| 1. |
- Andersson, Arne, et al.
(författare)
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Ottenby fågelstation : Årsrapport 1999
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Decenniets, seklets och milleniets sista år blev ett år av stora förändringar vid Ottenby fågelstation. Deföregående tre-fyra åren hade präglats av mycket dålig ekonomi och därtill personalproblem. Under 1998blev situationen akut. Som ett första led i att förbättra situationen ombildades Ottenbykommittén (avSveriges Ornitologiska Förening satt att sköta fågelstationen) under hösten 1998. Den störstaförändringen blev sedan att Jan Pettersson, platschef sedan 1978, sades upp. Därtill kom uppsägning,pensionering, dödsfall (se nedan) och sedan tidigare överflyttade tjänster till OFAB, vilket innebar detatt den “fast” anställda personalstyrkan, som 1992 var 7 personer, reducerades till noll!Ottenbykommittén har nu fått en mycket mer aktiv roll i stationens arbete. Olika verksamhetsdelar haridentifierats och ledamöterna har getts olika ansvarsområden.Kommittén bestod under året av :Åke Lindström (ordförande)Christian Hjort (sekreterare, utlandsverksamheten)Dennis Kraft (ekonomi)Arne Andersson (datafrågor)Dennis Hasselquist (samordning av ansökningar)Anders Hedenström (forskningssamordnare)Niclas Jonzén (personal)Lars Lindell (SOF:s styrelse).Aktiviteterna inom dessa olika områden redovisas nedan och här skallbara de generella linjerna i arbetet läggas fram.Tvivelsutan förbättrades arbetsklimatet för den ideellt arbetandepersonalen på fågelstationen och glädjande nog var tillströmningen storav arbetsvilliga ungdomar. Stationen blev på många sätt öppnare, inteminst mot fågelskådarleden. Fler personer besökte stationen och pådetta sätt kan många fler känna sig delaktiga och trivas. Nackdelen äratt det rent praktiskt blir svårare att driva verksamheten med mångamänniskor närvarande och relativt stor omsättning på personer.Genom mycket hård åtstramning på utgiftssidan kunde ett förväntat rejält underskott i budgeten vändastill en liten vinst. Alla inblandade skall ha stor ära av detta eftersom både stora som små uppoffringarkrävts för att styra ekonomin rätt. Den lilla vinsten användes till att börja täcka det underskott somunder många år ackumulerats. Även om det nu känns som att vi har en god kontroll över den löpandeekonomin så måste vi på lång sikt hitta fler finansieringskällor till stationens verksamhet. Det är tillexempel mycket otillfredsställande att vi nu inte har någon heltidsanställd personal, något som på siktmåste lösas.Fågelstationens gamla dröm om att ha en egen filial söder om Sahara gick i uppfyllelse under 1999 meden månads försöksverksamhet i Nigeria under våren. Denna slog väl ut på alla sätt och verksamhetenskall nu intensifieras under 2000.Datahanteringen fick sig en rejäl skjuts framåt under året och kan vi bara snart förnya maskinparken finnsgrunden för en smidig och effektiv datahantering vid stationen. Detta kommer att underlätta bådeutåtriktad verksamhet (Internet) och eget analysarbete.Ottenby Försäljnings AB (OFAB), som drivit den affärsmässiga delen av stationens verksamhet sedan1995, fortsatte sin verksamhet parallellt med fågelstationens ideella verksamhet. Genom verksamheten iNaturum och restaurang Fågel Blå svarar OFAB för en viktig del av fågelstationens publika aktiviteter.Det är av stor vikt för framtiden att behålla och utveckla det goda samarbetet mellan fågelstationen ochOFAB.Figur 1. Åke LindströmFigur 2. Patrik Rhönnstad, platschef 1999Kontinuiteten i det praktiska arbetet på stationen blev naturligtvis något lidande av att den rutineradepersonalen försvunnit. Situationen hjälptes dock upp signifikant av att OFABs personal fanns på plats(Håkan och Annika Lundkvist, Gösta Friberg) samt att nye platschefen och många av de ideelltarbetande hade erfarenhet från tidigare år.
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| 2. |
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| 3. |
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| 4. |
- Bensch, Staffan, et al.
(författare)
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Temporal dynamics and diversity of avian malaria parasites in a single host species
- 2007
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Ingår i: Journal of Animal Ecology. - : Wiley. - 1365-2656 .- 0021-8790. ; 76:1, s. 112-122
-
Tidskriftsartikel (refereegranskat)abstract
- We have used molecular methods to unravel a remarkable diversity of parasite lineages in a long-term population study of great reed warblers Acrocephalus arundinaceus that was not foreseen from traditional microscopic examination of blood smears. This diversity includes eight Haemoproteus and 10 Plasmodium lineages of which most probably represent good biological species.Contrary to expectation, the relative frequency of parasite lineages seemed not to change over the 17-year study period and we found no effects of the parasites on a male secondary sexual ornament (song repertoire size) and two measures of fitness (adult survival and production of recruited offspring).We discuss whether the absence of fitness consequences of the parasites might relate to the fact that we have studied the host at the breeding sites in Europe, whereas the transmission seems to take place at the wintering sites in Africa, where the naive birds encounter the parasites for the first time and the resulting primary infections likely make them sicker than during the chronic phase of the infection.The prevalence of the three most common lineages appeared to fluctuate in parallel with a periodicity of approximately 3-4 years. Theoretical models based on intrinsic interactions between parasite antigen and host immune genes cannot explain such dynamics, suggesting that knowledge of extrinsic parameters such as vector distribution and alternative hosts are required to understand these patterns.
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| 5. |
- Gunnarsson, Gunnar, 1976-, et al.
(författare)
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Survival estimates, mortality patterns, and population growth of Fennoscandian mallards Anas platyrhynchos
- 2008
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Ingår i: Annales Zoologici Fennici. - 0003-455X .- 1797-2450. ; 45:6, s. 483-495
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Tidskriftsartikel (refereegranskat)abstract
- Long-term mallard capture-recapture data from Sweden and Finland were analyzed to describe temporal mortality patterns and reasons. We used program MARK and Seber models to estimate annual survival (S) and recovery (r) rates. Survival rates were used in a Monte Carlo simulation to evaluate the correspondence between observed and predicted annual population sizes of a Finnish sub-population. About 90% of recovered birds died from hunting. Most recoveries were from the hunting season, and more males than females were shot. Predation was the most common cause of natural mortality. Finnish capture-recapture data fitted best the global model in which survival and recovery vary with age and sex. Annual survival and recovery rates for adult and juvenile males and females were overlapping, ranging from 0.46 to 0.90 (survival) and 0.07 to 0.17 (recovery), whereas pulli had lower survival rates (0.21-0.42). Pulli that were successfully sexed at the time of ringing had higher recovery rates (female pulli: 0.23; male pulli: 0.32) than juveniles and adults. Density-dependent fledgling production was detected in the Finnish sub-population and was accounted for in the Monte Carlo simulation, which estimated predicted breeding population size quite well, although one of the observed annual values (2003) fell outside the 95% confidence limits.
