AnZF 40(6)

ISSN 0003-455X
© Finnish Zoological and Botanical Publishing Board

Contents of Volume 40 Number 6, 2003

Murray, B. G. Jr. 2003: A new equation relating population size and demographic parameters: some ecological implications. — Ann. Zool. Fennici 40: 465–472.
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Angelstam, P. K., Bütler, R., Lazdinis, M., Mikusinski, G. & Roberge, J.-M. 2003: Habitat thresholds for focal species at multiple scales and forest biodiversity conservation — dead wood as an example. — Ann. Zool. Fennici 40: 473–482.
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Haikola, S. 2003: Effects of inbreeding in the Glanville fritillary butterfly (Melitaea cinxia). — Ann. Zool. Fennici 40: 483–493.
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Komonen, A. 2003: Distribution and abundance of insect fungivores in the fruiting bodies of Fomitopsis pinicola. — Ann. Zool. Fennici 40: 495–504.
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Pérez-Contreras, T., Soler, J. J. & Soler, M. 2003: Why do pine processionary caterpillars Thaumetopoea pityocampa (Lepidoptera, Thaumetopoeidae) live in large groups? An experimental study. — Ann. Zool. Fennici 40: 505–515.
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Correia, A. M. 2003: Food choice by the introduced crayfish Procambarus clarkii. — Ann. Zool. Fennici 40: 517–528.
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Juskaitis, R. 2003: Breeding by young-of-the-year females in common dormouse, Muscardinus avellanarius, populations in Lithuania. — Ann. Zool. Fennici 40: 529–535.
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Ylönen, H., Jacob, J. & Kotler, B. P. 2003: Trappability of rodents in single-capture and multiple capture traps in arid and open environments: Why don't Ugglan traps work? — Ann. Zool. Fennici 40: 537–541.
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Murray, B. G. Jr. 2003: A new equation relating population size and demographic parameters: some ecological implications. — Ann. Zool. Fennici 40: 465–472.

A simple equation relates mean population size (), mean initial size of cohorts (), and life expectancy at birth () in persisting populations that are fluctuating between upper and lower boundaries: . This equation indicates that the study of differences in size between two populations, of global and local commonness and rarity, and of the limitations to population growth should focus on ecological factors affecting and . The equation also has a potential practical application for those countries, such as China, interested in designing policies for limiting population growth.

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We present an example of how systematic studies of habitat loss thresholds at multiple scales can be used for assessing the functionality of habitat networks. The different steps are: (1) carefully select a suite of species representing each land cover type; (2) use quantitative targets based on the requirements of the focal species at multiple scales; (3) make regional gap analysis for the different land cover types; (4) use habitat modelling to build spatially explicit maps describing the probability that existing habitat patches really contribute to the functional connectivity of that theme in the landscape. The latter is important, since gap analyses alone neglect aspects like the quality, size, duration and configuration of land cover patches, and therefore overestimate the amount of functional habitats. The presence of thresholds at different scales suggests that the conservation management should be planned in a spatially explicit way.

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Haikola, S. 2003: Effects of inbreeding in the Glanville fritillary butterfly (Melitaea cinxia). — Ann. Zool. Fennici 40: 483–493.

Previous studies suggest that inbreeding depression may be strong enough to elevate the rate of extinction of local populations in a metapopulation of the Glanville fritillary butterfly. Laboratory experiments were conducted to assess the consequences of inbreeding for fitness components through two generations of inbreeding. Clutch size, egg hatching rate, survival of the progeny until diapause and larval weight at diapause were measured in crosses between individuals from different small populations and in within-family crosses. The magnitude of inbreeding depression did not differ significantly between the two generations, with the exception that there was a marked increase in the proportion of pairs that failed to produce any offspring in the second generation of full-sib mating. As expected, the effect of inbreeding on clutch size was evident only in the second generation, where the parents themselves were highly inbred. Inbreeding depression of the magnitude reported here can explain the increased extinction risk of natural small populations of the Glanville fritillary butterfly.

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Komonen, A. 2003: Distribution and abundance of insect fungivores in the fruiting bodies of Fomitopsis pinicola. — Ann. Zool. Fennici 40: 495–504.

