Posts Tagged ‘population’

  • Describe and evaluate methods for measuring changes in abiotic and biotic components of an ecosystem along an environmental gradient.
Ecological gradients are often found where two ecosystems meet. Biotic and abiotic factors change and form gradients in which then can be recorded. All parts of the gradient needs to be sampled, so a transect is used. The simplest one is when a line of tape is layed down across the area wanted to be measured then to take samples of all the organisms touching the tape. Many transects should be taken to obtain quantitative data. A belt transect is used for bigger samples.
  • Describe and evaluate methods for measuring changes in abiotic and biotic components of an ecosystem due to a specific human activity.
Chernobyl 1986, Russia:
Nuclear reactor blew up
  • design drawback
  • human errors due to poor supervision
The cause:
This caused an increase in thermal power which lead to more explosions. This contaminated soil, plants and animals.
  • Fire fighters tried to turn it off, it took 5000 tonnes of sand, lead and clay.
  • The UN gave £75 million to make it safe and it was fixed by an international team ten years later.
  • People had to evacuate 30km away
  • The town was cleared of everything
  • 15cm of soil depth was removed
  • land washed away and dams were built
  • wall built around it
  • food was contaminated
  • Describe and evaluate the use of environmental impact assessment (EIA).
EIA: Environmental Impact Assessment
Process for identifying the likely consequence for the biophysical environment and for man’s health and welfare of implementing particular activities and for conveying information at a stage where it can materially affect the decision, to those for sanctioning the proposals. (long definition)
Purpose of the EIA:
Helps the decision making process by providing information about the consequences of the environment. Promotes sustainable development by identifying environmentally sound practice and migration measures for development.
Used for: 
Planning process that governments set out in law when large developments are considered. They provide a documented way of examining environmental impacts that can be used as evidence in the decision making process of any new development.
What developments used in the EIA:
  • Major new road networks
  • Airport/port developments
  • Building power stations
  • Building dams and reservoirs
  • Quarrying
  • Large scale housing projects.
  • Explain the concepts of limiting factors and carrying capacity in the context of population growth.
Carrying  capacity is the maximum number of organisms that an area or ecosystem can sustainably support over a long period of time.
There are however limiting factors including temperatures, water and nutrient availability. The main factors are temperature and water availability.
Limiting factors are factors that limit the distribution or numbers of a particular population. Limiting factors are environmental factors which slow down population growth.
There are many ways the temperature can affect species. For example some seeds only grow in extremely high temperatures as it enriches the soil with nutrients and kills competition. However some are damaged if they are too warm or too cold. Some are able to survive low temperature. Animals adapt to the hot/ cold temperature either by burrowing under the ground to avoid heat or having cold blood in the heat.
All plants/animals need water to survive, for plants have no water could cause the plant to not germinate or seeds to die. No water = Death.
  • Describe and explain S and J populations curves.
S-curve (Sigmoidal) : population growth curve that shows a rapid growth at the beginning then a slow down as the carrying capacity is reached.
A population curve which shows only exponential growth. It starts slow the becomes increasingly fast.
  • Describe the role of density-dependent and density-independent factors, and internal and external factors, in the regulation of populations.
Density-dependent factors:
Factors that lower the birth rate or raise the death rate as a population grows in size. They are negative feedback mechanisms leading to the stability or regulation of the population.
When prey increases so does the predator, but when this occurs the prey decreases and then again the predators decrease too causing the prey to increase again.
Density-independent factors:
