Mechanisms for Population Extinction in Southwestern Aguilegia

EPA Grant Number: U914822
Title: Mechanisms for Population Extinction in Southwestern Aguilegia
Investigators: Strand, Allan E.
Institution: New Mexico State University - Main Campus
EPA Project Officer: Broadway, Virginia
Project Period: January 1, 1995 through January 1, 1996
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1995) Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Ecology


Molecular markers have the potential to provide insight into ecological processes that are not possible using classical ecological techniques alone. Two examples of such ecological processes are those that determine the distribution of populations: colonization of new habitat, and the loss of existing populations. For the inference of process from the patterns of molecular marker diversity, data in addition to those obtained from genetic markers must be employed. The overall objectives of this research project are to demonstrate the utility of effective size as an indicator by establishing baseline effective sizes over recent geological history in Aquilegia populations, and compare them to current estimates of effective size in the same populations. The specific objectives of this research project are to: (1) measure the historical effective size in 10 populations located in the southwestern United States, which uses a genetic estimator based on times to common ancestry of alleles; (2) measure current effective population size by collecting information required by a demographically based estimator, which requires detailed work in a single population and censuses in the other nine; and (3) compare the two estimates to estimate population demographic change over recent geological history.


I estimate the rate of seed movement by estimating the rate of gene flow in the chloroplast genome using variation resolved at the DNA level by means of polymerase chain reaction and denaturing gradient gel-electrophoresis. Then, I subtract the effects of nonequilibrium population structure on inferred gene-flow to obtain an estimate of ongoing migration via seed. The effects of nonequilibrium population structure are subtracted by estimating the time since populations diverged from the fossil record, and estimating the average per-population effective population size from demographic analysis. These parameters were used to predict the effects of nonequilibrium population structure under a model of instantaneous population subdivision with no subsequent migration. The difference between the model's predictions and the genetic estimates yielded realized migration rates. The demographic analysis also was used to predict the likelihood of population extinction. When the effects of nonequilibrium population structure were considered, the rate of migration via seed was zero. Therefore, no colonization currently is possible. Demographic analysis demonstrated that population growth rates were extremely sensitive to amounts of precipitation. The finite rate of increase was well below 1 (0.45) in 1 year where precipitation was at drought levels, while it was substantially greater than 1 (1.44) in years with higher than average rainfall.

Supplemental Keywords:

fellowship, molecular markers, population, colonization, Aquilegia, northern Mexico, southwestern United States, polymerase chain reaction, PCR, denaturing gradient gel-electrophoresis, nonequilibrium, genetic marker diversity., Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Habitat, Environmental Monitoring, Ecology and Ecosystems, habitat dynamics, plant population dynamics, community composition, community genetic diversity, genetic consequences, habitat loss, plant diversity, ecological consequences, genetic markers