Journal of Experimental Biology and Agricultural Sciences, November - 2013; Volume – 1(5)

Journal of Experimental Biology and Agricultural Sciences

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ISSN No. 2320 – 8694

ASPECTS OF THE ECOLOGY OF THE TULLBERG’S SOFT-FURRED MOUSE (PRAOMYS TULLBERGI: THOMAS 1894) IN MOUNT AFADJATO, GHANA

Benjamin Yeboah Ofori*, Daniel Korley Attuquayefio and Erasmus Henaku Owusu

Department of Biology and Conservation Science, University of Ghana, Legon, P.O. Box LG67, Legon, Accra, Ghana.

Received: September 01, 2013; Revision: October 16, 2013; Accepted: November 20, 2013 Available Online November 30, 2013.

KEYWORDS ABSTRACT Relative abundance The relative abundance, age-structure, sex-ratio, biomass and breeding activity of Praomys tullbergi Age structure (Tullberg’s soft-furred mouse) were studied over an eight-month period (June 2008 to January 2009) at Mount Afadjato Conservation Area in the Volta Region of Ghana. The methodology involved the use of Sex ratio live-trapping techniques using Sherman collapsible traps. There were 183 captures of 80 individual mice in 3,360 trap-nights, giving overall trapping success and relative abundance of 5.4% and 2.4%, Small respectively. Adults constituted about 93% of the total number of individuals captured, while the remaining 7% were all sub-adults. Majorities (59%) of the individuals recorded were males, and these Species complex were generally slightly heavier than their non-pregnant female counterparts. Breeding activity was evident throughout the study period, peaking during the wet season. All the captured female individuals showed evidence of breeding activity (perforate vaginas, enlarged nipples, pregnancy), whereas 84% of the males had scrotal testes. The highest number of individuals was recorded in August. The year-round breeding activity of P. tullbergi may, to a large extent, account for their dominance in most forests in Ghana.

* Corresponding author E-mail: [email protected] (Benjamin Yeboah Ofori)

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1 Introduction understanding of the factors contributing to their proliferation and mono-dominance. play critically important roles in forest ecosystems, and contribute to biological and functional diversity of many Effective forest management requires that potential effects of ecosystems (Nicolas et al., 2010). They influence the structure management practices on small mammals and the processes and composition of the environment through consumption and dependent upon them are considered (Pearson, 2000). distribution of foliage, seeds and fungal spores (Angelici & Knowledge of the ecology of P. tullbergi can inform Luiselli, 2005). They also serve as prey for carnivorous conservation measures aimed at increasing the diversity of mammals, birds and reptiles, particularly snakes, helping to small mammals inhabiting the West African sub-region maintain energy flow and material recycling. The composition through the promotion of coexistence of the species with other of communities in many vegetation types in Ghana is forest-specialists. however poorly known despite numerous attempts to bridge this knowledge gap (Decher & Bahian, 1999; Barriere et al., The present study investigated aspects of the ecology of P. 2009; Ofori et al., 2013). The main reason for this is the tullbergi at Mount Afadjato Conservation Area in Ghana. difficulty in correctly identifying rodents due to low levels of Recent studies (Ofori, 2009) at the site recorded two small morphological differentiation among species, particularly species, P. tullbergi and Crocidura olivieri, with the sibling ones (Nicolas et al., 2005). former comprising 98% of the total number of captured individuals. Mount Afadjato therefore provides a suitable Currently, the systematics and of many genera of environment for studying the ecology of P. tullbergi. The murid rodents are shrouded in controversy (Nicolas et al., objective of the present study was to determine the relative 2010). Recent technological and analytical advances in abundance, age structure, sex ratio, biomass, breeding activity molecular genetics present an invaluable opportunity to resolve and temporal distribution of P. tullbergi at Mount Afadjato. these discrepancies. Already, some studies have succeeded in separating and providing detailed descriptions of some closely- 2 Materials and Methods related and sibling species (Nicolas et al., 2008, Nicolas et al., 2010). 2.1 Study Area

