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Sagebrush (Artemisia tridentata) ecosystems are declining due to biological invasions and changes in fire regimes. Understanding how ecosystem changes influence functionally important animals such as ecosystem engineers is essential to conserve ecological functions. American badgers (Taxidea tax-us) are an apex predator and ecosystem engineer in that they redistribute large amounts of soil within sagebrush ecosystems. Piute ground squirrels (Urocitellus mollis) are also an ecosystem engineer as well as an essential prey resource for many predators, including badgers. Our research objective was to evaluate the relative importance of biological invasions and fire, abiotic factors, and biotic factors on badgers and ground squirrels. We sampled 163 1-ha plots during April-June across a gradient of burn histories within a 1962 km 2 study area in southern Idaho, USA. At each plot, we characterized occupancy of ground squirrels and badgers and relative abundance of ground squirrels. Additionally, we characterized soil texture, climate, connectivity and dispersal potential, fire frequency, grazing, and cover of many plant species including a highly invasive exotic annual grass (cheatgrass; Bromus tectorum). We used an integrated approach to evaluate competing hypotheses concerning factors influencing occupancy and abundance. Results suggested that occupancy of ground squirrels was positively associated with long-term precipitation, dispersal potential, and fine-grained soil. Abundance of ground squirrels was positively associated with fine-grained soil, but negatively associated with cheatgrass, fire frequency, agriculture, and shrub cover. Badger occupancy was positively associated with ground squirrel occupancy and agriculture, which indicated affinity to prey. Our results provide insight into the relative influence of abiotic and biotic factors on predator and prey, and highlight how effects change across different population parameters. Our research suggests that widespread environmental change within sagebrush ecosystems, especially the fire-cheatgrass cycle (e.g., invasion of cheatgrass and increased fire frequency) and human land disturbances, are directly and indirectly influencing ground squirrels and badgers. However, we also found evidence that efforts to mitigate these stressors, for example, establishing bunchgrasses postfire, may provide targeted conservation strategies that promote these species and thus preserve the burrowing and trophic functions they provide.
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v v Article e013071v
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123
1Department of Fish and Wildlife Sciences, University of Idaho, Moscow, Idaho 83844-1136 USA
2U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Boise, Idaho 83706 USA
3Department of Statistical Science, University of Idaho, Moscow, Idaho 83844-1104 USA
Citation:
             
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Abstract.    Artemisia tridentata        
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Taxidea tax-
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Urocitellus mollis
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

    

          

Key words:     Artemisia tridentata   Bromus tectorum  
Taxidea taxusUrocitellus mollis
Received
E-mail:
Copyright:  

v v Article e013072v www.esajournals.org
HOLBROOK ET AL.
IntroductIon





     
 
        
        
       


    

    

 
       
    

     
      
      
    

 
   Artemisia tridentata)
     
     
  Taxidea taxus  
Urocitellus mollis



sensu


    
    
     
   
  
       

Athene cunicularia 

   
      
     
   



     
     



     
     

     

    




    
      
    


       
    

     
      

    
       


     
      
    





    
      


      
     
     
    

v v Article e013073v www.esajournals.org
HOLBROOK ET AL.
     
 

    
  A. t. wyomingensis
 

      Bromus
tectorum       
     2  
 2       
  
      


    
    
        
      

     

      
  

       
     
      
     
   
      
     
      
     
      






    
       
    
 


     
     
     
     
    
       

    

     
     
     
    

(Urocitellus mollisTaxidea taxus
             


v v Article e01307v www.esajournals.org
HOLBROOK ET AL.

     
  
     


   




       a
 
     
  
 

      

Methods
Study area and sampling
      
      


2

       
    
      
     

       
       
     
      
     
(A. t. wyomingensisKrascheninnikovia
lanataAtriplex confertifolia
    Poa
secunda     
       
  
       a,
b
       
  
     
     
    

n = 
(Urocitellus mollis   Taxidea taxus    

v v Article e01307v www.esajournals.org
HOLBROOK ET AL.
      



