Form 6 Biology – ECOLOGY

CARBON CYCLE

Carbon is an element found in all organisms. It is a basic building block of all living things it is essential part of carbohydrates, fats and proteins. Carbon is present in the atmosphere as carbon dioxide the carbon enters the ecosystem through the producers.

In carbon cycle organisms in both terrestrial and aquatic ecosystem, exchange CO₂ from the air and through photosynthesis they incorporate carbon into food that is used by themselves and heterotophs.

When any organism respires a portion of carbon is returned into the atmosphere as CO₂.
In aquatic ecosystem, the exchange of CO₂ with atmosphere is indirect. Carbon dioxide from the air combines with water to give carbonic acid, which break down to bicarbonate ions.

(HCO₃^–). Bicarbonate ions are the source of CO₂ for algae, which produce food for themselves and for heterotrophic.

Similarly when aquatic animals respire, the CO₂ they give off becomes bicarbonate. The amount of bicarbonate in water equilibrates with the amount of CO₂ in air.
       Carbon cycle can be summarized as follows.

• The producers (green plants and algae) use CO₂ to make food.
• Herbivores eat plants and carbon gets into the body of carnivores.
• Both plants and animals respire. The process returns CO₂ to the atmosphere.
• When plants and animals die, the decomposers break down dead bodies and carbon is released to the soil where it is absorbed by plant roots.

edu.uptymez.com

Some organic matter does not decompose easily instead, it build up in the earth’s crust oil and coal were formed from the building of the plants and animal’s matters millions of years ago.

The burning of fossil fuels has added much of carbon in the atmosphere in form of CO₂.

Reservoirs of Carbon

• Oceans and seas are large reservoir of carbon in form of HCO₃^–. This can be used to build up shells of marine organisms. Some reaction change bicarbonate into CO₂ that return to the atmosphere. 
• Living and dead organisms contain organic carbon and serve as one reservoir for carbon cycle.

edu.uptymez.com

Living things particularly trees remains of plants and animals are estimated to hold billions of tons of organic carbon.

Some plants and animals remains before complete decomposition, were subjected to physical process that transformed these into coal, oil and natural gas. We call the material fossil fuels.

• Calcium carbonate that accumulate in limestone and calcium carbonate in carbonate shells.

  The influence of Human on carbon cycle
  

  The activities of human beings have increased large amount of CO₂ in the atmosphere. These activities includes: 
  

• Burning of fossil fuels e.g.; coal and oils used for running machines and automobiles. These results into release of much CO₂ and other gases in the atmosphere.
• Burning of fuel wood i.e. firewood and charcoal
• Deforestation i.e. destruction of forests through burning on cutting trees.

  Deforestation reduces the total world volume of photosynthetic materials and thus reduces consumption of atmospheric carbon dioxide in photosynthesis.
  

  Removal of the tree canopy exposes the forest floor to sunlight and warmer temperatures. In forest or woodlands with significant filter and soil humus contents this expose will favor accelerated rates of decomposition and carbon dioxide release. 
  

  ECOLOGICAL NICHE
  

  Ecological niche is the ecological team which is used to refer to the physical space as well as its functional role of a particular group of organisms. 
  

  Ecological niche have been defined in different ways. 
  

• The niche of organism is defined as its profession or total role in a community, e.g. an organism can be producer, consumer, predator, scavenger or a decomposer.
• Defined as a place occupied by a species in an ecosystem and the way it use the resources of the ecosystem.
• The niche of an organism means its place in a biotic environment and its relation to food, enemies, habits and biological factors.

  A Population of each species within a community has a separate need. No two species within a community can have the exact same need. If two species do occupy the same need, it leads to competition until one is displaced. 
  

edu.uptymez.com

Similar habitat in the world have similar ecological niches but may have different animals e.g. Open grasslands all over the world produce a need for fast running herbivores like horses, kangaroo, and antelopes.

ECOLOGICAL SUCCESSION

Formation of a community

A group of organisms of different populations co. existing in the same habitat

• Community ecology focuses on the development and stability of the communities.

edu.uptymez.com

A community is built up over a period of time

Does the community remain the same indefinitely?

A community is a dynamic unit

• A stable community is established through number of stages which are orderly.
• During the time of development there will be an orderly and progressive replacement of one community by another till a relatively stable community is established. This is called ecological succession.
• Ecological succession is the process in which a community is evolved from simple beginning to more complex which is more or less stable. A complete succession is called a sere.

  A sere is made up of a number of several stages. 
  

• A complete stable community is called a climax community.

