| 21. |
- Clausen, P, et al.
(författare)
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Energy limitations for spring migration and breeding: the case of brent geese Branta bernicla tracked by satellite telemetry to Svalbard and Greenland
- 2003
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 103:2, s. 426-445
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Konferensbidrag (refereegranskat)abstract
- Brent geese were tracked by satellite telemetry from spring staging areas in Denmark to Arctic breeding areas in Svalbard and Greenland in 1997 and 2001. From estimated departure masses and carcass analysis we used flight mechnical theory to estimate maximum flight ranges of both sexes, and remaining stores of fat and protein upon arrival in females. Model predictions suggested that all birds but one exceptionally thin male could easily reach Svalbard, but that approximately one third of the males and half of the females would have problems with flying to Greenland. Nevertheless, some birds even flew longer than the models predicted. In addition, females predicted to be capable of making the flight to Greenland, were predicted to arrive almost lean of fat. This contradicts our expectation that these birds are capital breeders - that they depend on endogenous stores of fat and protein when initiating and incubating their eggs. We discuss how the Greenland breeding sub-population during 1985-1998 has been able to grow at the same rate as the sub-population breeding in Svalbard, despite the added flight distance of 700-1000 km, and despite the birds predicted shortage of fat stores on arrival. We suggest four hypotheses that alone or in combination could explain the discrepancy between model predictions and observations. These are that most birds: (1) refuel on stop-overs in Spitsbergen en route to Greenland; (2) pick favourable tail-winds enabling them to reduce flight costs; (3) fly in formation and thereby save energy; and/or (4) undergo gut atrophy immediately prior to departure, and use the nutrients mobilised by catabolism of the digestive system to build larger pectoral muscles. The latter option would both reduce their airframe fraction, and increase their fat and flight-muscle fractions, enabling them to fly longer. We conclude that the latter option seems less likely to operate in brent geese.
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| 22. |
- Drent, R, et al.
(författare)
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Pay-offs and penalties of competing migratory schedules
- 2003
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 274-292
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Tidskriftsartikel (refereegranskat)abstract
- We relate variation in the timing of arrival by migrating birds breeding at northerly latitudes to individual differences in the prior accumulation of energy stores. Balancing starvation risks early in the season against the almost universal declining trend in reproductive prospects with advancing date is seen as an individual decision with fitness consequences. We review three studies implicating events at the staging sites or in winter in setting the individual migratory schedule. Climate change influences the timetable of a pied flycatcher (Ficedula hypoleuca) population breeding in The Netherlands and wintering in West Africa, followed since 1960. Mean air temperature in the period mid April-mid May (arrival and laying) increased and laying date advanced by 10 days. Still, in recent years most birds did not lay early enough to maximise fitness (determined by recruitment and parental survival) whereas many parents achieved this goal in 1980-1985. As the flycatchers have not started to arrive earlier, some ecological constraint further upstream is postulated (possibly the hurdle of the crossing of Sahara and Mediterranean). The ability to follow individual migrants provides a second avenue to assess the fitness implications of migratory schedules. Thus, brightly coloured male bar-tailed godwits (Limosa lapponica) captured in the Dutch Wadden Sea (the intermediate staging site linking a West African wintering area with breeding sites in arctic Russia) and traced with miniature radio-transmitters did not depart early. The 'best' males (with bright breeding plumage) were picked up by the listening stations in Sweden 650 km further along the migratory route ten days later than the paler individuals. If early arrival confers the competitive advantage of prior occupancy but increases mortality, the 'best' males may be able to afford arriving later and thus avoid some of the survival costs. Return rate of the 'bright' males to the staging site in later seasons was indeed higher than for the 'pale', early males. Intensive observation of pink-footed geese (Anser brachyrhynchus) fitted with coded neck-collars substantiate the tight relationship between energy stores (fat) accumulated up to final departure from the final staging site (Vesteralen, N. Norway) en route to the nesting grounds (Spitsbergen) and subsequent success. The breeding outcome of individual parents (accompanied by juveniles or not) could be related to observations of body condition before departure (visual 'abdominal profile index'). Recently, perceived conflicts with agriculture have resulted in widespread harassment by humans. The geese have: drastically shortened their stay on the Vesteralen, fail to achieve the body condition usual a decade ago and reproductive output has fallen. Although the geese are currently pioneering new staging sites, an adequate alternative has not materialised, underlining the critical role of the final take-off site.
