Testing for size-dependent tradeoffs of clustering in Nephila clavipes
Laura Sauvage (CMC ‘14)
& Haley Godtfredsen (Scripps ‘16)
Introduction
Web ecology
• Prey capture
• Males
• Kleptoparasites
• Predation
Nephila clavipes
Large
Medium
Small
Another component of web environment:
Solitary (built alone)
Clustered (attached to
other webs)
Theoretical costs and benefits of
cluster formation:
Cost = competition for food
Benefit = less predation risk per
spider
Daniella Barraza, 2012
• Cost: Medium spiders caught more prey if
solitary than clustered.
- No difference for small spiders.
• Benefit: Longer web tenure if clustered.
- More so for medium than small spiders.
Sauvage & Godtfredsen, 2013
Hypothesis: Costs & benefits of clustering will
be size-dependent.
Preliminary data• Frequency of
clustering
• Variation in web
experience based
on spider size and
clustering
Methods
• Firestone Center for Restoration Ecology
•
Baru, Costa Rica
Initial Measurements
Spider ID
Solitary/
Clustered
Date
Found
Color
Neighbor
Females
Spider
Size (mm)
Web
Size (m)
1
S
7/5/2013
N/A
N/A
1.78
0.18
2
S
7/5/2013
N/A
N/A
4.74
0.43
3
C
7/5/2013
Blue
4
2.57
0.30
4
C
7/6/2013
Green
3
2.91
0.31
5
S
7/6/2013
N/A
N/A
3.40
0.36
(example data)
Monitoring Data
Spider
ID
Date
Web
Condition
# Prey
# Legs
# Neighbor
Females
1
7/15/2013
Good
0
8
N/A
2
7/15/2013
Good
2
8
N/A
3
7/15/2013
Poor
0
7
1
4
7/15/2013
Good
0
8
1
5
7/15/2013
Okay
1
7
N/A
(example data)
Measuring costs and benefits of cluster
formation:
Competition for food: prey capture rate
Lower predation risk
● Web duration
● Leg autotomy
● Web condition
● Reason for disappearance
Frequencies of….
Clustering
Clustered: 191 webs (48%)
Solitary: 209 webs (52%)
Frequencies of….
Clustering
Leg Autotomy
Clustered: 191 webs (48%)
No: 367 webs (94%)
Solitary: 209 webs (52%)
Yes: 25 webs (6%)
Frequencies of….
Clustering
Leg Autotomy
Web Fate
Clustered: 191 webs (48%)
No: 367 webs (94%)
Moved: 160 webs (65%)
Solitary: 209 webs (52%)
Yes: 25 webs (6%)
Depredated: 86 webs (35%)
Influence of spider size on …
Spider
Size
Clustering
Prey
Capture
Leg
Autotomy
Spider/Web
Fate
NS
+
NS
NS
NS = not significant
+ = positive correlation
Influence of spider size on …
Spider
Size
Clustering
Prey
Capture
Leg
Autotomy
Spider/Web
Fate
NS
+
NS
NS
Prey
Capture
Leg
Autotomy
Spider/Web
Fate
NS
NS
NS
Influence of clustering on …
Clustered
compared
to Solitary
Significance
● Studying the
costs/benefits of living in
a group (cluster)
● Do these trade-offs differ
with spider size?
Preliminary Data
Prey capture
Spider Size
Clustering
Predation
X
X
X
To Be Determined
•
Do size-dependent trade-offs
exist in clusters?
● Frequency with which spiders
of different sizes are clustered or
•
solitary.
Cluster formation
•
•
Order of arrival
Effect of size
Acknowledgements
Keck Science Department
Professor E. Ferree
Professor D. McFarlane
Greddy Arias-- Firestone Caretaker
Pitzer College
Mean web diameter (mm)
Preliminary Results
Bigger spiders
have bigger webs.
n=17
n=183
n=138