One individual, however, expresses only a small number of these molecules—up to six different class I molecules and 12 or more different class II molecules.

TLS Online TPP Program

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#Unit 10. Ecological Principles

Communities in Climatically Similar Habitats May Themselves Be Similar in Species Richness

A stable community changes little in species richness over time

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#Id: 5736

#Unit 10. Ecological Principles

Proposed attributes of successfully invading species

a. Shedding of natural enemies during colonization 

b. Absence of natural enemies in recipient community 

c. Better competitor than native species 

d. Presence of mutualists in recipient community 

e. High dispersal ability 

f. Association with humans 

g. High reproductive rate (r-selected species) 

h. High growth rate (r-selected species) 

i. Ability to thrive in disturbed areas 

j. Asexual reproduction (plants) 

k. Unique ways of life; occupy vacant niches 

TLS Online TPP Program

#Id: 5737

#Unit 10. Ecological Principles

Five Hypotheses Explain How Species Richness Affects Community Services Diversity-stability hypothesis, more species are present, the more stable the community.

TLS Online TPP Program

#Id: 5738

#Unit 10. Ecological Principles

Elton’s hypothesis suggests there is a linear correlation between species richness and community services

TLS Online TPP Program

#Id: 5739

#Unit 10. Ecological Principles

Paul and Ann Ehrlich (1981) proposed an alternative called the rivet hypothesis Some species play a small but critical role in keeping the plane, the community, airborne, while other species do not

TLS Online TPP Program

#Id: 5740

#Unit 10. Ecological Principles

 Brian Walker (1992) proposed the Redundancy hypothesis Species that play the same roles in a community can compensate for each other if some are lost under particular conditions