Biogeography and Ecology of Bulgaria

Abstract

Our present knowledge of the terrestrial mammals of Bulgaria is reviewed on the basis of published records and original data\r collected in 1990–2002. The study is based on 93 species of terrestrial mammals. They are classified into four faunal complexes\r reflecting the influence of historical and environmental factors. The spatial differentiation of the mammalian fauna is considered\r within a network of landscape territorial units, or natural regions (NRs). Physiographic and climatic indices of each NR are\r used in the quantitative analyses in order to explore the environmental causes of the observed patterns. The variability of\r species richness across the NRs does not correlate with environmental variables and seems to depend on the completeness of\r regional inventory. However, the species richness of carnivores and artiodactyls shows patterns which could be due to the\r human impact in the lowlands and the greater habitat diversity in the mountains. Faunal differentiation of the Bulgarian mammals\r is primarily related to the altitudinal gradient and secondarily, to the humidity and continentality of the climate in the\r lowlands. Detailed analyses are performed on a set of 83 local assemblages of small epigean mammals (pitfall data) from 16\r sampling areas. Each assemblage represents a specific habitat type within the sampling area hypothesized as perceived by the\r small mammals. Conditions within the habitats are described through the environmental variables. The ordination analyses reveal\r that, again, the composition and structure of the local assemblages are primarily affected by the altitudinal gradient, the\r secondary group of factors being local vegetation type and humidity. The classification analysis distinguishes five assemblage\r types. The structure of the local assemblages is affected primarily by the external environmental factors; the role of internal\r factors, such as competition, could be suggested only in one case. The environmental relationships of species change along\r the overall gradient. On the basis of the observed patterns we propose a zoogeographical subdivision of Bulgaria into two\r districts, with two subdistricts each. The changes of the zoogeographical structure of the mammalian fauna in Bulgaria are\r due to environmental differentiation, modified by human impact since the middle of Holocene