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Habitat Structure and Colonial Behavior in Metepeira Spinipes (Araneae: Araneidae), an Orb Weaving Spider From Mexico

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HABITAT
STRUCTURE
AND
COLONIAL
BEHAVIOR
IN
METEPEIRA
SPINIPES
(ARANEAE:
ARANEIDAE),
AN
ORB
WEAVING
SPIDER
FROM
MEXICO
BY
GEORGE
W.
UETZ
AND
J.
WESLEY
BURGESS
INTRODUCTION
The
topic
of
social
phenomena
in
spiders
has
received
much
attention
in
the
literature
recently
(Shear
1970;
Kullman
1972;
Bur-
gess
1976,
1978;
Buskirk,
in
press).
Colonial,
communal
and
cooper-
ative
behaviors
have
been
observed
in
a
variety
of
families
and
genera,
mostly
from
tropical
and
subtropical
regions
around
the
world.
Among
the
species
of
group-living
spiders
found
in
Mexico
and
Central
America
is
Metepeira
spinipes
F.
Pickard-Cambridge,
an
araneid
reported
to
be
the
only
colonial
species
in
its
genus
(Levi
1977).
We
observed
large
numbers
of
these
spiders
in
Central
Mex-
ico
in
1975,
and
were
able
to
collect
some
data,
which
we
present
here.
METHODS
AND
STUDY
AREA
The
site
of
our
observations
was
Tepotzotlan,
Mexico,
located
35
km
North
of
Mexico
City.
The
area
is
an
agricultural
valley
sur-
rounded
by
mountains
(thus
the
habitat
must
be
considered
"dis-
turbed"
by
the
activities
of
humans).
Major
agricultural
activities
include
cultivation
of
corn
and
maguey
(an
Agave
sp.
grown
to
make
pulque,
a
fermented
beverage)
with
open
range
grazing
of
cattle,
and
several
feedlots.
Our
visit
took
place
in
late
July
1975,
during
the
rainy
season.
Temperatures
were
typically
warm
during
the
day
(20-30
C)
and
cool
at
night
(5-15
C).
It
generally
rained
once
a
day
in
the
late
afternoon
15-17h
pm
CST).
Metepeira
spinipes
spiders
were
studied
in
3
sites,
all
located
near
the
KOA
campground
where
we
stayed.
One
site,
a
roadside,
con-
tained
a
variety
of
types
of
vegetation,
including
Agave,
Opuntia,
Department
of
Biological
Sciences,
University
of
Cincinnati,
Cincinnati,
Ohio
45221.
2North
Carolina
Mental
Health
Research,
Raleigh,
North
Carolina
27611
[Present
add.ress:
Department
of
Psychology,
University
of
California,
Davis,
California
95616].
Manuscript
received
b.l’
the
editor
June
28,
1979
79
80
Psyche
[March
Acacia
(?)
trees
and
numerous
unidentified
shrubs,
forbs
and
grasses.
This
roadside
area
was
bordered
on
one
side
by
a
large
cornfield
and-on
the
other
by
an
irrigation
ditch.
A
second
roadside
area
was
perpendicular
to
the
first,
bordering
the
same
cornfield.
This
site
has
a
larger
irrigation
ditch,
the
sides
covered
by
dense,
low
growing
willows
(Salix
sp.).
A
third
site,
a
maguey
plantation,
was
located
approximately
1.2
km
east
of
the
other
sites.
The
area
was
planted
in
large
(>1.5
m)
Agave
(approximately
5-7
yrs
old),
interspersed
with
grasses
and
occasional
trees.
The
plantation
has
the
appearance
of
an
Agave
"orchard",
due
to
the
semi-regular
dispersion
of
the
large
plants.
These
three
areas
represent
the
char-
acteristic
habitats
where
Metepeira
were
found
in
the
Tepotzotlan
area.
To
assess
habitat
preferences
of
Metepeira,
a
series
of
6
200
m
quadrats
was
delineated
in
the
roadside
area
containing
a
variety
of
vegetation
types.
Within
each
quadrat,
the
percent
cover
and
per-
cent
volume
of
each
vegetation
type
was
estimated.
Frequency
of
occurrence
of
Metepeira
spinipes,
(both
colonies
and
solitary
indi-
viduals)
was
recorded
within
each
vegetation
type.
In
both
the
maguey
plantation
and
the
roadside
ditch
covered
by
willows,
counts
were
made
of
spider
group
size.
In
addition,
meas-
urements
of
colonial
web
dimensions
and
habitat
dimensions
were
made
for
selected
groups.
RESULTS
AND
DISCUSSION
The
web
of
individual
Metepeira
spinipes
is
characteristic
of
the
genus,
and
is
a
three-dimensional
space
web/orb
web
composite
with
a
retreat
in
the
space
web
(also
called
a
barrier
web;
Levi
1977)
(Fig.
