Chapter 9: Population Structure & Distribution Flashcards
What are the times specific assumptions of life tables?
- Each age class was sampled in proportion to the number in population
- Age specific mortality rates (birth rates) are constant
Tables displaying age specific mortality and survival
Life tables
Number of births per female of age group x
Birth rate
What does the net reproductive rate show?
Whether or not the females will replace themselves in the environment
Attained when proportion of each age group in the population remain the same year after year (even though Nt increases)
Stable age distribution
What does λ display?
Estimated population growth rate
Random changes in birth and death rates from year to year
Demographic stochasticity
Random change in environment
Natural disasters
Directly influence birth and death rates
Can cause local extinction
Environmental stochasticity
What are the five factors that can cause population extinction?
Extreme environmental events Severe shortage of resources Intro of novel competitor, predator, or disease Habitat loss Small population size
Decline in survival and reproduction at low population densities
Allee effect
What does r represent?
Instantaneous per capita rate of growth
What does the model of exponential growth predict?
The rate of population change through time
A group of individuals born in the same period of time
Cohort
Constructs a cohort from individuals born over several time periods instead of just one
Dynamic composite life table
Constructed by sampling the population in some manner to obtain a distribution of age classes during a specific time period
Time specific life table
When individuals tend to live out their physiological life span
Survival rate is hi rough out the life span followed by a heavy mortality at the end
Examples include humans and other mammals
Type I survivorship curve
Survival rates do no vary with age
Examples include adult birds, rodents, reptiles
Type II survivorship curve
Mortality rates are extremely high early in life
Examples include oysters, fish, invertebrates, and many plants
Type III survivorship curve
