| 1. |
- Brodin, Anders, et al.
(författare)
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Optimal energy allocation and behaviour in female raptorial birds during the nestling period
- 2003
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Ingår i: Écoscience. - : University Laval. - 1195-6860. ; 10:2, s. 140-150
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Tidskriftsartikel (refereegranskat)abstract
- In many raptors and owls the male is the main provider of food in the early phase of the nestling period while the female incubates the eggs and broods the young. In the nestling period the female often helps the male to feed the young, but the factors affecting whether and when she leaves the brood to hunt have not been investigated in detail. We present a dynamic state variable model that analyses female behaviour and fat storage dynamics over the nestling period. The results show that in the first half of the nestling period the female faces a conflict between the need to brood the young and the need to hunt to provision them with food. This conflict arises because the energy needs of the young peak early in the nestling period, at a time when they still cannot thermoregulate and therefore need brooding from the female. The most critical period is the second nestling week, when both female and nestling fat reserves will decrease to low levels. Large female fat reserves in the early nestling period provide a solution to this conflict and are essential for successful breeding. Stochasticity in male provisioning is thus not needed to explain why females should be fat when the eggs hatch. Under normal circumstances, the female broods during the first two weeks and leaves the young only if hunting is absolutely necessary. After the second week the energy requirements are relaxed, and whether the female assists the male in hunting or not depends on factors such as male hunting success, environmental stochasticity, and energy requirements of the young. Our model provides a framework for empirical investigations on female behaviour during breeding in raptors, owls, and other birds with marked division of labour.
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| 2. |
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| 3. |
- Brodin, Anders, et al.
(författare)
-
Optimal energy allocation and behaviour in female raptorial birds during the nestling period
- 2003
-
Ingår i: Ecoscience. - : University Laval. - 1195-6860. ; 10:2, s. 140-150
-
Tidskriftsartikel (refereegranskat)abstract
- In many raptors and owls the male is the main provider of food in the early phase of the nestling period while the female incubates the eggs and broods the young. In the nestling period the female often helps the male to feed the young, but the factors affecting whether and when she leaves the brood to hunt have not been investigated in detail. We present a dynamic state variable model that analyses female behaviour and fat storage dynamics over the nestling period. The results show that in the first half of the nestling period the female faces a conflict between the need to brood the young and the need to hunt to provision them with food. This conflict arises because the energy needs of the young peak early in the nestling period, at a time when they still cannot thermoregulate and therefore need brooding from the female. The most critical period is the second nestling week, when both female and nestling fat reserves will decrease to low levels. Large female fat reserves in the early nestling period provide a solution to this conflict and are essential for successful breeding. Stochasticity in male provisioning is thus not needed to explain why females should be fat when the eggs hatch. Under normal circumstances, the female broods during the first two weeks and leaves the young only if hunting is absolutely necessary. After the second week the energy requirements are relaxed, and whether the female assists the male in hunting or not depends on factors such as male hunting success, environmental stochasticity, and energy requirements of the young. Our model provides a framework for empirical investigations on female behaviour during breeding in raptors, owls, and other birds with marked division of labour.
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| 4. |
- Frost, Ingela, et al.
(författare)
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Spatial pattern and size distribution of the animal-dispersed tree Quercus robur in two spruce-dominated forests
- 2000
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Ingår i: Ecoscience. - 1195-6860. ; 7:1, s. 38-44
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the degree to which the spatial distribution of oaks (Quercus robur L.) was related to habitat conditions, as reflected by vegetation type and structural features presumed to attract animal dispersers (trails, community borders). We hypothesized that the distribution pattern of oaks, with their potential to establish in many habitats, depends on the behaviour of the dispersing animals to a greater extent than micro-habitat conditions. One 100 m x 100 m plot was surveyed in each of two coniferous forests in east-central Sweden. No adult oak trees grew in the forests; all oaks were considered as dispersed into the plots by animals. We tested whether oak distribution was clumped with spatial autocorrelation analyses and whether oak distribution was related to vegetation type, species composition, tree cover, distance to nearest fertile oak tree, or distance to animal trails. Our study showed that oak trees were also spatially aggregated in a small-scale context. The spatial distribution of seedlings and older trees were associated with species richness and tree cover but not with any specific vegetation type, even though fewer oaks than expected grew in spruce forest habitats. Furthermore, we found that oak trees were associated with trails. There were differences in oak distribution between the two study sites in total number of oaks, the number of first-year seedlings, caches, and oak occurrence in relation to species richness and distance to nearest fertile oak. Seed-dispersing animals seem to be of importance for oak distribution even though animal activities seem to differ between sites.
