chapter 51 - population ecology Flashcards
describe and name variances in population distribution
distributions may be
- random (position independent from others)
- clumped (patchy habitat or social organisms)
- uniform (if they have negative interactions that space them evenly)
different ways populations can be described
- density
- distribution
- range
- metapopulation
define metapopulation
- a population of populations connected by migration
- more species being forced into a metapopulation as habitats fragment from human activities
how do you measure population distributions?
different methods for diff species
for sedentary species
- counting along TRANSECTS (lines)
- counting in QUADRATS (plots of known size)
for mobile species
- MARK-RECAPTURE method
- catch, tag, release (to mix with unmarked), catch again (% of marked recorded)
- solve for (marked/total) = (marked recaptured/2nd total capture)
describe mark recapture method and the assumptions required for it
to measure population distribution in mobile populations
- catch, tag, release (to mix with unmarked), catch again (% of marked recorded)
- solve for (marked/total) = (marked recaptured/2nd total capture)
ASSUMPTIONS
- individuals are moving out of study area
- individuals mix between captures
- no bias in who’s caught in each recapture
- individuals don’t learn to avoid traps
- individuals don’t change behaviour during study
what factors does population size depend on?
DEMOGRAPHY - structure and change
basically gains and losses
- births
- deaths
- immigration
- emmigration
demography: how do you predict future population size?
- AGE STRUCTURE: # of individuals @ each age
- # likely to survive to following year
- # of offspring produced
- # of individuals of different ages that immigrate/emmigrate each generation
- GENERATION LENGTH: average time between mother’s first offspring and daughter’s.
what is a life table? why/how do we use it?
determine whether populations in different environments vary in basic demographic features
- shows probability that an individual will survive + reproduce at a given time in its life
- used to understand population dynamics (increases, decreases, stagnation)
- track short-lived species for their whole lives (hard, but lots of info)
- track long-lived species by taking ‘snapshot’ of population’s age structure @ given time (easier, less data)
define age class and cohort
age class: individuals of a specific age
cohort: group of individuals of the same age that can be followed through time
define survivorship and why we use it
proportion of offspring that survive, on average, to a particular age
survivorship curve (# survivors vs age): used to make comparisons among populations
- 3 lines
- high to low, steady and low to high survivorship
net reproductive rate
= sum of all ages (survivorship @ age x * fecundity @age x)
‘net’ accounts for all the losses
life-history tradeoffs
- high fecundity + low survivorship
- low fecundity + high survivorship
population growth equations
∆N/∆t = births - deaths + immigrant - emigrants
where N is population size and t is time
IF NO IMMIGRATION/EMIGRATION
∆N/∆t = (births - deaths)N
per capita rate of increase (r)
difference between birthrate and death rate per individual
- usually in terms of females
- when r doesn’t change over time, population increases @ accelerating rate
- r @ max when b @ max and d @ min (intrinsic rate of increase, rmax)
equation for exponential change in population size over time
∆N/∆t =rN
- independant of density
