Retention Time Variability as a Mechanism for Animal Mediated Long-Distance Dispersal

Long-distance dispersal (LDD) events, although rare for most plant species, can strongly influence population and community dynamics. Animals function as a key biotic vector of seeds and thus, a mechanistic and quantitative understanding of how individual animal behaviors scale to dispersal patterns at different spatial scales is a question of critical importance from both basic and applied perspectives. Using a diffusion-theory based analytical approach for a wide range of animal movement and seed transportation patterns, we show that the scale (a measure of local dispersal) of the seed dispersal kernel increases with the organisms' rate of movement and mean seed retention time. We reveal that variations in seed retention time is a key determinant of various measures of LDD such as kurtosis (or shape) of the kernel, thinkness of tails and the absolute number of seeds falling beyond a threshold distance. Using empirical data sets of frugivores, we illustrate the importance of variability in retention times for predicting the key disperser species that influence LDD. Our study makes testable predictions linking animal movement behaviors and gut retention times to dispersal patterns and, more generally, highlights the potential importance of animal behavioral variability for the LDD of seeds

Spatial Population Dynamics In A Producer-Scrounger Model

The spatial population dynamics of an ecological system involving producers and scroungers is studied using a reaction-diffusion model. The two populations move randomly and increase logistically, with birth rates determined by the amount of resource acquired. Producers can obtain the resource directly from the environment, but must surrender a proportion of their discoveries to nearby scroungers through a process known as scramble kleptoparasitism. The proportion of resources stolen by a scrounger from nearby producers decreases as the local scrounger density increases. Parameter combinations which allow producers and scroungers to persist either alone or together are distinguished from those in which they cannot. Producer persistence depends in general on the distribution of resources and producer movement, whereas scrounger persistence depends on its ability to invade when producers are at steady-state. It is found that (i) both species can persist when the habitat has high productivity, (ii) neither species can persist when the habitat has low productivity, and (iii) slower dispersal of both the producer and scrounger is favored when the habitat has intermediate productivity

A model for the spatial transmission of dengue with daily movement between villages and a city

Dengue is a re-emergent vector-borne disease affecting large portions of the world\u27s population living in the tropics and subtropics. The virus is transmitted through the bites of female Aedes aegypti mosquitoes, and it is widely believed that these bites occur primarily in the daytime. The transmission of dengue is a complicated process, and one of the main sources of this complexity is due to the movement of people, e.g. between home and their places of work. Hence, the mechanics of disease progression may also differ between day and night. A discrete-time multi-patch dengue transmission model which takes into account the mobility of people as well as processes of infection, recovery, recruitment, mortality, and outbound and return movements is considered here. One patch (the city) is connected to all other patches (the villages) in a spoke-like network. We obtain here the basic reproductive ratio (a \u3e (0)) of the transmission model which represents a threshold for an epidemic to occur. Dynamical analysis for vector control, human treatment and vaccination, and different kinds of mobility are performed. It is shown that changes in human movement patterns can, in some situations, affect the ability of the disease to persist in a predictable manner. We conclude with biological implications for the prevention and control of dengue virus transmission

Effect Of Resource Subsidies On Predator-Prey Population Dynamics: A Mathematical Model

Second-order competences, a type of dynamic capability, enable firms to engage in a process of Schumpeterian competition. This study examines the effects of marketing and R&D second-order competences (the abilities to create new market-related and technological resources) on firm profitability. Based on multiple informant surveys and archival data from U.S. public manufacturing firms, competitive turbulence is found to present contrasting contingencies for the effects of these competences on return on assets (ROA). The effect of marketing competence on ROA was positive under stable and moderate competitive conditions, whereas the effect of R&D competence on ROA was positive under volatile competitive conditions. © 2012 Strategic Management Society

Stability Of Choice In The Honey Bee Nest-Site Selection Process

We introduce a pair of compartment models for the honey bee nest-site selection process that lend themselves to analytic methods. The first model represents a swarm of bees deciding whether a site is viable, and the second characterizes its ability to select between two viable sites. We find that the one-site assessment process has two equilibrium states: a disinterested equilibrium (DE) in which the bees show no interest in the site and an interested equilibrium (IE) in which bees show interest. In analogy with epidemic models, we define basic and absolute recruitment numbers (R0 and B0) as measures of the swarm\u27s sensitivity to dancing by a single bee. If R0 is less than one then the DE is locally stable, and if B0 is less than one then it is globally stable. If R0 is greater than one then the DE is unstable and the IE is stable under realistic conditions. In addition, there exists a critical site quality threshold Q* above which the site can attract some interest (at equilibrium) and below which it cannot. We also find the existence of a second critical site quality threshold Q** above which the site can attract a quorum (at equilibrium) and below which it cannot. The two-site discrimination process, in which we examine a swarm\u27s ability to simultaneously consider two sites differing in both site quality and discovery time, has a stable DE if and only if both sites\u27 individual basic recruitment numbers are less than one. Numerical experiments are performed to study the influences of site quality on quorum time and the outcome of competition between a lower quality site discovered first and a higher quality site discovered second. © 2009 Elsevier Ltd

Stability of Choice in the Honey Bee Nest-Site Selection Process

A pair of compartment models for the honey bee nest-site selection process is introduced. The first model represents a swarm of bees deciding whether a site is viable, and the second characterizes its ability to select between two viable sites. The one-site assessment process has two equilibrium states: a disinterested equilibrium (DE) in which the bees show no interest in the site and an interested equilibrium (IE) in which bees show interest. In analogy with infectious disease models, basic and absolute recruitment numbers (R0 and B0) are defined as measures of the swarm’s sensitivity to dancing by a single bee. If R0 is less than one then the DE is locally stable, and if B0 is less than one then it is globally stable. If R0 is greater than one then the DE is unstable and the IE is stable under realistic conditions. In addition, there exists a critical site quality threshold Q ∗ above which the site can attract some interest (at equilibrium) and below which it cannot. There also exists a a second critical site quality threshold Q ∗ ∗ above which the site can attract a quorum (at equilibrium) and below which it cannot. The two-site discrimination process, which examines a swarm’s ability to simultaneously consider two sites differing in both site quality and discovery time, has a stable DE if and only if both sites ’ individual basic recruitment numbers are less than one. Numerical experiments are performed to study the influences of site quality on quorum time and the outcome of competition between a lower quality site discovered first and a higher quality site discovered second