What is the difference between a biome and an ecosystem?
A biome is a subset of an ecosystem.
A biome may be characterized more by the similarities of its life-forms than the interactions (and differences) between them, as is the case with an ecosystem.
An example would be the ocean as an ecosystem, and a coral reef, with all of its attendant plant and animal life as a biome. Another one would be a forest on a mountainside as a biome (again, with all of the other animals and plants associated with it), where the mountain range and surrounding plains are the ecosystem. The following link has very good examples of different biomes.
'If individual ecosystems are species of ecology , then biomes are the phyla '-- Chapman and Reiss (Ecology: principles and applications).
Ecologists identified different terrestrial biomes in this world on the basis of principal vegetation types. Later aquatic biomes have been recognised. Concept of biome makes it convenient to briefly describe flora and fauna of this world.
'Biome is a grouping of terrestrial ecosystems on a given continent that are similar in vegetation structure, physiognomy, features of the environment and characteristics of their animal communities. ' - from Page 2, Biomes by Keneisha Boozer
Ecologists rarely agree upon the number of biomes present on earth, because this classification is not natural. On the other hand ecosystem is a dynamic entity: an interactive association of living organisms and their physical environment.
WWF has identified 14 terrestrial biomes: other than the freshwater and marine biomes.
The major difference between these two terms is in regards to the scale they cover.
Ecosystems can be large or small in terms of the amount of geographic area they cover. Biomes are, by definition, large areas with a similar climate that are often named for the dominant vegetation type found in the area (tropical rainforest vs grassland).
The first image below is one rendering of different ecosystems across the planet. As you can see, there are a lot of different ecosystems of varying size. *Note that this is just one person's interpretation of ecosystems across the world.
In the second image below, we have one widely accepted classification of the world's biomes. We see far fewer biomes than ecosystems. While scientists still disagree over the number of biomes in the world, regardless of the exact number, multiple ecosystems fit within any biome.