  Types of Ecological succession
  

• Primary succession
• Secondary succession

edu.uptymez.com

1. Primary succession – Is a type of succession when the community is established where no community has previously existed.

edu.uptymez.com

E.g. On sandunes, volcanic island larva flows (bare rocks). The area is devoid of any organisms.

              2.Secondary succession – Occurs where a community has been disrupted and the surface is completed or largely devoid of vegetation. It may be due to earth quake, fire or even clearing of forest by man.

METHODS OF STUDYING ECOLOGY

Sampling Technique

Sampling technique is a method of establishing a sample.

Sample – is a number of items all things taken from large group and used to provide information about the whole group.

Types of sampling

(i)  Random sampling

• Is a type of sampling in which every item of the universe has an equal chance of inclusion in the sample

edu.uptymez.com

    (ii)  Systematic sampling

• It involves selection of every in the item in a list (an element of randomness is introduced into this kind of sampling by using random numbers to pick up the unit to which to start.

edu.uptymez.com

    (iii) Stratified sampling

• Is a type of sampling in which the population is divided into several sub population on that are individuals more homogenous group than the total population.

  The size of a sample (sample size)
  

• This refers to the number of item to be selected from the set of objects (population or universe) to constitute a sample excessively.

edu.uptymez.com

ADVANTAGES OF SAMPLING

• It makes the study easier since few organisms are involved.
• Since only few organisms are under study this save time and reduce the financial cost if large group of organisms were to be studied.

edu.uptymez.com

Sampling methods

• By transects
• By quadrants
• Point frame
• Pit fall
• Box trapping.
• Ways of establishing a sample
• Transects – line transect
• Belt transect.
• Quadrants – quadrat
• Pin frame (point quadrant)
• permanent quadrat.

edu.uptymez.com

Line transect

• Is a method where a tape or string is run along a ground in a straight line between two points or poles .

  Belt transect
  

• A belt transect is simply a strip of chosen width through the habitat made by setting up two line transects say 0.5m to 1m a part.

edu.uptymez.com

What is a Quadrant?

• A quadrant frame is a metal of wooden frame preferably collapsible to facilitate carrying, which forms a square of known area such as 0.25m² or 1m²
• The way a quadrant is used

  i) Random throw
  

edu.uptymez.com

ii) Used with line transects

• The use of these methods depends on (number of factors) nature of investigation.

edu.uptymez.com

Other types of quadrants

Pin frame (point quadrant).

• This is a frame bearing a number of holes through which a pin “such as knitting needle can be passed”

  Permanent quadrant
  

• This is used in long term ecological investigation involving the study of community change (succession or seasonal changes).

  Other methods
  

• Computer program
• Direct observation
• Photographs
• Pit fall trap
• Box trapping

  Capture – recaptured methods
  

  This methods involves capturing the organisms, marking it in some way without causing it any damage and replacing it so that it can resume a normal role in a population e.g. Fish are netted. 
  

  
  

• The capture – recapture method of sampling is used to try to estimate the entire population, a sample of animals is caught and tagged their number noted and then released into their habitat. Later another sample is captured and the proportion of tagged animal in this sample should be representative of the proportion of tagged animal in the whole population and then the total population size can be estimated using this formula.

  Total = original no tagged x total recaptured
  

  No. of tagged on recapture 
  

  Some examples of how to use this formula
  

  Example 1
  

  50 animals are caught and tagged and released. Later 220 animals are caught and it is noted that 35 of their animals are tagged. What will be the total population estimate? 
  

  
  

  = 50 × 220 ÷ 35
  

  = 314.28
  

  Example 2.

  A biologist caught 100 deers in a forest, tags them and releases them back in the forest. A year later he caught 90 of which 12 had tags, estimate the total population of the dear.
  

edu.uptymez.com

      

The use of quadrats direct observation and photography are known as direct counting methods, where as capture recapture technique is indirect counting method. 

Different methods that are used to establish the samples provide the means of calculating three aspects of species nglish-swahili/distribution” target=”_blank”>distribution.

• Species density

edu.uptymez.com

This is the number of individual of a given species in a given area such as 10 per meter² (10m^-2)

• Species Frequency

edu.uptymez.com

This is measure of the probability (chance) of finding a given species with any one throw of a quadrat in a given area.

Example:

If the species occur once in any 10 quadrats it has a frequency of 10%.

• Species cover

  This is a measure of the proportion of ground occupied by the species and gives an estimate of the area covered by the species as a percentage of the total area. 
  