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| 6. |
- Gunnarsson, Gunnar, et al.
(författare)
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Survival estimates, mortality patterns, and population growth of Fennoscandian mallards Anas platyrhynchos
- 2008
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Ingår i: Annales Zoologici Fennici. - : Finnish Zoological and Botanical Publishing Board. - 0003-455X. ; 45:6, s. 483-495
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Tidskriftsartikel (refereegranskat)abstract
- Long-term mallard capture-recapture data from Sweden and Finland were analyzed to describe temporal mortality patterns and reasons. We used program MARK and Seber models to estimate annual survival (S) and recovery (r) rates. Survival rates were used in a Monte Carlo simulation to evaluate the correspondence between observed and predicted annual population sizes of a Finnish sub-population. About 90% of recovered birds died from hunting. Most recoveries were from the hunting season, and more males than females were shot. Predation was the most common cause of natural mortality. Finnish capture-recapture data fitted best the global model in which survival and recovery vary with age and sex. Annual survival and recovery rates for adult and juvenile males and females were overlapping, ranging from 0.46 to 0.90 (survival) and 0.07 to 0.17 (recovery), whereas pulli had lower survival rates (0.21-0.42). Pulli that were successfully sexed at the time of ringing had higher recovery rates (female pulli: 0.23; male pulli: 0.32) than juveniles and adults. Density-dependent fledgling production was detected in the Finnish sub-population and was accounted for in the Monte Carlo simulation, which estimated predicted breeding population size quite well, although one of the observed annual values (2003) fell outside the 95% confidence limits.
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| 7. |
- Gårdmark, Anna, et al.
(författare)
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Density-dependent body growth reduces the potential of marine reserves to enhance yields
- 2006
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Ingår i: Journal of Applied Ecology. - : Wiley. - 1365-2664 .- 0021-8901. ; 43:1, s. 61-69
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Tidskriftsartikel (refereegranskat)abstract
- 1. Some models of marine no-take reserves predict that reserves can enhance fishery yield. However, empirical evidence of this remains inconclusive. One reason for this may be the disregard for density-dependent body growth in most models. Density-dependent body growth links the number and size of individuals, and thus could influence the biomass of fishery yield. 2. We developed an age- and size-structured model of an exploited population and analysed the effect of implementing a no-take reserve of varying size. 3. Protecting part of a population from exploitation in a no-take reserve results in a rapid build-up of biomass inside the reserve because of increased survival. However, when body growth is density-dependent it also results in reduced length at a given age within the no-take reserve because of crowding effects. This prediction is backed up by empirical observations. 4. If there is export of individuals (here larvae) from the no-take reserve, length at a given age will also decrease in the fished part of the population outside the reserve. An increase in the number of exploitable individuals thus results in decreased individual body mass. The positive effect of larval drift on fished population size and catch numbers will therefore rarely translate into an increase in equilibrium yield biomass. 5. Synthesis and applications. When body growth is density-dependent, implementation of no-take reserves affects the body size of both protected and exploitable individuals. Although reserves can have several benefits besides increasing yields, our study shows that, if density-dependent somatic effects are important, a general increase in yield biomass cannot be expected. In populations with density-dependent body growth, reserves are more likely to decrease yield biomass unless the population is severely overexploited. Analyses of the efficiency of marine reserves as a means of enhancing the yield of fisheries need to account for ecological processes, and density-dependent body growth is likely to be key.
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| 8. |
- 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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| 9. |
- 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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| 10. |
- Hedenström, Anders, et al.
(författare)
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Migration speed and scheduling of annual events by migrating birds in relation to climate change
- 2007
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Ingår i: Climate Research. - : Inter-Research Science Center. - 1616-1572 .- 0936-577X. ; 35:1-2, s. 79-91
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Tidskriftsartikel (refereegranskat)abstract
- Empirical evidence for changed timing of migration in birds is emerging from both American and Euro-African migration systems. These changes are usually interpreted as a consequence of changes in climate. Responses in timing of migration and breeding may differ among species, and the adaptive significance is not well understood. There is a lack of theoretical understanding about time-shifts in life-history events due to climatic changes. In the present paper, we use 2 separate modelling approaches to investigate the effects of climate change on migration. We first use a simple model of flight speed and foraging to explore which factors may influence migration speed and stopover itinerary. Our second approach derives predictions based on an annual routine model, where behavioural strategies regarding timing of migration, breeding, moult and number of breeding attempts are modelled in an environment comprising 4 locations (breeding and wintering sites and 2 stopover sites). This approach takes account of interrelationships between behaviours and seasons as a step towards realistic modelling of migratory connectivity. Departure from the wintering site is advanced in relation to the advancement of spring if the moult is in summer, but not so for species with a winter moult, while arrival at the breeding site is advanced for both moult scenarios. Timing of breeding and number of successful broods were also affected by spring advancement, while start of moult is relatively unaffected by climate change. These optimal solutions under the modelled set of parameters are discussed with respect to current knowledge of the mechanisms underlying seasonal timing in birds.
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| 11. |
- Jiguet, Frederic, et al.
(författare)
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Current population trends mirror forecasted changes in climatic suitability for Swedish breeding birds
- 2013
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Ingår i: Bird Study. - : Informa UK Limited. - 0006-3657 .- 1944-6705. ; 60:1, s. 60-66
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Tidskriftsartikel (refereegranskat)abstract
- Capsule Swedish breeding bird species that are predicted to experience a more suitable climate by 2050 are currently increasing in numbers. Aims To test, for a large set of breeding birds, if recent population trends mirror the changes in predicted climatic suitability across the Swedish distribution range, and to test if considering natal dispersal improves the fit of the predictive models. Methods Recent decadal population trends of 131 species of birds breeding in Sweden were compared to forecasted change in their future national distribution range by 2050, as simulated by suitability distribution models using climate and natal dispersal scenarios. Two other potential predictors of recent demographic trends are controlled for - namely habitat specialization and generation time. Results The 1998-2009 population trends were positively correlated with predicted changes in distribution range. Thus, forecasted changes in climatic suitability predict recent population trends. Accounting for the species-specific natal dispersal provided only a slightly better fit. Conclusion Recent climate change has affected the population size of Swedish breeding birds. Climatic suitability models can be an efficient tool for predicting the impacts of climate change on the abundance of birds.
