3.7.4 Populations in Ecosystems

ecosystem

made up of organisms living in a community (biotic) + the non-living components in environment (abiotic)

population

a group of interbreeding organisms of one species in a particular place at a particular time

community

all the populations of different species living and interacting in the same habitat

habitat + microhabitat

-place where a community of organisms normally live in an ecosystem

-within each there are smaller units each with their own microclimate

niche

how an organism fits/adapts into the environment, the role of a species within its habitat e.g. biotic + abiotic interactions

-competitive exclusion principle = no two species occupy the same niche

carrying capacity

the maximum size of a population that an ecosystem can sustainably support

-affected by abiotic + biotic factors

abiotic factors

-temperature + pH = enzymes

-light = photosynthesis

-water + humidity = transpiration

biotic factors -competition

2 types: -intraspecific = when individuals of the same species compete e.g. mates, availability of resources - more resources = larger population

-interspecific = when individuals of the different species compete e.g. food, space - initially occupy the same niche but over time one’s population size will grow while the other shrinks

biotic factors -predation

effect of predator-prey relationship cycle

-prey is eaten by predator so predator population increases + prey population decreases

-fewer prey means increased competition for food so predator population decreases

-fewer predators means more prey survive so prey population increases + repeats

types of quadrat

-frame quadrat = place in different locations within the area being studied, abundance of each species then recorded

-point quadrat = pins in each hole at set intervals, each species that touches pin is recorded

measuring abundance

-number of individuals in a species in a given area

can measure by:
-frequency = likelihood of particular species in a quadrat
-percentage cover = estimate of the area within a quadrat that a particular plant species covers

random sampling method

1) mark out grid of known area

2) random number generator for coordinates

3) place quadrat at coordinates

4) measure abiotic/biotic factors

5) repeats + large sample size = representative

systematic sampling method

quadrats placed at set intervals along a belt transect

mark-release-recapture method

1) a set of organisms caught and then marked + then released back
2) after a period of time, the community is revisited + another sample is captured

3) the number of marked individuals is counted

mark-release-recapture equation

estimated population size =

total number of individuals in first sample x total number of individuals in second sample / number of marked individuals recaptured

mark-release-recapture assumptions

-proportion of marked to unmarked individuals in second sample is the same as proportion of marked to unmarked individuals in population as a whole

-few deaths and births

-method of marking is not toxic or makes individuals more prone to predation

-mark/label is not lost or rubbed off