121 research outputs found
Density-dependent selection and the maintenance of colour polymorphism in barn owls
The capacity of natural selection to generate adaptive changes is (according to the fundamental theorem of natural selection) proportional to the additive genetic variance in fitness. In spite of its importance for development of new adaptations to a changing environment, processes affecting the magnitude of the genetic variance in fitness-related traits are poorly understood. Here, we show that the red-white colour polymorphism in female barn owls is subject to density-dependent selection at the phenotypic and genotypic level. The diallelic melanocortin-1 receptor gene explained a large amount of the phenotypic variance in reddish coloration in the females (R2 Œ 59:8%). Red individuals (RR genotype) were selected for at low densities, while white individuals (WW genotype) were favoured at high densities and were less sensitive to changes in density.We show that this density-dependent selection favours white individuals and predicts fixation of the white allele in this population at longer time scales without immigration or other selective forces. Still, fluctuating population density will cause selection to fluctuate and periodically favour red individuals. These results suggest how balancing selection caused by fluctuations in population density can be a general mechanism affecting the level of additive genetic variance in natural populations.Density-dependent selection and the maintenance of colour polymorphism in barn owlspublishedVersio
Age-dependent patterns of spatial autocorrelation in fish populations
The degree of spatial autocorrelation in population fluctuations increases with dispersal and geographical covariation in the environment, and decreases with strength of density dependence. Because the effects of these processes can vary throughout an individualâs lifespan, we studied how spatial autocorrelation in abundance changed with age in three marine fish species in the Barents Sea. We found large interspecific differences in age-dependent patterns of spatial autocorrelation in density. Spatial autocorrelation increased with age in cod, the reverse trend was found in beaked redfish, while it remained constant among age classes in haddock. We also accounted for the average effect of local cohort dynamics, i.e. the expected local density of an age class given last yearâs local density of the cohort, with the goal of disentangling spatial autocorrelation patterns acting on an age class from those formed during younger age classes and being carried over. We found that the spatial autocorrelation pattern of older age classes became increasingly determined by the distribution of the cohort during the previous year. Lastly, we found high degrees of autocorrelation over long distances for the three species, suggesting the presence of far-reaching autocorrelating processes on these populations. We discuss how differences in the speciesâ life history strategies could cause the observed differences in age-specific variation in spatial autocorrelation. As spatial autocorrelation can differ among age classes, our study indicates that fluctuations in age structure can influence the spatio-temporal variation in abundance of marine fish populations.publishedVersio
Spatial scaling of population synchrony in marine fish depends on their life history
The synchrony of population dynamics in space has important implications for ecological processes, for example affecting the spread of diseases, spatial distributions and risk of extinction. Here, we studied the relationship between spatial scaling in population dynamics and species position along the slowâfast continuum of life history variation. Specifically, we explored how generation time, growth rate and mortality rate predicted the spatial scaling of abundance and yearly changes in abundance of eight marine fish species. Our results show that population dynamics of species' with âslowâ life histories are synchronised over greater distances than those of species with âfastâ life histories. These findings provide evidence for a relationship between the position of the species along the life history continuum and population dynamics in space, showing that the spatial distribution of abundance may be related to life history characteristics.acceptedVersio
How are species interactions structured in species-rich communities? A new method for analysing time-series data
Estimation of intra- and interspecific interactions from time-series on species-rich communities is challenging due to the high number of potentially interacting species pairs. The previously proposed sparse interactions model overcomes this challenge by assuming that most species pairs do not interact. We propose an alternative model that does not assume that any of the interactions are necessarily zero, but summarizes the influences of individual species by a small number of community-level drivers. The community-level drivers are defined as linear combinations of species abundances, and they may thus represent e.g. the total abundance of all species or the relative proportions of different functional groups. We show with simulated and real data how our approach can be used to compare different hypotheses on community structure. In an empirical example using aquatic microorganisms, the community-level drivers model clearly outperformed the sparse interactions model in predicting independent validation data.Peer reviewe
