ArticlePDF Available

Occupancy and abundance of predator and prey: Implications of the fire-cheatgrass cycle in sagebrush ecosystems

Wiley
Ecosphere
Authors:
Joseph D Holbrook at University of Wyoming
Joseph D Holbrook
Robert S. Arkle at United States Geological Survey
Robert S. Arkle
Janet L. Rachlow at University of Idaho
Janet L. Rachlow
Kerri T. Vierling at University of Idaho
Kerri T. Vierling
Show all 6 authorsHide
Download full-text PDF
Read full-text
Download citation

Abstract and Figures

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.
Hypothesized strength of effect across biotic and abiotic themes for occupancy of Piute ground squirrels (Urocitellus mollis) and American badgers (Taxidea taxus) and abundance of ground squirrels. Abiotic themes include soil, climate, and disturbance (i.e., fire), whereas biotic themes include landscape, dispersal, disturbance (i.e., grazing), predation, prey, and forage. Asterisks indicate an ecosystem stressor (i.e., biological invasions and fire) is embedded within the theme. See Appendix S2: Tables S1–S3 for specific variables within biotic and abiotic themes.
Hypothesized strength of effect across biotic and abiotic themes for occupancy of Piute ground squirrels (Urocitellus mollis) and American badgers (Taxidea taxus) and abundance of ground squirrels. Abiotic themes include soil, climate, and disturbance (i.e., fire), whereas biotic themes include landscape, dispersal, disturbance (i.e., grazing), predation, prey, and forage. Asterisks indicate an ecosystem stressor (i.e., biological invasions and fire) is embedded within the theme. See Appendix S2: Tables S1–S3 for specific variables within biotic and abiotic themes.
… 
(a) Location of Morley Nelson Snake River Birds of Prey National Conservation Area (i.e., study area) in southwestern Idaho, USA. (b) Distribution of 1-ha plots (n = 163) that were sampled for Piute ground squirrels (Urocitellus mollis) and American badgers (Taxidea taxus). (c) Photograph of a badger on one of our 1-ha plots (taken by J. Holbrook).
(a) Location of Morley Nelson Snake River Birds of Prey National Conservation Area (i.e., study area) in southwestern Idaho, USA. (b) Distribution of 1-ha plots (n = 163) that were sampled for Piute ground squirrels (Urocitellus mollis) and American badgers (Taxidea taxus). (c) Photograph of a badger on one of our 1-ha plots (taken by J. Holbrook).
… 
Standardized parameter estimates (±90% credible intervals) describing the effect of explanatory variables (x-axis) on occupancy of Piute ground squirrels (Urocitellus mollis). Data were collected on the Morley Nelson Snake River Birds of Prey National Conservation Area in southern Idaho, USA. Variable descriptions are as follows: precipitation – mean annual precipitation from 1979 to 2008, DI – dispersal index (i.e., number of burrows at the nearest sampled 1-ha plot/distance to the plot), and soil texture – % surface soil passing through a #4 sieve.
Standardized parameter estimates (±90% credible intervals) describing the effect of explanatory variables (x-axis) on occupancy of Piute ground squirrels (Urocitellus mollis). Data were collected on the Morley Nelson Snake River Birds of Prey National Conservation Area in southern Idaho, USA. Variable descriptions are as follows: precipitation – mean annual precipitation from 1979 to 2008, DI – dispersal index (i.e., number of burrows at the nearest sampled 1-ha plot/distance to the plot), and soil texture – % surface soil passing through a #4 sieve.
… 
