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Biomedical subjects

P R Ehrlich

Publications and source records attributed to P R Ehrlich.

16 recordsLinked to original sources
PubMed1997

Population diversity: its extent and extinction.

Genetically distinct populations are an important component of biodiversity. This work estimates the number of populations per area of a sample of species from literature on population differentiation and the average range area of a species from a sample of distribution maps. This yields an estimate of about 220 populations per species, or 1.1 to 6.6 billion populations globally. Assuming that population extinction is a linear function of habitat loss, approximately 1800 populations per hour (16 million annually) are being destroyed in tropical forests alone.

Animals↗
PubMed1996

Nocturnality and species survival.

Surveys of butterfly and moth diversity in tropical forest fragments suggest that nocturnality confers a dispersal, and possibly a survival, advantage. The butterfly faunas of smaller fragments were depauperate; in contrast, the species richness of nocturnal moths was similar in all fragments and even in pasture. The lack of correlation between butterfly and moth species richness among fragments (r2 = 0.005) is best explained by movements of moths at night when ambient conditions in forest and pasture are most similar; butterflies face substantial daytime temperature, humidity, and solar radiation barriers. This interpretation is supported by information on birds, beetles, and bats.

Animals↗
PubMed1990

An exploratory model of the impact of rapid climate change on the world food situation.

A simple, globally aggregated, stochastic-simulation model was constructed to examine the effects of rapid climatic change on agriculture and the human population. The model calculates population size and the production, consumption and storage of grain under different climate scenarios over a 20-year projection time. In most scenarios, either an optimistic baseline annual increase of agricultural output of 1.7% or a more pessimistic appraisal of 0.9% was used. The rate of natural increase of the human population exclusive of excess hunger-related deaths was set as 1.7% per year and climatic changes with both negative and positive impacts on agriculture were assessed. Analysis of the model suggests that the number of hunger-related deaths could double (with reference to an estimated 200 million deaths in the past two decades) if grain production keeps pace with population growth but climatic conditions are unfavourable. If the rate of increase in grain production is about half that of population growth, the number of hunger-related deaths could increase about fivefold (over past levels); the impact of climatic change is relatively small under this imbalance. Even favourable climatic changes that enhance agricultural production may not prevent a fourfold increase in deaths (over past levels) under scenarios where population growth outpaces production by about 0.8% per annum. These results may foreshadow a fundamental change where, for the first time, absolute global food deficits compound inequities in food production and distribution in causing famine. The model also highlights the effectiveness of reducing population growth rates as a strategy for minimizing the impact of global climate change and maintaining food supplies for everyone.

Biometry↗
PubMed1985

A direct assessment of the role of genetic drift in determining allele frequency variation in populations of Euphydryas editha.

Estimates of allele frequencies at six polymorphic loci were collected over eight generations in two populations of Euphydryas editha. We have estimated, in addition, the effective population size for each generation for both populations with results from mark-recapture and other field data. The variation in allele frequencies generated by random genetic drift was then studied using computer simulations and our direct estimates of effective population size. Substantial differences between observed values and computer-generated expected values assuming drift alone were found for three loci (Got, Hk, Pgi) in one population. These observations are consistent with natural selection in a variable environment.

Alleles↗
PubMed1983

Long-term biological consequences of nuclear war.

Subfreezing temperatures, low light levels, and high doses of ionizing and ultraviolet radiation extending for many months after a large-scale nuclear war could destroy the biological support systems of civilization, at least in the Northern Hemisphere. Productivity in natural and agricultural ecosystems could be severely restricted for a year or more. Postwar survivors would face starvation as well as freezing conditions in the dark and be exposed to near-lethal doses of radiation. If, as now seems possible, the Southern Hemisphere were affected also, global disruption of the biosphere could ensue. In any event, there would be severe consequences, even in the areas not affected directly, because of the interdependence of the world economy. In either case the extinction of a large fraction of the Earth's animals, plants, and microorganisms seems possible. The population size of Homo sapiens conceivably could be reduced to prehistoric levels or below, and extinction of the human species itself cannot be excluded.

Animals↗
PubMed1975

Population genetics of euphydryas butterflies. I Genetic variation and the neutrality hypothesis.

Twenty-one populations of the checkerspot butterfly, Euphydryas editha, and ten populations of Euphydryas chalcedona were sampled for genetic variation at eight polymorphic enzyme loci. Both species possessed loci that were highly variable from population to population and loci that were virtually identical across all populations sampled. Our data indicate that the neutrality hypothesis is untenable for the loci studied, and therefore selection is indicated as the major factor responsible for producing these patterns. Thorough ecological work allowed gene flow to be ruled out (in almost all instances) as a factor maintaining similar gene frequencies across populations. The Lewontin-Krakauer test indicated magnitudes of heterogeneity among standardized variances of gene frequencies inconsistent with the neutrality hypothesis. The question of whether or not to correct this statistic for sample size is discussed. Observed equitability of gene frequencies of multiple allelic loci was found to be greater than that predicted under the neutrality hypothesis. Genetic differentiation persisting through two generations was found between the one pair of populations known to exchange significant numbers of individuals per generation. Two matrices of genetic distance between populations, based on the eight loci sampled, were found to be significantly correlated with a matrix of environmental distance, based on measures of fourteen environmental parameters. Correlations between gene frequencies and environmental parameters, results of multiple regression analysis, and results of principle component analysis showed strong patterns of association and of "explained" variation. The correlation analyses suggest which factors might be further investigated as proximate selective agents.

Animals↗