San Diego State University Variation of Kaibab Deer Population with Time Questions

  

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Name:  __________________________  
Bio  240,  Community  Ecology  
Land  Management:  The  Lesson  of  the  Kaibab  Deer    
Objectives:  
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Graph  data  on  the  Kaibab  deer  population  of  Arizona  from  1905  to  1939  
Determine  factors  responsible  for  the  changing  populations  
Determine  the  carrying  capacity  of  the  Kaibab  Plateau  
 
The  environment  may  be  altered  by  forces  within  the  biotic  community,  as  well  as  by  relationships  
between  organisms  and  the  physical  environment.  The  carrying  capacity  of  an  ecosystem  is  the  
maximum  number  of  organisms  that  an  area  can  support  on  a  sustained  basis.  The  density  of  a  
population  may  produce  such  profound  changes  in  the  environment  that  the  environment  becomes  
unsuitable  for  the  survival  of  that  species.  For  instance,  overgrazing  of  land  may  make  the  land  unable  to  
support  the  grazing  of  animals  that  lived  there.  
Background  
Before  1905,  the  deer  on  the  Kaibab  Plateau  were  estimated  to  number  about  4000.  The  average  
carrying  capacity  of  the  range  was  then  estimated  to  be  about  30,000  deer.  On  November  28th,  1906,  
President  Theodore  Roosevelt  created  the  Grand  Canyon  National  Game  Preserve  to  protect  the  “finest  
deer  herd  in  America.”  
Unfortunately,  by  this  time  the  Kaibab  forest  area  had  already  been  overgrazed  by  sheep,  cattle,  and  
horses.  Most  of  the  tall  grasses  had  been  eliminated.  The  first  step  to  protect  the  deer  was  to  ban  all  
hunting.  In  addition,  in  1907,  The  Forest  Service  tried  to  exterminate  the  predators  of  the  deer.  Between  
1907  and  1939,  816  mountain  lions,  20  wolves,  7388  coyotes  and  more  than  500  bobcats  were  killed.  
Signs  that  the  deer  population  was  out  of  control  began  to  appear  as  early  as  1920  -­‐  the  range  was  
beginning  to  deteriorate  rapidly.  The  Forest  Service  reduced  the  number  of  livestock  grazing  permits.  By  
Name:  __________________________  
Bio  240,  Community  Ecology  
1923,  the  deer  were  reported  to  be  on  the  verge  of  starvation  and  the  range  conditions  were  described  
as  “deplorable.”  
The  Kaibab  Deer  Investigating  Committee  recommended  that  all  livestock  not  owned  by  local  residents  
be  removed  immediately  from  the  range  and  that  the  number  of  deer  be  cut  in  half  as  quickly  as  
possible.  Hunting  was  reopened,  and  during  the  fall  of  1924,  675  deer  were  killed  by  hunters.  However,  
these  deer  represented  only  one-­‐tenth  of  the  number  of  deer  that  had  been  born  that  spring.  Over  the  
next  two  winters,  it  is  estimated  that  60,000  deer  starved  to  death.  
Today,  the  Arizona  Game  Commission  carefully  manages  the  Kaibab  area  with  regulations  geared  to  
specific  local  needs.  Hunting  permits  are  issued  to  keep  the  deer  in  balance  with  their  range.  Predators  
are  protected  to  help  keep  herds  in  balance  with  food  supplies.  Tragic  winter  losses  can  be  checked  by  
keeping  the  number  of  deer  near  the  carrying  capacity  of  the  range.    
DATA  
1.  Graph  the  deer  population  data.  Determine  the  independent  variable  (X  axis)  and  dependent  variable  (Y  axis)
DATA TABLE
Year
Deer Population
1905
4,000
1910
9,000
1915
25,000
1920
65,000
1924
100,000
1925
60,000
1926
40,000
1927
37,000
1928
35,000
1929
30,000
1930
25,000
1931
20,000
1935
18,000
1939
10,000
 
Analysis  
1.  During  1906  and  1907,  what  two  methods  did  the  Forest  Service  use  to  protect  the  Kaibab  deer?  
   
 
2.  Were  these  methods  successful?  Use  the  data  from  your  graph  to  support  your  answer.  
   
Name:  __________________________  
Bio  240,  Community  Ecology  
 
3.  Why  do  you  suppose  the  population  of  deer  declined  in  1925,  although  the  elimination  of  predators  occurred?  
   
 
4.  Why  do  you  think  the  deer  population  size  in  1900  was  4,000  when  it  is  estimated  that  the  plateau  has  a  
carrying  capacity  of  30,000?  
   
 
5.  Suggest  what  YOU  would  have  done  in  the  following  years  to  manage  deer  herds.  
1915:  
   
1926:  
   
 
6.  It  is  a  criticism  of  many  population  ecologists  that  the  pattern  of  population  increase  and  subsequent  crash  of  
the  deer  population  would  have  occurred  even  if  the  bounty  had  not  been  placed  on  the  predators.  Do  you  agree  
or  disagree  with  this  statement.  Explain  your  reasoning.  
   
 
 
 
7.  What  future  management  plans  would  you  suggest  for  the  Kaibab  deer  herd?  
 
 
 
 
 
Adapted  from  The  Biology  Corner  

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