Standardized parameter estimates (±90% confidence intervals) describing the effect of explanatory variables (x-axis) on occupancy of American badgers (Taxidea taxus). If a variable does not have a parameter estimate labeled top model it was not included. Data were collected on the Morley Nelson Snake River Birds of Prey National Conservation Area in southern Idaho, USA. Variable descriptions are as follows: firefreq – number of times the area burned from 1957 to 2013, GSOcc – occupancy of Piute ground squirrels (Urocitellus mollis) at plot-level, human – % human disturbance within a 2.4 km 2 area, and soil texture – % surface soil passing through a #4 sieve.
Standardized parameter estimates (±90% confidence intervals) describing the effect of explanatory variables (x-axis) on occupancy of American badgers (Taxidea taxus). If a variable does not have a parameter estimate labeled top model it was not included. Data were collected on the Morley Nelson Snake River Birds of Prey National Conservation Area in southern Idaho, USA. Variable descriptions are as follows: firefreq – number of times the area burned from 1957 to 2013, GSOcc – occupancy of Piute ground squirrels (Urocitellus mollis) at plot-level, human – % human disturbance within a 2.4 km 2 area, and soil texture – % surface soil passing through a #4 sieve.
… 
Standardized parameter estimates (±90% confidence intervals) describing the effect of explanatory variables (x-axis) on relative abundance of Piute ground squirrels (Urocitellus mollis). If a variable does not have a parameter estimate labeled top model it was not included. Data were collected on the Morley Nelson Snake River Birds of Prey National Conservation Area in southern Idaho, USA. Variable descriptions are as follows: BRTE – plot-level % cover of cheatgrass (Bromus tectorum), precipitation – mean annual precipitation from 1979 to 2008, DI – dispersal index (i.e., number of burrows at the nearest sampled 1-ha plot/distance to the plot), firefreq – number of times the area burned from 1957 to 2013, human – % human disturbance within a 0.79 km2 area, season – binary variable to account for within season decline in active burrows (Van Horne et al. 1997b), shrub – plot-level % cover of shrub functional group, shrubland – % shrubland within a 0.79 km2 area, and soil texture – % surface soil passing through a #4 sieve.
+1
Standardized parameter estimates (±90% confidence intervals) describing the effect of explanatory variables (x-axis) on relative abundance of Piute ground squirrels (Urocitellus mollis). If a variable does not have a parameter estimate labeled top model it was not included. Data were collected on the Morley Nelson Snake River Birds of Prey National Conservation Area in southern Idaho, USA. Variable descriptions are as follows: BRTE – plot-level % cover of cheatgrass (Bromus tectorum), precipitation – mean annual precipitation from 1979 to 2008, DI – dispersal index (i.e., number of burrows at the nearest sampled 1-ha plot/distance to the plot), firefreq – number of times the area burned from 1957 to 2013, human – % human disturbance within a 0.79 km2 area, season – binary variable to account for within season decline in active burrows (Van Horne et al. 1997b), shrub – plot-level % cover of shrub functional group, shrubland – % shrubland within a 0.79 km2 area, and soil texture – % surface soil passing through a #4 sieve.
… 
Figures - uploaded by Joseph D Holbrook
Author content
All figure content in this area was uploaded by Joseph D Holbrook
Content may be subject to copyright.
Content uploaded by Joseph D Holbrook
Author content
All content in this area was uploaded by Joseph D Holbrook on Jun 13, 2016
Content may be subject to copyright.
v v Article e013071v


