Small Heterogeneity Has Large Effects on Synchronization of Ecological Oscillators

Heterogeneity in habitat plays a crucial role in the dynamics of spatially extended populations and is often ignored by both empiricists and theoreticians. A common assumption made is that spatially homogeneous systems and those with slight heterogeneity will behave similarly and, therefore, the results and data from studies of the former can be applied to the latter. Here, we test this assumption by deriving a phase model from two weakly coupled predator-prey oscillators and analyze the effect of spatial heterogeneity on the phase dynamics of this system. We find that even small heterogeneity between the two patches causes substantial changes in the phase dynamics of the system which can have dramatic effects on both population dynamics and persistence. Additionally, if the prey and predator time scales are similar, the effect of heterogeneity is much greater.     

Survival in continuous structured populations models

The extended McKendrick-von Foerster structured population model is employed to derive a nonautonomous ordinary differential equation model of a population. The derivation assumes that the individual life history can be delineated into several physiological stages. We study the persistence of the population when the model is autonomous and base the nonautonomous survival analysis on the autonomous case and a comparison principle. A brief excursion into alternate life history strategies is presented.This work was supported in part by the U.S. Environmental Protection Agency under cooperative agreement CR 813353010     

How does adaptive consumer movement affect population dynamics in consumer-resource metacommunities with homogeneous patches?

This article uses simple models to explore the impact of adaptive movement by consumers on the population dynamics of a consumer-resource metacommunity consisting of two identical patches. Consumer-resource interactions within a patch are described by the Rosenzweig-MacArthur predator-prey model, and these dynamics are assumed to be cyclic in the absence of movement. The per capita movement rate from one patch to the other is an increasing function of the difference between the per capita birth minus death rate in the destination patch and that in the currently occupied patch. Several variations on this model are considered. Results show that adaptive movement frequently creates anti-phase cycles in the two patches; these suppress the predator-prey cycle and lead to low temporal variation of the total population sizes of both species. Paradoxically, even when movement is very sensitive to the fitness difference between patches, perfect synchrony of patches is often much less likely than in comparable systems with random movement. Under these circumstances adaptive movement of consumers often generates differences in the average properties of the two patches. In addition, mean global densities and responses to global perturbations often differ greatly from similar systems with no movement or random movement.     

Weak trophic interactions and the balance of enriched metacommunities

Weak trophic interactions have been shown to promote the stability of ecological food webs characterized by perfect mixing. However, their importance at the landscape level and response to enrichment has not been extensively examined. In this paper we examine the food-web model explored by McCann et al. [1998. Weak trophic interactions and the balance of nature. Nature 395, 794-798]. The model is expanded into a metacommunity construct where local communities are coupled through global or local dispersal. We analyze global and local stability, as well as spatial synchrony in relation to trophic interaction strength and dispersal regimes. Results reveal that weak interactions can operate through two scale-dependent mechanisms: (i) under low local dispersal regimes, local stabilization of each community under weak interactions directly scales-up to global stability. (ii) Under high local dispersal, asynchronous local destabilization associated with weak interactions proves the driver behind global stability. In the face of enrichment, weak trophic interactions are shown to be instrumental in promoting global stability when dispersal is local. These results demonstrate how the importance of weak trophic interactions can be generalized at the landscape level despite contrary local predictions.     

Marine metapopulations: a useful concept?

We discuss the potential and limitations of the metapopulation concept in marine ecology. The usefulness of the concept in terrestrial ecology is neither based on its simplicity or generality nor on overwhelming empirical evidence. The usefulness is in the questions which are asked when the metapopulation concept is applied. These questions address spatial phenomena and processes on different spatial scales. They help in acknowledging that every population, be it terrestrial or marine, has a spatial organization. Understanding this spatial organization is also important for tackling specific applied problems, i.e. to avoid overexploitation of living marine resources or for configuring marine reserves. The 'openness' of coastal populations, whose larvae enter larval pools or which are holoplanktonic, is no reason for not asking the questions implied by the metapopulation concept. For marine ecology, the real problem is to delineate populations, which then may possibly correspond to the 'local populations' of metapopulations. Thus, the answer to the question in the title of this paper, whether 'marine metapopulation' is a useful concept, is 'yes', if the concept is considered a working hypotheses, if the concept is explicitly defined, and if the questions linked to the concept are clearly stated. Even if it eventually transpires that only very few marine metapopulations actually exist, marine ecology would still have gained some important new insights. Electronic Publication     

