| 61. |
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| 62. |
- Lacoursière, Jean O., 1958-, et al.
(författare)
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Use of the continuity principle to evaluate water processing rate of suspension-feeding mosquito larvae
- 1999
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Ingår i: Journal of the American Mosquito Control Association. - 8756-971X .- 1943-6270. ; 15:2, s. 228-237
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Tidskriftsartikel (refereegranskat)abstract
- Water processing rates of active suspension-feeding larvae of Culiseta morsitans and Cities quinquefasciatus 2nd and 4th instars were estimated through video image analysis of the conical jet flow driving the large recirculation patterns surrounding the organisms. In accordance with the principle of continuity, individual processing rates (PRs) were assessed by averaging a series of consecutive flow rates (Q(x)) defined as the product of the water velocity (U-x) and the associated cross-sectional area (A(x)) along a transect passing through the center of the delineated jet flow. Results clearly show very tight adherence to the principle of continuity. They also demonstrate that, although extreme care must be taken when streamtube delineation is performed, the methodology used can generate reliable assessment of individual processing rates regardless of the instars or species studied. The small coefficient of variation observed in assessing PR at the larval level further underlines the consistency of the method. Significant differences in water processing rates were observed for different species and instars. These could partially be related to body size, head width, and the length of the lateral palatal brushes (LPBs, which are the structures involved in the production of the water jet. Assessment of the jet velocity at the feeding groove level suggests the keg role of LPB beating frequency in the jet intensity, and consequently the magnitude of the processing rate. Analysis of data further indicates that obligate suspension feeders such as Cs. morsitans must sustain a larger flow pattern around the larvae to ensure sufficient particle entrapment than facultative suspension feeders (or even brushers) such as Cs. quinquefasciatus.
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| 63. |
- Liljebäck, Niklas, et al.
(författare)
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Learning from long time series of harvest and population data : Swedish lessons for European goose management
- 2021
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Ingår i: Wildlife Biology. - : Nordic Council for Wildlife Research (NKV). - 0909-6396 .- 1903-220X. ; 1, s. 1-10
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Recension (refereegranskat)abstract
- Goose management in Europe is faced by multiple challenges, as some species are declining and in need of conservation actions, while other populations have become very abundant, resulting in calls for increased harvest. Sweden has long-term series of harvest data and counts of breeding and autumn-staging geese. We used national data (indices) for greylag goose, bean goose and Canada goose to study shifts in temporal trends and correlative patterns, and to infer possible causal links between harvest and population trends. Our study provides an opportunity to guide management given the data collected within the present monitoring, as well as to suggest improvements for future data collection. The populations of greylag and Canada geese increased in Sweden 1979–2018, but this long-term trend included a recent decrease in the latter species. Bean goose breeding index decreased, whilst staging numbers and harvest varied with no clear long-term trend. For Canada goose, our analysis suggests that harvest may affect population growth negatively. For bean goose and greylag goose we could not detect any effect of harvest on autumn counts the following year. We find that the present data and analysis of coherence may suffice as basis for decisions for the current management situation in Sweden with its rather unspecific goals for greylag (very abundant) and Canada goose (invasive species) populations. However, for management of bean geese, with international concerns of over harvest, data lack crucial information. For future management challenges, with more explicit goals, for all goose species we advocate information that is more precise. Data such as hunting effort, age-structure of goose populations and mark–recapture data to estimate survival and population size, is needed to feed predictive population models guiding future Swedish and European goose management.
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| 64. |
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| 65. |
- Olsson, Camilla, et al.
(författare)
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Field preference of Greylag geese Anser anser during the breeding season
- 2017
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Ingår i: European Journal of Wildlife Research. - 1612-4642 .- 1439-0574. ; 63
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Tidskriftsartikel (refereegranskat)abstract
- Few studies address food preference of geese on agricultural land (utilization related to availability) and only a handful so for the breeding season. We studied Greylag geese Anser anser during the breeding season in an intensively farmed area in southern Sweden. Few of 22 available field types were truly preferred. Pastureland was the most consistently preferred, by goslings (with parents) as well as by nonbreeders. In some sampling periods, goslings also preferred grazed hay, ley, and carrot fields. Non-breeders exploited a greater variety of crops/fields, feeding also on barley, fallow, grazed hay, lettuce, oats, potatoes, and carrots. Most of these crops were preferred on at least one sampling occasion, except for fallow, grazed hay, and wheat, which were always used less than expected from availability. GLMs revealed that goslings rested more than they fed and preferred shorter vegetation before higher. Moreover, goslings occurred in higher densities in younger age classes than in older and preferred nearshore areas. In contrast, density of non-breeders was only related to field type and sampling occasion (higher densities as the season progressed). The maximum number of broods observed (106) implies a breeding success of 34% based on311 active nests earlier in the season. Brood size decreased from 3.5 to 2.1 during the study period. Our study shows that goose management during the breeding season should consider goslings and their parents separately from non-breeders, and it implies little potential conflict between Greylag geese and agriculture during the breeding period.
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| 66. |
- Olsson, Camilla, 1991-, et al.
