Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Chapter 1 - Populations
What is meant by the terms environment, biotic, abiotic and biosphere?

The environment is the compilation of all biotic and abiotic components in an area
...

The biosphere is the life supporting layer of land, water and atmosphere surrounding the
earth
...

Within an ecosystem there is the flow of energy and cycling of elements - both of which are
necessary to support life
...
A
community is the interactions between different populations in a habitat and a habitat is
the environment where a community of organisms resides
...

No two species can occupy the same niche
...
A method of randomly
taking quadrat samples is as follows:




Lay out 2x10m tape measures at a right angle to one another to make a grid
Using a random number generator on calculator, find the coordinates on the grid
Place the quadrat where the coordinates lie and take a reading

How is a transect used to obtain quantitative data about changes in communities along a line?

A transect involves measuring the distribution of organisms systematically, by placing the
quadrant along a straight line and taking repeated measurements this way
...

A transect allows us the measure the progressive change in species distribution as a result of
gradual changes in the environment
...
g
...
The mark-release-recapture method involves catching a sample of a target
organism population, marking them in an inconspicuous and non-harmful manner then
releasing this marked sample back into the wild
...

The data is then input into this equation:
𝐸𝑠𝑡𝑖𝑚𝑎𝑡𝑒𝑑 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑠𝑖𝑧𝑒 =

𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑖𝑛 𝑓𝑖𝑟𝑠𝑡 𝑠𝑎𝑚𝑝𝑙𝑒 × 𝑛𝑢𝑚𝑏𝑒𝑟 𝑖𝑛 𝑠𝑒𝑐𝑜𝑛𝑑
𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑚𝑎𝑟𝑘𝑒𝑑 𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙𝑠 𝑖𝑛 𝑠𝑒𝑐𝑜𝑛𝑑 𝑠𝑎𝑚𝑝𝑙𝑒

Nevertheless, this method relies on several key assumptions:





Marking the organisms has not increased their susceptibility to predation
The marked individuals in the first sample are evenly dispersed in the regular
population
There are few births or deaths
There is no immigration/emigration into/out of the population

What factors determine the size of a population?

Population growth will usually follow the same trend:


Lag – there is very slow population growth due to the small number of organisms in
the population to reproduce



Log – the population size rises
exponentially as abundant resources
allows organisms to reproduce rapidly



Stationary phase – population size stops
rising as limiting factors/resources
prevents further growth, there might be
slight fluctuations but population size
will remain at about carrying capacity

Biotic and abiotic factors will determine where log phase ends and stationary phase begins
...

Organisms can compete for:





Food/water
Space (habitat/territory)
Light
Mates

What is interspecific competition? How does interspecific competition affect population size?

Interspecific competition is competition between organisms of different species
...

If this is allowed to continue the less adapted species will die out, known as the competitive
exclusion principle
...

What is predation?

Predation occurs where one organism consumes another (prey)
...

In the natural environment, the vast range of diverse habitats over a much wider area
means that whilst prey population levels may lower, they will rarely become extinct
...


How does the human population growth curve differ from that of most other organisms?

Human population size remained relatively low until the development of agriculture and the
industrial revolution allowed it to increase exponentially
...
However humans differ from this trend in that the
exponential rise has continued without capping
...

Factors affecting birth rate:





Religious/cultural backgrounds – some countries encourage large families and some
religions oppose birth control
Birth control – countries without or which deny access to birth control will often
have higher birth rates
Economic conditions – low per capita income countries have higher birth rates
Political factors – high levels of taxation/education policies influence birth rates

Factors affecting death rates:








Life expectancy – MEDC populations often live longer than LEDC populations (the
age at which 50% of the individuals of a population are still alive)
War – results in the immediate loss of lives and a long term drop due to loss of
fertile adults
Age profile – the greater the proportion of elderly people the greater the death rate
Food supplies – lack of adequate nutrition increases chances of an earlier death
Sanitation – better sanitation reduces risk of contracting water borne diseases
Medical care – better treatment of trivial illnesses
Natural disasters – more natural disasters increases the death rate
𝐵𝑖𝑟𝑡ℎ 𝑜𝑟 𝑑𝑒𝑎𝑡ℎ 𝑟𝑎𝑡𝑒 =

𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑏𝑖𝑟𝑡ℎ𝑠 𝑜𝑟 𝑑𝑒𝑎𝑡ℎ𝑠 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟
× 1000
𝑡𝑜𝑡𝑎𝑙 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑡ℎ𝑎𝑡 𝑦𝑒𝑎𝑟

Human populations can be represented on population pyramids, there are 3 main types:




Stable – birth and death rate are balanced, there is little change in population size
Increasing – birth rate is greater
than death rate
Decreasing – death rate is greater
than birth rate



---