Factors that affect a population irrespective of population density notably environmental change. Abiotic factors are density-independent factors, the most important ones are the extremes of weather (droughts, fires and hurricane) and long-term climate change.
These factors have an impact that can increase the death rate and reduce the birth rate, it all depends on how severe the event was.
Factors which regulate population size can be divided into either INTERNAL or EXTERNAL.
Internal:  fertility rates, territory sizes
External: predation, pressure, parasitism
The major cause of population regulation are in the environments, these can be physical or biological.
The physical class of environmental factors are water availability, nutrient availability anf so on.
Biological factors include predators, and competition.
Ways humans can cause population growth:
  • increase available resources
  • reduce competition
  • reduce pressure from predators
  • introduce animals to new areas
Ways to decline population:
  • change environment, cause habitat disruption
  • change the biological environment by introducing new species
  • cause secondary extinctions
  • overkill
  • Describe the principles associated with survivorship curves including, K and r strategists.
Survivorship curves and r and k strategists:
K-strategists are slow growing and produce few, large offspring that mature slowly.
R-strategists, slow and mature quickly and produce many, small offspring.
K= carrying capacity
R= growth rate
  • low reproductivity
  • large investment in parental care
  • late maturity/longer living
  • slow growth
  • larger size
  • require stable environment
  • high reproductivity
  • short life
  • low investment in parental care
  • early maturity
  • rapid growth
  • small organisms
  • highly adaptable
  • large number of few species
Survivorship rates:
What influences survivorship rates:
  • competition for resources
  • adverse environmental conditions
  • predator-prey relationships
Example of survivorship curve:
  • curve for species where individuals survive for their potential life span, and die at the same time. Salmons/humans (K-strategists)
  • curve for species where individuals die young but who survives lives very long life turtles/ oysters. (r-strategists)
  • Describe the concept and processes of succession in a named habitat.
Succession: Change in the community structure of a particular area over time.
Primary succession: colonization of newly created land by organisms (rock).
Secondary succession: occurs in places where a previous community has been destroyed. (forest/fire) It is faster than primary succession because of the presence of soil and a seed bank.
Pioneer= earliest community of the succession.
Climax community= the last and final community.
The change from pioneer to climax is called a sere.
Succession is the process of change over time in a community changes in the community of organisms frequently cause changes in the physical environment that allow another community to become established and replace the former through competition. They get more complex at the end.
The arrangement or patterning of plant communities or ecosystems into bands in response to change, over a distance, in some environmental factor.
The main biomes display zonation with altitude on a mountain, or around the edge of a pond in relation to soil moisture.
  • Explain the changes in energy flow, gross and net productivity, diversity and mineral cycling in different stage of succession. 
GP, NP and diversity will change over time as a ecosystem goes through succession. GP is low in early stages then increases as soils become more structured. As food webs become more structured NPP and diversity stabilize as the ecosystem reach climax population.
  • Describe factors affecting the nature of climax communities. 
Climax community:
  • greater biomass
  • higher levels of species diversity
  • more favourable soil condition
  • better soil structure
  • lower pH
  • taller and longer living plant species
  • more k-strategies or fewer r-strategist
  • greater habitat diversity
  • steady state equilibrium
Climate and edaphic factors determine the nature of a climax community. Human factors frequently affect this process through, for example; fire, agricultures, grazing and/or habitat destruction.
  • Construct simple keys and use published keys for the identification of organisms.