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| 12. |
- Johansson, Jacob, et al.
(författare)
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Adaptation of reproductive phenology to climate change with ecological feedback via dominance hierarchies.
- 2014
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Ingår i: Journal of Animal Ecology. - : Wiley. - 1365-2656 .- 0021-8790. ; 83:2, s. 440-449
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Tidskriftsartikel (refereegranskat)abstract
- Phenological shifts belong to the most commonly observed biological responses to recent climate change. It is, however, often unclear how these shifts are linked to demography and competitive interactions. We develop an eco-evolutionary model to study adaptation of timing of reproduction in organisms with social dominance hierarchies. We focus on residential birds with winter flocks, where success in competition for territories among offspring depends on ranking given by prior residence. We study the effects of environmental change on breeding population densities, ensuing selection pressures and long-term evolutionary equilibria. We consider changes in food peak date, in winter survival, in total reproductive output and in the width of the food distribution. We show that the evolutionarily stable hatching date will advance with increasing winter survival and reproductive output since these parameters increase habitat saturation and post-fledging competition. Increasing the length of the breeding season also selects for earlier hatching date due to the reduced costs for producing offspring with high ranking. Our analysis shows that there is little correlation between short-term and long-term population responses across different scenarios of environmental change. However, short-term population growth consistently predicts selection for earlier reproduction. Hence, the model identifies changed breeding population density as a key factor to understanding phenological adaptation in systems with prior residence advantages. While selection for change in reproductive phenology is often explained by changed seasonal variation in environmental variables, such as food abundance, we show that environmental change without apparent effects on seasonality can critically affect phenological adaptation. Such factors can mask or even override influences of changed seasonality on phenology. The model thus offers a conceptually new set of explanations for understanding phenological and demographic trends in a changing climate.
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| 13. |
- Johansson, Jacob, et al.
(författare)
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An eco-evolutionary model for demographic and phenological responses in migratory birds
- 2012
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Ingår i: BMC Biology. - : MDPI AG. - 1741-7007. ; 1:3, s. 639-657
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Tidskriftsartikel (refereegranskat)abstract
- Many migratory birds have changed their timing of arrival at breeding grounds in response to recent climate change. Understanding the adaptive value and the demographic consequences of these shifts are key challenges. To address these questions we extend previous models of phenological adaptation to climate change under territory competition to include feedback from population dynamics, winter survival and habitat productivity. We study effects of improved pre-breeding survival and of earlier food abundance peak. We show that phenological responses depend strongly on equilibrium population density via effects on territory competition. When density is high, improved pre-breeding survival affects selection pressures more than shifts of the resource peak. Under certain conditions, an advanced food peak can even select for later arrival due to competitive release. Improved pre-breeding survival has positive effects on population density that in many cases is stronger than negative effects of an advanced food peak. The fraction of young in the population decreases in all scenarios of change, but food peak shifts only affect population structure marginally unless population density is low. This work thus provides several missing links between phenological adaptation and demographic responses, and augments the toolbox for interpreting ongoing phenological shifts in migratory birds. We illustrate the utility of our model by explaining different patterns in demographic trends and phenological shifts in populations of Pied flycatchers (Ficedula hypoleuca) across Western Europe.
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| 14. |
- Johansson, Jacob, et al.
(författare)
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Climate change and the optimal flowering time of annual plants in seasonal environments
- 2013
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 19:1, s. 197-207
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Tidskriftsartikel (refereegranskat)abstract
- Long-term phenology monitoring has documented numerous examples of changing flowering dates during the last century. A pivotal question is whether these phenological responses are adaptive or not under directionally changing climatic conditions. We use a classic dynamic growth model for annual plants, based on optimal control theory, to find the fitness-maximizing flowering time, defined as the switching time from vegetative to reproductive growth. In a typical scenario of global warming, with advanced growing season and increased productivity, optimal flowering time advances less than the start of the growing season. Interestingly, increased temporal spread in production over the season may either advance or delay the optimal flowering time depending on overall productivity or season length. We identify situations where large phenological changes are necessary for flowering time to remain optimal. Such changes also indicate changed selection pressures. In other situations, the model predicts advanced phenology on a calendar scale, but no selection for early flowering in relation to the start of the season. We also show that the optimum is more sensitive to increased productivity when productivity is low than when productivity is high. All our results are derived using a general, graphical method to calculate the optimal flowering time applicable for a large range of shapes of the seasonal production curve. The model can thus explain apparent maladaptation in phenological responses in a multitude of scenarios of climate change. We conclude that taking energy allocation trade-offs and appropriate time scales into account is critical when interpreting phenological patterns.
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| 15. |
- Johansson, Jacob, et al.
(författare)
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Effects of territory competition and climate change on timing of arrival to breeding grounds: a game-theory approach.
- 2012
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 179:4, s. 463-474
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Phenology is an important part of life history that is gaining increased attention because of recent climate change. We use game theory to model phenological adaptation in migratory birds that compete for territories at their breeding grounds. We investigate how the evolutionarily stable strategy (ESS) for the timing of arrival is affected by changes in the onset of spring, the timing of the resource peak, and the season length. We compare the ESS mean arrival date with the environmental optimum, that is, the mean arrival date that maximizes fitness in the absence of competition. When competition is strong, the ESS mean arrival date responds less than the environmental optimum to shifts in the resource peak but more to changes in the onset of spring. Increased season length may not necessarily affect the environmental optimum but can still advance the ESS mean arrival date. Conversely, shifting a narrow resource distribution may change the environmental optimum without affecting the ESS mean arrival date. The ESS mean arrival date and the environmental optimum may even shift in different directions. Hence, treating phenology as an evolutionary game rather than an optimization problem fundamentally changes what we predict to be an adaptive response to environmental changes.
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| 16. |
- Johansson, Jacob, et al.
(författare)
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Game theory sheds new light on ecological responses to current climate change when phenology is historically mismatched.
- 2012
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X. ; 15:8, s. 881-888
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Phenological changes are well documented biological effects of current climate change but their adaptive value and demographic consequences are poorly known. Game theoretical models have shown that deviating from the fitness-maximising phenology can be evolutionary stable under frequency-dependent selection. We study eco-evolutionary responses to climate change when the historical phenology is mismatched in this way. For illustration we model adaptation of arrival dates in migratory birds that compete for territories at their breeding grounds. We simulate climate change by shifting the timing and the length of the favourable season for breeding. We show that initial trends in changes of population densities can be either reinforced or counteracted during the ensuing evolutionary adaptation. We find in total seven qualitatively different population trajectories during the transition to a new evolutionary equilibrium. This surprising diversity of eco-evolutionary responses provides adaptive explanations to the observed variation in phenological responses to recent climate change.
