Concept 18 - Concept 53.2 Dominant and keystone species...

Concept 53.2 Dominant and keystone species exert strong controls
on community structure
Species diversity is a fundamental aspect of community structure.
A small number of species in the community exert strong control on that community’s
structure, especially on the composition, relative abundance, and diversity of species.
The species diversity of a community is the variety of different kinds of organisms that
make up the community.
Species diversity has two components.
Species richness is the total number of different species in the community.
The relative abundance of the different species is the proportion each species represents
of the total individuals in the community.
Species diversity is dependent on both species richness and relative abundance.
Measuring species diversity may be difficult, but is essential for understanding community
structure and for conserving biodiversity.
Trophic structure is a key factor in community dynamics.
The trophic structure of a community is determined by the feeding relationships between
organisms.
The transfer of food energy up the trophic levels from its source in autotrophs (usually
photosynthetic organisms) through herbivores (primary consumers) and carnivores
(secondary and tertiary consumers) and eventually to decomposers is called a food chain.