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Understanding the role that extrinsic processes play in shaping animal population dynamics and demography is a central tenet of population ecology and an issue of vital importance for conservation and wildlife management. The top-down impact of predation and bottom-up influence of food availability are thought to be two of the most important extrinsic processes affecting population dynamics and demography of species occupying middle trophic levels. However, many studies only focus on quantifying the impact of one of these processes in isolation and it is not clear whether the impact of one extrinsic factor on population dynamics and demographic rates is augmented or lessened by changes in other extrinsic factors. In this thesis I examine the extent to which both top-down and bottom-up processes shape population dynamics (population size, recruitment and immigration) and demography (survival, reproduction, life-history trade-offs and reproductive strategies) in a long-lived species, the tawny owl, by taking advantage of a natural increase in predation risk (goshawk abundance) and a decline in food availability (field vole densities). Despite the increase in predation and the decline in food availability, the owl population remained stable, which we posit is due to goshawk predation being selective on individuals with a low reproductive value (juveniles and old individuals) and an increasing number of immigrants entering the population. Selective predation on older owls had a negative impact on the survival of this age class and appeared to be shaping the pattern of actuarial senescence and influencing the strength of the intrinsic trade-off between survival and reproduction. As food availability declined and predation risk increased owls appeared to be switching from an 'eggs in one basket strategy' of saving resources to invest more in fewer breeding attempts in the future, to a 'bet-hedging' strategy of reproducing more often, but investing less per breeding attempt.

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Bank voles, grey-sided voles, and field voles had synchronous 3-4 year density cycles with variable amplitudes which averaged about 200-fold in each species. Cycles of vole predators (red fox and Tengmalm's owl), and their (foxes') alternative prey (mountain hare and forest grouse) lagged behind the vole cycles. The nomadic Tengmalm's owl responded with a very rapid and strong numerical increase to the initial cyclic summer increase of voles (the owl’s staple food). Owl breeding densities in the springs were highly correlated with vole supply in the previous autumns. This suggested that the number of breeding owls was largely determined in the autumn at the time of the owl's nomadic migrations, and that immigration was crucial for the rapid rise in owl numbers. The owl's numerical response was reinforced by the laying of earlier and larger clutches when food was plentiful. In addition, the owl has an early maturation at one year of age. The transition between subsequent vole cycles was characterized by a distinct shift in rate of change in numbers from low to high or markedly higher values in both summer and winter. Regulation increased progressively throughout the cycle since the rate of change decreased continuously in the summers. Moreover, there was a similar decrease of the rate of change in winter. Rate of change was delayed density-dependent. The delayed density-dependence had an 8 month time-lag in the summers and a 4 month time-lag in the winters relative to the density in previous autumns and springs, respectively. These findings suggest that vole cycles are likely to be generated by a time-lag mechanism. On theoretical grounds, it has been found that a delayed density- dependence of population growth rate with a 9 month time-lag caused stable limit cycles with a period between 3 and 4 years. Some mechanisms for the delayed density-dependence are