Ecosystems

(a)    Ecosystems, which range in size, are dynamic and are influenced by both biotic and abiotic factors.

·         Biotic factors are living features of an ecosystem, for example the presence of predators or food.

·         Abiotic factors are non-living features of an ecosystem, for example temperature and rainfall.

·         Rock pools:

o   Biotic factors – seaweed is a food source for consumers and intense competition for food can limit the number of organisms living in a small rock pool.

o   Abiotic factors – heavily influenced by tides, at high tide they are submerged by the ocean so have similar abiotic factors as the ocean (eg pH, salinity) but at low tide they experience more extreme abiotic conditions so only few organisms can survive in an environment like this.

·           Playing field:

o   Biotic factors – wide range of producers eg grass daisies & clovers this attracts a wide range of consumers eg rabbits & caterpillars.

o   Abiotic factors – rainfall and sunlight may affect the growth of producers. In a very wet year soil may become waterlogged making it hard for plants to grow. This will decrease the number of producers therefore decrease number of consumers the ecosystem is able to support.

·           Large tree:

o   Biotic factors – insects can use leaves as a food source however if they eat all of the leaves it can slow the growth of the tree and eventually this will lead to death.

o   Abiotic factors – drought conditions can negatively impact the growth of a tree due to the lack of water available.

(b)   Biomass transfers through ecosystems

·           To measure energy transfer between two trophic levels you need to calculate the difference between the net productivity in each level, you can do this by measuring the dry mass (biomass). First calculate biomass of a sample of organisms, and then multiply results by the size of total population to give total amount of energy in organisms of that trophic level. The difference between trophic levels is the amount of energy transferred.

·           1-3% of sun light is converted to biomass. 90% of sun light is reflected or the wrong wavelength. Energy is lost through photosynthesis as it’s inefficient. 20-50% of energy is lost in respiration.

·           Net Production = Gross Production – Respiratory Losses

·           Primary Net Production = Gross Production of Producer–Respiratory Losses of Producer

·           Human activity:

o   Herbicides kill weeds that compete with agricultural crops for energy so crops get more energy so grow larger and faster increasing productivity.

o   Fungicides kill fungal infections which damage agricultural crops, crops can use more energy for growth as they aren’t fighting infection.

o   Natural predators introduced to eat pests, crops lose less energy and biomass which increases productivity.

o   Using fertilisers replaces minerals that crops have lost so more energy can be used to grow.

o   Intensive farming…