       
      
     
     
   
   
     

      

     



       

Badger and ground squirrel surveys
       
  
    


      
   
     
     

       
       
        

a, b     
     
     
      
       b) in
    
      
   
     
        
      


    


          

        

Dipodomys
b
      
  

       
      
       
        
      
      

    


     



        
      
      

      
      
      


       



 
       

     
     



Environmental data
Abiotic and biotic factors 
   
      
    
v v Article e013076v www.esajournals.org
HOLBROOK ET AL.
    
    
     
      
    
    
     

     


      
      
     

    
     
       
        
       
         
     
     
    
      
    
         
      
      


     




        

   
     
       
     

  2


2 
      
   
 


      
     




     
     

     

  


     

      
    



   
       
      


  

     
      
      
       
   



    
      




      
       
     




       
v v Article e013077v www.esajournals.org
HOLBROOK ET AL.
          

 


      

      
       
    
    
    


    
      
     
   
     
      
      
  
      

  
Artemisia


     
      
     



     
      




     

       
       
      
     
 
       
      
    
      

    
       

1∕(
̄
xd1,d2,d3,d4)2
  d   
        

̄
x


      
      
     


       

       

      


     
      

Ecosystem stressors: the re- cheatgrass cycle
       


     
        
     
       

     

      



        
     
       
      

   
       
  
       
      
      
    
    
v v Article e01307v www.esajournals.org
HOLBROOK ET AL.


       
         
   
       

     
      

      

     

    

Data analysis
   
    


(xi
̄
x)∕(2× σ)
xi
  i     


     
        

     
 
   
     
  
     
     
       
       
     
   
      
     
     
      


    



      



  
    
  b   
        

       
     
     
     


c

c    
    
c       

     
  c     
       

      
       


      

      
     
 c   

     
    
      
 
      

     
  





    

     
  
    
v v Article e01307v www.esajournals.org
HOLBROOK ET AL.

    



     
    

     
     
     



      


     


     
       
     
     
   

       

      



results
     
   
       
       
       
      


       
      
      
      
      

      
     
      
     
       
    r =  n = 30)

         
  
Occupancy
     
      
      
    
wi        
      
       
      Χ2  
   P = .  

        
      
     
      
      
      
       

    
     
     
   
   
c < 6 (wi 
 c

  
    
       
       
       
(Χ2P = 
  


     
     
    

       

       
v v Article e0130710v www.esajournals.org
HOLBROOK ET AL.
      
      

Abundance
  
    
   cwi  
c
      

    
      
    
     
      
      
   ρ    
   c     
    ρ   

      
      


    

 x     
Urocitellus mollis
       
   
      


         


(Urocitellus mollis


        k  wi.        

  k  wi
    0 
      
 

7   
  3   
  2   




   
  3   
      
  2   
  3   
  3   
  2   
  2   
      
  3   
  2   
      
v v Article e0130711v www.esajournals.org
HOLBROOK ET AL.
     
      
    
     
 
     
     
 
      
      
      

      
 


       
       
      
      
     


     
       
             
(Taxidea taxus   
c

kwi

  kccwi


 3 0
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    
  2  
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
    


     

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

6   
  2  0
  2  0
  2  0
  2  0
  2  0
  2  0
  3  0

    

 x     
(Taxidea taxus
  top model     


       
         
Urocitellus
mollis       
2  

v v Article e0130712v www.esajournals.org
HOLBROOK ET AL.
     

dIscussIon
       
     

       

     
     
      
    
     
     
       
     
     
     



     
  
   

Urocitellus mollis        
c
k
wiρ

  kccwiρ


RA

11  0


RA

10   



RA


12   


RA

11    


RA

    
 RA     
 RA 7   
 RA     
 RA 6   
 RA     
 RA    
 RA     
 RA 6   
 RA     
 RA     
 RA     
 RA     
 RA     
 RA

    
 RA     
 RA     
 RA     
 RA 6   
 RA

10    
 RA     

v v Article e0130713v www.esajournals.org
HOLBROOK ET AL.
        
xUrocitellus mollis
top model        
   
Bromus tectorum
                
2
 b
2

x
n = 
Urocitellus mollis
          

v v Article e01307v www.esajournals.org
HOLBROOK ET AL.
     
