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Population DynamicsChapter 10

Honeybees pollinate one-third of the fruits, nuts and vegetables that end up in our homey kitchen baskets. Fall 2006- the nation’s beekeepers watched in horror as more than a quarter of their 2.4 million colonies collapsed, killing billions of nature’s little fertilizers.

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Outline

• Dispersal– In Response to Climate Change– In Response to Changing Food Supply– In Rivers and Streams

• Metapopulations• Estimating Patterns of Survival• Survivorship Curves• Age Distribution• Rates of Population Change

– Overlapping Generations

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dispersal

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Dispersal

• Africanized Honeybees– Honeybees (Apis melifera) evolved in Africa

and Europe and have since differentiated into many locally adapted subspecies.

• Africanized honeybees disperse much faster than European honeybees.

– Within 30 years they occupied most of South America, Mexico, and all of Central America.

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Africanized Honeybees

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Collared Doves

• Collared Doves, Streptopelia decaocto, spread from Turkey into Europe after 1900.– Dispersal began suddenly.

• Not influenced by humans.• Took place in small jumps.

– 45 km/yr

Mourning Dove (left) with Eurasian Collared-Dove (right). Photo by Marie Weinstein, Alabaster, AL.

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Collared Doves

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Rapid Changes in Response to Climate Change

• Organisms began to spread northward about 16,000 years ago following retreat of glaciers and warming climate.– Evidence found in preserved pollen in lake

sediments.– Movement rate 100 - 400 m/yr.

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Rapid Changes in Response to Climate Change

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Dispersal in Response to Changing Food Supply

• Holling observed numerical responses to increased prey availability.– Increased prey density led to increased

density of predators.• Individuals move into new areas in response to

higher prey densities.

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Dispersal in Rivers and Streams

• Stream dwellers have mechanisms to allow them to maintain their stream position.– Streamlined bodies– Bottom-dwelling– Adhesion to surfaces

• Tend to get washed downstream in spates.– Muller hypothesized populations maintained via

dynamic interplay between downstream and upstream dispersal.

• Colonization cycle

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Dispersal in Rivers and Streams

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Metapopulations

• A metapopulation is made up of a group of subpopulations living on patches of habitat connected by an exchange of individuals.– Alpine Butterfly - Roland et.al.– Lesser Kestrels - Serrano and Tella.

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Estimating Patterns of Survival

• Three main methods of estimation:– Cohort life table

• Identify individuals born at same time and keep records from birth.

– Static life table• Record age at death of individuals.

– Age distribution• Calculate difference in proportion of individuals in

each age class.• Assumes differences from mortality.

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High Survival Among the Young

• Murie collected Dall Sheep skulls, Ovis dalli.– Major Assumption: Proportion of skulls in

each age class represented typical proportion of individuals dying at that age.

• Reasonable given sample size of 608.

– Constructed survivorship curve.• Discovered bi-modal mortality.

– <1 yr.– 9-13 yrs.

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Fig. 10.13

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Fig. 10.14

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Survivorship Curves

• Type I: Majority of mortality occurs among older individuals. – Dall Sheep

• Type II: Constant rate of survival throughout lifetime.– American Robins

• Type III: High mortality among young, followed by high survivorship.– Sea Turtles

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Survivorship Curves

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Age Distribution

• Age distribution of a population reflects its history of survival, reproduction, and growth potential.

• Miller published data on age distribution of white oak (Quercus alba).– Determined relationship between age and

trunk diameter.– Age distribution biased towards young trees.

• Sufficient reproduction for replacement.– Stable population

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Age Distribution

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Age Distribution

• Rio Grande Cottonwood populations (Populus deltoides wislizenii) are declining.– Old trees not being replaced.– Reproduction depends on seasonal floods.

• Prepare seed bed.• Keep nursery areas moist.

– Because floods are absent, there are now fewer germination areas.

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Fig. 10.20

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Dynamic Population in a Variable Climate

• Grant and Grant studied Galapagos Finches.– Drought in 1977 resulted in no recruitment.

• Gap in age distribution.• Additional droughts in 1984 and 1985.• Reproductive output driven by exceptional year in

1983.– Responsiveness of population age structure to environmental

variation.

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Fig. 10.21a

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Fig. 10.21b

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Rates of Population Change

• Birth Rate: Number of young born per female.

• Fecundity Schedule: Tabulation of birth rates for females of different ages.

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Estimating Rates for an Annual Plant• P. drummondii

– Ro = Net reproductive rate; Average number of seeds produced by an individual in a population during its lifetime.

– Ro= Σ lxmx

• X= Age interval in days.

• lx = % pop. surviving to each age (x).

• mx= Average number seeds produced by each individual in each age category.

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Estimating Rates for an Annual Plant

• Because P. drummondii has non-overlapping generations, can estimate growth rate.– Geometric Rate of Increase (λ):

• λ=N t+1 / Nt

• N t+1 = Size of population at future time.

• Nt = Size of population at some earlier time.

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Estimating Rates when Generations Overlap

• Common Mud Turtle (K. subrubrum)– About half turtles nest each year.– Average generation time:

T = Σ xlxmx / Ro

– X= Age in years – Per Capita Rate of Increase:

r = ln Ro / T

– ln = Base natural logarithms

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Review• Dispersal

– In Response to Climate Change– In Response to Changing Food Supply– In Rivers and Streams

• Metapopulations• Estimating Patterns of Survival• Survivorship Curves• Age Distribution• Rates of Population Change

– Overlapping Generations

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