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Biology 20C - Fall 1998 |
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ECOLOGY AND EVOLUTIONARY BIOLOGY |
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Lecture 19 - Populations: Introduction |
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Conceptual: (genetic) (evolutionary) |
A population is a group of individuals of the same species that (potentially) interbreed with one another, and are more or less isolated from other such groups of the same species. |
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Empirical: (practical) (ecological) |
A population is a group of individuals of the same species living in a specified area, exposed to the same environment, using the same resources, and involved in the same ecological processes. |
Individuals vs. Populations:
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A. STATES (Instantaneous) |
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Individual |
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Population |
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Location |
è |
Distribution (area or volume) |
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è |
Dispersion (spacing: clumped, uniform or random) |
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Size (body) |
not è |
Population size (numbers = N) |
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not è |
Density (N/area or N/volume) |
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Size (body) |
è |
Size structure ( = ns : proportions) |
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Age (x) |
è |
Age structure ( = nx : proportions) |
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Developmental stage |
è |
Stage structure (proportions) |
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Sex |
è |
Sex ratio (proportions) |
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Genotype |
è |
Gene pool (proportions) |
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B. PROCESSES (Changing over time; create patterns in space and time) |
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Locomotion (movement) |
è |
Dispersal (not = dispersion) |
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Growth |
not è |
Population growth (dN/dt) |
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Reproduction |
è |
Fecundity (age-specific = bx ) |
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Survival |
è |
Survivorship (age-specific = lx ) |
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Death |
è |
Mortality (age-specific = dx ) |
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C. HISTORIES |
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Birth |
not è |
Founding |
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"Life" |
è |
"Life History" |
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Death |
not è |
Extinction |
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Demography of Age-Structured Populations |
Demography: The study of processes affecting the structure and growth of populations.
Life History Characteristics (LHC): Those properties of individuals that, when expressed in populations, affect the distribution and abundance of populations. LHC have three components:
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1. Evolutionary constraints |
Genetically fixed in species, cannot be altered |
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2. Adaptations |
Genetically determined variation among individuals, within and between populations |
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3. Ecological responses |
Phenotypic plasticity; non-genetic variation among individuals responding independently to their micro-environments |