T15 - Population ecology Flashcards
what is population dynamics?
The study of how comlex interactions between biotic and abiotic factors influence variations in population size
Biotic factors such as avail of N2 source, temperature, availability of light
How do we estimate population size using the mark-recapture method?
- sample s indivs
- mark all s indivs
- release all s indivs back
- resample r indivs
- count the number of m of resampled marked indivs
- estimate the population size using m/r=s/N
What are the assumptions of the mark-recapture method?
- Marked and unmarked indivs have the same probability of being sampled (shy = you might not be able to cath them, bold = higher chance of being sampled)
- the marking of indivs does not affect the probability of being resampled (experience) - if you give the sample organisms a treat before you release them they may wait around until you resample so they can get another treat, or you may have traumatized them and they stay away so they dont experience being sampled again
- the marked indivs have mixed completely back into the population
- no indivs are born, die immigrate and emigrate during the resampling interval
What is population density? What is the chage in population size formula?
The number of individuals per unit of area or volume
Can increase with immigration and birth
Can decrease with emigration and deaths
∆population size = births + immigrants - deaths - emigrants
What is the survivorship curse? What are the different types?
The proportion of indivs in a cohort that are still alive at each age
Type 1; low death rate of juveniles and adults followed by rapid increase in old age groups (youths are more nourished because less offspring are produced)
Type 2; constant death rate (seen on a log scale) mortality is same for juveniles, adults and old age groups
Type 3; high mortality rate for the young followed by a flattening of the death rate in adults (many invertebrates that do not provide plentiful nourishment for the young because of such a large amount of offspring)
what are the different components (variables) in exponential population growth ?
∆N/∆t = (r∆t)N ->long term growth rate over generations
dN/dt = rN -> short term growth rate foreach instant in time
(r∆t) = indiv growth rate contribution to the population growth
r = per capita change in population size at each instant in time
What is exponential population growth?
Growth of a population in ideal, unlimited environment
dN/dt=rN
r is constant but the number of indivs added to the entire population each generation increases
very large areas, low predation, no competition = exponential growth
What is logistic population growth?
Because resources are finite (not unlimited), the population grows exponentially until it reaches an upper limit
What is the carrying capacity (K)?
The maximum population size that a particular environment can sustain
K can vary depending on the abundance of limiting resources
using K we can rewrite the exponential growth equation;
dN/dt = rN[(K-N)/K]
What does the logistic model assume?
- populations can adjust instantaneously to the increase in density (they might overshoot their carrying capacity)
- the environment stays the same (predators can regulate the population size)
What is r selection?
Selection that favours traits at low densities for a high reproductive success; density independent selection (low competition)
- matures rapidly
- early age of first reproduction
- short lifespan
- large number of offspring
- few reproductive events
- high mortality rate
- low offspring survival rate
- minimal parental care/investment
r strategy = increase the growth rate of the population with low density
What is K selection?
Selection that favours traits at high densities, at or near the carrying capacity; density dependent selection (high competition)
- matures more slowly
- late age of first reproduction
- longer lifespan
- fewer offspring at a time
- more reproductive events
- low mortality rate
- high offspring survival rate
- high parental investment
K strategy = increase survival rate in an environment with many competitors
