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1

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Population oscillations of boreal rodents: regulation by mustelid predators leads to chaos (1993)

Hanski, Ilkka ; Turchin, Peter ; Korpimäki, Erkki ; [et al.]

[s.l.] : Nature Publishing Group

Nature 364 (1993), S. 232-235

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] As a starting point we use the general predator-prey model12 d/V d7 dt N\ cPN K) N+D N (D where N and P are the prey and predator densities (numbers of individuals per hectare). Numerical responses of both species are logistic, with r and v being the intrinsic growth ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/364232a0

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2

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Analysing interspecific associations in parasites: alternative methods and effects of sampling heterogeneity (1998)

Haukisalmi, Voitto ; Henttonen, Heikki

Springer

Oecologia 116 (1998), S. 565-574

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ISSN: 1432-1939

Keywords: Key words Helminths ; Shrews ; Sorex ; Null models ; Interspecific associations

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The purpose of the present study was (1) to test the ability of six alternative methods to detect random and non-random patterns of overall association in artificial presence/absence data sets, and (2) to analyse overall associations and effects of sampling heterogeneity in four empirical presence/absence data sets of helminths of the common shrew Sorex araneus. In the null model, the expected distribution was created by means of a randomisation procedure. Application of methods on artificial data sets indicated a generally low probability of type I statistical error. All methods were more likely to detect positive non-randomness than negative non-randomness of comparable strength, which may partly explain the predominance of positive overall associations in empirical data sets. The analyses based on artificial data sets indicated slight differences between methods in their ability to detect non-randomness of known strength (type II error). However, some of the methods failed to detect strong overall association when the artificial assemblages consisted of roughly equal numbers of positive and negative pairwise interactions. The structure of the artificial data sets always disappeared when the expected distribution was constrained to account for “sampling heterogeneity”, i.e. varying prevalence of species among subsamples. The patterns of overall association in real helminth communities were variable, depending on the locality and association method used, but not usually on the simulation constraint used. Of the four empirical data sets analysed, one showed an unequivocal positive structure, in one the structure depended on the method used, and two data sets from the same locality were unequivocally unstructured (random). We discuss the applicability of various association measures, and the possible causes of positive overall associations in parasites.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420050622

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3

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Cocoon predation on diprionid sawflies: the effect of forest fertility (1998)

Kouki, Jari ; Lyytikäinen-Saarenmaa, Päivi ; Henttonen, Heikki ; [et al.]

Springer

Oecologia 116 (1998), S. 482-488

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ISSN: 1432-1939

Keywords: Key words Predation ; Forest site ; Diprion ; Neodiprion ; Fertilization

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Predation by small mammals is thought to be one of the main regulators of outbreaking sawfly species. It has been suggested that predation may be lower in poor and dryish forests, and this is the reason why outbreaks often begin from this type of environment. We studied experimentally how fertility of the forest site affects cocoon predation experienced by two sawfly species, the common pine sawfly Diprion pini (Linnaeus) and the European pine sawfly Neodiprion sertifer (Geoffroy). We applied a fertilization treatment to selected pine-dominated barren forest sites in Finland, and 2–4 years later monitored predation on the sawfly cocoons in fertilized and control areas. The results did not support the idea that forest fertility was related to cocoon predation. We also could not verify that small mammal abundance was related to fertility of the forest. The most obvious pattern we observed was that the two sawfly species differed dramatically in predation experienced. N. sertifer has its cocoon phase in mid-summer and experienced only moderate predation (37%) whereas D. pini, with its cocoon phase in autumn, suffered from very heavy predation (96%). Our observations suggest that if predation is important in controlling the population dynamics of the species, its impact depends more on the sawfly species and season than on the fertility of the forest site.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s004420050613

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4

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The impact of climatic factors and host density on the long-term population dynamics of vole helminths (1990)

Haukisalmi, Voitto ; Henttonen, Heikki

Springer

Oecologia 83 (1990), S. 309-315

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ISSN: 1432-1939

Keywords: Helminths ; Microtine rodents ; Long-term dynamics ; Climatic factors ; Host density

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary The seasonal and long-term population dynamics of helminths parasitizing voles suggested that density-dependent factors might be important in the population dynamics of common species, whereas density-independent factors predominate in the regulation of the rare species. To test this, we used single and multiple regression to analyse the effects of climatic factors and host density on populations of six species of vole helminths over 12 years. The data do support the idea of a difference between common and rare species of helminths, but they clearly do not support the above hypothesis. The common helminths Heligmosomum mixtum (Nematoda) and Catenotaenia sp. (Cestoda) responded to changes in temperature sum (〉5° C days) and precipitation during summer. The combined effect of climatic factors and host density explained most of the variation in the long-term dynamics of these common species. By contrast, the long-term dynamics of the rare helminths Paranoplocephala kalelai (Cestoda), Mastophorus muris, Capillaria sp. and Syphacia petrusewiczi (Nematoda) were explained less well by weather and host density than those of the common ones. Furthermore, the common and rare helminths differed in some ways in their responses to climatic factors.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00317553

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5

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Gradients in density variations of small rodents: the importance of latitude and snow cover (1985)