LifeâHistory Variation Predicts the Effects of Demographic Stochasticity on Avian Population Dynamics
Demographic routes to variability and regulation in bird populations
There is large interspecific variation in the magnitude of population fluctuations, even among closely related species. The factors generating this variation are not well understood, primarily because of the challenges of separating the relative impact of variation in population size from fluctuations in the environment. Here, we show using demographic data from 13 bird populations that magnitudes of fluctuations in population size are mainly driven by stochastic fluctuations in the environment. Regulation towards an equilibrium population size occurs through density-dependent mortality. At small population sizes, population dynamics are primarily driven by environment-driven variation in recruitment, whereas close to the carrying capacity K, variation in population growth is more strongly influenced by density-dependent mortality of both juveniles and adults. Our results provide evidence for the hypothesis proposed by Lack that population fluctuations in birds arise from temporal variation in the difference between density-independent recruitment and density-dependent mortality during the non-breeding season.Peer reviewe
The Nature Index: A General Framework for Synthesizing Knowledge on the State of Biodiversity
The magnitude and urgency of the biodiversity crisis is widely recognized within
scientific and political organizations. However, a lack of integrated measures
for biodiversity has greatly constrained the national and international response
to the biodiversity crisis. Thus, integrated biodiversity indexes will greatly
facilitate information transfer from science toward other areas of human
society. The Nature Index framework samples scientific information on
biodiversity from a variety of sources, synthesizes this information, and then
transmits it in a simplified form to environmental managers, policymakers, and
the public. The Nature Index optimizes information use by incorporating expert
judgment, monitoring-based estimates, and model-based estimates. The index
relies on a network of scientific experts, each of whom is responsible for one
or more biodiversity indicators. The resulting set of indicators is supposed to
represent the best available knowledge on the state of biodiversity and
ecosystems in any given area. The value of each indicator is scaled relative to
a reference state, i.e., a predicted value assessed by each expert for a
hypothetical undisturbed or sustainably managed ecosystem. Scaled indicator
values can be aggregated or disaggregated over different axes representing
spatiotemporal dimensions or thematic groups. A range of scaling models can be
applied to allow for different ways of interpreting the reference states, e.g.,
optimal situations or minimum sustainable levels. Statistical testing for
differences in space or time can be implemented using Monte-Carlo simulations.
This study presents the Nature Index framework and details its implementation in
Norway. The results suggest that the framework is a functional, efficient, and
pragmatic approach for gathering and synthesizing scientific knowledge on the
state of biodiversity in any marine or terrestrial ecosystem and has general
applicability worldwide
Contrasting patterns of density-dependent selection at different life stages can create more than one fastâslow axis of life-history variation
There has been much recent research interest in the existence of a major axis of lifeâhistory variation along a fastâslow continuum within almost all major taxonomic groups. Ecoâevolutionary models of densityâdependent selection provide a general explanation for such observations of interspecific variation in the "pace of life." One issue, however, is that some largeâbodied longâlived âslowâ species (e.g., trees and large fish) often show an explosive âfastâ type of reproduction with many small offspring, and species with âfastâ adult life stages can have comparatively âslowâ offspring life stages (e.g., mayflies). We attempt to explain such lifeâhistory evolution using the same ecoâevolutionary modeling approach but with two life stages, separating adult reproductive strategies from offspring survival strategies. When the population dynamics in the two life stages are closely linked and affect each other, densityâdependent selection occurs in parallel on both reproduction and survival, producing the usual oneâdimensional fastâslow continuum (e.g., houseflies to blue whales). However, strong density dependence at either the adult reproduction or offspring survival life stage creates quasiâindependent population dynamics, allowing fastâtype reproduction alongside slowâtype survival (e.g., trees and large fish), or the perhaps rarer slowâtype reproduction alongside fastâtype survival (e.g., mayfliesâshortâlived adults producing few longâlived offspring). Therefore, most types of species life histories in nature can potentially be explained via the ecoâevolutionary consequences of densityâdependent selection given the possible separation of demographic effects at different life stages.publishedVersio
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