†21
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:
             

Abstract.    Artemisia tridentata        

Taxidea tax-
us        
Urocitellus mollis



2

             
Bromus tectorum
 


 
  

 


    

          

Key words:     Artemisia tridentata   Bromus tectorum  
Taxidea taxusUrocitellus mollis
Received
†E-mail:
Copyright:  

v v Article e013072 v www.esajournals.org
HOLBROOK ET AL.
IntroductIon





     
 
        
        
       


    

    

 
       
    

     
      
      
    

 
   Artemisia tridentata)
     
     
  Taxidea taxus  
Urocitellus mollis



sensu


    
    
     
   
  
       

Athene cunicularia 

   
      
     
   



     
     



     
     

     

    




    
      
    


       
    

     
      

    
       


     
      
    





    
      


      
     
     
    

v v Article e013073 v www.esajournals.org
HOLBROOK ET AL.
     
 

    
  A. t. wyomingensis
 

      Bromus
tectorum       
     2  
 2       
  
      


    
    
        
      

     

      
  

       
     
      
     
   
      
     
      
     
      






    
       
    
 


     
     
     
     
    
       

    

     
     
     
    

(Urocitellus mollisTaxidea taxus
             


v v Article e01307 v 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 e01307 v 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 e013076 v www.esajournals.org
HOLBROOK ET AL.
    
    
     
      
    
    
     

     


      
      
     

    
     
       
        
       
         
     
     
    
      
    
         
      
      


     




        

   
     
       
     

  2


2 
      
   
 


      
     




     
     

     

  


     

      
    



   
       
      


  

     
      
      
       
   



    
      




      
       
     




       
v v Article e013077 v www.esajournals.org
HOLBROOK ET AL.
          

 


      

      
       
    
    
    


    
      
     
   
     
      
      
  
      

  
Artemisia


     
      
     



     
      




     

       
       
      
     
 
       
      
    
      

    
       

1∕(
̄
xd1,d2,d3,d4)2
  d   
        

̄
x


      
      
     


       

       

      


     
      

Ecosystem stressors: the re- cheatgrass cycle
       


     
        
     
       

     

      



        
     
       
      

   
       
  
       
      
      
    
    
v v Article e01307 v www.esajournals.org
HOLBROOK ET AL.


       
         
   
       

     
      

      

     

    

Data analysis
   
    


(xi−
̄
x)∕(2× σ)
xi
  i     


     
        

     
 
   
     
  
     
     
       
       
     
   
      
     
     
      


    



      



  
    
  b   
        

       
     
     
     


c

c    
    
c       

     
  c     
       

      
       


      

      
     
 c   

     
    
      
 
      

     
  





    

     
  
    
v v Article e01307 v www.esajournals.org
HOLBROOK ET AL.

    



     
    

     
     
     



      


     


     
       
     
     
   

       

      



results
     
   
       
       
       
      


       
      
      
      
      

      
     
      
     
       
    r =  n = 30)

         
  
Occupancy
     
      
      
    
wi        
      
       
      Χ2  
   P = .  

        
      
     
      
      
      
       

    
     
     
   
   
c < 6 (wi 
 c

  
    
       
       
       
(Χ2P = 
  


     
     
    

       

       
v v Article e0130710 v 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 e0130711 v www.esajournals.org
HOLBROOK ET AL.
     
      
    
     
 
     
     
 
      
      
      

      
 


       
       
      
      
     


     
       
             
(Taxidea taxus   
c

kwi

  kccwi


 3 0†


    †
  2  †


    †


     




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 e0130712 v 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 e0130713 v 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 e0130716 v www.esajournals.org
HOLBROOK ET AL.

    
      
      
      


Effects of ecosystem stressors: The fire- cheatgrass
cycle
     

     
       

     
       
     
    
   
  
     
      
      
     
    

       
    
      
    

        
     
    

     
        
    
     
    
          
      
      
        

      
     
     
       
      
 
      
       
      
     
       
     
     
 



       

     
      


 
      

    
      



  

   

     
       
 

     




      
    
     
     
     a    


    
     
      


v v Article e0130717 v 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 e0130720 v www.esajournals.org
HOLBROOK ET AL.



      
       


        
     

       


         
    
     
   in     
     
       


          
       
    
     
       

 

      
   


    
      

     


 

        
      



     
      

   
    
    

         
    
   










    



Meriones hurrianae

Spermophilus townsendii



     

 

      

  



  
     

 

  







   
a
     
     


b
   

  
     
v v Article e0130721 v www.esajournals.org
HOLBROOK ET AL.
      