   
       

     
    
      
       
     

      
       
     

  
     
     
     
  
Effects of abiotic and biotic factors
      
     
      

      
     
          

     
       
      
      
     
     
       
   Urocitellus colum-
bianus   
     
      
    
       

     
     
      
         
      
Urocitellus endemicus
      
     
    

     
      

     
      
   
     
     
     

 Spermophilus parryii  

     
    
    
     

   
       
      

      
      
      
   
  
    

     
       

      
   
      

      
   
      
Ochotona curzoniae
Vulpes
ferrilata  


Felis silvestris silvestris
     



      
v v Article e01307v www.esajournals.org
HOLBROOK ET AL.
     
       
  






      
     
     
     




       
     



     
       


   
    


    
      
    
      

    
    



     
   
     
      


      



     
      


      

   

     



      





   
     

        
       


 
    



     
     
      
     


      
     



   
      
  
        
       
       
      
   


  
v v Article e0130716v www.esajournals.org
HOLBROOK ET AL.

    
      
      
      


Effects of ecosystem stressors: The fire- cheatgrass
cycle
     

     
       

     
       
     
    
   
  
     
      
      
     
    

       
    
      
    

        
     
    

     
        
    
     
    
          
      
      
        

      
     
     
       
      
 
      
       
      
     
       
     
     
 



       

     
      


 
      

    
      



  

   

     
       
 

     




      
    
     
     
     a    


    
     
      


v v Article e0130717v www.esajournals.org
HOLBROOK ET AL.
      

    

      


Implications
    
       
     
          
       
       
      
      
    
       
      
    
   
    

      
       
     
      
        
     
      
      
       
     
     
       
      
      
        
     
     

     
      
   

      
     

       
      
      
    
    
     
     


     
   
     
     

    
      
         
      



        
 


      
   




      

AcknowledgMents
       
        
        

      
       
     
       
       


        
    
lIterAture cIted
        
      
v v Article e01307v www.esajournals.org
HOLBROOK ET AL.
     









     

      


    
       
  


      


          




 
    
    

       
      



 
       

   

    





           
    
      



Chthamalus stellatus

     
     



     

   
     
     
      

      
       
 
    


     


  


      
Taxidea taxus
    

     Taxidea taxus 
      
    

Taxi-
dea taxus   
  




     

 
    



    



 

        

v v Article e01307v www.esajournals.org
HOLBROOK ET AL.
    






Taxidea taxus)
Cynomys leucurus

  

     

        
     


       
     





      
      
    
       

         


  

     

       







        


   

        
 


   


 

       

        


       
     
     
 

   
       






in


     




       
      

     


    
       
Meles meles

    
       

       
 


 






    
v v Article e0130720v www.esajournals.org
HOLBROOK ET AL.



      
       


        
     

       


         
    
     
   in     
     
       


          
       
    
     
       

 

      
   


    
      

     


 

        
      



     
      

   
    
    

         
    
   










    



Meriones hurrianae

Spermophilus townsendii



     

 

      

  



  
     

 

  







   
a
     
     


b
   

  
     
v v Article e0130721v www.esajournals.org
HOLBROOK ET AL.
      

     
      

       
   Spermophilus colum-
bianus







  






