Nest mortality in a population of small mammals

Female white-footed micePeromyscus leucopus (Rafinesque, 1818) and their dependent offspring were monitored in nest boxes to determine the extent and causes of nest mortality. The mortality of dependent young was high (561 of 838; 66%) and variable among years. Most mortality involved the loss of entire litters (112 of 183 litters; 61%), with half of these losses attributed to the death of lactating females before the young were weaned (59 of 112 litters; 53%). Most mortality was from unknown causes, although infanticide, energetic constraints and predation were identified in a small number of cases. Predation is likely the major source of mortality in this population.     

Prospecting and dispersal: their eco-evolutionary dynamics and implications for population patterns

Dispersal is not a blind process, and evidence is accumulating that individual dispersal strategies are informed in most, if not all, organisms. The acquisition and use of information are traits that may evolve across space and time as a function of the balance between costs and benefits of informed dispersal. If information is available, individuals can potentially use it in making better decisions, thereby increasing their fitness. However, prospecting for and using information probably entail costs that may constrain the evolution of informed dispersal, potentially with population-level consequences. By using individual-based, spatially explicit simulations, we detected clear coevolutionary dynamics between prospecting and dispersal movement strategies that differed in sign and magnitude depending on their respective costs. More specifically, we found that informed dispersal strategies evolve when the costs of information acquisition during prospecting are low but only if there are mortality costs associated with dispersal movements. That is, selection favours informed dispersal strategies when the acquisition and use processes themselves were not too expensive. When non-informed dispersal strategies evolve, they do so jointly with the evolution of long dispersal distance because this maximizes the sampling area. In some cases, selection produces dispersal rules different from those that would be ‘optimal’ (i.e. the best possible population performance—in our context quantitatively measured as population density and patch occupancy—among all possible individual movement rules) for the population. That is, on the one hand, informed dispersal strategies led to population performance below its highest possible level. On the other hand, un- and poorly informed individuals nearly optimized population performance, both in terms of density and patch occupancy.     

A developmental bottleneck in dispersing larvae: implications for spatial population dynamics

We found evidence for a critical population bottleneck at a developmental‐stage transition in larvae of the zebra mussel Dreissena polymorpha Pallas from field estimates of mortality. Identification of this critical period in the field was made possible by closely tracking cohorts of larvae over 5 days of development as they dispersed 128 km in a river system. The presence of a survival bottleneck during development was confirmed in laboratory studies of zebra mussel larvae. Development‐specific mortality has important implications for spatial population dynamics of the zebra mussel in particular, and all species with indirect development in general. Marine reserves that do not take development‐specific mortality into account may dramatically underestimate reserve size needed to protect rare and/or exploited marine populations. Conversely, for the zebra mussel, the lower contribution of dispersing individuals to population growth downstream of reserves can lead to more feasible control through the blocking of dispersal.     

New approaches for field studies of mammals: experiences with marine mammals

The constraints imposed by studying a mammal in an aquatic environment and by the nerd to use benign methods have made it necessary to develop novel approaches in order to investigate the biology of marine mammals. The approaches have been made possible by recent technological advances and by the willingness of granting agencies to fund expensive, high–risk projects in marine science.
We review new trchniques which have been developed for estimating the population size of marine mammals, for investigating the relationsip between individuals and populations, for studying the behaviour and energetics of animals in the open sea, and for the management of small and endangered populations. We also indicate how these techniques may be applied to a variety of terrestrial mammals.     

metasim 1.0: an individual‐based environment for simulating population genetics of complex population dynamics

metasim provides a flexible environment in which to perform individual‐based population genetic simulations. A wide range of landscape‐level dynamics, population structures, and within‐population demographies can be represented using the framework implemented in this software. In addition, temporal variation in all demographic characteristics can be simulated, both deterministically and stochastically. Such simulations can be used to produce null distributions of genotypes under realistic conditions. These genotypic data can then be used by a variety of analytical programs to develop null expectations of any population genetic statistic estimated from genotypic data.     

