This document discusses several key concepts relating to populations: 1) Populations are groups of the same species that live in the same area. Factors like temperature, water, food, and habitat affect how populations are distributed. 2) Population dynamics involve birth rates (natality), death rates (mortality), immigration, and emigration. A population's change over time depends on births and newcomers minus deaths and those who leave. 3) Population growth follows a sigmoid curve with exponential, transitional, and plateau phases driven by factors like available resources, predation, and disease. Carrying capacity limits population size when births and deaths balance out.

1. Populations

2. Population
• Group of individuals of the same
species occupying a common
geographical area (a species is an
interbreeding group of organisms
that produces fertile offspring).
– Same species, same place, same
time!

3. Factors affecting Population
• G.1.1 Outline the factors that affect
the distribution of plant species,
including temperature, water, light,
soil pH, salinity and mineral
nutrients.
• G.1.2 Explain the factors that affect
the distribution of animal species,
including temperature, water,
breeding sites, food supply and
territory.

4. Population Dynamics
• Natality – offspring are produced and
added to the population (birth)
• Mortality – individuals die and are
lost from the population (death)
• Immigration – individuals move into
the area from somewhere else and
add to the population
• Emigration – individuals move out of
the area and are lost from the
population

5. Population Dynamics
∀∆ = N + I – M – E
• In closed populations: ∆ = N – M
• In English: Change = Births +
Newcomers – Deaths – Exiters

6. Populations
5.3.2: Draw a graph
showing the sigmoid
(S-shaped) population
growth curve.
5.3.3: Explain reasons
for the exponential
growth phase, the
plateau phase and the
transitional phase
between these two
phases.

7. Exponential Phase
• Population increases exponentially
because the natality rate is higher
than the mortality rate.
• This is because there is an
abundance of food, and disease and
predators are rare.

8. Transitional Phase
• Difference between natality and
mortality rates are not as great, but
natality is still higher so population
continues to grow, but at a slower
rate.
• Food is no longer as abundant due to
the increase in the population size.
May also be increase predation and
disease.

9. Plateau Phase
• Natality and mortality are equal so
the population size stays constant.
• Limiting Factors (5.3.4):
– shortage of food or other resources
– increase in predators
– more diseases or parasites
• If a population is limited, then it has
reached its carrying capacity

11. Other Population Curves
Growth curve for
bacteria
bacteria
#
time
• Boom and bust

12. Factors Limiting the Growth of Natural
Populations
• All populations have a limit for exponential
growth  biotic potential (intrinsic rate of
increase), r, under perfect conditions
• Dependent on - # offspring/birth, capacity for
survival, procreation rate, maturity
• Since population is mainly affected by B-D, the
factors that limit growth either  birth rate or 
death rate
• Abiotic factors – blizzards, hurricanes, floods
(weather) – density independent regulation
(death rate is independent of the population)
• Biotic factors – predators, competitors, parasites
– density dependent regulation (the proportion of
individuals that die will depend on the size of the
population – the birth rate and death rate are
affected by the size of the population)

13. Survivorship Patterns (r-
and K-)
• r- (small
letter, small
creatures)
• K- (large
letter, large
creatures)

14. r- selected
• r-selected populations (small letter – small creatures)
• variable, unpredictable climate  ability to adapt
• density independent factors  mortality
• lots of offspring
• high juvenile mortality
• population below carrying capacity
• low level of competition
• early development, reproduction, small body size, high
reproductive capacity, reproduce only one, many offspring
• short life-span (less than one year)
• little/no parental care

15. K- selected
• K-selected populations (capital letter – large creatures)
• offspring’s survival depends on ability to obtain limited
resources – produce a few highly competitive offspring
(many young die if climate changes drastically)
• fairly constant/predictable offspring
• density-dependent mortality
• low juvenile mortality
• fairly constant population – at/near carrying capacity
• high levels of competition
• slow development, greater competitive ability, large body
size, delayed & repeated reproduction, fewer, larger
offspring
• life-span longer