1).
Signal
threads
connect
the
hub
of
the
spiral
and
the
retreat,
where
the
spider
rests
(Burgess
&
Witt
1976).
Only
the
threads
of
the
orb’s
spiral
are
sticky,
and
the
orb
is
the
primary
prey
catching
device.
Prey
are
often
entangled
in
the
space
web
and
occasionally
are
caught
there.
Individuals
of
M.
spinipes
in
Central
Mexico
usu-
ally
occur
in
aggregations,
although
solitary
individuals
of
this
spe-
cies
are
also
found.
Most
of
the
groups
we
examined
consisted
of
5-30
individuals,
but
much
larger
groups
(50-80)
were
seen.
In
the
groups
we
observed,
individuals
had
their
own
retreats
and
orbs
but
space
webs
were
joined.
Although
orbs
are
usually
renewed
on
a
daily
basis
(spiders
rebuild
radii
and
sticky
spirals
during
the
night)
1979]
Uetz
&
Burgess
Behavior
in
M.
spinipes
81
Figure
1.
Metepeira
spinipes,
compound
web.
(1)
Space
web;
(2)
retreat
where
spider
sits,
holding
signal
threads
(4)
to
(3)
catching
spiral.
Mature
females
may
construct
tiers
of
egg
sacs
(5).
[Courtesy
of
Dr.
Peter
N.
Witt,
North
Carolina
Division
of
Mental
Health
and
Mental
Retardation
Services.
Used
with
permission.]
the
colonial
space
web
persists
and
is
elaborated
on
by
the
web
building
activities
of
numerous
individuals.
The
resultant
colonial
web
is
a
mass
of
interconnected
individual
webs
supporting
each
other,
attached
at
its
periphery
to
the
vegetation.
The
colonies
we
observed
contained
adults
and
immatures
of
indeterminate
age
and
wide
size
variation.
Metepeira
spinipes
colonial
webs
are
usually
associated
with
microhabitats
of
a
somewhat
permanent
structure:
succulents,
dead
branches,
shrubs,
man-made
objects,
etc.
In
the
Tepotzotlan
area,
maguey
(Agave
sp.)
plants
were
the
most
common
site
of
M.
spi-
nipes
colonies.
Habitat
preferences
of
this
species
were
examined
in
an
area
containing
a
variety
of
microhabitat
types.
The
null
hypoth-
eses
that
spiders
are
equally
distributed
in
all
microhabitat
types,
or
are
distributed
on
the
basis
of
the
frequency
of
occurrence
of
micro-
habitat
types
are
rejected
based
on
Chi-square
tests
(Table
1).
These
data
suggest
that
M.
spinipes
colonies
and/or
individuals
occur
more
frequently
in
Agave
plants
than
in
other
microhabitat
sites.
82
Psyche
[March
Most
of
the
solitary
individuals
were
found
in
grasses
and
forbs,
but
in
frequencies
proportionate
to
the
occurrence
of
that
type
of
microhabitat.
There
are
several
possible
reasons
why
M.
spinipes
exhibit
a
habi-
tat
preference
for
the
maguey
plant.
Agave
sp.
are
perennial,
succu-
lent
plants
with
stiff
leaves
capable
of
providing
strong
support
for
web
attachments.
These
plants
have
lanceolate
leaves
with
cupped
leaf
bases,
radiating
from
a
basal
rosette.
Such
a
leaf
arrangement
provides
much
support
for
the
three-dimensional
colonial
web.
Colinvaux
(1973)
suggests
that
plants
with
physiognomy
similar
to
Agave
sp.
(i.e.
Yucca)
are
adapted
for
arid
environments,
in
that
their
leaf
shape
reduces
heat
load,
and
cupped
leaf
bases
concentrate
moisture.
Agaves
might
be
a
localized
source
of
moisture
during
the
dry
season,
or
even
at
mid-day
during
the
rainy
season
when
solar
radiation
is
intense
and
humidity
is
low.
We
have
observed
water
accumulating
at
the
base
of
some
plants.
There
is
also
some
evi-
dence
that
agaves
are
sites
of
high
insect
activity.
Debris
from
nearby
flowering
plants
and
trees
and
other
organic
matter
some-
times
accumulates
about
the
base
of
these
plants.
Decomposition
of
this
matter
and
lower
leaves
of
older
agaves
attracts
flying
insects,
creating
a
microhabitat
with
extremely
abundant
prey
resources.
These
findings
raise
questions
about
the
nature
of
M.
spinipes
aggregations.
Do
these
spiders
exhibit
grouping
tendencies
that
may
be
considered
social,
or
do
they
exist
in
fortuitous
aggregations
associated
with
habitat
resources
that
are
patchily
distributed?
There
is
some
evidence
that
these
spiders
aggregate
independently
of
habitat.