Transmission intensity and drug resistance in malaria population dynamics: implications for climate change

Although the spread of drug resistance and the influence of climate change on malaria are most often considered separately, these factors have the potential to interact through altered levels of transmission intensity. The influence of transmission intensity on the evolution of drug resistance has been addressed in theoretical studies from a population genetics' perspective; less is known however on how epidemiological dynamics at the population level modulates this influence. We ask from a theoretical perspective, whether population dynamics can explain non-trivial, non-monotonic, patterns of treatment failure with transmission intensity, and, if so, under what conditions. We then address the implications of warmer temperatures in an East African highland, where, as in other similar regions at the altitudinal edge of malaria's distribution, there has been a pronounced increase of cases from the 1970s to the 1990s. Our theoretical analyses, with a transmission model that includes different levels of immunity, demonstrate that an increase in transmission beyond a threshold can lead to a decrease in drug resistance, as previously shown, but that a second threshold may occur and lead to the re-establishment of drug resistance. Estimates of the increase in transmission intensity from the 1970s to the 1990s for the Kenyan time series, obtained by fitting the two-stage version of the model with an explicit representation of vector dynamics, suggest that warmer temperatures are likely to have moved the system towards the first threshold, and in so doing, to have promoted the faster spread of drug resistance. Climate change and drug resistance can interact and need not be considered as alternative explanations for trends in disease incidence in this region. Non-monotonic patterns of treatment failure with transmission intensity similar to those described as the 'valley phenomenon' for Uganda can result from epidemiological dynamics but under poorly understood assumptions.     

Snowshoe hare optimal foraging and its implications for population dynamics

The results of an optimal foraging model using linear programming with constraints for feeding time, digestive capacity, sodium requirements, and energy requirements indicate that snowshoe hare (Lepus americanus) may forage as energy maximizers. The solution provides the quantities of major food classes (leaves, herbs, fungus, twigs) included in the diet. The species composition of each diet class also is determined using a simultaneous search model based upon the probability of encounter, the probability of sufficient item size, and the probability of sufficient quality. The results also indicate that hare life history parameters (weaning size, size at first reproduction, average adult size) and potential demographic changes in hare populations may be controlled by foraging considerations.     

Stochastic population dynamics and life-history variation in marine fish species

Abstract We examined whether differences in life-history characteristics can explain interspecific variation in stochastic population dynamics in nine marine fish species living in the Barents Sea system. After observation errors in population estimates were accounted for, temporal variability in natural mortality rate, annual recruitment, and population growth rate was negatively related to generation time. Mean natural mortality rate, annual recruitment, and population growth rate were lower in long-lived species than in short-lived species. Thus, important species-specific characteristics of the population dynamics were related to the species position along the slow-fast continuum of life-history variation. These relationships were further associated with interspecific differences in ecology: species at the fast end were mainly pelagic, with short generation times and high natural mortality, annual recruitment, and population growth rates, and also showed high temporal variability in those demographic traits. In contrast, species at the slow end were long-lived, deepwater species with low rates and reduced temporal variability in the same demographic traits. These interspecific relationships show that the life-history characteristics of a species can predict basic features of interspecific variation in population dynamical characteristics of marine fish, which should have implications for the choice of harvest strategy to facilitate sustainable yields.     

Variation in foraging success among predators and its implications for population dynamics

The effects of the expected predation rate on population dynamics have been studied intensively, but little is known about the effects of predation rate variability (i.e., predator individuals having variable foraging success) on population dynamics. In this study, variation in foraging success among predators was quantified by observing the predation of the wolf spider Pardosa pseudoannulata on the cricket Gryllus bimaculatus in the laboratory. A population model was then developed, and the effect of foraging variability on predator–prey dynamics was examined by incorporating levels of variation comparable to those quantified in the experiment. The variability in the foraging success among spiders was greater than would be expected by chance (i.e., the random allocation of prey to predators). The foraging variation was density‐dependent; it became higher as the predator density increased. A population model that incorporates foraging variation shows that the variation influences population dynamics by affecting the numerical response of predators. In particular, the variation induces negative density‐dependent effects among predators and stabilizes predator–prey dynamics.     

