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Outline• 44.1 Scope of Ecology• 44.2 Demographics of Populations• 44.3 Population Growth Models• 44.4 Regulation of Population Size• 44.5 Life History Patterns• 44.6 Human Population Growth
44.1 Scope of Ecology
• Ecology The study of the interactions of organisms with
• Other organisms and the physical environment Habitat - Place where an organism lives Population - All the individuals of a species within a
particular space Community – Various populations of multiple species
interacting with each other Ecosystem - Community interacting with the
environment Biosphere - All the communities on Earth whose
• Composed of all the members of a population born at the same time
– Life tables demonstrate how many members of a cohort are still alive after certain intervals of time
Survivorship• The probability that newborn individuals of a cohort
will survive to a particular age
• Survivorship Curves– A plot of the number of organisms surviving at each age
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A Life Table for a Bluegrass Cohort
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Demographics of Populations
• Survivorship Curves Type I
• Characteristic of a population in which most individuals survive past the midpoint of the life span and death does not come until the end of the life span
Type II• Death is linear over time (unrelated to age)
Type III• Typical of a population in which most individuals die very
• Carrying Capacity The maximum number of individuals of a
species the environment can continuously support
• The closer the population to the carrying capacity, the more likely its resources will become scarce and that biotic effects such as competition and predation will become apparent
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44.4 Regulation of Population Size
• Density-independent Factors The population density does not influence
the intensity of the factor’s effect• Natural disasters
• Density-dependent Factors The percentage of the population affected
increases as the population density increases• Competition• Predation• Parasitism
• Life histories contain characteristics of a population such as The number of births per reproduction The age of reproduction The life span The probability of an individual living the entire life span
• Each population distributes energy among its life span, reproduction events, and care of offspring.
• Related species may have different life history patterns.
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Parental Care Among Frogs and Toads
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a. Mouth-brooding frog,Rhinoderma darwinii
b. Strawberry poison arrow frog,Dendrobates pumilio
• r is the rate of natural increase of a population.
• K is the carrying capacity of the environment.
• Some populations are subject to r-selection, and other populations are subject to K-selection.
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Life History Patterns
• r - Selection In unstable or predictable environments, population
growth is controlled by density-independent factors. Population size is low relative to K.
• r - Strategists (opportunistic species) Produce large numbers of offspring Have a small body size Mature early Have a short life span Do not invest energy in parental care Tend to be good dispersers and colonizers
Life History Patterns
• K - Selection In stable, predictable environments, population size is
controlled by density-dependent factors. Population size tends to be near K.
• K - Strategists (equilibrium species) Produce small numbers of offspring Have a large body size Mature late Have a long life span Invest energy in parental care Tend to be strong competitors
• More-Developed Countries (MDCs) North America, Europe, Japan, and Australia
Slow population growth
High standard of living
A demographic transition (decreased death rate followed by decreased birth rate) has occurred, so population growth has stabilized.
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Human Population Growth
• Less-Developed Countries (LDCs) Latin America, Africa, and Asia Rapid population growth Low standard of living Strategies to reduce population growth
• Family planning programs
• Social progress, which may reduce the desire for large families