1. Studying organisms in their environment
Bio biosphere
ecosystem
community
population
organism
organism
biosphere

2. Populations Occupy niches in ecosystems
Grow exponentially or logistically (carrying capacity)
A group of the same kind of organisms living in the same place at the same time.
EVOLVE! Allele frequencies can be described by the Hardy-Weinberg Equilibrium:
p2 + 2pq + q2 = 1
Measured by random sampling
Not realistic but, offers a standard to compare rates of evolution to – Null Hypothesis
Will remain the same if no migration, no selection, random mating. No evolution

3. Life takes place in populations
group of individuals of same species in same area at same time
rely on same resources
interact
interbreed
Population Ecology: What factors affect a population?

4. Population Size Changes to population size
adding & removing individuals from a population
birth
death
immigration
emigration

5. Population growth rates
Factors affecting population growth rate
sex ratio
how many females vs. males?
generation time
at what age do females reproduce?
age structure
how females at reproductive age in cohort?

6. Population growth change in population = births – deaths
Exponential model (ideal conditions)
dN = riN dt
growth increasing at constant rate
N = # of individuals
r = rate of growth
ri = intrinsic rate
t = time
d = rate of change
every pair has 4 offspring
every pair has 3 offspring
intrinsic rate = maximum rate of growth

7. Exponential growth rate
Characteristic of populations without limiting factors
introduced to a new environment or rebounding from a catastrophe
Whooping crane
coming back from near extinction
African elephant
protected from hunting

8. Introduced species Non-native species kudzu
transplanted populations grow exponentially in new area
out-compete native species
loss of natural controls
lack of predators, parasites, competitors
reduce diversity
examples
African honeybee
gypsy moth
zebra mussel
purple loosestrife
gypsy moth
kudzu

9. Zebra musselssel reduces diversity
~2 months
ecological & economic damage
reduces diversity
loss of food & nesting sites for animals
economic damage

10. Purple loosestrife reduces diversity
1968
1978
reduces diversity
loss of food & nesting sites for animals

11. Regulation of population size
marking territory = competition
Limiting factors
density dependent
competition: food, mates, nesting sites
predators, parasites, pathogens
density independent
abiotic factors
sunlight (energy)
temperature
rainfall
swarming locusts
competition for nesting sites

12. Logistic rate of growth
Can populations continue to grow exponentially?
Of course not!
no natural controls
K = carrying capacity
effect of natural controls
What happens as N approaches K?

13. Carrying capacity
Time (years)
1915
1925
1935
1945 10 8 6 4 2
Number of breeding male
fur seals (thousands)
Maximum population size that environment can support with no degradation of habitat
varies with changes in resources
500
400
300
200
100 20 10 30 50 40 60
Time (days)
Number of cladocerans
(per 200 ml)
What’s going on with the plankton?

14. Human population growth
Population of… China: 1.3 billion
India: 1.1 billion
Human population growth
adding 82 million/year
~ 200,000 per day!
Doubling times
250m  500m = y ()
500m  1b = y ()
1b  2b = 80y (1850–1930)
2b  4b = 75y (1930–1975)
20056 billion
Significant advances
in medicine through
science and technology
What factors have contributed to this exponential growth pattern?
Industrial Revolution
Is the human population reaching carrying capacity?
Bubonic plague "Black Death"
1650500 million

15. Populations evolve Natural selection acts on individuals
differential survival
“survival of the fittest”
differential reproductive success
who bears more offspring
Populations evolve
genetic makeup of population changes over time
favorable traits (greater fitness) become more common
Presence of lactate dehydrogenase
Mummichog

16. 5 Agents of evolutionary change
Mutation
Gene Flow
Non-random mating
Genetic Drift
Selection

17. Variation & natural selection
Variation is the raw material for natural selection
there have to be differences within population
some individuals must be more fit than others

18. Where does Variation come from?
Mean beak depth of parents (mm)
Medium ground finch 8 9 10 11
1977
1980
1982
1984
Dry year
Wet year
Beak depth
Beak depth of
offspring (mm)
Mutation
random changes to DNA
errors in mitosis & meiosis
environmental damage
Sex
mixing of alleles
recombination of alleles
new arrangements in every offspring
new combinations = new phenotypes
spreads variation
offspring inherit traits from parent

19. 1. Mutation & Variation Mutation creates variation
new mutations are constantly appearing
Mutation changes DNA sequence
changes amino acid sequence?
changes protein?
changes structure?
changes function?
changes in protein may change phenotype & therefore change fitness

20. 2. Gene Flow Movement of individuals & alleles in & out of populations
seed & pollen distribution by wind & insect
migration of animals
sub-populations may have different allele frequencies
causes genetic mixing across regions
reduce differences between populations