Population dynamics

6 EFFECTS OF CHEMICALS AT THE POPULATION LEVEL 4.6.1 Population Dynamics 

In environmental risk assessment, the objective is to establish the likelihood of a chemical (or chemicals) expressing toxicity in the natural environment. Assessment is based on a comparison of ecotoxicity data from laboratory tests with estimated or measured exposure in the field. The question of effects at the level of population that may be the consequence of such toxicity is not addressed. This issue will now be discussed. 

In general, it can be stated that the population density of an animal depends on the balance between the rate of recruitment and the rate of mortality. In the context of ecotoxicology, the influence of pollutants upon either of these factors is of fundamental interest and importance. When a population is at or near its carrying capacity, these two factors are in balance, and the critical question about the effects of pollutants is whether they can adversely affect this balance and bring a population decline. 

The population growth rate of an organism can be calculated from the Euler-Lotka equation 

Organic Pollutants An Ecotoxicological Perspective, Second Edition 

For the sake of illustration, we will calculate the Nd isotope composition of continents in a very simple model of crustal evolution. A newly formed crustal segment results from the addition of both juvenile mantle and material recycled from the 

we assume that juvenile crust is extracted from the mantle at a constant rate g. Therefore 

The amount dM(T,t) of crust formed between T and T+dT still surviving at t is 

The increment of crust newly formed at t is created at a rate g for the juvenile part, and, for the recycled part, as the negative of the erosion rate. Therefore 

Note that the left-hand side has not been expressed as dM(r, t)/dt as in Michard et al. (1985), which would incorrectly imply a crustal growth rate, but as a density of probability of the crustal ages for T in the vicinity of t. The integral in the middle term represents the eroded components summed over all the class ages [T, T + dT] from T = 0 to T = t. 

Microbes use enzymes as catalysts to obtain the desired or beneficial reaction and typically under mild conditions. The brewing of beer and fermentation of fruit and vegetable mass high in starches to produce consumable ethanol are the oldest and most familiar examples of using microbial action to achieve a desired end. But now much more has been demonstrated, from the production of essential human hormones to the synthesis of specialty chemicals. 

In a reactor containing substrate a colony of microbes is irmoculated and brought to maturity. As the colony grows the substrate is consumed to supply the microbes with their 

Chapter 7 Reacting Systems—Kinetics and Batch Reactors 

The basis of life is molecular. Therefore we can describe the rates of substrate consumption, product formation, and even microbe population growth in much the same way that we would describe the rates of molecular-level chemical processes. 

We will take the microbe, substrate, and product concentrations to be a[t], b[t], c[t], respectively. The ways in which these kinetics are written are somewhat different. The equations that describe the rates of change of each of these are shown in the following  

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It has been demonstrated that the whole photoexcitation dynamics in m-LPPP can be described considering the role of ASE in the population depletion process [33], Due to the collective stimulated emission associated with the propagation of spontaneous PL through the excited material, the exciton population decays faster than the natural lifetime, while the electronic structure of the photoexcited material remains unchanged. Based on the observation that time-integrated PL indicates the presence of ASE while SE decay corresponds to population dynamics, a numerical simulation was used to obtain a correlation of SE and PL at different excitation densities and to support the ASE model [33]. The excited state population N(R.i) at position R and time / within the photoexcited material is worked out based on the following equation ... 

FIGURE 2.6 Population dynamics predicted by the Lotka-Volterra model for an initial population of 100 rabbits and 10 lynx. 

FIGURE 14.2 Population dynamics on a well-mixed grassy plain with constant migration of rabbits and lynx. Compare to the nonmigratory case in Figure 2.6. 

Meinke, LJ USDA To study the influence of methyl parathion on western corn rootworm behavior and population dynamics. 

Coffin JM (1995) HIV population dynamics in vivo implications for genetic variation, pathogenesis, and therapy. Science 267 483 89... 

G. F. Webb, Theory of Nonlinear Age-Dependent Population Dynamics (1985)... 

Girguis PR, AE Cozen, EF Delong (2005) Growth and population dynamics of anaerobic methane-oxidizing archaea and sulfate-reducing bacteria in a continuous-flow reactor. Appl Environ Microbiol 71 3725-3733. 

Watanabe K, S Yamamoto, S Hino, S Harayama (1998a) Population dynamics of phenol-degrading bacteria in activated sludge determined by gyrB-targeted quantitative PGR. Appl Environ Microbiol 64 1203-1209. 

Barr JF. 1986. Population dynamics of the Common Loon (Gavia immer) associated with mercury-contaminated waters in northwestern Ontario. Canadian Wildlife Service Occasional Paper 56. 

Evers DC, Jodice P. 2002. Winter population dynamics of Common Loons on the Florida gulf coast a preliminary report. Unpublished report, alaska.fws.gov/mbsp/mbm/ loons/pdf/Common Loon Status Assessment.pdf... 

Habermann, R. (1976) Mathematical Models Mechanical Vibration, Population Dynamics and Traffic Flow, Prentice-Hall. 

P. R. Darrah, Models of the rhizosphere. I. Microbial population dynamics around the root releasing. soluble and in.soluble carbon. Plant Soil 733 187 (1991). 

N. Panikov, Population dynamics of microorganisms with different life strategies. Environmental Gene Release Models, Experiments and Risk A.s.se.s.sment (M. J. Bazin and J. M. Lynch, eds.). Chapman and Hall, London, 1994, p. 47. 

V. Goddard, Population dynamics of fluorescent pseudomonads in the rhizosphere, D. Phil, thesis, Oxford University, 1999. 

Methodological Approaches to the Study of Rhizosphere Carbon Flow and Microbial Population Dynamics... 

Such differences in the amount and type of rhizodeposition that occur on the root with time result in concomitant variations in microbial populations in the rhizosphere, both within the root (endorhizosphere), on the surface of the root (rhizoplane), and in the soil adjacent to the root (ectorhizosphere). The general microbial population changes and specific interaction of individual compounds from specific plants or groups of plants with individual microbial species are covered in detail elsewhere (Chap. 4). Consequently, this chapter is restricted to consideration of methodologies used to study carbon flow and microbial population dynamics in the rhizosphere, drawing on specific plant-microbe examples only when required. 

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