suggested and discussed. The mechanisms are assumed to be related to remaining effects of vole populations past interactions with predators, food supplies, and/or diseases. Unlike the other voles, the bank vole had regular and distinct seasonal declines in density over winter. These declines are proposed to be due to predation, mainly by Tengmalm's owl. Supranivean foraging for epiphytic tree lichens and conifer seeds most likely explains why this species was frequently taken by the owl under snow-rich conditions. The alternative prey hypothesis predicts that a reduction of predator numbers should increase the number of alternative prey. Alternative prey should be less effectively synchronized to the vole cycle by predation at declining and low vole (main prey) densities; they may also lose their 3-4 year cyclicity. The appearance of sarcoptic mange among foxes in northern Sweden in the mid 1970s provided an opportunity to "test" these ideas, and these were found to be supported. In areas with highest mange infection rates, foxes declined markedly from the late 1970s to mid 1980s, whereas hare numbers rose rapidly and appeared non-cyclic. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1991, härtill 7 uppsatser</p> / digitalisering@umu

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Insgesamt 1746 Kleinsäuger aus den Familien Muridae (Murinae, Arvicolinae) und Soricidae aus dem Naturschutzgebiet ”Großer Hakel” (Sachsen-Anhalt) und der Tagebaufolgelandschaft ”Phönix-Ost und Rusendorf” Meuselwitz (Thüringen) wurden auf einen Befall mit Capillaria hepatica und Metazestoden von Bandwürmern (Cyclophyllida) untersucht. Das Tiermaterial stammte aus genehmigten faunistischen Untersuchungen aus den Jahren 1993 bis 1997 in Zusammenarbeit mit der Universität Halle und dem Naturkundemuseum "Mauritianum" Altenburg. Alle Mäuse wurden seziert und der Brust- und Bauchraum einschließlich aller Organoberflächen, der Subkutis, des Gehirns und der Leber untersucht. Eine Altersbestimmung der Wirte erfolgte bei den untersuchten Rötelmäusen (Clethrionomys glareolus). Erstmals in Deutschland konnte im Hakel ein stabiles Endemiegebiet von Capillaria hepatica bei Wildmäusen nachgewiesen werden. Die aus dem ”Großen Hakel” stammenden Gelbhals- (Apodemus flavicollis) und Rötelmäuse wiesen Befallshäufigkeiten von 8,5 bzw. 15,1 % auf, die Eizahlen pro Leber lagen zwischen 67 und 3 600 000. Weibliche Mäuse zeigten eine höhere Befallshäufigkeit als männliche Mäuse. Bei den Rötelmäusen konnte ein Anstieg der Befallshäufigkeit von 5,8 % der bis zu 3 Monate alten bis auf 28,6 % der bis zu einem Jahr alten Tiere beobachtet werden. Patente Infektionen waren erst in der Altersgruppe 3-6 Monate nachzuweisen. In dem Untersuchungsgebiet Meuselwitz war Capillaria hepatica bei den untersuchten 1069 Muridae und Soricidae nicht nachweisbar. Eine aktuelle Übersicht der weltweit in 53 Ländern festgestellten 137 Wirtsarten aus 25 Säugetierfamilien von Capillaria hepatica wurde zusammengestellt. Die Familie Muridae stellt mit 83 Arten die bedeutendste Wirtsgruppe dar. Bisher wurde über 56 Capillaria-hepatica-Infektionen beim Menschen (davon 39 Kinder) aus 18 Ländern berichtet. Die Leitsymptome der Erkrankung beim Menschen sind intermittierendes Fieber, Hepatomegalie, Leukozytose mit hochgradiger, persistierender Eosinophilie, Anämie, Hypergammaglobulinämie und Hypoalbuminämie. Die Serumaktivitäten von AST, ALT und LDH sind erhöht. Die Diagnose der zum Teil tödlich verlaufenden Erkrankung ist intra vitam bisher nur durch Leberbiopsie oder Laparotomie möglich. Einzelne Versuche mit serologischen Tests scheinen erfolgversprechend. Die Einzelnachweise von Capillaria hepatica bei Mensch, Hase und Sumpfbiber in Deutschland (Bayern, Sachsen und Sachsen-Anhalt) sind als Hinweise auf bestehende Endemiegebiete zu werten. Aufgrund der weiteren Verbreitung und der diagnostischen Probleme kann von einer höheren Gefährdung des Menschen (insbesondere Kleinkinder) und der Haustiere