  Capture method by removal
  

• In this method the number of animals captured is recorded and the animal kept. This procedure is repeated a further three times and the gradually reducing number recorded. A graph is plotted of number of animals captured per sample against the previous cumulative number of animal captured. By extrapolating the line of the graph to the point at which no further animal would be captured (i.e. number in sample = 0)

edu.uptymez.com

Example

Population dynamics

• A group of organism of the same species occupying a particular species and usually isolated to some extent from other similar groups by geographical factor / topography.
• Population studies are not just about the number of a given species living in a given area at given moment in time but it includes also how population grow, how population is maintained and how and why population decline.

edu.uptymez.com

Define population dynamics

• Population dynamics is the study of how and why population size changes over time. It examines the characteristics of a group of organisms such as density, natality (birth rate), survival ship, age structure, migration and from of growth of the population.

edu.uptymez.com

The population size – refers to the number of individuals / species in a population.

Factors that affect the size of population

1. Birth rate (Natality rate)

2. Mortality rate

3. Migration

Population size increase or decrease depending on the number of factors

What causes population increase?

Population size increases as a result of immigration from neighboring populations or by reproduction of individuals within a population. Reproduction is expressed as birth rate or natality.

Birth rate – refers to the number of Youngs produced per female per unit time (usually per year)

Population size may decrease as result of emigration or death (mortality). In population biological mortality strictly means rate of death it can be expressed in terms of percent or numbers per thousand dying per year.

Population growth – Refers to the increase in population.

Population growth can decline in characteristics ways

The factors that affect population growth

• Reproductive potential of the organism
• The rate of reproduction given unlimited environmental resource.
• Environmental resistance
• This is the sum of total limiting factor both biotic and abiotic which act together to prevent the maximum reproductive potential from being realized. It includes external factor such as predation, food supply, heat, light and space, and internal regulatory mechanisms such as intra specific competition and behavioral adaptation.

  Factors within the species which affects population growth
  

  Population growth may change as a result of changes in birth or death rate. Food shortage and increase in predation are two factors which have direct effect on mortality.
  

  Birth rate is affected by two regulatory mechanisms;
  

• The territorial behavior
• Physical effects of over crowding

edu.uptymez.com

Many animals exhibit territorial behavior

A territory – is an area usually fixed in location that individuals defend and from which other members of the same species are usually excluded.

• Territories are typically used for feeding, mating, rearing of young or combination of these activities. 
• Territorial animals benefit in several ways they have exclusive access to food supplies and breeding areas within their territories.
• Also familiarity with their areas help them to obtain food there and avoid predators
• Moreover they can care for their young without interference from other individuals of the same species.

  Over crowding
  

  In a number of mammals high population density reduces greatly the birth rate even if there is good shortage.
  

  Various hormonal changes occur which affect the reproductive behaviors in a number of ways e.g. Failure to copulate infertility, number of abortion and eating of the young by the parents all increase and parental care disease. 
  

  Factors between species which affect population growth
  

  A number of well recognized types of interactions may occur between populations of different species. These are termed as interspecific interaction, population from different trophic levels may also interact as for e.g. in case of predator- prey relationship and host parasite relationship. 
  

• Population growth curves
• Two basic forms of growth curves can be identified. 
• The j-shaped growth curves
• The S-shaped growth curves or sigmoid growth curve.

edu.uptymez.com

The S- Shaped or sigmoid growth curve

This describes a situation in which in new environment, the population density of an organism increases slowly initially, as it adapt to new conditions and establish itself, then increases rapidly approaching an exponential growth rate. It then shows a declining rate of increase until zero population growth rate is achieved where rate of reproduction (Natality) equals rate of death (mortality).

The slowing rate of population growth result from increasing competition for a essential resources such as food or nesting material.

The decline in growth rate continues until eventually feedback in terms of increased mortality and reproduction fails (fewer mating, stress induced abortion) reduces population growth rate to zero.

This type of population growth is said to be density dependant since for a given set of resources, growth rate depends on the numbers present in the population.

• J-Shaped growth curve
• This type of growth curves describes a situation in which after initial establishment phase (lag phase) population growth continues in an exponential form until stopped abruptly as the environmental resistance becomes suddenly effective.
• Growth is said to be density independent since regulation of growth rate is not tied to the population density until the final cash.
• The crash may be triggered by factor such as seasonality or the end of a breeding phase, either of the organism itself or of an important prey species. It may also be associated with a particular stage in a life cycle such as seed production or it may be included by human intervention.

edu.uptymez.com