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Biodiversity - Notes:: Surprise) Associated With This Prediction

The document discusses four key metrics for measuring biodiversity: relative abundance, species richness, species evenness, and species diversity. It also outlines several trends in biodiversity, including latitudinal and elevational diversity gradients where biodiversity typically decreases with increasing latitude but increases with elevation up to a point. The document also mentions Rapoport's Rule about species ranges being smaller at lower latitudes and altitudes. Finally, it notes historical trends in biodiversity have followed a hyperbolic growth model but the current Holocene extinction event poses a threat to many species.

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Abhisek Sarkar
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68 views2 pages

Biodiversity - Notes:: Surprise) Associated With This Prediction

The document discusses four key metrics for measuring biodiversity: relative abundance, species richness, species evenness, and species diversity. It also outlines several trends in biodiversity, including latitudinal and elevational diversity gradients where biodiversity typically decreases with increasing latitude but increases with elevation up to a point. The document also mentions Rapoport's Rule about species ranges being smaller at lower latitudes and altitudes. Finally, it notes historical trends in biodiversity have followed a hyperbolic growth model but the current Holocene extinction event poses a threat to many species.

Uploaded by

Abhisek Sarkar
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Biodiversity

 -­‐  notes:  

1. Four  metrics/indices  of  interest:  


a. Relative  Abundance  (pi)  
i. What  portion  of  the  total  population  (N)  is  one  particular  species  (ni)  
ii. pi  =  ni  /  N  
iii. For  example,  two  communities  may  both  contain  the  same  number  of  species  
but  one  community  may  be  dominated  by  one  species  while  the  other  
community  may  contain  large  numbers  of  all  species  
b. Species  Richness  (S)  
i. Total  number  of  species  present  within  an  ecosystem  
c. Species  Evenness  (J’)  
i. how  close  in  numbers  each  species  in  an  environment  are  
ii. can  be  represented  by  Pielou's  Evenness  Index:  
1. J’  =  H’/ln(S)  
a. Where  H’  is  the  Shannon  Diversity  Index  and  S  is  the  total  
number  of  species  
2. J'  is  constrained  between  0  and  1.  The  less  variation  in  communities  
between  the  species,  the  higher  J'  is  
d. Species  Diversity  
i. A  measure  of  the  diversity  within  an  ecological  community  that  incorporates  
both  species  richness  and  species  evenness  
ii. Shannon  Diversity  Index  (H’)  
1. Used  to  quantify  the  entropy  (uncertainty)  in  population.  The  idea  is  
that  the  more  different  species  there  are,  and  the  more  equal  their  
proportional  abundances  in  the  ecosystem,  the  more  difficult  it  is  to  
correctly  predict  which  species  will  be  the  next  one  selected  at  random.  
The  Shannon  entropy  quantifies  the  uncertainty  (entropy  or  degree  of  
surprise)  associated  with  this  prediction.  

   

 
 
2. Biodiversity  Trends:  
a. Latitudinal  Diversity  Gradient  (LDG)  
i. In  general,  as  latitude  increases,  biodiversity  decreases  
ii. There  exists  a  general  lack  of  consensus  as  to  why  this  pattern  exists  (see  
Wikipedia  for  a  good  summary  of  the  major  theories  to  date)  
 
 
 
 
 
 
     
b. Elevational  Diversity  Gradient  (EDG)  
i. Species  richness  (S)  tends  to  increase  as  elevation  increases,  up  to  a  certain  
point,  creating  a  "diversity  bulge"  at  middle  elevations  (approx.  1,000m-­‐1,300m  
[3,200-­‐4,300  ft])  
c. Rapoport’s  Rule  (Eduardo  Rapoport)  
i. States  that  latitudinal  ranges  of  plants  and  animals  are  smaller  at  low  latitudes  
and  altitudes  
1. Niche  specialization  
d. Biodiversity  trends  through  history:  
i. See  Phanerozoic  biodiversity  graph  on  course  website  
1. Growth  follows  hyperbolic  model,  in  which  second-­‐order  positive  
feedback  of  an  increase  in  biodiversity  causes  an  increased  growth  in  
biodiversity  (goes  beyond  first-­‐order  positive  feedback  system  where  
resource  availability  alone  allows  for  more  biodiversity)  
2. In  the  midst  of  the  Holocene  extinction  event  since  the  emergence  of  
humans,  some  arguing  that  current  rate  is  enough  to  eliminate  most  
species  on  earth  within  next  100  years  
 

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