1,721,002 research outputs found
Demographic consequences of rapid climate change and density dependence in migratory Arctic geese
Full text linkClimate change effects are being felt across ecological levels and most strongly in the Arctic. Scaling up from effects on demographic rates to the population-level, and even community-level, is a daunting task. This is particularly the case for migratory species that experience different climate and density regimes over their annual cycle. However, increasingly sophisticated statistical tools provide us with the means to do so. In this thesis, I used state-of-the-art analytical approaches to provide a mechanistic and holistic understanding of the impacts of climate change and density dependence on the population dynamics of a migratory Arctic herbivore, the barnacle goose (Branta leucopsis). The study population of barnacle geese breeds in higharctic Svalbard but spends the winter at Solway Firth, UK, with a spring stopover on mainland Norway. I investigated the dynamics of a local population breeding on western Svalbard, close to the settlement of Ny-Ålesund, using 28 years of individual-based data. In paper I, I used an integrated population model to quantify density dependent effects on vital rates in this population, following their colonisation of new breeding grounds in a period of overall population increase. Local density regulation at the breeding grounds reduced population growth through negative effects on reproduction. This led to density-dependent changes in vital rate contributions to the population growth rate. These results provided empirical evidence that the population dynamics of capital breeders may be more reproduction driven. In paper II, I disentangled climate, density and trophic interaction effects on population dynamics, considering the annual cycle of barnacle geese, i.e., breeding and non-breeding season effects on vital rates. Climate change in Svalbard positively affected egg production and hatching success through rapid advancement of spring onset. However, this was offset by reduced pre-fledging survival due to increasing predation by Arctic foxes, an indirect consequence of climate change linked with changes in abundance of overwintering herbivores. In this way, climate effects on one population can cascade throughout a community. Climate and density also influenced reproduction and survival during the non-breeding season, via carryover effects. Overall, counteracting density, carryover and (direct and indirect) climate effects stabilized breeding population size. In paper III, I analysed variation in an important life-history trait: age at first reproduction (AFR). As established in paper II, advancing spring onset increased the probability of females producing goslings in general, but importantly, this effect was stronger for first-time than experienced breeders. The two week advance in spring phenology led to an earlier AFR, by more than doubling the proportion of two-year-olds reproducing (one year- olds do not reproduce). How the effects of environmental change on such demographic rates are coupled to traits reflecting body condition is important to understand and predict population growth. Body mass is a key fitness related trait for herbivores and fluctuates with resources, which are highly variable in the Arctic. Consequently, coupled trait-demography responses may be important in Arctic herbivores, particularly geese, where body mass has declined in response to habitat degradation. In paper IV, I quantified population-dynamic consequences of changes in body mass in barnacle geese. Despite a 10% decline in body mass, and positive effects of mass on survival and reproduction, this did not translate into trait-mediated effects on population growth. Consequently, the population dynamics of Arctic geese, and possibly other Arctic herbivores, may be more resilient to changing body condition than expected. In this thesis, I highlight the sensitivity, but also resilience, of an Arctic herbivore population to climate change, and other sources of environmental change, and the complex mechanisms by which effects of climate change are translated into changes in population dynamics and abundance. The dynamics of this population were predominantly driven by variation in reproduction, which is the demographic rate most affected by climate change, directly and indirectly. However, mechanisms buffering population dynamics against environmental variation were also evident, such as the lack of demographic effects of declining body condition on the population growth rate. Overall, this work illustrates that a holistic approach, jointly modelling vital rates and the mechanisms for how they influence population dynamics, are necessary to understand effects of e.g. climate change
Demographic consequences of rapid climate change and density dependence in migratory Arctic geese
