Communities and Ecosystems

Food Web: Is a diagram that shows how food chains are linked together into more complex feeding relationships within a community.

Skills:

Food Webs consist of many interlinked food chains. Therefore organisms exist in multiple food chains often at different trophic levels.

When stating an organism's trophic level, it needs to be done, relative to a particular food chain.

Gersmehl Diagrams: Showing the inter-relationship between nutrient stores and flows between taiga, desert and tropical rainforest.

When used to analyze a particular ecosystem: diameter of sinks are proportional to the mass of nutrients stored in each sink. The thickness of the arrows are proportional to the rate of the nutrient flow.

Gross Production Vs. Net Production

Energy is not entirely lost; organisms do trap some of the energy in the form of biomass.

Gross Production (GP): Total amount of energy trapped in organic matter produced by plants in an ecosystem.

Net Production (NP): GP - energy lost through respiration. Amount of biomass that is available to the next trophic level

Trophic Level

The percentage of ingested energy converted to biomass is dependent on the respiration rate.

Energy flows through the ecosystem.


Net production: the amount of organic matter remaining after respiration .


Gross Production: The total amount of organic matter produced in an ecosystem.


Respiration: Stored energy used in the cellular respiration of ATP.

Organic matter: starch (stored energy) proteins & structural molecules. A lot of stored energy and nutrients are used by each individual.

Food Conversion Ratio:

In commercial (animal) food production, farmers measure the food conversion ratio (FCR). It is a measure of an animal's efficiency in converting feed mass into the desired output. For dairy cows, for example, the output is milk, whereas animals raised for meat, for examples, pigs the output is the mass gained by the animal.

FCR = Mass of the food eaten (g) / (Increase in) desired (g)

A good (low) FCR is obtained by minimizing the losses of energy by respiration, for example:

  • Restricting animal movement.
  • Slaughtering the animal at a young age (older animals have higher FCRs as they grow more slowly).
  • Optimizing feed so it is efficiently digested.

Pyramids of energy

Show the flow of energy between trophic levels

Transfer of energy is never 100% efficient.

Around 90% of energy is lost between tropic levels:

Not ingested (eaten. Not digested or assimilated. Excreted. Lost as heat from respiration.

Tertiary, secondary, primary consumers and producers.

Becomes: Biomass the total dry mass of organic matter in organisms or ecosystems.

What affects the transfer of nutrients between litter, soil and biomass is temperature and amount of rainfall.

Reasons for high net productivity of an ecosystem

  1. High primary productivity (by producers) means more energy is available to the ecosystem.
  1. The higher the efficiency of energy transfer between trophic levels the higher the net productivity. Energy transfer us typically 10%.
  1. Higher the primary productivity and greater the efficiency of energy transfer mean that more energy is available at high tropic levels. This can support longer the food chains, hence and more trophic levels increasing net productivity. Ecosystems rarely have more than 4 or 5 trophic levels.
  1. Trophic Levels
  1. Trophic Levels

Biome: Is a geographical area that has a particular climate and sustains a specific community of plants and animals.

Biosphere: Is the total of all areas where living things are found.

The main factors affecting the distribution of biomes is temperature and rainfall.

Varying according to latitude and longitude, elevation and proximity to the sea.

Temperature is influential because it affects the rate of metabolism - the pases in the life cycles of many organisms are temperature dependent.

Ecological Succesion

A climograph is a diagram which shows the relative combination of temperature and precipitation in an area.

The predictable and orderly changes in composition of an ecosystem over time.

Primary: The emergence of an entirely new ecosystem, such as a volcanic island.

Secondary: The replacement of one ecosystem by another following environmental change.

Gross production increases:

First colonizers are lichens on rock surfaces. Soil builds up, following death of smaller lichens. Larger plants take root as soil deepens. Productivity plateus as soil's carrying capacity is reached.

Soil is produced by detritivores (worms) following death of other plants and animals.

Microclimates are generated - small niches of differing temperature, light levels and humidity.
These new niches provide opportunities for more species, in turn affecting the abiotic environment.

Secondary Succession are disturbances that caan be natural or caused by human activity

Agriculture

Humans practices can accelerate the the flow of matter into and out of ecosystems. This by implication (and often design) alters the nutrient cycling in ecosystems.