Ecology of rodent species in the Ukaguru mountains within the Eastern ARC mountains, Tanzania
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Date
2021
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Publisher
Sokoine University of Agriculture
Abstract
Rodents, one of the diverse groups of mammals, are important contributors to biodiversity
and good ecological indicators of habitat disturbance and their assessment is an important
component of the study of forest ecosystems. Forested mountains in East Africa, which
are home to diverse flora and fauna with sizeable endemics, include the Eastern Arc
mountains (EAM) region and collectively with its adjacent lowland coastal forests
recognized as one of the top 25 biodiversity “hotspots” worldwide. As conservation of
any landscape requires knowledge of the available resources in the area, it is critical to
study the rodents of the EAM due to the high degree of endemism in these mountain
ranges and the rapid degradation of the remaining montane forests. However, research on
rodents in sub-Saharan Africa has focused on pest species, and data on non-pest species is
rare, however, needed for the implementation of effective conservation measures. The
Ukaguru Mountains within the EAM are of particular interests because the forests of this
range have received little/no attention on rodents and are facing alarming rate of
anthropogenic disturbances such as grazing, firewood collection, tree/pole cutting and
clearance of forest for agriculture which may impact on the diversity, population structure
and demography of rodents. This study, therefore, aimed at understanding the ecology of
the rodents, population and demographic parameters of the dominant species in disturbed
and undisturbed habitats of the Ukaguru Mountains.
There are two seasons in the landscape: wet and dry seasons; the wet season is October to
May while the dry season is between June and September. Three methods were
employed. In the first, the habitat association of the diversity and abundance of small
mammals in the Ukaguru Mountains was assessed, by estimating the vegetation
parameters using a Modified-Whittaker method and live-trapping of small mammals by
Capture-Mark-Recapture (CMR) technique for three consecutive nights per month in
farmland, disturbed and intact forests from June 2018 to February 2020. Two 70 m x 70
m grids, 600 m apart, were set in each habitat; each grid consisted of seven parallel lines,
10 m apart, and seven trapping stations per line, also 10 m apart (a total of 49 trapping
stations per grid). The two grids in the disturbed forest were in proximity (50 m) to
human settlements and farmlands and were characterized by cattle grazing, illegal
hunting, tree cutting and wood collection. The two grids in the intact forests were devoid
of human activities and were farther than 3 km away from disturbed forests. With the
second method, the data derived from the CMR trapping in the disturbed and intact
forests, was used to investigate the impact of anthropogenic forest disturbance on the
abundance, breeding patterns and sex ratios and two demographic parameters: survival
and maturation rate of the dominant rodent species i.e. Praomys delectorum. With the
third method, removal trapping technique was used in the survey for rodents trapped for
13 months to determine the dietary composition of rodents in the landscape. Fifty snap
(kill) traps were set separately in farm/fallow lands and forest habitats and trapping of
rodents was conducted for three consecutive nights per month. Micro-histological
analysis of the stomach contents of rodents collected from various habitats was carried
out to determine the food categories. Small mammals were identified to species levels
using relevant keys and confirmed by sequencing the mitochondrial cytochrome b gene.
