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Results for “Population Growth Estimation”

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PubMed1979

[Population].

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Americas↗
PubMed1994

Precursors of macrophages in embryonic rat lungs fail to exhibit granulocyte-forming potential.

BACKGROUND: Mesenchyme-like macrophage (M) precursors called angular cells are present in rat lungs on the thirteenth day of gestation and by then can differentiate into outright macrophages. Based on studies of bone marrow-derived cells, it is widely believed that the macrophage line necessarily proceeds from a colony-forming unit with dual granulocyte-macrophage potential (CFU-GM). In embryos this seems doubtful since macrophages are already scattered throughout the body before the first granulocytes appear. We examined the question in organ cultured 14 day prenatal rat lungs after having shown earlier that the macrophage population developed in explants is increased by exposure to M- and GM-colony-stimulating factors (CSFs) but is unaffected by multi (IL-3)- or granulocyte (G)-CSF. Reportedly retinoic acid (RA) shifts CFU-GM strongly towards granulocytic differentiation and inhibits mitosis of unipotential macrophage precursors but not differentiated cells. Transforming growth factor beta 1 (TGF) inhibits multipotential blood progenitors but allows proliferation of committed precursors, and TGF together with GM-CSF induces granulocytopoiesis from CFU-GM. METHODS: Lung pairs were grown on a serum-containing medium or one supplemented either by RA, TGF, or TGF/GM-CSF to form a control and three experimental groups. A fourth experiment compared responses to M-CSF exposure and M-CSF/TGF. Macrophage population growth was estimated by measuring the areas of coronas formed by macrophages emerged from the explants. F-actin was stained with fluorescein-labeled phalloidin. RESULTS: In all experiments macrophages were produced unmixed with granulocytes. By +8 days they had largely emerged to form coronas about the lungs. In cultures exposed to RA, macrophages were less intensely stained for actin and slower to emerge than controls. At +8 days, however, coronal areas were not significantly different from controls, as was also true for the TGF group. In contrast, coronal areas of cultures grown with TGF/GM-CSF were much larger. At +17 days, mean coronal area of TGF cultures was about half that of controls (P < 0.05), whereas mean coronal area of the TGF/GM-CSF group was 5.4 times greater (P < 0.001). Macrophages from control and TGF-exposed cultures responded to M-CSF by an increase in coronal area which was greater among cultures given M-CSF alone than those given TGF + M-CSF (both P < 0.005). CONCLUSIONS: Macrophage precursors in embryonic lungs are distinct from CFU-GM.

Animals↗
PubMed2005

Demography in an increasingly variable world.

Recent advances in stochastic demography provide unique insights into the probable effects of increasing environmental variability on population dynamics, and these insights can be substantially different compared with those from deterministic models. Stochastic variation in structured population models influences estimates of population growth rate, persistence and resilience, which ultimately can alter community composition, species interactions, distributions and harvesting. Here, we discuss how understanding these demographic consequences of environmental variation will have applications for anticipating changes in populations resulting from anthropogenic activities that affect the variance in vital rates. We also highlight new tools for anticipating the consequences of the magnitude and temporal patterning of environmental variability.

Animals↗
PubMed2004

Evaluating habitat as a surrogate for population viability using a spatially explicit population model.

Because data for conservation planning are always limited, surrogates are often substituted for intractable measurements such as species richness or population viability. We examined the ability of habitat quality to act as a surrogate for population performance for both Red-shouldered Hawks (Buteo lineatus) and Northern Goshawks (Accipiter gentilis). We compared simple measures of habitat quality to estimates of population growth rates obtained from a spatially explicit model of population dynamics. We found that habitat quality was a relatively poor predictor of simulated population growth rates for several reasons. First, a relatively small proportion of the potential habitat for each species served as population sources in our simulations--15% for Red-shouldered Hawks and 2% for Goshawks. Second, when habitat quality correctly predicted demographic sources on the landscape, it consistently underestimated the contribution of these areas to the population. In areas where habitat quality correctly anticipated the presence of demographic sinks, we found no useful quantitative relationship between the two measures. Our simulation model captured the influence of habitat quality on the hawk populations, but it also incorporated interactions between dispersing individuals and landscape patterns. Thus, the discrepancies we observed likely reflected the influence of forest fragmentation and the spatial arrangement of forest patches on the populations. We conclude that simple measures of habitat quality will often be poor surrogates for population persistence, but that spatially explicit population models can help inform the development of better indices.

Animals↗
PubMed1992

A recurring question--how many beds for dementia?

Experience at Crichton Royal in dealing with dementia over a thirty year period has been used to develop two models of bed requirements for dementia sufferers. The first based on results from the periods 1957 to 1959 and 1974 to 1976 and the second on experience in the years 1974-75 and 1984-85. The variables considered were demographic change, admission of a constant proportion of the at risk group and changes in individual patient survival between groups of patients admitted. Projections based on the earlier model suggested that the SHAPE provision of 10 beds per 1000 of the over 64 population would be insufficient to maintain established standards of care. The later model, however, finds SHAPE numbers appropriate. The reasons for the change of view--inaccuracy in estimate of increasing male survival and significant under-estimates of population growth--nullify each other. The conclusion is that SHAPE is a useful model provided the demographic changes and patient survival change are carefully monitored.

Aged↗
PubMed2006

Demography of central and marginal populations of monkeyflowers (Mimulus cardinalis and M. lewisii).

Every species occupies a limited geographic area, but how spatiotemporal environmental variation affects individual and population fitness to create range limits is not well understood. Because range boundaries arise where, on average, populations are more likely to go extinct than to persist, range limits are an inherently population-level problem for which a demographic framework is useful. In this study, I compare demographic parameters and population dynamics between central and marginal populations of monkeyflowers, Mimulus cardinalis and M. lewisii, along an elevation gradient spanning both species' ranges. Central and marginal populations of both species differed in survival and fecundity. For M. lewisii, these components of fitness were higher in central than in marginal populations, but for M. cardinalis the converse was true. To assess spatiotemporal variation in population dynamics, I used transition matrix models to estimate asymptotic population growth rates (lambda) and found that population growth rates of M. lewisii were highest at the range center and reduced at the range margin. Population growth rates of M. cardinalis were highest at the range margin and greatly reduced at the range center. Life table response analysis decomposed spatiotemporal variation in lambda into contributions from each transition between life stages, finding that transitions from large nonreproductive and reproductive plants to the seed class and stasis in the reproductive class made the largest contributions to spatial differences in lambda. These transitions had only low to moderate sensitivities, indicating that differences in projected population growth rates resulted mainly from observed differences in transition matrix parameters and their underlying vital rates.

Altitude↗