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| 17. |
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| 18. |
- Johansson, Jacob, et al.
(författare)
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The eco-evolutionary consequences of interspecific phenological asynchrony - a theoretical perspective
- 2015
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 124:1, s. 102-112
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Forskningsöversikt (refereegranskat)abstract
- The timing of biological events (phenology) is an important aspect of both a species' life cycle and how it interacts with other species and its environment. Patterns of phenological change have been given much scientific attention, particularly recently in relation to climate change. For pairs of interacting species, if their rates of phenological change differ, then this may lead to asynchrony between them and disruption of their ecological interactions. However it is often difficult to interpret differential rates of phenological change and to predict their ecological and evolutionary consequences. We review theoretical results regarding this topic, with special emphasis on those arising from life history theory, evolutionary game theory and population dynamic models. Much ecological research on phenological change builds upon the concept of match/mismatch, so we start by putting forward a simple but general model that captures essential elements of this concept. We then systematically compare the predictions of this baseline model with expectations from theory in which additional ecological mechanisms and features of species life cycles are taken into account. We discuss the ways in which the fitness consequences of interspecific phenological asynchrony may be weak, strong, or idiosyncratic. We discuss theory showing that synchrony is not necessarily an expected evolutionary outcome, and how population densities are not necessarily maximized by adaptation, and the implications of these findings. By bringing together theoretical developments regarding the eco-evolutionary consequences of phenological asynchrony, we provide an overview of available alternative hypotheses for interpreting empirical patterns as well as the starting point for the next generation of theory in this field.
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| 19. |
- Jonzén, Niclas, et al.
(författare)
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A theory of stochastic harvesting in stochastic environments
- 2002
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Ingår i: American Naturalist. - 0003-0147. ; 159:5, s. 427-437
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Tidskriftsartikel (refereegranskat)abstract
- We investigate how model populations respond to stochastic harvesting in a stochastic environment. In particular, we show that the effects of variable harvesting on the variance in population density and yield depend critically on the autocorrelation of environmental noise and on whether the endogenous dynamics of the population display over- or undercompensation to density. These factors interact in complicated ways; harvesting shifts the slope of the renewal function, and the net effect of this shift will depend on the sign and magnitude of the other influences. For example, when environmental noise exhibits a positive auto correlation, the relative importance of a variable harvest to the variance in density increases with overcompensation but decreases with undercompensation. For a fixed harvesting level, an increasing level of autocorrelation in environmental noise will decrease the relative variation in population density when overcompensation would otherwise occur. These and other intricate interactions have important ramifications for the interpretation of time series data when no prior knowledge of demographic or environmental details exists, These effects are important whenever the harvesting rate is sufficiently high or variable, conditions likely to occur in many systems, whether the harvesting is caused by commercial exploitation or by any other strong agent of density-independent mortality.
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| 20. |
- Jonzén, Niclas, et al.
(författare)
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Autumn migration of raptors on Capri
- 1999
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Ingår i: Avocetta: journal of ornithology. - 0404-4266. ; 23, s. 65-72
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Tidskriftsartikel (refereegranskat)
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| 21. |
- Jonzén, Niclas, et al.
(författare)
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Bird migration and climate - Introduction
- 2007
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Ingår i: Climate Research. - : Inter-Research Science Center. - 1616-1572 .- 0936-577X. ; 35:1-2, s. 1-3
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 22. |
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| 23. |
- Jonzén, Niclas, et al.
(författare)
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Climate change and the optimal arrival of migratory birds
- 2007
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 274:1607, s. 269-274
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Tidskriftsartikel (refereegranskat)abstract
- Recent climate change has sparked an interest in the timing of biological events, which is a general problem in life-history evolution. Reproduction in many organisms breeding in seasonal environments, e. g. migratory birds, is dependent on the exploitation of a short but rich food supply. If the seasonal timing of the food peak advances owing to climate change, then one would expect the bird to track those changes, hence, initiate migration and breeding earlier. However, when there is competition for territories and a risk of pre-breeding mortality, the optimal response to a shifting food distribution is no longer obvious. We develop a theoretical model to study how the optimal arrival time depends on the mean and variance of the food distribution, the degree of competition for territories and the risk of mortality. In general, the optimal shift in arrival date should never be as extreme as the shift in food peak date. Our results also show that we should expect the high variation of trends in arrival date observed among migratory birds, even if migration and information about climate change were unconstrained.
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| 24. |
- Jonzén, Niclas, et al.
(författare)
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Climate patterns and the stochastic dynamics of migratory birds
- 2002
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 97:3, s. 329-336
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Tidskriftsartikel (refereegranskat)abstract
- We analyse time series data of 17 bird species trapped at Ottenby Bird Observatory, Sweden, during spring migration 1972-1999. The species have similar demography but respond differently to variation in the North Atlantic Oscillation (NAO) - a strong determinant of winter climate in the northern Hemisphere. Species wintering in northern Europe, compared to species having winter quarters in the Mediterranean area, tend to respond positively to variation in NAO. The variation within each group is high due to wide-ranging winter-distribution in many species, probably smoothing out the effect of spatial variation in NAO. Whereas mild winters (high NAO) are benign for many - but not all - birds wintering in northern Europe, the effect of drier-than-normal conditions in the Mediterranean area during high NAO index winters is uncertain. The work presented here goes beyond simple correlative studies and help identifying which species that are most affected by variation in winter climate. This is a first important step that calls for a more mechanistic approach when analysing possible changes to climate change.
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| 25. |
- Jonzén, Niclas, et al.
(författare)
-
Habitat selection and population regulation in temporally fluctuating environments
- 2004
-
Ingår i: American Naturalist. - 0003-0147. ; 164:4, s. 103-114
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding and predicting the distribution of organisms in heterogeneous environments lies at the heart of ecology, and the theory of density-dependent habitat selection (DDHS) provides ecologists with an inferential framework linking evolution and population dynamics. Current theory does not allow for temporal variation in habitat quality, a serious limitation when confronted with real ecological systems. We develop both a stochastic equivalent of the ideal free distribution to study how spatial patterns of habitat use depend on the magnitude and spatial correlation of environmental stochasticity and also a stochastic habitat selection rule. The emerging patterns are confronted with deterministic predictions based on isodar analysis, an established empirical approach to the analysis of habitat selection patterns. Our simulations highlight some consistent patterns of habitat use, indicating that it is possible to make inferences about the habitat selection process based on observed patterns of habitat use. However, isodar analysis gives results that are contingent on the magnitude and spatial correlation of environmental stochasticity. Hence, DDHS is better revealed by a measure of habitat selectivity than by empirical isodars. The detection of DDHS is but a small component of isodar theory, which remains an important conceptual framework for linking evolutionary strategies in behavior and population dynamics.
