| 1. |
- Angerbjörn, Anders, et al.
(författare)
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Predator-prey relationships : Arctic foxes and lemmings
- 1999
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Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 68:1, s. 34-49
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Tidskriftsartikel (refereegranskat)abstract
- 1. The number of breeding dens and litter sizes of arctic foxes Alopex lagopus were recorded and the diet of the foxes was analysed during a ship-based expedition to 17 sites along the Siberian north coast. At the same time the cyclic dynamics of coexisting lemming species were examined. 2. The diet of arctic foxes was dominated by the Siberian lemming Lemmus sibiricus (on one site the Norwegian lemming L. lemmus), followed by the collared lemming Dicrostonyx torquatus. 3. The examined Lemmus sibiricus populations were in different phases of the lemming cycle as determined by age profiles and population densities. 4. The numerical response of arctic foxes to varying densities of Lemmus had a time lag of 1 year, producing a pattern of limit cycles in lemming-arctic fox interactions, Arctic fox litter sizes showed no time lag, but a linear relation to Lemmus densities. We found no evidence for a numerical response to population density changes in. Dicrostonyx. 5. The functional or dietary response of arctic foxes followed a type II curve for Lemmus, but a type III response curve for Dicrostonyx. 6. Arctic foxes act as resident specialist for Lemmus and may increase the amplitude and period of their population cycles. For Dicrostonyx, on the other hand, arctic foxes act as generalists which suggests a capacity to dampen oscillations.
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| 2. |
- Merilä, Juha, et al.
(författare)
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Mass loss in breeding blue tits : The role of energetic stress
- 1997
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Ingår i: Journal of Animal Ecology. - 0021-8790 .- 1365-2656. ; 66:4, s. 452-460
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Tidskriftsartikel (refereegranskat)abstract
- 1. The hypothesis that mass reduction in breeding passerines results from energeticstress was evaluated using data on body mass changes in female blue tits Paruscaeruleus.2. In accordance with both the adaptive adjustment and the physiological stresshypotheses, females with experimentally enlarged broods lost more mass than femalesrearing reduced or control broods. However, the ability to allocate energy to selfmaintenance(as measured by the regrowth rate of a tail feather removed duringincubation) was negatively correlated with the amount of lost body mass.3. In one of the study years, loss of body mass was more pronounced among smallfemales, suggesting that larger females are better able to cope with poor food conditionsduring breeding.4. In a poor-weather year, 30% of the females deserted their clutches, comparedwith 8% in a good year. Females that deserted their clutches before hatching weresignificantly lighter during incubation than non-deserters, indicating that good bodycondition is important for successful reproduction.5. In one year young females lost more mass than older females and therefore theability to maintain adequate body condition in the face of energetic stress appears tobe age-dependent.6. Taken together, these results suggest that mass loss in breeding blue tits is, to somedegree, attributable to energetic stress, although we have not ruled out the possibilitythat flight cost reductions may help explain the phenomenon.
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| 3. |
- van der Jeugd, Henk P, et al.
(författare)
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Pre-Breeding Survival of Barnacle Geese Branta leucopsis in Relation to Fledgling Characteristics
- 1998
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Ingår i: Journal of Animal Ecology. - : British Ecological Society. - 0021-8790 .- 1365-2656. ; 67:6, s. 953-966
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Tidskriftsartikel (refereegranskat)abstract
- 1. Pre-breeding survival, i.e. survival from fledging up to the third winter, of barnacle geese (Branta leucopsis) was analysed by using more than 45 000 resightings of 1302 individually marked birds. Since observations from the wintering areas only were used, the survival estimates obtained were not confounded by natal dispersal. 2. Post-fledging survival, i.e. survival from fledging to the start of the first winter, differed significantly among the 10 cohorts analysed. These differences were related to the mean body weight and mean tarsus length of cohorts just before fledging. In further analyses, when data from all cohorts were combined, body weight and tarsus length of individuals just before fledging were found to be positively related to Post-fledging survival. 3. Post-fledging survival rates were, on average, lower than survival rates after the first winter. This age effect was largest in cohorts with low mean body weight at capture and was absent in cohorts with high mean body weight at capture. 4. The age effect on survival could only partly be explained by individuals with low body weight having lower survival and successively disappearing from the cohort. It was therefore concluded that other factors must have contributed to the age effect as well. 5. It is hypothesized that lightweight birds are more vulnerable to, for example, diseases, parasites and predation during the first months of their life. Once they have survived this critical period, the effects of characters related to low body weight at capture seem to disappear. 6. Body size of juveniles just before fledging has previously been found to be greatly affected by weather factors and the availability of high quality food during the growth period. Hence, a considerable part of the observed variation in Pre-breeding survival appears to be outside the individual's control.
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| 4. |
- Bensch, Staffan
(författare)
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Female mating status and reproductive success in the great reed warbler: Is there a potential cost of polygyny that requires compensation?