Demographic models of the northern spotted owl (Strix occidentalis caurina)

Summary Calassical demographic methods applied to life history data on the northern spotted owl yield and estimate of the annual geometric rate of increase for the population of λ=0.96±0.03, which is not significantly different from that for a stable population (λ=1.00). Sensitivity analysis indicates that adult annual survivorship has by far the largest influence on λ, followed by the probability that juveniles survive dispersal, and the adult annual fecundity. Substantial temporal fluctuations in demographic parameters have little effect on the long-run growth rate of the population because of the long adult life expectancy. A model of dispersal and territory occupancy that assumes demographic equilibrium is evaluated using data on the amount of old forest habitat remaining in the Pacific Northwest and the current occupancy of this habitat by northern spotted owls. This model is employed to predict the effect of future habitat loss and fragmentation on the population, implying that extinction will result if the old forest is reduced to less than a proportion 0.21±0.02 of the total area in a large region. The estimated minimum habitat requirement for the population is greater than that allowed in management plants by the USDA Forest Service.     

环境污染中三维时变Volterra捕食-被捕食系统的持续生存

对环境容量很大且被污染的三种群时变系统进行了研究,给出了三维时变Ｖｏｌｔｅｒｒａ捕食－被捕食系统弱平均持续生存与绝灭的充分条件。     

体内毒素浓度不相同的三维时变Volterra系统的持续生存

在环境容量很大且被污染的情形下,对体内毒素浓度不相同的三种群时变Volterra系统进行了研究,并给出了三维时变Volterra捕食系统弱平均持续生存与灭绝的条件。     

Evolution of Dispersal in a Structured Metapopulation Model in Discrete Time

In this article, a structured metapopulation model in discrete time with catastrophes and density-dependent local growth is introduced. The fitness of a rare mutant in an environment set by the resident is defined, and an efficient method to calculate fitness is presented. With this fitness measure evolutionary analysis of this model becomes feasible. This article concentrates on the evolution of dispersal. The effect of catastrophes, dispersal cost, and local dynamics on the evolution of dispersal is investigated. It is proved that without catastrophes, if all population–dynamical attractors are fixed points, there will be selection for no dispersal. A new mechanism for evolutionary branching is also found: Even though local population sizes approach fixed points, catastrophes can cause enough temporal variability, so that evolutionary branching becomes possible.     

Metapopulation structure in the lagoon cockle <Emphasis Type="Italic">Cerastoderma lamarcki</Emphasis> in the northern Wadden Sea

Benthic invertebrates in discontinuous inshore habitats and with short or no pelagic larval dispersal are likely to exhibit regional metapopulation dynamics with partially isolated local populations. Near the island of Sylt, the bivalve Cerastoderma (Cardium) lamarcki (Reeve, 1844, syn. in part with C. glaucum Bruguiére, 1789) was widespread in intertidal seagrass beds, coexisting with the sibling species C. edule (Linné, 1758). However, the last C. lamarcki in this habitat was found in 1980. At present the lagoon cockle is restricted to disjunct ditches, creeks and ponds within island salt marshes. There it differs in year-class structure between localities. Successful recruitment events did not coincide. At one locality, a period with regular recruitment was followed by 5 years of recruitment failure, resulting in an overaged population probably at the rim of extinction. In a nearby brackish pond, extinction was followed by recolonization 3 years later. Other lagoonal habitats which seem to be suitable are without cockles. It is speculated that small and isolated habitats occasionally receive colonizers by eggs and juveniles adhering to avian vectors. Electronic Publication     

Do species population parameters and landscape characteristics affect the relationship between local population abundance and surrounding habitat amount?