No full textClimate change effects are being felt across ecological levels and most strongly in the Arctic. Scaling up from effects on demographic rates to the population-level, and even community-level, is a daunting task. This is particularly the case for migratory species that experience different climate and density regimes over their annual cycle. However, increasingly sophisticated statistical tools provide us with the means to do so. In this thesis, I used state-of-the-art analytical approaches to provide a mechanistic and holistic understanding of the impacts of climate change and density dependence on the population dynamics of a migratory Arctic herbivore, the barnacle goose (Branta leucopsis). The study population of barnacle geese breeds in higharctic Svalbard but spends the winter at Solway Firth, UK, with a spring stopover on mainland Norway. I investigated the dynamics of a local population breeding on western Svalbard, close to the settlement of Ny-Ålesund, using 28 years of individual-based data. In paper I, I used an integrated population model to quantify density dependent effects on vital rates in this population, following their colonisation of new breeding grounds in a period of overall population increase. Local density regulation at the breeding grounds reduced population growth through negative effects on reproduction. This led to density-dependent changes in vital rate contributions to the population growth rate. These results provided empirical evidence that the population dynamics of capital breeders may be more reproduction driven. In paper II, I disentangled climate, density and trophic interaction effects on population dynamics, considering the annual cycle of barnacle geese, i.e., breeding and non-breeding season effects on vital rates. Climate change in Svalbard positively affected egg production and hatching success through rapid advancement of spring onset. However, this was offset by reduced pre-fledging survival due to increasing predation by Arctic foxes, an indirect consequence of climate change linked with changes in abundance of overwintering herbivores. In this way, climate effects on one population can cascade throughout a community. Climate and density also influenced reproduction and survival during the non-breeding season, via carryover effects. Overall, counteracting density, carryover and (direct and indirect) climate effects stabilized breeding population size. In paper III, I analysed variation in an important life-history trait: age at first reproduction (AFR). As established in paper II, advancing spring onset increased the probability of females producing goslings in general, but importantly, this effect was stronger for first-time than experienced breeders. The two week advance in spring phenology led to an earlier AFR, by more than doubling the proportion of two-year-olds reproducing (one year- olds do not reproduce). How the effects of environmental change on such demographic rates are coupled to traits reflecting body condition is important to understand and predict population growth. Body mass is a key fitness related trait for herbivores and fluctuates with resources, which are highly variable in the Arctic. Consequently, coupled trait-demography responses may be important in Arctic herbivores, particularly geese, where body mass has declined in response to habitat degradation. In paper IV, I quantified population-dynamic consequences of changes in body mass in barnacle geese. Despite a 10% decline in body mass, and positive effects of mass on survival and reproduction, this did not translate into trait-mediated effects on population growth. Consequently, the population dynamics of Arctic geese, and possibly other Arctic herbivores, may be more resilient to changing body condition than expected. In this thesis, I highlight the sensitivity, but also resilience, of an Arctic herbivore population to climate change, and other sources of environmental change, and the complex mechanisms by which effects of climate change are translated into changes in population dynamics and abundance. The dynamics of this population were predominantly driven by variation in reproduction, which is the demographic rate most affected by climate change, directly and indirectly. However, mechanisms buffering population dynamics against environmental variation were also evident, such as the lack of demographic effects of declining body condition on the population growth rate. Overall, this work illustrates that a holistic approach, jointly modelling vital rates and the mechanisms for how they influence population dynamics, are necessary to understand effects of e.g. climate change
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Climate change influences reproduction in Arctic breeding geese through altered predator-prey interactions
