Lecture PowerPoint to accompany
Inquiry into Life
Twelfth Edition
Sylvia S. Mader
Chapter 33
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
33.1 The Scope of Ecology
• Modern ecology focuses on developing testable
hypotheses.
• One goal of ecology is to develop models that
explain and predict the abundance of
populations.
Levels of Ecological Organization
33.2 Patterns of Population Growth
• Growth Rate = Per capita rate of increase
– Example: A population has 1000 members
Birth rate = 30 / year
Death rate = 10 /year
The growth rate per year will be:
30 - 10 / 1000 = 0.02 = 2.0% per year
33.2 Patterns of Population Growth
• Biotic potential is the highest per capita rate of
increase for a population
• Factors that influence biotic potential:
–
–
–
–
Average number of offspring per reproduction
Chances of survival until age of reproduction
Age at first reproduction
How often each individual reproduces
Patterns of Population Growth
33.2 Patterns of Population Growth
• J-shaped Curve
– Lag phase: Growth is small because the population is small
– Exponential growth phase: Growth is accelerating, and the
population is exhibiting its biotic potential
• S-shaped Curve
– Lag phase: Growth is small because the population is small
– Exponential growth phase: Growth is accelerating, and the
population is exhibiting its biotic potential
– Deceleration phase: The rate of population growth slows down
– Stable equilibrium phase: Little if any growth takes place because
births and deaths are about equal.
33.2 Patterns of Population Growth
• Carrying Capacity:
The number of
individuals of a species
that a particular
environment can support
33.2 Patterns of Population Growth
• Survivorship
– Growth curves assume all individuals are identical
• In real life, individuals are in different life stages
– Cohort-group of individuals born at the same time
• Plotting the number surviving over time gives us a survivorship
curve
– Type I survivorship curve- most individuals survive until old age
• Ex: humans
– Type II- survivorship curve- decreases consistently over time
• Ex: songbirds
– Type III survivorship curve- most individuals die early
• Ex: oysters
Survivorship Curves
33.2 Patterns of Population Growth
• Human Population Growth
– Approximately 225,000 people are added to the
world’s population every day.
– Approximately 82 million people are added to the
world’s population every year.
– Current doubling time is 56 years
• (length of time it takes for population size to double)
World Population Growth
33.2 Patterns of Population Growth
• Human Population Growth
– More Developed Countries (MDC’s) versus Less Developed
Countries (LDC’s)
– MDC’s
• Population growth is low and standard of living high
• Increased rapidly between 1850 and 1950 due to decreased death
rate
• Then came a decrease in birth rate(demographic transition)
• Population growth in MDC’s has stabilized at 0.1%
• Germany, Hungary, Italy, Greece, Sweden are actually decreasing
in size
• The United States has a low yearly growth rate (0.6%), however
many people immigrate to the United States each year.
33.2 Patterns of Population Growth
• Human Population Growth
– More Developed Countries (MDC’s) versus Less Developed
Countries (LDC’s)
– LDC’s
• Population growth is expanding rapidly and standard of living is low
• Population of LDC’s could reach 11 billion by 2100
– Most of this increase in Latin America, Africa, and Asia
• Ways to decrease this expected growth are
– Establish/strengthen family planning programs
– Use social progress to reduce desire for large families
– Delay onset of childbearing
Age Structure Diagram
33.3 Regulation of Population Growth
• Two Types of Life History Patterns
– Opportunistic Pattern
• Many offspring are produced
• Short life spans
• Weeds and insects are examples
– Equilibrium Pattern
• Few offspring are produced
• Longer life spans
• Birds and mammals are examples
Life History Patterns
33.3 Regulation of Population Growth
• Abiotic and Biotic Factors
– Abiotic factors are called density-independent factors
• Weather, natural disasters
• Effects are the same for all sizes of populations
– Biotic factors are called density-dependent factors
• Competition, predation, parasitism
• Effects depend on the size of the population
33.3 Regulation of Population Growth
• Competition
– Occurs when members of two different species try to
utilize the same resource
– Competitive Exclusion Principle: no two species can
occupy the same ecological niche at the same time
• Ecological Niche: role organism plays in the community;
includes habitat, resources used, and interactions
– Resource Partitioning
• Slight differences in the way a resource is utilized
• Decreases competition
Competition Between Two Laboratory
Populations of Paramecium
Competition Between Two Species
of Barnacles
33.3 Regulation of Population Growth
• Predation
– Predator-Prey Population Dynamics
• Cycling of predator and prey populations
• Occurs when either predators overkill prey, or when prey
overuse resources and their numbers crash
– In either case, predator numbers also decrease from a
decrease in food source
Predatory-Prey Cycling of a Lynx
and a Snowshoe Hare
33.3 Regulation of Population Growth
• Predation
– Antipredator Defenses
• Coevolution is present when each of two species adapts in
response to selective pressures imposed by the others.
Antipredator Defenses
33.3 Regulation of Population Growth
• Predation
– Antipredator Defenses
– Mimicry: One species resembles another species
• Can help capture food or avoid being preyed upon
• Batesian Mimicry: A prey that is not harmful mimics another
species that has a successful antipredator defense.
– Warning colorations.
• Mullerian mimicry: Species that resemble each
other all have successful defenses.
Mimicry Among Insects
33.3 Regulation of Population Growth
• Symbiosis: Close interactions between
members of two species.
33.3 Regulation of Population Growth
• Parasitism
– Parasite derives nourishment from host
• Parasite benefits and the host is harmed
• Examples:
– Disease-causing Bacteria
– Ticks
– Leeches
33.3 Regulation of Population Growth
• Symbiosis
– Commensalism
• One species benefits,
the other is not effected
• Examples:
– Clownfish and sea
anemones
– Cattle egrets and
cows
33.3 Regulation of Population Growth
• Symbiosis
– Mutualism
• Both members of the
association benefit.
• Plants and pollinators
• Small fish and large
organism
33.3 Regulation of Population Growth
• Ecological Succession
– A change in a community’s composition that is
directional and follows a continuous pattern of
extinction and colonization by new species.
– Primary Succession (land): Establishment of a plant
community in a newly formed area where there is no
soil formation
– Secondary Succession: The return of a community to
its natural vegetation following a disturbance
• Pioneer Species: Plants that begin the process of secondary
succession
Secondary Succession in a Forest
33.3 Regulation of Population Growth
• Ecological Succession
– Models of Succession
• Climax-pattern model: particular areas will always lead to a
specific climax community
– Based on the fact that climate determines what plants survive
– Exact composition of climax community need be the same
» For example, the climax community in an area may be
deciduous forest, but the tree species may differ
• Facilitation model: each successive community prepares the
environment for the next
– Grasses are necessary before shrubs, and then shrubs before
trees
33.3 Regulation of Population Growth
• Ecological Succession
– Models of Succession
• Inhibition model: colonizing species hold on to space until
they die or are damaged
• Tolerance model: different species can colonize at the same
time
– Random chance determines which arrives first