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| 26. |
- Jonzén, Niclas
(författare)
-
Habitat Selection: Implications For Monitoring, Management, And Conservation
- 2008
-
Ingår i: Israel Journal of Ecology & Evolution. - 1565-9801. ; 54:3-4, s. 459-471
-
Tidskriftsartikel (refereegranskat)abstract
- Habitat selection is an important process that affects the distribution and abundance of organisms, and habitat selection theory is one of the flagships of theoretical ecology. Because of the importance of habitat selection in natural ecosystems and the successful history of the theoretical concepts, it has been Suggested that habitat selection theory can inform decision-making in population monitoring and solve management and conservation problems. In this paper I further emphasize the potential for habitat selection theory to be a useful framework to address fundamental problems of relevance for monitoring, management, and conservation. I also identify what I perceive as important gaps in our knowledge and weaknesses of current habitat selection theory when approaching real-world problems.
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| 27. |
- Jonzén, Niclas, et al.
(författare)
-
Harvesting-induced population fluctuations?
- 2003
-
Ingår i: Wildlife Biology. - 0909-6396. ; 9:1, s. 59-65
-
Tidskriftsartikel (refereegranskat)abstract
- It has recently been shown that damped endogenous dynamics is a common feature in Finnish grouse species; In this paper, we demonstrate that time-variant harvesting may turn damped dynamics to quasi-periodic fluctuations. Exploited populations, e.g. grouse, may therefore fluctuate more than expected if we do not manage to keep the harvest fraction constant over time. However, the harvest fraction of Finnish grouse varies with the phase of the cycle. Such a harvesting strategy could potentially change the periodicity of the fluctuations, as can a threshold harvest strategy where a constant fraction is harvested above a density threshold. The two non-linear harvesting strategies investigated here can modulate the dynamic properties of the population in a way not predicted by linear models. We argue that the behaviour of exploited populations and the role of harvesting can only be understood if we identify and understand the interplay of endogenous and exogenous components of population dynamics.
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| 28. |
- Jonzén, Niclas, et al.
(författare)
-
Harvesting spatially distributed populations
- 2001
-
Ingår i: Wildlife Biology. - 0909-6396. ; 7:3, s. 197-203
-
Tidskriftsartikel (refereegranskat)abstract
- Spatial structure has a paramount influence on population dynamics. This has until recently been neglected in harvesting theory. In this paper, we demonstrate how source-sink and habitat selection theory can provide guidance for harvesting spatially structured populations. We also show how harvesting can affect the spatial distribution of the exploited resource, which has consequences for the design of protected areas. This implicit treatment of space is complemented by a spatially explicit predator-prey model. It turns out that harvesting of the prey and/or the predator species in one patch in space sometimes has effects on the other species outside the harvested patch. We stress the importance of considering how realistic the representation of the spatial dimension has to be in population management.
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| 29. |
- Jonzén, Niclas
(författare)
-
Inference and management of populations in variable environments
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Population dynamics in space and time are manifested as changes in the distribution and abundance of organisms. To couple such patterns to the underlying processes is a central question in ecology and also key to successful management. In this thesis, I use theoretical models as well as time series data to analyze population dynamics in environments that are variable in space or time. An example of spatial heterogeneity is when we establish a reserve - where individuals are protected from exploitation - and let individuals distribute themselves between the reserve and the surrounding exploited area. I show that if a population conforms to the ideal free distribution (IFD), the harvest rate resulting in the maximum sustainable yield is unaffected by the size as well as the quality of the reserve. Source-sink systems, where there is a net flow from "good" to "bad" habitats, complicate population management, and optimal harvesting decisions are contingent on dispersal rates and quality differences among habitats. Populations also experience temporal variation within a year (seasonality) as well as between years. By incorporating seasonality in a population harvesting model, I give an explanation to the observation that pre-harvest population densities are sometimes unaffected by harvesting. Between-year variability is studied by building stochastic population models that can be approximated by statistical time series models and applied to real data. In exploited populations, the harvesting process itself is another stochastic factor that influences the dynamics. I demonstrate that under many circumstances, variable harvest can explain a considerable proportion of the variation in population density, sometimes even more than explained by environmental stochasticity. The eastern Baltic cod (Gadus morhua) seems to be an example of that. Finally, I show that if the environmental stochasticity is temporally autocorrelated, any attempt to disentangle demographic and environmental impact on population dynamics will be problematic. I nevertheless try to get around some of the difficulties and present a case study on how winter climate patterns are visible in time series of passerine birds wintering in northern Europe. In conclusion, my thesis shows the need to, and potential of, using ecological theory expressed as mathematical models, to guide our thinking and analysis of population patterns and processes. I have analyzed mathematical models with the purpose of understanding the structure of real systems and what it takes to analyze data from them. The two case studies presented, explicitly couple observed dynamics to the underlying processes with some success.
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| 30. |
- Jonzén, Niclas, et al.
(författare)
-
Of sheep and rain: large-scale population dynamics of the red kangaroo
- 2005
-
Ingår i: Journal of Animal Ecology. - : Wiley. - 1365-2656 .- 0021-8790. ; 74:1, s. 22-30
-
Tidskriftsartikel (refereegranskat)abstract
- 1. We analysed time-series data from populations of red kangaroos (Macropus rufus, Desmarest) inhabiting four areas in the pastoral zone of South Australia. We formulated a set of a priori models to disentangle the relative effects of the covariates: rainfall, harvesting, intraspecific competition, and domestic herbivores, on kangaroo population-growth rate. 2. The statistical framework allowed for spatial variation in the growth-rate parameters, response to covariates, and environmental variability, as well as spatially correlated error terms due to shared environment. 3. The most parsimonious model included all covariates but no area-specific parameter values, suggesting that kangaroo densities respond in the same way to the covariates across the areas. 4. The temporal dynamics were spatially correlated, even after taking into account the potentially synchronizing effect of rainfall, harvesting and domestic herbivores. 5. Counter-intuitively, we found a positive rather than negative effect of domestic herbivore density on the population-growth rate of kangaroos. We hypothesize that this effect is caused by sheep and cattle acting as a surrogate for resource availability beyond rainfall. 6. Even though our system is well studied, we must conclude that approximating resources by surrogates such as rainfall is more difficult than previously thought. This is an important message for studies of consumer-resource systems and highlights the need to be explicit about population processes when analysing population patterns.
