Posts Tagged ‘formula’

  • 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.
  • Explain the role of producers, consumers and decomposers in the ecosystem.
Producer: can make their own food, as they use sunlight to make food and are called  the basis of every ecosystem which helps the rest of the species through input of energy and new biomass. This all happens through photosynthesis which is the process when the producer uses the sun for energy.
Consumer: feed on other organisms, they do not contain photosynthesis pigments so they cannot make their own food. They have to get energy, minerals and nutrients by eating other organisms. This makes the heterotrophs. Herbivores feed on autotrophs, carnivores on other heterotrophs and omnivores on both.
Decomposer: get their food from the breakdown of a dead organism matter. They break down tissue and release nutrients for absorption by other producers. Decomposers also improve the nutrient capacity in the soil by breaking down the organic material.
  • Describe photosynthesis and respiration in terms of inputs, outputs and energy transformations.
Photosynthesis: needs carbon dioxide, water, chlorofyll and certain visible wave lengths of light to produce organic matter and oxygen.
  • inputs: sunlight as energy resource, carbon dioxide and water
  • processes: chlorofyll traps sunlight; energy is used to split water molecules; hydrogen from water is combined with carbon dioxide to produce glucose.
  • outputs: glucose used as an energy source for the plant and as a building block for other organic molecules; oxygen is released to the atmosphere through stomata.
  • transformations: light energy is transformed to store chemical energy.
Respiration: needs organic matter and oxygen to produce carbon dioxide and water.
  • inputs: glucose and oxygen
  • processes: oxidation processes inside cells
  • outputs: release of energy for work and heat
  • transformations: stored chemical energy to kinetic energy and heat
  • Describe and explain the transfer and transformation of energy as it flows through an ecosystem.
Not all solar radiation ends up being stored as biomass. Losses include_
  • reflection from leaves
  • light not hitting chloroplasts
  • light of the wrong wavelengths (not absorbed by chloroplast pigments)
  • transmission of light through the leaf
  • inefficiency of photosynthesis
In this diagram we can see the energy flow through an ecosystem.
  • Describe and explain transfer and transformation of materials such as they cycle within an ecosystem.
The Carbon Cycle:
The Hydrological cycle:

The nitrogen cycle:
  • Define the terms gross productivity, net productivity, primary productivity, and secondary productivity.
*Productivity is production per unit time.
Primary productivity is the gain by producers (autotrophs) in energy or biomass per unit area per unit time. It is when solar energy is converted, it depends on the amount of sunlight the ability of the producers to use energy to synthesize organic compounds and the availability of other things needed for growth, like minerals and nutrients.
Primary production is highest were conditions for growth are optimal, where there are high levels of insolation, good water supply, warm temperatures and high nutrient levels.
You can then divide primary productivity into gross and net profits.
*GROSS is the income
*NET is the incomes minus costs
Secondary productivity depends on the amount of food there is and the efficiency of the consumers turning this into new biomass. Unlike the primary productivity net productivity involves feeding or absorption.
Gross productivity (GP): The total gain in energy or biomass per unit area per unit time.
Net productivity (NP): The gain of energy or biomass per unit area per unit time remaining after allowing for respiratory losses. It is the energy left for the next trophic level to consume.
  • Define the terms and calculate the values of both gross primary productivity and net primary productivity from given data.
Gross primary productivity (GPP): is gained through photosynthesis in primary producers.
Net primary productivity (NPP): is the gain by prodicers in energy or biomass per unit area per unit time remaining after allowing for respiratory losses. (Available for consumers in ecosystem)
Productivity calculation:
Primary productivity:

where R = energy used in respiration
  • Define the terms and calculate the values of both gross secondary productivity and net secondary productivity from given data.
Gross secondary productivity(GSP): is gained through absorption in consumers.
Net secondary productivity(NSP): The gain by consumers in energy or biomass per unit area per unit time remaining after allowing for respiratory losses.
Secondary productivity:
GSP = food eaten – faecal loss
where R = respiratory loss
  • 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.
  • 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.