For several mammalian species, both population levels and distribution ranges are predicted to change due to changing habitat conditions caused by climate change. A general decrease in the amplitude ...of small rodent population cycles in northern Europe since the late 1980s has commonly been attributed to a lack of permanent snow cover during winter, or to unfavourable snow conditions. An alternative explanation is that increasing summer temperatures and an extended growing season are unfavourable for herbivorous rodents, by reducing the forage quality. If so, the negative effect should be stronger for the strictly herbivorous Microtus voles than for the herbivorous-granivorous Myodes voles. In a previous study small rodents were snap trapped in 22 regions in Norway during 1971–1979. We found that the trapping index of Microtus voles, but not Myodes voles, in this study was negatively related to summer temperatures. Both in this study and in a snap trapping study from 1994 to 2015, conducted in 13 study areas in Norway, the proportion of Microtus voles among voles captured was negatively related to summer temperatures. Summer temperature was a better predictor than snow depth, but both variables contributed significantly in multiple regression models. We conclude that summer temperature is likely to be a more important factor than snow cover for the population dynamics of herbivorous voles in northern Europe.
•Low vole numbers during the 1990s and early 2000s has been linked to climate change.•Possible drivers are unfavourable snow conditions and high summer temperatures.•Decreased forage quality in warm summers should mainly affect herbivorous species.•Summer temperatures was the best predictor for herbivorous vole number in Norway.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Forage quality is rarely the focus of studies on grouse performance. The plant stress hypothesis predicts that the protein digestibility of a focal food plant for grouse in Norway, the bilberry ...Vaccinium myrtillus should be highest after a peak in seed production. Protein digestibility may also be affected positively by cosmic ray (muon) fluxes, which fluctuate with the 9.3-year lunar nodal phase cycle, and negatively by high temperatures in the preceding summers. The annual change (first difference) in ln-transformed black grouse Tetrao tetrix and capercaillie T. urogallus hunting statistic indices from southern Norway 1999–2017 was positively related to the mean June temperature, which is assumed to have a direct positive impact on chick survival. In multiple regression models, there was also a positive relationship with the seed production of bilberry in the preceding year, the lunar nodal phase index with a two-year time lag, and a negative relationship with the combined mean June–September temperature of the two preceding years. Small rodent numbers did not contribute significantly in these models. In further monitoring of grouse populations, the seed production of bilberry or other important food plants should also be recorded.
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DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
The hypothesis that predation is the cause of the regular small rodent population oscillations observed in boreal and Arctic regions has long been debated. Within this hypothesis, it is proposed that ...the most likely predators to cause these destabilizing effects are sedentary specialists, with small mustelids being possible candidates. One such case would be the highly specialized least weasel (
Mustela nivalis
) driving the Norwegian lemming (
Lemmus lemmus
) cycle in Fennoscandia. These predators are often elusive and therefore distribution data can only be based on field signs, which is problematic when various mustelid species are sympatric, such as weasels and stoats (
Mustela erminea
). Here we present the results of using mustelid faeces in predated winter lemming nests to correctly identify the predator and thus discern which species exerts the strongest predation pressure on lemming winter populations. Samples were obtained during different phases in the lemming cycle, spanning 6 years, to account for different prey densities. Faecal mitochondrial DNA extraction and amplification of a 400-bp fragment was successful in 92/114 samples (81%); the sequencing of these samples proved that most predation occurrences (83%) could be attributed to the least weasel. These findings support the hypothesis that weasels in particular show high specificity in predation and could therefore be candidates to driving the lemming cycle in this area. We conclude that DNA analysis of faecal remains around predated nests can be a useful tool for further investigations concerning predator–prey interactions in the tundra.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Fire is a significant disruptive agent in various ecosystems around the world. It can affect the availability of resources in a given area, modulating the interaction between competing species. We ...studied the diet of the culpeo fox (Lycalopex culpaeus) and cougar (Puma concolor) for two consecutive years in a protected area of southern–central Chile which was affected by a wildfire. Significant differences were observed in the dietary pattern between the two species, showing their trophic segregation. In the two years of the study, the predominant prey for cougar was an exotic species, the European hare (Lepus europaeus), implying a simplification of its trophic spectrum with respect to that reported in other latitudes. The ecological consequences related to this scenario are discussed.