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| 5. |
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| 6. |
- Jönsson, Ingemar
(författare)
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Life history consequences of fixed costs of reproduction
- 2000
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Ingår i: Écoscience. - 1195-6860. ; 7:4, s. 423-427
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Tidskriftsartikel (refereegranskat)abstract
- The distinction between fixed and variable factors of production and their corresponding costs has: long played a fundamental role in economic theory. However, in analyses of life history evolution a distinction between fixed and variable costs of reproduction has not been made. In this paper. I discuss these concepts and analyze some effects of fixed costs of reproduction on reproductive decisions. While some fitness functions do not allow fixed costs of reproduction to affect optimal reproductive effort, others do. Increasing fixed costs reduces total fitness and increases the level of investment required to obtain a reproductive profit. Increased fixed costs may also narrow the parameter space of reproductive effort for positive profit. These results are discussed in the perspectives of age at maturity and the evolution of semelparity.
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| 7. |
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| 8. |
- Karlsson, Staffan, et al.
(författare)
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Seasonal variation in 15-N natural abundance in subarctic plants of different life-forms
- 2000
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Ingår i: Ecoscience. - 1195-6860. ; 7:3, s. 365-369
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Tidskriftsartikel (refereegranskat)abstract
- Plants can be expected to utilize different sources of nitrogen with different proportions of 15N at different times of the year. It was hypothesized that this may be reflected in a seasonal variation in the natural abundance of plant 15N, and that this pattern would vary among life-forms or species. To test this hypothesis, we studied the δ15N of eight different life-forms, selecting two representatives from each of four categories (woody deciduous, woody evergreen, graminoid, and cryptogam life-forms) at two locations in N. Sweden having different levels of precipitation, over a six-month period. Sampling was conducted in mid-winter, during snowmelt in May, after leaf emergence, in mid-August, and in September. The sampled species showed a highly significant seasonal pattern in the natural abundance of 15N. Within each species and site, the δ15N showed a difference on average of 3.6% (range from 2.1 to 5.3%) between minimum and maximum over the sampling period. In most cases δ15N was highest in mid-winter and lowest at the start of the growing season. Most species studied showed some common trends: (i) a decline in δ15N from mid-winter to pre-snowmelt (May); (ii) an increase from snowmelt to mid-June (mainly in plants sampled at one site); and (iii) a late-season decline in δ15N (August to September). Life-forms differed from each other in terms of their pattern of seasonal variation (harvest×life-form interaction) and between sites (site×life-form interaction). Thus, the outcome of comparisons of natural δ15N within and among species or sites depends on the time of year of sampling.
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| 9. |
- Karlsson, Staffan, et al.
(författare)
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Seedling growth characteristics in three birches originating from different environments
- 2000
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Ingår i: Ecoscience. - 1195-6860. ; 7:1, s. 80-85
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Tidskriftsartikel (refereegranskat)abstract
- The mountain birch (Betula pubescens ssp. czerepanovii) is considered to have originated through introgressive hybridization between B. pubescens and B. nana. It is intermediate between the putative parent species in terms of growth form and distribution. Consequently, we hypothesized that the mountain birch should have growth characteristics intermediate between the other two birch forms. This hypothesis was tested in an experiment using first-year seedlings. Only in three out of 15 characteristics studied were mountain birch characteristics clearly intermediate between B. pubescens and B. nana. In some cases the mountain birch was most similar to B. pubescens, while in others it resembled B. nana most closely. In certain other respects, B. pubescens and B. nana were more similar to each other than to mountain birch. In three measures of plant productivity, i.e. , relative growth rate, leaf area productivity, and plant nitrogen productivity, mountain birch showed the highest values. Cluster analyses of thirteen growth-related characteristics indicate that at a low fertilizer supply, B. pubescens and B. nana are more similar to each other than to the mountain birch. At a high fertilizer supply, mountain birch was more similar to B. pubescens. The results indicate that the growth characteristics of mountain birch seedlings are not inherited from its two ?parent? species in any simple way.
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| 10. |
- Merila, J, et al.
(författare)
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Adaptive phenotypic plasticity in timing of metamorphosis in the common frog Rana temporaria
- 2000
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Ingår i: ECOSCIENCE. - : UNIVERSITE LAVAL. - 1195-6860. ; 7:1, s. 18-24
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Tidskriftsartikel (refereegranskat)abstract
- Unpredictable environments are expected to select for adaptive plasticity in traits enabling adjustment of phenotype to prevailing environmental conditions. Common frogs (Rana temporaria) breed frequently in ponds, which dry up before the aquatic larvae h
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