Environmental conditions experienced during early growth and development markedly shape phenotypic traits. Consequently, individuals of the same cohort may show similar life-history tactics ...throughout life. Conditions experienced later in life, however, could fine-tune these initial differences, either increasing (cumulative effect) or decreasing (compensatory effect) the magnitude of cohort variation with increasing age. Our novel comparative analysis that quantifies cohort variation in individual body size trajectories shows that initial cohort variation dissipates throughout life, and that lifetime patterns change both across species with different paces of life and between sexes. We used longitudinal data on body size (mostly assessed using mass) from 11 populations of large herbivores spread along the "slow-fast" continuum of life histories. We first quantified cohort variation using mixture models to identify clusters of cohorts with similar initial size. We identified clear cohort clusters in all species except the one with the slowest pace of life, revealing that variation in early size is structured among cohorts and highlighting typological differences among cohorts. Growth trajectories differed among cohort clusters, highlighting how early size is a fundamental determinant of lifetime growth patterns. In all species, among-cohort variation in size peaked at the start of life, then quickly decreased with age and stabilized around mid-life. Cohort variation was lower in species with a slower than a faster pace of life, and vanished at prime age in species with the slowest pace of life. After accounting for viability selection, compensatory/catch-up growth in early life explained much of the decrease in cohort variation. Females showed less phenotypic variability and stronger compensatory/catch-up growth than males early in life, whereas males showed more progressive changes throughout life. These results confirm that stronger selective pressures for rapid growth make males more vulnerable to poor environmental conditions early in life and less able to recover after a poor start. Our comparative analysis illustrates how variability in growth changes over time in closely related species that span a wide range on the slow-fast continuum, the main axis of variation in life-history strategies of vertebrates.
In polar seas, the seasonal melting of ice triggers the development of an open-water ecosystem characterized by short-lived algal blooms, the grazing and development of zooplankton, and the influx of ...avian and mammalian predators. Spatial heterogeneity in the timing of ice melt generates temporal variability in the development of these events across the habitat, offering a natural framework to assess how foraging marine predators respond to the spring phenology. We combined 4 yr of tracking data of Antarctic petrels Thalassoica antarctica with synoptic remote-sensing data on sea ice and chlorophyll a to test how the development of melting ice and primary production drive Antarctic petrel foraging. Cross-correlation analyses of first-passage time revealed that Antarctic petrels utilized foraging areas with a spatial scale of 300 km. These areas changed position or disappeared within 10 to 30 d and showed no spatial consistency among years. Generalized additive model (GAM) analyses suggested that the presence of foraging areas was related to the time since ice melt. Antarctic petrels concentrated their search effort in melting areas and in areas that had reached an age of 50 to 60 d from the date of ice melt. We found no significant relationship between search effort and chlorophyll a concentration. We suggest that these foraging patterns were related to the vertical distribution and profitability of the main prey, the Antarctic krill Euphausia superba. Our study demonstrates that the annual ice melt in the Southern Ocean shapes the development of a highly patchy and elusive food web, underscoring the importance of flexible foraging strategies among top predators.
During breeding, long-lived species face important time and energy constraints that can lead to breeding failure when food becomes scarce. Despite the potential implications of intra-season dynamics ...in breeding failure for individual behavior, carry-over effects, dispersal decisions and population dynamics, little information is currently available on these dynamics at fine temporal scales. Here, we monitored the foraging behavior and the proportion of successful black-legged kittiwake pairs from nest construction to chick fledging in a colony of the southern Barents Sea, to relate foraging effort to the dynamics of breeding failure over an entire breeding season, and to infer the environmental conditions leading to this failure. Specifically, we tracked kittiwakes with GPS and satellite tags during incubation and early chick-rearing to document nest attendance, foraging range, time budgets and daily energy expenditures (DEE). We also monitored diet changes over time. We predicted that breeding failure would follow a non-linear trend characterized by a break point after which breeding success would drop abruptly and would be related to a substantial increase in foraging effort. Kittiwakes showed contrasting foraging patterns between incubation and chick-rearing: they extended their foraging range from 20 km during incubation to more than 450 km during chick-rearing and switched diet. They also increased their DEE and readjusted their time budgets by increasing time spent at sea. These changes corresponded to a break point in breeding dynamics beyond which the proportion of successful pairs abruptly dropped. At the end of the season, less than 10% of kittiwake pairs raised chicks in the monitored plots. This integrative study confirms that breeding failure is a non-linear process characterized by a threshold beyond which individuals face an energetic trade-off and cannot simultaneously sustain high reproductive and self-maintenance efforts. In this way, the occurrence of sudden environmental changes complicates our ability to predict population dynamics and poses conservation challenges.
