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Prime real estate matters: effects of population density on spatial distributions of a
Neotropical glassfrog
Nicole F. Angeli1,2, Grace V. DiRenzo2,Alexander Cunha3, and Karen R. Lips2
1Applied Biodiversity Sciences, Texas A&M University2Department of Biology, University of Maryland, College Park
3Organismal and Evolutionary Ecology Program, Harvard University
Random
Different patterns predict processes
Many Neotropical stream frogs are aggregated (Atelopus varius, Pounds and Crump, 1987; Craugastor punctariolus, Ryan, Lips and Eichholz, 2008)
Uniform Clustered
(Clark, 1946; Diggle, 1985; Ripley, 1991; Bivand et al., 2008)
Clustered animals may fight for resources
‘Limiting wars’ Maynard Smith and Price, 1973
Espadarana prosoblepon; Jacobson, 1985
Espadarana prosoblepon are aggregated (CD=3.215, Witters and Lips, unpub)
Why do E. prosoblepon cluster, and why do we care?
Declines in amphibian community at Omar Torrijos H.D. NP, El Copé, Coclé, Panama
t =-24.44, df=486, P < 0.0001 Lips et al. 2006 PNAS
Quantify lethal and non-lethal effects of declines
Males: night, on stream banks;
Fighting, calling, mating;
lifespan ~ 5 years
(Jacobson, 1985; Guayasamin et al., 2009)
Females: cryptic
(Savage, 2002)
Juveniles: hatch and fall into
stream leaf litter to develop (Cisneros-Heredia et al., 2006)
Espadarana (Centrolene) prosoblepon
Espadarana prosoblepon
Can the spatial organization of E. prosoblepon change over time and space?
1. Does clustering occur on the streams?
Map male E. prosoblepon along streams
2. Will clustering change before and after Bd?
Detect changes in dispersion at varying densities
3. Are clusters based on resources or interactions?
Quantify animal arrangement and habitat
4-200 m permanent stream transects
LoopCascadaSilenciosaGuabal
Visual Encounter Surveys extending 2 m onto stream banks
Adults sexed by calling and presence of humeral spines
Individual Toe Clips
(Heyer et al., 1994)
Microhabitat variables
Canopy
Veg at 0.5 m
Veg at 1.0 m
Veg at 1.5 m
Sand
Gravel
Cobble
Boulder
CWD
Stream Width
Stream Depth
Complete Data Set:
X=13 years
225 surveys
480 meters of habitat data
N= 1,678 male E. prosoblepon881 unique males
- X-Y locality data- Individual marks
Density of captures during 225 surveys annualized over 13 years
Loop Guabal Cascada SilenciosaPercent change in
abundance after Bd -46.3% -5.9% -68.3% -31.8%
Years with frogs: 11 11 8 7
Low intensity, no frogs
a. Visualize clusters using density maps smoothed with Gaussian kernel (Baddeley and Turner, 2005)
b. Kuldorff (2006) SatScanStatistic to identify clusters independent of space, time
Distance from stream (meters)
1. Identify and compare hotspots over time
Tran
sect
Le
ngt
h (
me
ters
)
2. Detect changes in dispersion at varying densities
a. Detect patterns using linearized Ripley’s Kb. Use derived inflection points to calculate nearest
neighbor and inter-cluster distance
(Bikhofer et al. ,2006; Cowling, 1998; O’Driscoll ,1998; Stoyan ,1992; Ripley, 1981)
3. Predict frog locality by microhabitat traits
a. Transformvariables with PCA
b. Use mixed effects generalized linear models to assess predictability
1. Frog hotspots before and after Bd
Twenty-one hotspots,
9 persist over all years (42.8%)
Post-decline:
8 disappear and 4 appear
…..independent of local density.
2000 2001 2002 2003 2004 2005 2007 2010 2011
Results: Loop
* * **
* * ** * * * *
* ** * * *
* *
Clusters p<0.01*
Tran
sect
Le
ngt
h (
me
ters
)
Results: Cascada
*
2000 2001 2002 2003 2004 2005 2006 2007 2010 2011 2012
**
** * *
**
*
* *
*
*
** *
**
*
*
* **
Clusters p<0.01*
Tran
sect
Le
ngt
h (
me
ters
)
Results: Guabal
2000 2001 2002 2003 2004 2005 2011 2012
* ** * **
* *
** * ***
*
Clusters p<0.01*
Tran
sect
Le
ngt
h (
me
ters
)
Results: Silenciosa
2000 2001 2002 2003 2004 2006 2012
*
*
*
*
*
*
**
*
*
** *
****
Clusters p<0.01*Tr
anse
ct L
en
gth
(m
ete
rs)
P=0.45
P=0.45
P=0.29P=0.03
2. Results: Cluster arrangement differs among transects but not PRE and POST
P=0.36
P=0.17
P=0.49
P=0.53
Results: Nearest Neighbors does not change PRE and POST, or among transects
Nearest-neighbor0.692±0.74 m
3. Can we predict frog abundance by PC-transformed habitat?Pre-decline Post-decline
Summary: No changes in dispersion occur before and after Bd arrives in the system
Individuals interact similarly, and cluster arrangement varies by transect
Pre Post Pre Post Pre Post Pre Post
Are clusters hotspots for resources?
E. prosoblepon clusters of new individuals persist in the same locations with similar habitat-associations
New and unique contributions
E. prosoblepon clusters persist in the same locations,
individuals interact similarly,
…..independent of local density.
Community analysesof disease transmission
Microhabitat attributes of disease
See changes tadpole community atby DiRenzo, Graziella et al., at 4:00 in L100B (COS 71).
Future Work
Acknowledgments
Lips lab at University of Maryland, College Park
Appalachian Lab: Dr. Robert Gardner and Dr. Matt Fitzpatrick
National Science Foundation provided support to KRL
TAMU herpetology for support and comments
Tweet me for R codeand conservation news
@auratus_nicole
Can we predict frog abundance by PC-transformed habitat?
2001 GLMM Model Coefficient T-value P value
Intercept 1.534 5.788 >0.001
PC1 -0.413 -2.294 0.034
PC2 0.098 0.383 0.705
PC3 0.062 -0.363 0.720
2012 GLMM
Intercept 0.802 3.264 >0.001
PC1 0.129 0.930 0.365
PC2 0.201 1.334 0.199
PC3 0.278 1.586 0.131
PRE
POST
Cluster arrangement varies by transect, but individuals interact similarly
Nearest-neighbor0.692±0.74 m
Summary: Vegetation is always important
1. Vegetation is important PRE and POST Bd on streams
2. Changes in substrate (small to large) and canopy (open) in the Post years
PRE POST
Microhabitat
Canopy
Veg at 0.5 m
Veg at 1.0 m
Veg at 1.5 m
Sand
Gravel
Cobble
Boulder
CWD
Stream Width
Stream Depth
Microhabitat variables
Canopy
Veg at 0.5 m
Veg at 1.0 m
Veg at 1.5 m
Sand
Gravel
Cobble
Boulder
CWD
Stream Width
Stream Depth
El Copé, Panama
Espadarana prosoblepon distribution(BerkeleyMapper 2.0)
700 m elevation8°40’ N, 80°37’17” W
Costa Rica
Colombia
Caribbean Sea
Pacific Ocean
m
Loop Cascada Guabal Silenciosa
Vegetation is always important