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| 31. |
- Jonzén, Niclas, et al.
(författare)
-
Population dynamics of the Swedish Ornithological Society.
- 2003
-
Ingår i: Ornis Svecica. - 1102-6812. ; 13:4, s. 107-114
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- It has recently been recognized that there is declining interest in ornithology among the younger generations. In this paper we analyse the short and long-term dynamics of the Swedish Ornithological Society (SOF) and the Swedish Society for Nature Conservation (SNF) by using analytical tools from population ecology. We first show that the increasing number of SOF and SNF members is not the result of a constant proportion of ornithologists or people interested in nature conservation among a growing Swedish population. Hence, the number of members most likely reflects the true interest in joining organizations such as SOF. We also demonstrate that the growth rate of SOF can be fairly well estimated, but the possible equilibrium size is uncertain. Removing the long-term trend reveals a cyclic pattern with a period of 23 years. This pattern was not found when analysing the SNF data and we discuss the observed patterns in relation to human and member generation time. Finally, we present an improved population model based on data up to 1998 and show how model predictions compare with the observed number of members in year 2002.
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| 32. |
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| 33. |
- Jonzén, Niclas, et al.
(författare)
-
Rapid advance of spring arrival dates in long-distance migratory birds
- 2006
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 312:5782, s. 1959-1961
-
Tidskriftsartikel (refereegranskat)abstract
- Several bird species have advanced the timing of their spring migration in response to recent climate change. European short-distance migrants, wintering in temperate areas, have been assumed to be more affected by change in the European climate than long-distance migrants wintering in the tropics. However, we show that tong-distance migrants have advanced their spring arrival in Scandinavia more than short-distance migrants. By analyzing a long-term data set from southern Italy, we show that long-distance migrants also pass through the Mediterranean region earlier. We argue that this may reflect a climate-driven evolutionary change in the timing of spring migration.
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| 34. |
- Jonzén, Niclas, et al.
(författare)
-
Response to comment on "Rapid advance of spring arrival dates in long-distance migratory birds"
- 2007
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 315:5812, s. 598-598
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Both's comment questions our suggestion that the advanced spring arrival time of long-distance migratory birds in Scandinavia and the Mediterranean may reflect a climate-driven evolutionary change. We present additional arguments to support our hypothesis but underscore the importance of additional studies involving direct tests of evolutionary change.
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| 35. |
- Jonzén, Niclas, et al.
(författare)
-
Risk of collapse in the eastern Baltic cod fishery
- 2002
-
Ingår i: Marine Ecology - Progress Series. - 1616-1599. ; 240, s. 225-233
-
Tidskriftsartikel (refereegranskat)abstract
- The eastern Baltic cod fishery, as many fisheries worldwide, is experiencing a major crisis. The combination of current environmental conditions, fishing mortality rates, and stock size indicates that this fishery is not sustainable. In order to rebuild the population and sustain the fishery in the future, it is essential to define a biologically appropriate exploitation level. In this paper, we take a decision-theoretical approach and use risk analysis to compare different management actions in terms of fishing mortality rates, and predict stock size in a short, medium and long-term perspective. We consider alternative hypotheses about the stock biomass in 1999 and analyse the risk of stock decline below three thresholds: quasi-extinction (Bext, defined by us), the safe biological limit, and the precautionary approach limit as defined by the International Council for the Exploration of the Sea (ICES). Results show that the current fishing mortality implies a tremendous risk of driving the Baltic cod stock below Bext (1000 t) within 10 yr. This result is robust to alternative assumptions about model structure as well as to the magnitude of environmental stochasticity. Hence, we consider a substantial reduction of the fishing mortality to be the only way of avoiding the far-reaching ecological and socio-economic consequences of continued exploitation at current levels.
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| 36. |
- Jonzén, Niclas, et al.
(författare)
-
Seasonal herbivory and mortality compensation in a swan-pondweed system.
- 2002
-
Ingår i: Ecological Modelling. - 0304-3800. ; 147:3, s. 209-219
-
Tidskriftsartikel (refereegranskat)abstract
- Many birds feed on submerged macrophytes during a temporally discrete period every year, for instance during migratory stopover or at the wintering grounds. Hence, seasonal herbivory is a common feature of the life cycle in many aquatic macrophytes. We are interested in the effect of Bewick's swans (Cygnus columbianus bewickii) feeding on the tubers of fennel pondweed (Potamogeton pectinatus) in the Netherlands every autumn. For that purpose, we developed a sequential macrophyte population model, including seasons of tuber production, herbivory and winter mortality as distinct and unambiguously defined events. The model is characterised and parameterised with both field and laboratory data. Tuber consumption inevitably decreases the density of ramets sprouting next spring, but it may actually increase the density of tubers produced in the following autumn. Hence, we can only understand the effect of grazing on the fennel pondweed population by recognising the seasonal structure of density-dependence. The mean density of fennel pondweed and the yield taken by swans are dependent on the foraging threshold below which no grazing takes place. Furthermore, the consumption has a stabilising effect for a wide range of parameter values.
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| 37. |
- Jonzén, Niclas, et al.
(författare)
-
Sharing the bounty-Adjusting harvest to predator return in the Scandinavian human-wolf-bear-moose system
- 2013
-
Ingår i: Ecological Modelling. - : Elsevier BV. - 0304-3800 .- 1872-7026. ; 265, s. 140-148
-
Tidskriftsartikel (refereegranskat)abstract
- The increase and range extension of wolves (Canis lupus L) and brown bears ( Ursus arctos L) in Scandinavia inevitably impacts moose (Alces alces L.) populations and, as a consequence, the size and composition of the hunter harvest must be adjusted. We used a sex- and age-structured moose population model to delineate optimal harvest strategies under predation and to compare the resulting harvest composition with the strategy commonly implemented in practice. We examined how much moose density or adult sex ratio needs to change to fully compensate for losses to predation. We found a harvest allocation pattern in commonly used practical management across calves, bulls and cows that indicated a trade-off strategy between maximising the number of shot moose, the yield biomass and the number of shot prime bulls. This strategy performed quite well with respect to all yield measures and yielded an age structure most similar to the strategies maximising harvest biomass and prime bulls. Unless predation pressure was very high, the harvest loss could be completely compensated for by allowing a higher moose density. In other situations the current hunting strategy was not possible to implement and the moose density needed to sustain predation even without hunting increases dramatically. An alternative option to balance the predation loss was to accept a more female-biased sex ratio in the winter population. Hence, it may be possible to keep 50% calves in the harvest and still obtain the same total harvest if the proportion of bulls in the harvest is increased to compensate for predation. The increase of large carnivores competing with moose hunting creates conflicts and will inevitably reduce harvest yield unless hunting strategies change. We show how increased moose density and redistribution of the harvest towards bulls can mitigate this conflict and we provide a web-based tool, where stakeholders can compare the long-term effects of alternative management decisions and eventually adjust their hunting strategy accordingly. (C) 2013 Elsevier B.V. All rights reserved.
