1) The document discusses different life history strategies in organisms, including trade-offs between offspring number and size. It also discusses variation in life histories based on factors like adult survival rates. 2) Organisms are classified based on their life histories as either r-selected or K-selected. R-selected organisms thrive in unpredictable environments while K-selected organisms do better in predictable environments. 3) Competition, both intra-specific and inter-specific, is examined through mathematical models like Lotka-Volterra and laboratory experiments. The models and experiments demonstrate how competition affects population growth and can restrict species to their realized niches over time.

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Biology 205
Ecology and Adaptation
Lecture 10: Population Life History
Competition
Dr. Erik D. Davenport
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Outline
• Offspring Number Versus Size
• Life History Variation Among Species
• Life History Classification
– r - Selected
– k - Selected
• Resource Competition
• Niches
• Mathematic and Laboratory Models for competition
– Lotka-Volterra model
• Competition and Niches
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Different life history – why?
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• Principle of Allocation: Only certain amount of
energy is available to a living organism. If
organisms use energy for one function such as
growth, the amount of energy available for
other functions is reduced.
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Main concept 1:
Offspring Number Versus Size
Because all organisms have access to limited
energy and other resources, there is a trade-
off between the number and size of offspring;
those that produce larger offspring are
constrained to produce fewer; while those
that produce smaller offspring may produce
larger numbers.
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Egg Size and Number in Fish
• Fish show more variation in life-history than any
other group of animals.
• Darter fish as an example….
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Seed Size and Number in Plants
• In addition to the number of the seed
– Plant growth form will influence seed size
– Dispersal mode might influence seed size.
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Seed Size and Number in Plants
• Westoby et.al. recognized four
plant growth forms:
– Graminoids: Grass and grass-like
plants.
– Forbs: Herbaceous, non-
graminoids.
– Woody Plants: Woody thickening of
tissues.
– Climbers: Climbing plants and
vines.
– Woody plant and climbers
produced 10x the mass of seeds
than either graminoids or forbs.
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Seed Size and Number in Plants
Westoby et.al. recognized six
seed dispersal strategies:
– Unassisted: No specialized
structures.
– Adhesion: Hooks, spines, or
barbs.
– Wind: Wings, hair, (resistance
structures).
– Ant: Oil surface coating
(elaisome).
– Vertebrate: Fleshy coating
(aril).
– Scatterhoarded:
Gathered,stored in caches.
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Main concept 2:
Adult survival rate vs. reproduction age
When adult survival is lower, organisms begin
reproducing at an younger age and invest a
greater proportion of their energy budget into
reproduction;
where adult survival is higher, organism defer
reproduction to a later age and allocate a smaller
proportion of their resources to reproduction.
What will be the results on individual body size?
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Life History Variation Among Species
• Shine and Charnov pointed out vertebrate
energy budgets are different before and after
sexual maturity.
– Before - maintenance or growth.
– After - maintenance, growth, or reproduction.
– Individuals delaying reproduction will grow faster
and reach a larger size.
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Life History Variation
• Bertschy and Fox studied the influence of
adult survival on pumpkinseed sunfish life
histories.
– Findings supported theory that when adult
survival is lower, natural selection will favor
allocating greater resources to reproduction.
– Smaller or bigger body size???
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Concept 3: Life History Classification
• MacArthur and Wilson
– r selection (per capita rate of increase)
• Characteristic high population growth rate.
– K selection (carrying capacity)
• Characteristic efficient resource use.
• Pianka : r and K are ends of a spectrum, while
most organisms are in-between.
– r selection: Unpredictable environments.
– K selection: Predictable environments.
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r and K: Fundamental Contrasts
• Per captia Rate of Increase:
– Highest in r selected species.
• Competitive Ability:
– Highest in K selected species.
• Reproduction:
– r: Numerous individuals rapidly produced.
– K: Fewer larger individuals slowly produced.
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IMPORTANT!!!!

