Transcript Understanding Populations Section 1

Understanding Populations
Section 1
Objectives
• Describe the three main properties of a population.
• Describe exponential population growth.
• Describe how the reproductive behavior of individuals
can affect the growth rate of their population.
• Explain how population sizes in nature are regulated.
Understanding Populations
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What Is a Population?
• a group of same species organisms that live in a specific
area and interbreed
• population came mean
– the group
– the size [of the population]
– number of individuals
Understanding Populations
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Properties
• Density: number of individuals of a species in a given
area.
• Dispersion: pattern of distribution of organisms
– even, clumped, or random.
Understanding Populations
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How Does a Population Grow?
• Growth rate represented by the equation:
• Computed for a specific period of time
• Changes because birth & death rates increase/ decrease.
• Can be positive, negative, or zero
Understanding Populations
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• Zero: average births = average deaths
– each pair of adults have two offspring who survived to
reproduce
• Negative: adults not replaced by new births, population
shrinks
Understanding Populations
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How Fast Can a Population Grow?
• In most cases barely change year to year
• Factors controlling growth
– Biotic potential: fastest rate of population growth
– Reproductive potential: maximum number of
offspring organism can produce
Understanding Populations
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Reproductive Potential
• increases
– produce more offspring at a time
– reproduce more often
– reproduce earlier in life
• has the greatest effect on reproductive potential
• Small organisms-high potentials
• Large organisms-low potentials
Understanding Populations
Exponential Growth
• logarithmic growth
• populations must have
plenty of food & space, no
competition or predators
– Ex: bacteria or molds
grow on a new source of
food
• large number s added each
succeeding time period
Section 1
Understanding Populations
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What Limits Population Growth?
• Natural conditions limit growth
– resources used up
– environment changes
– deaths increase or births decrease
• Natural selection only allows some members to survive
and reproduce
– properties of a population can change over time
Understanding Populations
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Carrying Capacity
• largest population an environment can support at any
given time.
• may increase beyond this number, can’t stay there
• estimated by:
– looking at average population sizes
– observing a population crash after a certain size has
been exceeded
Understanding Populations
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Understanding Populations
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Resource Limits
• Population at carrying capacity when a particular natural
resource consumed at rate produced
• Resource is limiting
– supply of the most severely limited resources
determines the carrying capacity
Understanding Populations
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Competition Within a Population
• Members use the same resources in the same ways, so
they will eventually compete as population approaches
its carrying capacity
• may compete for social dominance or for a territory
– Indirect resource competition: space , shelter, food, or
breeding sites
Understanding Populations
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Two Types of Population Regulation
• Density dependent
– deaths occur more quickly in a crowded population
than in a sparse population
– limited resources, predation and disease result in
higher rates of death in dense populations
Understanding Populations
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• Density independent
– a certain proportion of population dies regardless of
the population’s density
– affects all populations same way
– typical causes: severe weather, natural disasters