Do population or individuals evolve?
populations
define a population
- a group of individuals of a single species living in the same general area
- rely on the same resources
- influenced by similar environmental factors
- interact with one another
- have demographic and genetic cohesiveness
why would it be more difficult to census how many individuals a plant population includes sometimes?
plants have a dormant stage as seeds in the ground
define the mark and recapture method
- capture individuals, mark them, release them, then later capture another sample
- proportion of marked individuals that you recapture will indicate the size of the population
- must ensure that the method does not cause mortality, as it will mess up your results
Describe how people are estimating polar bear populations in Canada.
- genetically indentifying individuals who leave feces or hair behind
- it is a genetic mark and recapture method
- but they don’t have to capture anything
- indentify and re indentify indivduals by thier DNA
describe what demographic and genetic cohesiveness means.
- demographic cohesiveness: shared environment and resources
- genetic cohesiveness: individuals breeding with one another
how can a population grow or shrink, in a “measureable” way?
how many are born, die, leave (emmigrate), join (immigrate)
why are chickadees easy to observe when defining populations?
do not migrate
describe what a life table is.
- age (x)
- survival (Ix)
- births (bx)
- can calculate important population parameters
- Ro: reproductive rate (average number of offspring produced per female) (births and deaths)
- Generation time: products of age, times specific survival times and age specific birth, add them ip, and divide it by the reproductive rate, the average interval between the birth of an individual and the birth of its offspring.
what does a shorter generation time mean?
shorter generation time has the potential to grow more quickly
What is a survival curve? define each type of the survival curves.
- repersents the interaction between the species and the environment a species lives in, and the species’ evolved life history traits, which ultimately turn into natural selection
- Type I: invest heavily in the offspring, which results in high survival during early part of their life
- Type II: survivorship maintains relatively constant
- Type III: produce many tiny offspring, and have low prospects for survival
what is investment in offspring as a trait?
evolves in relation to the timing of mortality in the environment
when does exponential growth occur for a population?
- when a population of a species is growing without limits
describe the logistic growth model
- as population size increases, the rate of growth slowss down to one, and population plateaus at the carry capacity (zero growth)
- when population size if very small, this term becomes equal to one, and the population grows near exponentially
what could happen in a population where individuals have a hard time finding mates when they occur at very low density?
- population may not grow very exponentially when small as predicted by the logistic growth model, as it doesn’t work for them
- important when you are a conservation biologst trying to enhance the growth of an endangered species population
what is the maximum productivity of a population in terms of new individuals?
when the population size is equal to exactly 1/2 of the carrying capacity
What does keeping the harvesting population so that the population is half of the carrying capacity cause?
Maximum sustainable yield
(MSY)
how would a death and birth rate change or not change with density independent or density dependent factors?
- density independent: does not change with poopulation density
- density dependent: does change with poopulation density
what is population dynamics?
fluctuations in size from year to year for populations
describe the cause and effect relation between predator and prey, with the lynx and the hare example.
- the population cycle of the predator, the lynx, lags behind the population size of the prey, the hare
- this might suggest that cycles are driven by predator and prey interactions
- developed two hypothesis: food shortage and predation hypothesis
- food shortage: the hare cycle is determined by a cycle in the availbility of food, so the lynx follows the abundance of hares
- predation hypothesis: hare cycle is driven by predation,
what is meta population model of population dynamics
- a species in a habitat patch will go extinct there
- that vacant patch will be re colonized by individuals from a differently occupied habitat patch
what are some insights that can be gathered from the meta population model of population dynamics?
- it is essential for species persistance that a species can move from an occupied patch to an unoccupied, but suitable patch
- species will only occupy some fraction of the availble habitate patches at any given time, but it needs unoccupied but suitable patches to persist on the landscape
how are wildlife corridors helpful?
- maintain gene flor
- ensure viable meta population dynamics
what are life history traits?
- characeristics of a species that directly affect population dynamics
- traits that are also likely to be the subject to quite strong natural selection
*
