A LEVEL: Biology (F215), Ecosystems and Sustainability

Biology F215

Ecosystems and Sustainability

A Habitat: The place where an organism lives. 

A Population: All of the organisms of one species that live in the same place at the same time, and that can breed together.

A Community: Is all the populations of different species that live in the same place at the same time, and can interact with each other. 

 Role played by the species: it’s Niche

Biotic Factors: any living component that affects another organism, including animals that consume the organism in question, and the living food that the organism consumes. Each biotic factor needs energy to do work and food for proper growth. Biotic factors include human influence.

Abiotic Factors: abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems

Ecosystems are Dynamic

Due to interaction, population sizes can either rise or fall. So much depends on the interactions between living things and their physical environment. A small change can affect another. 

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UNDERSTANDING ENERGY TRANSFER:

Trophic Level: the level at which an organism feeds in a food chain. 

At each trophic level, energy is lost:

• from metabolic reactions
• energy remains in dead matter which is broken down by bacteria/microorganisms,  cannot be digested by consumers. 

MEASURING THE EFFICIENCY OF ENERGY TRANSFERS

Pyramids of Biomass:

• Area of the bars are equal to the dry mass of all the organisms at that trophic level. 
• You must collect all the organism and place them in a oven of 80 degrees until all water has evaporated.
• Ecologist usually use the wet mass and then use past data. 

Pyramids of Energy:

• Burning the organisms in a calorimeter. 
• Working out from the heat energy how much energy is released. 

Productivity 

Disadvantages of pyramids of energy:

• Only a snapshot of the ecosystem at that moment in time
• Population sizes fluctuate a lot, and provide a distorted idea of the efficiency of the energy transfer. 

Productivity: rate at which energy passes through each trophic level.

• An idea of how much energy is available to organisms at particular trophic levels. (kilojoules/megajoules of energy per square metre per year)
• Plants: Primary productivity
• Gross Primary Productivity = rate at which plants convert light energy into chemical.
• Net Primary Productivity = remaining energy after some is lost via respiration. 

MANIPULATING ENERGY TRANSFER

Primary Productivity: 

< 1% of the sun’s energy is used for photosynthesis. The rest is reflected back up to the clouds or the earth’s surface. 

the energy captured by the leaves for photosynthesis is called the primary productivity. 

some energy may be lost as respiratory heat and the product:

primary productivity - respiratory heat = net primary productivity. 

net productivity is also known as NPP and is the rate of production of new biomass available for consumption by heterotrophs. 

Improving Primary Productivity

• light levels can affect NPP and so some farmers may grow plants earlier during the year to maximise light absorption
• lack of water is important, drought resistant strains of crops have been bred to resist lack of water
• temperature is able to limit the speed of chemical reactions within a plant. Greenhouses can control the internal temperature and increase NPP. 
• lack of nutrients can reduce the rate of photosynthesis and growth, crop rotation can help or nitrogen fixing crops
• spraying with pesticides can also increase NPP. 

Improving Secondary Productivity

transfer of energy from primary to consumers is inefficient. 

primary consumers don’t make full use of plants’ biomass

• young animals use a lot more energy fuelled into growth, harvesting animals before adulthood minimises energy loss in the food chain.
• some farm animals used to be treated with steroids in order to make them grow faster, so more energy is allocated to growth. this is now OUTLAWED in the EU.
• selective breeding is used to produce breeds that grow at a faster rate, increased egg or milk production
• animals are sometimes treated to antibiotics to avoid unnecessary usage of energy due to pathogens and parasites.
• mammals and birds waste quite a bit of energy when they walk around to maintain their core body temperature, but zero grazing means that they are able to maximise muscle growth. 

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Succession (directional change in a community of organisms over time)

SECONDARY SUCCESSION: takes place on previously colonised land, but disturbed or   

1. Pioneer plants colonise land just above high water mark. They are adapted to withstand lack of fresh water, unstable land and salt water spray.
2. Wind blown sand builds up, forms a mini sand dune. The plants die and nutrients begin to accumulate. New plants begin to colonise. 
3. With more stability and accumulation of more nutrients, new plants begin to grow.
4. Bacteria in the root nodules convert nitrogen into nitrates, and with more nitrates more species colonise the dunes and stabilise the land more.

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Nitrogen Cycle - 

Bacteria and fungi involved in decomposition feed in a different way -

SAPROTROPHICALLY 

they are SAPROTROPHS!!

• Secrete enzymes onto dead matter.
• enzymes digest the material into small molecules.
• reabsorbed into the organism, stored or respired to release energy. 

RECYCLING NITROGEN WITHIN AN ECOSYSTEM

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WHAT AFFECTS POPULATION SIZE

Carrying capacity: the maximum population size that can be maintained over a period of time in a particular habitat. 

Size of a population depends on mortality rate and the rate of reproduction.

Lag phase:

few individuals, but they are still acclimatising to the new surroundings, rate of reproduction is low as is the growth in population size.

Log phase:

many resources, good conditions, rate of reproduction is exceeding mortality rate. population size increases rapidly. 

Stationary phase:

Population size has levelled at the carrying capacity of the habitat. The habitat cannot support a larger population and the rate of mortality and reproduction are equal. 

