Latitudinal gradients in avian clutch size
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Latitudinal Gradients in Avian Clutch Size. Daylength Hypothesis Prey Diversity Hypothesis (search images) Spring Bloom or Competition Hypothesis Nest Predation Hypothesis (Skutch) Hazards of Migration Hypothesis Please study Handouts 1, 2, 3, and 4 in preparation for next Thursday’s exam.

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Latitudinal gradients in avian clutch size
Latitudinal Gradients in Avian Clutch Size

  • Daylength Hypothesis

  • Prey Diversity Hypothesis (search images)

  • Spring Bloom or Competition Hypothesis

  • Nest Predation Hypothesis (Skutch)

  • Hazards of Migration Hypothesis

    Please study Handouts 1, 2, 3, and 4 in preparation for next Thursday’s exam


Evolution of Death Rates, Senescence, old age, genetic dustbinMedawar’s Test Tube Model, Lactose intolerance Recession of time of expression of the overt effects of a detrimental allele

Precession of time of expression of the positive effects of a beneficial allele

Pearl-Verhulst Logistic Equation: Sigmoidal Population GrowthDensity Dependence versus Density Independence

Density Dependent versus Density Independent Selection

Equilibrium, Opportunistic, and Fugitive Species

r-strategists versus K-strategists




Verhulst-Pearl Logistic Equation dustbin dN/dt = rN – rN (N/K) = rN – {(rN2)/K}dN/dt = rN {1– (N/K)} = rN [(K – N)/K] dN/dt = 0when [(K – N)/K] = 0 [(K – N)/K] = 0when N = K dN/dt = rN – (r/K)N2


Inhibitory effect of each individual dustbin

On its own population growth is 1/K


At equilibrium, birth rate must equal death rate, dustbinbN = dNbN = b0 – x N dN = d0 + y N b0 – x N = d0 + y NSubstituting K for N at equilibrium and r for b0 – d0 r = (x + y) K or K = r/(x +y)


Derivation of the Logistic Equation dustbin

Derivation of the Verhulst–Pearl logistic equation is easy. Write an

equation for population growth using the actual rate of increase rN

dN/dt = rN N = (bN – dN) N

Substitute the equations for bNand dN into this equation

dN/dt = [(b0 – xN) – (d0 + yN)] N

Rearrange terms,

dN/dt = [(b0 – d0 ) – (x + y)N)] N

Substituting r for (b – d) and, from above, r/K for (x + y), multiplying

through by N, and rearranging terms,

dN/dt = rN – (r/K)N2


Density dependence versus density independence
Density Dependence versus Density Independence dustbin

Dramatic Fish Kills, Illustrating Density-Independent Mortality

_______________________________________________________

Commercial Catch Percent

–––––––––––––––––––––

Locality Before After Decline

_______________________________________________________

Matagorda 16,919 1,089 93.6

Aransas 55,224 2,552 95.4

Laguna Madre 12,016 149 92.6

________________________________________________________

Note: These fish kills resulted from severe cold weather on the

Texas Gulf Coast in the winter of 1940.


Parus major dustbin



Some of the Correlates of dustbinr- and K-Selection

_______________________________________________________________________________________

r-selection K-selection

______________________________________________________________________________________________________________________________

Climate Variable and unpredictable; uncertain Fairly constant or predictable; more certain

Mortality Often catastrophic, nondirected, More directed, density dependent

density independent

Survivorship Often Type III Usually Types I and II

Population size Variable in time, nonequil- Fairly constant in time,

ibrium; usually well below equilibrium; at or near

carrying capacity of envi- carrying capacity of the

ronment; unsaturated com- environment; saturated

munities or portions thereof; communities; no recolon-

ecologic vacuums; recolon- ization necessary

ization each year

Intra- and inter- Variable, often lax Usually keen

specific competition

Selection favors 1. Rapid development 1. Slower development

2. High maximal rate of 2. Greater competitive ability

increase, rmax

3. Early reproduction 3. Delayed reproduction

4. Small body size 4. Larger body size

5. Single reproduction 5. Repeated reproduction

6. Many small offspring 6. Fewer, larger progeny

Length of life Short, usually less than a year Longer, usually more than a year

Leads to Productivity Efficiency

Stage in succession Early Late, climax

________________________________________________________________________________________________________________________________





Frequencies of Positive and Negative Correlations Between Percentage

Change in Density and Population Density for a Variety of Populations

in Different Animal Groups

___________________________________________________________________

Numbers of Populations in Various Categories

____________________________________________

Positive Positive Negative Negative Negative

Taxon (P<.05) (Not sig.) (Not sig.) (P<.10) (P < .05) Total

___________________________________________________________________

Inverts 0 0 0 0 4 4

Insects 0 0 7 1 7 15

Fish 0 1 2 0 4 7

Birds 0 2 32 16 43 93

Mammals 1* 0 4 1 13 19

Totals 1* 3 45 18 71 138

___________________________________________________________________

* Homo sapiens (the “sap”)


Negative correlations between percentage change in density Percentage and population density for a variety of populations in different animal groups except for Homo the sap 4 and 10 year population “cycles” microtines and snowshoe hares Sunspot Hypothesis — dark tree ring marks Time Lags Stress Phenomena Hypothesis Predator-Prey Oscillations Epidemiology-Parasite Load Hypothesis Food Quantity Hypothesis Nutrient Recovery Other Food Quality Hypotheses Genetic Control Hypothesis – Optimal reproductive tactics Could optimal reproductive tactics drive population cycles?



Snowy owls Percentage

Microtines: Voles and lemmings: 4 year cycles

Fabled lemming marches into the sea




Population cycles
Population “Cycles” Percentage

  • 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

    Bb:Read Krebs et al. “What drives the 10-year cycle of snowshoe hares?”


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