Populations A2 Flashcards
define community
all populations of different organisms living and interacting in a particular place at the same time
define habitat
place where organism usually lives
define population
group of individuals of the same species occupying the same habitat at the same time
define niche
all conditions and resources needed for an organism to survive and reproduce
how an organism fits into the environment
governed by abiotic and biotic conditions
define ecosystem
all the interacting biotic and abiotic features in a specific environment
abiotic factors
non-living features of an environment
examples of abiotic factors
temperature, pH, light
define biotic factors
living features of an environment
why use random sampling
to avoid bias
how to use a quadrat
set up grid
choose random coordinates using random number generator
measure percentage cover or species frequency
place a large number of quadrats on coordinates and calculate a mean per quadrat
times mean number of plants per quadrat by number of quadrats in the area
what does percentage cover measure
abundance
when is percentage cover useful
when counting number of individuals is impractical e.g too many, hard to distinguish individuals so finds an estimate
cons of quadrats
underestimates small organisms and overestimates large ones
define species frequency
number of individuals of each species in a quadrat
why use a large number of quadrats
keep going until the mean is stable and there’s enough for a statistical test
why is deforestation/the removal of hedgerow bad
fewer species
less habitats
fewer food sources
increase in CO2 in the air since less photosynthesis
why do farmers benefit from the removal of hedgerow
more predators for pests able to get in
when to use a transect
when there is a transition in the environment
how to make a transect
place quadrats at a regular interval along the line
count plants/percentage cover
use several quadrats
may not be representative of area
how to do mark release recapture
capture smaple, mark and release
appropriate method of marking (doesn’t harm/rub off)
take a second sample and count marked organisms
population = number in sample 1 x number in sample 2/number marked in sample 2
assumptions of mark release recapture
population must remain stable no emigration/immigration no loss to predation marking does not affect survival birth rate and death rate equal all belong to one population
define carrying capacity
ecosystem can only support populations of a specific size
affected by abiotic factors, inter and intraspecific competition and predation
define intraspecific competition
between members of same species
define interspecific competition
between members of different species
when does interspecific competition stop
when one species outcompetes the other for things like food space light breeding territory
why are predator prey relationships difficult to work out
they are hard to show in a lab
data from natural environments should be taken with caution