Keys called dichotomous keys are used to identify species, the key is written so that the identification is done in steps. At each step two options are given based on different possible characteristics of the organism you are looking at.  You go through all the steps until the name of the species is discovered. This is an example of a dichotomous key that divides 4 types of egg-laying species:

For the exams you need to have at least eight species in the key you construct. This can also be shown graphically:

  • Describe and evaluate methods for estimating abundance of organisms.
It is impossible for you to study every organism in an ecosystem, so limitations must be put on how many plants and animals you study. There are trapping methods which help obtain more samples, like:
  • pitfall traps
  • small mammal traps
  • light traps
  • tullgren funnels
You can either count them all or using percentage cover of an organism in a selected area or by using the Lincoln index and calculating the abundance.
Lincoln index:
This method allows you to estimate the total population size of an animal in your study area. This method includes collecting a sample from a population, then marking them like painting or attaching something to the animal, releasing them back into the wild, then resampling some time later and counting how many marked individuals you find in the second capture. IT is important to take into consideration that the marking methods are not harmful to the animal and clear so that they do not become easy targets for prey.
This method is also known as capture-release-mark-release-recapture techniques because of the processes involved. If all the marked animals are recaptured that is assumed to be the total population size of that species. whereas if half of the species is captured it is estimated to be twice as much as the first sample. The formula used to calculate population size:
N= total population size of animals in the study site
n1= number of animals captured of first day
n2= number of animals recaptured
m= number of marked animals recaptured on the second day
N= (n1 x n2) / m
Quadrats are used to measure the percentage cover of a certain species. Ecologists want to find out how many organisms are living in a specific area, however they cannot count them all so they make a sample count. Percentage cover is the area within the quadrat being used by one particular species.
Percentage cover is worked out for each species present. Dividing the quadrat into a 10×10 grid helps to estimate percentage cover.
Sample methods must allow for the collection of that is scientifically representative and appropriate, and allow the collection of data on all species present. Results can be used to compare ecosystems.
Percentage frequency is the percentage of the total quadrat number that the species was present in.
  • Describe and evaluate methods for estimating the biomass of trophic levels in a community.
*Biomass:  the mass of organic material in organisms or ecosystems, usually per unit area. Biomass is calculated to indicate the total energy within in a living being or trophic  level. The greater the mass of the living material the greater the amount of energy present. Biomass is taken as the mass of an organism minus water content, like dry weight biomass. Water is not included in biomass measurements because the amount varies from organisms to organism, it does not contain energy and is not organic.
To obtain the samples, the biological material is dried to constant weight. It is then weighed. The specimens are then heated in a  oven which is not hot enough to burn the tissue and left for a certain amount of time. Biomass is usually measured per unit area so that comparisons can be made between the trophic levels present.
  • Define the term biodiversity.
Diversity is often considered as a function of two components: the number of different species and the relative numbers of individuals of each species. This is different from species richness, which refers only to the number of species in a sample area.
  • Apply Simpson’s diversity index and outline its significance.
There are many ways of quantifying diversity, one of the ways is using the Simpson’s diversity index:
D= diversity index
N= total number of organisms of all species found
n= number of individuals of a particular species
E= sum of
D= (N(N-1)) / (En(n-1))
*It is not important to remember the whole formula, but good to know the meaning of the symbols.
D is a measure of species richness. A high value of D suggests a stable and ancient site, and a low value of D could suggests pollution, recent colonization or agricultural management. The index is normally used in studies of vegetation but can also be applied to comparisons of animal diversity.
  • Distinguish between biotic and abiotic (physical) components of an ecosystem.

*Biotic: refers to the living components of an ecosystem. (the community)

*Abiotic: refers to the non-living factors of an ecosystem. (the environment)

Ecosystems are made up of living and non-living components. The living part of the environment consists of the organic part of the ecosystem; animals, plants, algae, fungi and bacteria. These are called biotic components. The non-living part of the environment is made up of physical components such as; air, light, water, temperature, soil, minerals and climatic atmosphere. These are called abiotic components. These two components work together to sustain the environment.

  • Define the term trophic level.

Trophic level refers to the feeding level within a food chain. It is the position that an organism occupies in a food chain, or a group of organisms in a community that occupy the same position in food chains.

  • Trophic level 1 – producer
  • Trophic level 2 – herbivore (primary consumers)
  • Trophic level 3 – carnivore (secondary consumers)
  • Trophic level 4 – carnivore (tertiary consumer)
    • Identify and explain trophic levels in food chains and food webs selected from the local environment.

    *Producer: The organism in the ecosystem that converts abiotic components into living matter, they help the ecosystem by producing new biological matter.

    *Consumer: These organisms cannot produce their own food, so they eat other organisms to get the energy and matter they need.

    * Decomposer: Feed on dead biomass which is created by the ecosystem.

    *Herbivore: Only feed on producers.

    *Carnivore: Feed on all organisms including producers and consumers.

    *Top carnivore: This organism can not be eaten by any other organism.

    Sun: Provides the abiotic matter to the grass

    Grass: Producer and autotroph, provide food for the deer.

    Deer: The primary consumer and herbivore of the grass.

    Wolf: The secondary consumer/Top consumer and carnivore, feeds on the deer and cannot be eaten by any other organism.

    Ecosystems contain many interconnected food chains that form food webs. Food chains always begin with the producers (usually photosynthetic organisms), followed by primary consumers (herbivores), secondary consumers (omnivores or carnivores) and then higher consumers (tertiary, top). Decomposers feed at every level of the food chain.

    Diagrams of food webs can be used to estimate the knock-on effects of changes to the ecosystem.

