7. Environmental carrying capacity

P.B. Dharmasena
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https://independent.academia.edu/PunchiBandageDharmasena
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http://www.slideshare.net/DharmasenaPb
Poverty and Environment
Course code: ECON/EMGT 4214
Friday from 8.30-12.30 a.m
Lesson 7 – Environmental Carrying Capacity
P.B. Dharmasena
0777 613234, 0717 613234

Environmental carrying capacity
P.B. Dharmasena
0777 - 613234, 0717 - 613234

What is Carrying Capacity?
• Is the maximum
population a habitat can
support indefinitely
• Population exceeds it,
for long periods,
degrades its
environment and
reduces future carrying
capacity

Carrying capacity of environment
1. Generally carrying capacity reflects ability of bearing or containing
something in maximum continuously
2. Therefore, carrying capacity of an environment with regard to a
biological species is the maximum population size of the species that
the environment can sustain indefinitely, given the food,
habitat, water and other necessities available in the environment.
3. In population biology, carrying capacity is the environment's maximal
load, which is different from the concept of population equilibrium.
4. With regard to the human population, more complex variables such
as sanitation and medical care are sometimes considered as part of the
necessary establishment.
5. As population density increases, birth rate often decreases and death
rate typically increases.
6. The difference between the birth rate and the death rate is the "natural
increase".
7. The carrying capacity could support a positive natural increase, or
could require a negative natural increase.

1. Carrying capacity is the number of individuals an environment
can support without significant negative impacts to the given
organism and its environment.
2. Below carrying capacity, populations typically increase, while
above, they typically decrease.
3. A factor that keeps population size at equilibrium is known as
a regulating factor.
4. Population size decreases above carrying capacity due to a range
of factors depending on the species concerned,
5. but can include insufficient space, food supply, or sunlight.
6. The carrying capacity of an environment may vary for different
species and may change over time
7. due to a variety of factors, including:
food availability,
water supply,
environmental conditions and
living space.

1. Several estimates of the carrying capacity have been made with a
wide range of population numbers.
2. UN report (2001) said that two-thirds of the estimates fall in the
range of 4 billion to 16 billion (with unspecified standard errors),
with a median of about 10 billion.
3. More recent estimates are much lower, particularly if resource
depletion and increased consumption are considered.
4. The application of the concept of carrying capacity for the human
population has been criticized for not successfully capturing the
multi-layered processes between humans and the environment,
which have a nature of fluidity and non-equilibrium, and for
sometimes being employed in a blame-the-victim framework.
5. Supporters of the concept argue that the idea of a finite carrying
capacity is just as valid when applied to humans as when applied
to any other species.
6. Animal population size, living standards, and resource depletion
vary, but the concept of carrying capacity still applies.
7. Waste and over-consumption especially by wealthy people and
nations, is putting more strain on the environment than
overpopulation.

Carrying Capacity
Time
Populationsize
Graph line = Population
size at a specific time
Dotted line = Carrying Capacity

Carrying Capacity
• When a population is BELOW its carrying
capacity, it will INCREASE in size
• Birth rate exceeds death rates
Time
Populationsize

Carrying Capacity
• But if it increases too much and rises ABOVE
its carrying capacity, it will DECREASE in size
• Death rate exceeds birth rate
Time
Populationsize

Carrying Capacity
• This happens over and over… but the increases
and decreases get smaller and smaller…
Time
Populationsize

Carrying Capacity
• Until eventually, the population size BECOMES
STABLE AT THE CARRYING CAPACITY
• Birth rate = death rate
Time
Populationsize

Carrying Capacity
• Carrying capacity can also have a broader
meaning. It can be defined as the number of
living things (plants and animals) any area of
land or water can support at any one time.
• Different organisms will have different
carrying capacities in the same area. Thus, the
carrying capacity of an ecosystem affects
everything that lives in it.

