Butterfly communities in the natural landscape of West Khentej, northern Mongolia: diversity and conservation value

Abstract

This thesis provides an insight into the natural history of butterfly species which are found in the West Khentej mountains of northern Mongolia. The study area is located in the transition zone between southern Siberia and Asian steppe and it includes forests, woodlands, steppe, and different types of grassland, forming a heterogeneous landscape mosaic with nearly no human impact. The region has a rich flora with boreal, temperate and mandshurian elements. The study on West Khentej butterflies is the first investigation of species richness and relative abundances of butterfly species in northern Mongolia. The objectives of this research were: 1) to describe the butterfly fauna of West Khentej in terms of taxonomic composition and biogeography and temporal variability in natural communities, 2) to describe the influence of landscape structure and vegetation on butterfly community by comparing habitat occupancy of West Khentej butterfly fauna in four different habitat types, 3) to analyse the habitat factors that influence butterfly diversity in natural landscape by comparing different grassland habitats, and 4) to asses the importance of the study region to the conservation of butterflies.Different habitat types were identified according to vegetation analysis and butterfly communities were examined within these natural landscape to identify factors that influence the diversity and composition of butterfly assemblages. In four vegetation types (forest openings, herb meadow, mountain dry steppe, and wet grassland) the relative abundance, faunal similarity, species richness and other diversity measures were estimated with 4 study plots as replicates for four years (200-2003). The netting method was used for collecting the butterflies during a standardised 1 hour sample in an area each of 0,5 ha. The total sampling effort over four years was 164 catch hours. 150 butterfly species have been reported during the survey period in 9993 individuals. 15 species have been reported for the first time in the West Khentej region by this study.Plant cover was analysed in detail only in two vegetation types, in herb meadow and mountain dry steppe. Estimated plant species richness in herb meadow and mountain dry steppe were 64 and 29, respectively. The plant community showed only 10% similarity in species composition between the two sampled habitats, documenting the difference between the moist tall herb meadow on river terraces and the dry short mountain steppe on southern slopes. But butterfly species were not significantly related to the vegetation cover. The butterfly community showed 80% similarity in species composition between these study sites. A total of 80 species were common in all four surveyed habitat types in West Khentej. The observed number of butterfly species was not significantly different between the four habitat types. The expected total species richness, calculated as ICE estimator was significantly different between the four opening ranked highest in species richness. The log-normal dominance-diversity curve of butterfly species indicates a natural rich community.The butterflies in West Khentej can be classified into four biogeographic categories, from which the palearctic group constitutes the biggest part with 59 % of the total species. Lycaenidae and Nymphalidae were the dominant families among palearctic and central Asian species, the two families together comprise 59% and 67%, respectively. Nymphalids also dominated the holarctic species assemblage (52%), whereas the dominant family (45%) of the East Asian species belongs to the Satyridae. Among the species with a more restricted geographical distribution like the central Asian or eastern Asian species, the specialist (classified by niche width in habitat occupancy with < 0.5) had a higher percentage than species with broad geographical distribution. Species with higher abundance belong more to the generalists (niche width > 0.5). Palearctic species constituted a higher proportion of habitat generalists than of habitat specialists (71% and 46% respectively). Specialist species which geographical restriction to central and East-Asia were found more in grassland biotopes, but the specialist species with palearctic and holarctic distribution peaked at forest opening and forest margin biotopes. Butterflies with a taxonomically wide range of food plants (polyphagous) tend to be more widely distributed than butterflies that use only one species or genus of host plant (mono- and oligophagous). The majority (70% of total butterfly fauna of Khentej) in the study area are herb/grass feeders, 7% of the total were feeders on woods. Polyphagous species were dominant in West Khentej, and they constitute about 40% of total butterfly species. The distribution of monophagous and strongly oligophagous species are not significantly different among habitat types. In summary , the findings indicate that the butterflies of West Khentej show an overall low habitat-specificity.Analysis of the relative abundances of 144 species from the survey period 2000-2003 revealed for few species an increasing trend and for few other species a decreasing trebd, but most of the species showed relatively constant population size. Population fluctuation could be related in many cases to variable weather conditions. Flight period of butterfly species living in West Khentej was shorter than that of the same species in Germany. The majority of West Khentej species is usually univoltine, as well the time of being on the wing was shorter than in Germany. The difference was marginally significant.Adult movement and population size of the scarce copper (Lycaena virgaureae) was estimated using the capture-recapture data. This species is near-threatened in Europa and was selected for some detailed analyses as a model. There were several significant relationships between the abundance of Lycaena virgaureae and its nectar plants. 19% of 1345 marked individuals were recaptured within 4 weeks. The results showed that the mobility of these butterflies is higher in the natural landscape than in the fragmented and human dominated landscape at a smaller scale (comparison with data from Germany), but far movements are rare in the natural landscape. Lycaena virgaureae seams to live in West Khentej in large open populations. This is also suspected for most of the other species and may explain, why the species-area relationship of butterfly community was not significant for the selected study plots in West Khentej.The West Khentej region supports a high number of butterflies species. In about 100 km2 a similar species richness is found as in the entire Germany. Many butterfly species occur in West Khentej which are listed in Europe as threatened in the Bern Convention and national Red Data Books. The populations in the Khentej are large and widespread and there is so far no sign of threat or a decline natural fluctuations. There results clearly indicate the high value of West Khentej for the conservation of butterfly communities and they highlight the importance of naturalness in a heterogeneous which sustains the coexistence of many species.