    Biomass and energy decrease at each trophic level so there is a limit in how much trophic levels can be supported in a ecosystem. Energy is lost as heat at each stage of the food chain, on only energy stored in biomass is passed on to the next trophic level. After 4 or 5 trophic levels there is not enough energy to support another stage.

    Local example: (Lake in Sweden)

    Producer: Freshwater shrimp

    Primary consumer: Bleak

    Secondary consumer: Perch

    Secondary consumer: Northen Pike

    Top consumer: Osprey

    • Explain the principles of pyramids of numbers, pyramids of biomass, and pyramids of productivity, and construct such pyramids from given data.

    Pyramids are graphical models showing the quantitative differences between the trophic levels of an ecosystem. There are three types:

    • Pyramids of numbers: This records the number of individuals in each trophic level.

    • Pyramid of biomass: This represents the biological mass of the standing stock at each trophic level at a particular point in time. Biomass should also be measured in units of energy, such as J m-2. They can show greater quantities at higher trophic levels because they represent the biomass present at a given time. Both pyramids of numbers and biomass represent storages.

    • Pyramid of productivity: This shows the flow of energy through each trophic level. Measured in units of flow gm-2 yr-1 or Jm-2 yr.

    In accordance with the second law of thermodynamics, there is a tendency for numbers and quantities of biomass and energy to decrease along food chains; therefore pyramids become narrower as one ascends.

    • Discuss how the pyramid structure affects the functioning of an ecosystem.

    This Youtube clip explains the interactions in food chains and the vulnerability of the top carnivores.

    • Define the term species, population, habitat, niche, community and ecosystem with reference to local examples.

    *Species: A group of of organisms that interbreed and produce fertile offspring. If two species breed together they create a hybrid, this cannot produce viable gametes and is sterile.

    *Population: A group of the same species living in the same area at the same time, and can interbreed.

    *Habitat: The environment in which a species normally lives.

    *Niche: Where and how a species lives. A species share of a habitat and the resources in it.

    *Community: A group of populations living and interacting with each other in a common habitat.

    *Ecosystem: A community of inter-independent organisms and the physical environment they inhabit.

    • Describe and explain population interactions using examples of named species.

    Ecosystems contain many interactions between the populations, the interactions are varied and can be divided into; competition, predation, mutualism and parasitism.

    *Competition: A common demand by two or more organisms upon a limited supply of a resource; for example, food, water, light, space, mates, nesting sites. It may be intraspecific or interspecific.

    *Parasitism: A relationship between two species in which one species (the parasite) lives in or on another (the host), gaining all or much (in the case of the partial parasite) of its food from it.

    *Mutualism: A relationship between individuals of two or more species in which all benefit and non suffer.

    *Predation: This is when on animal or plant hunts and eats another animal.

    Here are 3 Youtube links about Interspecific interactions.

    • Explain difficulties in applying the concept of carrying capacity to local human populations.

    If one were to examine the needs of a given species and the resources available, it could be possible to estimate the carrying capacity of that environment for the species. This is problematic when it comes to the human population for many reasons like:

    • Resources used by humans are much more than any other species and when this source becomes limited humans begin to substitute one resource for another. The use of resources change from person to person, lifestyle to lifestyle, time to time and population to population.
    • Developments in technology increase the changes of the resource consumption.
    • The human population also import resources very often which come from outside their environment, which makes the grow beyond the boundaries set by their local resources and lets their carrying capacity increase. This however does not affect the global carrying capacity.

    These variables make it almost impossible to make reliable estimates of carrying capacities for the human populations.

    *Carrying capacity: The maximum number of a species or ”load” that can be sustainably supported by a given environment.

    Here we can see 3 models of a population growing and approaching carrying capacity.

    *Optimum population: the number of people which when working with all the available resources, will make the highest per capita economic return. it shows the point at which the population has the highest standard of living and quality of life.

    Standard of living is the result of the interaction between physical and human resources and can be expressed as:

    Standard of living: (natural resources X technology) / population

    *Over-population: this happens when there are too many people compared to the resources and technology available for the standard of living. They suffer from natural disasters such as droughts and famine, low incomes, poverty, poor living conditions and a lot of emigration.

