1. POPULATION ECOLOGY

2. Key Features of Populations
1. Size - number of individuals in a population
- determines ability of population to survive
small populations: most likely to become extinct
- more inbreeding increases bad alleles
and reduces fitness
2. Density - number of individuals /area
small populations: individuals rarely meet and reproduce due to low density

3. Dispersion - pattern of spacing between individuals
uniform: evenly spaced intervals, antagonistic
interactions
random: unpredictable spacing, not common
clumped: bunched in clusters, most common

4. Populations are affected by:
growth rate
- available resources
predators and disease

5. Population Density
Number of individuals of a particular species per unit area or volume
ex: number of alligators/km2 of swamp number of bacteria/cm2 of agar plate
number of earthworms/cc of soil
If there are 1000 beech trees in a km2 forest, what is the population density of the beech trees?
population density = individuals
unit area

6. Tracking Population Growth
Population Age Structure Pyramid
X-axis : population
Y axis: age
males on left
females on right
shows the distribution of various age groups in a human population
forms the shape of a pyramid when the region is healthy
indication of the reproductive capabilities and likelihood of the continuation of a species

7. Limits to Population Growth
Carrying capacity (K)
maximum number of organisms in a population that an environment can maintain or “carry” without a net increase or decrease

8. Tracking Survival Rates
Survivorship Curve: # individuals alive at each age
Type I High low death rate early in life
Type II Steady constant death rate over lifespan
Type III Low high death rate early in life

9. Factors That Affect Population Growth Limiting Factor: a condition that restricts population growth
Density Independent Factor factors that limit population growth that are unrelated to population density ex: weather events, fires, floods, major changes in a habitat
Density Dependant Factor factor that limits a population more as population density increases ex: food, water, predation, space, disease, waste accumulation, competition

10. MODELS IN POPULATION GROWTH
Demography: the study of vital statistics that affect population size
Population Model: hypothetical population which exhibits key characteristics of a real population
- allows demographers to predict outcomes that might occur in a real population

11. MODELS IN POPULATION GROWTH
1. Stage I model
growth rate
- birth rate vs death rate
expressed as:
# births and deaths/ 1000 people/ year
2 configurations for a stable human population (zero population growth):
- High birth / high death
- Low birth / low death

12. Growth Rate Calculation
Calculating change in population size
dN/dt = B - D
(change in population) = (births) - (deaths)
N - population size
t - time

13. Stage II model (exponential)
- population size vs time
- J shaped curve
- ideal conditions
- population grows very rapidly
- calculation to predict the number of individuals added to a population
- Carrying Capacity (k) – pop. size an environment can sustain

14. Exponential Growth Equation
dN/dt = change in population r = growth rate of pop. N = population size

15. Stage III model (logistical)
- S shaped - incorporates carrying capacity (K)
- exponential growth limited by a density dependant factor
(food and water)
- refers to ability of population to solve day to day problems of living
Size below K: rapid growth rate
Size near K: death rates rise, births
decline growth of population slows
At K: birth = death
population stops growing
- most realistic model in nature

16. Logistic Growth Equation
dN/dt = change in population r = growth rate of pop. N = population size K = carrying capacity

18. Life History Strategies
Traits that affect an organism’s schedule
of reproduction and survival
3 Variables:
Age of sexual maturation
How often organism reproduces
# offspring during each event
Note: These traits are evolutionary outcomes, not conscious decisions by organisms

19. Reproductive Strategies
Semelparity
- single reproductive episode before death
- many offspring produced at once
- less stable environments
Iteroparity
- multiple reproductive cycles over the course of its lifetime
- few, but large offspring
- more stable environments

20. Reproductive Strategies
r strategists
- maximize reproductive success
- rapidly growing populations
- large population size
- density independent factors
- in good conditions, grow exponentially
- in poor conditions, population size drops quickly
short life span, reproduce early, many offspring
ex: insects, plants, bacteria
k strategists
- population density near K
- grow slowly
- density dependant factors
- small population size
- long life span, few young, slow maturation, repro. late in life, take care of young
ex: humans, whales , redwoods

21. Population Growth Cycles
Boom and Bust Cycle
- direct relationship between predator and prey
- causes fluctuations in populations in stable ecosystems
ex: increases in hare population are followed closely by increases in lynx population

22. Study for the test !