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Population interactions
competition
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Modes of Competition
• Interference:
– Direct aggressive interaction between individuals.
• Intraspecific:
– Competition with members of own species.
• Interspecific:
– Competition between individuals of two species -
reduces fitness of both.
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Intraspecific Competition Among Herbaceous
Plants
• Plant growth rates and weights have been found
to increase in low density populations.
• Competition for resources is more intense at
higher population densities.
• Usually leads to mortality among competing
plants.
• Self-Thinning: As the population of the trees
develops, more and more biomass is composed of
fewer and fewer individuals, this process is called
self-thinning. Why??????
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• Self-thinning appears to result from intraspecific
competition for limited resources, as a local
population of plants develops, individual plants take
up increasing quantities of nutrients, water, and
space for which some individuals compete more
successfully, the loser in this competition for
resources die, and population density decrease as a
consequence. Over time, the population is composed
of fewer and fewer large individuals.
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Plant population density declines more rapidly then biomass increase

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Niches (very very important!!)
• Niche: Summarizes environmental factors that
influence growth, survival, and reproduction
of a species.
• Gause: Principle of Competitive Exclusion
– Two species with identical niches cannot coexist
indefinitely.
– One will be a better competitor and thus have
higher fitness and eventually exclude the other.
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Niches
• Hutchinson defined niche as:
– n-dimensional hyper-volume
– n equates the number of environmental factors
important to survival and reproduction of a
species.
– Fundamental niche – hyper-volume
– Realized niche includes interactions such as
competition that may restrict environments where
a species may live.
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Feeding Niches of Galapagos Finches
– Grant found differences in beak size among
ground finches translates directly into diet.
– Size of seeds eaten can be estimated by
measuring beak depths.
– Individuals with deepest beaks fed on hardest
seeds.
– After 1977 drought, the remaining seeds were
very hard. Thus, mortality was most heavy in birds
with smaller beaks.
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Feeding Niches of Galapagos Finches
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Mathematical and Laboratory Models
• Metz summarized models:
–Abstractions and simplifications, not
facsimiles of nature.
–Man-made construct; partly empirical and
partly deductive.
–Used to provide insights into natural
phenomena.
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What model is used for the intraspecific
competition??
dN/dt = rN(1-N/K)
• r = per capita rate of increase under ideal
conditions.
• Logistic population growth model.
• What term in this model describe the
intraspecific competition???
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Lotka Volterra
• Effect of interspecific competition on
population growth of each species:
– dN1 / dt = rm1N1 ((K1-N1- α 12N2) / K1)
– dN2 / dt = rm2N2 ((K2-N2- α 21N1) / K2)
• α12: Effect of individual of species 2 on rate of pop.
growth of species 1.
• α21: Effect of individual of species 1 on rate of pop.
growth of species 2.
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Lotka-Volterra
• The Lotka-Volterra model incorporates interspecific
competition by using a parameter called α.
• α is the coefficient of competition (or competition
coefficient) and measures the competitive effect of
one species on another. (IMPORTANT!!!!)
• For example: α12 is the effect of species 2 on
species 1, α21 is the effect of species 1 on species 2.
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Predicting the outcome of competition
• The outcome of competition, according to the
Lotka-Volterra model, is ultimately
determined by
• carrying capacity (Ki) and
• the competition coefficient (aij) of the two
species
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examples
• Green sunfish Bluegill
• K1 = 600 K2 = 600
• r1 = 0.10 r2 = 0.10
• α12 = 1.50 α21 = 0.90
• What is the results of this completion?
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Lab Experiments
• Gause demonstrated resource limitation with
Paramecium caudatum and Paramecium
aurelia in presence of two different
concentrations of Bacillus pyocyaneus.
– When grown alone, carrying capacity determined
by intraspecific competition.
– When grown together, P. caudatum quickly
declined.
– Reduced resource supplies increased competition.
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Paramecia Lab Experiments
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Flour Beetle Experiments
• Tribolium beetles infest stored grain products.
– Park studied interspecific competition between T.
confusum and T. castaneum under varied
environmental conditions.
– Growing the two species together suggested
interspecific competition restricts the realized
niches of both species to fewer environmental
conditions.
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Competition and Niches
• Competition can restrict species to their
realized niches.
– But if competitive interactions are strong and
pervasive enough, they may produce an
evolutionary response in the competitor
population.
– Changes fundamental niche.
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Niche Overlap and
Competition Between Barnacles
• Connell discovered interspecific competition in
barnacles. Balanus plays a role in determining
lower limit of Chthamalus within intertidal
zone.
– Did not account for all observed patterns.
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Character Displacement
• Because degree of competition is assumed to
depend upon degree of niche overlap,
interspecific competition has been predicted
to lead to directional selection for reduced
niche overlap.
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Character Displacement
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