Praomys tullbergi is an eight-species complex, notably P. Mount Afadjato (0o 15’- 0o 45’E; 6o 45’- 7o 15’N) (Fig. 1), at tullbergi, P. misonnei, P. morio, P. petteri, P. rostratus, P. about 900 m above sea level, is the highest mountain in Ghana hartwigi, P. obscures and P. coetzeei (recent addition from the (Owusu et al., 2006). It forms part of the Akuapim-Togo northwest Angola) (Van der Straeten, 2008). Praomys Ranges together with the Agumatsa range, and both are located tullbergi, P. misonnei, P. morio, and P. petteri occur in the in the Hohoe District of the Volta Region of Ghana. primary and secondary lowland forests of West, Central and East Africa (Nicolas et al., 2008; Nicolas et al., 2010), whereas Mount Afadjato and part of the Agumatsa range together P. rostratus, P. hartwigi, P. obscures are found in the constitute an area of about 12km2, are currently being managed mountain forests of West Cameroon (Missoup et al., 2012). collaboratively as a conservation area by the Gbledi and Praomys tullbergi and P. misonnei are believed to co-occur in Fodome-Ahor traditional authorities in Hohoe in the Volta eastern Guinea and Cote D’ ivoire (Nicolas et al., 2008), but Region of Ghana (Owusu et al., 2006). only the former has been reported in Ghana (Akpatou et al., 2007). In their study of the small mammal fauna of the Volta Region of Ghana (including the Agumatsa Range), Decher & Abedi-Lartey (2002) confirmed that all the Praomys species they captured were P. tullbergi despite apparent individual differences in size and pelage colour.

Recent studies in both primary and secondary forests in Ghana have reported disproportionately high numbers of P. tulbergi (Yeboah, 1998; Decher & Bahian, 1999; Barriere et al., 2009; Garshong & Attuquayefio, 2013). This mono-dominance of P. tullbergi could have conservation implications by largely impoverishing the diversity of the country’s forest-specialist small mammals. The loss of some species and over-abundance of others could have potent negative impacts on a wide range of ecological processes, because of the diverse ecological roles played by different small mammal species in the forest ecosystem (Chung & Corlett, 2006; Nicolas et al., 2010). There Figure 1 A Topographic Map of the Mount Afadjato- is therefore a pressing need for studies of the ecology of the Agumatsa Area species in as many forests as possible to enable a better

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Aspects of the Ecology of the Tullberg’s Soft-furred Mouse (Praomys tullbergi: Thomas 1894) in Mount Afadjato, Ghana. 400

The climate of the area is typically Dry Semi-deciduous forest, 2.4.2 Relative Abundance (Ar) with Moist Semi-deciduous Forest in a few specific areas. Rainfall is single-peak between April and October, with June, This was estimated as the total number of individuals captured September and October having a higher precipitation. Rainfall per 100 trap-nights. Thus, figures range from 1,594.8mm to 1,762.2mm (mean: 1,650mm). Prevailing winds blow north-south, and average relative humidity is 90%. Annual temperature ranges from 19oC and 29oC (Hawthorne & Abu-Juam, 1993). Vegetation follows a characteristic pattern of relief and exposure, with Dry Semi-deciduous forest occupying the western slopes, and the Where: steeper eastern side dominated by savanna and tree steppe Ar = relative abundance (Hall & Swaine, 1981; Hawthorne & Abu-Juam, 1993). A Ts = trap-success baseline survey of the area recorded over 450 plant species, Nc = total number of captures 350 butterfly species with significant degree of endemism, Ni = total number of individuals captured over 112 bird species, and 33 mammal species including bats, Tn = total number of trap-nights rodents and shrews (GWS, 2007). 2.4.3 Age 2.2 Selection of Study Sites The weight of individuals was used as an index of age. In order to obtain a representative sample of P. tullbergi at the Following Garshong & Attuquayefio (2013), individuals study area, we surveyed three different zones at the Mount weighing 30 g and more were considered adults, those Afadjato as follows: (i) Lowland Zone (LLZ), an area at the weighing between 20 g to 30 g sub-adults and those weighing foot of the mountain, (ii) Midslope Zone (MSZ), middle-level below 20 g juveniles. area between the foot and summit, and (iii) Submontane Zone (MSZ), an area just below the summit. 2.4.4 Biomass