Concentrations of organochlorine contaminants (OCs) and associations between OCs and fitness components were examined in great black-backed gulls (Larus marinus) in three colonies along the coast of ...northern Norway. In one of the colonies, data were collected in two subsequent seasons. Concentrations of four OCs (HCB, oxychlordane, DDE and PCB) were measured in blood (n=260) and fitness components (reproductive variables and adult return rate between breeding seasons) were recorded. In the first year, in two of the colonies, body condition and reproductive performance among the gulls were poor compared to the third colony, suggesting spatial variation in environmental conditions, especially food availability. However, in the third colony, body condition and reproductive performance were even better in the second season; i.e. environmental conditions varied temporally. OC residues were higher in the colonies where environmental conditions were poor, but much of this variation was explained by differences in body condition among colonies. Moreover, concurrent with improved body condition from one season to the next, the concentrations of OCs were halved. In the two colonies where environmental conditions were poor, female OC residues were negatively related to egg-laying date, egg size and nesting success, and in the colony where the concentrations of OC were highest, gulls with elevated DDE residues had low probability of returning between breeding seasons. In comparison, in the colony where environmental conditions were better in the first year, other types of adverse relationships between OCs and fitness components were found; i.e. chicks from females with high OC concentrations were in poor condition at hatching, suggesting maternal transfer of OCs to the eggs, and males with high OC residues had poor nesting success and chick survival, suggesting OC-mediated behavioural changes. With improved environmental conditions and lower OC concentrations in the second season, no significant adverse relationships between OCs and fitness components were found. This study thus suggests that there are complex interrelationships between both concentrations and ecological effects of OCs, and the environment, indicating that effects of OCs in nature may only be assessed after considering environmental variation.
Mothers are predicted to invest in their offspring depending on the quality of their mate, their opportunity to invest in future reproduction and the characteristics of the habitat in which their ...offspring will be born. Recent studies have suggested a transfer of maternal immunity to offspring as an induced response to the local presence of parasites in the environment, but evidence has been indirect. Here, we show the presence of antibodies against the Lyme disease agent Borrelia burgdorferi sensu lato, a spirochaete transmitted by the seabird tick Ixodes uriae, in the eggs of kittiwakes Rissa tridactyla. We report higher prevalence of antibodies against Borrelia in eggs from breeding areas with higher prevalence and abundance of ticks. Further, high repeatabilities of antibody-positive eggs within clutches and between first and replacement clutches show that, within a breeding season, females differ consistently with respect to the expression of this induced maternal response. Our results suggest that mothers can alter investment in their young depending on local conditions. Such maternal effects clearly have implications for the ecology and evolution of host-parasite interactions.
Parasites extract part or all their resources from their host depriving them of energy that could be normally used for growth, self‐maintenance or reproduction. Thus, parasites are playing a major ...role in the evolution of life‐history traits of their host through direct or indirect fitness costs. The current experiment investigated the effect of parasitic warble flies (Hypoderma tarandi), on the life‐history traits of reindeer (Rangifer tarandus tarandus). In autumn‐winter 2005, 52 free‐ranging female reindeer were administrated with an anti‐parasite drug (treatment group), whereas 56 females remained untreated (control group). Subsequently, body mass, reproductive success and calf body mass were recorded in summer and winter the following year for all individuals. Reproductive success, measured as the probability of producing an offspring, was not affected by the treatment. However, the manipulation positively affected female body mass in the summer but not in the winter and a positive trend was observed for the calves during the same season. Overall, our findings indicate that warble flies have a negative impact on reindeer through their effect on body mass and consequently, are likely to affect reindeer life history and population dynamics.
Large herbivores living in seasonal environments are generally food-limited through density dependence and climatic factors. This may result in starvation and increased mortality in winter and ...reduced fecundity the following summer. Variability in winter conditions has the potential to create persistent fitness differences at the cohort- and the individual-level in iteroparous species. Using a 9-year dataset from two herds of individually marked free-ranging reindeer we assessed whether population growth rates, somatic allocation (female body mass) and reproductive allocation (reproductive success and calf body mass) were affected by supplementary feeding, population density and the timing of the onset of spring (i.e., vegetation onset). The supplementary fed population had a higher population growth rate, the females were more likely to reproduce and their calves were heavier than in the control population. Female body mass was negatively related to timing of vegetation green-up in both herds. Since both populations increased in the last decade we found support to our prediction that density-dependence negatively affected our study herds. Indeed, density negatively affected growth rates, female body mass, reproductive success and calf body mass in both populations and, as expected, this effect was more marked in the control herd. We suggest that food supplemented females may, at least partially, be able to compensate for the energetic costs of negative density-dependence following late vegetation green-up while control females may not. Our findings reveal that late winter conditions have an important limiting role in the study area and that density-dependent food limitation in late winter/early summer acts as a main factor affecting our reindeer population.
