ecosystem
A community of organisms and its environment.

ecosystem services
The products and services humans receive from functioning ecosystems.

ecotone
The region that encompasses the shift between two biological communities.

effective number of alleles
The number of equally frequent alleles that would create the same heterozygosity as observed in the population.

effective population size (Ne)
The size of the ideal, panmictic population that would experience the same loss of genetic variation, through genetic drift, as the observed population.

electrophoresis
The movement of molecules through a medium across an electric field. Electrophoresis is used to separate allelic enzymes (allozymes) and DNA molecules of differing charge, size, or shape.

EM
See expectation maximization algorithm.

Endangered Species Act of the United States
ESA.

endonuclease
An enzyme that cleaves either a single, or both, strands of a DNA molecule. Bacterial endonucleases are used to split genomic DNA at specific sites for analysis. See restriction enzyme.

Environmental Protection Agency of the United States
EPA.

environmental stochasticity
Random variation in environmental factors that influence population parameters affecting all individuals in that population.

EPA
Environmental Protection Agency of the United States.

epidemiology
The study of the spread and control of a disease in a population.

epistatic genetic variation
The proportion of total genetic variation that can be attributed to the interaction between loci producing a combined effect different from the sum of the effects of the individual loci.

ESA
Endangered Species Act of the United States.

ESPA
Endangered Species Protection Act of Australia.

ESU
See evolutionary significant unit.

evolutionary significant unit (ESU)
A classification of populations that have substantial reproductive isolation which has led to adaptative differences so that the population represents a significant evolutionary component of the species. Evolutionary significant units have also been classified as populations that exhibit reciprocal monophyly and no recent gene flow. The original term used was “evolutionarily” rather than “evolutionary” (Ryder 1986). However, both terms are currently used in the literature.

ex situ conservation
The conservation of important evolutionary lineages of species outside the species natural habitat.

exact tests
An approach to compute the exact P-value for an observed result rather than use an approximation, such as the chi-square distribution.

exon
A coding portion of a gene that produces a functional gene product (e.g., a peptide).

expectation maximization algorithm (EM)
A computational tool in statistics for finding maximum likelihood estimates of parameters in probabilistic models, where the model depends on unobserved variables. It can provide an estimate of the most likely allele frequencies assuming the sample is in Hardy–Weinberg proportions. Bayesians also use the EM algorithm to optimize the a posteriori distribution to compute the maximum a posteriori (MAP) estimate of an unknown parameter.

extant
Currently living; not extinct.

extinction
The disappearance of a species or other taxon so that it no longer exists anywhere.

extirpation
The loss of a species or subspecies from a particular area, but not from its entire range.