Full text linkKlimaendringer påvirker Arktiske herbivorer både direkte og indirekte gjennom endringer i tilgang på ressurser. I senere tid er det også funnet bevis som indikerer at effektene av klimaendringer også kan forekomme gjennom endringer i antall og atferd hos predatorer. Det er blitt foreslått at økte temperaturer i Arktis har vært fordelaktig for polarrev, den vanligste predatoren på gås som hekker i Arktis, gjennom økt på tilgang på byttedyr som for eksempel kadaver fra reinsdyr. I tillegg har isbjørner blitt nødt til å finne alternative matkilder ettersom sjøisen har trukket seg tilbake i tilknytning til klimaendringer. Én av disse alternative matkildene er eggene til fugler som hekker på bakken i Arktis. Nylige observasjoner og funn over store deler av Arktis indikerer at predasjon fra isbjørn kan ha katastrofale konsekvenser for reproduksjon hos hekkende gås. I denne avhandlingen var målet å kvantifisere effekten av isbjørnpredasjon, mens jeg tok hensyn til andre abiotiske og biotiske faktorer som påvirket populasjonsdynamikk hos en lokal populasjon med hvitkinngås som hekker i Kongsfjorden, Svalbard. For å oppnå dette, analyserte jeg tre tiår med data på individ-nivå i en integrert populasjons modell, basert på tidligere studier av populasjonsdynamikk i den lokale populasjonen. Estimatene fra modellen inkluderte reproduksjonsrater, overlevelse, populasjonsstørrelser og effekten av abiotiske og biotiske variabler, inkludert predasjon fra polarrev og isbjørn. Resultatene fra denne avhandlingen bekreftet at (1) predasjon fra polarrev har en sterk negativ effekt på reproduksjon, (2) en stadig tidligere vår påvirker antallet gåsunger per hunn positivt, (3) reproduksjon og overlevelse er tetthetsavhengig og (4) varmere temperaturer ved lokasjonen der gjessene overvintrer har en positiv påvirkning på overlevelse. Men det viktigste funnet i denne avhandlingen var at økningen i antall isbjørn som har besøkt Kongsfjorden under hekkingen til hvitkinngås sannsynligvis har hatt en negativ effekt på reproduksjon. Effekten av isbjørn, som virker gjennom predasjon på egg, var bare tydelig i den andre halvdelen av studieperioden. Funnene i denne avhandlingen og en rekke andre studier over store deler av Arktis tyder på at det skjer fundamentale endringer i miljøet i regionen. Endringer som resulterer i endret samfunnsdynamikk, inkludert indirekte klimaeffekter som opererer gjennom endringer i antall og atferd hos predatorer.Climate change is affecting Arctic herbivores both directly and indirectly via bottom-up
mechanisms. However, recent evidence suggests that indirect effects of climate change may
also occur through changes in abundance and behaviour of predators. It has been proposed
that warming has benefitted the Arctic fox, the main predator on Arctic breeding geese,
through an overall increase in prey and reindeer carcasses. Also, as sea-ice have contracted in
parallel with climate change, polar bears have been forced to use alternative food sources in
summer, particularly the eggs of ground-breeding birds. Previous observations across the
Arctic indicate that polar bear predation may have devastating consequences for reproduction
in geese. In this thesis, I aimed to quantify the effect of polar bear predation while accounting
for other biotic and abiotic factors affecting population dynamics in a local population of
barnacle geese that breed in Kongsfjorden, Svalbard. To achieve this, I used three decades of
individual-based data and population count data in an integrated population model, extending
previous population dynamical studies on the same population. The model estimated
reproduction, survival, population sizes and effects of abiotic and biotic variables, including
predation from Arctic foxes and polar bears. The results confirmed that (1) predation from
Arctic fox had a strong negative effect on fledging rates, (2) advancing spring onset affected
the number of goslings positively, (3) reproduction and survival was density dependent, and
(4) warmer temperatures on the wintering grounds had a positive influence on survival. Most
importantly however, I found that the marked increase in the number of bears visiting
Kongsfjorden during the breeding period caused a strong tendency for a negative effect of
polar bear predation on reproduction. The polar bear effect, acting through egg predation, was
only evident in the second half of the study period. These findings add to the growing body of
evidence suggesting that Arctic ecosystems are undergoing fundamental environmental
changes. Changes which result in changing community dynamics, including indirect climate
change effects operating through altered top-down dynamics due to shifts in predator
abundances and behaviour
Climate change influences reproduction in Arctic breeding geese through altered predator-prey interactions
