Population & Community
Ecology
Chapter 35
35.1 A population is a local
group of organisms of one
species
I. Defining Populations
A. A populations size is determined by the
availability of food and space, weather
conditions, and breeding patterns
B. When scientists study populations they
must determine its boundaries, such a lake, a
state or the whole country
What is a species?
• Distinct form of life
• Population of organisms which
can breed and produce
offspring
What about these?
Peacock + Peahen =
Peachicks
Horse + Donkey = Mule
Boundaries
Regional
Local
II. Population Density
A. Population Density is the number
of individuals of a particular species
per unit of area or volume
B.Population density is useful when
comparing two populations in
different areas
Class Example.
III. Sampling Techniques
A. Since it is impossible to count every member
of a population scientists use sampling
techniques to estimate the size of a
population
1.
2.
3.
Quadrats- scientists mark off a square boundary at
several locations and take an average (plants)
Indirect Counting- counting nests, burrows or tracks
instead of the organisms themselves (insects)
Mark-Recapture- scientists trap and mark individuals
(birds)
B. Most sampling techniques involve making
assumptions about the populations being
studied
Which sampling technique?
Black bear:
indirect
Bats: mark-recapture
Cactus:
quadrat
Population Distribution
Which distribution pattern?
Termite Mound
Rattlesnake
Clumped
Random
35.2 Limits to population
growth
I. Exponential Growth of Populations
A. A population’s ability to grow
partly depends on the rate at which
its organisms can reproduce
B. Exponential Growth is when the
population multiplies at a constant
factor at constant time intervals i.e.
bacteria doubling every 20 minutes
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1. Compare and contrast the two growth curves.
Both curves show a period of rapid population growth, but the fur seal
population eventually levels off. The bacterial population appears to
continue growing exponentially.
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2. Which curve do you think more closely resembles the growth of most
populations in nature? Explain.
Limited growth curve; populations in nature are subject to limiting factors
that prevent long-term exponential growth.
II. Carrying Capacity
A. A population may start to grow
exponentially, but eventually one or
more environmental factors will limit its
growth
B. A limiting factor is a condition that can
restrict a population’s growth
C. The carrying capacity is the number of
organisms in a population that the
environment can maintain or “carry”
III. Factors Affecting Population
Growth
A. Density Dependent Factors is a
factor that limits a population more
as a population density increases
B. Density-Independent Factors are
factors that limit population but are
unrelated to population density
Population Growth
Temperature and
humidity
Food availability
Density- Independent
Density-dependent
IV. Population Cycling
A. A “boom” and “bust” growth cycle
is one that increases rapidly
followed by a sharp decline
B. Other growth cycles are
influenced by those of other
populations in their environments
Population Cycling
V. Survivorship Curves
A. Type I - reflect relatively low death rates early in
life and through midlife, with a sharp increase in
death rate among older-age groups (e.g., humans).
B. Type II - illustrate a fairly even mortality rate
throughout the life span of the organism (e.g.,
birds).
C. Type III - Populations with high death rates early
in life followed by a sharp decline of death rates
for the survivors are represented by Type III
survivorship curves (e.g., fish and many insect
populations).
Survivorship Curves
35.3 Predicting the impact of
human population growth
10 Largest Countries - 2009
Country
Population (Millions)
1. China
1,338
2. India
1,156
3. United States
307
4. Indonesia
240
5. Brazil
190
10 Largest Countries - 2009
Country
Population (Millions)
6. Pakistan
174
7. Bangladesh
156
8. Nigeria
149
9. Russia
140
10. Japan
127
10 Largest Countries - 2050
Country
Population (Millions)
1. India
1,614
2. China
1,417
3. United States
404
4. Pakistan
335
5. Nigeria
289
10 Largest Countries - 2050
Country
Population (Millions)
6. Indonesia
288
7. Bangladesh
222
8. Brazil
219
9. Ethiopia
174
10. Rep. of Congo
148
History of Human Population
History of Human Population
Human Pop Graph
6.7
Billion
in
2009
9.3
Billion
in
2050
I. History of Global Population
Growth
A. For most of human history, the human
population has grown very slowly or not at
all
B. Human population growth depends on birth
rates and death rates
C. The introduction of farming has provided a
stable food supply so birth rates have gone
up
D. Advances in modern medicine, nutrition and
sanitation have caused death rates to go
down
E. These factors have caused the human
population to increase dramatically
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1. Which age group forms the largest bulge in the age-structure graph of
the United States? Of Kenya?
