Second Exam: Thursday 2 April 2015Covers Chapters 5, 8, 9, and 10Lectures 10 to 19 plus Agriculture Global Warming The Vanishing Book of Life on Earth Plastics Intelligent Design?The Weakest Link TechnologyEconomics
Population Growth and Regulation
S - shaped sigmoidal population growth
Verhulst-Pearl Logistic Equation: dN/dt = rN [(K – N)/K]
Assumptions, Derivation
Density Dependence versus Density Independence
Equilibrium, Opportunistic, and Fugitive species
r-selection versus K-selection (r-K selection Continuum)
Correlates of r and K-selection, Bet Hedging
Winemiller’s 3-dimensional fish life history surface
Population Change versus Population Density Plots
Microtine Rodent Population Fluctuations
Hudson Bay Fur Company: Snowshoe Hare and Lynx “Cycles”
Population “Cycles”• Sunspot Hypothesis• Time Lags• Stress Phenomena Hypothesis• Predator-Prey Oscillations• Epidemiology-Parasite Load Hypothesis• Food Quantity Hypothesis• Nutrient Recovery• Other Food Quality Hypotheses• Genetic Control Hypothesis
Sunspot Hypothesis (Sinclair et al. 1993. Am. Nat.)
10 year cycle embedded within 30-50 year periods
Maunder minimum: 1645-1715
Three periods of high sunspot maxima:
1751-1787 1838-1870 1948-1993
Canadian Government survey 1931-1948
Hare cycle synchronized across North America
Yukon: 5km strip, tree growth rings (N = 368 trees)
One tree germinated in 1675 (>300+ years old)
Hares prefer palatable shrubs,
but will eat spruce
leaving dark tree ring marks
Other Food Quality Hypotheses:
Microtus (Freeland 1974) palatability <–––> toxic
Snowshoe hares: Plant chemical defenses against herbivory
(Bryant 1980)
Chitty’s “Genetic Control” Hypothesis
Could optimal reproductive tactics be involved in driving population cycles?
Population “Cycles”• Sunspot Hypothesis
• Time Lags
• Stress Phenomena Hypothesis
• Predator-Prey Oscillations
• Epidemiology-Parasite Load Hypothesis
• Food Quantity Hypothesis
• Nutrient Recovery
• Other Food Quality Hypotheses
• Genetic Control Hypothesis
Social Behavior
Hermits must have lower fitness than social individualsClumped, random, or dispersed (variance/mean ratio)mobility = motility = vagility (sedentary sessile organisms)
Use of SpacePhilopatryFluid versus Viscous Populations
Individual Distance, Daily MovementsHome RangeTerritoriality (economic defendability)Resource in short supply
Feeding TerritoriesNesting TerritoriesMating Territories
Sexual Reproduction
Monoecious versus DieciousEvolution of Sex —> AnisogamyDiploidy as a “fail-safe” mechanismCosts of Sexual Reproduction (halves heritability!)Facultative Sexuality (Ursula LeGuin -- Left Hand of Darkness)Protandry <—> Protogyny (Social control)Parthenogenesis (unisexual species)Possible advantages of sexual reproduction include:
two parents can raise twice as many progeny
mix genes with desirable genes (enhances fitness)reduced sibling competitionheterozygositybiparental origin of many unisexual species
Why have males? “The biological advantage of a sex ratio that is unbalanced
in favor of females is readily apparent in a species with a
promiscuous mating system. Since one male could fertilize
several females under such a system, survival of a number
of males equal to the number of females would be wasteful
of food, home sites, and other requirements for existence.
The contribution of some of the surplus males to feeding the
predators on the population would be economically
advantageous. In other words, the eating of the less valuable
(to the population) males by predators would tend to
reduce the predator pressure on the more valuable
females.” — Blair (1960) The Rusty Lizard
W. Frank Blair
Sceloporus olivaceus
Sex Ratio
Proportion of MalesPrimary, Secondary, Tertiary, QuaternaryWhy have males?Fisher’s theory: equal investment in the two sexes
Ronald A. Fisher
Comparison of the Contribution to Future Generations of Various Families in Case a in Populations with Different Sex Ratios__________________________________________________________________Case a Number of Males Number of Females__________________________________________________________________Initial population 100 100
Family A 4 0Family C 2 2
Subsequent population (sum) 106 102CA = 4/106 = 0.03773CC = 2/106 + 2/102 = 0.03846 (family C has a higher reproductive success)
__________________________________________________________________
Note: The contribution of family x is designated Cx.
Comparison of the Contribution to Future Generations of Various Families in Case a in Populations with Different Sex Ratios__________________________________________________________________Case a Number of Males Number of Females
__________________________________________________________________
Initial population 100 100Family E 0 4Family C 2 2
Subsequent population (sum) 102 106
CE = 4/106 = 0.03773CC = 2/106 + 2/102 = 0.03846 (family C has a higher reproductive success)
__________________________________________________________________
Note: The contribution of family x is designated Cx.
Comparison of the Contribution to Future Generations of Various Families in Case a in Populations with Different Sex Ratios__________________________________________________________________Case a Number of Males Number of Females
__________________________________________________________________
Initial population 100 100Family A 4 0Family C 2 2Family E 0 4
Subsequent population (sum) 106 106
CA = 4/106 = 0.03773CC = 2/106 + 2/106 = 0.03773 All three families have equal successCE = 4/106 = 0.03773
__________________________________________________________________
Note: The contribution of family x is designated Cx.
___________________________________________________________________________Case b Number of Males Number of Females____________________________________________________________________________Initial population 100 100
Family A 2 0Family B 1 2
Subsequent population (sum) 103 102CA = 2/103 = 0.01942CB = 1/103 + 2/102 = 0.02932 (family B is more successful)
Initial population 100 100Family B 1 2Family C 0 4
Subsequent population (sum) 101 106CB = 1/101 + 2/106 = 0.02877CC = 4/106 = 0.03773 (family C is more successful than family B)
Natural selection will favor families with an excess of females until the population reaches its equilibrium sex ratio (below).Initial population 100 200
Family B 1 2Family C 0 4
Subsequent population (sum) 101 206CB = 1/101 + 2/206 = 0.001971CC = 4/206 = 0.01942 (family B now has the advantage)
_____________________________________________________________________________Note: The contribution of family x is designated Cx.
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