Zero population growth

In 1968, Ann and Paul Ehrlich published The Population Bomb, warning of dire threats to the future of all living things because of growing human encroachment into all of nature s domains. The book led to the creation of an organization called Zero Population Growth (ZPG), which in 2002 renamed itself The Population Connection. They offer evidence that every environmental problem would be easier to solve if the human population were smaller and growing more slowly than it is. 

Do you know some people with large families If it is possible to do so tactfully, see what their attitudes are toward zero population growth. 

In the 70s, a great deal of heat was expended - at least in the U.S. - on the issue of zero population growth. The world s population has grown by several billion people since then and now stands upwards of 6,793,485,080 individuals. ... 

Population growth is a function of the level of wealth. In Western society the natural population growth is less than zero (the birth rate is less than 2 per woman). The same could happen in developing countries once a certain level of wealth has been reached. 

Zero net growth isocline (ZNGI). The ZNGI is the line in the resource space that represents the lowest concentration of resources that can support a species. In an equilibrium situation, the equilibrium will eventually be drawn to a point along the ZNGI. In the shaded area of the resource space, the population will grow. In the whiter area, extinction will eventually occur. 

There are certain scientific situations where a fixed point must exist for all values of a parameter and can never be destroyed. For example, in the logistic equation and other simple models for the growth of a single species, there is a fixed point at zero population, regardless of the value of the growth rate. However, such a fixed point may change its stability as the parameter is varied. The transcritical bifurcation is the standard mechanism for such changes in stability. 

The induction period in latex drying ends when the polymer spheres begin to flatten against the substrate as a consequence of their filling the Interstices where water originally resided. About one-third of the latex volume is interstitial, so that by the time (t> reaches 0.67 the population growth has started. At this point the percentage of substrate surface that contacts solid polymer is zero. 

Those field studies that include water samples collected during winter months all show undetectable tamarensis concentrations (5, 18, 21). Given the relatively small volumes of water typically collected and counted, this does not preclude the presence of a few cells (the "hidden flora"), but it does indicate that motile populations are extremely small at best. Furthermore, since the growth rate of tamarensis is essentially zero at very low temperatures, the appearance of even a few hundred cells in early spring when waters are still very cold suggests that it is excystment and not division of surviving motile cells that initiates the bloom development. 

The cell-kill hypothesis states that the effects of antitumor drugs on tumor cell populations follow first-order kinetics. This means that the number of cells killed is proportional to the dose. Thus, chemotherapy follows an exponential or log-kill model in which a constant proportion, not a constant number, of cancer cells are killed. Ilieoretically. the fractional reductions possible with cancer chemotherapy can never reduce tumor populations to zero. Complete er ica-tion requires another effect, such as the immune response. A modified form of the first-order log-kill hypothesis holds that tumor regressions produced by chemotherapy are de-.scribed by the relative growth fraction present in the tumor at the lime of treatment This idea is consistent with the finding that very small and very large tumors are less responsive than tumors of intermediate size. ... 

From the above we can see that when A = p, the expected rate of growth is zero and the mean population size is stationary. 

It should be noted that in cases where the cell population is reduced to zero, the model exhibits curative properties as regrowth of the cells cannot occur since the growth rate is a first-order rate depending on an existing population. 

This adaptation of the Gompertz growth function allows for the sensitive cell population to reach zero but will then show delayed regrowth in both sensitive and resistant cell populations as the resistant cell population continues to grow and then transfers to the sensitive cell type. 

Fig. 15.3. Pheise portrait of the modified Lotka-Volterra models in the (R, Ai)-phase plane (solid lines). Graphical analysis revolves around plotting the isoclines in the prey-predator phase plane that denote zero-growth of the model predator and prey populations [13] (dashed lines), a) Nonlinear density dependence g R) leads to a decreasing prey isocline and is stabilizing, b) Type-II functional response f R) gives rise to an increasing prey isocline and is destabilizing.

These equations are based on the assumption that at any given moment the population of micro-organisms (bacteria) in a culture will multiply as long as either there is nutrient available or, the concentration of the inhibitory product is not limiting. The rate of multiplication within the biofilm will vary according to these criteria. Belkhadir et al [1988] described the fundamental growth phases in a biofilm. The growth of active biomass is assumed to have an order of zero in relation to the nutrient and an order of unity in relation to the active bacteria so that ... 

---