Eccard, J. A. & Ylönen, H. 2006: Adaptive food choice of bank voles in a novel environment: choices enhance reproductive status in winter and spring. — Ann. Zool. Fennici 43: 2–8.

Using wild and laboratory animals, we studied the food preference of bank voles, Clethrionomys glareolus, as a function of sex and reproductive status. Wild voles were captured in winter and early spring in central Finland, and during one day of captivity, were examined for food preferences. Pregnant females consumed significantly larger quantities of food rich in animal oil and protein than did non-reproductive females and males. Food preferences of pregnant females may indicate that spring breeding is constrained by access to fat and animal protein. Non-reproductive males showed a preference for spruce seeds, which may indicate a specific value of spruce seeds for this group, possibly related to the maturation process. Species-specific food constraints can differ between sexes and across seasons. Tests with laboratory animals revealed that voles prefer both artificial and unfamiliar food items over their staple diet. These data suggest that food choice in voles may have an unlearned component, and that animals can make adaptive food choices under experimental conditions. We suggest that food preference under experimental conditions can be a useful indicator for food constraints in the wild.

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Fey, K., Banks, P. B. & Korpimäki, E. 2006: Different microhabitat preferences of field and bank voles under manipulated predation risk from an alien predator. — Ann. Zool. Fennici 43: 9–16.

Avoiding predators spatially or selecting safer habitats can improve survival prospects of potential prey animals. However, in the case of introduced predators, prey populations might lack the behavioural traits to escape predation. We studied responses of native voles to removal of an alien predator, the American mink (Mustela vison), on small islands in the outer archipelago of the Baltic Sea, SW Finland. Voles were live-trapped on 10 manipulation and 10 control islands in a grid of 50 traps per island. Microhabitat characteristics around trap locations were classified to four types reflecting risks of mink predation and suitability for foraging: grassy patches, juniper bushes, berries and open habitats. Microhabitat use of voles was analysed in relation to microhabitat availability. Field voles (Microtus agrestis) responded to the presence of mink with a microhabitat shift from open grassy habitats to juniper bushes. Bank voles (Clethrionomys glareolus), however, avoided juniper in the presence of mink and were significantly more often captured in juniper in removal areas. Use of open habitats by bank voles was also affected by their own density on islands. These divergent results may reflect species-specific differences in the social system, diet selection and escape behaviour of voles, but provide novel evidence for a microhabitat shift of native prey animals induced by an alien predator.

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Lane, S. D., St. Mary, C. M. & Getz, W. M. 2006: Coexistence of attack-limited parasitoids sequentially exploiting the same resource and its implications for biological control. — Ann. Zool. Fennici 43: 17–34.

Theory predicts that competing species cannot coexist on a single, non-replaceable resource unless the resource is partitioned. Host–parasitoid complexes (common in nature) admit hosts supporting more than one parasitoid species, a significant fraction of which specialize on that host. A simple one-host, two-parasitoid (1H2P) model indicates that stable three-species coexistence occurs under a wide range of conditions; shows that a parasitoid with attack aggregation sufficient to stabilize a one-parasitoid system can stabilize an otherwise-unstable two-parasitoid system; and contradicts, under these conditions, the generalization that the stronger competitor will draw down the resource to the point of excluding the weaker. When both parasitoid species are ecologically identical, except that one parasitoid species attacks earlier than the second, this difference alone is insufficient to cause competitive exclusion of the inferior competitor (the later attacker), under a wide range of host ecological values. For biological control purposes, our analysis illustrates potential conflict between the properties of a 1H2P system that provide the maximal absolute host suppression, and those properties that provide the maximal additional host suppression resulting from the presence of the second parasitoid.

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Lappalainen, J., Olin, M. & Vinni, M. 2006: Pikeperch cannibalism: effects of abundance, size and condition. — Ann. Zool. Fennici 43: 35–44.

The possible effects of pikeperch abundance, size and condition on cannibalism were studied in 1999–2001 in two basins of lake Hiidenvesi, Finland. Cannibalism was found only during the warm summer of 1999 when the abundance of young-of-the-year (YOY) fish was the highest. In July 1999, YOY pikeperch were the smallest prey (2.5–3.5 cm TL) recorded from pikeperch stomachs. In September 1999, only the smallest YOY juveniles (6.5–8.6 cm) were predated of the available size-distribution of YOY juveniles in the lake (6.5–13.8 cm) showing that the risk of cannibalism was highest among the smallest juveniles. There was no effect of prey or predator condition on cannibalism.

