This document defines key concepts in population ecology, including population, population ecology, population size, density, dispersion, structure, growth, pyramids, demography, and survivorship curves. It explains that population ecology studies how biotic and abiotic factors influence population density, dispersion, and size. It also describes different population structures, growth patterns, survivorship curves that reflect varying reproductive strategies and death rates at different ages among species.

1. • Population
• A group of individuals that belong in the same species and live in the
same area; for example, the stray cats of New York City
• Population ecology
• The ecological study of how biotic (living) and abiotic (non-living) factors
influence the density, dispersion, and size of a population
• Population ecology is the branch of ecology that studies the structure and
dynamics of populations.

2. • For example, why do some organisms die
immediately after reproducing (some salmon and
bamboos, many insects, and all grain crops).
• While others live on to reproduce repeatedly
(most plants and vertebrates)?
• The study of population ecology includes
understanding, explaining, and predicting species
distributions.

3. Characteristics of Population Ecology
• Population Size
• Population size represents the total number of individuals in a
habitat.
• Population Density
• Population density refers to how many individuals reside in a
particular area
• Population Dispersion
• Population distribution describes how individuals of a species are
spread out, whether they live in close proximity to each other or far
apart, or clustered into groups.

4. Population Structure
• Population structure means the 'make up' or composition of
a population.
• Looking at the population structure of a place shows how
the population is divided up between males and females of
different age groups.
• The factors of population structure are:
• Population growth
• Population Pyramids

5. Demography
• Demography is the study of human populations – their size,
composition and distribution across space – and the process
through which populations change.
• Births, deaths and migration are the ‘big three’ of demography,
jointly producing population stability or change.
Plant Demography
Plant demography is the study of population size (abundance) and
its underlying parameters.
It describes the state of a particular population of a species and
how this state changes through time.

6. Population growth
• Population growth is the change in the size of the population over
time.
• An important factor in population growth is age-sex structure.
• This is the number of individuals of each sex and age in the
population.
• The age-sex structure influences population growth.
• This is because younger people are more likely to reproduce, while
older people have higher rates of dying.

7. Population Pyramids
• Age-sex structure is
represented by a population
pyramid.
• This is a bar graph, like the
one Figure below.
• In this example, the bars
become narrower from
younger to older ages.
• Can you explain why?

8. Survivorship Curves
• Another way to show how
deaths affect populations is
with survivorship curves.
• These are graphs that represent
the number of individuals still
alive at each age.
• Examples are shown
inFigure below.
Survivorship curves
reflect death rates at
different ages.

9. • The three types of curves shown in the figure actually represent different
strategies species use to adapt to their environment:
• Type I: Parents produce relatively few offspring and provide them with a
lot of care. As a result, most of the offspring survive to adulthood so they
can reproduce. This pattern is typical of large animals, including humans.
• Type II: Parents produce moderate numbers of offspring and provide
some parental care. Deaths occur more uniformly throughout life. This
pattern occurs in some birds and many asexual species.
• Type III: Parents produce many offspring but provide them with little or
no care. As a result, relatively few offspring survive to adulthood. This
pattern is typical of plants, invertebrates, and many species of fish.