No full textKlimaendringer påvirker Arktiske herbivorer både direkte og indirekte gjennom endringer i tilgang på ressurser. I senere tid er det også funnet bevis som indikerer at effektene av klimaendringer også kan forekomme gjennom endringer i antall og atferd hos predatorer. Det er blitt foreslått at økte temperaturer i Arktis har vært fordelaktig for polarrev, den vanligste predatoren på gås som hekker i Arktis, gjennom økt på tilgang på byttedyr som for eksempel kadaver fra reinsdyr. I tillegg har isbjørner blitt nødt til å finne alternative matkilder ettersom sjøisen har trukket seg tilbake i tilknytning til klimaendringer. Én av disse alternative matkildene er eggene til fugler som hekker på bakken i Arktis. Nylige observasjoner og funn over store deler av Arktis indikerer at predasjon fra isbjørn kan ha katastrofale konsekvenser for reproduksjon hos hekkende gås. I denne avhandlingen var målet å kvantifisere effekten av isbjørnpredasjon, mens jeg tok hensyn til andre abiotiske og biotiske faktorer som påvirket populasjonsdynamikk hos en lokal populasjon med hvitkinngås som hekker i Kongsfjorden, Svalbard. For å oppnå dette, analyserte jeg tre tiår med data på individ-nivå i en integrert populasjons modell, basert på tidligere studier av populasjonsdynamikk i den lokale populasjonen. Estimatene fra modellen inkluderte reproduksjonsrater, overlevelse, populasjonsstørrelser og effekten av abiotiske og biotiske variabler, inkludert predasjon fra polarrev og isbjørn. Resultatene fra denne avhandlingen bekreftet at (1) predasjon fra polarrev har en sterk negativ effekt på reproduksjon, (2) en stadig tidligere vår påvirker antallet gåsunger per hunn positivt, (3) reproduksjon og overlevelse er tetthetsavhengig og (4) varmere temperaturer ved lokasjonen der gjessene overvintrer har en positiv påvirkning på overlevelse. Men det viktigste funnet i denne avhandlingen var at økningen i antall isbjørn som har besøkt Kongsfjorden under hekkingen til hvitkinngås sannsynligvis har hatt en negativ effekt på reproduksjon. Effekten av isbjørn, som virker gjennom predasjon på egg, var bare tydelig i den andre halvdelen av studieperioden. Funnene i denne avhandlingen og en rekke andre studier over store deler av Arktis tyder på at det skjer fundamentale endringer i miljøet i regionen. Endringer som resulterer i endret samfunnsdynamikk, inkludert indirekte klimaeffekter som opererer gjennom endringer i antall og atferd hos predatorer
Effects of experimental winter icing and summer warming on high Arctic tundra vascular plants: a comparison of growth forms
No full textNo other place has experienced such pronounced changes in temperature and precipitation due to climate change, as the terrestrial Arctic. Ecological responses to warmer summers are already well documented, yet the responses to increasing winter temperature and precipitation, are far from understood. Precipitation combined with increased temperature, can result in solid ice layers on the ground, with impacts on plants and animals. Changed climate may cause changes in the plant community, if species respond differently. Understanding responses to changes in the climate and phenomena like rain on snow (ROS) are therefore needed.
I study responses in growth and flowering on plants in Adventdalen (78°N). To simulate the environmental effect of ROS events in winter, ice encasement on the ground was simulated during winter 2015/2016, and established open-top chambers increased the summer temperature (2016) with 0.85 °C and 0.98 °C, then inside control plot. I studied the impact of icing and summer warming treatments through a full factorial randomized block design (n= 36 plots, three blocks) on three key species, the perennial forb Bistorta vivipara and the grasses Poa arctica and Alopecurus borealis. Abundance, flower production, inflorescence height, leaf length, leaf weight, leaf width, surface area and specific leaf area were measured. Except for leaf width in B. vivipara, I found no evidence for interactions between icing and warming. Experimental icing increased the abundance of A. borealis significantly, had no effect on P. arctica, while B. vivipara decrease non-significantly. No icing effect was found on inflorescence height, but it decreased the total flower production. During the peak season, A. borealis leaves tended to be longer in icing plots, while icing did not affect leaf length and leaf weight of P. arctica. Icing had a positive effect on leaf width of B. vivipara (in reproductive type in plots with no summer warming), surface area and leaf weight. Summer warming resulted in increased abundance of both grasses, while B. vivipara abundance was unaffected. Summer warming also resulted in significant taller inflorescence of B. vivipara, greater P. arctica mass and showed a tendency for increased total flower production for the three species. This study show large variation among the species in their responses to experimental icing and summer warming. Although responses to icing and warming varied, even small changes in climate influence plant species. Still, climate change will likely be more pronounced in the long term, and affect other trophic levels. Knowledge about responses of key species are important to be able to predict how the ecosystem on Svalbard will respond to future climate change
Environmental drivers of multi-species synchrony in seabird breeding success