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| 23. |
- Dänhardt, Juliana, et al.
(författare)
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Farmland as stopover habitat for migrating birds - effects of organic farming and landscape structure
- 2010
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 119:7, s. 1114-1125
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Tidskriftsartikel (refereegranskat)abstract
- Agricultural intensification in Europe has affected farmland bird populations negatively, both during summer and winter. Although the migratory period poses separate challenges on birds than breeding and wintering, the consequences of farming practices for birds during migration remain poorly investigated. We monitored abundance and species richness of migratory birds in autumn at matched pairs of organic and conventional farms situated either in intensively farmed open plains (homogeneous landscapes) or in small-scale farming landscapes (heterogeneous landscapes) in southern Sweden. Total bird density did not differ between landscape types but was marginally higher on organic compared to conventional farms. When including taxonomic status in the model (passerines vs non-passerines), we found significantly more birds on organic farms, and more non-passerines in the homogeneous landscapes. The effect of farming practice and landscape type on density differed between functional groups. Omnivore density was higher in the homogeneous landscapes, and invertebrate feeders were marginally more abundant on organic farms. The effects of farming practice on the overall species richness and on the density of granivorous birds were landscape dependent. In the homogeneous landscapes, organic farms held a higher number of species and density of granivorous birds than conventional farms, but there was no such difference in the heterogeneous landscapes. Thus, organic farming can enhance abundance and species richness of farmland birds during migration, but the effect differs between landscape types and species. The effectiveness of organic farming was highest in the homogeneous landscape making it important to promote organic farming there. However, for some species during migration, increased heterogeneity in homogeneous landscapes may have negative effects. We propose that migratory bird diversity in homogeneous landscapes may be best preserved by keeping the landscape open, but that a reduced agricultural intensity, such as organic farming, should be encouraged.
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| 24. |
- Griffiths, B S, et al.
(författare)
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Ecosystem response of pasture soil communities to fumigation-induced microbial diversity reductions: an examination of the biodiversity-ecosystem function relationship
- 2000
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 90:2, s. 279-294
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Tidskriftsartikel (refereegranskat)abstract
- A technique based on progressive fumigation was used to reduce soil microbial biodiversity, and the effects of such reductions upon the stability of key soil processes were measured. Mineral soil samples from a grassland were fumigated with chloroform for up to 24 h and then incubated for 5 months to allow recolonisation by surviving organisms. The diversity of cultivable and non-cultivable bacteria, protozoa and nematodes was progressively reduced by increasing fumigation times, as was the number of trophic groups, phyla within trophic groups, and taxa within phyla. Total microbial biomass was similar within fumigated soils, but lower than for unfumigated soil. There was no direct relationship between biodiversity and function. Some broad-scale functional parameters increased as biodiversity decreased, e.g. thymidine incorporation, growth on added nutrients, and the decomposition rate of plant residues. Other more specific parameters decreased as biodiversity decreased, e.g. nitrification, denitrification and methane oxidation. Thus specific Functional parameters may be a more sensitive indicator of environmental change than general parameters. Although fumigation reduced soil microbial biodiversity, there was evidence to suggest that it selected for organisms with particular physiological characteristics. The consequences of this for interpreting biodiversity - function relationships are discussed. The stability of the resulting communities to perturbation was further examined by imposing a transient (brief healing to 40 degrees C) or a persistent (addition of CuSO4) stress. Decomposition of grass residues was determined on three occasions after such perturbations. The soils clearly demonstrated resilience to the transient stress; decomposition rates were initially depressed by the stress and recovered over time. Resilience was reduced in the soils with decreasing biodiversity. Soils were not resilient to the persistent stress, there was no recovery in decomposition rate over time, but the soils with the highest biodiversity were more resistant to the stress than soils with impaired biodiversity. The study of functional stability under applied perturbation is a powerful means of examining the effects of biodiversity.
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| 25. |
- Hagberg, Jacob, et al.
