7.4 - Populations in ecosystems Flashcards
Define habitat
area where 1 or more organisms live
Define carrying capacity
certain size of population of a species which an ecosystem can support
Why do population sizes vary?
- effect of abiotic factors
- interactions between organisms i.e interspecific and intraspecific competition, predation
Name the 2 ways the size of a population can be estimated
slow moving/non-motile organisms: randomly placed quadrats/quadrats along belt transect
motile organisms: mark-release-recapture
How can species abundance be measured for slow-moving/motile organisms?
% cover or frequency
Describe how you could estimate a population size of a non-motile species
- use a grid
- use a random number generator to obtain coordinates
using % cover
- divide total % by number of quadrats
using frequency
- count frequency of organisms from species in a quadrat
- use a large sample size and calculate mean
total population size = mean no. organisms of that species per quadrant x number of quadrats
Name the assumptions made when using the mark-release-recapture method
- marked individuals from first capture distribute randomly
- no marks rub off
- mark is not toxic and does not reduce chance of survival
- few, if any, births or deaths in population
- no immigration in or emigration out of population
- proportion of marked to unmarked individuals in second sample is representative of individuals in population as a whole
Describe the procedure of mark-release-recapture method
- collect sample of known number, mark (non-harmful) and release in same area they were caught
- allow organisms to randomly distribute before collecting second sample of known number and record number of these that are marked
estimated population size = no. in 1st sample x no. in 2nd sample /no. marked in 2nd sample
Give 3 features of a climax community
- same species present over long time
- abiotic factors constant
- populations are stable
Which abiotic factors affect population growth?
- temperature
- light intensity
- pH
- water + humidity
Name factors that individuals of the same species compete for (most apply to organisms of other species)
- food sources
- water
- mates
- shelter
- minerals
- light
When does interspecific competition most commonly occur?
when 2 species occupy the same niche
Define predation
when one species is caught by another species
Describe the predator-prey relationship
- when prey is eaten by predator, prey population decreases
- so predator population increases, but this means more prey is consumed
- so prey population decreasing means increased competition for prey between predators
- lack of food for predators = predator population decreases so less prey eaten
- allows prey population to recover and cycle occurs over in an oscillating manner
Define succession
the change of one community of organisms into the other
Describe and explain how primary succession occurs
- colonisation by pioneer species, adapted to survive in harsh conditions
- it changes the environment (organisms die so they are decomposed by microorganisms which adds humus, leading to soil formation)
- makes environment less hostile for new species with different adaptations (could cause environment to become less suitable for previous species)
- over time soil becomes more mineral rich
- increase in biodiversity
- climax community established
What is a climax community?
a self-sustaining and stable community of organisms
How could the formation of a climax community be stopped?
controlled burning of land
Describe how secondary succession occurs
- previously colonised area where an existing community has been cleared e.g after forest fires
- soil layer already present so succession begins at later stage
Define conservation
- human management of the Earth’s resources
- typically involves managing succession
Define ecosystem
community and non-living components of its environment
- dynamic system
- vary in size from very small to very large
Define community
populations of different species
