Biotic factors that affect communities

A tree suffering from Ash dieback disease
Ash dieback disease

The abundance and distribution of organisms in an ecosystem are affected by biotic factors, which involve living organisms.

The harlequin ladybird
The harlequin ladybird

They include:

  • availability of other organisms for food
  • the arrival of new predators:
    • in balanced ecosystems, predators and prey have evolved together
    • the arrival of a new predator will disrupt numbers of prey and other organisms
    • for example, the introduction of rats to certain Pacific islands has led to the extinction of bird species
  • new diseases:
    • when organisms are brought into new ecosystems, they often bring new pathogens
    • for example, ash dieback, caused by a fungus identified in Poland in 1992, and thought to have arrived in the UK in 2012
  • one species outcompeting another:
    • when a newly-introduced species outcompetes a native species
    • for example, in the 19th century, grey squirrels were brought over from North America and outcompeted the smaller native red squirrel - and also transmitted deadly pox virus
    • for example, the harlequin ladybird, which arrived in the UK in 2004, outcompetes British ladybirds for food, and also preys on them
Map showing the spread of the harlequin ladybird across the UK from 2003 to 2014The spread of the harlequin ladybird in the British Isles, 2004-2014