PREDATORS AND PREY:

1. Predator population increases, more prey is eaten.
2. prey population drops, less food for the predator. 
3. less food, fewer predators can survive so population size reduces.
4. fewer predators means few prey are being eaten, and prey population size increases.
5. with more prey, the predator population increases, and the cycle repeats.

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COMPETITION

• happens when resources (food & water) are not present in adequate amounts to satisfy the needs of all the individuals who depend on those resources)

If any resource is in short supply, there will be competition between organisms in order to access that resource.

reproduction rate decreases and mortality rate increases. 

Two types of competition:

infraspecific:

• individuals of the same species.
• best adapted individuals often survive, 
• if population size decrease, competition reduces, population size then increases.

interspecific: 

• between individuals of different species
• affects both population sizes of a species and the distribution of different species in the ecosystem
• (page 206-207 for paramecium growth)

Competition between plants

allelopathy: former competition that stops its neighbours from using all the resources in the habitat. the released chemicals may leach out of leaves and fruits when a plant sheds them. 

the chemicals can be found in any plant, 

• into the soil directly from the roots, 
• leach out from leaves and fruits

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SUSTAINABLE MANAGEMENT

Due to rapid human population growth, new means of exploitation are required to support our need for resources. 

But approaches to exploit the land can come with consequences:

(destroying ecosystems, reduce biodiversity, or completely get rid of all the resources.)

Potential conflict between sustainability and our need for wood and timber. We need sustainable management to maintain biodiversity.

MANAGING SMALL SCALE TIMBER MANAGEMENT

Coppicing: involves cutting a tree trunk close to the ground to encourage new growth.

• harvesting wood but it keeps the tree alive in the process. 
• cut the trunk of a deciduous tree near the ground
• after it’s cut new shoots grow from the new surface. 
• they mature into stems of narrow diameter
• after cutting, new shoots grow so the coppice style continues.

POLLARDING- It involves cutting the trunk higher and is useful when the population size of deer is high. 

For a continuous supply of wood, managers will choose sections of a tree every year till it is all cut. This is called rotational coppicing

Some trees are left to grow larger without being coppiced these are called standards. 

Rotational coppicing is good for biodiversity because it helps to provide different types of habitats. 

MANAGING LARGE-SCALE TIMBER PRODUCTION 

 Clear-felling: involves clearing all the trees in one particular area:

• devastating to habitats
• large scale
• rarely practiced in the UK
• reduces soil mineral levels
• soil is susceptible to erosion

The soil is also able to run into waterways, and end up polluting the water.

This is because trees usually:

1. remove water from the soil and stops the soil getting washed away in the rain
2. maintenance of soil mineral levels, because of the trees’ roles in the nitrogen and carbon cycles.

what can we do? Leaving trees to mature during a period of 50-100 years can increase biodiversity. 

^ THIS IS NOT COST EFFECTIVE ^

Modern sustainable forestry works on some of these principles:

• when trees are harvested, a new one replaces it, either grown naturally or planted.
• the forest must be able to maintain its ecology (nitrogen/carbon cycles) despite extractions for timber
• local people should gain benefit from the forest. 

Selective cutting has benefits because only some are chosen to be removed. and the forest remains largely unaffected. 

However, being able to sustainably manage a forest is hard. To avoid too many trees having to be felled for timber foresters need to make sure that each tree provides more wood. 

This is done by:

• control of pests and pathogens
• only plant tree species that will be ale to grow well. 
• position trees an optimal distance apart so that each sapling receives a sufficient amount of minerals and ions to grow well. Planting trees too close would mean competition for light, and result in poorer quality of wood. 

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CONSERVATION

(The maintenance of biodiversity, including diversity between species, genetic diversity within species and maintenance of a variety of habitats and ecosystems.)

conservation is less about keeping things natural and rather about maintaining biodiversity.  

However human population increase greatly affects biodiversity:

• over-exploitation of wild populations for food, the rate of consumption is exceeding the rate at which species populations are able to replenish themselves. 
• habitat disruption and fragmentation as a result of intensive agricultural practices - increased population and widespread building
• species introduced to ecosystems may out-compete the native animals and the native animals may become extinct. 

Ethics

• every species has a value in its own right (financial benefits do not affect this)
• every living thing has the right to survive
• humans have an ethical responsibility to look after them

Economic and Social Reasons

why do we harvest things? More often than not it’s because of their economic value or they have valuable future value.

• more species = more diversity, for gene manipulation or for new strains of domestic animals
• natural environments are a source of beneficial resources (drugs)
• biological agents, cheaper

indirect value: biological pollinators, break down, recycling, 

Ecotourism and recreation has financial value

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HUMANS AND THE GALAPAGOS

Charles Darwin visited the Galapagos Islands in 1835.

He set out the motion that would change biological sciences. 

Some of the best-conserved tropical archipelagos with its own native species. 

Habitat Disturbances

Increase in population has put a strain on the resources: water, energy and population

Over exploitation of resources

sailors captures tortoises in order to survive and be eaten and killed, for food. 

Introduced species

are able to feed on the native species or compete for resources and this damages the survival of native species, because they’re more unique to the island, therefore native species may be eradicated. They can outcompete species and also new diseases are also able to come to the island.