Migratory species have a limited time for habitat selection upon arrival at the breeding grounds. This is especially evident in arctic migrants, which are restricted by a narrow window of opportunity ...when environmental conditions are favorable for breeding. This general time constraint is amplified in rough-legged buzzards (
Buteo lagopus
) who, as many other arctic predators, rely on rodent (lemming) cycles during the breeding season, a 3–5 year period of waxing and waning local food abundance. It remains unclear how arctic predators, especially migrants, can find nesting areas where rodents are numerous when their selection time is so limited. We hypothesized that rough-legged buzzards select nesting areas during the previous breeding season. We tracked 43 rough-legged buzzards using GPS telemetry and assessed their movements post-breeding prospecting behavior to test our hypothesis. Here we show that rough-legged buzzards search for a nesting location during the previous breeding season in a post-breeding period. In the following year, individuals return to and attempt to breed in the area they inspected the year before. Rough-legged buzzards, regardless of breeding success, remained in the Arctic all breeding season until the end of September. Failed breeders prospected more than successful ones. At the same time, buzzards that bred in the rodent-free ecosystem prospected less and showed a high level of philopatry. Therefore, as rodent cycles have been predicted to collapse in the warming Arctic, we can expect arctic predators to change their movement patterns in the future with serious potential consequences for their conservation. We anticipate our study provides a step forward toward understanding movement and settlement decisions in animals experiencing high inter-annual environmental variation.
Most organisms live in changing environments or do not use the same resources at different stages of their lives or in different seasons. As a result, density dependence will affect populations ...differently at different times. Such sequential density dependence generates markedly different population responses compared to the unrealistic assumption that all events occur simultaneously. Various field studies have also shown that the conditions that individuals experience during one period can influence success and per capita vital rates during the following period. These carry-over effects further complicate any general principles and increase the diversity of possible population dynamics. In this review, we describe how studies of sequential density dependence have diverged in directions that are both taxon-specific and have non-overlapping terminology, despite very similar underlying problems. By exploring and highlighting these similarities, we aim to improve communication between fields, clarify common misunderstandings, and provide a framework for improving conservation and management practices, including sustainable harvesting theory.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
We quantify the expected demographic benefit to a seabird of conservation concern, the ashy storm‐petrel Oceanodroma homochroa, from the proposed eradication of introduced house mice Mus musculus on ...the South Farallon Islands, California. A key objective of the eradication is to reduce storm petrel predation by burrowing owls Athene cunicularia, which stopover on the island during their fall migration. Mouse trapping and field surveys of both owls and depredated storm petrel carcasses conducted during 2000–2012 reveal a strongly seasonal, inter‐related pattern among the three species: When owls arrive during the fall, mice are super‐abundant and the overwhelming choice of prey for those owls that remain. In the winter, the mouse population crashes just as storm petrels begin to arrive in large numbers; owls that remain on the island switch to preying upon storm petrels until May, when they depart to breed. Capture–recapture analyses of storm petrels showed (1) annual adult survival was inversely related to owl abundance, especially during January–April, and (2) storm petrels demonstrated a declining trend in abundance 2006–2012. The latter was associated with low rates of adult survival, high abundance of overwintering burrowing owls, and high incidence of depredated storm petrels. To evaluate projected impacts to storm petrels of a change in owl predation, we developed a Leslie matrix model, incorporating environmental stochasticity. We modeled future storm petrel population trajectories, allowing for different levels of owl‐mediated predation. Our results suggest that a reduction in owl abundance, a projected consequence of the elimination of mice, has the potential to substantially reduce overall storm petrel mortality, thereby reducing storm petrel declines and increasing the likelihood of stable trends in the future. While long‐term benefits to storm petrels of mouse eradication are apparent, the risk of increased predation due to prey‐switching by owls also needs to be addressed. This study highlights uncertainty of outcomes, which must be considered in evaluating management impacts. This study demonstrates the value of concurrent, continuous, long‐term datasets in providing a quantitative basis for management to aid the conservation of species of concern.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Conspicuous cyclic changes in population density characterize many populations of small northern rodents. The extreme crashes in individual number are expected to reduce the amount of genetic ...variation within a population during the crash phases of the population cycle. By long‐term monitoring of a bank vole (Myodes glareolus) population, we show that despite the substantial and repetitive crashes in the population size, high heterozygosity is maintained throughout the population cycle. The striking population density fluctuation in fact only slightly reduced the allelic richness of the population during the crash phases. Effective population sizes of vole populations remained also relatively high even during the crash phases. We further evaluated potential mechanisms contributing to the genetic diversity of the population and found that the peak phases are characterized by both a change in spatial pattern of individuals and a rapid accession of new alleles probably due to migration. We propose that these events act together in maintaining the high genetic diversity within cyclical populations.
