Populations and Ecosystems

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ECOSYSTEM: All the organisms living in a certain area and non-living conditions found there.

ABIOTIC: Non-living features of an ecosystem.

BIOTIC: Living features of an ecosystem

HABITAT: Place where an organism lives within an ecosystem, within this each species has its own niche

NICHE: Role of a species within a habitat. The niche a species occupies include; biotic interactions and abiotic interactions -every species has its own niche and it can only be occupied by own species

If 2 species try to occupy the same niche, they will compete, until only one is left.


They increase the chance of survival and reproduction, by passing on alleles these adaptations become more commone --> Natural Selection. These can be Physiological, Behavoral or Anatomical

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Variations in Population size

POPULATION: All organisms of one species in a habitat.

ABIOTIC FACTORS: e.g. amount of light, water or space avaliable.  -When abiotic conditions are ideal for a species, organisms can grow fast and reproduce successfully.    -When abiotic conditions aren't ideal for a species, organisms can't grow as fast or reproduce as successfully.

BIOTIC FACTORS: Interspecific competition: -Organisms of different species compete with each other for the same resources.   -Can mean resources avaliable to both are reduced ---> Both populations are limited --> less energy for growth and reproduction, so theres a lower population size.        -If one species is better adapted the other species is likely to be out-competed. Intraspecific: Organisms of the same species compete for the same resources. It can cause a cyclic change in popuation size (Population increase, then decrease then increase again)   -Because population increases when there is alot of resources ---> more organisms competeing for the same space and food ---> eventually food and space become limiting ---> population begins to decline and the cycle begins again.

Predation: -Organisms kill and eat eachother ---> populations of predatiors and prey are linked. As prey population increases, more food so predator population increases. more prey eaten so population decreases...  -Relationship more complicted, other factors involved.

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Mark & Release

Collection: Pitfall Traps: containers sunk in ground, top partially openn, insects fall in, hidden from predators. Also Pooters.

Mark-Release-Recapture    -Used to measure the abundance of mobile species.                                 1. Capture the sample of species, using an appropriate technique and then count the sample.            2.Mark them in a harmless way.                                                                                                             3.Release them back into their habitat                                                                                                  4.Wait a week, take a second sample from the sample population, Count how many are in this second sample.       5. Use this equation to estimate population size:       

                                         Number caught in 1st sample       x      Number caught in 2nd sample

Total Population Size=                                        Number marked in 2nd sample

Accuracy depends on wether the marked sample has enough time to mix back in with population.

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Samples must be random to avoid bias.  Repeats should also be taken for a reliable result.

Random number generator used when investigation populations in a field.  1. Divide the field into a grid  2. using random number generator to find coordinates, that is where you take your sample.

Running Means; take enough samples for a reliable result ---> use a running mean.


QUADRATS: -Placed on ground at area of study.  Species frequency or number of individuals of each species is recorded in each quadrat.   % cover can also be measured by counting how much of the quadrat is covered.

TRANSECTS: Finds out how plants are distributed across an area.

Line; tape measure along a transect, species that touch the tape are measured.

Belt; Quadrats placed next to each other along transect to work out species frequency and % cover.

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Human Populations

Birth Rate

Death Rate

Population Growth (pre 1000 people per year)= BR - DR

Demographic Transition Model

Population Pyramids ----> Male and Females at different age groups within a population.

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