BIOL 1911 Chapter 54.2: 54.2 – Diversity and trophic structure characterize biological communities
54.2 – Diversity and trophic structure characterize
biological communities
• Ecologies can be characterized by certain general attributes
o Diversity
o Feeding relationship of their species
o The control of a few species on a community structure (its composition, relative abundance and diversity)
Species Diversity
• Species diversity of a community = the variety of different kinds of organisms that make up the community
o Species richness = number of different species in the community
o Relative abundance = proportion each species represents of all individuals in the community
• Ecologists calculate indexes of species diversity based on species richness and relative abundance
o Ex: Shannon diversity (H)
• Determining the number and relative abundance of a species in a community can be challenging
o Because most species in a community are relatively rare, it may be hard to obtain a sample size large enough
to be representative
o Can also be difficult to identify some of the species in the community
▪ If some unknown organisms cannot be identified on the basis of morphology alone, it is useful to
compare all or part of its genome to a reference database of DNA sequences from known organisms
▪ Researchers are increasingly using DNA sequencing for species identification as it becomes cheaper
and as DNA sequences from more organisms are added to comparative databases
o Can be difficult to census the highly mobile or less visible members of communities
▪ Microorganisms, deep-sea creatures and nocturnal species
▪ Ecologists now commonly use molecular tools to help determine microbial diversity given the small
size of microorganisms
Diversity and Community Stability
• Ecologists manipulate diversity in experimental communities in nature and in the laboratory
• Many experiments examine the potential benefits of diversity
o Ex: increased productivity and stability of biological communities
• H y a…
o More productive
o Better able to withstand and recover from environmental stresses
o More stable year to year in their productivity
o Produce more biomass (total mass of all organism in a habitat)
o More resistant to invasive species
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