Haag, C. R. & Ebert, D. 2004: A new hypothesis to explain geographic parthenogenesis. — Ann. Zool. Fennici 41: 539–544.
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Ruusila, V. & Pesonen, M. 2004: Interspecific cooperation in human (Homo sapiens) hunting: the benefits of a barking dog (Canis familiaris). — Ann. Zool. Fennici 41: 545–549.
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Clavero, M., Prenda, J. & Delibes, M. 2004: Influence of spatial heterogeneity on coastal otter (Lutra lutra) prey consumption. — Ann. Zool. Fennici 41: 551–561.
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Bruce, M. J., Heiling, A. M. & Herberstein, M. E. 2004: Web decorations and foraging success in `Araneus' eburnus (Araneae: Araneidae). — Ann. Zool. Fennici 41: 563–575.
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Ylönen, O., Heikkilä, J. & Karjalainen, J. 2004: Metabolic depression in UV-B exposed larval coregonids. — Ann. Zool. Fennici 41: 577–585.
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Pérez-Contreras, T. & Soler, J. J. 2004: Egg parasitoids select for large clutch sizes and covering layers in pine processionary moths (Thaumetopoea pityocampa). — Ann. Zool. Fennici 41: 587–597.
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Reif, V., Jungell, S., Korpimäki, E., Tornberg, R. & Mykrä, S. 2004: Numerical response of common buzzards and predation rate of main and alternative prey under fluctuating food conditions. — Ann. Zool. Fennici 41: 599–607.
Abstract
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Haag, C. R. & Ebert, D. 2004: A new hypothesis to explain geographic parthenogenesis. — Ann. Zool. Fennici 41: 539–544.
In many plants and animal species, asexuals are more common in marginal habitats such as high latitudes or altitudes than their closely related sexual counterparts. Here we propose a new hypothesis to explain this pattern called "geographic parthenogenesis". In marginal habitats, populations may often exist as metapopulations with high degrees of subdivision and local extinction and recolonization, resulting in genetic bottlenecks during colonization. Our hypothesis states that such dynamics could play a key role in geographic parthenogenesis. Genetic bottlenecks and subsequent drift have stronger negative fitness consequences in sexuals than in asexuals because genetic drift leads to increased homozygosity and inbreeding depression in sexual but not in asexual populations. Migration, leading to inter-population hybridisation, may induce temporary fitness recovery in sexuals. Asexuals arising from such hybrids have an increased likelihood of invading sexual populations because they keep their high fitness, whereas the fitness of sexuals is doomed to decrease due to subsequent inbreeding and inbreeding depression. Therefore, asexuals may replace sexuals in subdivided habitats with local extinction and recolonization while they would not succeed in unstructured habitats without local turnover dynamics.
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Ruusila, V. & Pesonen, M. 2004: Interspecific cooperation in human (Homo sapiens) hunting: the benefits of a barking dog (Canis familiaris). — Ann. Zool. Fennici 41: 545–549. Back to the top
Clavero, M., Prenda, J. & Delibes, M. 2004: Influence of spatial heterogeneity on coastal otter (Lutra lutra) prey consumption. — Ann. Zool. Fennici 41: 551–561. Back to the top
Bruce, M. J., Heiling, A. M. & Herberstein, M. E. 2004: Web decorations and foraging success in `Araneus' eburnus (Araneae: Araneidae). — Ann. Zool. Fennici 41: 563–575. Back to the top
Ylönen, O., Heikkilä, J. & Karjalainen, J. 2004: Metabolic depression in UV-B exposed larval coregonids. — Ann. Zool. Fennici 41: 577–585. Back to the top
Pérez-Contreras, T. & Soler, J. J. 2004: Egg parasitoids select for large clutch sizes and covering layers in pine processionary moths (Thaumetopoea pityocampa). — Ann. Zool. Fennici 41: 587–597. Back to the top
Reif, V., Jungell, S., Korpimäki, E., Tornberg, R. & Mykrä, S. 2004: Numerical response of common buzzards and predation rate of main and alternative prey under fluctuating food conditions. — Ann. Zool. Fennici 41: 599–607.
The first wild animal humans domesticated was the wolf (Canis lupus). The benefits of dog presence for human hunting success is often mentioned as a probable factor initiating the domestication of the wolf. We compared the per-hunter moose (Alces alces) hunting success of four hunter groups of different sizes with and without a dog. Groups with a dog had a higher hunting success for every group size. The difference was most pronounced for the smallest group (< 10 hunters) — hunters with a dog obtained 56% more prey than those without a dog. Indeed, the mean hunting success was the highest for the smallest groups with a dog. Among larger groups, hunting success was independent of the group size regardless of whether or not a dog was present. In groups over ten hunters, hunting success correlated with the number of dogs. The benefit of hunting with a dog had a density-dependent pattern: the benefit increased when moose density was low. Our results give quantitative support to the hypothesis that the benefits of cooperative hunting was a potentially important factor in the wolf domestication process.
