Sampling Methods

Do you remember all the sampling techniques we used to sample the habitat at the Braunton Burrows sand dunes on our lovely fieldtrip back last summer!? Well hopefully you do!!!

When sampling a habitat, there are 3 things we need to find out:
1. What species are present
2. The abundance of each species present
3. The distribution of each species

Organisms are distributed unevenly in most environments, so random sampling is ised to determine the number and abundance of species present. Also random sampling eliminates bias.
QUADRATS
- can find percentage cover by looking at the proportion of the quadrat's area occupied by a species
- can find species density by counting the number of individueals present and calculating the mean number per quadrat
- can find species frequency by looking at the proportion of quadrats with a particular species in them

POINT QUADRATS
- each species that touches a pin is recorded, together with the total number of times it is touched
- a point quadrat has to be randomly positioned

LINE TRANSECTS
- all species touching a line are identified and their position that touches the line recorded
- suitable for habitats with gradations in conditions

BELT TRANSECTS
- quadrats are placed sequentially along a line transect, making the transect wider

Succession

SUCCESSION = a directional change in a community of organisms over time

Succession is a change in the structure and species composition of a community, which occurs because of the canges caused by the preseence of established organisms, or by external influence.

PRIMARY SUCCESSION occurs in an area where there is no soil or living organisms so in areas like sand dunes (which display of seres of succession in the same place!), on top of landslides, lava flows or depositional features like moraines left my retreating glaceirs (I am going to move on before I start talking Geography!!!) - so basically any bare land that has nothing growing or living on it!

PIONEER SPECIES are the first to colonise. They:
- are able to tolerate extreme conditions, primarily the very poor nutriential value of the soils, and high salinity
- very good at dispersing their seeds to grow; through aeolian transport normally
- are not influenced by or dependent upon animal species

This can basically be summarised to: they can tolerate harsh abiotic conditions. There death is crucial to succession though as their death provides organic material (known as HUMUS) which can hold water and provide nutrients for the next plants.

STABILISING SPECIES (e.g marram grass), stabilises sand dunes, for example, using their roots and underground stems. Humus and nutrients accumulates, improving the conditions even more for the next stage.

Legumes eventually colonise and these are crucial as they play a key role in nirtogen fixation which enables larger plants to succeed the smaller ones.

The final stable community is called the CLIMAX COMMUNITY, which in the UK is deciduous woodland. Climax community species:
- have large seeds so that the seedling can tolerate low light intensity
- have a specialised niche
- unable to tolerate great fluctuations in soil water content, hence why it is so important that humus accumulates before this stage can be reached
- are strongly influenced by other organisms

DEFLECTED SUCCESSION is holding succession at a particular point (e.g mowing or cutting vegetation back) which prevents the climax community from being formed.

So, I think we need to know an example and the one we got taught was the process of succession when a glacier melts and leaves behind moraines:
- nitrogen concentration increases as legumes perfomr nitrogen fixation
- spruce trees absorb nitrogen
- pioneer plants improve soil conditions
- spruce tress outcompete the smaller plants
- more spruce trees and more alder (the climax communtiy) increase the biomass

When an established community is destroyed a new community will eventually develop and secondary succession will take place.
SECONDARY SUCCESSION occurs where an existing community has been cleared by a distrubance (more geography references here! Disturbances are often natural disasters like floods, volcanic activity etc. although human activity can have a similar effect)

Limiting Factors on Population Size

Limiting factors stop the population size of a species increcreasing......

Animals:-                                                                    Plants:-
- competition for food and water                                - light intensity and temperature
- competition for mates                                               - pH
- availability of burrows and space                             - water and nutrients
- predation                                                                   - pollinators
- disease/parasitse                                                       - disease

Therefore, limiting factors can be either biotic or abiotic.

DENSITY DEPENDENT FACTORS have more impact as popoulation becomes more dense
DENSITY INDEPENDENT FACTORS affect the population in the same way regardless of density
CARRYING CAPACITY is the maximum population size that can be maintained over a period of time in a particular habitat

In a closed system, population growth will follow a standard pattern....


