1 Population Dynamics Chapter 8

2 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

3 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.

4 Africanized Honeybees

5 Collared Doves Collared Doves, Streptopelia decaocto, spread from Turkey into Europe after  Dispersal began suddenly.  Not influenced by humans.  Took place in small jumps.  45 km/yr

6 Collared Doves

7 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 m/yr.

8 Rapid Changes in Response to Climate Change

9 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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11 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

12 Dispersal in Rivers and Streams

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14 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.

15 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.

16 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.

17 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

18 Survivorship Curves

19 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

20 Age Distribution

21 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.

22 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  Reproductive output driven by exceptional year in  Responsiveness of population age structure to environmental variation.

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24 Rates of Population Change Birth Rate: Number of young born per female. Fecundity Schedule: Tabulation of birth rates for females of different ages.

25 Estimating Rates for an Annual Plant P. drummondii  R o = Net reproductive rate; Average number of seeds produced by an individual in a population during its lifetime.  R o = Σ l x m x  X= Age interval in days.  l x = % pop. surviving to each age (x).  m x = Average number seeds produced by each individual in each age category.

26 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 / N t  N t+1 = Size of population at future time.  N t = Size of population at some earlier time.

27 Estimating Rates when Generations Overlap Common Mud Turtle (K. subrubrum)  About half turtles nest each year.  Average generation time: T = Σ xl x m x / R o  X= Age in years  Per Capita Rate of Increase: r = ln R o / T  ln = Base natural logarithms

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