Population ecology is the study of populations in relation to their environment. It examines factors like population size, density, dispersion patterns, demographics, survivorship curves, and population growth. Population size is influenced by birth rate, death rate, immigration, and emigration. Population density is measured as the number of individuals per unit area. A population's dispersion can be random, uniform, or clumped. Demographic factors include age structure, sex ratio, and life tables. Survivorship curves illustrate survival rates at different ages. Population growth can be exponential or logistic depending on environmental limits.

2.  Population ecology is the study of
populations in relation to the environment. It
includes environmental influences on
population density and distribution, age
structure, and variations in population size.

3.  Population size
 Population density
 Dispersion
patterns
 Demographics
 Survivorship curves
 Population growth

4.  “In population genetics and population
ecology, population size (usually denoted N)
is the number of individual organisms in a
population”.
 Factors that Govern Population
Size
1. Crude Birth Rate (CBR)
2. Crude Death Rate (CDR)
3. Immigration
4. Emigration

5. Natality
 The birthrate, which is the ratio of total live
births to total population in a particular area
over a specified period of time
Mortality
 The death rate, which is also the ratio of the
total number of deaths to the total population.
Immigration
 The number of organisms moving into area
occupied by the population is called
immigration.
Emigration
 The number of organisms moving out of the area
occupied by the population is called emigration.

6.  Factors that increase population size
1. Natality is recruitment to a population
through reproduction.
2. Immigration from external populations e.g.
Bird migration.
 Factor reducing population size
1. Mortality which is the death rate from any
source e.g. predation.
2. Emigration, where individuals leave the
population for another habitat.

8.  Population Change = (births +
immigration) – (deaths + emigration)
Parameters that effect size or density of a
population

9.  “Population density is a measurement of
the number of people in an area. It is an
average number”.
 It is usually shown as the number of
people per square kilometer.
Density = Population/ Area

11. 1. How to quantify nature – ecologist
role
2. Estimates are allows for
comparisons between different
populations in terms of space and
time measure.

12. Mobility
Based on movements of these
organisms
2 attributes
Size
Small animals/plants are usually
more abundant than large
animals/plants

13.  Density is measured by two methods.
1. Total count method
2. Sampling method

14.  Direct counting of populations.
 Possible for few animals.
 Breeding colonies can be photographed then
later counted.
Examples
 Human pop census
 Trees in a given area

15.  Depends on the type of organism and its
natural abundance and distribution.
 Two broad categories:
1. Plot-based (quadrant) methods
2. Capture-based methods

16.  Widely used in plant
studies
 Total population =
Average number per
quadrat × Total area/Area
of quadrat

17.  Used for very
mobile or elusive
species
 First
used in the
1890s by C. G.
Peterson to
estimate fish
abundance.

18.  The dispersion of a population is the pattern of
spacing among individuals within the
geographic boundaries.
random
clumped 3 types uniform

19.  Clumped is a pattern when individuals are
aggregated in patches.
 Most frequent pattern of distribution in a
population
Reasons:
 Some area of habitat are more suitable than
others
 Heterogeneous environment with resources
concentrated in patches
 Tendency of offspring to remain with parents
 Mating or social behavior of the individuals

21.  Evenly spaced distributions, in which
members of the population maintain a
minimum distance from one another.
 In plants due to competition for water,
sunlight, or available nutrients
Example
Creosote bushes in the Mojave desert
 In animals due to strong territoriality
Example
The desert lizard Uta sp

23.  It is a spacing pattern based on total
unpredictability.
 Least common pattern of distribution
Reasons
 Members of a species do not frequently
interact with one another
 Not heavily influenced by the
microenvironments within their habitat

25. Density Independent Density Dependant
 Floods  Competition for
 Hurricanes Resources
 Unseasonable  Predation
Weather  Parasitism
 Fire  Infectious Disease
 Clear Cutting
 Pesticide Spraying

26.  Demography is the study of the vital
statistics of a population and how they
change over time
 Twostatistics that are of particular import
are a population's age structure and a
population's sex ratio.

27.  Itis the ratio of males to females in a
population.
 Primary sex ratio
 Secondary sex ratio
 Tertiary sex ratio
 The human sex ratio is of particular interest
to anthropologists and demographers.

