Dynamics Of Single Species Research Articles

Species interactions can explain Taylor's power law for ecological time series.

One of the few generalities in ecology, Taylor's power law, describes the species-specific relationship between the temporal or spatial variance of populations and their mean abundances. For populations experiencing constant per capita environmental variability, the regression of log variance versus log mean abundance gives a line with a slope of 2. Despite this expectation, most species have slopes of less than 2 (refs 2, 3-4), indicating that more abundant populations of a species are relatively less variable than expected on the basis of simple statistical grounds. What causes abundant populations to be less variable has received considerable attention, but an explanation for the generality of this pattern is still lacking. Here we suggest a novel explanation for the scaling of temporal variability in population abundances. Using stochastic simulation and analytical models, we demonstrate how negative interactions among species in a community can produce slopes of Taylor's power law of less than 2, like those observed in real data sets. This result provides an example in which the population dynamics of single species can be understood only in the context of interactions within an ecological community.

Landscape structure, habitat fragmentation, and the ecology of insects

Landscape structure, habitat fragmentation, and the ecology of insects

Plant species diversity and grazing in the Scandinavian mountains ‐ patterns and processes at different spatial scales

There is a long tradition of grazing by semi‐domestic reindeer and sheep in alpine and sub‐alpine Scandinavian habitats, but present management regimes are questioned from a conservation point of view. In this review we discuss plant diversity patterns in the Scandinavian mountains in a global, regional and local perspective. The main objective was to identify processes that influence diversity at different spatial scales with a particular focus on grazing. In a global perspective the species pool of the Scandinavian mountains is limited. partly reflecting the general latitudinal decline of species but also historical and ecological factors operating after the latest glaciation. At the local scale, both productivity and disturbance are primary factors structuring diversity, but abiotic factors such as soil pH, snow distribution and temperature are also important. Although evidence is scarce, grazing favours local species richness in productive habitats, whereas species richness decreases with grazing when productivity is low. Regional patterns of plant diversity is set by, 1) the species pool. 2) the heterogeneity and fragmentation of communities, and 3) local diversity of each plant community. We suggest that local shifts in community composition depend both on the local grazing frequency and the return‐time of the plant community after a grazing session. In addition, an increasing number of grazing‐modified local patches homogenises the vegetation and is likely to reduce the regional plant diversity. The time scale of local shifts in community composition depends on plant colonisation and persistence, From a mechanistic point of view, diversity patterns at a regional scale also depend on the regional dynamics of single species. Colonisation is usually a slow and irregular process in alpine environments, whereas the capacity for extended local persistence is generally high. Although the poor knowledge of plant regional dynamics restricts our understanding of how grazing influences plant diversity, we conclude that grazing is a key process for maintaining biodiversity in the Scandinavian mountains.

Mutualism, parasitism and competition in the evolution of coviruses.

Coviruses are viruses with the property that their genetic information is divided up among two or more different viral particles. I model the evolution of coviruses using information on both viral virulence and the interactions between viruses and molecules that parasitize them: satellite viruses, satellite RNAs and defective interfering viruses. The model ultimately, and inevitably contains within it single-species dynamics as well as mutualistic, parasitic, cooperative and competitive relationships. The model shows that coexistence between coviruses and the self-sufficient viruses that spawned them is unlikely, in the sense that the quantitative conditions for coexistence are not easy to satisfy I also describe an abrupt transition from mutualistic two-species to single-species dynamics, showing a new sense in which questions such as 'Is a lichen one species or two?' can be given a definite answer.

The trade‐off between dispersability and longevity ‐ an important aspect of plant species diversity

Abstract. Local presence of plant species is determined by population colonizations and extinctions. All traits that influence the capacity of individuals to colonize patches and survive within patches, are therefore important for community diversity. Spatial models can explain the coexistence of species provided that the inferior competitor has a greater spatial mobility and thereby can avoid competition. We searched the literature for empirical evidence for such trade‐offs and included all available information on correlations between traits associated with the capacity to colonize and traits promoting the ability to survive.A lower reproductive effort of a species is associated with a longer life span and a higher competitive ability. Morphological adaptations for dispersal are less common in species which better tolerate stress, that are better competitors or possess seed dormancy. Such patterns suggest that species that are good survivors may have a limited ability to colonize new patches and vice versa. A negative correlation between dispersability and longevity has important effects on the regional dynamics of single species as well as on the coexistence of species. From a conservation perspective differences in the colonization capacity among species imply that restoration of plant biodiversity must not only focus on conditions within patches, but also consider the spatial arrangement of patches in order to enable plants to bridge gaps in time and space.

Structured Population Models of Herbivorous Zooplankton

In this paper, we investigate whether a stage—structured population model can explain major features of dynamics of the herbivores Daphnia galeata and Bosmina longirostris reared under controlled laboratory conditions. Model parameters are determined from independent individual—based information gleaned from the literature on feeding, growth, reproduction, and survivorship of these herbivores. We tested predictions of our model against published observations on the dynamics of laboratory populations. The feeding protocols used in these experiments present a highly dynamic food environment that rigorously challenges the ability of stage—structured models to predict the dynamics of populations as they approach equilibrium. For both herbivore species, the models correctly predict feasible equilibria and some features of their dynamics (e.g., periodicity, cycle amplitude, demography, and fecundity) for experiments in which the species were raised in isolation and food transfers were relatively frequent (at least one transfer per instar). With frequent food transfers, the model also correctly predicts coexistence of the herbivores during competition experiments and suggests a novel mechanism for coexistence. The model fails to predict correctly single—species dynamics and the outcome of competition in experiments where food transfers were infrequent and utilization of internal reserves by individuals in the populations must have been high.

