Sinks population biology

In population biology, plants and animals evolve in time and space in ways that can often be described by diffusion equations. Births, deaths, migration, and competition are sources, sinks, and fluxes into or out of the system that are subject to diffusion in time and space. We develop such equations one step at a time. We start with the simplest time dependence for the growth of populations, then add the effects of competition, and finally we introduce the spatial dependence, following the discussion in reference [3]. 

PbB concentrations reflect the absorbed dose of lead. However, the interpretation of PbB data depends on a knowledge of the past history of exposure to lead. This is because in the body, bone constitutes the major lead sink and this results in lead having a long body half-life. Thus, in the absence of intense exposure to lead for a considerable period up to its body half-life, the PbB concentrations reflect recent lead exposures. However, if intermittent exposure to lead is occurring in several distinct environments, the PbB concentration reflects both recent and past exposures to lead. Thus, biological effects for populations with the same PbB concentrations may not be the same since different exposure times scales may be involved. This is the reason why free erythrocyte protoporphyrin (FEP) and erythrocyte zinc protoporphyrin (ZPP) have been used as additional biological markers since their elevation is more related to chronic lead exposure than acute lead exposure (see Section 2.7). 

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