A total of 1196 individuals of small mammals comprising 13 species were captured from
the CMR trapping in farmland, disturbed and intact forests; in the order of relative
abundance, these are: P. delectorum (52.26%), Mus triton (21.07%), Mastomys natalensis
(17.14%), Mus minutoides (2.93%), Lophuromys kilonzoi (2.26%), Crocidura hirta
(1.59%), Beamys hindei (1.59%), Grammomys surdaster (0.59%), Graphiurus cf. raptor
(0.17%), Lemniscomys rosalia (0.17%), Hylomyscus arcimontensis (0.08%), Pelomys
fallax (0.08%) and Xerus sp. (0.08%). Mastomys natalensis, Mus triton and Praomys
delectorum accounted for 90% of total captures. Mus triton and Mastomys natalensis
were the most abundant in farmland with 46.75% and 42.77% of total captures
respectively while P. delectorum accounted for 90% and 80% total captures in disturbed
and intact forests respectively but the mean abundances in both habitats were not
significantly different (p = 0.72). Species diversity and evenness in intact forest were
much higher compared to disturbed forest. Principal component analysis (PCA) explained
87.70% of the variance with two factors. PCA 1 (67.47%) consists majorly of canopy
cover, ground cover, shrubs and litter depth, with P. delectorum, B. hindei and L. kilonzoi
loading positively. In the same component, herbs, Mastomys natalensis and Mus triton
loaded negatively. Distance to human settlement contributed greatly to PCA 2 (20.23%)
with G. cf. raptor, L. kilonzoi and C. hirta having greater than 0.5% loading. Mastomys
natalensis and Mus triton associated with the herbaceous vegetation while P. delectorum
correlated with litter depth and trees. The results suggest that vegetation and habitat
disturbances are factors responsible for the observed diversity of small mammals in the
Ukaguru Mountains.
Analysis on sex ratios, population structure and breeding parameters were carried out on
the dominant species i.e. P. delectorum in the two forest types. The population density of
P. delectorum varied temporally with peaks attained in the wet seasons in both disturbed
and intact forests. Population structure showed few juveniles in most months and sub-
adults accounted for the population increases in the wet seasons in all habitats, high
number of adults from the late wet season to the end of the dry season in disturbed forest
but a greater number of adults in the wet season in intact forest. The sex ratios showed
highly significant number of males in intact forest compared to disturbed forest
(χ 2 = 10.71, df = 1, p = 0.001). The proportion of reproductively active individuals variedv
temporally in both disturbed and intact forests while habitat disturbance showed no effect
on the breeding activity of this species. Overall, these results suggest that rainfall and
habitat disturbances as factors responsible for the varying sex ratios and population
structure of P. delectorum in the landscape.
Furthermore, the effects of habitat disturbance on abundance as well as two demographic
traits: survival and maturation of P. delectorum were investigated. Abundance was
estimated using the Minimal Number of animals Alive and subjected to a generalized
linear mixed model. Survival and maturation probabilities were estimated using multi-
event capture-recapture models using the software E-SURGE. There was no variation in
abundance or maturation between intact and disturbed forests, but habitat type did affect
survival. However, this effect was sex-dependent since female survival was higher in
disturbed forests while male survival remained similar across the two forest types
potentially due to differences in predation pressure or food availability between the two
habitats. These results highlight the need for continuous demographic monitoring of
P. delectorum in the EAM given that the increasing human population surrounding the
landscape is leading to higher deforestation rates, and expansion of the pine plantation in
the forest reserve.
In the food analysis, Mastomys natalensis, Lemniscomys rosalia and Mus triton,
seed/grain showed greater importance (> 35, > 55 and 60% respectively) whereas for
Lophuromys kilonzoi (farm/fallow land), plant materials were more important (> 55%)
than other categories. Seed/grains were more important (> 20%) in the diet
P. delectorum, while plant materials were more important (> 45 %) in the diet of forest-
dwelling L. kilonzoi. Food diversity for rodents in farm/fallow land was relatively low
compared to forest dwelling rodents. Niche overlap between L. kilonzoi and
P. delectorum was found to be relatively high. Given the interspersion of the forests with
farmlands and their proximity, this may favour the establishment of farm generalists in
the forests.
The findings of the present study are of concern in conservation of this landscape and
necessitate urgent conservation actions in this EAM block to limit the effects of
anthropogenic activities in the landscape. As the human population surrounding the
Ukaguru Mountains and their encroaching activities increase, continuous exploitation of
the forests of this landscape should be discouraged as this was shown to modify the
habitats of the small mammals, reducing their diversity and evenness and affecting other
demographic parameters.
Description
Dissertation
Keywords
Rodent, Ecology of rodent species, Eastern ARC mountains, Tanzania