28.  The age structure describes the number of
individuals in each age class as a ratio of one
class to another.
 Age classes can be specific categories, such
as people in the same age range.

29.  Age structure diagram
 Graphical illustration that shows the
distribution of various age groups & sex ratio
in a population.
 Three age categories:
1. Prereproductive (ages 0-14)
2. Reproductive (ages 15-44)
3. Postreproductive (ages 45 and up)

31. A life table (mortality table ) is a table which
shows, for each age, what the probability is
that a person of that age will die before his or
her next birthday.
 From this starting point, a number of
inferences can be derived.
1. The probability of surviving any particular
year of age
2. Remaining life expectancy for people at
different ages
 Separately for men and for women because of
their substantially different mortality rates.

33.  Graph showing the number or proportion of
individuals surviving at each age for a given
species or group (e.g. males/females).
 Constructed for a given cohort (a group of
individuals of roughly the same age) based on
a life table.
 Three types
1. Type I
2. Type II
3. Type III

35.  Type I survivorship curves are characterized
by high survival in early and middle life,
followed a rapid decline in survivorship in
later life.
Example: Humans
 Type II curves are an intermediate between
Type I and III, where roughly constant
mortality rate is experienced regardless of
age.
Example: Some birds
 In Type III curves, the greatest mortality is
experienced early on in life, with relatively
low rates of death for those surviving this
bottleneck.
Example: Octopus

36.  Refers
to how the number of individuals in a
population increases (or decreases) with
time.
 Controlled by the rate at which new
individuals are added to the population -- the
birth rate, and the rate at which individuals
leave the population -- the death rate.

37. Exponential
population growth
dN = rmaxN
dt
2 types of pop growth
Logistic population
Population Growth growth
Mathematically
Defined dN = rmaxN (K-N)
dt K

38. N=K/2

39.  If a population has a constant birth rate
through time and is never limited by food or
disease, it has what is known as exponential
growth.
 With exponential growth the birth rate alone
controls how fast (or slow) the population
grows.

40.  Continuouspopulation growth in an unlimited
environment can be modeled exponentially.
dN / dt = rmax N
 As population size (N) increases, rate of
population increase (dN/dt) gets larger.

41.  For an exponentially growing population, size at
any time can be calculated as:
Nt = Noert
 Nt = number individuals at time t.
 N0 = initial number of individuals.
 e = base of natural logarithms.
 r (rmax ) = per capita rate of increase.
 t = number of time intervals.

44.  As resources are depleted, population growth
rate slows and eventually stops: logistic
population growth.
 Sigmoid (S-shaped) curve
 Carryingcapacity (K) is the number of individuals
of a population the environment can support.
 Finite amount of resources can only support a
finite number of individuals.

45. dN/dt = rmaxN(1-N/K)
 rmax= Maximum per capita rate of increase under
ideal conditions.
 When N nears K, the right side of the equation
nears zero.
 As population size increases, logistic growth rate
becomes a small fraction of growth rate.
 Highest when N=K/2

47. Carrying capacity Environmental limits
result in logistic
growth
No limits
New or changed
environment
Logistic growth curve

49.  Environment limits population growth by
altering birth and death rates.
 Density-dependent factors
 Disease, Parasites, Resource Competition
 Populations do not show continuous geometric increase
 When density increases other organisms reduces the fertility
and longevity of the individuals in the population
 This reduces the rate of increase of the pop until eventually the
pop ceases to grow
 The growth curve is defined as the sigmoid curve, S – shaped
 K = carrying capacity (upper asymptote or maximum value) – the
maximum number of individuals that environment can support
 Density-independent factors
 Natural disasters
 Climate

50. K and r selection (MacArthur and Wilson 1967)
r-selected species
•r refers to the per capita rate of
increase
•Selection favoring rapid growth
•Should be favored in new or disturbed
environments
•Less competition
K-selected species
•K refers to carrying capacity
•More prominent in species that are
typically at their carrying capacity
•Favors more efficient use of resources
•Live with competition

53.  The history of human population growth
Figure 35.8A