• Population: all the individuals of a
species that live together in an area
• Demography: the statistical study of
populations, make predictions about how
a population will change
POPULATIONS
& CARRYING CAPACITY

Three Key Characteristics
of Populations
• Size, number of
individuals (N)
• Density (N/ area)
• Dispersion,
– Random, uniform,
clumped,
• (appropriate scale)

Three Key Characteristics of
Populations
• 1. Size: number of individuals in an area
– Characterized by (N)
Growth Rate:
Birth Rate (natality) - Death Rate (mortality)
(How many individuals are born vs. how many die)

Three Key Characteristics of Populations
• 2. Density: measurement of population per unit area or
unit volume
Pop. Density = # of individuals
unit of space
16
4 Factors that affect density
1. Immigration- movement of individuals into a population
2. Emigration- movement of individuals out of a population
3. Density-dependent factors- Biotic factors in the environment that have
an increasing effect as population size increases
Ex. Disease, competition, parasites
4. Density-independent factors- Abiotic factors in the environment that affect
populations regardless of their density
Ex. Temperature, storms, habitat destruction, drought

Three Key Characteristics of
Populations
02 June 2010 Populations.ppt 17
• Dispersion: describes
their spacing relative to
each other

Dynamic characteristics
of populations
• Age distribution,
– proportions of young, middle-aged, old
– Differs in growing, stable, decreasing populations

Immigration
Emigration
Natality MortalityPopulation
+
+
-
-
Factors That Affect Future Population
Growth

Changes in populations
• Growth
– Expansion of species’ populations may lead to
evolution of new species
• Decline
– Shrinking species’ populations may lead to
extinction
• Small populations
• Narrowly specialized species
02 June 2010 20Populations.ppt

Changes in populations
• ΔN = +B +I –D –E
– +B = births (birth rate)
– +I = immigrants (immigration rate)
– – D = deaths (death rate)
– – E = emigrants (emigration rate)
– (For many [most] natural populations I and E
are minimal.)

Other factors that affect population
growth
Limiting factor- any biotic or abiotic
factor that restricts the existence of
organisms in a specific environment.
–EX.- Amount of water
Amount of food
Temperature

Other factors that affect population
growth
• Carrying Capacity- the maximum population
size that can be supported by the available
resources
• There can only be as many organisms as the
environmental resources can support

Carrying Capacity
Carrying Capacity (k)
Number
Time
J-shaped curve
(exponential growth)
S-shaped curve
(logistic growth)

Logistic model
• Logistic model works, to a point.
– Real organisms have time lags for growth, time to
develop eggs, flowers, etc.
• seasonality, longevity
– Real populations may exceed carrying capacity.
• Easter Island
• Pribloff Reindeer
• Kaibab Deer

Easter Island – An Example
• Discovered by Polynesians ~ A.D. 1000
• Population grew to several thousand
– Used trees for canoes to hunt dolphins
– Used wood for cooking
– Also ate birds, eggs, vegetables
• Resources (trees) depleted
– No canoes, no dolphins
– Warfare over land, food resources
• Population fell to ~ 100 when discovered by
Dutch, Easter Sunday 1722.

2 Life History Patterns
1. “R” Strategists
short life span
small body size
reproduce quickly
have many young
little parental care
Ex: cockroaches, weeds,
bacteria

2 Life History Patterns
2. “K” Strategists
 long life span
 large body size
 reproduce slowly
 have few young
 provides parental care
 Ex: humans, elephants

Two general types of
Life History Strategies
Life History trait r-adapted,
Opportunistic
K-adapted,
Equilibrium
Offspring Many, small (high r) Fewer, large (low r)
Offspring survival Low High
Parental care Rare Common
Reproductive age Early Later
Reprod. “seasons” 1-few Many
Habitat Unstable, temporary Stable, permanent
Competitiveness Low High
Population regulation Density independent Density dependent
Population fluctuation Irruptive Stable near K

• Survivorship curves of Opportunistic and
Equilibrium species
– Opportunistic have Type III
– Equilibrium have Type I

• Fluctuating populations of two interacting populations
– Based on pelts sold by Canadian trappers to the Hudson Bay
Company, ~1840-1940.

7. Environmental carrying capacity

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