Full text linkPopulations living close together in space are likely to experience more similar environmental fluctuations, and thus may display similar temporal changes in population parameters, in other words synchrony. Interspecific synchrony has implications for ecosystem stability, and highly synchronous populations and communities tend to have a higher risk of extinction. In this thesis, I used long-term data from six seabird species, breeding at Hornøya colony in the Barents Sea, to analyse the degree of synchrony in breeding success. I then investigated potential environmental drivers of inter-specific synchrony, and also asynchrony, in their breeding success. A generalized linear model (GLMs) was fitted to the breeding success data of each species. Pairwise correlations of the model residuals were calculated for all species combinations. Model selection was performed including climate and oceanographic covariates, which were considered to possibly influence breeding success, to identify the best model of breeding success for each species. If a covariate was included in the best-fitting model for multiple species, I tested the extent to which that shared effect led to interspecific synchrony. A higher level of synchrony in breeding success was found between auks and between gulls, than between these groups of birds. Atlantic water-inflow during winter was identified as a driver of breeding success, with potential synchronizing effect for kittiwakes (Rissa tridactyla), great black-backed gulls (Larus marinus) and herring gulls (Larus argentatus). For Atlantic puffins (Fratercula arctica) and razorbills (Alca torda), a lagged effect of Atlantic water-inflow during winter on breeding success was found. Sea surface temperature was identified as a potentially synchronizing driver of breeding success for great black-backed gulls and herring gulls. The results indicate that climate-induced changes in the Barents Sea ecosystem can have pronounced effects on seabirds breeding on Hornøya
Effects of experimental winter icing and summer warming on high Arctic tundra vascular plants: a comparison of growth forms
Full text linkNo other place has experienced such pronounced changes in temperature and precipitation due to climate change, as the terrestrial Arctic. Ecological responses to warmer summers are already well documented, yet the responses to increasing winter temperature and precipitation, are far from understood. Precipitation combined with increased temperature, can result in solid ice layers on the ground, with impacts on plants and animals. Changed climate may cause changes in the plant community, if species respond differently. Understanding responses to changes in the climate and phenomena like rain on snow (ROS) are therefore needed.
I study responses in growth and flowering on plants in Adventdalen (78°N). To simulate the environmental effect of ROS events in winter, ice encasement on the ground was simulated during winter 2015/2016, and established open-top chambers increased the summer temperature (2016) with 0.85 °C and 0.98 °C, then inside control plot. I studied the impact of icing and summer warming treatments through a full factorial randomized block design (n= 36 plots, three blocks) on three key species, the perennial forb Bistorta vivipara and the grasses Poa arctica and Alopecurus borealis. Abundance, flower production, inflorescence height, leaf length, leaf weight, leaf width, surface area and specific leaf area were measured. Except for leaf width in B. vivipara, I found no evidence for interactions between icing and warming. Experimental icing increased the abundance of A. borealis significantly, had no effect on P. arctica, while B. vivipara decrease non-significantly. No icing effect was found on inflorescence height, but it decreased the total flower production. During the peak season, A. borealis leaves tended to be longer in icing plots, while icing did not affect leaf length and leaf weight of P. arctica. Icing had a positive effect on leaf width of B. vivipara (in reproductive type in plots with no summer warming), surface area and leaf weight. Summer warming resulted in increased abundance of both grasses, while B. vivipara abundance was unaffected. Summer warming also resulted in significant taller inflorescence of B. vivipara, greater P. arctica mass and showed a tendency for increased total flower production for the three species. This study show large variation among the species in their responses to experimental icing and summer warming. Although responses to icing and warming varied, even small changes in climate influence plant species. Still, climate change will likely be more pronounced in the long term, and affect other trophic levels. Knowledge about responses of key species are important to be able to predict how the ecosystem on Svalbard will respond to future climate change
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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