Mechanisms for maintaining species diversity in tropical forests by gjjur4356

VIEWS: 15 PAGES: 11

									                                          FOR201
                                                                                          There may be between 100 and 300
                                                                                          tree species per ha in tropical moist
   Diversity & Dynamics in Tropical                                                       forests
       and Sub-Tropical Forests
                                                                                          As many as 2,500 species of vines
                                                                                          and lianas




 Insect diversity in tropical forests                                                     Alpha, Beta, Gamma Diversity

                               Terry Erwin’s famous study (1982)                         • Alpha diversity: diversity at one site
                               • Insecticide fogging of tree species
                               Luehea seemannii yielded 163 species of
                               beetles exclusive to this tree.
                               • 163 beetles / tree x 50,000 tree species =
                               8,150,000 beetle species.
                               • Beetles represent ~40% of insects.
                               • Thus, the total number of tropical insect
                               species was estimated at ~30,000,000




    Alpha, Beta, Gamma Diversity                                                          Alpha, Beta, Gamma Diversity

                                                                                        • Alpha diversity: diversity at one site

                                                                                        • Beta diversity: diversity related to habitat
                                                                                        differences
                                                                                           • number of species common to both sites
                                                                                           • B= 2C/(S1+S2)
                                                                                             Where C is the number of species common to site 1 and 2, S1 is the
                                                                                             number of species at site 1



http://redpath-museum.mcgill.ca/Qbp/2.About%20Biodiversity/definition.htm Jan 29 2007




                                                                                                                                                                  1
  Alpha, Beta, Gamma Diversity                                                                              Species-area curves




http://redpath-museum.mcgill.ca/Qbp/2.About%20Biodiversity/definition.htm Jan 29 2007




  Alpha, Beta, Gamma Diversity                                                            Alpha, Beta, Gamma Diversity

 • Alpha diversity: diversity at one site

 • Beta diversity: diversity related to
 habitat differences

 • Gamma diversity: total or regional
 diversity

                                                                                        http://redpath-museum.mcgill.ca/Qbp/2.About%20Biodiversity/definition.htm Jan 29 2007




                    Species-area curves
                      and g diversity




                                                                                                                                                                                2
                                                               Niches and Plants
   Mechanisms for maintaining
species diversity in tropical forests            ALL plants share same basic set of
                                                 resources -- namely: Light, water,
  • Niche partitioning                           carbon dioxide, mineral nutrients, space
    (regeneration/structural/edaphic niches)     BUT, plants can differ in subtle ways --
  • Natural enemies                              such as resource uptake rate, timing,
     (“Janzen-Connell hypothesis”)               efficiency, & tolerance of low resources
  • Intermediate Disturbance




 Niches and Species Coexistence                                Niche Partitioning
  General idea: diversity is maintained by       General idea: diversity is maintained by
  ecological differences between species         ecological differences between species
  -- in accordance with Gause’s “law”.           -- in accordance with Gause’s “law”.
                                                                   A             B              C
                                                 performance
                                                   Species




  “No two species can coexist
  indefinitely on the same
  limiting resource.”                                               Resource (type or amount)




            Niche Partitioning                   Animal specialization on plant
                                                         food sources
      Niche partitioning implies that
                                               Herbivores, pollinators,
      species CO-EVOLVE so that such           frugivores, wood-consumers, and
      ecological differentiation occur.        their predators & parasitoids




                                                                                                    3
Niche partitioning in tropical mammals                  Regeneration Niches
                                                                           Light gap



                                                                         Potential for
                                            Crown zone                   specialization




                                                          Tip-up mound                     Pit (w/ exposed
                                                                                               mineral soil)




           Regeneration Niches
                                           Structural Niches
 Species diversity
 maintained by
 specialization on                            Vertical
 different parts of
 gap phase mosaic,
                                           gradients in the
 different gap sizes,                          micro-
 or different
 positions within                           environment
 gaps




     Soil-related (edaphic) niches              Soil-related (edaphic) niches

                                            “The fact that up to half of the species (in
   May be related to:                       plots in Panama, Ecuador and Columbia) are
                                            showing an association with one or more
   • mineral nutrients,                     nutrients is quite remarkable.”
   • water availability / flooding,         J.W. Dalling U of Illinois January 2007
                                            http://www.news.uiuc.edu/news/07/0111trees.html Accessed Jan 31
   • toxic elements (e.g., heavy metals)    2007




                                                                                                               4
                                                       Evidence for J-C hypothesis
   The Janzen-Connell Hypothesis
                                                   • Well-known examples of “natural enemies”
               Natural enemies                     killing off monoculture plantations of native
                                                   tropical trees (e.g. Rubber, Hevea braziliensis)
                                                   • Many tropical trees show little recruitment
                                                   under parent tree crowns
            Density-dependent mortality
                                                   • Species-specific effects have been shown, in
                                                   some cases, to be due to specific pathogens or
                                                   herbivores

                    Distance-dependent mortality




 Future of oil palm (Elaeis guinensis)?                    Current status of J-C

                                                     • Spatial analyses of forest dynamics suggest
                                                     that Janzen-Connell effect is widespread,
                                                     particularly in commoner tree species.

                                                     • Fungal diseases are likely most important
                                                     “natural enemy”.