Hansson, Lennart ; Henttonen, Heikki

Springer

Oecologia 67 (1985), S. 394-402

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ISSN: 1432-1939

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Microtine rodents are known to show extreme population variations (cycles) but non-cyclic populations have also been recognized during recent years. The cyclic populations have been widely thought to be regulated by intrinsic mechanisms. However, such predictions for cyclic populations are usually not applicable to non-cyclic ones and extrinsic factors may have to be included in any explanation. A hypothesis that the degree of fluctuations in small rodent numbers is related to the sustainable number of generalist predators was tested on mainly literature data by computing “indices of cyclicity” for local populations. These indices were related to latitude and snow cover (two measures) as these variables will affect the amount of alternative prey available for these generalists. Within Fennoscandia such indices for Clethrionomys glareolus and Microtus agrestis were clearly positively related to latitude and snow cover. The fraction of populations with summer declines in numbers, characterizing highly cyclic populations, increased in the same way. Cyclicity indices in Great Britain were similar to those in southern Fennoscandia, both areas being poor in snow, but were higher at the same latitudes in eastern Europe with more snow. Indices of density variations were generally low in North American Clethrionomys species and very variable in Microtus species. The gradients observed and differences between continents are interpreted as due to microtine-vegetation interactions in northern European areas poor in generalist predators but with important small mustelid predation, and to similar snowshoe hare-vegetation interactions in mainly Canada-Alaska, where small rodents may serve as alternative prey for numerically fluctuating hare predators, at least in the forests. Western European microtine populations, and probably many others, seem to be regulated by generalist predators.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00384946

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6

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Distribution patterns and microhabitat segregation in gastrointestinal helminths of Sorex shrews (1994)

Haukisalmi, Voitto ; Henttonen, Heikki

Springer

Oecologia 97 (1994), S. 236-242

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ISSN: 1432-1939

Keywords: Helminths ; Shrews ; Sorex ; Coexistence ; Intestinal distribution

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract We studied the distribution patterns and microhabitat use in gastrointestinal helminths of the shrews Sorex araneus and S. caecutiens in Finland. The distribution of species prevalences was bimodal, and in S. araneus the abundance (mean intensity) was positively associated with commonness (prevalence), as assumed by the core-satellite species hypothesis (Hanski 1982). However, the positive correlation between prevalence and intensity was observed only when the effects of helminth body size and taxonomic group (cestodes vs nematodes) on intensity were controlled for. The nematodes of the genus Longistriata occurred predictably as core species, whereas the identity of the core cestodes was more variable between host species and regions. Helminth body size and taxonomic group were not related to the degree of aggregation in shrew populations, but helminth body size seemed to explain the differences in the distribution patterns of helminths between shrews and voles. The core species did not show more segregation in microhabitat use than randomly selected species. In fact, the two core nematodes showed largely overlapping intestinal distributions. We conclude that linear intestinal space is not a key resource for shrew nematodes, but it may be for shrew cestodes.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00323155

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7

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Description and morphometric variability of Paranoplocephala serrata n. sp. (Cestoda: Anoplocephalidae) in collared lemmings (Dicrostonyx spp., Arvicolinae) from Arctic Siberia and North America (2000)

Haukisalmi, Voitto ; Henttonen, Heikki

Springer

Systematic parasitology 45 (2000), S. 219-231

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ISSN: 1573-5192

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Abstract We describe Paranoplocephala serrata n. sp. (Cestoda, Anoplocephalidae) from collared lemmings Dicrostonyx torquatus and D. groenlandicus (Arvicolinae, Rodentia) in Arctic Siberia and North America. The new species was recorded from the Yamal Peninsula (type-locality), Yana Delta, Kolyma Delta, Wrangel Island, Alaska and Victoria Island/Kent Peninsula (Northwest Territories). P. serrata n. sp. is characterised by a long, ribbon-like strobila, distinctly serrated segments, a small scolex, unilateral or infrequently alternating genital pores and testes confined to the antiporal part of the segment. It differs from the related species (Andrya bairdi, Parandrya feodorovi and Paranoplocephala maseri) by several morphological features, including the distribution of testes (several testes antiporal to ventral longitudinal osmoregulatory canal), structure of the cirrus-sac and vagina, and large eggs (0.053–0.068 mm in the type-material). The material of P. serrata n. sp. from North America differs from the Siberian material by the shorter cirrus-sac, smaller dimensions of the female reproductive organs, larger seminal receptacle and larger eggs. However, the statistical differences in the dimensions of reproductive organs mainly reflect the larger size of mature segments in Siberian specimens compared with North American specimens. The main diagnostic features, i.e. the size and form of scolex and suckers, number and distribution of testes, position of female glands, vagina/cirrus-sac ratio and morphology of reproductive organs, do not differ markedly between the Palaearctic and Nearctic specimens. According to the structure of the early-stage uterus, A. bairdi Schad, 1954 belongs to the genus Paranoplocephala. Parandrya Gulyaev & Chechulin, 1996 is probably a synonym of Paranoplocephala. A redescription is provided for Paranoplocephala bairdi n. comb.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1006244331243

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