Browsing by Author "Ranawana, K. B."

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    Correlation between pest gastropod occurrence and selected environmental variables in agricultural lands in the Nuwara Eliya district, Sri Lanka
    (Faculty of Science, University of Kelaniya, Sri Lanka., 2021) Thilakarathne, K.G. D. D.; Ranawana, K. B.; Kumburegama, S.
    Many of the exotic terrestrial pest gastropods introduced to Sri Lanka, either intentionally or accidentally, are well established as pests in agricultural lands, but hardly any studies have been carried out to determine the factors affecting their occurrence. Hence, this study was conducted to determine the correlation between selected environmental factors and density of gastropod pest species in some agricultural lands in the Nuwara Eliya district. A total of 80 agricultural lands were sampled from 2017 to 2019, where each land was surveyed for pest gastropods by establishing ten 1 m2 sampling plots for a maximum of 15 minutes/plot. Species richness and abundance were recorded in the field and species were identified at the field using available guides. Unidentified species were brought to the laboratory for further identification. Elevation, atmospheric temperature, rainfall, relative humidity and soil pH were measured using a Magellan Explorist 310 portable GPS, a Kestrel 4000nv weather tracker and a HANNA-HI-99121 electronic digital pH meter at each sampling location. Canonical correspondence analysis (CCA), Pearson’s correlation and generalized linear mixed model (GLMM) in R studio were used to analyze data. The first two axis of CCA explained 85% of the total variation. Species were ordered along the first axis in the CCA primarily affected by elevation while the second axis affected by rainfall and soil pH. CCA results indicated that the measured environmental factors influencing the occurrence of the gastropod species. For example, Deroceras laeve (Muller, 1774), Deroceras reticulatum (Miller, 1774), Milax gagates (Draparnaaud, 1801) and Mariella dussumieri (Gray, 1856) were influenced by the elevation and atmospheric temperature; Cryptozona chenui (Pfeiffer, 1847), Macrochlamys indica (Godwin and Austen, 1883), Subulina octona (Bruguiere, 1789) and Euplecta emiliana (Pfeiffer, 1854) were influenced by the rainfall and soil pH; while Allopeas gracile (Hutton, 1834), Leavicaulis alte (Ferussac, 1822), Lissachatina fulica (Bowdich, 1822), Cryptozona bistrialis (Beck, 1837) and Ratnadvipia irradians (Pfeiffer, 1853) were influenced by the relative humidity. According to the correlation analysis, the gastropod species richness was positively correlated to the daily rainfall (r=0.34, p<0.05); the total species abundance at all the sites were positively correlated to the elevation (r=0.56, p<0.05) and negatively correlated to the atmospheric temperature (r=-0.42, p<0.05). The results of this study indicate that gastropods could become invasive and pests due to changes in climatic and environmental factors whilst causing severe economic losses to agricultural crops in the Nuwara Eliya district. Therefore, the knowledge on the effects of environmental factors, as revealed by the results of this study, can be used to formulate management plans to control the occurrence and distribution of pest gastropods in the Nuwara Eliya district.
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    Troop composition of free-ranging Toque macaque in dry and wet zones of Sri Lanka: reviewed by a multivariate method using R
    (Faculty of Science, University of Kelaniya Sri Lanka, 2022) Weerasekara, W. M. L. S.; Wijesooriya, W. M. K. B.; Britto, C. S. A.; Ranawana, K. B.
    Macaques are group-living primates, and their unit of reproduction and social life is the troop. The Toque macaque (Macaca sinica) found in Sri Lanka is the smallest macaque among the recognized 22 species and is endemic to the island. Studies on population, behaviour, and ecology have been carried out extensively but mainly on a single or few troops of Toque macaques. Thus, this study applied principal component analysis and discriminant analysis to the troop composition data for 42 troops using statistical software package R (Version 3.4.1). The findings of this study might act as an essential parameter of demography which summarizes the variation of troop compositions of Toque macaques in the dry and wet zone of Sri Lanka for wildlife management purposes. Troop composition data was obtained by extensive literature revisions (N=25) and ongoing fieldwork (N=17). Troop composition was represented by the five-dimensional vector X = (X1: adult male, X2: adult female, X3: sub-adult, X4: juvenile, and X5: infant). The troops had a high socionomic sex ratio (XI/X2). X1-X2 and X2-X5 were strongly correlated, indicating those variables ‘shape’ the troop size. X1, X2, and X5 were probably isotropic due to the high positive correlation. Troops were sorted into the wet zone (N=35) and dry zone (N=12). The low sample size in the dry zone might lead to misclassification in the dry zone, yet a linearly independent discriminant function indicated 85.11% accuracy. However, this function might help categorize the climatic zone of a troop of Toque macaque. Further, the study can be developed by adding the montane subspecies M. s. opisthomelas troop data. This study revealed the correlation between macaque individuals within the troop. It can be helpful to regulate the troop structure of the Toque macaque for wildlife management purposes since they are considered both endangered species and a pest. Further studies on demographic data collection are needed to be carried out continuously to monitor the changes of wildlife, not only on Toque macaques but also on other endangered fauna or pests, to secure the welfare of wildlife and humankind.