Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 86. (Budapest 1994)

Kemenes, I. ; Demeter, A.: Uni- and multivariate analyses of the effects of environmental factors on the occurrence of otters (Lutra lutra) in Hungary

In our survey it was impossible to give an accurate, scaled estimate of the number of otters living in an area, therefore the dependent variable had only two values. The distributions of the independent variables also differs from normality, and they can only be interpreted on an ordinal scale. For estimating the probability of occurrence of an event, given several ordinarily scaled, categorical variables, a multiple logistic regression model can be constructed. A detailed description of this technique for use on PCs as part of the SPSSPC+ statistical package is given by NORUSIS (1990). We used this technique to analyze the occurrence of otters depending on several categorical environmental variables, such as the depth of the water, steepness of the water bank, density of the bank vegetation and a variety of disturbance factors. Based on this analysis a more general logistic regression model was formed which would also make it possible to predict the occurrence of otters given a set of known environmental variables. RESULTS 1. Univariate analysis Fig. 1 shows the number of sites found to belong to the different scaled categories of water depth, density of vegetation and bank steepness, based on the data collected during the nationwide survey of the Hungarian otter populations (KEMENES 1991). The solid part of the bars in the diagram shows the number of sites at which signs of the presence of otters were found within each category. The number of positive results was very low at sites with shallow water (5=5.9% of total) or having no bank vegetation (5=6.4% of total) and by a qualitative assessment it seemed relatively low at water bodies having steep banks (10=17% of total). Table 2. Association between the presence of otters and the depth of water, steepness of the bank and density of the bank vegetation. First column: Cramur's statistic, columns 2-4: Spearman's rank correlation coefficient Otter Water depth Bank Bank steepness vegetation Otter 1.000 Water depth 0.3479 1.000 Bank steepness 0.259 0.087 1.000 Bank vegetation 0.421 0.394 0.096 1.000 Table 2 shows the coefficients of association between the presence of otters and the depth ab c Fig. 1. The number of survey sites found to belong to the différent scaled categories of water depth (a), density of vegetation (b) and bank steepness (c), based on the data collected during the nationwide survey of the Hungarian otter populations (KEMENES 1991). The solid part of the bars in the diagram shows the number of sites at which signs of the presence of otters were found within each category