This paper describes patterns of distribution and abundance of insect fungivores inhabiting the polypore Fomitopsis pinicola. I sampled fruiting bodies of the polypore from nine old-growth forest sites in southern Finland. Most species encountered in the present study were rare and only a few species were abundant and widely distributed among the fruiting bodies and study sites. Feeding guild and host-fungus specificity were the best predictors of species abundance and distribution in the fruiting bodies in that obligate fungivores, and F. pinicola specialists were more common than generalists, facultative fungivores and parasitoids. Two specialist beetles on F. pinicola, Cis glabratus and C. quadridens (Cisidae), constituted over 78% of all individuals in the pooled sample. Cis quadridens, an old-growth forest species, had lower abundance and frequency of occurrence in the fruiting bodies than C. glabratus, which is a common species also in managed forests.

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Optimal group size of gregarious larvae is the result of a trade-off between the costs and benefits undergone by individuals living in groups of different sizes. Thus, females should adjust their clutch size to an optimal-minimum group size. In this study, we experimentally manipulated the size of colonies of pine processionary caterpillars, a capital breeder species, to test the hypothesis that a large group size enhances larval growth and survival. We also explored whether this relationship fits a quadratic or an asymptotic curve and estimated an optimum or a minimal-optimum group size. The results showed significant differences in the final larval sizes in the various treatments, being greater in the larger groups. In addition, according to the existence of a minimal-optimum group size, we found that a Piecewise Linear Regression fits the above relationship better than does a linear regression. Groups larger than 32 individuals did not differ in growth or survival parameters. Although the number of dead larvae per group did not differ between experimental treatments, large experimental colonies suffered a lower percentage of mortality. Thus, the probability of reaching the pupal stage was greater for larvae from large colonies because of dilution effects. Our results demonstrated a minimum group size, above which group size did predict larval growth or mortality, thereby explaining why pine processionary caterpillars live in large groups.

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Correia, A. M. 2003: Food choice by the introduced crayfish Procambarus clarkii. — Ann. Zool. Fennici 40: 517–528.

Predicting the effects of invasive species demands detailed studies on intra and interspecific trophic interactions. To better understand the trophic role of Procambarus clarkii in rice fields, I quantified stomach contents and assessed temporal, ontogenetic and sexual trophic selection of macroinvertebrates. Detritus and plants occurred frequently in the stomach of P. clarkii, but animals formed the highest fraction of the diet. A seasonal pattern in the proportion of animals in the diet was observed for the total population, different sizes and both sexes. Pre-adults and adults tended to be more herbivorous, whereas juveniles tended to be predatory. Trophic selection of macroinvertebrates appeared related to their availability. Food choice by different life stages indicates that alterations in the demography or abundance of P. clarkii may change its structural and functional trophic role in rice field aquatic ecosystems.

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Juskaitis, R. 2003: Breeding by young-of-the-year females in common dormouse, Muscardinus avellanarius, populations in Lithuania. — Ann. Zool. Fennici 40: 529–535.

Breeding by young-of-the-year females comprised 12.7% of 479 breeding cases of the common dormouse (Muscardinus avellanarius), recorded in two Lithuanian populations during 1981–2002. These females were born in late May–early July, and their age was 60–80 days at their first parturition. Average litter size of young-of-the-year females was smaller than of adult females (3.6 and 4.1 juveniles, respectively). A significant negative correlation between dormouse population density in spring and the percentage of breeding cases involving young-of-the-year females was established (r = –0.76; p < 0.001). When population density is low, young-of-the-year females have a greater possibility of finding free territories in which to breed. Overwinter survival of breeding and non-breeding young-of-the-year females from the same cohort did not differ in either of the populations. Early born females can breed in the year of their birth and do not reduce their chances of surviving the winter, but adult established females suppress their breeding at moderate population density.

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Obtaining reliable data on small mammal population structure and numbers requires efficient traps that trap all functional categories of the population. We compared three types of live-traps (Ugglan, Sherman, Longworth) in a pairwise comparison in two arid environments, the Negev Desert in Israel and in south-eastern Australia. Ugglan traps did not capture a single gerbil in the Negev whereas Sherman traps captured probably all resident gerbils in the trapping grid in ten trap nights. Significantly more mice were captured with Longworth traps than with Ugglans in arid and open Australian grain-growing area. Ugglan traps have a very high trapping efficiency in boreal habitats with a dense undercover, but seem to be inefficient in arid and open environments.

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