supportIng InforMAtIon
        

... Badgers excavate burrows for foraging, resting, and denning (Bylo et al., 2014). Badgers prey upon ground squirrels (Urocitellus sp.), prairie dogs (Cynomys sp.), and other ground-dwelling organisms (Eldridge, 2004;Grassel et al., 2015;Holbrook et al., 2016;Messick & Hornocker, 1981), primarily through the excavation of the prey species' burrows. The denning burrows of badgers exhibit a diversity of subterranean structures; they are generally larger and more complex than foraging excavations. ...
... Burrows are excavated year-round, but only a small proportion are occupied by badgers at any point in time, leaving many vacant burrows behind for potential use by other burrow dwellers (Eldridge, 2004). Estimates indicate badgers can generate up to 790 burrows/ha (Eldridge, 2004;Holbrook et al., 2016), which generally have 1-2 entrances (Symes et al., 2019) as opposed to other species like ground squirrels and prairie dogs where many entrances exist. Burrowing activity has biophysical consequences on soil properties such as texture, fertility, bulk density, and porosity (Eldridge, 2004;Eldridge & Whitford, 2009), as well as the distribution of water and other resources for vegetation (Kucheravy et al., 2021;Kurek et al., 2014). ...
... We sampled both areas to capture some variation in plant and animal communities within the sagebrush-steppe. In both study areas, we visually surveyed transects to detect evidence of badger activity, which was characterized by burrows with round or oval entrances of 16-30 cm in diameter and a mound of soil outside the entrance that was fanshaped (Eldridge, 2004;Holbrook et al., 2016). Both locations exhibited substantial badger activity as indexed by high burrow densities; additionally, we observed an individual badger foraging in each location. ...
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Abstract Ecosystem engineers are organisms that influence their environment, which includes alterations leading to habitat provisioning for other species. Perhaps the most well‐examined guild of species provisioning habitat for other species is tree cavity excavators or woodpeckers (Picidae). Many studies have examined the suite of secondary cavity users that rely on woodpeckers, and how the ecological network of secondary users, collectively referred to as the nest web, changes across communities. Despite similar habitat provisioning processes, fewer studies have assessed the suite of species associated with burrowers providing access to subterranean habitat. Here, we begin to characterize the burrow web provisioned by American badgers (Taxidea taxus) and evaluate the diversity and frequency of species interactions we detected at abandoned badger burrows in Wyoming, USA. We deployed camera traps at 23 badger burrows and identified interactions with the burrow by birds, mammals, and reptiles. Overall, we discovered 31 other species utilizing badger burrows, consisting of 12 mammals, 18 birds, and 1 reptile. Mammals, other than American badgers themselves and other fossorial species such as ground squirrels (Urocitellus sp.), frequently using burrows included mice (Peromyscus sp.), long‐tailed weasel (Mustela frenata), pygmy rabbit (Brachylagus idahoensis), and desert cottontail (Sylvilagus audubonii). Of the 18 bird species detected, most accounted for
... In southwestern Idaho, USA for example, the cheatgrass-fire cycle is burning so frequently that the area has experienced a vast conversion of shrub-steppe to mostly annual grasslands intermixed with some fire-resistant perennial bunchgrasses, such as Poa secunda (Knick & Rotenberry, 1997, Davies et al., 2012, Shi et al., 2018, Barker et al., 2019. This widespread shrubland to grassland conversion has altered plant diversity, vegetation structure, soil crusts, and bare ground to such an extent that habitats and microhabitats of most sagebrush steppe-associated wildlife are now fundamentally different (Freeman et al., 2014, Dumroese et al., 2015, Coates et al., 2016, Holbrook et al., 2016. ...
... Our findings suggest that the cheatgrass-fire cycle negatively impacts lizards and snakes, but some species may be more affected than others. Unfortunately, few comparisons are available for a few taxa (but see Holbrook et al., 2016), which is worrisome given the occurring ecological transformations. Thus, a call for more research is warranted for further investigation on reptiles, and other taxa. ...
... Within the Holloway fire perimeter, only 25% of the landscape was unburned, leaving substantially less cover for sage-grouse post-fire . Annual and perennial grasses have reoccupied the burned areas, and some mammalian predators might avoid areas with high cheatgrass canopy cover (Holbrook et al., 2016). However, sagebrush is slow to recover post fire (15-100 years depending on species), and the low vegetation structure following the fire may increase predators' ability to detect sage-grouse, especially where topographic ruggedness is high (Dinkins et al., 2014). ...
