Lemniscomys barbarus (Linnaeus), Otomys thomasi (Thomas) and Acomys percivali (Dollman) were the most abundant with percentage abundance values of 35.6%, 35.2% and 16.4% of total captures. Burrows were found to occur with greater incidence near the edges of cultivated areas while in uncultivated (fallow and bushy grassland) sites burrows were situated under trees and shrubs alongside mounds. Mounds distribution was associated with distribution of woody plants. However, no relationship between mounds or burrows to particular plant species was observed although both tended to occur less frequently under trees than shrubs. Unlike burrows, vegetation cover was correlated with abundance of rodent species. Bushy grassland and fallow sites provided greater diversity of plant (H' = 1.20; 1.21) and small mammal species (H' = 0.5; 0.7) resp,ectively, compared to cultivated and grazed lands. Abundance of Lemniscomys barbarus and Acomys percivali was found to be

greatest in uncultivated (bushy and fallow) sites, while Otomys thomasi was dominant in cultivated and grazing sites. The fallow land, which is considered intermediate between cultivated and bushy sites (based on the measured habitat £.'lra~eters), had the highest diversity of trees/shrubs (H' =•1.21), grass (H' = 1.08) and small mammal species (H' = 0.7). This site hosted all of the five species of rodents in varying proportions. This study demonstrates that non-opportunistic small mammal species like Arvicanthis niloticus was restricted to natural bushy environment, and therefore requires persistence such habitats to survive. Bush clearing in this area therefore jeopardizes the future survival of the species. The rodent species composition in Mbeere was nevertheless found to be comparable to that of other semi-arid areas in East, Central and part of Southern Africa, 15° Nand S of equator.