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| 38. |
- Jonzen, Niclas, et al.
(författare)
-
Stochastic demography and population dynamics in the red kangaroo Macropus rufus
- 2010
-
Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 79:1, s. 109-116
-
Tidskriftsartikel (refereegranskat)abstract
- 1. Many organisms inhabit strongly fluctuating environments but their demography and population dynamics are often analysed using deterministic models and elasticity analysis, where elasticity is defined as the proportional change in population growth rate caused by a proportional change in a vital rate. Deterministic analyses may not necessarily be informative because large variation in a vital rate with a small deterministic elasticity may affect the population growth rate more than a small change in a less variable vital rate having high deterministic elasticity. 2. We analyse a stochastic environment model of the red kangaroo (Macropus rufus), a species inhabiting an environment characterized by unpredictable and highly variable rainfall, and calculate the elasticity of the stochastic growth rate with respect to the mean and variability in vital rates. 3. Juvenile survival is the most variable vital rate but a proportional change in the mean adult survival rate has a much stronger effect on the stochastic growth rate. 4. Even if changes in average rainfall have a larger impact on population growth rate, increased variability in rainfall may still be important also in long-lived species. The elasticity with respect to the standard deviation of rainfall is comparable to the mean elasticities of all vital rates but the survival in age class 3 because increased variation in rainfall affects both the mean and variability of vital rates. 5. Red kangaroos are harvested and, under the current rainfall pattern, an annual harvest fraction of c. 20% would yield a stochastic growth rate about unity. However, if average rainfall drops by more than c. 10%, any level of harvesting may be unsustainable, emphasizing the need for integrating climate change predictions in population management and increase our understanding of how environmental stochasticity translates into population growth rate.
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| 39. |
- Jonzén, Niclas, et al.
(författare)
-
Temporally structured density-dependence and population management
- 1999
-
Ingår i: Annales Zoologici Fennici. - 0003-455X. ; 36:1, s. 39-44
-
Tidskriftsartikel (refereegranskat)abstract
- We used a simple discrete-time population model to investigate how temporally structured density-dependence influences a population's response to loss due to harvesting. We assumed that reproduction is a relative discrete event in time, followed by density-dependent mortality and then harvesting, or followed by harvesting and then density-dependent mortality. Such an ordering of events in time may have profound influences on the dynamics of the population. The extra mortality due to harvesting may either be additive or compensatory depending on the strength of the density-dependence and the ordering of events. Population stability is also strongly affected by the temporal structure of density-dependence. Moreover, the yield and the (unconstrained) optimal harvest rate will vary depending on when harvesting occurs in the annual cycle. We argue that a correct identification of the temporal structure of density-dependence may be of great importance for understanding population dynamics in general and population management in particular.
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| 40. |
- Jonzén, Niclas, et al.
(författare)
-
The irreducible uncertainty of the demography–environment interaction in ecology
- 2002
-
Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 269:1488, s. 221-225
-
Tidskriftsartikel (refereegranskat)abstract
- The interpretation of ecological data has been greatly improved by bridging the gap between ecological and statistical models. The major challenge is to separate competing hypotheses concerning demography, or other ecological relationships, and environmental variability (noise). In this paper we demonstrate that this may be an arduous, if not impossible, task. It is the lack of adequate ecological theory, rather than statistical sophistication, which leads to this problem. A reconstruction of underlying ecological processes can only be done if we are certain of either the demographic or the noise model, which is something that can only be achieved by an improved theory of stochastic ecological processes. Ignoring the fact that this is a real problem may mislead ecologists and result in erroneous conclusions about the relative importance of endogenous and exogenous factors in natural ecosystems. The lack of correct model identification may also have far-reaching consequences for population management and conservation.
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| 41. |
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| 42. |
- Jonzén, Niclas, et al.
(författare)
-
The timing of spring migration in trans-Saharan migrants: a comparison between Ottenby, Sweden and Capri, Italy
- 2006
-
Ingår i: Ornis Svecica. - 1102-6812. ; 16:1-2, s. 27-33
-
Tidskriftsartikel (refereegranskat)abstract
- Some migratory birds have advanced their spring arrival to Northern Europe, possibly by increasing the speed of migration through Europe in response to increased temperature en route. In this paper we compare the phenology of spring arrival of seven trans-Saharan migrants along their migration route and test for patterns indicating that migration speed varied over the season using long-term data collected on the Italian island of Capri and at Ottenby Bird Observatory, Sweden. There was a linear relationship between median arrival dates on Capri and at Ottenby. The slope was not significantly different from one. On average, the seven species arrived 15 days later at Ottenby compared to Capri. There was a (non-significant) negative relationship between the species-specific arrival dates at Capri and the differences in median arrival dates between Capri and Ottenby, possibly indicating a tendency towards faster migration through Europe later in the season. To what extent different species are able to speed up their migration to benefit from the advancement of spring events is unknown.
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| 43. |
- Jonzén, Niclas, et al.
(författare)
-
Trend detection in source-sink systems: when should sink habitats be monitored?
- 2005
-
Ingår i: Ecological Applications. - : Wiley. - 1051-0761. ; 15:1, s. 326-334
-
Tidskriftsartikel (refereegranskat)abstract
- We determine the power of population monitoring in source or sink habitat to detect declining reproductive success in source habitat using a stochastic population model. The relative power to detect a trend in the source by monitoring either the source or the sink Varies with life history parameters, environmental stochasticity, and observation uncertainty. The power to detect a decline monitoring either source or sink habitat is maximized when the reproductive surplus in the source is low. The power to detect a decline by monitoring the sink increases with increasing reproductive deficit in the sink. If environmental stochasticity in the source increases, the power in the sink goes down due to a lower signal-to-noise ratio. However, the power in the sink increases if environmental stochasticity is increased further, because increasing stochasticity reduces the geometric mean growth rate in the source. Intriguingly, it is often most efficient to monitor the sink even though the actual reproductive decline occurs in the source. If reproductive success is declining in both habitats, censusing the sink will always have higher power. However, the probability of Type 1 error is always higher in the sink. Our results clearly have implications for optimal population monitoring in source-sink landscapes.
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| 44. |
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| 45. |
- Jonzén, Niclas, et al.
