Population Ecologyand Ecosystems
Concepts and Applications: Chapters 40 & 43
Basic Concepts: Chapters 27 & 30
http://darwin.bio.uci.edu/~sustain/bio65/lec16/b65lec16.htm
Ecology
• Certain ecological principles govern the growth and sustainability of all populations
• Human populations are no exception
Ecology: The study of how organisms interact with one another and with their environment
PopulationEcology
Human Population Problems
• Over 6 billion people alive
• About 2 billion live in poverty
• Most resources are consumed by the
relatively few people in developed countries
PopulationEcology
Population
• A group of individuals of the same species
occupying a given area
• Can be described by demographics
– Vital statistics such as size, density,
distribution, and age structure
PopulationEcology
Population Age Structure
• Divide population into age categories
• Population’s reproductive base includes
members of the reproductive and pre-
reproductive age categories
PopulationEcology
Density & Distribution
• Number of individuals in some specified area of habitat
• Crude density information is more useful if combined with distribution data
PopulationEcology
Fig 40.2
Determining Population Size
• Direct counts are most accurate but seldom feasible
• Can sample an area, then extrapolate
• Capture-recapture method is used for mobile species
Mark and Recapture
# marked Captured = Number releasedTotal Captured Total Pop
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Assumptions in Capture-Recapture
• Marking has no effect on mortality
• Marking has no effect on likelihood to being captured
• There is no immigration or emigration between sampling times
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Changes in Population Size
• Immigration adds individuals
• Emigration subtracts individuals
• Births add individuals
• Deaths subtract individuals
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Zero Population Growth- ZPG
• Interval in which number of births is balanced by
number of deaths
• Assume no change as a result of migration
• Population size remains stable
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Per Capita Rates
• Rates per individual
• Total number of events in a time interval divided by the number of individuals
• Per capita birth rate per month =
Number of births per month
Population size
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Exponential Growth
• Population size expands by ever increasing increments during successive intervals
• The larger the population gets, the more individuals there are to reproduce
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Fig 40.4
r
• Net reproduction per individual per unit time
• Variable combines per capita birth and death rates (assuming both constant)
• Can be used to calculate rate of growth of a population
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Exponential Growth Equation
G = rN
• G is population growth per unit time• r is net reproduction per individual per unit
time• N is population size
PopulationEcology
Biotic Potential
• Maximum rate of increase per individual
under ideal conditions
• Varies between species
• In nature, biotic potential is rarely reached
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Limiting Factors
• Any essential resource
that is in short supply
• All limiting factors acting
on a population dictate
sustainable population
size
Space
Food
Shelter
Temperature
Mates
Pollution
Disease
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Carrying Capacity (K)
• Maximum number of individuals that can be
sustained in a particular habitat
• Logistic growth occurs when population size
is limited by carrying capacity
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Logistic Growth Equation
G = rmax N (K-N/K)
• G = population growth per unit time
• rmax = maximum population growth rate per
unit time
• N = number of individuals
• K = carrying capacity
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Logistic Growth
• As size of the population increases, rate of reproduction decreases
• When the population reaches carrying capacity, population growth ceases
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Overshooting Capacity
• Population may temporarily increase above carrying capacity
• Overshoot is usually followed by a crash; dramatic increase in deaths
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Fig 40.7
Resetting the Carrying Capacity
• Major changes in environment can change the carrying capacity of a local system
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Fig 40.6
Density-Dependent Controls
• Logistic growth equation deals with density-dependent controls
• Limiting factors become more intense as population size increases
• Disease, competition, parasites, toxic effects of waste products
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Density-Independent Controls
• Factors unaffected by population density
• Natural disasters or climate changes affect
large and small populations alike
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Life History Patterns
• Patterns of timing of reproduction
and survivorship
• Vary among species
• Summarized in survivorship curves
and life tables
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Life Table
• Tracks age-specific patterns
• Population is divided into age categories
• Birth rates and mortality risks are calculated
for each age category
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Survivorship Curves
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Fig 40.8
Human Population Growth
• Population now exceeds 6 billion
• Rates of increase vary among countries
• Average annual increase is 1.26 percent
• Population continues to increase exponentially
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Fig. 40.9, p. 695
Human Population GrowthPopulationEcology
How Humans have Side-Stepped density dependent controls
• Expanded into new habitats
• Agriculture increased carrying capacity; use
of fossil fuels aided increase
• Hygiene and medicine lessened effects of
density-dependent controls
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Future Growth• Exponential growth cannot
continue forever
• Breakthroughs in technology may further increase carrying capacity
• Eventually, density-dependent factors will slow growth
Population Momentum
• Lowering fertility rates cannot immediately slow population growth rate. Why?
• If every couple had just two children, population would still keep growing for another 60 years
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Resource Consumption
• United States has 4.7 percent of the world’s population
• Americans have a disproportionately large effect on the world’s resources
• Per capita, Americans consume more resources and create more pollution than citizens of less developed nations
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Effects of Economic Development
• Total fertility rates (TFRs) are highest in developing countries, lowest in developed countries
• When individuals are economically secure, they are under less pressure to have large families
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Slowing Growth in China
• World’s most extensive family planning program
• Government rewards small family size, penalizes larger families, provides free birth control, abortion, sterilization
• Since 1972, TFR down to 1.8 from 5.7
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Community Ecology
• Community: Populations of all species in a habitat.
• Niche: Sum total of all a species activities and relationships as species do what they do.– Fundamental, Realized
Community Ecology
Types of Interactions
• Neutral• Commensalism• Mutualism• Competition• Predation• Parasitism
Who benefits?Spp 1 Spp 2
0 0Y 0Y YN NY NY N
Community Ecology
Competition
• Competitive Exclusion– Paramecium
• Resource Partitioning– Fruit eating birds,
Barnacles
Community Ecology
Predator-Prey Interactions
• The Classic Lynx / Hare system
Community Ecology
Ecosystems
• Energy is transferred from the SUN to all organisms
• Primary Producers• Consumers• Decomposers
• Energy is LOST with each transition
Ecosystems
Food Webs• A composite picture
of an ecosystem’s membership and their interaction
Ecosystems
Fig. 43.6, p. 740
Do not post photos on Internet
Food Webs can be Disrupted
• Natural Disasters
• External inputs– Pesticides, Pollution
Ecosystems
Ecosystems
Fig. 43.14, p. 746
The Hydrologic Cycle
Other Cycles
• Carbon• Nitrogen• Phosphorus
Ecosystems
Quiz