durch den Zoonoseerreger Capillaria hepatica ausgegangen werden. Bei 10,5 % aller untersuchten Mäuse wurden Metazestoden gefunden. Die Rötelmaus wies insgesamt mit durchschnittlich 23,5 % (Meuselwitz 30,2 %, Hakel 15,1 %) die signifikant höchsten Befallshäufigkeiten mit Metazestoden auf. Insgesamt konnten bei Muridae und Soricidae in Sachsen-Anhalt und Thüringen Metazestoden von 8 Bandwurmgattungen bzw. -arten (Cladotaenia globifera, Mesocestoides spp., T. crassiceps, T. martis martis, T. martis americana, T. mustelae, T. polyacantha, T. taeniaeformis) nachgewiesen werden. Die breiteste Metazestodenfauna mit insgesamt 7 Arten wurde bei der Feldmaus (Microtus arvalis), nur jeweils eine Metazestodenart dagegen bei Brandmaus (Apodemus agrarius), Zwergmaus (Micromys minutus), Feldspitzmaus (Crocidura leucodon) und Waldspitzmaus (Sorex araneus) gefunden. Die Zwergspitzmaus (Sorex minutus) war nicht von Metazestoden befallen. Eine deutliche Wirtsspezifität (Feldmaus) konnte für T.-crassiceps- und T.-polyacantha-Metazestoden festgestellt werden. Im Gebiet Meuselwitz dominierten bei Muridae Metazestoden von T. mustelae (Befallshäufigkeit 9,3 %) sowie von T. martis martis (Befallshäufigkeit 6,4 %), im Hakel von T. martis martis (Befallshäufigkeit 2,5 %) sowie T. mustelae (Befallshäufigkeit 2,2 %). Während in Meuselwitz die höchsten Befallshäufigkeiten mit Metazestoden von T. mustelae (24,7 %) bei der Rötelmaus und von T. martis martis (13 %) bei der Gelbhalsmaus vorlagen, waren im Hakel die Rötelmäuse am häufigsten mit T.-mustelae- (8,2 %) und T.-martis-martis- Metazestoden (4,8 %) befallen. Mit zunehmendem Alter der Rötelmäuse stieg die Befallshäufigkeit mit Metazestoden bei dieser Tierart an. Rötelmäuse unter einem Alter von 2 Monaten waren noch nicht von Metazestoden befallen. Infektionen mit 2 Metazestodenarten traten erstmals bei 4 Monate alten Rötelmäusen auf, bei zwei Tieren im Alter von 9 bzw. 12 Monaten wurden Infektionen mit 3 Metazestodenarten (Cladotaenia globifera + T. martis americana + T. mustelae; Cladotaenia globifera + T. martis martis + T. mustelae) nachgewiesen. Bei insgesamt 10 Muriden konnten Mischinfektionen mit Capillaria hepatica und Metazestoden von Bandwürmern festgestellt werden. Bei Mäusen der Familie Soricidae sind ausschließlich Metazestoden von Cladotaenia globifera gefunden worden. Erstnachweise für Deutschland stellen Funde der Metazestoden von Cladotaenia globifera bei der Feldspitzmaus, T. martis americana bei der Rötelmaus, T. mustelae bei Erd- und Zwergmaus und T. polyacantha bei der Waldmaus dar. Das erste Mal in Europa konnten T.-martis-americana-Metazestoden bei der Feldmaus gefunden werden. Eine wichtige Einflußgröße auf die Metazestodenfauna war das Aufeinandertreffen von End- und Zwischenwirt in bestimmten Biotopen. / The occurrence of Capillaria hepatica and metacestodes of Cyclophillida was investigated in 1746 small mammals of the families Muridae (Murinae, Arvicolinae) and Soricidae from the nature reserve ”Grosser Hakel” (Saxony-Anhalt) and the former open-cast mining area "Phoenix-Ost and Rusendorf" Meuselwitz (Thuringia). The animals came from approved faunistic surveys in co-operation with the University of Halle and the natural history museum ”Mauritianum” Altenburg. All mice were sectioned and the thoracic as well as the abdominal cavity including all organ surfaces, subcutaneous tissue, brain and liver were examined. The age of all bank voles (Clethrionomys glareolus) was determined. In the nature reserve "Grosser Hakel"an stable endemic area of Capillaria hepatica in wild mice could be detected for the first time in Germany. The percentage of yellow-necked mice (Apodemus flavicollis) infected with Capillaria hepatica in that area was 8.5 %, the percentage of bank voles infected with Capillaria hepatica in that area reached 15.1 % respectively. The number of eggs per liver ranged from 67 to 3,600,000. The proportion of infected mice was higher in female than in male mice. In bank voles