Lecture 20 Population Growth and Demography Flashcards
Population Ecology
Population ecology studies abundance and distribution of a populations over time
- Population parameters are
influenced by both biotic and
abiotic factors - Can describe populations in
terms of: - Dispersion
- Size and Density
- Demographics
Population
organisms of the
same species in a location
Population Dispersion
describes the pattern of individuals in space
slide 6
Population Size & Density
- Population size and density
tell us about the stability of a
population! - Methods of estimation:
- Sample (Census) Plots
- Mark Recapture
- Population Genetics
Population Density
describes the number of
individuals in a defined area
Measuring Populations: Sample Plots
- Also known as ecological census or quadrats
- Count every individual in a randomly selected area (population density)
- Extrapolate to get total population size
- Most effective for evenly spaced or sedentary organisms
slide 8-10
Measuring Populations: Mark Recapture
- Assumes marked and unmarked individuals have
equal probability of sampling - Assumes no birth, death, immigration, emigration
during resampling - Useful for mobile
organisms but more
challenging for
hard to find species
slide 11-16
Measuring Populations: DNA Approaches
Genetic Profiling
(DNAfingerprinting)
Individuals are identified by
unique DNA sequences
Population Genetics
* Genetic diversity is correlated with
population size
* Total population size can be misleading
because not everyone reproduces!
* Effective population size (number of
breeding individuals in a population)
can be calculated from DNA
slide 17-18
Demography
- Demography is the study of populations and how they change over time
- Age & Sex structure provides insight into future population growth trends
- Life tables summarize survival and reproductive rates of individuals
- Survivorship curves represent age-specific mortality (proportion of a
cohort alive at each age)
Age & Sex Structure
- Age structure describes distribution
of individuals at different ages in a
population - “Snapshot” of a population in time
- Gives insight into growth (or
decline) of a population - Can be used to predict how likely a
population is to grow or shrink
slide 20-21
Life Tables
- Life tables summarize mortality and survival in a population by age-group
- They are constructed by following a cohort (age group) through time or
analysis of dead per age group over time from a random sample (time-specific
life table)
This same concept is used in medicine
slide 22-23
Survivorship Curves
slide 24-28
Life History
- Life History describes traits that
affect reproduction and survival - Natural selection shapes life history
because resources are limited - Trade-offs between survival and
reproduction over lifetime of parent
(when and how often to reproduce) - These tradeoffs determine fecundity
(an organism’s reproductive capacity) - Reproductive output
- Reproductive onset
- Reproductive frequency
slide 29-30
Reproductive Onset
- Age at maturity / onset of
reproduction - Early reproduction lowers
risk of dying without
producing offspring
(but at the expense of their
growth and health) - Later reproduction may
produce more offspring that
are more likely to survive
(but at the risk of not
surviving to reproduce at
all!) - Linked to lifespan: short-lived species often
reproduce early
long-lived species more likely to delay
slide 31
Reproductive Frequency
- How many times an organism reproduces over its lifetime
- Reproduction is energetically costly!
- Frequency of reproduction reflects resource availability and cost to parents
slide 32