(författare)
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Uncertain biotic and abiotic interactions in benthic communities
- 2003
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 100:2, s. 353-361
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Tidskriftsartikel (refereegranskat)abstract
- We analyze marine benthic communities at different sites in Skagerrak with the purpose of understanding the role of exogenous and endogenous factors in explaining the species' temporal dynamics. The previous finding that the dynamics of these species communities are mainly driven and synchronized by environmental (temperature) forcing was only weakly supported when analyzing single-species dynamics at five sites where four of the species were present every year. There was no consistent pattern in how the temperature affected the realized per capita growth rate, either across species at a given site, or among sites for a given species. Furthermore, there was no net-interaction from the community on a given species strong enough to give rise to second-order dynamics. However, when implementing a Multi Dimensional Scaling (MDS) analysis and incorporating all sampling sites and species -we found that the different communities clustered in relation to depth, hence, communities at the same depth were more "similar" than communities at different depth. Revealing the underlying interactions shaping these marine benthic communities is a challenge that calls for an array of various and complementary approaches.
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| 26. |
- Hake, M, et al.
(författare)
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Age-dependent migration strategy in honey buzzards Pernis apivorus tracked by satellite
- 2003
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 385-396
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Tidskriftsartikel (refereegranskat)abstract
- Six adult and three juvenile honey buzzards Pernis apivorus were radio-tracked by satellite during autumn migration from southwestern Sweden. All adults crossed the Mediterranean Sea at the Strait of Gibraltar and continued across the Sahara desert to winter in West Africa, from Sierra Leone to Cameroon. Analysing three main steps of the migration, (1) from the breeding site to the southern Mediterranean region, (2) across the Sahara and (3) from the southern Sahara to the wintering sites, the adults changed direction significantly between these steps, and migrated along a distinct large-scale detour. In contrast, the juveniles travelled in more southerly directions, crossed the Mediterranean Sea at various places, but still ended up in the same wintering areas as the adults. Average speeds maintained on travelling days were similar for the two age groups, about 170 km/day in Europe, 270 km/day across Sahara and 125 km/day in Africa south of Sahara. However, as the adults used fewer stopover days en route, they maintained higher mean overall speeds and completed migration in a shorter time (42 days) than the juveniles (64 days). Although the juveniles set out on more direct courses towards the wintering grounds, they did not cover significantly shorter distances than the adults, as they tended to show a larger directional scatter between shorter flight segments. The results corroborate previous suggestions that adult and juvenile honey buzzards follow different routes during autumn migration, and that the birds change migration strategy during their lifetime. While juveniles may use individual vector orientation, social influences and learning may be of great importance for the detour migration of adults. The remarkable and distinct age-dependent shift in migratory route and orientation of the honey buzzard provides a challenging evolutionary problem.
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| 27. |
- Hansson, Bengt, et al.
(författare)
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The quality and the timing hypotheses evaluated using data on great reed warblers
- 2000
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 90:3, s. 575-581
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Tidskriftsartikel (refereegranskat)abstract
- The seasonal decline in reproductive success observed in many animal species may be caused by timing per se (timing hypothesis) or by variation in phenotypic quality between early and late breeding females (quality hypothesis). To distinguish between these two hypotheses, several studies of birds have used clutch removal experiments to manipulate breeding date. However; removal experiments also increase the females' previous reproductive effort due to the production of an extra clutch and a longer incubation period. According to life-history theory an increase in reproductive effort lowers future reproduction. Hence, life-history theory predicts lowered success of replacement broods for other reasons than expected from the timing hypothesis. Female great reed warblers, Acrocephalus ni arundinaceus, studied in Sweden are frequently exposed to nest predation, after which many lay replacement clutches. In order to examine possible effects of previous reproductive effort on different fitness components, we analysed the re-laying frequency and the reproductive success of replacement broods in relation to time of the season and previous reproductive effort (measured as the length of the previous breeding attempt, LPB). In clutches of re-laying females both the number of fledglings and the proportion of recruits were negatively correlated with LPB, whereas re-laying frequency and clutch size were not related to LPB. We expect such relationships to be present also among other species. Consequently, the use of replacement clutches, as for example in clutch removal experiments, in evaluations of the cause of the often observed seasonal decline in various fitness components, might exaggerate the importance of the timing hypothesis over the quality hypothesis.
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| 28. |
- Hargeby, Anders, et al.
(författare)
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Does a long-term oscillation in nitrogen concentration reflect climate impact on submerged vegetation and vulnerability to state shifts in a shallow lake?