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Koivisto, E. & Pusenius, J. 2006: The effects of weasel proximity on the foraging activity of voles. — Ann. Zool. Fennici 43: 45–51.

The presence of a predator can cause changes in the feeding behaviour of prey. These changes may have consequences on ecological systems, i.e. behavioural trophic cascades. The proximity of the prey and predator is likely to vary in nature and the intensity of prey responses may vary accordingly. Therefore the occurrence of behavioural trophic cascades may partly depend on whether the prey changes its behaviour when not in immediate contact with the predator. We conducted a laboratory experiment where we measured the foraging activity of wild-caught and laboratory-born voles at different distances from a caged weasel. Both groups responded by reduced activity at the closest distance, 0.15 m. The feeding behaviour of neither group deviated from control (no weasel) when the distance to the weasel was 3.5 metres. At an intermediate distance, 1.5 metres, only the wild-caught voles responded. The response of voles to the presence of a weasel varies between laboratory-born and wild-caught voles and seems to be restricted only to the immediate surroundings of the weasel.

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Pola, M., Vallès, Y., Cervera, J. L., Medina, M. & Gosliner, T. M. 2006: Taxonomic status of Tambja abdere and Tambja fusca based on morphological and molecular evidence, with comments on the phylogeny of the subfamily Nembrothinae (Nudibranchia, Polyceridae). — Ann. Zool. Fennici 43: 52–64.

The use of morphological characters as the basis for species recognition and identification has permitted the development of a consistent taxonomy. However, limitations are evident when dealing with cryptic speciation or when intra-specific variability matches the total inter-species variation. Molecular techniques complement or enhance morphological inference by providing sets of data directly applicable to the taxonomic problem. Cases in which molecular techniques are particularly relevant are those involving larval or juvenile identification for which taxonomic characters are based on adult organisms and also those in which the original taxon description leads to uncertainty over the applicability of the species name. In this paper we report the use of mitochondrial DNA sequence data in a group of nudibranchs to exemplify the two cases mentioned above. The first issue is the longstanding debate on the taxonomic status of Tambja abdere and Tambja fusca, and the second issue is the identification of two juvenile specimens previously considered to represent two different undescribed species of the genus Tambja from the scarcely explored waters of Costa Rica. We also present a preliminary molecular phylogeny of the subfamily Nembrothinae.

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Václav, R. & Prokop, P. 2006: Does the appearance of orbweaving spiders attract prey? — Ann. Zool. Fennici 43: 65–71.

Recent studies proposed that the colouration of diurnal orbweaving spiders can attract hymenopteran prey. The main assumption behind the prey-attraction hypothesis is that orbweavers might lure pollinators by mimicking floral images. However, the visual appearance of spiders hunting in webs seems to mimic foliage, soil or a dead leaf. Here, we performed a field experiment with artificial webs to test the hypothesis that the appearance of diurnal orbweavers serves to attract pollinating insects. We predicted that if the presence of diurnal spiders attracts prey, the nets containing diurnal Argiope bruennichi should intercept more prey than both empty nets and the nets with nocturnal Larinioides cornutus. Alternatively, if diurnal spiders are cryptic to diurnal prey, Argiope nets should collect more prey than Larinioides nets, but Argiope's capture success should be similar to that of empty nets. We found that Argiope webs collected more insects than Larinioides webs, yet their capture success was comparable to that of the nets containing no spider. Also, Argiope showed less saturated colouration than Larinioides. Our work supports the hypothesis that the physical appearance of diurnal orbweavers might have evolved to camouflage them in their hunting habitat.

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Vila, M., Cassel Lundhagen, A., Thuman, K. A., Stone, J. R. & Björklund, M. 2006: A new conservation unit in the butterfly Erebia triaria (Nymphalidae) as revealed by nuclear and mitochondrial markers. — Ann. Zool. Fennici 43: 72–79.

Priorities for conservation of biological units should ideally combine ecology and genetics. The European butterfly Erebia triaria (Nymphalidae: Satyrinae) has disappeared from several sites in Europe during the 20th century. In order to assess the conservation values of this species in NW Iberia, we screened the genetic variability and differentiation of four nuclear microsatellite markers in five populations from this area. We used a Pyrenean population as an outgroup. One particular population (Xistral, NW Iberia) was significantly different from the others. Thus, the nuclear results fully agreed with the pattern found using mitochondrial DNA sequences, and the hypothesis of incipient speciation of this population, due to an ancient isolation event, gained additional support. By combining our genetic findings with morpho- and ecological data, we argue that this population be considered a distinct unit for conservation.

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