- 1996
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Ingår i: Journal of Animal Ecology. - 1365-2656. ; 65:3, s. 283-296
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Tidskriftsartikel (refereegranskat)abstract
- 1. Using data from a 9-year study of the great reed warbler Acrocephalus arundinaceus L. carried out in Sweden, I tested the main assumption of the polygyny threshold model (that there is a cost of polygyny) and the main prediction (that this cost is compensated for). The main question was whether a female that chose a mated male (secondary females) experienced the same fitness as a female that at the same time chose an unmated male (primary females). The study includes a total of 192 breeding seasons of 104 individual females of which 40% settled with already mated males. 2. Eight potential correlates of fitness were examined; namely, clutch size, hatching success, hedging success, survival until breeding age, nest survival, mass of fledglings, mass of feeding females and annual survival rate of breeding females. I started each analysis by controlling for four potential confounding variables (year, study site, female age and breeding date). Then I compared the average fitness measure of primary and secondary females. 3. The only detected potential component cost of polygyny was a higher mortality among nestlings if a non-primary position within the harem was retained until hatching. This was supported by a natural experiment. Females that initially chose mated males but which achieved a primary position after failure of the originally primary female's nest enjoyed an increased fledging success, probably because of more male assistance. 4. The number of recruits, controlling for settling dates, for the two categories of females were almost identical (primary females 0 . 53 recruits per year, secondary females 0 . 51 recruits per year). Since secondary and primary females showed similar rates of survival until next breeding season the fitness of the two strategies appears to be equal. These findings strongly suggest that polygyny in the great reed warbler is best explained by the compensation models such as the polygyny threshold model.
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| 6. |
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| 7. |
- Kenward, RE, et al.
(författare)
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Demographic estimates from radio-tagging: models of age-specific survival and breeding in the goshawk
- 1999
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Ingår i: JOURNAL OF ANIMAL ECOLOGY. - : BLACKWELL SCIENCE LTD. - 0021-8790. ; 68:5, s. 1020-1033
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 1. Age-specific survival and breeding (ASSAB) models were developed with data from 318 goshawks (Accipiter gentilis L.) fitted during 1980-7 on the Baltic island of Gotland with tail-mounted radio-tags. 2. Comparisons with recaptures and recoveries of 238
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| 8. |
- Laurila, A, et al.
(författare)
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Habitat duration, predation risk and phenotypic plasticity in common frog (Rana temporaria) tadpoles
- 1999
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Ingår i: JOURNAL OF ANIMAL ECOLOGY. - : BLACKWELL SCIENCE LTD. - 0021-8790. ; 68:6, s. 1123-1132
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 1. Common frogs (Rana temporaria) breed readily in small pools and thus expose their offspring to catastrophic mortality by desiccation, Amphibian larvae exhibit considerable phenotypic plasticity in metamorphic traits, and some species respond to environ
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| 9. |
- Nilsson, Jan Åke, et al.
(författare)
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Sibling competition affects nestling growth strategies in marsh tits
- 1996
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Ingår i: Journal of Animal Ecology. - : JSTOR. - 0021-8790. ; 65:6, s. 825-836
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Tidskriftsartikel (refereegranskat)abstract
- 1. We manipulated the size hierarchy in broods of marsh tits (Parus palustris L.) by simulating hatching asynchrony to study how nestlings of different competitive ability, allocate their share of parental feedings to different growth strategies. 2. The mean rate of mass increase and the mass when the growth curve had reached an asymptote increased with the predicted competitive ability of nestlings. In contrast, rate of wing length increase was not related to overall competitive ability. The smallest nestlings in a brood even grew their wings significantly faster than the largest ones. 3. Nestlings that died due to sibling competition showed a steady reduction in the rate of mass increase compared to surviving nestlings from at least 6 days before death. Rate of wing length increase in these dying nestlings was, however, equal to surviving ones right until the last day before death. 4. Nest-leaving was initiated by the largest nestlings in a brood. When the process had started all nestlings left the nest in close succession with the result that the young/small nestlings had to leave at a younger age than their larger nestmates. 5. It seems as if individual nestlings are able to choose how to allocate resources to growth of the wing in relation to mass. In this way small nestlings are able to keep pace with their larger and older nestmates with respect to wing length. 6. The selective pressure responsible for the growth strategy of small nestlings may be the need to leave the nest together with their larger nestmates, which depends on their ability to fly and, thus, the development of the wing. 7. We suggest that sibling competition is one of the most powerful forces to explain intra-brood variation in growth and survival.
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| 10. |
- Van, der Jeugd HP, et al.
(författare)
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Pre-breeding survival of barnacle geese Branta leucopsis in relation to fledgling characteristics
- 1998
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Ingår i: JOURNAL OF ANIMAL ECOLOGY. - : BLACKWELL SCIENCE LTD. - 0021-8790. ; 67:6, s. 953-966
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- 1. Pre-breeding survival, i.e. survival from fledging up to the third winter, of barnacle geese (Branta leucopsis) was analysed by using more than 45 000 resightings of 1302 individually marked birds. Since observations from the wintering areas only were
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