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Species responses to disturbance influence their extinction risks. Greater sage-grouse (Centrocercus urophasianus) are bioindicators of sagebrush ecosystem health and the loss of sagebrush (Artemisia spp.) due to wildfire, can cause long-term declines in sage-grouse populations and other sagebrush obligate species. We examined the demographic response of a greater sage-grouse population following a mega-wildfire using stochastic age-structured female-based matrix models over 6 years (2013–2018). Notably, chick survival (range = 0.18–0.38) and female survival (yearling range: 0.20–0.68; adult range: 0.27–0.75) were low compared to values reported for greater sage-grouse in other parts of their distribution. Greater sage-grouse displayed variation in demographic tactics after the fire; however, adult female survival explained most of the variation in λ during each year, which reflected a declining population in 3 of 6 years with more uncertainty observed in 2015 when populations may have been increasing, and 2017 and 2018, when populations may have been declining. The continued annual population decline observed since 2016 suggested there were additional strong environmental impacts that may have been compounded by the fire effects, prolonging recovery of greater sage-grouse. Our results support others that reported negative effects to greater sage-grouse demographics from broad-scale fire and provide a baseline for understanding how this species responds to loss of sagebrush cover based on their life history strategy.
... Apex predators may actually move into developed areas while searching for food resources, drawn by the large numbers of rodent prey. Rodents may therefore be helping to regulate apex predator abundance from the bottom-up in this system, rather than the opposite (Holbrook et al. 2016). The extent to which topdown and bottom-up forces affect local trophic dynamics remains a seminal question in ecology (Elmhagen and Rushton 2007), particularly within the context of habitat alteration. ...
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Anthropogenic activities are changing landscapes and the context in which predator–prey dynamics evolved, thereby altering key ecological processes and community structure. Yet, the specific mechanisms underlying such changes are rarely understood. We tested whether a mesopredator release explained increased rodent density and concomitant predation of songbird nests near natural gas development. From 2015 to 2016, we surveyed apex predators (coyotes, badgers, raptors, and corvids) and measured apparent survival and perceived predation risk of deer mice (Peromyscus maniculatus; a primary nest predator), at 12 plots spanning a gradient of surface disturbance caused by energy development in Wyoming, USA. Additionally, we measured densities of three nest predators: deer mice, least chipmunks (Tamias minimus), and thirteen‐lined ground squirrels (Ictidomys tridecemlineatus). Contrary to the mesopredator release hypothesis, counts of apex predators and perceived predation risk of deer mice increased with surface disturbance from energy development, whereas apparent survival of mice decreased. Densities of mice and ground squirrels, however, increased with surface disturbance, despite increased predation pressure. We therefore rejected the mesopredator release hypothesis as a potential mechanism underlying altered trophic dynamics near energy development. Our results suggest that apex predator control measures would not benefit declining songbirds on natural gas fields. Rather, apex predator abundance may be regulated from the bottom‐up by rodents in this system. Our results corroborate a pattern showing weakened effects of mesopredator release in habitats modified by humans. Understanding how predator–prey dynamics may be altered in novel environments requires an understanding of how predators and prey alike respond to habitat change under different contexts.
... Cheatgrass, a non-native annual grass, is one of the most notorious and problematic invasive plants in the United States. The grass primarily colonizes and becomes established in shrublands of the Intermountain West, including the Great Basin, where it is negatively associated with the richness and abundance of small mammals (Freeman et al. 2014;Holbrook et al. 2016) and reduces habitat quality for Greater Sage-Grouse (Centrocercus urophasianus; e.g., Crawford et al. 2004;Lockyer et al. 2015), a species of concern for regional management. Cheatgrass also increases the abundance and connectivity of fine fuels, and has altered fire frequency throughout the Intermountain West (D'Antonio and Vitousek 1992;Brooks and Pyke 2001;Pilliod et al. 2017). ...
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Abundance–occupancy relationships predict that species that occupy more sites are also more locally abundant, where occupancy is usually estimated following the assumption that species can occupy all sampled sites. Here we use the National Ecological Observatory Network small-mammal data to assess whether this assumption affects abundance–occupancy relationships. We estimated occupancy considering all sampled sites (traditional occupancy) and only the sites found within the species geographic range (spatial occupancy) and realized environmental niche (environmental occupancy). We found that when occupancy was estimated considering only sites possible for the species to colonize (spatial and environmental occupancy) weaker abundance–occupancy relationships were observed. This shows that the assumption that the species can occupy all sampled sites directly affects the assessment of abundance–occupancy relationships. Estimating occupancy considering only sites that are possible for the species to colonize will consequently lead to a more robust assessment of abundance–occupancy relationships.
