Download Unit 2.3.1 – Biodiversity

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Unit 2.3.1 Biodiversity
Unit 2.3.1 – Biodiversity
Organisms do not live in isolation from one another BUT in structured communities within
“dynamic (changing) and well defined ecosystems” through within energy flows (in linear
fashion) and nutrients are recycled.
Ecology is the study of how plants and animals interact with each other and their (nonliving) environment.
Biotic factors
living parts of the environment
e.g.
predation, bacteria
food availability,
competition
Abiotic factors
non-living parts of the environment
e.g.
rainfall,
temperature,
soil pH
Species:
“A group of organisms capable of interbreeding to produce fertile
offspring”
Habitat:
“Where an organism USUALLY lives”
Biodiversity:
“Variation of life forms within a particular ecosystem”
It is often used as a measure of health of biological systems.
Biodiversity is split into three types:
Genetic diversity: “Total number of genetic characteristics in the genetic makeup of a
species”
Species diversity: “Simply the measure of the number of different species in a given area”
Note that humans play a major role in this by destruction,
overharvesting, global climate change and introduction of species not
used to being there.
Ecosystem diversity:
This just refers to the diverse ecosystems present
Sampling
It is impossible to count every individual in a given area. Thus an ecologist is forced to
measure a smaller sub-set of the population: from which the conclusions can be made with
regards to the whole population.
The sub-set is a SAMPLE.
SICM Tuition
Unit 2.3.1 Biodiversity
Biased samples
prejudice for/against some items being sampled
Bias does NOT imply the investigator is deliberately doing this.
Ecological investigations always involve the collection of data and its subsequent analysis.
Random Sampling
e.g.:
Quadrat
outline of a square made of plastic which is placed in an area
school playing fields:
use 0.5m2 / 0.25m2 quadrat
barnacles on sea-shore
use 1m2 quadrat
Transects:
-
line placed on an area and the area around the line analysed
suitable for rocky shore (i.e. where habitat is not uniform)
where location of organisms is determined by environmental gradient
quick and easy, but less informative
not likely to be representative of the habitat unless repeated several
times
To take a random sample, you can label your area with coordinates. You can then use a
random number generator or a book of random numbers to give the coordinates that you use
for the samples. Remember that it is best to use many areas as it would then be more
representative of the entire area.
Species diversity (richness) index
-
the number and range of different species found in an ecosystem
-
a measure of the species diversity is helpful when considering the interaction
of the following factors and their influence on the ecosystem:
o eclaphic (soil)
o climatic
o biotic
In general, a stable ecosystem has a wide range of different species each with a
similar population size. (See later…high SID):
o such populations are dominated by biotic factors
A less stable ecosystem (i.e. one which is under stress – due to pollution or extreme
climate conditions) has just a few species with very large populations
o such populations are dominated by abiotic factors
SICM Tuition
Unit 2.3.1 Biodiversity
Simpsons index of diversity
-
measures species diversity
-
often used to estimate plant diversity
Involves counting the numbers of each type of plant found in a given area.
Diversity is calculated by the formula:
D=
n (n-1)
Σ N (N-1)
Where:
D = diversity index
N = total number of individuals of all species
n = total number of each species
Σ = sum of
SID = 1 - D
Weakness of SID
(a)
No allowance for differences in size of individuals (e.g. 1 elephant = 1
bacterium)
(b)
Difficult to calculate index for plants as it is not always easy to decide what
constitutes as an individual plant.
(e.g. suckers – plant may have same root system but look like it is individual)
Extreme Environment
(a)
Diversity low
(b)
unstable ecosystem
(c)
dominated by abiotic factors
Less Hostile environment
(a)
diversity high
(b)
stable ecosystem
(c)
dominated by biotic factors
-
sometimes used as an indicator of ecological stability assuming that the
greater the diversity, the greater the stability.
-
BUT stability has several meanings:
o Resistance:
to change following disturbance
o Resilience:
ability to change to original state after change
o Local stability: tendency to return to original state after small disturbance
o Global stability: tendency to return to original state after large disturbance