the frequency of infection increased with age (from 5.8 % in the age of 3 months to 28.6 % in the age of one year). Patent infections were first detected in the age group of 3 to 6 month. No Capillaria hepatica could be found in 1069 Muridae and Soricidae examined in the Meuselwitz area. A current survey of the world-wide occurrence of Capillaria hepatica in 137 hosts of 25 mammal families was prepared. The family of Muridae (with 83 species) is the most important host group. Up to now 56 Capillaria-hepatica-infections in humans (including 39 children) from 18 different countries were reported. Major symptoms in humans are intermittent fever, hepatomegaly, leucocytosis with severe, persistent eosinophilia, anaemia, hypergammaglobulinaemia and hypoalbuminaemia. The serum activities of AST, ALT and LDH are elevated. Intra-vitam diagnosis of this partly lethal disease is only possible by liver biopsy or laparatomy. First serological tests are promising. Sporadic detection of Capillaria hepatica in humans, hares and nutria in Germany (Bavaria, Saxony and Saxony-Anhalt) can be regarded as an indication of existing endemic areas. A higher risk of Capillaria-hepatica-infection in humans (especially in small children) and domestic animals can be assumed on the basis of the wide distribution and the diagnostic problems. Metacestodes were found in 10.5 % of all examined mice. The bank voles showed the significantly highest rate of infection with 23.5 % (Meuselwitz 30.2 % and Hakel 15.1 %). Altogether metacestodes of 8 tapeworm genuses (Cladotaenia globifera, Mesocestoides spp., T. crassiceps, T. martis martis, T. martis americana, T. mustelae, T. polyacantha, T. taeniaeformis) could be detected in Muridae and Soricidae in Saxony-Anhalt and Thuringia. The broadest metacestode-fauna (with 7 species) was found in the common vole (Microtus arvalis). Only one metacestode-species was detected in the stripped field mouse (Apodemus agrarius), the harvest mouse (Micromys minutus), the bicoloured whitetoothed shrew (Crocidura leucodon) and the eurasion common shrew (Sorex araneus). The pygmy shrew (Sorex minutus) was not infected by metacestodes. A distinct host specificity (in the common vole) could be established for T. crassiceps and T. polyacantha. Metacestodes of T. mustelae (infection rate 9.3 %) and T. martis martis (infection rate 6.4 %) dominated in Muridae of the Meuselwitz area. In the Hakel area T. martis martis (infection rate 2.5 %) and T. mustelae (infection rate 2.2 %) dominated as well. Whereas metacestodes of T. mustelae occurred in the bank vole with an infection rate of 24.7 % and T. martis martis in yellow-necked mice with an infection rate of 13.0 % in the Meuselwitz area, T. mustelae occurred in bank voles with an infection rate of 8.2 % and T. martis martis in yellow-necked mice with an infection rate of 4.8 % in the Hakel area. The infection rate of bank voles with metacestodes increased with age. No metacestodes were found in bank voles younger than 2 month of age. Infection with 2 different metacestode-species occurred in bank voles for the first time at the age of 4 month. 3 metacestode-species were found in 2 animals at the age of 9 to 12 months (Cladotaenia globifera + T. martis americana + T. mustelae; Cladotaenia globifera + T. martis martis + T. mustelae). In 10 Muridae occurred a mixed infection with Capillaria hepatica and metacestodes of tapeworms. In mice of the Soricidae-family only metacestodes from Cladotaenia globifera could be found. For the first time in Germany were detected metacestodes of Cladotaenia globifera in the bicoloured whitetoothed shrew, of T. martis americana in bank voles, of T. mustelae in the common field vole and the harvest mouse and of T. polyacantha in the wood mouse. For the first time in Europe T. martis americana-metacestodes could be detected in the common vole. Of high importance to the metacestode-fauna was the encounter of final host and intermediate host in certain biotopes.