2.3 Live-trapping of P. tullbergi The fresh biomass of each small mammal species was estimated as the mean weight (mass) of adult males and non In each zone, two permanent 100 m long transects were pregnant females to avoid biases due to overweight imposed by established to the left and right of Mount Afadjato, using a pregnancy. Total biomass was estimated as the product of the hiking trail as a reference point. Each transect was supplied mean weight and the number of adult individuals recorded. with 10 standard Sherman live-traps placed at about 10 m intervals along its length. Traps baited with a mixture corn 2.5 Statistical Analysis meal and peanut butter were set during the day and checked from 07:30 to 10:00 hours GMT the following morning. The test of variance (one-way ANOVA) was used to establish significant differences in mean weight of individuals. Traps were set for seven consecutive nights per month for eight consecutive months (June 2008 to January 2009). 3 Results Captured individuals were weighed (in grams), sexed (using anal-genital distance, which is shorter in females), aged 3.1 Trap Success and Relative Abundance (individuals were assigned to three age groups: adult, sub- adult, juvenile based on weight), checked for reproductive Eighty-two individuals of P. tullbergi were recorded from a condition (scrotal testes in males and perforate vagina, total of 185 captures in 3,360 trap-nights. The LLZ recorded enlarged nipples and pregnancy in females), and marked by 22 individuals from 49 captures, whereas the MSZ recorded 25 toe-clipping before released at the point of capture. individuals from 70 captures and the SMZ recorded 33 individuals from 64 captures (Fig. 2). The relative abundance 2.4 Analysis of Data and trap-success were therefore 1.96% and 4.38% for the LLZ, 2.23% and 6.25% for the MSZ, 2.92% and 5.71% for the SMZ 2.4.1 Trap Success (Ts) and 2.38% and 5.45% for the overall study area, respectively (Table 1). This was estimated as the total number of captures (i.e. new individuals + recaptures) per 100 trap-nights (a trap-night = 1 3.2 Age-structure and Sex-ratio trap set for 1 night). Thus, The majority (92.5%) of P. tullbergi individuals recorded were adults, with the remaining 7.5% being sub-adults, which were captured in the MSZ and SMZ, with each zone recording three individuals each.

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401 Ofori et al Table 1 Trap Success, Relative Abundance and Biomass of P. tullbergi at Mount Afadjato.

Parameter Trapping Zone LLZ MSZ SMZ Overall No. of Trap-nights 1,120 1,120 1,120 3,360 Relative abundance 1.96 2.23 2.92 2.44 Trapping success 4.38 6.25 5.71 5.45 Biomass (Mean weight) 40g 41g 39g 40g

Table 2 Age-structure and Sex-ratio of P. tullbergi at Mount Afadjato, Ghana.

SEX AGE LLZ MSZ SMZ TOTAL No. of Male Adults 15 11 18 44 Sub-adults 0 3 1 4 Juveniles 0 0 0 0 Total 15 14 19 48 No. of Female Adults 7 11 12 30 Sub-adults 0 0 2 2 Juvenile 0 0 0 0 Total 7 11 14 32

No juveniles were recorded. Of the total number of adults differences in biomass across the three trapping zones were not recorded, 59.5% (44 out of 74 individuals) were males, of significant (ANOVA: N=45, df=42; p> 0.05). which 15 were captured in the LLZ, 11 in the MSZ and 18 in the SMZ. For the females, seven individuals were recorded in 3.4 Temporal Distribution Patterns the LLZ, 11 in the MSZ and 12 in the SMZ (Table 2). Praomys tullbergi was recorded during all trapping sessions, 3.3 Biomass with the total number of captures (including recaptured individuals) increasing gradually from the beginning of the The mean weight (biomass) of adult male and non-pregnant study (June 2008) to the end (January 2009). The highest female P. tullbergi was 40g, with the total biomass being 2,960 number of captures (including recaptures) (39) was recorded in g. The biomass was highest in the MSZ (41g), followed by the August, and the least in June (10). The month of August also LLZ with 40g and the SMZ with 39g, even though the recorded the highest number of individuals, with September recording the lowest (Figure. 3).

