An empirically based model for latitudinal gradient in vole population dynamics

Vole dynamics in northern Europe exhibit a well-defined geographical gradient, with oscillatory populations being confined to high latitudes. It has been proposed that oscillations in northern vole populations are driven by their interaction with specialist predators (weasels), while the more southern rodent populations are relatively stable because of regulation by generalist predators. We tested this generalist/specialist predation hypothesis by constructing an empirically based model for vole population dynamics, estimating its parameters, and making predictions about the quantitative pattern of the latitudinal shift in vole dynamics. Our results indicated that the model accurately predicted the latitudinal shift in the amplitude and periodicity of population fluctuations. Moreover, the model predicted that vole dynamics should shift from stable to chaotic as latitude is increased, a result in agreement with nonlinear time-series analysis of the data. The striking success of the model at predicting the shifts in amplitude and stability along the geographical gradient in northern Europe provides strong support for the key role of specialist and generalist predators in vole population dynamics.     

Multiple interactions: An empirically suggested model

A modified version of Schoener's non-linear competition model is presented. The model describes the competitive dynamics of two species competing for a common resource. A second resource made available by species 1 for the exclusive use of species 2 is also present. This second resource is generated in an undefined way from the common resource. The presence of the exclusive resource serves to prevent the extinction of species 2 even when that species is at a great competitive disadvantage in obtaining the common resource. A feedback loop is established, dependent on the exclusive resource, making possible an increase in numbers of species 2 as the numbers of species 1 increase. This is represented as a reversal in the slope of the species 2 isocline. The behavior of the isoclines of both species is examined as certain key parameters are varied. The model is related to the results obtained from experiments involving Tribolium and Drosophila.     

An integrated approach to identify spatiotemporal and individual-level determinants of animal home range size

Animal home range use is a central focus of ecological research. However, how and why home range size varies between individuals is not well studied or understood for most species. We develop a hierarchical analytical approach--using generalized linear mixed-effects modeling of time series of home range sizes--that allows variance in home range size to be decomposed into components due to variation in temporal, spatial, and individual-level processes, also facilitating intra- and interspecific comparative analyses. We applied the approach to data from a roe deer population radiotracked in central Italy. Over multiple timescales, temporal variation is explained by photoperiod and climate and spatial variation by the distribution of habitat types and spatial variance in radiotracking error. Differences between individuals explained a substantial amount of variance in home range size, but only a relatively minor part was explained by the individual attributes of sex and age. We conclude that the choice of temporal scale at which data are collected and the definition of home range can significantly influence biological inference. We suggest that the appropriate choice of scale and definition requires a good understanding of the ecology and life history of the study species. Our findings contrast with several common assumptions about roe deer behavior.     

An allometric model of home range formation explains the structuring of animal communities exploiting heterogeneous resources

Understanding and predicting the composition and spatial structure of communities is a central challenge in ecology. An important structural property of animal communities is the distribution of individual home ranges. Home range formation is controlled by resource heterogeneity, the physiology and behaviour of individual animals, and their intra‐ and interspecific interactions. However, a quantitative mechanistic understanding of how home range formation influences community composition is still lacking. To explore the link between home range formation and community composition in heterogeneous landscapes we combine allometric relationships for physiological properties with an algorithm that selects optimal home ranges given locomotion costs, resource depletion and competition in a spatially‐explicit individual‐based modelling framework. From a spatial distribution of resources and an input distribution of animal body mass, our model predicts the size and location of individual home ranges as well as the individual size distribution (ISD) in an animal community. For a broad range of body mass input distributions, including empirical body mass distributions of North American and Australian mammals, our model predictions agree with independent data on the body mass scaling of home range size and individual abundance in terrestrial mammals. Model predictions are also robust against variation in habitat productivity and landscape heterogeneity. The combination of allometric relationships for locomotion costs and resource needs with resource competition in an optimal foraging framework enables us to scale from individual properties to the structure of animal communities in heterogeneous landscapes. The proposed spatially‐explicit modelling concept not only allows for detailed investigation of landscape effects on animal communities, but also provides novel insights into the mechanisms by which resource competition in space shapes animal communities.     