NOTE: we call death phase, declining phase instead




LAG PHASE = plateau before a steady increase as the species is acclimatising to conditions
LOG PHASE = expotential growth as represented very steep positive gradient of the line
STATIONARY PHASE = limiting factors start being influential and limit the size that the population can reach
DECLINING PHASE = limiting factors start to make the population size decrease

However, in a open system, as in nature, the pattern is slightly different....

This main difference, in nature, to the above closed system, is that the carrying capacity limits the population size, with limiting factors preventing the carrying capacity level to be exceeded

One of the most influential factors in dictated population size is the predator/prey relationship. Changes in one cause changes in the other, and generally speaking they run a 10 year cycle

Using the relationship between hares and lynx as an example:
- a small population of hares cannot support many lynx, so the lynx population crashes
- however, this means there are fewer lynx to prey on the hares, so the hare population starts to rise
- this, in turn, supports more lynx, so the lynx population starts to rise
- however, more lynx means more hares are eaten so the hare population falls - so the cycle has to start all over again!

However, to complicate this, when studying hare populations where there are no lynx, the hares still display a similar 10 year cycle! This implies that fluctuations in the number of hares affects the lynx population, but that number of lynx do not cause fluctuations in the hare population, to the same extent. So what do the result from....
- changes in availability of vegetation
- changes in the nutritional value of the available vegetation
- reduction in the breeding success of hares when the population density increases

Competition between organisms for resources and space is another abiotic limiting factor on population size and there are two forms of competition.......
INTRASPECIFIC = competition between members of the SAME species
---> density dependent factors that limit population growth = causes natural selection
INTERSPECIFIC = competition between members of DIFFERENT species
---> competitive exclusion, researched by Gausse in 1934 using two species of paramecium.               
         - Concluded that if two species occupy excatly the same niche, one would be out-competed and would become extinct in that habitat
NICHE = the role that a species plays in an ecosystem

Pyramids.....

I kind of missed this bit out so this will only be really short!

Pyramid of numbers have limitations and you can get inverted pyramids so ecologists started to use biomass.....
Then a pyramid of energy was developed:
- collect organism
- burn in calorimeter
- calculate how much energy is released per gram

BUT, pyramids of energy have limitations too
- provide only a snapshot at one moment in time
- populations fluctuate over time, and this cannot replicate those changes
- gives a distorted idea of time efficiency of energy transfer

Instead, therefore, we look at the rate at which energy passes through each tropic level - so essentially productivity

- how much energy (in kJ or MJ) is available........
                 ......... per unit area (m2)......
                                 ......... in a given time (year)
e.g 54 000kJm-2year-1

Nitrogen Cycle

DECOMPOSERS are organism that feed on waste from other organisms, or dead organism
     ---> feed saprotrophically so are saprotrophs, i.e they release enzymes on too dead/waste matter which digest material into smaller molecules which are then absorbed into the organisms body where they are stored or respired to release energy
- If this did not happen then energy and valuable nutrients would remian trapped within dead organisms. Micro-organisms, therefore, have a particularly important role to play in the cycling of carbon and nitrogen within ecosystems

- Nirtogen must be fixed
     ---> converted into a more usable form e.g ammonium ions or nitrate ions

- Nitrogen fixation can happen through bacteria
    ---> nodules provide place for Rhizobium bacteria
    ---> leghaemoglobin mops up unwanted O2

- Rhizobium uses nitrogenase (enzyme) that converts N2 in the air to nitrates
       - Rhizobium bacteria invades roots
       - Stimulates nodules to develop
       - Bacteria forms colonies inside nodules
       - Use a nitrogenase enzyme to covert nitrogen gas (N2) into ammonium ions (NH4+)

- Nitrogen is assimilated by animals
      - Animals eat plant proteins
      - These are digested to amino acids
      - Amino acids are re-built into proteins in the animal
      - Nitrogen is returned to the soil when the plant or animal dies or during excretion
---> Excretion = Ammonification

- Denitrification
     ---> In waterlogged soils, nitrates and ammonium ions are in short supply

This animation is an interesting take on the nitrogen cycle (be warned the guys voice gets a little annoying after a while) if you are a more visual learner you may find this useful.....