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On the Ground •Available rangeland data, from field-measured plots to remotely sensed landscapes provide much needed information for mapping and modeling wildlife habitats. •Better integration of wildlife habitat characteristics into rangeland monitoring schemes is needed for most rangeland wildlife species at varying spatial and temporal scales. •Here, we aim to stimulate use of and inspire ideas about rangeland monitoring data in the context of wildlife habitat modeling and species conservation.
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Knowledge of how disturbances such as fire shape habitat structure and composition, and affect animal interactions, is fundamental to ecology and ecosystem management. Predators also exert strong effects on ecological communities, through top‐down regulation of prey and competitors, which can result in trophic cascades. Despite their ubiquity, ecological importance and potential to interact with fire, our general understanding of how predators respond to fire remains poor, hampering ecosystem management. To address this important knowledge gap, we conducted a systematic review and meta‐analysis of the effects of fire on terrestrial, vertebrate predators worldwide. We found 160 studies spanning 1978–2018. There were 36 studies with sufficient information for meta‐analysis, from which we extracted 96 effect sizes (Hedge's g) for 67 predator species relating to changes in abundance indices, occupancy or resource selection in burned and unburned areas, or before and after fire. Studies spanned geographic locations, taxonomic families, and study designs, but most were located in North America and Oceania (59% and 24%, respectively), and largely focussed on felids (24%) and canids (25%). Half (50%) of the studies reported responses to wildfire, and nearly one third concerned prescribed (management) fires. There were no clear, general responses of predators to fire, nor relationships with geographic area, biome or life history traits (e.g. body mass, hunting strategy and diet). Responses varied considerably between species. Analysis of species for which at least three effect sizes had been reported in the literature revealed that red foxes (Vulpes vulpes) mostly responded positively to fire (e.g. higher abundance in burned compared to unburned areas) and eastern racers (Coluber constrictor) negatively, with variances overlapping zero only slightly for both species. Our systematic review and meta‐analysis revealed strong variation in predator responses to fire, and major geographic and taxonomic knowledge gaps. Varied responses of predator species to fire likely depend on ecosystem context. Consistent reporting of ongoing monitoring and management experiments is required to improve understanding of the mechanisms driving predator responses to fire, and any broader effects (e.g. trophic interactions). The divergent responses of species in our study suggest that adaptive, context‐specific management of predator‐fire relationships is required.
Technical Report
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The sagebrush (Artemisia spp.) ecosystem extends across a large portion of the Western United States, and the greater sage-grouse (Centrocercus urophasianus) is one of the iconic species of this ecosystem. Greater sage-grouse populations occur in 11 States and are dependent on relatively large expanses of sagebrush-dominated habitat. Sage-grouse populations have been experiencing long-term declines owing to multiple stressors, including interactions among fire, exotic plant invasions, and human land uses, which have resulted in significant loss, fragmentation, and degradation of landscapes once dominated by sagebrush. In addition to the sage-grouse, over 350 species of plants and animals are dependent on the sagebrush ecosystem. Increasing knowledge about how these species and the sagebrush ecosystem respond to these stressors and to management actions can inform and improve strategies to maintain existing areas of intact sagebrush and restore degraded landscapes. The U.S. Geological Survey (USGS) has a broad research program focused on providing the science needed to inform these strate-gies and to help land and resource managers at the Federal, State, Tribal, and local levels as they work towards sustainable sage-grouse populations and restored landscapes for the broad range of uses critical to stakeholders in the Western United States. USGS science has provided a foundation for major land and resource management decisions including those that precluded the need to list the greater sage-grouse under the Endangered Species Act. The USGS is continuing to build on that foundation to inform science-based decisions to help support local economies and the continued conservation, management, and restoration of the sagebrush ecosystem. This report contains descriptions of USGS sage-grouse and sagebrush ecosystem research projects that are ongoing or were active during 2017 and is organized into five thematic areas: Fire, Invasive Species, Restoration, Sagebrush and Sage-Grouse, and Climate and Weather.