In landscape ecology, correlational approaches are typically used to analyse links between local population abundance, and the surrounding habitat amount to estimate biologically-relevant landscape size (extent) for managing endangered or pest populations. The direction, strength, and spatial extent of the correlations are then sometimes interpreted in terms of species population parameters. Here we simulated the population dynamics of generalized species across spatially explicit landscapes that included two distinct habitat types. We investigated how characteristics of a landscape (structure), including the variation in habitat quality and spatial aggregation of the habitat, and the precise population-dynamic properties of the simulated species (dispersal and growth rates) affect the correlation between population abundance and amount of surrounding favourable habitat in the landscape. To evaluate these spatial extents of correlation, proportions of favourable habitat were calculated within several circles of increasing diameter centred on sampling patches of favourable habitat where population abundance was recorded.We found that the value of the correlation coefficients between population abundance and amount of surrounding favourable habitat depended on both population dynamic parameters and landscape characteristics. Coefficients of correlation increased with the variation in habitat quality and the aggregation of favourable habitat in the landscape, but decreased with the dispersal distance. The distance at which the correlation was maximized was sensitive to an interaction between the level of aggregation of the habitat and the dispersal distance; whereas the greatest distance at which a significant correlation occurred was more sensitive to the variation in habitat quality. Our results corroborate the view that correlational analyses do provide information on the local population dynamics of a species in a given habitat type and on its dispersal rate parameters. However, even in simplified, model frameworks, direct relationships are often difficult to disentangle and global landscape characteristics should be reported in any studies intended to derive population-dynamic parameters from correlations. Where possible, replicated landscapes should be examined in order to control for the interaction between population dynamics and landscape structure. Finally, we recommend using species-specific, population-dynamic modelling in order to interpret correctly the observed patterns of correlation in the landscape.     

The Role of Density Regulation in Extinction Processes and Population Viability Analysis

We review the role of density dependence in the stochastic extinction of populations and the role density dependence has played in population viability analysis (PVA) case studies. In total, 32 approaches have been used to model density regulation in theoretical or applied extinction models, 29 of them are mathematical functions of density dependence, and one approach uses empirical relationships between density and survival, reproduction, or growth rates. In addition, quasi-extinction levels are sometimes applied as a substitute for density dependence at low population size. Density dependence further has been modelled via explicit individual spacing behaviour and/or dispersal. We briefly summarise the features of density dependence available in standard PVA software, provide summary statistics about the use of density dependence in PVA case studies, and discuss the effects of density dependence on extinction probability. The introduction of an upper limit for population size has the effect that the probability of ultimate extinction becomes 1. Mean time to extinction increases with carrying capacity if populations start at high density, but carrying capacity often does not have any effect if populations start at low numbers. In contrast, the Allee effect is usually strong when populations start at low densities but has only a limited influence on persistence when populations start at high numbers. Contrary to previous opinions, other forms of density dependence may lead to increased or decreased persistence, depending on the type and strength of density dependence, the degree of environmental variability, and the growth rate. Furthermore, effects may be reversed for different quasi-extinction levels, making the use of arbitrary quasi-extinction levels problematic. Few systematic comparisons of the effects on persistence between different models of density dependence are available. These effects can be strikingly different among models. Our understanding of the effects of density dependence on extinction of metapopulations is rudimentary, but even opposite effects of density dependence can occur when metapopulations and single populations are contrasted. We argue that spatially explicit models hold particular promise for analysing the effects of density dependence on population viability provided a good knowledge of the biology of the species under consideration exists. Since the results of PVAs may critically depend on the way density dependence is modelled, combined efforts to advance statistical methods, field sampling, and modelling are urgently needed to elucidate the relationships between density, vital rates, and extinction probability.     

Resolving the dynamics of EEG generators by multichannel recordings

The voltage recorded over the cortex (ECoG) or over the scalp (EEG) is generated by currents derived from many sources called “generators”. Different patterns and amplitudes are observed in aroused, sleepy, epileptic or other brain states. Differences in amplitude are generally attributed to differences in synchrony among generators. The degree of EEG synchrony is measured by the correlation between electrodes placed over different cortical regions. We present a new way to quantitatively assess the degree of synchronization of these generators via multichannel recordings. We illustrate how situations where there are several groups of generators with different inter-group and intra-group synchronies can be analyzed. Finally, we present a way to identify the organization of groups exhibiting topographic organization. Although the model presented here is highly simplified, several methods are based on averaging activity over increasingly larger areas. These types of measurements may be applied as well to EEG and ECoG recordings.     

