Understanding components of interspecific competition has long been a major goal in ecological studies. Classical models of competition typically consider equal responses of all individuals to the ...density of competitors, however responses may differ both among individuals from the same population, and between populations.
Based on individual long‐term monitoring of two chamois populations in sympatry with red deer, we built a multi‐event capture‐recapture model to assess how vital rates of the smaller chamois are affected by competition from the larger red deer.
In both populations, mortality and breeding probabilities of female chamois depend on age and in most cases, breeding status the preceding year. Successful breeders always performed better the next year, indicating that some females are of high quality. In one population where there was high spatial overlap between the two species, the survival of old female chamois that were successful breeders the preceding year (high‐quality) was negatively related to an index of red deer population size suggesting that they tend to skip reproduction instead of jeopardizing their own survival when the number of competitors increases. The breeding probability of young breeders (ages 2 and 3) was similarly affected by red deer population size. In contrast, in the second site with low spatial overlap between the two species, the vital rates of female chamois were not related to red deer population size.
We provide evidence for population‐specific responses to interspecific competition and more generally, for context‐, age‐ and state‐dependent effects of interspecific competition.
Our results also suggest that the classical assumption of equal responses of all individuals to interspecific competition should be relaxed, and emphasize the need to move towards more mechanistic approaches to better understand how natural populations respond to changes in their environment.
Thanks to long‐term monitoring of two interacting species (chamois and red deer) at several locations and multi‐event capture‐recapture modelling, the authors show that breeding probabilities of female chamois could be affected by the presence of red deer competitors. These effects of red deer abundance on chamois were population‐, age‐ and state‐dependent.
Recently accumulated evidence has documented a climate impact on the demography and dynamics of single species, yet the impact at the community level is poorly understood. Here, we show that in ...Svalbard in the high Arctic, extreme weather events synchronize population fluctuations across an entire community of resident vertebrate herbivores and cause lagged correlations with the secondary consumer, the arctic fox. This synchronization is mainly driven by heavy rain on snow that encapsulates the vegetation in ice and blocks winter forage availability for herbivores. Thus, indirect and bottom-up climate forcing drives the population dynamics across all overwintering vertebrates. Icing is predicted to become more frequent in the circumpolar Arctic and may therefore strongly affect terrestrial ecosystem characteristics.
The effects of spatial structure on metapopulation dynamics depend upon the interaction between local population dynamics and dispersal, and how this relationship is affected by the geographical ...isolation and spatial heterogeneity in habitat characteristics.
Our aim is to examine how emigration and immigration of house sparrows Passer domesticus in a Norwegian archipelagic metapopulation are affected by key factors predicted by classic metapopulation models to affect dispersal—spatial and temporal variation in population size, inter‐island distance, local demography and habitat characteristics.
This metapopulation can be divided into two major habitat types: (a) islands closer to the mainland where sparrows breed in colonies on farms, and (b) islands without farms, situated farther away from the mainland where sparrows are exposed to harsher environmental conditions.
Dispersal was spatially structured within the metapopulation; there was proportionally and numerically less emigration and immigration involving farm islands, as compared to non‐farm islands. Furthermore, emigration and immigration occurred mostly between nearby islands. Moreover, emigration in response to spatial differences in mean population size differed between the habitat types, but populations with large mean received more immigrants in both habitat types. The number of emigrants and immigrants was negatively related to long‐term recruit production, which was not the case in non‐farm islands. The proportion and number of emigrants was positively related to temporal increases in recruit production on farm islands, however not on non‐farm islands.
Our results demonstrate that spatial heterogeneity in environmental conditions influences how spatial variation in long‐term mean population size, and temporal and spatial variation in recruit production, affects dispersal dynamics. The spatial structure of this metapopulation is therefore best described by a spatially explicit model in which the exchange of individuals within each habitat type is strongly affected by the degree of geographical isolation, population size and recruit production. However, these relationships differed between the two habitat types; non‐farm islands showing similarities to a mainland‐island model type of structure, whereas farm islands showed features more associated with source–sink or balanced dispersal models. Such differential dispersal dynamics between habitat types are expected to have important consequences for the ecological and evolutionary dynamics within this metapopulation.
