1. Population Ecology

2. Population Dynamics and Carrying Capacity
study of how populations change in size, density, and age distribution
populations respond to their environment
change according to distribution

3. Dynamics of Natural Populations
Population growth curves
Biotic potential - the ability to increase population numbers
Environmental resistance - the combination of all the biotic and abiotic factors that limit a population’s increase.
Carrying capacity – the upper limit to the population of any particular organism that an ecosystem can support

4. Density Dependence And Critical Number
Environmental resistance factors can be density dependent.
If population density increases, environmental resistance becomes more intense and causes in increase in mortality.
If population density decreases, environmental resistance lessens, allowing the population to recover.
Food, Water, Disease, Predation
Environmental factors that cause mortality can be density independent
A sudden deep freeze in spring
A fire that may kill all small mammals
Natural Disasters

5. Biotic Potential and Environmental Resistance
Lack of food or nutrients
Lack of water
Lack of suitable habitat
Adverse weather
Predators
Disease
Parasites
Competitors
Biotic Potential
Reproductive rate
Ability to migrate (animals) or disperse (seeds)
Ability to invade new habitats
Defense mechanisms
Ability to cope with adverse conditions

7. Exponential and Logistic Growth
- Rapid exp. growth followed by steady dec. in pop. Growth w/time until pop. Size levels off
EXPONENTIAL GROWTH
Population w/few resource limitations; grows at a fixed rate

9. Natural Population Curves

10. STABLE
pop. Size fluctuates above or below its carrying capacity
Stable population size
EX: undisturbed tropical rain forests
IRRUPTIVE
pop. Growth occasionally explodes to a high peak then crashes to stable low level
EX: Algae, insects
CYCLIC
Fluctuations occur in cycles over a regular time period
EX: Lynx & snowshoe hare
IRREGULAR
No recurring pattern in changes of population size

11. The Role of Predation in Controlling Population Size
Top-down control
- lynx preying on hares periodically reduce the hare pop.
Bottom-up control
- the hare pop. may cause changes in lynx pop.

12. Species Interactions Niche Competition Symbiotic Relationships
Interspecific
Intraspecific
Symbiotic Relationships
Mutualism
Parastism
Commensalism

13. How do Species Reproduce
ASEXUAL REPRODUCTION
all offspring are exact genetic copies of a single parent
Common in single celled species (bacteria)
Each cell divides to produce 2 identical cells
SEXUAL REPRODUCTION
Organisms produce offspring by combining sex cells or gametes from both parents
Produces offspring with combination of genetic traits from each parent
Provides greater genetic diversity in offspring
DISADVANTAGES
Males do not give birth
Increased chance of genetic errors and defects
Courtship & mating rituals consume time & energy and transmit diseases

14. Reproductive Patterns and Survival
OBJ 9.10
Reproductive Patterns and Survival
r-selected species vs. K-selected species
Fig p. 170

15. Survivorship Curves
Shows the % of members in a pop. Surviving at different ages
LATE LOSS
High survivorship to certain age; then high mortality
EX: elephants, rhinos, humans
CONSTANT LOSS
Fairly constant death rate at all ages
EX: songbirds
EARLY LOSS
Survivorship is low early in life
EX: annual plants, bony fish sp.

16. Age Structure Stages PREREPRODUCTIVE AGE
- Not mature enough to reproduce
REPRODUCTIVE AGE
- Capable of reproducing
POSTREPRODUCTIVE AGE
- too old to reproduce

17. Factors Governing Changes in Population Size
Four variables
births, deaths, immigration and emigration
Population Change = (births + immigration) – (deaths + emigration)
Crude Birth Rate = CBR = (births/population)*1000
Crude Death Rate = CDR = (deaths/population) *1000
Immigration and emigration are calculated the same way
Crude Growth Rate = CBR = CDR
Population Growth Rate = CGR * 100

18. Calculating Population Growth
N0 is the starting population
N is the population
after a certain time, t ,
has elapsed,
r is the rate of natural increase expressed as a percentage (birth rate - death rate) and
e is the constant (the base of natural logarithms)

19. Growth Curves – Two Types J or S
Exponential growth results in population explosion
Rule of 70
to find the doubling time of a quantity growing at a given annual percentage rate, divide the percentage number into 70 to obtain the approximate number of years required to double.
For example, at a 10% annual growth rate, doubling time is 70 / 10 = 7 years.
This results in a J curve graph.