     
      

       
   Spermophilus colum-
bianus







  






supportIng InforMAtIon
        

... Cheatgrass, an invasive non-native annual grass, significantly impacts the fire regimes across the Intermountain West, particularly in the Great Basin. It negatively affects the richness and abundance of small mammals [13], [14] and degrades habitat for the Greater Sage-Grouse [15], [16], a species vital for regional ecological management. By increasing the connectivity and availability of fine fuels, Cheatgrass leads to more frequent fires compared to those in native ecosystems [17], [18]. ...
From Vegetation to Vulnerability: Integrating Remote Sensing and AI to Combat Cheatgrass-Induced Wildfire Hazards in California
Preprint
Full-text available
  • Dec 2024
Wildfire risk is on the rise around the world. In places like California, this risk is further instigated by the invasive species cheatgrass (Bromus tectorum). Cheatgrass is highly flammable and benefits from wildfires, allowing it to replace native plant communities. Through increasing both the intensity and the frequency of wildfires, it endangers not only its natural environment but also human habitats. Here, we present a novel approach to map the distribution and expansion of cheatgrass and predict potential wildfire risk zones. Utilizing the open-source CalFlora dataset, alongside data from the Sentinel–2 satellites, we created a comprehensive spatial analysis framework. We integrated temporal dynamics via Vegetation Index statistical bands that encapsulate annual vegetation information. We employed semi-supervised learning techniques to refine and filter our data labels, thereby ensuring robust model training. We utilized machine learning algorithms Random Forest and XGBoost for model training. Our models exhibited a test accuracy of 91.1% in multiclass classification and achieved a precision rate of 91% specifically for the Cheatgrass class. Our multiclass classification model demonstrates exceptional discriminative ability and agreement with the actual classifications, with an ROC-AUC Score of 0.99 indicating near-perfect performance in distinguishing between the different classes, and a Cohen’s Kappa of 0.89 signifying a strong agreement, accounting for chance. We demonstrate the efficacy of our methodology in identifying regions at high risk of wildfires due to Cheatgrass proliferation, highlighting the potential for broader application across California’s diverse landscapes. Our analysis effectively predicts the distribution of Cheatgrass and other vegetation with data available only until June, providing insight before the peak forest fire season, which spans from mid-July to September. This capability delivers actionable intelligence for assessing fuel load and connectivity, thus laying the groundwork for targeted wildfire prevention strategies and enhanced ecological management practices in fire-prone areas.
View
... For example, a well-documented positive feedback loop between the expansion of invasive annual grasses like Cheatgrass (Bromus tectorum) and an accelerated fire regime has led to significant sage-steppe landscape conversion in western North America (Knick and Rotenberry 1997;Bradley et al. 2018;Crist et al. 2023). The Snake River Plain is an epicenter of this phenomenon, having experienced widespread conversion from a shrub and forb mosaic dominated primarily by Sagebrush (Artemisia spp.) to one of cheatgrass and other exotic annual grasses (Boyte and Wylie 2017), which can directly impact some ground squirrels (Yensen et al. 1992;Steenhof et al. 2006;Lohr et al. 2013;Holbrook et al. 2016). Obligate heterotherms, like all small-eared Urocitellus, are vulnerable to food availability in the active and breeding seasons since they emerge in late winter and begin the estivation/hibernation phase in early summer (Davis 1939;Rickart 1987). ...
Integrative species delimitation reveals an Idaho-endemic ground squirrel, Urocitellus idahoensis (Merriam 1913)
Article
Full-text available
  • Dec 2024
  • J MAMMAL