Memory keeps you at home: a mechanistic model for home range emergence

Despite its central place in animal ecology no general mechanistic movement model with an emergent home-range pattern has yet been proposed. Random walk models, which are commonly used to model animal movement, show diffusion instead of a bounded home range and therefore require special modifications. Current approaches for mechanistic modeling of home ranges apply only to a limited set of taxa, namely territorial animals and/or central place foragers. In this paper we present a more general mechanistic movement model based on a biased correlated random walk, which shows the potential for home-range behavior. The model is based on an animal tracking a dynamic resource landscape, using a biologically plausible two-part memory system, i.e. a reference- and a working-memory. Our results show that by adding these memory processes the random walker produces home-range behavior as it gains experience, which also leads to more efficient resource use. Interestingly, home-range patterns, which we assessed based on home-range overlap and increase in area covered with time, require the combined action of both memory components to emerge. Our model has the potential to predict home-range size and can be used for comparative analysis of the mechanisms shaping home-range patterns.     

The ecology and macroecology of mammalian home range area

Although many studies employ allometric relationships to demonstrate possible dependence of various traits on body mass, the relationship between home range size and body mass has been perhaps the most difficult to understand. Early studies demonstrated that carnivorous species had larger home ranges than herbivorous species of similar mass. These studies also argued that scaling relations (e.g., slopes) of the former were steeper than those of the latter and explained this in terms of the distribution of food resources, which are more uniformly distributed for most herbivores than for carnivores. In contrast to these studies, we show that scaling relations of home ranges for carnivorous mammals do not differ significantly from those of herbivorous and omnivorous species and that all three exhibit slopes that are significantly steeper than predicted on the basis of energetic requirements. We also demonstrate that home range size is constrained to fit within a polygonal constraint space bounded by lines representing energetic and/or biophysical limitations, which suggests that the log-linear relationship between home range area and mass may not be the appropriate function to compare against the energetically predicted slopes of 0.75 or 1.0. It remains unclear, however, why the slope of the relationship between home range area and body mass, whether based on raw data or on constraint lines, always exceeds that predicted by the energetic needs hypothesis.     

Eliminating autocorrelation reduces biological relevance of home range estimates

1. Destructive subsampling or restrictive sampling are often standard procedures to obtain independence of spatial observations in home range analyses. We examined whether home range estimators based upon kernel densities require serial independence of observations, by using a Monte Carlo simulation, antler flies and snapping turtles as models.
2. Home range size, time partitioning and total straight line distances travelled were tested to determine if subsampling improved kernel performance and estimation of home range parameters.
3. The accuracy and precision of home range estimates from the simulated data set improved at shorter time intervals despite the increase in autocorrelation among the observations.
4. Subsampling did not reduce autocorrelation among locational observations of snapping turtles or antler flies, and home range size, time partitioning and total distance travelled were better represented by autocorrelated observations.
5. We found that kernel densities do not require serial independence of observations when estimating home range, and we recommend that researchers maximize the number of observations using constant time intervals to increase the accuracy and precision of their estimates.     

An alternative concept to home range theory with respect to populations of cyprinids in major river systems

Homing behaviour in cyprinid species has been demonstrated by a number of research workers during the past 35 years. The British work has been principally conducted through tank experimentation with roach, gudgeon and minnows, but limited field data indicating home range behaviour have also been published. Evidence is now presented, from a fish population assessment and management programme covering 6000 km of river fisheries in the Anglian region of eastern England, to suggest that home range mechanisms do not play a significant role in the overall stock dynamics of cyprinid species in major river systems.
An alternative hypothesis which fits the range of observed circumstances more closely is described, based on a perception of cyprinid communities as totally mobile populations influenced predominantly by river flow characteristics and behavioural responses to flow and seasonal temperature factors. This concept is illustrated with a sequential series of schematic diagrams of a river catchment in which the key factor of infinitely variable movement patterns interspersed with periods of passive downstream displacement (negatively size-related) is modified by increasing degrees of interference by river structures.
The implications of the alternative concept to the management of riverine fish populations is discussed and alternative strategies to the traditional style cyprinid stockings illustrated within the paper are suggested which do not rely on home range mechanisms.     

