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Tropical temperate gradient
 

Tropical temperate gradient

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    Tropical temperate gradient Tropical temperate gradient Presentation Transcript

    • BiodiversityTropical-Temperate Gradient
      Dr. Mark A. McGinley
      Fulbright Visiting Scholar
      University of Malaya
      2010
    • Biodiversity Challenge
      Who has more biodiversity, Texas or Malaysia?
    • Biodiversity Challenge!
      Area
      Texas - 696,241 km2
      Malaysia 328,600 km2
      Number of Ecoregions
      Texas- 13
      Malaysia- 12
      Therefore, Texas is larger and has more habitat diversity than Malaysia.
    • Lessons From Biogeography
      Species-area curves show that larger areas often contain more species
      Species richness is correlated with habitat diversity
      Thus, predict that there will be more species in Texas than in Malaysia
      Not surprising- Everything is Bigger in Texas!!!!
    • Biodiversity Challenge
      Because of its large size and habitat diversity, Texas is one of the most diverse states in the USA.
      #1 in number of bird species (477)
      #1 in the number ofreptiles species (149)
      # 2 in the number of mammals species (159)
      # 2 in the number of vascular plant (4,509).
    • How About Malaysia?
      Mammals = 313 species
      Birds = 746 species
      Vascular plants = 15,500 species
    • Terrestrial Biodiversity
      Texas data from The Nature Conservancy of Texas
      Malaysia data from Wikipedia and www.mongabay.com
    • Much Greater Terrestrial Species Richness in Malaysia Than in Texas!
      Texas is an unusually species rich region in the US so it is not a problem with Texas.
      What causes there to be so many more species in Malaysia than in Texas?
    • Temperate-Tropical Gradient
      It has been well known for over 200 years than there tend to be more species of organisms living in tropical regions than in temperate regions
      Temperate-tropical gradient in species richness
      One of the most studied questions in biology
      But still don’t understand it very well
      Over 30 different hypotheses have been proposed
    • Temperate-Tropical Gradient in Species Richness
      • In many groups of organisms there are more species found in tropics than there are in the temperate regions.
      • Why?
      • Suggests that there is some sort of physical,biological, or geographical factors going on in the tropics that cause there to be more species
    • Tropical-Temperate GradientNull Effect
      • It is possible that the pattern might have nothing to do with biology
      • Instead the pattern might arise because the tropics lie in the center of the globe
      • Mid domain effect
      • Colwell, Willig
    • Null Models in Ecology
      It is possible that many of the patterns that ecologists have used to suggest that ecological interactions such as competition are structuring ecological communities are merely the result of random chance.
      Null Models are used to investigate this possibility.
    • Mid-Domain Effect
      If species vary in their latitudinal ranges (i.e., some species are found across a large range of latitudes and others are found across a very small range) then if the location of species on the globe is random then there will still be more species in the tropics.
    • Mid-Domain Effect
      The mid-domain effect probably doesn’t explain all of the pattern, but we need to examine whether tropics are more diverse than expected by random chance.
      Other factors can help to explain the “extra diversity”
    • How Should We Try To Study What Factors Cause Greater Species Richness in the Tropics?
      Go back to the library analogy for biodiversity
      How we should attempt to understand patterns of diversity depends on whether ecological communities are full or empty.
    • Tropical-Temperate Gradient
      Full
      Number species = number of niches
      Why more niches in tropics?
      Not Full
      Number of species = number of species added – number of species lost
      Need to focus on biological processes that increase the number of species (speciation and immigration) and those that decrease the number of species (extinction)
    • Temperate-Tropical Gradient
      To understand why there are so many more species in the tropics than in the temperate regions we need to think about
      Genetics
      Evolution
      Ecology
      Biogeography
    • Who Has More Money?Me or You?
    • Money Example
      • What determines the amount of money that someone has?
      • How much money they can store (silly, but possible)
      • How much money they make (ringgit per year)
      • How much money they spend
      • How long they have been making and spending that amount of money
    • Biodiversity
      • Making money = adding new species
      • Speciation
      • Immigration
      • Spending money = losing new species
      • Extinction
      • (not emigration – because rarely do all members of a species leave a region)
    • Making New Species“Speciation”
      Allopatric speciation
      Requires isolation by “geographic barrier”
      Requires long periods of time
      Thought to be the most common mechanism in most groups of organisms
      Sympatric speciation
      Does not require isolation
      Can be “instantaneous”
      Hybridization
      Host shifts
      For more info on speciation see http://www.slideshare.net/secret/3eX72KxuoWZn6R
    • What Determines Rates of Speciation
      Probability of forming geographic isolating barriers
      And maintaining them long enough for speciation
      Rate of selection
      Rate of mutation
      Generation time
    • More Time For Speciation in the Tropics
      Some people have proposed that the reason that there are more species in the tropics is that the temperate zones have been colonized more recently so there has been less time for the evolution of new species
    • Higher Rates of Speciation in the Tropics
      Data from plants show that plants in lower elevations have higher mutation rates than plants from higher elevations
      Suggest higher metabolic rates in warm temperatures causes higher rates of mutation
    • Lower Rates of Extinction in the Tropics
      Tropics are the largest biome in the world
      Large area allows for large population sizes
      Large population sizes correlate with lower rates of extinction
      If a species does go locally extinct, then it has the possibility of being “rescued” by immigration from another location in the tropics.
    • Higher Rates of Speciation in the Tropics
      • Because tropical plants live where it is warmer, they might have higher rates of mutation than plants in temperate regions
      Higher mutation rates might allow for faster natural selection
      Would allow for more allopatric speciation
    • Higher Rates of Speciation in the Tropics
      Plants are ectothermic whereas mammals maintain their bodies at a constant level no matter where they live.
      Thus, mammals may be less affected by this than plants.
      Compare mammal species from tropics to temperate zone
      Found faster evolution
      Cool climates caused less mutation
      Red Queen Hypothesis
    • Higher Rates of Speciation in the Tropics
      Some researchers have found no relationship between rates of mutations and latitude in birds
      Suggest that the differences in rates of evolution and speciation might be due to differences in generation times.
      Tropical species breed more often than temperate species so they should evolve faster.