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 1900. 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 100 - 400 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.

10

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

13

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 1985. Reproductive output driven by

exceptional year in 1983. Responsiveness of population age

structure to environmental variation.

23

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 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.

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 / Nt

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

Nt = 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 xlxmx / Ro

X= Age in years Per Capita Rate of Increase:

r = ln Ro / T ln = Base natural logarithms

28