Home range, home range overlap, and species energy use among herbivorous mammals

Harestad & Bunnell (1979) showed that, at least for North American species, home ranges of large herbivorous mammals are relatively larger than we would expect on metabolic grounds, and suggested that the productivity of the environment for mammal species decreases with increasing body size. This interpretation assumes that the number of conspecifics that share an individual's home range is independent of body size. Data presented here show that this is not true for the species in their sample; the home range is shared with an increasing number of conspecifics in larger herbivore species. The productivity of the environment for a species is independent of body size and the area available to an individual for its own use scales approximately as do individual metabolic requirements. These results agree with conclusions based upon the scaling of population density with body mass and illustrate the interrelationship between home range and dietary and social organization trends among mammalian herbivores. Individual home range area is a function of the way in which the local population of a species, not merely an individual, exploits the environment.     

An estimate of large-scale sequencing accuracy

The accuracy of large-scale DNA sequencing is difficult to estimate without redundant effort. We have found that the mobile genetic element IS10, a component of the transposon Tn10, has contaminated a significant number of clones in the public databases, as a result of the use of the transposon in bacterial cloning strain construction. These contaminations need to be annotated as such. More positively, by defining the range of sequence variation in IS10, we have been able to determine that the rate of sequencing errors is very low, most likely surpassing the stated aim of one error or less in ten thousand bases.     

On the pathophysiology of migraine--links for "empirically based treatment" with neurofeedback

Psychophysiological data support the concept that migraine is the result of cortical hypersensitivity, hyperactivity, and a lack of habituation. There is evidence that this is a brain-stem related information processing dysfunction. This cortical activity reflects a periodicity between 2 migraine attacks and it may be due to endogenous or exogenous factors. In the few days preceding the next attack slow cortical potentials are highest and habituation delay experimentally recorded during contingent negative variation is at a maximum. These striking features of slow cortical potentials are predictors of the next attack. The pronounced negativity can be fed back to the patient. The data support the hypothesis that a change in amplitudes of slow cortical potentials is caused by altered habituation during the recording session. This kind of neurofeedback can be characterized as empirically based because it improves habituation and it proves to be clinically efficient.     

Territorial dynamics and stable home range formation for central place foragers

Uncovering the mechanisms behind territory formation is a fundamental problem in behavioural ecology. The broad nature of the underlying conspecific avoidance processes are well documented across a wide range of taxa. Scent marking in particular is common to a large range of terrestrial mammals and is known to be fundamental for communication. However, despite its importance, exact quantification of the time-scales over which scent cues and messages persist remains elusive. Recent work by the present authors has begun to shed light on this problem by modelling animals as random walkers with scent-mediated interaction processes. Territories emerge as dynamic objects that continually change shape and slowly move without settling to a fixed location. As a consequence, the utilisation distribution of such an animal results in a slowly increasing home range, as shown for urban foxes (Vulpes vulpes). For certain other species, however, home ranges reach a stable state. The present work shows that stable home ranges arise when, in addition to scent-mediated conspecific avoidance, each animal moves as a central place forager. That is, the animal's movement has a random aspect but is also biased towards a fixed location, such as a den or nest site. Dynamic territories emerge but the probability distribution of the territory border locations reaches a steady state, causing stable home ranges to emerge from the territorial dynamics. Approximate analytic expressions for the animal's probability density function are derived. A programme is given for using these expressions to quantify both the strength of the animal's movement bias towards the central place and the time-scale over which scent messages persist. Comparisons are made with previous theoretical work modelling central place foragers with conspecific avoidance. Some insights into the mechanisms behind allometric scaling laws of animal space use are also given.