The “small-eared” species group of Urocitellus ground squirrels (Sciuridae: Xerinae: Marmotini) is endemic to the Great Basin, United States, and surrounding cold desert ecosystems. Most specific and subspecific lineages in this group occupy narrow geographic ranges, and some are of significant conservation concern; despite this, current taxonomy remains largely based on karyotypic or subtle pelage and morphological characteristics. Here, we leverage 2 multilocus DNA sequence data sets and apply formal species delimitation tests alongside morphometric comparisons to demonstrate that the most widespread small-eared species (U. mollis Kennicott, 1863 sensu lato; Piute Ground Squirrel) is comprised of 2 nonsister and deeply divergent lineages. The 2 lineages are geographically separated by the east-west flowing Snake River in southern Idaho, with no sites of sympatry currently known. Based on robust support across the nuclear genome, we elevate populations previously attributed to U. mollis from north of the Snake River to species status under the name Urocitellus idahoensis (Merriam 1913) and propose the common name “Snake River Plains Ground Squirrel” for this taxon. We delimit 2 subspecies within U. idahoensis; U. i. idahoensis (Merriam 1913) in western Idaho and U. i. artemesiae (Merriam 1913) in eastern Idaho. Urocitellus idahoensis is endemic to Idaho and has a maximal range area of roughly 29,700 km2 spanning 22 counties but occurs discontinuously across this area. Our work substantially expands knowledge of ground squirrel diversity in the northern Great Basin and Columbia Plateau and highlights the difficulty in delimiting aridland mammals whose morphological attributes are highly conserved.
View
... Increasing cheatgrass density results in decreases in the diversity and abundance of small mammals, with potential consequences for populations of their predators, from badgers to raptors (Freeman et al. 2014. Holbrook et al. (2016) documented that cheatgrass has a significant negative effect on ground squirrel abundance, fire in an uninvaded shrubsteppe has a positive effect on ground squirrel populations by eliminating shrubs and stimulating bunchgrass growth, while fire in a cheatgrass-invaded setting imposed an additional negative stressor on ground squirrel populations. However, even though cheatgrass invasion radically increases the abundances of available seeds, populations of granivorous rodents may show no population response (Lucero et al. 2015). ...
View
... Cheatgrass invasion is considered a significant ecological issue throughout the Great Basin (Mack 1981, Knapp 1996, Smith et al. 2022). Cheatgrass has invaded and established monoculture plant communities in many areas, often leading to reduced perennial plant diversity, disrupted vertebrate and invertebrate communities, and exacerbated fire regimes in the Great Basin (Knapp 1996, Balch et al. 2013, Chambers et al. 2014, Freeman et al. 2014, Holbrook et al. 2016, Cumberland et al. 2017, Bradley et al. 2018, Williamson et al. 2020. Increased fire and decreased biodiversity associated with increased cheatgrass presence may negatively impact sage-grouse habitat and recruitment , Miller et al. 2011, Chambers et al. 2014. ...
Nonnative ungulate impacts on greater sage-grouse late brood-rearing habitat in the Great Basin, USA
Article
Full-text available
  • Aug 2023
Domestic livestock grazing is the dominant land use on much of the current range inhabited by greater sage-grouse (Centrocercus urophasianus; sage-grouse) in the western United States. Nonnative feral horses (Equus ferus caballus) also inhabit important sage-grouse seasonal habitats. Overabundant feral horse populations and improper grazing by domestic cattle (Bos taurus) can impact the health of sagebrush (Artemisia spp.) and desert shrub rangeland communities and native wildlife. These impacts to sage-grouse can be exacerbated when they affect late brood-rearing habitat, which provide the forbs and arthropods required to fledge broods. Managers require better information regarding the extent of these impacts. In 2020, we assessed the potential impact of feral horses and domestic cattle on sage-grouse late brood-rearing habitats in western Utah and eastern Nevada, USA. We acquired late brood-rearing location data from sage-grouse marked with global positioning system and very-high frequency radio-transmitters from both east and west Nevada data to delineate late brood-rearing habitats. Using these location data, we compared 8 sites (4 pairs) within horse and non-horse use areas to assess sage-grouse habitat quality characteristics between areas that have been predominantly horse and cattle grazed versus sites that have been predominantly cattle grazed. For each pairing, 1 site was located within and the other outside of a Bureau of Land Management herd management area boundary, and both sites shared similar habitat characteristics (i.e., topography, dominant vegetation, soils, and climate) and selection probability for broods. We collected vegetation and dung count data at each site to assess characteristics related to habitat quality for sage-grouse brood-rearing, based on ungulate presence. We used a mixed model analysis of variance to detect differences between each