How animals change their movement patterns in relation to the environment is a central topic in a wide area of ecology, including foraging ecology, habitat selection, and spatial population ecology. ...To understand the underlying behavioral mechanisms involved, there is a need for methods to measure changes in movement patterns along a pathway through the landscape. We used simulated pathways and satellite tracking of a long-ranging seabird to explore the properties of first-passage time as a measure of search effort along a path. The first-passage time is defined as the time required for an animal to cross a circle with a given radius. It is a measure of how much time an animal uses within a given area. First-passage time is scale dependent, and a plot of variance in first-passage time vs. spatial scale reveals the spatial scale at which the animal concentrates its search effort. By averaging the first-passage time on a geographical grid, it is possible to relate first-passage time to environmental variables and the search pattern of other individuals.
Abstract
The concept of cumulative impacts is widespread in policy documents, regulations and ecological studies, but quantification methods are still evolving. Infrastructure development usually ...takes place in landscapes with preexisting anthropogenic features. Typically, their impact is determined by computing the distance to the nearest feature only, thus ignoring the potential cumulative impacts of multiple features. We propose the
cumulative ZOI approach
to assess whether and to what extent anthropogenic features lead to cumulative impacts.
The approach estimates both effect size and zone of influence (ZOI) of anthropogenic features and allows for estimation of cumulative effects of multiple features distributed in the landscape. First, we use simulations and an empirical study to understand under which circumstances cumulative impacts arise. Second, we demonstrate the approach by estimating the cumulative impacts of tourist infrastructure in Norway on the habitat of wild reindeer (
Rangifer t. tarandus
), a near‐threatened species highly sensitive to anthropogenic disturbance.
In the simulations, we showed that analyses based on the nearest feature and our cumulative approach are indistinguishable in two extreme cases: when features are few and scattered and their ZOI is small, and when features are clustered and their ZOI is large. The empirical analyses revealed cumulative impacts of private cabins and tourist resorts on reindeer, extending up to 10 and 20 km, with different decaying functions. Although the impact of an isolated private cabin was negligible, the cumulative impact of ‘cabin villages’ could be much larger than that of a single large tourist resort. Focusing on the nearest feature only underestimates the impact of ‘cabin villages’ on reindeer.
The suggested approach allows us to quantify the magnitude and spatial extent of cumulative impacts of point, linear, and polygon features in a computationally efficient and flexible way and is implemented in the
oneimpact
R package. The formal framework offers the possibility to avoid widespread underestimations of anthropogenic impacts in ecological and impact assessment studies and can be applied to a wide range of spatial response variables, including habitat selection, population abundance, species richness and diversity, community dynamics and other ecological processes.
Sammendrag
Konseptet kumulative effekter, ofte kalt samlet belastning, er mye brukt i politiske dokumenter, forskrifter og økologiske studier, og de kvantitative metodene for å måle dette er i stadig utvikling. Utbygging av infrastruktur skjer i hovedsak i områder som allerede er påvirket av menneskelig utvikling. Normalt blir miljøpåvirkningen av slik utbygging beregnet ut fra avstanden til den nærmeste strukturen og man ser bort ifra den samlede belastingen av flere strukturer i samme område. Vi foreslår en tilnærming kalt kumulativ influenssone (ZOI) for å undersøke om, og i hvor stor grad, menneskeskapte strukturer fører til kumulative effekter på miljøet.
Metoden estimerer både effektstørrelsen og størrelsen på influenssonen til menneskeskapte inngrep, og gir oss mulighet til å estimere den kumulative effekten av flere inngrep i samme område. Vi undersøker først i hvilke situasjoner kumulative effekter oppstår ved hjelp av simuleringer og en empirisk studie. Deretter viser vi tilnærmingen ved å estimere kumulative virkninger av private hytter, hyttefelt og turisthytter i Norge på Villrein,
Rangifer t. tarandus
, en nær utrydningstrua art som er svært sensitiv til menneskelige forstyrrelser.
Simuleringene viser at analyser som baserer seg på avstand til nærmeste strukutur og vår kumulative tilnærming gir like resultat i to ekstremtilfeller; når det er få og spredde strukturer med små influenssoner, og når strukturene er klumpete fordelt og influenssonene er store. I empiriske analyser fant vi kumulative effekter av private hytter og turisthytter på Villrein helt opp til en avstand på 10 og 20 km, men med ulike funksjoner for hvordan effekten avtar med avstand fra hyttene. Selv om effekten av en privat hytte var neglisjerbar, kunne effekten av et hyttefelt med mange hytter være mye større enn effekten av en stor turisthytte. Analysen viste at å kun måle avstanden til det nærmeste bygget underestimerte hyttefelt sin påvirkning på Villrein.
