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1.
J Theor Biol ; 585: 111797, 2024 May 21.
Article in English | MEDLINE | ID: mdl-38518828

ABSTRACT

The success of individual species under a change to the environment is dependent on a number of factors, which include the changes to habitat, competition with other species and adaptability. Here we investigate the impact of differing dispersal characteristics of two competing species responding to the change using an idealized spatio-temporal model. The rate of dispersion is given by a combination of the growth term and the form of the diffusion term, which is set to give either normal diffusion or anomalous (super) diffusion. The later is brought about by employing fractional diffusion and we characterize the population as being more adventurous than the population undergoing normal diffusion. The more adventurous population is found, not surprisingly, to reach and occupy uninhabited ground before the population undergoing normal diffusion can get there. Interbreeding is found to be important in that it can aid the spread of the less adventurous population preventing its extinction. The response to an abrupt environment change, taken here to be a change in the distribution of the growth rate, is dependent on the initial conditions, the dispersion characteristics, and the level of interbreeding, leading to very different intermediate and final states. Our results highlight instances when a particular dispersal strategy gives a population an edge over another. In the cases considered here we find states where the more adventurous population can dominate across the domain, the two populations exist in separate parts of the domain separated by fronts, and both populations coexist across the domain in the medium term with one or other of the populations dominating across the domain in the long term. Given the long time to reach equilibrium where one or other of the populations dominate, consideration needs to be put to the time scale of change, as sufficiently frequent change can allow coexistence. We demonstrate the need to include dispersion characteristics when considering the factors affecting the response of species to a change in the environment.


Subject(s)
Ecosystem , Population Dynamics
2.
J Theor Biol ; 412: 27-35, 2017 01 07.
Article in English | MEDLINE | ID: mdl-27693364

ABSTRACT

Viruses are known to impact blooms of phytoplankton in the ocean, in some cases causing the bloom to crash. Here, using a population model that includes viral infection, we investigate the conditions under which the presence of a virus significantly impacts the population dynamics. A major focus is how spatial variability influences the spread of an epidemic in a stirring and mixing field. The combination of viral infection and diffusion can cause waves of the epidemic to sweep through the domain, with the epidemic lasting much longer than in the homogeneous case. Stirring by the fluid flow can greatly increase this effect causing an increase in the fraction of the bloom that is affected and in certain circumstances (high diffusion and stirring) can totally suppress the bloom. The fluid environment affects the relative spatial structure of the components of the system. High values of the concentrations of the virus and infected phytoplankton are found in thin filaments along fronts of uninfected (susceptible) phytoplankton.


Subject(s)
Models, Biological , Plankton/virology , Virus Diseases , Viruses , Animals , Oceans and Seas , Population Dynamics
3.
ISME J ; 8(6): 1175-85, 2014 Jun.
Article in English | MEDLINE | ID: mdl-24477197

ABSTRACT

Nitrogen-fixing microorganisms (diazotrophs) are keystone species that reduce atmospheric dinitrogen (N2) gas to fixed nitrogen (N), thereby accounting for much of N-based new production annually in the oligotrophic North Pacific. However, current approaches to study N2 fixation provide relatively limited spatiotemporal sampling resolution; hence, little is known about the ecological controls on these microorganisms or the scales over which they change. In the present study, we used a drifting robotic gene sensor to obtain high-resolution data on the distributions and abundances of N2-fixing populations over small spatiotemporal scales. The resulting measurements demonstrate that concentrations of N2 fixers can be highly variable, changing in abundance by nearly three orders of magnitude in less than 2 days and 30 km. Concurrent shipboard measurements and long-term time-series sampling uncovered a striking and previously unrecognized correlation between phosphate, which is undergoing long-term change in the region, and N2-fixing cyanobacterial abundances. These results underscore the value of high-resolution sampling and its applications for modeling the effects of global change.


Subject(s)
Nitrogen Fixation , Seawater/microbiology , Bacteria/classification , Bacteria/genetics , Bacteria/isolation & purification , Cyanobacteria/classification , Cyanobacteria/genetics , Cyanobacteria/isolation & purification , Genomics , Pacific Ocean , Polymerase Chain Reaction , Robotics
4.
J Theor Biol ; 238(2): 340-7, 2006 Jan 21.
Article in English | MEDLINE | ID: mdl-16076475

ABSTRACT

We investigate the combined effects of diffusion and stirring on the dynamics of interacting populations which have spatial structure. Specifically we consider the marine phytoplankton and zooplankton populations, and model them as an excitable medium. The results are applicable to other biological and chemical systems. Under certain conditions the combination of diffusion and stirring is found to enhance the excitability, and hence population growth of the system. Diffusion is found to play an important role: too much and initial perturbations are smoothed away, too little and insufficient mixing takes place before the reaction is over. A key time-scale is the mix-down time, the time it takes for the spatial scale of a population to be reduced to that of a diffusively controlled filament. If the mix-down time is short compared to the reaction time-scale, then excitation of the system is suppressed. For intermediate values of the mix-down time the peak population can attain values many times that of a population without spatial structure. We highlight the importance of the spatial scale of the initial disturbance to the system.


Subject(s)
Models, Statistical , Population Dynamics , Animals , Diffusion , Emigration and Immigration , Models, Biological , Phytoplankton , Population Density , Time Factors , Zooplankton
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