1. Population Dynamics

2. Objectives
How do populations change in size, density, and makeup in response to environmental stress?
What is the role of predators in controlling population size?
What different reproductive patterns do species use to enhance their survival?

3. Population Dynamics: How can populations change?
1. Size (number of individuals)
2. Density (population size in a certain space at a given time)
3. Dispersion (spatial pattern in habitat)
Clumped
Uniform
Random
4. Age distribution (proportion of individuals in each age group in population)

4. When do populations change?
In response to…
Environmental stress
Changes in environmental conditions

5. Population Size
Total number of individual organisms in a population (# of organisms of the same species in the same place at the same time)
Natality- Number of individuals added through reproduction
Crude Birth Rate: Births per 1000 individuals per year
Mortality - Number of individuals removed through death
Crude Death Rate: Deaths per 1000 individuals per year

6. Population Density
Population Density :the amount of individuals in a population per unit area (or volume if aquatic)
Some species exist in high densities - Mice
Some species exist in low densities - Mountain lions
Density can depend upon
social/population structure
mating relationships
time of year

7. Population Distribution (Dispersion)
Dispersion is the spatial pattern of distribution
clumped
uniform
random

8. Age Structure
Shows the % of the population in age groups (e.g. 0-4 years, years, etc.)
The age structure of a population dictates whether is will grow, shrink, or stay the same size

9. Age Structure Diagrams
Positive Growth Zero Growth Negative Growth
Pyramid Shape Vertical Edges Inverted Pyramid

10. What’s going on in Qatar?
(CIA factbook)

11. Zero Population Growth (ZPG)
Population growth depends upon
birth rates
death rates
immigration rates (into area)
emigration rates (exit area)
Pop = Pop0 + (b + i) - (d + e)
Zero Population Growth (ZPG)
(b + i) = (d + e)

12. Population Growth Populations show two types of growth Exponential
J-shaped curve
Growth is independent of population density
Logistic
S-shaped curve
Growth is dependent on population density

13. Exponential Growth Graph

14. Logistic Growth

15. Exponential Growth?
One female elephant will produce 6 young over her 100 year life span. In a population, this amounts to a growth rate of 2%
how many elephants could result from one male and one female in 750 years
N = 2e0.02 x750 = 2e15 = 6.5 million elephants!
Even counting the deaths, there would be TOO MANY ELEPHANTS for their habitat to support!
CLEARLY elephants do
NOT grow exponentially!
They must follow logistic
growth!

16. Carrying Capacity
Basic Concept: Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths)

17. Carrying Capacity (K)
Exponential curve is not realistic due to carrying capacity of area
K = maximum number of individuals a habitat can support over a given period of time
Not a fixed quantity – can change based on several factors

19. Logistic Growth Reproductive time lag causes population overshoot
Could lead to a die-off
Population will not be steady curve due to resources (prey) and predators

21. Reproductive Strategies
“Goal” of every species is to produce as many offspring as possible
Each individual has a limited amount of energy to put towards life and reproduction
This leads to a trade-off of long life or high reproductive rate
Natural Selection has lead to two strategies for species: r - strategists and K - strategists

22. r – Strategists (rate) K
Opportunists – reproduce and disperse rapidly if conditions are favorable or after a disturbance
Spend most of their time in exponential growth
Maximize reproductive life
Minimum life expectancy
Populations crash as new species move in and outcompete K

23. K - Strategists Maintain population at carrying capacity (K)
Thrive with fairly stable environmental conditions
Maximize lifespan K

24. R Strategists

25. R-strategists Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapted to unstable climate and environmental conditions
High population growth rate – (r)
Population size fluctuates wildly above and below carrying capacity – (K)
Generalist niche
Low ability to compete
Early successional species

26. K- Strategist Fewer, larger offspring
High parental care and protection of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental conditions
Lower population growth rate (r)
Population size fairly stable and usually close to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species