This paper highlights how the contribution of spatial and temporal variation in population size and population recruit production on dispersal dynamics are dependent on habitat type in a metapopulation of house sparrows
Summary
Life history theory predicts that available energy is limited and needs to be allocated among different processes such as growth, reproduction and self‐maintenance. Basal metabolic rate ...(BMR), a common measure of an animal's maintenance cost, is therefore believed to be a trait of ecological and evolutionary significance. However, although BMR is often assumed to be correlated with fitness, its association with individual variation in fitness in free‐living populations is virtually unknown.
We examined the relationship between BMR in late winter prior to the breeding season and recruit production (number of offspring recorded the subsequent year), as well as adult survival, in two populations of house sparrow (Passer domesticus) on the islands Leka and Vega in northern Norway.
Number of recruits tended to be negatively related to BMR. However, analysing the data for each sex within the two populations revealed that the negative effect of BMR on recruit production was significant only for females in the Vega population.
Survival probability was associated with BMR, but the relationship differed both between sexes and populations. In the Leka population, we found evidence for stabilizing selection in the females and disruptive selection in the males. In contrast, there was no effect of BMR on survival in the Vega population.
Body mass influenced adult survival, but not recruit production. Furthermore, the relationship between BMR and fitness in females remained significant after controlling for body mass. Thus, the selection on BMR in females was not driven by a BMR‐body mass correlation.
Basal metabolic rate was significantly related to fitness in both populations. However, the results in the present study show spatial variation as well as sex specific differences in the influence of BMR on fitness in house sparrows.
Lay Summary
One of the most important challenges in conservation biology is to predict the viability of populations of vulnerable and threatened species. This requires that the demographic stochasticity strongly ...affecting the ecological and evolutionary dynamics of especially small populations is correctly estimated and modelled. Here, we summarize theoretical evidence showing that the demographic variance in population dynamics is a key parameter determining the probability of extinction and also is directly linked to the magnitude of the genetic drift in the population. The demographic variance is dependent on the mating system, being larger in a polygynous than in monogamous populations. Understanding factors affecting intersexual differences in mating success is therefore essential in explaining variation in the demographic variance. We hypothesize that the strength of sexual selection, for example, quantified by the Bateman gradient, may be a useful predictor of the magnitude of the demographic stochasticity and hence the genetic drift in the population. We provide results from a field study of moose that support this claim. Thus, including central principles from behavioural ecology may increase the reliability of population viability analyses through an improvement of our understanding of factors affecting stochastic influences on population dynamics and evolutionary processes. This article is part of the theme issue 'Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation'.
Pulsed resources influence the demography and evolution of consumer populations and, by cascading effect, the dynamics of the entire community. Mast seeding provides a case study for exploring the ...evolution of life history traits of consumers in fluctuating environments. Wild boar (Sus scrofa) population dynamics is related to seed availability (acorns/beechnuts). From a long-term monitoring of two populations subjected to markedly different environmental contexts (i.e., both low vs. high frequency of pulsed resources and low vs. high hunting pressure in Italy and in France, respectively), we assessed how pulsed resources shape the reproductive output of females. Using path analyses, we showed that in both populations, abundant seed availability increases body mass and both the absolute and the relative (to body mass) allocation to reproduction through higher fertility. In the Italian population, females equally relied on past and current resources for reproduction and ranked at an intermediate position along the capital-income continuum of breeding tactics. In contrast, in the French population, females relied on current more than past resources and ranked closer to the income end of the continuum. In the French population, one-year old females born in acorn-mast years were heavier and had larger litter size than females born in beechnut-mast years. In addition to the quantity, the type of resources (acorns/beechnuts) has to be accounted for to assess reliably how females allocate resources to reproduction. Our findings highlight a high plasticity in breeding tactics in wild boar females and provide new insight on allocation strategies in fluctuating environments.