Den kumulative influenssone tilnærmingen gir oss et verktøy til å kvantifisere den romlige utstrekningen og effektstørrelsen til både punkt, linjer og polygoner. Metoden er beregningsmessig fleksibel og effektiv og vi har samlet beregningsverktøy i R pakken oneimpact. Det metodiske rammeverket gir oss verktøy for å unngå den til nå utbredte underestimering av menneskelig påvirkning i økologiske studier og konsekvensutredninger, og kan bli benyttet på mange ulike romlige responsvariable, inkludert habitatseleksjon, populasjonsstørrelse, artsrikdom og diversitet, samfunnsdynamikk og andre økologiske prosesser.
Resumo
O conceito de impactos cumulativos é amplamente utilizado em políticas públicas, documentos regulatórios e estudos ecológicos, mas os métodos para quantificá‐los ainda estão se desenvolvendo. O desenvolvimento de infraestruturas frequentemente ocorre em paisagens com distúrbios antropogênicos pré‐existentes. Geralmente, seu impacto é determinado computando‐se a distância à infraestrutura mais próxima somente, ignorando o potencial impacto cumulativo de múltiplas infraestruturas. Aqui nós propomos a
abordagem da zona de influência (ZOI) cumulativa
para avaliar se e em que medida múltiplas infraestruturas antropogênicas levam a impactos cumulativos.
A abordagem estima tanto o tamanho do efeito como a zona de influência (ZOI) de infraestruturas antropogênicas e permite a estimação de efeitos cumulativos de múltiplos distúrbios distribuídos na paisagem. Primeiro, nós utilizamos simulações e um estudo empírico para compreendeer em quais condições os impactos cumulativos aparecem. Segundo, nós demonstramos a abordagem estimando os impactos de infraestruturas de turismo na Noruega no habitat de renas selvagens
Ranfiger t. tarandus
, uma espécie quase ameaçada e altamente sensível a distúrbios antrópicos.
As simulações mostraram que análises baseadas na infraestrutura mais próxima e a nossa abordagem cumulativa são indistinguíveis em dois casos extremos: quando as infraestruturas são poucas e esparsas e sua ZOI é pequena, e quando as infraestruturas estão agregadas e sua ZO é grande. As análises empíricas revelaram impactos cumulativos de cabanas privadas e
resorts
de turismo nas renas, extendendo‐se até 10 e 20 km, seguindo diferentes funcões de decaimento. Enquanto o impacto de uma cabana privada isolada foi negligível, o impacto cumulativo de ‘vilas de cabanas’ foi muito maior que o de
resorts
turísticos sozinhos. Focar somente no efeito das infraestruturas mais próximas subestima o impacto de ‘vilas de cabanas’ nas renas.
A abordagem aqui apresentada permite a quantifição da magnitude e extensão espacial dos impactos cumulativos de infraestruturas representadas como pontos, linhas, ou polígonos de uma maneira computacionalmente eficiente e flexível, implementada no pacote R
oneimpact
. O arcabouço formal oferece a possibilidade de se evitar a subestimação de impactos antrópicos em estudos de impacto ambiental e estudos ecológicos, e pode ser aplicado a uma vasta gama de variáveis respostas incluindo seleção de habitat, abundância populacional, diversidade e riqueza de espécies, dinâmica de populações, e outros processos ecológicos.
Abundant large herbivores can strongly alter vegetation composition, shifting the ecosystem into a lasting state of changed productivity. Previous studies of the effects of abundant reindeer on ...alpine and arctic vegetation have yielded equivocal results, probably due to differing environmental contexts. To overcome context dependency we devised a large-scale survey in the region of Finnmark, northern Norway, possessing some of the most densely stocked reindeer herds in the world. The effects of reindeer abundance on summer pasture vegetation were assessed by employing a quasi-experimental design, including site fertility as a potential modifier of the reindeer-vegetation interaction. The study design comprised ten pairs of neighboring management districts (encompassing 18,003 km²), where over the two last decades a high-density district on average had reindeer densities more than twice as high and calf weights consistently lower than the low-density district. The abundance of different plant functional groups, ranging from those having facilitating to retarding effects on ecosystem productivity, were quantified by the point intercept method on plots selected according to a hierarchical, stratified random sampling design. Species with strong retarding effects on ecosystem productivity (for example, ericoids) were by far the most abundant. However, we found no consistent effects of reindeer density on their abundance. The most consistent differences between high- and low-density districts were found in plant functional groups with facilitating to neutral effects on ecosystem productivity. In particular, the abundance of N-facilitators, large dicotyledons and grasses were substantially reduced in the high-density districts. However, this reduction was restricted to fertile sites. Thus, reindeer when present at high densities have homogenized the biomass of palatable plants across environmental productivity gradients according to predictions from exploitation ecosystem models. Such reduction of plants with facilitating to neutral effects on ecosystem productivity indicates a reduced state of ecosystem productivity in high-density districts.
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