Biotic Factors Noadswood Science, 2016

Saturday, June 16, 2018 Biotic Factors To be able to identify biotic factors and how these impact ecosystems

Precise Learning Students should be able to explain how a change in a biotic factor might affect a given community given appropriate data or context. Biotic (living) factors which can affect a community are: availability of food new predators arriving new pathogens one species outcompeting another so the numbers are no longer sufficient to breed Students should be able to extract and interpret information from charts, graphs and tables relating to the effect of biotic factors on organisms within a community.

Biotic Factors Biotic factors are the living factors in an ecosystem Biotic factors include: New predators arriving Competition (one species may outcompete another so that numbers are too low to breed) New pathogens Availability of food

Biotic Factors Biotic factors can also vary in an ecosystem – a change in the environment could be the introduction of a new biotic factor, e.g. a new predator or pathogen These changes can also affect the size of populations in a community which can have knock-on effects because of interdependence E.g. a new predator could cause a decrease in the prey population such as grey squirrels which out-compete the native red squirrel populations

Abiotic and Biotic Data In an investigation into the effects of fertiliser on the environment it was added to a field which contained a pond. The plants and wildlife in and around the pond were then studied for 40 days. The table shows the size of the fish population in the pond and the graph shows the percentage cover of the pond by algae over time A higher percentage cover means that less light is able to reach the plants below the surface of the water

Abiotic and Biotic Data The amount of algae increased because the fertiliser increased the amount of nutrients in the water. Explain whether the increase in algae was caused by a biotic or abiotic factor… Abiotic – nutrients in the water is a non-living factor

Abiotic and Biotic Data Describe the relationship between the percentage cover of algae and the size of the fish population Between 0-10 days the percentage cover of algae increases, but the fish population barely changes. Between days 10-40 the percentage covers continues to increase and the size of the fish population decreases rapidly

Abiotic and Biotic Data Suggest an abiotic factor that could be responsible for the change in the size of the fish population and explain why this is the case A reduced oxygen level – the algae cover reduces the amount of light reaching the plants below the surface of the water, so the plants cannot carry out photosynthesis and die off One of the products of photosynthesis is oxygen, so if there are fewer plants carrying out photosynthesis less oxygen is released The lack of oxygen means that the fish cannot survive, so the population decreases

Abiotic and Biotic Data The graph below shows how the size of the fish population and a population of fish-eating birds changed over the 40days of observation Suggest a biotic factor that could be responsible for the trend in the size of the fish-eating bird population between day 10 and 40

Abiotic and Biotic Data A shortage of food for the birds – the size of the bird population starts to decrease shortly after the size of the fish population starts to decrease As the size of the fish population decreases, there is less food available to the birds, so the birds either die or move elsewhere in search of food