    *Under-population: this happens when there are too many resources in one area that is too much for the people living there. Countries like this could export their surplus food, energy and mineral resources.

    • Explain how absolute reductions in energy and material use, reuse and recycling can affect human carrying capacity.

    Human carrying capacity is determined by the rate of energy and material consumption, the level of pollution and the extent of human interference in global life-support systems. While reuse and recycling reduce these impacts, they can also increase the human carrying capacity.

    *Recycle: when a household or industrial waste is reused and made into another product, like plastic, metals and paper.

    *Re-use: when a product is used more than once by returning it to the manufacturer or processor each time. This is very energy efficient and more efficient than recycling.

    *Reduce: this is when energy use is decrease for example turning off the lights when not needed or using the amount of water needed in a kettle.

    *Substitution: when using one resource over the other, the use of renewable source over a non-renewable source is a major benefit to the environment.


    • Describe the Earth’s water budget.

    There is only a small part of the Earth’s water that is fresh water, and of this over 80% is in the form of ice caps and glaciers, 0.6% is groundwater and the rest is made up of lakes, soil water, atmospheric water vapour, rivers and biota in decreasing order of storage. This means that most of the Earth’s water budget is not directly accessible by human populations. Fresh water is therefore an extremely limited resource. (precise numbers are not needed on exam)

    *Turnover time: The time it takes for water to completely replace itself in part of the system it is in, this charges from different parts of the systems.

    The degree to which water can be looked at as renewable or non-renewable depends on where it is found in the hydrological cycle. Renewable water resources are renewed yearly or even more frequently, however groundwater is non-renewable resource.

    • Describe and evaluate the sustainability of freshwater resource usage with reference to a case study.

    Irrigation, industrialization, and population increase all make demands on the supplies of fresh water. Global warming may disrupt rainfall patterns and water supplies. The hydrological cycle gives humans fresh water but we are taking up so much water from the underground aquifers that there is no time for it to replenish.

    The demand of water has increased in both MEDCs and LEDCs, as populations are increasing as well as agriculture changing and expanding industry. MEDCs need more water as they wash more often, water their gardens, and wash their cars. This means that the increasing use of water is making the demands higher. Water is not an infinite resource and has to be controlled more carefully, and new water resources need to be found.

    Water can be managed if individuals and communities make changes and this should be supported by the government. Water should not be over used or wasted so that it is insured it can be enough for everyone.

    This can be reached by:

    • making new buildings water efficient (rainwater for sanitation and showers)
    • fitting new homes with more water-efficient appliances (dishwashers and toilets)
    • expand metering to encourage households to use water more efficiently
    • in some rural areas drought resistant crops should be planted to reduce the need for irrigation
    • organic fertilizers cause less pollution and bio-control measures can be used to reduce crop pests

    Environmental philosophies:

    Environmental philisophies: plan to manage resources sustainability without diminishing them to a degree where they become non-replenishable. Techno-centrists would argue that solutions can be found to sustain both human population and overcome unsustainable use of water resources.

    As populations grow, greater demands are made on water resources. Water resources are now becoming a limiting factor in many societies, and the availability of water for drinking, industry and agriculture need to be considered. Many societies now are dependent on groundwater which is non-renewable. As societies develop, water needs to be increased. The increased demand for water can lead to inequity of use and political consequences. When water supplies fail, populations will be forced to take dramatic steps, such as mass migration. Water shortages may also lead to civil unrest and wars.


    Water shortages in the Middle East:

    Water shortages in the Middle Eastern countries are very common and as time passes their water supply is decreasing. Even though the region only inhabits 5% of the world’s population, it only has 0.5% of the worlds fresh water. It is predicted that the water supply will decrease from 3430 cubic meters per year to a 667 cubic meters by 2025. This is causing countries such as Israel who is suffering from a major drought to stop pumping from their major pumps of fresh water. Many factors have lead to the demand of more water and the droughts have made this worse. Despite the shortages Israel is still sharing their supply with neighbouring country Jordan. Israel is building at the moment plants that supply a third of the countries water supply and a few more plants are also going to be completed in 2013 which could double this amount. Future water shortages could lead to conflicts between the neighbouring countries.