Population Growth and Regulation II Flashcards
Exponential Growth
Continuous growth with “unlimited” resources without limitation
Geometric Growth
Seasonal growth with “unlimited resources”
Logistic Growth
“Limited resources”. Intraspecific competition.
Modeling Population Age Structure
A solution to birth and death rates being constant and not varying with age. Influenced by the proportions of individuals in different age classes. Also, in size and life history classes. Age structure pyramids
Life Table Analysis
Growth in a structured population
Life Table Analysis Terminology
x=age
nx=number of individuals surviving to age x
sx=age-specific survival
bx=age-specific fecundity, births
Step One Life Table Analysis
Sum up age classes to get No, the initial female population size.
Step Two Life Table Analysis
Multiply number of females in EACH age class by sx, age specific survival rate. This gives number surviving to next age class. (remember to put this is next level)
Step Three Life Table Analysis
Calculate new sum of survivors
Step Four Life Table Analysis
Calculate offspring per age class. Multiply the per capita fecundity (bx) but each number of survivors per age class. This gives the number of new offspring for each age class.
Step Five Life Table Analysis
Add up offspring.
Step Six Life Table Analysis
Calculate new age classes and population. Transfer total newborns in top row, and individual survivor classes in other rows. Add this total up. In reality the answer will be the same as just adding survivors + offspring.
If asked how many total individuals in new population and your original table analyses gave you 112, what would your answer be?
224, because chart only looks at females and usually males and females are about 50-50
After many generations of life table analysis…
The population will grow geometrically at a stable rate of increase. The population will reach a stable age distribution.
After initial fluctuations, per age class may go up or down but … stays the same
proportion
Survivorship
The probability of surviving from birth to any later age class. Denoted Ix.
Survivorship curves
Looks at chances of mortality throughout life
Type 1 Survivorship Curve
High mortality later in life
Type 2 Survivorship Curve
Constant mortality
Type 3 Survivorship Curve
High Mortality Early in Life
Calculating Survivorship (Ix)
First age class is always 1. Multiply survivorship by survival rate. Fill in the product in new row of survivorship column.
Net Reproductive Rate (Ro)
Average number of female offspring per female over her lifetime.
Calculating Net Reproductive Rate (Ro)
Multiply survivorship by fecundity rate.
What can you do with individuals post reproduction?
Add to new nx in new life table
Cohort Approach
Follow a group of same aged individuals (cohort) throughout lives. **Easy to apply to organisms that are sessile (dont move much) or easily tracked throughout lives. Results can be confounded with environmental change.
Static Approach
All individuals (of all ages) at a particular point in time. “snapshot”. Can be applied to more mobile and long lived organisms. Must identify age though. Multiple samples advised because of potential unusual age distribution and environmental conditions.