Why is this important? Well plants and animals need nitrogen...... going back to AS stuff this is......

Amino acids ---> proteins e.g haemoglobin, collagen, antibodies and enzymes

Nucleotide ---> DNA, RNA (mRNA, and tNRA)

Energy transfers within ecosystem

A food chain shows how energy is transferred from one living organism to another, through trophic levels

Producer ---> Primary Consumer ---> Secondary Consumer ---> Tertiary Consumer

Within an ecosystem, living organisms are usually members of more than one food chain and often at different trophic levels in different chains. Therefore, food webs are used to illustrate the complexities to help us understand just excatly how energy flows through the whole ecosystem.

Energy transfers can be calculated by measuring the energy content of samples of organisms from each trophic level. Each sample is dried to constant mass in an oven and then burned in oxygen in a bomb calorimeter. The heat energy produced by the oxidation passes to a known mass of water, and the temperature rise of the water is measured. Given that 4.14J of heat energy rises 1g of water 1C, the energy content of each sample can be calculated.

At each trophic level, some energy is lost from a food chain, and is therefore unavailable to the organism at the next trophic level. Energy is lost because organisms:
- never eat all the availabel food
- cannot digest all the food they eat
-use energy in respiration and other metabolic reactions
- lose heat energy to their surroundings
- lose energy in urine and faeces (although this energy often passes on to decomposers)

Because of this, there is less energy available to sustain living tissue at higher levels of the food chain, and so less living tissue can be kept alive. When the organisms in a food chain are about the same size, this means there will be fewer consumers at the higher levels. Pyramids of numbers represent this idea.....

Human activities in farming, forestry and fishing manipulate the flow of energy through an ecosystem by altering the productivity of one or more trophic levels.....
- replacing natural vegetation and fauna with crops and livestock
- deflecting natural succession to maintain grassland
- increasing productivity of producers through soil improvements, irrigation, fertilisers and removal of competing weeds and damaging pathogens and pests
- increasing productivity of producers and consumers through selective breeding and genetic engineering
- sheltering organisms from damaging environmental factors

How can we improve secondary productivity?
- harvest animals before adulthood
- treat with steriods (illegal in the UK)
- selective breeding to increase growth rate
- treat with antibiotics to avoid loss of energy to pathogens
- stop animals moving about

What is an Ecosystem?

Before I start, I just thought I would let you know how I am planning to structure these posts. When I revise in Biology and Chemistry I tend to do it slightly differently to how I do in Geography and History as I go through all the specification points, one by and one, and write notes on them. Therefore I am going to structure many of these posts in a similar way so hopefully they are in an order that makes sense  - first up I am going through the Ecosystems and Sustainability module (the one we studied in the summer after our AS exams - I know, a rather long time ago!)...... sorry but the start of any module will mean lots of lovely definitions!

ECOSYSTEM = community of organisms and their environments, in which ecologists study energy flows and nutrient cycling through trophic levels

- An ecosystem is a self-contained system including living organisms and the non-living components interacting with each other. Changes are happening all the time with ecosystems and energy constantly flows through them, from one organism to another through trophic levels and between organisms and the environment. Therefore we class all ecosystems as DYNAMIC SYSTEMS.

BIOTIC FACTORS = living component of environment that affects species distribution and abundance
                                      ---> predators, consumers, parasites, competitors
ABIOTIC FACTORS = non-living component of environment that affects species distribution and abundance
                                     ---> temperature, light intensity, soil type, pH of water and soil

PRODUCER = green pants which absorb inorganic compounds and use them, with sunlight, during photosynthesis to make the organic compounds on which the other organisms in the ecosystem depend

CONSUMERS = primary or secondary that eat producers and primary consumers, respectively

DECOMPOSERS = organisms that breakdown the organic remains of other organisms

TROPHIC LEVELS = a group of organisms which all obtain their energy in basically the same way e.g primary producers, primary consumers, decomposers