- 2006
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 115:2, s. 334-348
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Tidskriftsartikel (refereegranskat)abstract
- Various ecosystems, including shallow lakes, are suggested to possess alternative stable state dynamics. The response of such systems to environmental change is non-linear and not fully reversible, which calls for identification of feedback mechanisms and subtle changes connected to structural stability. Here, we used a 25-year data series on water chemistry to make inferences on processes prior to a recent shift from a clear to a turbid state in Lake Takern, Sweden. Before the shift, annual concentration of total organic nitrogen (TON) described a cyclic pattern, with a periodicity of eight years. Annual TON was negatively correlated with the magnitude of a summer decline in calcium carbonate, treated as a proxy of the seasonal production of submerged vegetation. Cross-correlations of TON and the north Atlantic oscillation (NAO) indicated a possible connection to climate. The strongest correlation was obtained by a three-year lag of the NAO index. Using a set of linear time series models, the most parsimonious model was a 3(rd) order autoregressive model with NAO, delayed three years, as a covariate. Analyses of seasonality indicated that the delayed NAO signal was strongly correlated with summer TON. Also, the autocorrelation function was very similar for these two time series, and autoregressive models including NAO as a covariate were strongly supported (sum of Akaike weights = 0.93). These results indicate that climate may have contributed to the regime shift through lowered macrophyte production at the time of the shift, and therefore most likely also a depleted resilience of the clear water state. The delayed effect of climate is suggested to result from indirect and inter-year dependent response of submerged vegetation to fish kills during harsh winters.
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| 29. |
- Harris, Sanna, et al.
(författare)
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Picking personalities apart: estimating the influence of predation, sex and body size on boldness in the guppy Poecilia reticulata
- 2010
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 119:11, s. 1711-1718
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Tidskriftsartikel (refereegranskat)abstract
- Predation is a strong selective force in most natural systems, potentially fueling evolutionary changes in prey morphology, life history and behaviour. Recent work has suggested that contrasting predation pressures may lead to population differentiation in personality traits. However, there are indications that these personality traits also differ between sexes and not necessarily in a consistent way between populations. We used an integrative approach to quantify boldness (latency to emerge from a shelter) in wild-caught guppies in relation to predation pressure, population origin, sex and size. In addition we quantified the repeatability of these personality traits. We show that predation regime had significant effects on emergence time. In general, fish from high predation localities emerged sooner from the shelter compared to those from low predation localities. We found strong sex differences; males were significantly bolder than females. The relationship between emergence time and body size was non-significant in all populations. We discuss what responses to expect from predator-nave versus predator-experienced individuals and how this can be linked to the shyness-boldness continuum.
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| 30. |
- Haubert, Dominique, et al.
(författare)
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Trophic structure and major trophic links in conventional vs organic farming systems as indicated by carbon stable isotope ratios of fatty acids
- 2009
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 118:10, s. 1579-1589
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Tidskriftsartikel (refereegranskat)abstract
- Using bulk tissue and fatty acid 13C analysis we investigated major trophic pathways from soil microorganisms to microbial consumers to predators in conventional versus organic farming systems planted for the first time with maize. Organic farming led to an increase in microbial biomass in particular that of fungi as indicated by phospholipid fatty acids (PLFAs). Microbial PLFAs reflected the conversion from C3 to C4 plants by a shift in δ13C of 2‰, whereas the isotopic signal in fatty acids (FAs) of Collembola was much more pronounced. In the euedaphic Protaphorura fimata the δ13C values in maize fields exceeded that in C3 (soybean) fields by up to 10‰, indicating a close relationship between diet and vegetation cover. In the epedaphic Orchesella villosaδ13C values shifted by 4‰, suggesting a wider food spectrum including carbon of former C3 crop residues. Differences in δ13C of corresponding FAs in consumers and resources were assessed to assign food web links. P. fimata was suggested as root and fungal feeder in soybean fields, fungal feeder in conventional and leaf consumer in organically managed maize fields. O. villosa likely fed on root and bacteria under soybean, and bacteria and fungi under maize. Comparison of δ13C values in FAs of the cursorial spider Pardosaagrestis and O. villosa implied the latter as important prey species in soybean fields. In contrast, the web-building spider Mangora acalypha showed no predator–prey relationship with Collembola. The determination of δ13C values in trophic biomarker FAs allowed detailed insight into the structure of the decomposer food web and identified diet-shifts in both consumers at the base of the food web and in top predators in organic versus conventional agricultural systems. The results indicate changes in major trophic links and therefore carbon flux through the food web by conversion of conventional into organic farming systems.
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