Ecology is the study of:
• the distribution and abundance of
• the interactions among organisms
(= biotic interactions)
• the interactions between
organisms and their non-living
environments (= abiotic interactions)
Population:All individuals of a single species that live together in the same place and time.
Populations are characterized by their:
• Size, the number of individuals in the population.
• Distribution, or the limits of their geographic range.
• Density, the number of individuals per unit area (e.g. 5 mice / 10 m2)
• Dispersion, the distribution of individuals within their range.
• Age Structure, the relative numbers of individuals in different age groups.
• Generation Time, the avg. time between an organism’s own birth and the birth of
• its offspring (reproduction).
• Sex Ratio, the relative number of males vs. females
• Proportion reproducing, proportion of individuals in a population actually producing offspring.
Distribution is used interchangeably with range.
The size of a species range may relate to its rarity.
• Avery large range may suggest that a species is common and adaptable. Lecture 2
• Avery small range suggests that a species is locally endemic or specialized to particular habitats.
Density: The number of individuals per unit area.
Where larger animals have lower population density.
Dispersion: The distribution of individuals within their range
Sex Ratio & Proportion Reproducing:
Sex Ratio is the relative proportions of males vs. females in the population.
The number of females usually has a larger impact on population growth than the number of males. Only
females actually produce offspring!
The Proportion Reproducing is the actual proportion of males or females contributing to population
Age Structure & Generation Time
Age Structure: the relative numbers of individuals in age groups
Generation Time: the average time between an organism’s own birth and the birth of its offspring (its
first reproductive event).
Age Structure and Generation Tim