Population Dynamics with Sequential Density-Dependencies

We analyse the importance of sequential density-dependent processes to population dynamics of single species. We divide a year into several processes of density-dependent reproduction and/or mortality. A sequence of n processes can be arranged in n ! different sequences. However, only (n - 1) ! of these represent unique relative orderings that have different stability properties and dynamics. Models with several sequential density-dependent processes have a much wider repertoire of dynamics than, e.g., ordinary models based on the logistic equation. Stable equilibrium density and the maximum density of cycles and unstable dynamics do not necessarily increase with increasing b (maximum per capita birth rate). The maps of density at time t + 1 (x t+1 ) versus density at time t (x t ) can have more than one hump, i.e., be bi- or multimodal, with multiple equilibria. In this type of system, chaos is not the only inevitable outcome of increased b. Instead stable equilibrium and/or periodic solutions may occur beyond the chaotic region as b increases. It is suggested that this type of model may apply to many kinds of organisms in seasonal environments. The explicit consideration of sequential density-dependence may be of critical importance for resource and conservation managers, to avoid switches between multiple equilibria or extinction due to poorly timed harvest or pest control.

Single species dynamics in changing environments

A priori bounds are obtained for positive solutions of scalar delay differential equations of the form modelling single species dynamics in a temporally changing environment. Sufficient conditions are derived for the existence of periodic and almost periodic solutions when fis aperiodic and almost periodic function respectively in t.Applications of our analysis enable the derivation of known results in Gopalsamy et al. (1994), Gopalsamy and Ladas (1990), Ladas and Qian (1993) and Lalli and Zhang (1994) as special cases.

Migration, Metapopulation Dynamics and Fugitive Co-existence

Many conclusions about migration in promoting persistence of metapopulations are based on very simple models, which ignore the effect of migration on local dynamics. These models are called patch models. Migration has typically several costs, including mortality of migrants en route, mortality owing to failure to establish a new population in an empty patch and, as costly migration decreases local population sizes, increased risk of extinction of local populations. We analyse metapopulation dynamics of single species and asymmetric competitors with models in which the equilibrium size of local populations is affected both by local processes and by migration. Our results clarify previous conclusions based on the simplified patch models which, when interpreted rigorously, deal only with colonization, not migration. Our results predict that species with an intermediate rate of migration are the ones which tolerate best habitat fragmentation. The general conclusion from these models is that "too much" migration can be as bad for metapopulation persistence as "too little" migration.

Thresholds and Multiple Stable States in Coral Reef Community Dynamics

Multiple stable states occur when more than one type of community can stably persist in a single environmental regime. Simple theoretical analyses predict multiple stable states for (1) single species dynamics via the Allee effect, (2) two-species competitive interactions characterized by unstable coexistence, (3) some predator-prey interactions, and (4) some systems combining predation and competition. Potential examples of transitions between stable states on reefs include the failure of Diadema antillarum and Acropora cervicornis to recover following catastrophic mortality, and the replacement of microalgal turf by unpalatable macroalgae after rapid increase in the amount of substratum available for colonization by algae. Subtidal marine ecosystems in general, and reefs in particular, have several attributes which favor the existence of multiple stable states. Studies of transitions between states often need to rely upon poorly controlled, unreplicated natural “experiments,” as transitions typically require pulses of disturbance over very large spatial scales. The stability of a state must often be inferred from analyses of the dynamics of participants at that state, as generation times and the potential for further extrinsic disturbance preclude the use of persistence as an indicator of stability. The potential for multiple stable states strongly influences our interpretation of variability in space and time and our ability to predict reef responses to natural and man-made environmental change.

Global stability in models of population dynamics with diffusion. I. Patchy environments

SynopsisA class of models of single-species dynamics with diffusion within and between patches is considered. It is shown that under our prescribed conditions, there is a unique, positive, globally asymptotically stable steady state.

Local vs. non-local interactions in population dynamics

In this work we examine two models of single-species dynamics which incorporate non-local effects. The emphasis is on the ability of these models to generate stable patterns. Global behavior of the bifurcating branches is also investigated.

Global stability in time-delayed single-species dynamics.

Criteria are established for three classes of models of single-species dynamics with a single discrete delay to have a globally asymptotically stable positive equilibrium independent of the length of delay.

Global stability in time-delayed single-species dynamics

Criteria are established for three classes of models of single-species dynamics with a single discrete delay to have a globally asymptotically stable positive equilibrium independent of the length of delay.

Theoretical Ecology: Principles and Applications

1. Introduction 2. How Populations Cohere: Five Rules for Cooperation 3. Single species dynamics 4. Metapopulations and Their Spatial Dynamics 5. Predator Prey Interactions 6. Plant Population dynamics 7. Interspecific Competition and Multispecies Coexistence 8. Diversity and stability in ecological communities 9. Community: Patterns 10. Dynamics of Infectious Diseases 11. Fisheries 12. A Doubly Green Revolution 13. Conservation Biology 14. Climate Change and Conservation Biology 15. Unanswered Questions and why they Matter

Boundary-layer model for the population dynamics of single species

We develop a new discrete-time model, called the boundary-layer model, to describe the dynamics of single species that have a capacity for fast growth at very low population densities. The model explicitly separates the dynamics of the population at very low densities (within the "boundary layer") and at high densities. The boundary-layer model provides a better fit than other models such as the logistic or the theta model to data from experimental populations of Drosophila willistoni and D. pseudoobscura.