(författare)
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Long-distance and local movements of greylag geese in present-day agricultural landscapes
- 2018
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Ingår i: 18th Conference of Goose Specialist Group. - : Marine Institute of Klaipeda University. - 9789955189794 ; , s. 77-
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Konferensbidrag (refereegranskat)abstract
- Recent changes in environmental conditions together with increasing goose populations have completely changed the ballgame for geese in Europe. To better understand their current distribution and foraging patterns, this project will explore how geese utilize the agricultural landscape, with focus on their movements, field selection and foraging patterns. We fitted 199 Greylag geese with neck-collars and 64 with GPS transmitters at 5 locations in Sweden. The tagged geese will be used for studying movement patterns at a field-tofield level. However, the GPS transmitters also deliver data that can be used together with re-sightnings of neck-collared geese to unravel large-scale movement patterns of the Swedish Greylag goose population. Preliminary results from GPS positions received June--November 2017 indicate a varation in migration patterns and wintering grounds, depending on the origin of the geese. Geese breeding and molting in the southern parts of Sweden seem to migrate shorter distances, and have spent most of their time during the autumn months in Denmark, or in the southernmost parts of Sweden, while the geese marked farther north migrated earlier and moved longer distances, with the majority spending the autumn in Germany and the Netherlands.
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| 67. |
- Petersen, Robert C., et al.
(författare)
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Influence of velocity and food availability on catchnet dimensions of Neureclipsis bimaculata (Trichoptera: Polycentropodidae)
- 1984
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Ingår i: Holarctic Ecology. - 0105-9327. ; 7:4, s. 380-389
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Tidskriftsartikel (refereegranskat)abstract
- Larvae of Neureclipsis bimaculata (Trichoptera: Polycentropodidae) construct elaborate catchnets in lotic habitats to trap small drifting invertebrate prey. Three populations located at two oligotrophic and one eutrophic site were studied in southern Sweden. Measurements were made of larval weight, net size, seston quality and quantity, and stream velocity.Neureclipsis larvae alter their net dimensions in response to both velocity and seston concentration. This was determined by comparing net structure and seston at the three locations. Larvae from the eutrophic, high quality seston site attain a significantly (P < 0.001) heavier instar V dry weight, spin a smaller catchnet, filter a volume of water dependent on body size, and slightly alter their catchnet dimensions with velocity. Larvae from the two oligothrophic sites are significantly smaller than those from the eutrophic site, spin a larger net at comparable velocities, filter a larger volume of water at comparable weights, and alter net dimensions with velocity.Estimates of silk production indicate that the net cost is minimized by spinning a very fine silken strand and by adding silk over a period of time. The cost while large is offset by a large capture rate of prey.The structure of Neureclipsis nets appears to be the result of a trade-off between maximizing food capture and minimizing hydraulic stress on the net.
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| 68. |
- Pöysä, Hannu, et al.
(författare)
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Changes in species richness and composition of boreal waterbird communities : a comparison between two time periods 25 years apart
- 2019
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Ingår i: Scientific Reports. - : Nature Publishing Group: Open Access Journals - Option C / Nature Publishing Group. - 2045-2322. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Global measures of biodiversity indicate consistent decline, but trends reported for local communitiesare more varied. Therefore, we need better understanding of mechanisms that drive changes in diversity of local communities and of differences in temporal trends between components of local diversity, such as species richness and species turnover rate. Freshwater ecosystems are vulnerable to multiple stressors, and severe impacts on their biodiversity have been documented. We studied species richness and composition of local boreal waterbird communities in 1990/1991 and 2016 at 58 lakes distributed over six regions in Finland and Sweden. The study lakes represented not only local trophic gradients but also a latitudinal gradient in the boreal biome. While species richness tended to be lower in 2016 than in 1990/1991, species turnover was relatively high. Within foraging guilds, local species richness of diving ducks and surface feeding waterbirds decreased, whereas that of large herbivores increased. The number of species gained in local communities was higher in lakes with rich vegetation than in lakes with sparse vegetation. Conservation of boreal freshwater ecosystems would benefit from recognizing hat large-scale environmental changes can affect local diversity via processes operating atfiner scales.
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| 69. |
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| 70. |
- Sjöberg, Kjell, et al.
(författare)
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Born to cope with climate change? : experimentally manipulated hatching time does not affect duckling survival in the mallard Anas platyrhynchos
- 2011
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Ingår i: European Journal of Wildlife Research. - 1612-4642 .- 1439-0574. ; 57:3, s. 505-516
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Tidskriftsartikel (refereegranskat)abstract
- Two main hypotheses proposed to explain the seasonal decline in reproductive performance in birds are (1) deterioration of environmental conditions and (2) lower parental quality of late breeders. Previous experimental work addressing these hypotheses generally have problematic biases pertaining to delay of hatching, costs of re-laying and incubation, as well as variation in the quality of eggs, territories, offspring and parental traits. We address these biases in an experimental test of the timing hypothesis (i.e. (1) above) in a precocial bird. Using a 2-year cross-over design and game-farm mallard (Anas platyrhynchos) eggs originating from a number of hens and a standardised delay procedure, we introduced early and late broods with a foster female onto boreal oligotrophic lakes and monitored subsequent duckling survival. Standardised invertebrate sampling was done concurrently to get a measure of lake-level abundance of aquatic prey, a likely causative agent of putative seasonal difference in duckling survival. Survival data and covariates (duckling age; days) were analysed by an information theoretic approach. There was no effect of treatment (i.e. manipulation of hatching date) on duckling survival, which was higher in 2005 than in 2004. In contrast to observational studies from more seasonal wetlands, our experiment demonstrates that duckling survival on boreal lakes was not affected by a 12-day delay in hatching date. Since we did not find any consistent trends in abundance of aquatic prey, i.e. neither clear peaks nor differences between treatment periods, we hypothesise that moderate climate change has minor effects on resource abundance and hence also on mallard duckling survival in boreal environments.
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