Patterns in Species Diversity

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					Patterns in Species Diversity   Community Saturation

 • Niche width, niche            • Local community richness should
   overlap, alpha, beta            be related to regional richness (a
   and gamma diversity.            nested subset).

 • R – range of                  • Saturated vs unsaturated
   resources                       communities
 • n – degree of
   specialization                • Role of biotic interactions
 • o – degree of niche
   overlap




                                Local vs. regional control of diversity
                                 •   Local control
                                      – Communities are saturated,
                                        resistant to invasion
                                      – Physically similar sites should
                                        have similar diversity,
                                        regardless of regional
                                        diversity
                                      – Local diversity independent of
                                        regional diversity

                                 •   Regional control
                                      – Communities tend not to be
                                        saturated, prone to invasion
                                      – Physically similar sites have
                                        different diversity due to
                                        different richness of regional
                                        pools
                                      – Local diversity closely linked
                                                                          Schluter and Ricklefs 1998
                                        to regional diversity




                                                                                                       1
         Largest scale



              saturated




                             Smallest scale



                                          unsaturated




Species Richness and Productivity                       Species Richness and Productivity

 • Strong relationship between                           • Best relationships with primary producers, animal diversity
   richness and energy available                           typically correlates with plant diversity.
   (PET).                                                • Physiological and phylogenetic constraints
 • Energy alone not adequate,
   need energy and available water.




                                                                                                                         2
                                 Species Diversity and Latitude

                                  • Evolutionary Time Hypothesis - the older a community
                                    the greater the opportunity for it to have accumulated
                                    species through speciation and/or emigration


                                             New area                        Old area




Species Diversity and Latitude   Species Diversity and Latitude

                                  • Ambient Energy Hypothesis
                                     – Lower latitudes are at or near physiological optima for
                                       greater proportion of time.
                                     – More energy invested in production, less in tolerance.
                                     – Support for more trophic levels, greater diversity
                                       within levels




                                                                                                 3
Species Diversity and Latitude                           Paradox of Enrichment

 • Evolutionary Speed Hypothesis                          • Controlling for
    – Lower latitudes feature                               phylogeny…
      habitats allowing:                                  • Low productivity →
       • Faster physiological                               resources rare,
         processes (growth)                                 intense competition
       • Faster generation times                            or insufficient
                                                            energy.
       • Greater mutation rates
                                                          • High productivity →
                                                            rapid competitive
                                                            exclusion.
                                                          • Intermediate
                                                            productivity
                                                            maximizes
                                                            diversity.




Environmental Stability                                  Species Diversity and Latitude

 • Non-seasonal environment → expect greater              • Geographic Area Hypothesis – the shape of the globe
   specialization, possibly greater diversity               results in greater area at the equator. Simple species-
 • Seasonal environment → changing climate facilitates      area relationship = lower diversity at higher latitudes
   temporal segregation
 • General trend of greater diversity in non-seasonal
   environments…circular?




                                                                                                                      4
                                       Species Area Relationship
•   Robert MacArthur and E. O.
                                        Largest area
    Wilson (1967). The theory of        7 species
    Island Biogeography.




                                                  Small area
                                                  1 species                    Large area
                                                               Medium area     6 species
                                                               3 species




Species Area Relationship on Islands   Species Area Relationship




                                                                               S = Cz A
                                                                             Where:
                                                                             S=# species
                                                                             C=ecosystem constant
                                                                             Z=slope, # species added
                                                                             per unit area
                                                                             A=area




                                                                                                        5
                                                Island Proximity and Species Diversity

• z values for various
  ecosystems




                                                Interaction between size and proximity




                                                       SDS = # species on a small, distant island

                                                       SCL = # species on a large, close island

                                                       Y-axis – turnover rates
              Ŝ=equilibrium number of species




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