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Lecture 25

01:119:115 Lecture Notes - Lecture 25: Lymph Node, Competitive Exclusion Principle, Ecological Footprint

4 pages67 viewsFall 2013

Biological Science
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Continuation of Lecture 24 (Chapter 53)
K-and r-selection
k-selection, or density-dependent selection, selects for life history traits that
are sensitive to population density, and are favored at high densities
operates at a density near the limit imposed by their resources
(carrying capacity K) and where competition is greatest (EX mature
trees in an old growth forest)
r-selection, or density-independent selection, selects for life history traits
that maximize reproductive success in uncrowded environments (low
operates when individuals face little competition (EX weeds in an
abandoned farmland field)
so why does population growth rate decrease as population size approaches
carrying capacity (K-selection)?
Concept 53.5: Many factors that regulate population growth are density-
dependent (K-selected)
There are two general questions about regulation of population growth
what environmental factors stop a population from growing
why do some populations show radical fluctuations in size over time,
while others remain stable?
To understand why a population stops growing ecologists study birth, death,
immigration 523and emigration changes in a population over time
Population Change and Population Density
If immigration and emigration offset each other, then a population grows
when birth overtakes death, and then declines when death exceeds birth
in density-independent populations, birthrates and death rate are
not affected with population density (r-selected)
in density-dependent populations, birth rates fall and death rates
rise depending on population density (k-selected)
Fig 53.16 if the birth rate changes with population density but
the death rate is constant, this would eventually lead to birth
and death rate equilibrium (Q)
Mechanisms of Density-Dependent Population Regulation
Density-dependent birth and death rate are an example of negative
feedback that regulation population growth; affected by many factors, such as
competition for resources, territoriality, disease, predation, toxic wastes, and
intrinsic factors:
Predation: as a prey population builds up, predators may feed
preferentially on that species
Intrinsic factors: for some population, intrinsic (physiological)
factors appear to regulate population size (EX white-footed mice)
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