Conspicuous cyclic changes in population density characterize many populations of small northern rodents. The extreme crashes in individual number are expected to reduce the amount of genetic variation within a population during the crash phases of the population cycle. By long‐term monitoring of a bank vole (Myodes glareolus) population we show that despite the substantial and repetitive crashes in the population size, high heterozygosity is maintained throughout the population cycle. The striking population density fluctuation in fact only slightly reduced the allelic richness of the population during the crash phases. Effective population sizes of vole populations remained also relatively high even during the crash phases. The peak phases are characterized by both a change in spatial pattern of individuals and a rapid accession of new alleles.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Ecology requires the conceptual and technical ability to analyse complex and dynamic systems consisting of a high and variable number of components and relations. These components are part of a ...variable interaction structure in a spatially heterogeneous context. The components of ecological interaction networks can give rise to self-organised, and scale-dependent interaction patterns and processes, which are the underlying causes of the overall ecological systems states.
The individual-based modelling approach provides a widely applicable simulation framework based on a ‘hierarchy theory’ view of ecological systems.
Here, we summarise and generalise the theoretical implications of the modelling studies presented in this volume in the field of terrestrial and aquatic, animal and plant ecology. The case studies cover a representative profile of processes related to ecological applications, such as food web interactions, population dynamics, dispersal, energy physiology, nutrient allocation and mutual impact of morphological and physiological development. The generic approach applied in this context allows a hierarchical representation of ecological systems and their components. Model results are obtained as self-organised structural relation networks and as aggregated quantitative states. In order to address different model characteristics we distinguish
collective and
emergent properties. Collective properties are those that are attributed equally to different organisation levels of the system. Emergent properties result from the activities of lower level entities on a higher organisation level, while not being present on the lower level. They can be subdivided into
aggregational and
connective properties. Emergent properties that are aggregational are those which emerge as a result of an aggregation procedure by an observer on the higher level which does not make sense or is not applicable on lower levels. Emergent properties that are connective, however, are based on an interaction network of lower level entities, which brings about the specific system characteristic.
This classification of model results will allow to generalise the achievements and potential of the individual-based modelling approach in ecology.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Community interactions of small rodents have attracted the attention of ecologists for many years due to their abrupt changes in population numbers, their impact on the whole biocoenosis and also ...because of immense damages to agricultural production and forestry. In particular, regularly oscillating rodent populations in Scandinavia have been subject of discussions among theoretically and empirically working ecologists for many decades. Spatial and temporal restrictions in empirical work led to various attempts to model these dynamics to understand large scale effects resulting from complex interactions in variable cause-effect networks of the numerous involved system components.
The presented individual-based model for the first time described small rodent communities as a set of interacting autonomously acting agents with a detailed life history and behavioural repertoire in a food-web setup composed of three trophic levels (rodents, rodents food and predators). It thus allowed to integrate all relevant factors accounting for the dynamics of rodents which acted in a simulated environment containing the spatial arrangement of habitats and seasonal changing conditions. Due to the representation with interacting entities, the dynamics on higher levels resulted in a self-organisation process as emergent properties. This differentiation between the focal and the operational level allowed to investigate processes interacting between different integration levels and to adapt the model to different scenarios easily as well as to specify it for a large range of rodents species.
Simulations have been executed for two different scenarios. The Bornhöved scenario simulating the situation of a Northern German rodent community in a beech forest represented bottom-up effects of mast events on population dynamics. The Scandinavian scenario which depicted the most important actors of these oscillating rodent communities, gave new insights into the processes causing the sudden decline of rodent populations. Both, lack of resources and predation, contributed to about 90% of mortality, but no pattern could be found when relating either cause with the properties of the respective cycle. Bottom up and top down control vary unpredictably and chaotically in the model. These results may explain considerable parts of contradicting empirical findings.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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