The diet of otters Lutra lutra was studied by spraint analysis in six river and stream habitats in eastern Poland. In all of them fish were the staple food of otters, constituting from 29 % to 96 % of prey consumed in particular seasons. In upland (river Tanew) and mountain (river San, streams Dwernik and Głęboki) habitats, bullheads (Cottus gobio) were the most frequently eaten fish throughout the year (with maximum contribution of 57 % in the winter diet on river Tanew). In these habitats otters preyed on total of 10 fish species, including: brown trout (Salmo trutta), stone loach (Barbatula barbatula ), brook minnow (Phoxinus phoxinus) and stickleback (Gasterosteus aculeatus). On the lowland rivers, otters relied on more fish species than on the upland and mountain rivers (14 species on river Czarna Hańcza and 12 species on the upper and lower course of river Biebrza). Beside various cyprinids, otters preyed on stickleback, perch (Perca fluviatilis), mud loach (Misgurnus fossilis), burbot (Lota lota) and pike (Esox lucius). On all rivers, except the lower Biebrza, most of fish (from 70% to 88%) captured by otters were less than 10 cm long. Amphibians and crayfish were two other important groups of prey. On small streams in the Bieszczady Mountains, frogs (mainly Rana temporaria) comprised up to 46% of otter prey. Crayfish (Ortonectes limosus) remains were recorded in otter spraints only on the lowland rivers: in summer crayfish comprised 52% of prey on the Czarna Hańcza River and 47% of prey on the upper Biebrza River. In upland and mountain habitats the food niche breadth of otters was lower (from B=2.62 to B=6.12) than on the lowland rivers (from B=3.10 to B=11.09) and did not differ much between the seasons. On the lowland rivers the food niche breadth was high in winter and low in summer, and the seasonal differences in otter diet were much more pronounced as compared to the upland and mountain habitats.
We investigated food niches, diet diversity and individual food specialization of the larvae and adults of four species of ladybirds, Sospita vigintiguttata (L.), Calvia quindecimguttata (F.), C. quatuordecimguttata (L.) and C. decemguttata (L.), co-occurring in European alder carr forests. The first two species are considered to be strict habitat specialists associated with alders (Alnus spp.) in marshy forests and the other two are less habitat-specialized, inhabiting various deciduous trees and shrubs. Our investigations were based on the analysis of food remains in frass produced by field-collected ladybirds. In each of the species studied, adults had more diversified diets than larvae based on Levins' D index of diversity. The most diverse diet recorded for adults was that for S. vigintiguttata followed by C. quatuordecimguttata, C. quindecimguttata and C. decemguttata. The diversity of larval diet was higher for the habitat specialists, C. quindecimguttata and S. vigintiguttata, than for the more habitat-generalists Calvia decemguttata and C. quatuordecimguttata. Although the main type of prey recorded for both adults and larvae of each of the species studied was aphids, other types of prey made up a relatively high part of the diet of different species/stage combinations. Psylla alni (L.), for example, was frequently recorded in the frass of adults and larvae of S. vigintiguttata and of adults of C. quatuordecimguttata and chrysomelid larvae commonly in the frass of adults and larvae of C. quindecimguttata. Quite a high proportion of the frass of all the species studied contained the remains of Psocodea. The niche width of adults was broader than that of larvae except in C. quindecimguttata in which it was the opposite. The larval niches of the strict habitat specialists, C. quindecimguttata and S. vigintiguttata, were broader than those of the less habitat-specialists C. decemguttata and C. quatuordecimguttata. Adults of all the species studied showed relatively higher levels of food specialization than larvae, except for C. quindecimguttata. The results of this study indicate that ecological specialization is a complex phenomenon and habitat specialization does not imply food specialization.
Coprophagous insect communities play a critical role in the decomposition of vertebrate dung and provide ecosystem
functions fundamental to modern agriculture. While the ecology of dung beetles is rather well understood, niche differentiation in
coprophagous fl ies is poorly studied. Sepsid fl ies (Diptera: Sepsidae) are a vital part of the European community of coprophages,
with 6–7 widespread species of Sepsis often found co-occurring in the same pasture. To advance our ecological understanding of
the mechanisms that enable species to coexist, we investigated the oviposition preferences and larval performance of 7 common
species of Sepsis in the dung of different large domestic and wild mammals. Substrate preferences and subsequent performance
of larvae in laboratory experiments did not vary greatly. All species did very well on cow dung, the most common substrate in
Central Europe, but also on dung of horse and wild boar. In contrast, fl ies did not prefer or grow well in dung of red and roe deer,
two of the most common wild vertebrates. Thus there were only minor differences among the species tested along the specialistgeneralist (dung) gradient, indicating that differences in the choice of oviposition sites by the adults of the different fl y species
and larval performance do not constitute a major axis of ecological differentiation. Nevertheless, there was a positive correlation
between substrate choice and larval performance indicating the preference of gravid females for particular oviposition sites is
adaptive. We conclude that sepsids are common in Europe because they are well adapted to the dung of herbivorous livestock
rather than wild animals. Nevertheless, specialization on particular types of dung does not defi ne the niche of Sepsis dung fl ies
and hence plays a minor role in mediating their species diversity.