3.4.1 Populations and the Environment (AQA A2 Biology)

Word doc including all areas of population section on the syllabus. Includes human populations, predation, competition, investigating populations, variations and equations.

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  • Created on: 01-05-14 18:02
Preview of 3.4.1 Populations and the Environment (AQA A2 Biology)

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3.4.1 The dynamic equilibrium of populations is affected by a number of
factors
POPULATIONS AND ECOSYSTEMS
A population is all the organisms of one species in a habitat. Populations
of different species form a community.
Within a habitat a species occupies a niche governed by adaptation to
both biotic and abiotic conditions.
What are these things?
Ecosystem: A specific area made of all
interacting biotic and abiotic features
Species: Organisms that share similar characteristics
and produce fertile offspring.
Population: A group of interbreeding organisms of one
species.
Community: All populations of different organisms
living and interacting in a habitat at one time.
Ecological niche: Refers to where an organism lives
and includes all of the conditions for the organism to
survive, reproduce and maintain its population. This
includes both biotic and abiotic features which are
described below:
Biotic Abiotic
Activities among living organisms. Non-living things.
Competition Temperature
Predation Water
Light

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The dynamic equilibrium of populations is affected by a number of
factors
INVESTIGATING POPULATIONS
A critical appreciation of some of the ways in which the numbers and
distribution of organisms may be investigated.
Random sampling with quadrats and counting along transects to obtain
quantitative data.
To study a habitat it is necessary to know the abundance of the individuals. This is the
number of individuals occupying one place at a given time.…read more

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The dynamic equilibrium of populations is affected by a number of
factors
Transects are a more systematic way of measuring the distribution of organisms,
particularly when there is some sort of regular change in the environment, e.g tidal
shore organisms depend on high or low tides which would affect the abundance
throughout out the day.
By measuring at regular intervals across the transect you gain a representation of the
populations present in the ecosystem. There are two types of transect:
A.…read more

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The dynamic equilibrium of populations is affected by a number of
factors
Mark-Release-Recapture Techniques
Measuring abundance is difficult with animals because they move around and tend to
hide away from potential risks which includes the presence of humans despite them
just doing an investigation. This is why it is better to use a mark-release-recapture
method when measuring the frequency of moving organisms.
To do this you must:
1. Capture your first sample.
2. Mark the animal and release it.
3.…read more

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The dynamic equilibrium of populations is affected by a number of
factors
VARIATION IN POPULATION SIZE
Population size may vary as a result of:
the effect of abiotic factors
biotic factors: interspecific, intraspecific competition and
predation
Population Growth Curves
1. Slow growth as individuals reproduce to grow numbers.
2. Rapid growth where there is lots of reproduction.
3. Stable population with slight fluctuations due to cyclic changes. (seasons etc)
Population Size
The growth of a population depends on limiting factors.…read more

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The dynamic equilibrium of populations is affected by a number of
factors
Predation
There is a relationship
between predator and prey as
when prey increases, so does
predator populations. The
raise in predation will cause
prey numbers to drop which
reduces resources for
predator so their population
size also decreases. This is
cyclic.
This causes selection pressure: Only those individuals who can escape predation,
disease or an extreme climate will survive to reproduce. The population evolves
to be better adapted to their environment.…read more

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The dynamic equilibrium of populations is affected by a number of
factors
Demographic transition is when a population goes from a low life expectancy and
high birth rates to low birth rates and high life expectancy. This is show through age
population pyramids.
Stable population: Birth and death rates are n balance so no change in population
size.
Increasing population: High birth rate with narrower top meaning a smaller elderly
population.
Decreasing population: Low death rate and low birth rate leading to more old people.…read more

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