3.7.4 Populations In Ecosystems

what is a population?

a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed

what is a habitat?

part of an ecosystem in which particular organisms live

what is a community?

all the populations of different species in the same area at the same time

what is a niche?

an organisms role within an ecosystem, including position in a food web and habitat

what is carrying capacity?

the maximum population size an ecosystem can support

abiotic meaning

non-living conditions of an ecosystem

the less harsh the abiotic factors, the larger the population

examples of abiotic factors

-CO2 concentration

-light intensity

-pH

-soil conditions (acidity eg)

how do adaptations to abiotic factors develop?

natural selection

biotic meaning

the living components of an ecosystem interacting

examples of biotic factors

predation

competition (inter / intra)

disease

what is intraspecific competition?

competition between members of the same species

links to courtship behaviour -> fitter individuals = more energy = better courtship + easier to attract mates

what is interspecific competition?

competition between different species

why do we sample?

it is more time efficient and if implemented correctly can be more accurate

what is the criteria for accurate sampling?

1. random sampling to eliminate bias

2.line transects to examine change of distance

3.large number of samples (30+)

the process of random sampling for uniform distribution

1.line two tape measures at right angles to create a gridded area

2.use a random number generator to generate two coordinates

3.place quadrats at coordinates and collect data (eg - density / % cover / frequency)

4.repeat at least 30 times and calculate a mean

how to use line transects for uneven distribution

used to estimate population size when they are unevenly distributed

1.place tape measures at a right angle to shore line

2.place quadrats every 5 metres

3.collect data (density / % cover / frequency)

4.repeat by placing another 30 transects along the beach at right angles to the shore

what are the two types of transects?

1.belt transect = quadrat is placed at every position along a tape measure

2.interrupted transect = quadrat is placed at uniform intervals along a tape measure (eg 5 metres)

what methods can be used to estimate abundance of a species?

1. local frequency = % of squares in quadrat with species present

2. density = the number of one species in a given area

3. percentage cover = the proportion of ground occupied by the species

local frequency pros and cons

+ Quick method to sample a large area

+ Useful if too difficult to identify individual organism (e.g. moss) or if too many to count (e.g• grass)

- Poor accuracy as doesn't consider overlapping plants or the size of the

density pros and cons

+ More accurate if you can easily distinguish an individual plant, and there are not too many to count.

E.g. Daisies

+ Can be used to estimate species richness (count the number of difference species present)

- More time consuming

percentage cover pros and cons

+ Quicker method than density

+ Useful if too difficult to identify individual organism (e.g. moss) or if too many to count (e.g. grass)

- Subjective limiting accuracy

- Doesn't consider overlapping plants or the size of the plant.

what is the mark-release-recapture method?

a technique used to estimate the size of populations of motile (moving) animals

what is the method for mark-release-recapture?

I. An initial sample of the population in question is captured.

2. These individuals are then marked and then released back into the wild, and a the number caught is recorded. The mark must be all weather resistant.

3. These marked individuals are released and are left for a period of time to allow them to randomly dispersed throughout the habitat.

4. Then a second sample is captured.

5. The total number captured in the second sample, and the number recaptured with the marking is recorded.

6. The size of the population is then estimated on the principle that the proportion marked in the second sample equals the proportion of marked individuals in the population as a whole

The more times this is repeated the more reliable the results.

what is the equation for mark-release-recapture?

Estimated population size =

total number of individuals in the first sample X total number of individuals in the second sample

number of marked individuals recaptured

ethics of mark-release-recapture

Capturing and marking must be done in a non-harmful way

1. Non-toxic

2. Doesn't increase chances of predation

3. Doesn't decrease chances of successful reproduction

what assumptions does the mark-release-recapture method make?

1. The population size is constant (no birth/death andno migration)

2. The animals always redistribute evenly (they may all huddle near food in reality)

so may NOT be accurate

what is succession?

the change in an ecological community over time

how does primary succession start?

1. a pioneer species colonises bare rock or sand

2. pioneers species such as lichen are adapted to survive in harsh abiotic factors

3. through their death and decomposition, they change the abiotic factors to become less harsh & form a thin layer of soil, humus

what occurs next in primary succession?

1. mosses and smaller plants can now survive and they further increase the depth and nutrient content of the soil

2. abiotic factors continue to become less harsh and larger plants can survive and change the environment further

3. each new species may change the environment to become less suitable for the previous species and each existing species is outcompeted by a new species colonising it

4. these changes in environment result in a less hostile environment and increase biodiversity

5. the final stage in succession is known as climax community and this is dominated by trees

what occurs in secondary succession?

1. the succession is disrupted and plants are destroyed

2. succession starts again but the soil is already created, so it does no start from the bare rock seral stage

what does succession cause?

increases species richness and number of organisms

food webs become more complex

how can habitats be conserved?

by managing succession and preventing a climax community

a greater variety of habitats are conserved - greater range of species