In (st)age-structured populations, the long-run population growth rate is negatively affected by temporal variation in vital rates. In most cases, natural selection should minimize temporal variation ...in the vital rates to which the long-run population growth is most sensitive, resulting in demographic buffering. By reviewing empirical studies on demographic buffering in wild populations, we found overall support for this hypothesis. However, we also identified issues when testing for demographic buffering. In particular, solving scaling problems for decomposing, measuring, and comparing stochastic variation in vital rates and accounting for density dependence are required in future tests of demographic buffering. In the current context of climate change, demographic buffering may mitigate the negative impact of environmental variation and help populations to persist in an increasingly variable environment.
Climate change is expected to increase the environmental variation of ecosystems on Earth, highlighting the need to understand how populations will respond to these new environmental conditions.The demographic buffering hypothesis is derived from classical models of population dynamics. It predicts selection for a reduction in variance of the vital rates with the strongest influence on population growth and individual fitness.We review current knowledge about demographic buffering and critically assess the various methods and results published so far.A pattern of reduced variation in the most influential vital rates emerges from the review.Differences in methodology highlight the need for further studies with standardized methods to reveal whether the observed pattern is a direct result of selection for lower variation of the most influential vital rates.Modern statistical methods that allow decomposing variation in population growth rate into environmental variation, density dependence, and demographic stochasticity can stimulate the search for improved models to predict the effect of increasing environmental variation on population dynamics and life-history evolution.
1. Studies of seasonality in ecological diversity rarely extend over more than a few years, and few studies of seasonal diversity have explicitly investigated the influence of environmental factors ...on seasonal community composition, especially in tropical communities. 2. Our 10 years of monthly sampling in Amazonian Ecuador yielded 20 996 individuals of 137 fruit-feeding butterfly species. Seasonal cycles of rainfall drive annual cycles in species diversity and community similarity. Undetermined processes operating most strongly during the dry season maintain species diversity and high community similarity across years. 3. Seasonal cycles in community diversity and similarity are superimposed on a gradual decline in similarity between community samples on a decadal time-scale because of long-term changes in species abundances. 4. Monitoring and analysis of changes in community composition over a range of time-scales can be used to refine models of community dynamics by incorporating environmental factors necessary to predict the ecological impact of future climate change.
•An approach that provides theoretical scenarios of harvest of interacting species for a sustainable use of natural resources.•A harvest approach of interacting species that accounts for predators ...and prey's joint dynamics, natural fluctuations in abundances and consider varying environments.•Correlated environmental effects are included in the model and affect both species at the same time.•Strong environmental stochasticity increased the variance of predator's and prey's yield, making the harvest of the interacting species less predictable.•Optimal yields for predators and prey can be obtained with different harvest strategies when both species are harvested simultaneously.
The effects of harvest and fluctuating environment on inter-dependent predators and prey are complex and not well-known. We define a stochastic model where the predators and prey dynamically interact. The novelty of the model holds on the fact that predators and prey dynamics are simultaneously affected by correlated environmental noises. Interacting predators and prey are harvested using a proportional threshold harvesting strategy that accounts for stochastic population dynamics. Optimal yield of prey can be obtained with identical harvesting strategies when the predators and prey responded to the environment similarly (i.e., synchrony between species) and differently (i.e., asynchrony between species). Remarkably, our study demonstrates that two different harvesting strategies, the proportional harvesting strategy for the prey and the proportional threshold harvesting strategy for the predators, are needed to optimize the annual yield of predators and prey when both species are harvested simultaneously. Our study finds optimal strategies for harvesting interacting species affected by environmental variations (i.e., correlated noises) with parameters representing the joint dynamics of predators and prey at a stable state.
Broad-scale environmental changes are altering patterns of natural selection in the wild, but few empirical studies have quantified the demographic cost of sustained directional selection in response ...to these changes. We tested whether population growth in a wild bird is negatively affected by climate change-induced phenological mismatch, using almost four decades of individual-level life-history data from a great tit population. In this population, warmer springs have generated a mismatch between the annual breeding time and the seasonal food peak, intensifying directional selection for earlier laying dates. Interannual variation in population mismatch has not, however, affected population growth. We demonstrated a mechanism contributing to this uncoupling, whereby fitness losses associated with mismatch are counteracted by fitness gains due to relaxed competition. These findings imply that natural populations may be able to tolerate considerable maladaptation driven by shifting climatic conditions without undergoing immediate declines.
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