1. Population Growth What factors limit the growth of populations?
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Population Growth
What factors limit the growth of populations?

2. Geometric Growth Nt = Noλt
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Geometric Growth
When generations do not overlap, growth can be modeled geometrically.
Nt = Noλt
Nt =
No =
λ (lambda) =
t =
λ =2.4

3. Population Growth What factors limit the growth of populations?
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Population Growth
What factors limit the growth of populations?

4. Exponential Growth dN / dt = rmax N
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Exponential Growth
Continuous population growth in an unlimited environment can be modeled exponentially.
dN / dt = rmax N
dN =
dt =
rmax =
N =
Rate of population growth

5. Exponential Growth dN / dt = rmax N
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Exponential Growth
dN / dt = rmax N
Appropriate for populations with overlapping generations.
As population size (N) increases, rate of population increase (dN/dt) gets…
Which variable above would best represent the “Intrinsic rate of increase”?

6. Exponential Growth Nt = Noer t
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Exponential Growth
For an exponentially growing population, size at any time can be calculated as:
Nt = Noer t
Nt =
N0 =
e =
rmax =
t =
max

7. Exponential Population Growth
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Exponential Population Growth

8. Logistic Population Growth
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Logistic Population Growth

9. Logistic Population Growth
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Logistic Population Growth
As resources are depleted, population growth rate slows and eventually stops: _________________ ________.
Sigmoid (S-shaped) _______________________.
_____________________ is the number of individuals of a population the environment can support.
Finite amount of resources can only support a finite number of individuals.

10. Logistic Population Growth
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Logistic Population Growth

11. Limits to Population Growth
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Limits to Population Growth
Environment limits population growth by altering birth and death rates.
Density-dependent factors?!?
Density-independent factors?!?

12. Logistic Population Growth
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Logistic Population Growth
dN/dt = rmaxN(1-N/K)
rmax = Maximum per capita rate of increase under ideal conditions.
When N nears K, the right side of the equation…
As population size increases, logistic growth rate becomes…
Highest when N=K/2.
N/K = Environmental resistance.

13. Galapagos Finch Population Growth
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Galapagos Finch Population Growth

14. Which graph on the left indicates growing, declining and stable populations?

15. BIOL 3240 Plant and Animal Ecology – Population Dynamics

16. BIOL 3240 Plant and Animal Ecology – Population Dynamics

17. BIOL 3240 Plant and Animal Ecology – Population Dynamics
In the presence of _________ ___________, populations can grow at ___________ or ___________ rates.
The environment limits population growth by changing _______ and _______ rates.
As resources are depleted, population growth… ; this is known as __________ __________ growth.

18. BIOL 3240 Plant and Animal Ecology – Population Dynamics

19. Cactus Finches and Cactus Reproduction
Grant and Grant documented several ways finches utilized cacti:
Open flower buds in dry season to eat pollen
Consume nectar and pollen from mature flowers
Eat seed coating (aril)
Eat seeds
Eat insects from rotting cactus pads

20. Cactus Finches and Cactus Reproduction
Finches tend to destroy stigmas, thus flowers cannot be fertilized.
Wet season activity may reduce seeds available to finches during the dry season.
Opuntia helleri main source for cactus finches.
Negatively impacted by El Nino (1983).
Stigma snapping delayed recovery.
Interplay of biotic and abiotic factors.

21. Galapagos Finch Population Growth
BIOL 3240 Plant and Animal Ecology – Population Dynamics
Galapagos Finch Population Growth
Boag and Grant - Geospiza fortis was numerically dominant finch (1,200).
After drought of 1977, population fell to (180).
Food plants failed to produce seed crop.
x normal rainfall caused population to grow (1,100) due to abundance of seeds and caterpillars.