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Degradation, fragmentation, and loss of native sagebrush (Artemisia spp.) landscapes have imperiled these habitats and their associated avifauna. Historically, this vast piece of the Western landscape has been undervalued: even though more than 70% of all remaining sagebrush habitat in the United States is publicly owned, <3% of it is protected as federal reserves or national parks. We review the threats facing birds in sagebrush habitats to emphasize the urgency for conservation and research actions, and synthesize existing information that forms the foundation for recommended research directions. Management and conservation of birds in sagebrush habitats will require more research into four major topics: (1) identification of primary land-use practices and their influence on sagebrush habitats and birds, (2) better understanding of bird responses to habitat components and disturbance processes of sagebrush ecosystems, (3) improved hierarchical designs for surveying and monitoring programs, and (4) linking bird movements and population changes during migration and wintering periods to dynamics on the sagebrush breeding grounds. This research is essential because we already have seen that sagebrush habitats can be altered by land use, spread of invasive plants, and disrupted disturbance regimes beyond a threshold at which natural recovery is unlikely. Research on these issues should be instituted on lands managed by state or federal agencies because most lands still dominated by sagebrush are owned publicly. In addition to the challenge of understanding shrubsteppe bird-habitat dynamics, conservation of sagebrush landscapes depends on our ability to recognize and communicate their intrinsic value and on our resolve to conserve them. ¿Tambaleando en el Borde o Demasiado Tarde? Asuntos de Conservación e Investigación para la Avifauna de Ambientes de Matorral de Artemisia spp Resumen. La degradación, fragmentación y pérdida de paisajes nativos de matorrales de Artemisia spp. han puesto en peligro a estos ambientes y su avifauna asociada. Históricamente, esta vasta porción del paisaje occidental ha sido subvalorada: aunque más del 70% de todo el hábitat de matorral de Artemisia de los Estados Unidos es de propiedad pública, <3% de éste es protegido por reservas federales o parques nacionales. En este artículo revisamos las amenazas a las que se enfrentan las aves de los matorrales de Artemisia para enfatizar la urgencia de emprender acciones de conservación e investigación, y sintetizamos la información existente que constituye la base para una serie de directrices de investigación recomendadas. El manejo y conservación de las aves de los matorrales de Artemisia necesitará más investigación en cuatro tópicos principales: (1) la identificación de prácticas primarias de uso del suelo y su influencia sobre los ambientes y las aves de Artemisia, (2) un mejor entendimiento de las respuestas de las aves a componentes del hábitat y a procesos de disturbio de los ecosistemas de Artemisia, (3) el mejoramiento de diseños jerárquicos para programas de censos y monitoreos y (4) la conexión de los movimientos de las aves y los cambios poblacionales durante la migración y en los períodos de invernada con la dinámica en las áreas reproductivas de matorrales de Artemisia. Estas investigaciones son esenciales porque ya hemos visto que los ambientes de Artemisia pueden ser alterados por el uso del suelo, la diseminación de plantas invasoras y la disrupción de los regímenes de disturbio más allá de un umbral en el que la recuperación natural es poco probable. La investigación en estos asuntos debe instituirse en tierras manejadas por agencias estatales o federales porque la mayoría de las tierras aún dominadas por Artemisia son de propiedad pública. Además del desafío de entender la dinámica aves-hábitat en las estepas arbustivas, la conservación de los paisajes de matorral de Artemisia depende de nuestra habilidad de reconocer y comunicar su valor intrínseco y de nuestra decisión para conservarlos.
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Using radiotelemetry, we monitored dispersing juvenile Western Burrowing Owls (Athene cunicularia hypugaea) within a migratory population in southwestern Idaho during 1994 and 1995. Owls remained within natal areas for an average (± SE) of 58 ± 3.4 days post-hatching before moving permanently beyond 300 m, which was our operational cutoff for dispersal from the natal area. On average, owls dispersed on 27 July (range: 15 July to 22 August), which was approximately 4 weeks after fledging. After initiating dispersal, juveniles continued moving farther away from their natal burrows and, by 61–65 days post-hatching, they had moved 0.6 ± 0.2 km. Each juvenile used 5.1 ± 1.2 satellite burrows, and individual satellite burrows were used for up to 14 days. The average date on which we last sighted radio-tagged juveniles was 13 August, and all but one juvenile departed the study area by early September. Our study illustrates the importance of satellite burrows to dispersing Burrowing Owls.