paired site comparison (α < 0.01). Horses or evidence of horse presence (i.e., dung) were not detected at our non-horse sites allowing for an unbiased comparison between paired sites. Cattle presence was noted at all our paired sites. Average annual grass frequency was 0.74 in horse and 0.17 in non-horse use areas (P = 0.20), and average annual grass cover was 4.0% compared to 0.2% in horse use areas (P = 0.32). Average annual grass biomass was 0.45 kg/ ha in horse and 0.04% in non-horse use areas (P = 0.34). Vegetation height was 44.2 cm in non-horse compared to 34.5 cm in horse use areas (P = 0.23). These results suggest that increased ungulate grazing and year-long use of late brood-rearing habitat by feral horses coupled with livestock grazing may impair habitat suitability, particularly considering ecological impacts from invasive plant species. Our results suggest that managing late brood-rearing habitats to reduce the frequency and intensity of year-long grazing by feral horses can be best accomplished by reducing horse numbers and the seasonal distribution of grazing by domestic livestock.
View
View
The effects of fire on large‐ and medium‐sized mammal communities: what do we know? A review
Article
  • Mar 2024
Large‐ and medium‐sized mammals play a unique role in ecosystem dynamics. They can change the physical and biotic landscape by altering the flow of resources among trophic levels, thereby affecting ecosystem functioning. Although the effects of fire on some ungulates have been well studied, data gaps exist for many species, including canids, felids, mustelids and ursids among others. To address this knowledge gap, we conducted a literature review to synthesize what is known about large and medium mammal responses to fire, including communities, species richness and species interactions in connection with fire. Twenty‐seven large and medium mammal species were studied. Fifty percent of the studies examined ungulates, far exceeding studies of other trophic levels. Eighty‐six percent were conducted on large mammals with significantly fewer studies on medium‐sized mammals. Only four studies examined multiple species responses to fire. Results indicated that fire had a largely positive effect on large‐ and medium‐sized mammals. However, considerable heterogeneity exists within and among taxa. Most fire research has been conducted on focal species rather than on biodiversity, and a large data gap exists on the interactions within or among large‐ and medium‐sized mammals. Forest management focus is changing from fire suppression to reinstating natural fire regimes. Effectiveness monitoring programmes will be needed to test the efficacy of restoration strategies in mammalian communities.
View
Cheatgrass, Mammals, Birds, Butterflies, and Wildfire: A Study of Ecosystem Interactions
Preprint
Full-text available
  • Apr 2024
Over two years of research, we used remotely triggering cameras, point counts, and transect counts to measure the number of mammals, birds, and butterflies across eight plots in the Rocky Mountain foothills that varied in cheatgrass cover. We found that mammals and butterflies were less numerous in areas infested with cheatgrass and that such areas sustained fewer butterfly species. Furthermore, butterflies appeared more sensitive to small changes in cheatgrass cover than mammals. Cheatgrass density decreased dramatically on heavily infested plots burned by a wildfire (at low intensity), consistent with the findings of other research projects in similar ecoregions and climates.
View
Long-term biocrust responses to wildfires in Washington, USA
Article
  • Nov 2023
  • AM J BOT
Premise Dryland ecosystems in the western US are affected by invasive species, wildfires, livestock grazing, and climate change in ways that are difficult to distinguish. Biocrusts perform important ecological roles in these systems and are sensitive to all of these pressures. Methods We revisited a Washington, USA site sampled for biocrusts in 1999 to focus on effects of exotic annual grass invasion and wildfires in the absence of livestock grazing. We examined changes between 1999 and 2020 using a Bayesian Directed Acyclic Graph (DAG) to interpret direct and indirect causal impacts of wildfire on perennial bunchgrasses, exotic annual grasses, and biocrusts. Results Between 1999 and 2020, exotic annual grass cover increased in all and unburned plots by 16% and 18%, bunchgrass cover decreased by 21% and 25%, and biocrust cover decreased by 8.9% and 9.8%. Our DAG suggested that decreases in bunchgrass increased exotic annual grass, which reduced biocrust cover. Wildfires did not directly influence changes in bunchgrass, exotic annual grass, or biocrust cover. Areas dominated by exotic annual grass had less abundant and diverse biocrusts compared with areas with less exotic annual grass. Conclusions Biocrust community changes were more strongly related to increasing exotic annual grasses than to wildfires. Changes may relate to other soil disturbances or broad scale changes in climate or air quality. The minimal influence of wildfire on exotic annual grass and biocrusts suggests that apparent negative impacts of wildfire at other sites may be due to exacerbation by livestock grazing or other surface disturbance. This article is protected by copyright. All rights reserved.