(författare)
-
Variable fishing mortality and the possible commercial extinction of the eastern Baltic cod
- 2001
-
Ingår i: Marine Ecology - Progress Series. - 1616-1599. ; 210, s. 291-296
-
Tidskriftsartikel (refereegranskat)abstract
- The recent decline in the Baltic cod Gadus morhua L. has been accompanied by an increase in population variability. Small population size, poor recruitment, and high population variability may be factors contributing to their imminent (commercial) extinction. Here we show that variable harvest rate, rather than variable recruitment, is the plausible cause of the increased variance in Baltic cod stock size. This calls for a reconsideration of the role of harvesting as a driving force in exploited populations. The mean exploitation rate, and also the variance, ought to be taken into account in fisheries and other population management.
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| 46. |
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| 47. |
- Knape, Jonas, et al.
(författare)
-
An analysis of hatching success in the great reed warbler Acrocephalus arundinaceus
- 2008
-
Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; :117, s. 430-438
-
Tidskriftsartikel (refereegranskat)abstract
- Hatching success is a potentially important fitness component for avian species. Previous studies of hatching success in natural populations have primarily focused on effects of inbreeding but a general understanding of variation in hatching success is lacking. We analyse data on hatching success in a population of great reed warblers Acrocephalus arundinaceus in Lake Kvismaren in south central Sweden. The effects of a range of covariates, including three measures of inbreeding as well as effects of classifications in the data (such as identities of individuals), on hatching success are analysed simultaneously. This is done by means of fitting Bayesian binomial mixed models using Markov chain Monte Carlo methods. Using random effects for each individual parent we check for unexplained variation in hatching success among male and female individuals and compare it to effects of covariates such as degree of inbreeding. Model selection showed that there was a significant amount of unexplained variation in hatching probability between females. This was manifested by a few females laying eggs with a substantially lower hatching success than the majority of the females. The deviations were of the same order of magnitude as the significant effect of parent relatedness on hatching success. Whereas the negative effect of parent relatedness on hatchability is an expression of inbreeding, the female individual effect is not due to inbreeding and could reflect maternal effects, that females differ in fertilisation and/or incubation ability, or an over representation of genetic components from the female acting on the early developing embryo.
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| 48. |
- Knape, Jonas, et al.
(författare)
-
Individual heterogeneity and senescence in Silvereyes on Heron Island
- 2011
-
Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 92:4, s. 813-820
-
Tidskriftsartikel (refereegranskat)abstract
- Individual heterogeneity and correlations between life history traits play a fundamental role in life history evolution and population dynamics. Unobserved individual heterogeneity in survival can be a nuisance for estimation of age effects at the individual level by causing bias due to mortality selection. We jointly analyze survival and breeding output from successful breeding attempts in an island population of Silvereyes (Zosterops lateralis chlorocephalus) by fitting models that incorporate age effects and individual heterogeneity via random effects. The number of offspring produced increased with age of parents in their first years of life but then eventually declined with age. A similar pattern was found for the probability of successful breeding. Annual survival declined with age even when individual heterogeneity was not accounted for. The rate of senescence in survival, however, depends on the variance of individual heterogeneity and vice versa; hence, both cannot be simultaneously estimated with precision. Model selection supported individual heterogeneity in breeding performance, but we found no correlation between individual heterogeneity in survival and breeding performance. We argue that individual random effects, unless unambiguously identified, should be treated as statistical nuisance or taken as a starting point in a search for mechanisms rather than given direct biological interpretation.
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| 49. |
- Knape, Jonas, et al.
(författare)
-
Multivariate state space modelling of bird migration count data
- 2009
-
Ingår i: Environmental and Ecological Statistics. - Berlin : Springer. - 1352-8505 .- 1573-3009. ; 3:1, s. 59-79
-
Tidskriftsartikel (refereegranskat)abstract
- We analyse 54 year long time series data on the numbers of common redstart (Phoenicurus phoenicurus), common whitethroat (Sylvia communis), garden warbler (Sylvia borin) and lesser whitethroat (Sylvia curruca) trapped in spring and autumn at Ottenby Bird Observatory, Sweden. The Ottenby time series could potentially serve as a reference on how much information on population change is available in count data on migrating birds. To investigate this, we combine spring and autumn data in a Bayesian state-space model trying to separate demographic signals and observation noise. The spring data are assumed to be a measure of the breeding population size, whereas the autumn data measure the population size after reproduction. At the demographic level we include seasonal density dependence and model winter dynamics as a function of precipitation in the Sahel region, south of the Sahara desert, where these species are known to spend the winter. Results show that the large fluctuations in the data restrict what conclusions can be drawn about the dynamics of the species. Annual catches are highly correlated between species and we show that a likely explanation for this is that trapping numbers are strongly dependent on local weather conditions. A comparative analysis of a related data set from the Courish Spit, Russia, gives rather different dynamics which may be caused by low information in the two data sets, but also by distinct populations passing Ottenby and the Courish Spit. This highlights the difficulty of validating results of the analyses when abundance indices derived by other methods or from other populations do not agree.
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| 50. |
- Knape, Jonas, et al.
(författare)
-
On observation distributions for state space models of population survey data
- 2011
-
Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 80:6, s. 1269-1277
-
Tidskriftsartikel (refereegranskat)abstract
- 1. State space models are starting to replace more simple time series models in analyses of temporal dynamics of populations that are not perfectly censused. By simultaneously modelling both the dynamics and the observations, consistent estimates of population dynamical parameters may be obtained. For many data sets, the distribution of observation errors is unknown and error models typically chosen in an ad-hoc manner. 2. To investigate the influence of the choice of observation error on inferences, we analyse the dynamics of a replicated time series of red kangaroo surveys using a state space model with linear state dynamics. Surveys were performed through aerial counts and Poisson, overdispersed Poisson, normal and log-normal distributions may all be adequate for modelling observation errors for the data. We fit each of these to the data and compare them using AIC. 3. The state space models were fitted with maximum likelihood methods using a recent importance sampling technique that relies on the Kalman filter. The method relaxes the assumption of Gaussian observation errors required by the basic Kalman filter. Matlab code for fitting linear state space models with Poisson observations is provided. 4. The ability of AIC to identify the correct observation model was investigated in a small simulation study. For the parameter values used in the study, without replicated observations, the correct observation distribution could sometimes be identified but model selection was prone to misclassification. On the other hand, when observations were replicated, the correct distribution could typically be identified. 5. Our results illustrate that inferences may differ markedly depending on the observation distributions used, suggesting that choosing an adequate observation model can be critical. Model selection and simulations show that for the models and parameter values in this study, a suitable observation model can typically be identified if observations are replicated. Model selection and replication of observations, therefore, provide a potential solution when the observation distribution is unknown.
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