Title: Population Ecology
1Population Ecology
- Population ecology is the study of populations in
relation to environment - Including environmental influences on population
density and distribution, age structure, and
variations in population size
2- Levels of Organization
- Organism
- Population
- Community
- Ecosystem
- Biome
3 4Describing populations
- Size total of individuals in a pop (N)
- Density / unit area
5Estimation of Population Size
Describing populations
- Sampling technique
- Mark and recapture
6Mark and Recapture
Describing populations
- Orgs are captured, tagged, and then released.
- Some time later, the same process is repeated and
the following is used
7Describing populations
- Ex
- Suppose that 50 zebra mussels are captured,
marked, and released. One week later, 100 zebra
mussels are captured and 10 are found to have
markings already. The estimated population would
then be - N (50100) / (10) 5000/10 500
- N500
8Dispersion
Describing populations
- Describes how individuals in a population are
distributed - Clumped
- Uniform
- Random
9- Clumped dispersion (most common)
- Individuals aggregate in patches
- May be influenced by resource availability
behavior
Describing populations
Fish travel in schools safety in numbers
10- Uniform dispersion
- -Individuals are evenly distributed
- -May be influenced by social interactions such as
territoriality
Describing populations
Some plants secrete toxins that keep others away
11- Random dispersion
- The position of each individual is independent of
other individuals
Describing populations
Dandelions grow from windblown seeds that land at
random and later germinate.
12Describing populations
Changes in Population Size
- Biotic potential of a population
- max rate at which a population could increase
under ideal conditions - Influenced by several factors
- Age at which reproduction begins
- Life span during which the organisms are capable
of reproducing - Number of reproductive periods in the lifetime
- Number of offspring the organism is capable of
having
13Age Structure
Describing populations
- Description of the abundance of individuals of
each age in a population.
14Age Structure Diagrams
Describing populations
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162004
China
India
United States
17Zero population growth
18Describing populations
1954
Animation
19Describing populations
20Survivorship Curves
Describing populations
- Describes how the mortality of individuals in a
species varies during their lifetime
- The survivorship curve for Beldings ground
squirrels - Shows that the death rate is relatively constant
21- Survivorship curves can be classified into three
general types Type I, Type II, and Type III
- Type I
- A species in which most survive to middle age
- Parenting
- Type II
- Length of survivorship is random. Death rate is
constant.
22- Type III
- Most individuals die young.
- Few reach reproductive maturity.
- Fish release 1000s of eggs.
- No parenting
Animation
23- Factors Affecting Population
24Limiting Factors
Factors Affecting Population
- Things that prevent a population from attaining
its biotic potential - 2 categories
- Density-dependent
- Density-independent
Density Dependent
Density Independent
25Density Dependent
Factors Affecting Population
- Populations regulated by density-dependent
factors are affected by the number of organisms
present. - Predation
- Parasitism
- Disease
- Competition
- -the more organisms crowd together, the more
damaging are food shortages, parasites, and
predators.
Intraspecific Competition the struggle between
members of a population for scarce resources
26Density Independent
Factors Affecting Population
- The number of organisms present does not affect
the influence of the factor. - Fire, earthquakes, storms, floods
- Density-independent factors show no correlation
with the size of the population.
27Describing Population Growth
Population ecologists describe two general
patterns of populations growth
- Exponential
- Logistic
28 - The growth of a population can be described by
the following equation - r reproductive rate (or growth rate)
- N population size at the beginning of the
interval for which the births and deaths are
counted. - r
- .
Types of Population Growth
Net increase of individuals
births-deaths N
Can r be negative? Zero?
29r
Types of Population Growth
births-deaths N
- Ex
- A population of 1000 had 60 births and 10 deaths
over a one year period. What is the growth rate? - 0.05 per year
30Exponential growth
rgt0
Types of Population Growth
In a population showing exponential growth the
individuals are not limited by food, disease,
predation or competition.
If the rate of reproduction per individual
remains constant through
time, then the
rate at which
the population
increases is a
multiple of the
number of
individuals in
the population.
31- Exponential population growth
- Results in a J-shaped curve
- Usually short lived in nature- not sustainable
rgt0
Types of Population Growth
Population size (N)
32 Carrying Capacity (K)
the real world
Types of Population Growth
- Populations usually reach a carrying capacity.
- Upper limit to the number of individuals the
environment can support.
33Logistic growth
Types of Population Growth
In most real populations both food and disease
become important as conditions become crowded.
- A population can grow exponentially only for
short periods of time, because it would very
quickly deplete all the resources necessary for
its survival. - Over long periods of time, populations tend to
attain an equilibrium population size which is
determined by the available resources.
Animation
34Types of Population Growth
- Zero population growth
- Occurs when the birth rate equals the death rate
- The population growth equation can be expressed as
35Life-history strategies
- Logistic and exponential growth are associated
with 2 kinds of life-history strategies - R-selected species (strategists)
- organisms are opportunistic they reproduce
rapidly when the environment is uncrowned and
resources are vast - K-selected species (strategists)
- operate at a density near K
36R-selected species
Life-history strategies
- a. Opportunistic species, which tend to be
colonizers. - b. Grasses, many insects
- -Usually quickly invade, reproduce many
offspring and die - -Offspring mature quickly and require very
little parental care - c. Strategies for continued existence is based
on individuals having the following traits
1) small size
2) short life span 3) mature
fast 4) produce many offspring
5) engage in little care of
offspring
37K-selected species
Life-history strategies
- sensitive to population density
Such populations are equilibrium species, tend to
be specialists rather than colonizers, and may
become extinct when their evolved way of life is
disrupted (e.g., the grizzly bear, Florida
panther, etc.). Overall strategy for continued
existence is based on having the following
traits 1) large size
2) long life span
3) slow to mature
4) produce few offspring
5) expend considerable energy in
care
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39Human Population Growth
- The following made exponential growth possible
- Increases food supply
- Reduction in disease
- Reduction in human waste
- Expansion of habitat
As of 28 April 2010, the human population of the
world is estimated by the United States Census
Bureau to be 6,817,500,000.
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41Countries Ranked by Population
2010 Source U.S. Census Bureau,
International Data Base.
6,817,500,000
42Map of countries by population for the year 2007
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