effects of density on spacing patterns and habitat associations of a neotropical glassfrog

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