View
Rangeland Biodiversity
Chapter
Full-text available
  • Sep 2023
In its simplest form, biodiversity is defined as species richness (the number of species in a given area). More complex definitions include the variety of life on Earth, from genes to ecosystems, and include the ecological and evolutionary processes that sustain that life. As in other ecosystems, biological communities in rangelands are influenced by a number of different abiotic and biotic drivers or “filters” at both broad and fine scales, and an understanding of these processes is critical for maintaining ecosystem services as well as addressing widespread biodiversity declines. In rangeland ecosystems specifically, the primary threats to biodiversity are habitat loss, fragmentation, and degradation through mismanagement, which includes suppression or mis-application of historical disturbance regimes. Restoring heterogeneity to rangelands by mimicking historical disturbance regimes has been shown to benefit biodiversity, but the exact role of disturbance varies widely throughout North American rangelands. As such, careful consideration of the type, duration/periodicity, intensity, and spatial and temporal extent and configuration of these disturbances is necessary when managing for site-specific biodiversity outcomes. It is important to consider the effects of both inherent (i.e., either natural or historical) and human-caused variability on rangeland plant and wildlife communities. In the future, practitioners should promote management practices that maintain and enhance biodiversity to maximize ecosystem functions and services that improve the quality and quantity of economic (e.g., livestock production, carbon banking) and ecological (e.g., biodiversity, sustainability) outcomes in North American rangelands.
View
Mesocarnivores of Western Rangelands
Chapter
Full-text available
  • Sep 2023
There are 22 species of mesocarnivores (carnivores weighing < 15 kg) belonging to five families that live in rangelands of the western United States. Mesocarnivores are understudied relative to large carnivores but can have significant impacts on ecosystems and human dimensions. In this chapter, we review the current state of knowledge about the biology, ecology, and human interactions of the mesocarnivores that occupy the rangelands of the central and western United States. In these two regions, mesocarnivores may serve as the apex predator in areas where large carnivores no longer occur, and can have profound impacts on endemic prey, disease ecology, and livestock production. Some mesocarnivore species are valued because they are harvested for food and fur, while others are considered nuisance species because they can have negative impacts on ranching. Many mesocarnivores have flexible life history strategies that make them well-suited for future population growth or range expansion as western landscapes change due to rapid human population growth, landscape development, and alterations to ecosystems from climate change; however other mesocarnivores continue to decline. More research on this important guild is needed to understand their role in western working landscapes.
View
Teetering on the Edge or too Late? Conservation and Research Issues for Avifauna of Sagebrush Habitats
Article
Full-text available
  • Nov 2003
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.
View
Post-Fledging Dispersal of Burrowing Owls in Southwestern Idaho: Characterization of Movements and use of Satellite Burrows
Article
Full-text available
  • Feb 2001
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.
View
View
Trophic Dynamics in Urban Communities
Article
  • May 2005
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.
View
View
Modern Applied Statistics with S
Book
  • Jan 2002
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.
View
View
MuMIn: Multi-model inference
Code
  • Jan 2013
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].
View
View
View