Globorotalia puncticulata: Population divergence, dispersal and extinction related to Pliocene–Quaternary water masses

The isolating effect of water mass partitioning of populations on the morphology, stratigraphic distribution and extinction of planktonic foraminifera is assessed from the Pliocene–Quaternary record of Globorotalia puncticulata. Southern Hemisphere, Mediterranean and North Atlantic data on these aspects of its history are examined and appear consistent with a limited dispersal biogeographic model wherein populations are largely confined by hydrographic barriers.Earliest populations appeared during the latest Miocene in Southern Hemisphere middle latitude water masses. However, morphometric analysis shows that significant differentiation in the axial shape of shells had developed by 4 Ma between Southwest Pacific populations from ODP Site 1123 (temperate water) and ODP Site 1119 (subantarctic water). These sites are in close proximity but separated by the Subtropical Front. At Site 1123 inflation of late-formed chambers and reduction in the number included in the outer whorl created shell profiles that anticipated the globose form of Globorotalia inflata. The latter's gradual evolution from G. puncticulata s.s. took place in this temperate water mass, with the earliest morphotypes with three chambers in the outer whorl present by 4.1 Ma. In contrast, subantarctic populations at Site 1119 retained four chambers but their axial shape was modified. The development of a large, highly arched aperture and increase in the number of chambers in the outer whorl in Mediterranean–North Atlantic Globorotalia puncticulata bononiensis is an example of population differentiation later in the Pliocene.Chronostratigraphy shows that the northward expansion of central temperate water populations commenced with their occupation of Southwest Pacific subtropical water about 4.8 Ma. The rather abrupt entry of substantial populations into Mediterranean and North Atlantic water at 4.5 Ma marked a major biogeographic expansion and established G. puncticulata as a bipolar species. It was widely distributed about 3 Ma, with major populations in several water masses during a period of middle Pliocene warmth.After this acme North Atlantic and Mediterranean G. puncticulata bononiensis populations collapsed as late Pliocene Northern Hemisphere glacials intensified. They were extinguished in MIS 96 (2.4 Ma). Concurrently, G. puncticulata s.s became extinct in the warm subtropical Southwest Pacific. Subantarctic populations persisted but in turn were decimated in severe glacials during the Middle Pleistocene Transition. Most had disappeared by MIS 16 (0.66 Ma). However, at Sites 594 and 1119 there was a small Lazarus-like revival in MIS 11 (0.41 Ma). The highest known occurrence is in MIS 9 (0.33 Ma) at Site 1119. Confinement of the species to subantarctic water in the Pleistocene may have raised its vulnerability to extinction.While stable isotope data indicate that the lineage's evolution is related to depth habitat selection about the thermocline, its biogeography suggests that hydrographic barriers significantly isolated populations and probably facilitated speciation. Eddies such as the North Brazil Current rings provide conduits for inter-water mass transfer of populations but the history of G. puncticulata suggests that such mechanisms seldom operated successfully.The morphology of the lectotype of G. puncticulata s.s., from beach sand at Rimini, Italy, is consistent with a lower Pliocene source. Reports of living occurrences are poorly documented and the species is considered to be extinct.     

Relative movement patterns of a tephritid fly and its parasitoid wasps

The extent of within-patch dispersal by a tephritid fly and its four major parasitoids was examined over three field seasons. Hosts and parasitoids were marked using acrylic paint and observed as they oviposited into the flowerheads of marsh thistle, Cirsium palustre. The average recapture rate pooled across all species was 22%. The four parasitoids showed consistently greater rates of movement than the host in all three years. In nearly all comparisons, male dispersal was less than female dispersal. There was no evidence that parasitoids moved longer distances after visiting low quality rather than high quality patches. In the one season it was studied, no correlations between movement and insect size were observed. The relevance of these observations to host-parasitoid population dynamics is discussed.