40–44; under 5
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2. Which country is likely to undergo the greatest increase in population in
the next 20 years? Explain.
Kenya; the majority of the population is under 25 years old, which is the
portion likely to have children in the next 20 years.
II. Predicting Future Population
Growth
A. The Age Structure of a population is the
proportion of people in different age groups
B. Prediction of future growth varies because of
the difficulty predicting future birth and death
rates of various countries
C. The question remains whether or not Earth
will have the capacity for the human
population
35.4 Species interact in
biological communities
I. Competition Between Species
A. Members of a population may compete for the
same limited resource
B. Within a community, interspecific competition
takes place when two or more species rely on
the same limited resource
C. If two species are so similar in their requirements
that the same resource limits both species’
growth it is called competitive exclusion
D. A niche includes an organisms living place, its
food source, the time of day it is most active
and many other factors that are specific to that
organism’s way of life
Competitive Exclusion
II. Predation
A. Predation is when one organism eats another
B. Eating and avoiding being eaten are important to
survival and predators and prey have
developed many adaptations
1. Predator adaptations include: being fast and
agile, coloring that camouflages, hunting in
groups, acute sense to find prey and having
claws, teeth, fangs and stingers to help catch
prey
2. Prey adaptations include: retreating or fleeing
from predators, camouflage, defensive
coloring, mimicry, secreting poisonous
chemicals, having spines and thorns
PredatorPrey
Relations
III. Symbiotic relationships
A. A symbiotic relationship is when two species live
in or on one another
B. There are three main types of symbiotic
relationships
1. Parasitism- A parasite gets it’s food at the
expense of another organism, i.e. mosquitos
and humans
2. Mutualsim- Both organism benefit from the
relationship, i.e. E.Coli and humans
3. Commensalism- One organism benefits and the
other is neither hurt nor helped, i.e. sharks and
remoras
Symbiosis
Parasitism
Win
+
Lose
-
Mutualism
Win
+
Win
+
Commensalism
Win
+
Tie
0
Symbiosis - Which is it?
Parasitism
Predator-Prey
Liver Fluke
Mongoose &
Cobra
Symbiosis - Which is it?
Commensalism
Mutualism
Clownfish &
Anemone
Air Plant
35.5 Disturbances in communities
I. Disturbances to Communities
A. Natural Disturbances are events such
as fires, volcanic eruptions, floods,
storms, and droughts all destroy
resources such as shelter and water
B. Disturbances can be either positive or
negative
C. Humans also have an impact on
communities which can be either
positive or negative
Surviving Environmental
Change
II. Ecological Succession
A. The series of changes in the species in a
community, often following a disturbance is
known as ecological succession
B. There are two types of succession:
1. Primary succession which is when new
community arises from a previously lifeless area
i.e. plants growing on a volcanic island
2. Secondary succession is when a new community
arises from a previous community i.e. a forested
are which has been cleared and abandoned
Primary Succession
Secondary Succession
III. Human activities and
species diversity
A. 60% of the Earth’s land is used by humans,
mainly for cropland or rangeland
B. Humans usually have a negative effect on
species in two ways
1. Clearing the Land- Humans clear vast amounts
of land to make way for farming and building
2. Introduced Species are species that are moved
from one location to another either accidentally
or on purpose. These new species may take
over an area and prey on native species or drive
them from their niches
Invasive species in Ohio
Emerald
ash borer
Canada
thistle
Dutch Elm
disease
Zebra
mussel