We studied otter diet in a heterogeneous coastal environment in S Spain including sandy and rocky coastal habitats as well as four small Mediterranean-regime streams. The main sources of environmental variation (rocky coast vs. sandy coast, coastal habitat vs. inland habitats) were clearly reflected in the otter diet composition. In rocky coastal transects otters intensely predated on wrasses, blennies and rocklings, while in sandy coastal ones eels, flatfish and crayfish were characteristic prey types. Grey mullet was the most important prey type in terms of biomass in both coastal environments. Fish consumption clearly decreased from coastal habitat to inland ones. Otter prey were heavier in coastal than in inland habitats, while consumed fish were heavier in the sandy coast than in the rocky one. Within the wide habitat variation in the study area, otter foraging efficiency was considered maximum in estuarine environments.
Visual signals are commonly used by animals to manipulate both their prey and predators. The conspicuous silk structures included in the webs of many orb-web spiders, termed web decorations or stabilimenta, could be an example of this. The function of these curious structures remains controversial with some authors suggesting that they attract insect prey, while others suggesting that they camouflage the spider or deter predators. Here we test the hypothesis that web decorations increase the foraging success of `Araneus' eburnus by attracting prey to the web. Using field correlations and field manipulations we show that decorated webs capture more prey per web area than undecorated webs under certain conditions.
Exposure to UV-B radiation has been found to have negative effects on fish, such as reduced survival and growth, but sublethal effects, such as metabolic costs of increasing UV-B irradiance, have received little attention. We studied the oxygen consumption rates of vendace and whitefish larvae under enhanced UV-B irradiance in the laboratory. In addition, we studied energy allocation for digestion and activity in whitefish larvae. UV-B exposure had no clear effect on the minimum or routine oxygen consumption rates of vendace larvae, but the metabolic scope of vendace larvae and the maximum oxygen consumption rates of both vendace and whitefish larvae decreased. In the allocation experiments, enhanced UV-B irradiance mainly decreased the oxygen consumption allocated for digestion in whitefish larvae. In the field, the direct impact of increased UV-B irradiance on coregonid digestion and growth will be negligible, but some indirect effects, such as increased risk of predation, are possible.
Female insects have a limited energy budget to invest in reproduction. Clutch size and egg size are two traits typically involved in energy budget trade-offs, and an optimum clutch size is generally predicted. This trade-off, however, is influenced by many factors including the probability of egg parasitism. We studied this possibility in the pine processionary moth (Thaumetopoea pityocampa), which frequently suffers from parasitoids. We found support for a trade-off between clutch size and egg size in this species, but the intermediate clutch size did not correspond to higher hatching success. We suggest that the lack of an optimum clutch size in relation to hatching success was mediated by parasitoids: parasitoids preferentially selected small clutches containing larger eggs. In addition, we experimentally tested whether the scales that coat egg batches reduce the effect of parasitism. Egg batches with experimentally removed scales showed a significantly higher parasitism rate than control batches, which demonstrates that scales protect egg batches from parasitoids. We discuss three possible explanations for our results.
We studied the numerical response of a population of the common buzzard Buteo buteo to the fluctuations of its main prey (voles) and alternative prey (forest grouse) in western Finland between 1979 and 1996. Populations of main prey fluctuated in a cyclic manner with three years between peak densities. The nesting success of buzzards averaged 1.7 fledglings per nesting attempt and the brood size averaged 2.2 fledglings per brood. The nesting rate (no. of active nests per number of occupied territories) and the productivity rate (no. of chicks for all territories) positively correlated with the abundance of Microtus voles in the current spring but not with the abundance of grouse. The Alternative Prey Hypothesis (APH) predicts that, in the years when the main prey species decline, generalist predators can shift their diet to alternative prey and thus cause its decline. The Shared Predation Hypothesis (SPH) states that all important prey species, including alternative prey, are under high hunting pressure when the density of predators is high. The predation rate (the combination of numerical response and previously studied functional response) of Microtus voles by buzzards was positively correlated with the densities of these voles in the current spring, whereas the predation rate of grouse tended to peak one year after peak densities of Microtus voles. Therefore, our results appear to support APH rather than SPH and indicate that predation by buzzards may dampen population cycles of main prey (voles) but amplify population fluctuations of grouse.