Figure 2 Total Number of P. tullbergi Individuals Captured at Figure 3 Temporal pattern of distribution of P. tullbergi at the

Mount Afadjato, Ghana. Mount Afadjato, Ghana.

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Aspects of the Ecology of the Tullberg’s Soft-furred Mouse (Praomys tullbergi: Thomas 1894) in Mount Afadjato, Ghana. 402

3.5 Breeding Activity findings of Ofori et al. (2013) and is in agreement with the general rule that male rodents are slightly heavier than their Reproductive activity was evident throughout the study period, female counterparts. but was higher during the rainy season. About 84% (37 out of 44) of the adult males had scrotal testes, while all the adult 4.4 Temporal Distribution Patterns females had perforated vaginas with most (about 70%) in some stage of pregnancy. The SMZ recorded the highest number (15 The abundance of Praomys tullbergi in the study area showed individuals) of males with scrotal testes, followed in that order monthly variations, with peak in August. The high abundance by the LLZ (12 individuals) and MSZ (10 individuals). The of the species in August may be due to high activity and SMZ recorded the highest number (10 individuals) of pregnant reproductive output during the rainy season (Nicolas & Colyn, females, followed by the MSZ (eight individuals) and LLZ 2003; Makundi et al., 2009). Seasonal variations and long-term (three individuals) in that order. cyclic fluctuations are evident in small mammal populations (Korpimaki & Krebs, 1996; Solonen, 2006). The time-span of 4 Discussions the present study was however not long enough to investigate this for P. tullbergi. 4.1 Relative Abundance 4.5 Breeding Activity The abundance and diversity of small mammals in forest ecosystems depend mainly on the nature and density of Breeding patterns of many tropical small mammals tend to be vegetation for food and shelter (Gebresilassie et al., 2004). seasonal and related to rainfall (Makundi et al., 2005; Fichet- Generally, the diversity of small mammals in forest ecosystems Calvet et al., 2009; Habtamu & Bekele, 2012). Most species is low and dominated by one species (Williams & Marsh, take advantage of the abundance of food (increased insect 1998; Balciauskas, 2005; Pupila & Bergmanis, 2006; Raoul et populations and adequate protein-rich diets for pregnant and al., 2008). However, the mono-dominance of P. tullbergi in lactating females and their offspring) and dense vegetation almost all Ghanaian forests is of conservation concern. The cover during the wet season to produce many offspring reasons for the dominance could either be their competitive (Attuquayefio & Wuver, 2003; Nicolas & Colyn, 2003; superiority, or their better adaptation to the current human- Makundi et al., 2005). This indirect influence of rainfall modified forest ecosystems in most parts of the country, or probably accounted for the high incidence of breeding activity both. Their even distribution in the study area confirms their of P. tullbergi. However, the incidence of sexual activity total dominance. throughout the eight month-study suggested that this species breeds continuously throughout the year. This claim which is 4.2 Age-structure and Sex-ratio supported by findings elsewhere in the West African sub- region (Happold, 1978; Iyawe, 1988; Nicolas & Colyn, 2003) The effect of age on the behavioural response of small may to a large extent, account for the dominance of P. tullbergi mammals to traps is well-documented, with various in most forests in Ghana. explanations given to the often low trappability of juveniles and sub-adults. The disproportionately low number of captures References of sub-adults and juveniles is supported by previous studies and may be due to low activity rates of these age-groups as Akpatou BK Nicolas V, Pires D, N’Goran E, Colyn M (2007) well as the sensitivity of the traps to them (Happold, 1979; Morphometric differentiation between two murid rodents, P. Golley et al., 2009; Gashong & Attuquayefio, 2013). The tullbergi (Thomas, 1894) and Praomys rostratus (Miller, 1900) higher number of males in the sample (1.5:1 male to female in West Africa. 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