Spatial population dynamics and the design of marine reserves

The failure of many fisheries world-wide, and the concern about marine biodiversity, has sparked a growing interest in the spatial aspects of harvested populations. If a population conforms to the Ideal Free Distribution and that one of the habitats is set aside as a reserve free from harvesting, the design of reserves may be problematic. If a substantial proportion of the unharvested population is to be preserved, then the reserve area must be unrealistically large, or have a much higher expected fitness than the unprotected area. Interestingly, the optimal harvest rate will be unaffected by both the size of the reserve and the quality of it relative to the harvested area. Even if the Ideal Free Distribution model is extended to include simple age-structure and "spillover" of recruits from the reserve, these conclusions largely remain intact. In a model that also includes spillover, the habitat quality of the reserve may also affect the catch.     

Spatial variation in population dynamics of juvenile Atlantic salmon: implications for conservation and management

Application of habitat models for predicting expected local densities of Atlantic Salmon Salmo salar in healthy populations has been hampered by a lack of generality in their fit to data from different systems. It is believed that this problem results at least in part from difficulties of effectively integrating factors that act across a range of spatial and temporal scales. Here, as an aid to developing more robust modelling and sampling methodologies, a simple process‐based model for local‐scale dynamics of Atlantic salmon juveniles is developed from first principles by integrating contemporary understanding of self‐thinning, density‐dependent growth and dispersal. The aim is to present a readily understood structure to illustrate the links between spawning and stocking strategies, habitat, migration and fish production. Based on this structure, contemporary understanding of the more complex biological processes that affect density, growth and habitat are discussed in relation to some of the key requirements of managers, including stocking for rehabilitation, assessment of predation impact and development of strategies for sampling populations effectively when deriving habitat‐production models. A major conclusion is that more structured, integrated research is required to provide the basic variables needed to model links between local and global scale habitat and fish production effectively. Nevertheless, application of the current understanding of the biology of Atlantic salmon should be of great benefit to managers in extracting key information from field surveys.     

Anoxic microniches in marine sediments induced by aggregate settlement: biogeochemical dynamics and implications

Spherical (~2 mm diameter) diatom (Skeletonema sp.) aggregates, representing analogues of “marine snow”, were placed at the sediment–water interface of an experimental sediment system. Optode measurements showed that, after an initial lag period, oxygen concentrations within the aggregates decreased and then were gradually replenished, resulting in a temporary anoxic microniche. A multi-species, 3-dimensional, reactive transport model was used to simulate the oxygen dynamics and the associated biogeochemical consequences. Temporal and spatial changes in oxygen were replicated assuming an exponential increase in the mineralisation rate constant and a gradual exhaustion of reactive organic material. The peak value of the time-dependent reaction rate constant of organic matter mineralisation (k _OMM) was seven to sixty times greater than analogous values measured previously in water column experiments. The validated model was used to investigate how the size and reactivity of parcels of organic matter influence the formation of anoxic microniches at the sediment–water interface of typical deep-sea environments. As well as k _OMM, the concentration of reactive organic matter in the aggregate, its size and porosity were also critical in determining the likelihood of anoxic microniche formation. For the optimum fitted parameters describing k _OMM and the concentration of reactive organic matter, the minimum diameter of the parcel to induce anoxia was 1.8 mm, whereas it was 2.8 mm to make a significant contribution to the denitrification occurring in a typical deep-sea sediment. This work suggests that anoxic microniches resulting from the settlement of marine aggregates may play an overlooked role for denitrification activities in deep-sea sediments.