Rita, H. & Ranta, E. 1999: An individual's gain in a foraging group. — Ann. Zool. Fennici 36: 129–138.
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Kauhala, K., Helle, P., Helle, E. & Korhonen, J. 1999: Impact of predator removal on predator and mountain hare populations in Finland. — Ann. Zool. Fennici 36: 139–148.
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Kinnunen, H. & Tiainen, J. 1999: Carabid distribution in a farmland mosaic: the effect of patch type and location. — Ann. Zool. Fennici 36: 149–158.
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Berg, L. & Berg, Å. 1999: Abundance and survival of the hazel dormouse Muscardinus avellanarius in a temporary shrub habitat: a trapping study. — Ann. Zool. Fennici 36: 159–165.
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Lõhmus, A. 1999: Vole-induced regular fluctuations in the Estonian owl populations. — Ann. Zool. Fennici 36: 167–178.
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Hämäläinen, H. 1999: Critical appraisal of the indexes of chironomid larval deformities and their use in bioindication. — Ann. Zool. Fennici 36: 179–186.
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Potti, J. 1999: From mating to laying: genetic and environmental variation in mating dates and prelaying periods of female pied flycatchers Ficedula hypoleuca. — Ann. Zool. Fennici 36: 187–194.
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Rita, H. & Ranta, E. 1999: An individual's gain in a foraging group. — Ann. Zool. Fennici 36: 129–138.
By modelling an individual's gain through waiting times between subsequent prey encounters we characterise its performance when foraging alone or in a group. The larger the group, the longer the time between successful prey captures. The waiting times also depend on how the grouping behaviour affects foraging efficiency of individuals, when joining a group. With full additivity (A = 1) grouping has no effect on an individual's foraging efficiency, while with larger values of additivity individuals co-operate. When A is below one subadditivity occurs and individuals interfere each other when foraging in the patch. With A < 0 competition in the group is so hard that the intake-rate for the group is less than the rate of gain of a solitary forager. When additivity equals zero the patch corresponds to a system with continuous input and immediate consumption of the arriving prey items. The model, via waiting times, renders it possible to examine different foraging scenarios. For example, assuming that the forager already has gained k prey, for solitary foragers waiting times for the (k + 1)th prey are not affected by time in the patch, whereas for an individual in a group the waiting times get longer with increasing time. This is because other individuals affect the prey availability by their foraging activity. Using the model we were able to uncover that in depleting patches under resource matching distribution of foragers food-intake rates of individuals differed in groups of different size. Finally, via modification of waiting times the finder's advantage (the gain accumulated before others in the group arrive) can be implemented into group foraging.
Kauhala, K., Helle, P., Helle, E. & Korhonen, J. 1999: Impact of predator removal on predator and mountain hare populations in Finland. — Ann. Zool. Fennici 36: 139–148.
The impact of predator removal on predator and mountain hare (Lepus timidus) populations was studied in southern, eastern and northern Finland in 1993–1998. In predator removal areas predators were intensively hunted, and in predator protection areas hunting was prohibited. Both predator (red fox Vulpes vulpes, pine marten Martes martes, stoat Mustela erminea and raccoon dog Nyctereutes procyonoides) and mountain hare populations were monitored in the study areas. Fox and marten populations were affected by predator removal/protection in eastern and northern Finland but the effect was not as evident in southern Finland. The stoat population was not affected by removal, but the raccoon dog population was to some extent. Trends in hare populations were similar in the removal and protection areas, indicating that localized control/protection of predators did not affect hare numbers. Hare population even increased in the protection area of northern Finland although predator numbers increased and vole numbers declined.
Kinnunen, H. & Tiainen, J. 1999: Carabid distribution in a farmland mosaic: the effect of patch type and location. — Ann. Zool. Fennici 36: 149–158.
The distribution and abundance of carabid beetles was studied in a large patch of farmland of 150 fields. If the species pool is supposed to be the same over the study area, differences between the occurrence of beetles on the fields are probably due to habitat choice. We investigated the carabid communities of 27 fields by pitfall trapping. The community composition of the green set-asides differed from those of the tilled fields. In the set-asides, the proportion of the autumn-breeding individuals was almost 70% at the beginning of June, while the potato fields and bare set-aside field supported mostly spring breeders. Morisita's index indicated that there was a relationship between the similarity of the communities and the distance between them. However, the distance was found to be an important factor in explaining dissimilarity only in barley fields. This may be because colonization of tilled fields occurs early in spring and is dependent on the species pool of neighbouring fields and field margins.