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Articles E cologists have long debated what factors control the trophic (feeding) structure and function of ecosystems. This is more than just a matter of determining "who eats whom"; ecologists have pondered whether there are fundamental rules for determining (a) how many trophic levels an ecosystem can support, (b) how much primary production is consumed by herbivores, and (c) whether resources from the bottom of the food chain, or consumers from the top, control biomass, abundance, and species diversity in food webs. These questions are not only fundamental to ecology but essential for conservation and management. For example, the loss of a top predator in a food web that is largely controlled by top-down forces may drastically alter biodiversity and ecosystem function (e.g., nutrient cycling), whereas the same loss may have little effect in a resource-controlled (i.e., bottom-up) food web. To answer these questions, ecologists have expended an enormous effort to understand the relative importance of pre-dation or parasitism (and, to a lesser extent, mutualism) and competition for resources in trophic organization. Three basic models of control of trophic structure have emerged from this endeavor. The first of these, the energetic model of food webs, holds that energy supply (from the bottom of food webs), in concert with the relative efficiencies of consumers, limits the number of trophic levels and the relative biomass of each level in natural ecosystems (Lindeman 1942). The second model, commonly known as the "green world" hypothesis (Hairston et al. 1960), states that predators and parasites exert top-down control on herbivore populations. According to this model, herbivores do not generally compete with each other, and plant resources are not limiting because herbivore population densities remain low as a result of top-down control. The third model (Menge and Sutherland 1987) hypothesizes that the relative effects of predation on species diversity vary as a function of environmental stress (e.g., exposure, desiccation, extreme temperatures) and productivity. Specifically, the Menge-Sutherland model suggests that pre-dation should be more important at low and intermediate levels of stress, because high stress limits the abundance of predators more than it limits herbivore competitors. Competition for resources should be more important at high levels of stress (and low levels of productivity). Various modifications and elaborations of these three basic models of food webs and trophic structure have proliferated in the past several decades (Oksanen et al. 1981, Power 1992). Empirical tests of the food web models, and modifications thereof, have been conducted mostly in non-human-dominated ecosystems ranging from marine environments to freshwater lakes and streams, tundra, deserts, forests, and grasslands, each test often producing a different answer (Con-nell 1983, Schoener 1983, Sih et al. 1985). Empirical tests and the development of theory for food web dynamics have historically involved human-dominated ecosystems, such as agroecosystems (Rosenheim 1998), or recovering agricul-Stanley H. Human activities dramatically change the abundance, diversity, and composition of species. However, little is known about how the most intense human activity, urbanization, alters food webs and trophic structure in biological communities. Studies of the Phoenix area, situated amid the Sonoran Desert, reveal some surprising alterations in the control of trophic dynamics. Species composition is radically altered, and resource subsidies increase and stabilize productivity. Changes in productivity dampen seasonal and yearly fluctuations in species diversity, elevate abundances, and alter feeding behaviors of some key urban species. In urban systems-in contrast to the trophic systems in outlying deserts, which are dominated by limiting resources-predation by birds becomes the dominant force controlling arthropods on plants. Reduced predation risk elevates the abundance of urban birds and alters their foraging behavior such that they exert increased top-down effects on arthropods. Shifts in control of food web dynamics are probably common in urban ecosystems, and are influenced by complex human social processes and feedbacks.
Book
A guide to using S environments to perform statistical analyses providing both an introduction to the use of S and a course in modern statistical methods. The emphasis is on presenting practical problems and full analyses of real data sets.
Code
Tools for performing model selection and model averaging. Automated model selection through subsetting the maximum model, with optional constraints for model inclusion. Model parameter and prediction averaging based on model weights derived from information criteria (AICc and alike) or custom model weighting schemes. [Please do not request the full text - it is an R package. The up-to-date manual is available from CRAN].