            Intermediate disturbance                 Intermediate disturbance in forests
                  hypothesis
                                                      • No disturbance = dominance by
                                                      most competitive (late-successional)
                                                      species.
diversity
Species




                                                      • High disturbance = only early-
                                                      successional species persist
                                                      • Intermediate disturbance = mix of
            Disturbance (intensity or frequency)
                                                      species types




                                                                                                      5
            Intermediate disturbance
                  hypothesis
                            Mixture of early and
                            late successional
diversity
Species




                                                   early
                                                                    Tropical Forest Dynamics
             Late
             successional                          successional




             Disturbance (intensity or frequency)




                                                                       Classes of Disturbance
  Old Field
  Succession                                                      Extent
                                                                  •   Major (large scale)
                                                                  •   Minor (small scale)

     Kimmins 1987                                                 Frequency

                                                                  Pattern




  Large-scale disturbance examples

   • Hurricane/typhoon damage: esp. Caribbean, Central
   America, Taiwan, parts of Philippines
   •Volcanic activity / earthquakes: along Andes, most
   of Indonesia, parts of Central Africa
   • Fire:most deciduous and semi-deciduous tropical
   forests
   • Wind storms: many parts of tropics




                                                                                                6
                                                                         Small-scale disturbance examples

     Logging /                                                           • small patches
    agricultural
                                                                           • insects, disease, animals (could also be
   conversion --                                                           large scale
analogous to natural
    large-scale                                                          • Wind throw
   disturbances?                                                         • Individual tree mortality




                                                                              Small-scale disturbance
                                                                                     examples
                                                                         • small patches
                                                                           • insects, disease, animals (could also be
                                                                           large scale
                                                                         • Wind throw

                                    W.A. Kenney                          • Individual tree mortality

 Pit Sawing Podocarpus falcatus. Amatola Mountains, Eastern Cape, S.A.          Gap Phase Dynamics




                      Forest Gaps                                         When a tree falls in the forest...




                                                                                                                        7
             Anatomy of a gap                                                                   Tip-up mound
                               Light gap




Crown zone




             Tip-up mound                         Pit (w/ exposed
                                                      mineral soil)




                                                                                            Effect of TMF canopy on the
                                                                                            quantity and quality of light

                                                                        Forest floor receives about
                                                                        2% of the PAR that reaches
                                                                        the surface of the canopy
                                         Pits & Mounds

                                                                        Shift in wavelength from
                                                                        red to far-red



                                                                      Whitemore, T.C. 1998. Tropical Rain Forests
   Photo by W.A. Kenney




Microenvironmental gradients                                               Microenvironmental gradients
                       Air temperature                                                                        Wind




                                                                                                   Dusk                          Dawn
                   Dusk                          Dawn
             Whitemore, T.C. 1998. Tropical Rain Forests                                   Whitemore, T.C. 1998. Tropical Rain Forests




                                                                                                                                         8
           Microenvironmental gradients                                             Microenvironmental gradients
                                    Relative humidity




                                    Dusk                          Dawn
                              Whitemore, T.C. 1998. Tropical Rain Forests
                                                                                                          Whitemore, T.C. 1998. Tropical Rain Forests




                        Tree successional status




                                                                            Gomez-Pompa, et al. 1991
                                                                            Rainforest regeneration and
                                                                            management. Man and the
                                                                            Biosphere Series. Vol. 6




                                                                                           Photosynthetic physiology




Gomez-Pompa, et al. 1991
Rainforest regeneration and
management. Man and the
Biosphere Series. Vol. 6




                                                                                                                                                        9
                       Growth curves                                                                   Survivorship




             Pioneer vs. Climax Tree Species
                  Pioneer                         Late-successional                        Seeds - the basic tradeoff
Germination       Triggered by heat, light        Germinates below canopy
Shade-tolerance   Cannot survive in shade         Survives in shade
Seeds             Small, many                     Large, few
Seed dormancy     Many form seed bank             Few spp. have do rmancy          Many and small                          Few and big
                  "orthodox"                      "recalcitrant"
Seed dispersal    Wind, animal                    Diverse
Growth rate       Rapid                           Slower
Physiology        High maximal photosynthesis,    Low maximal photosynthesis,
                  high light compensation point   low light compensation point
Growth            Indeterminate                   Determinate, resting buds
periodicity
Leaf life span    Short                           Long
Herbivory         Little herbivore defense        More herbivore defense, esp.
                                                  generalized defenses (tannins)
Wood              Low density, often pale         Higher density, gen. darker
Crown             Shallow; casts litt le shade    Deep ; casts deep shade
Bole              Clear; few knots                Knotty
Longevity         Short                           Long




            Seeds - late-successional spp.                                                   Seed germination types
                                                                                   “Orthodox”                       “Recalcitrant”

                                                                                   • Can survive in dormant         • Germinate or die within weeks
                                                         Brazil-nut:
                                                                                   state                            • Germination cue is endogenous
                                                         Bertholletia
                                                                                   • Often can be cold-stored       • Do not form seed banks
                                                         excelsa
                                                                                   • Form seed banks
                                                                                   • Germination triggered by       • Most late-successional trees
                                                                                   light (esp. R:FR ratio), heat,
                                                                                   and/or moisture
                                                                                   • Most pioneer trees




                                                                                                                                                      10
       Sapling architecture                                       Herbivory
  Light-demander
                     Shade-bearer          Pioneers: can
                                           “outgrow” herbivores
                                           Late-successional trees:
                                           higher investment in
                                           defensive chemicals


                                           Herbivores can make a
                                           big difference!!!




An understanding of this diversity in
    form and function (of species,
  communities and landscapes) and
 the role of disturbance is critical for
the conservation and management of
            tropical forests




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