Berg, L. & Berg, Å. 1999: Abundance and survival of the hazel dormouse Muscardinus avellanarius in a temporary shrub habitat: a trapping study. — Ann. Zool. Fennici 36: 159–165.
The knowledge of demography and abundance of the hazel dormouse Muscardinus avellanarius in Sweden in different habitats is poor. The hazel dormouse is classified as care-demanding on the national Red List in Sweden. In this study, dormice were live-trapped in a temporary mixed high shrub habitat in South-central Sweden, in order to estimate density and survival, and to evaluate a trap-based capture-mark-recapture method. Data on different trapping efforts suggested that 175 trap nights per ha were required for trapping most adults. The method seemed to be applicable for studies of dormice under natural conditions. The density of dormice was estimated at seven individuals per hectare. The average adult year-to-year survival rate was 56%–74%, which is higher than previously reported for this species. In our study, the trapping area should preferably be larger than 3.2 ha to avoid edge effects on density and survival estimates. To conclude, factors related to the survival of adult dormice might be important for the viability of populations.
Lõhmus, A. 1999: Vole-induced regular fluctuations in the Estonian owl populations. — Ann. Zool. Fennici 36: 167–178.
Estonia has been considered to hold non-cyclic vole populations, which should be revealed in owl productivity or movements. I asked (1) whether owl and vole populations fluctuate regularly in Estonia, (2) are the fluctuations in Estonia synchronous to those in its neighbouring areas, (3) do Estonian and northern owl populations exchange individuals? I found significant periodicity in owl reproduction, which was linked to vole abundance, suggesting that Estonia belongs to the transition zone between cyclic and non-cyclic vole populations. The migration intensities of nomadic owl species were positively correlated with each other, and in the long-eared owl related to its productivity. Having found that owl productivity fluctuates independently in Estonia and southern Finland, and owls do not move freely between the countries, I discussed possible causes for this.
Hämäläinen, H. 1999: Critical appraisal of the indexes of chironomid larval deformities and their use in bioindication. — Ann. Zool. Fennici 36: 179–186.
A recurring positive field correlation of deformity incidence (DI) in sediment dwelling chironomid larvae with environmental contamination suggests that DI is a potential indicator of the impact of contaminants in aquatic systems. Several researchers have developed indexes that take into account the severity of deformities to supplement the information that is obtained from the DI alone. Five such indexes are reviewed in this paper. The indexes can be reformulated into an identical general form that expresses a product of the DI and average severity of deformation. Assessment of the severity of deformities appears to be poorly grounded and subjective. Indexes and the DI are highly redundant, partly due to mathematical necessity. In the data sets of the proponents of the indexes there was a strong linear relationship (r2 = 0.77 – 0.99) between index values and DI. Along with this, other empirical evidence as well as tenuous foundation of the indexes suggest that the presented indexes are likely to be useless, albeit relatively harmless.
Potti, J. 1999: From mating to laying: genetic and environmental variation in mating dates and prelaying periods of female pied flycatchers Ficedula hypoleuca. — Ann. Zool. Fennici 36: 187–194.
The duration of the period comprised between mating and the onset of laying and its correlates and consequences for aspects of female breeding performance are investigated in a population of pied flycatchers studied for 5 years. That duration may represent a compromise between the selective pressure on females to breed as early as possible and the need for females attempting to breed to be in prime nutritional condition. It is shown that the duration of the prelaying period is shorter for late breeders, but is apparently unrelated to subsequent condition of the female and indices of breeding performance. A low, significant between-year repeatability (R = 0.16) in the duration of female prelaying period was detected. However, there was a large component of environmental, as opossed to genetic, variation which may reflect stochasticity affecting timing of breeding and age factors. Overall, the evidence supports models of strategic adjustment of breeding date to offspring prospects, rather than those based on condition-constrained breeding date.