Biotic factors are living. They include:
Both the abundance and distribution of living organisms in an ecosystem are affected by biotic factors.
Red squirrels are native to Great Britain. They weigh around 300 grams, and about half the mass of the larger grey squirrel. The red squirrel species was introduced around a hundred years ago from America by wealthy land owners who wanted a fashionable addition to their forests.
The larger grey squirrel has provided competition for the native red squirrel, which has resulted in a lack of food for the species. Organisations like the Red Squirrel Support Trust have sampled the numbers of both squirrel types over time. Their results are shown below.
What conclusions can you draw from this data?
In 1945 grey squirrels were only found in central Southern England and in small numbers on the East coast of Northern England. By 2000 they had spread throughout England and Wales. The red squirrel is now only found in parts of Scotland and Ireland. The pattern does not appear to have changed much between 2000 and 2015.
What limitations might there be in drawing these conclusions and how could these be improved?
This information is only from one source. It could be compared with others to ensure its reliability.