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Abstract
Habitats of pre-hibernating gregarious larvae of the endangered Marsh Fritillary butterfly (Euphydryas aurinia) were studied in field in Western Bohemia, Czech Republic. The species inhabits moist seminatural meadows managed by light grazing and haymaking; the only local host plant is Succisa pratensis. The redundancy analyses of the vegetation composition (around 166 nest-bearing and 381 unoccupied host plants) showed that nest presence was positively associated with short cushion-forming grasses (esp. Nardus stricta). It was negatively associated with competitively superior tall grasses (e.g., Deschampsia caespitosa) and tall herbs. Comparison of Ellenberg's indicator values of vegetation in occupied vs. unoccupied plots revealed that the nests were more often found in drier, nitrogen-poorer and more acidic conditions than unoccupied plants. Multiple regressions of nest presence against architecture of the host plants (170 occupied, 1280 unoccupied) revealed that the nests were associated with densely clumped host plants, low to medium height of sward and mechanical disturbance. The patterns agree with our knowledge of the biology of the larvae: short sward (related to low nitrogen, humidity, and low pH) facilitates larval basking; high host density reduces the likelihood of starvation. Sod disturbance facilitates host plant germination. The conditions favourable for the nests were also favourable for the host plant, but the plants grew in broader range of conditions than that occupied by the nests. The abandoning of a site results into a situation when the conditions first become intolerable for the butterfly, and ultimately for the plant. Since grazing and mowing have a different impact on vegetation composition and architecture, we propose that the studied populations have persisted in a semi-dynamic state in the two modes of management. Conservation management should mimic the dynamics of traditional land use on the smaller scales of extant colonies.
Highlights
Butterflies are among the best known and at the same time the most threatened group of temperate insects (Van Swaay & Warren, 1999)
The plots containing larval nests had a higher cover of Succisa pratensis (Mean = 36, SD = 18.1, median = 30, range = 5-90) than unoccupied plots (Mean = 30, SD = 20.1, median = 30, range = 2-90) (Mann-Whitney U: p < 0.001)
The occurrence of E. aurinia nests was asso ciated with a high cover of the host plant
Summary
Butterflies are among the best known and at the same time the most threatened group of temperate insects (Van Swaay & Warren, 1999). It is known that individual species exhibit more exacting habitat requirements than would be predicted from the distribu tion of their host plants. The selectivity is typically attrib utable to the specific needs of the developing larvae in terms of microclimate, host plant chemistry and phenol ogy, or avoiding of parasitoids (e.g., Weiss et al, 1988; Warren, 1987; Osborne & Redak, 2000). Narrow larval requirements combined with limited adult dispersal are associated with the vulnerability of many Melitaeini spe cies in Europe (e.g., Warren, 1994; Wahlberg et al, 1996). The Marsh Fritillary (Euphydryas aurinia Rottemburg, 1775) is threatened in most of Europe and is listed in the Berne Convention and in the EEC/EU Habitat Directive
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