The
mean
colony
size
of
M.
spinipes
in
two
contrasted
microhabitat
sites,
Agave
sp.
and
shrubs
is
not
significantly
differ-
ent
Table
1).
Although
other
Metepeira
species
are
associated
web
sites
of
a
particular
architecture
(McCook
1889;
Kaston
1948;
Levi
1977),
M.
spinipes
is
not.
This
species
occurs
in
a
variety
of
web
sites
with
widely
varying
structure.
Moreover,
the
shape
of
the
web
col-
ony
is
flexible,
and
conforms
to
that
of
the
web
site.
This
suggests,
at
least,
that
coloniality
of
M.
spinipes
is
independent
of
habitat
structure.
Spiders
brought
into
the
laboratory
and
released
into
cages
build
colonial
webs,
attaching
silk
of
one
animal
to
silk
of
another.
Moreover,
individuals
from
different
colonies,
even
as
far
apart
as
several
hundred
miles,
tolerate
each
other
and
build
webs
together
(Burgess
1976).
This
evidence
strongly
suggests
that
M.
1979]
Uetz
&
Burgess
Behavior
in
M.
spinipes
83
Table
1.
Distribution
of
Metepeira
spinipes
in
several
microhabitat
types.
Grasses
Microhabitat
Agave
Opuntia
Trees
Shrubs
+Forbs
percent
cover
4.3
1.0
4.6
5.0
85.1
percent
volume
4.9
2.3
20.9
7.6
64.4
No.
of
spiders
691
16
2
96
17
No.
of
colonies
47
0
9
3
colony
(+2
S.E.)
size
14.67+/-3.38
16.0
14.89+/-8.1
2.0-+-0.0
No.
of
solitary
individuals
2
0
22
11
Tests
of
significance:
no.
of
solitary
no.
of
spiders
no.
of
colonies
individuals
Ho
equal
frequencies
in
all
microhabitat
types
X
2141.8
X
93.7
X
22.12
p
<
.001
p
<
.001
p
<
.01
Ho
frequencies
proportionate
to
percent
cover
of
micro-habitat
type
X
12922.1
X
646.7
X
6.9
p
<
.001
p
<
.001
.2
<
p
<
.3
Ho
frequencies
proportionate
to
percent
volume
of
micro-habitat
type
X
11188.0
X
551.5
X
3.11
p
<
.001
p
<
.001
.5
<
p
<
.6
spinipes
aggregations
arise
from
some
kind
of
interattraction,
not
from
habitat
patchiness.
Another
means
of
gathering
evidence
for
or
against
a
social
ten-
dency
to
aggregate
is
an
analysis
of
the
frequency
distribution
of
group
size.
In
a
study
of
web-clumping
in
Nephita
clavipes,
Farr
(1977)
compared
group
size
distributions
to
a
Poisson
distribution
truncated
at
zero.
His
data
fit
the
distribution,
and
he
concluded
that
web
clumping
by
N.
clavipes
is
a
random
process.
Using
methods
described
in
A.
Cohen
(1960)
and
J.
Cohen
(1971),
we
attempted
this
with
data
on
M.
spinipes
group
size
from
two
con-
trasted
habitats
(the
maguey
plantation
and
the
willow
shrub
ditch
described
in
methods).
In
both
habitats,
the
distribution
of
spider
84
Psyche
[March
group
size
was
significantly
different
from
a
zero-truncated
Poisson
distribution
(Tables
2
and
3),
indicating
a
non-random
grouping
pattern.
The
distribution
did
fit
a
zero-truncated
Negative
Binomial
distribution
(Tables
2
and
3),
indicating
a
significant
tendency
to
aggregate.
The
fact
that
group
size
in
M.
spinipes
occurs
with
the
same
underlying
aggregated
distribution
in
such
divergent
habitat
types
argues
for
the
existence
of
a
social
grouping
tendency
rather
than
fortuitous
aggregation.
While
it
may
be
argued
that
in
Agaves,
structural
habitat
resources
are
concentrated
in
small
patches,
this
was
not
the
case
in
the
willow
shrubs.
The
willow
shrubs
appeared
to
be
uniformly
dense
and
of
equal
height
and
age.
There
was
no
a
priori
reason
to
suspect
that
web
site
resources
for
M.
spinipes
Table
2.
Frequency
distribution
of
group
size
in
Metepeira
spinipes
colonies
in
Agave
plants.
Truncated
Observed
Truncated
Negative
Group
Size
Frequency
Poisson
Binomi
0
.00011
.651}
2
0
.0009
.811
3
.005
[
.914
1
4
2
.017
!
.977
1.71
o
.o o
/
6
2
.124
t
1.010
7
0
.259
[
1.010
8
2
.475
/
’988
1
9
0
.775
!
.958
10
0
1.136
.920[
(
11
0
1.515
.881
1’2
1.850
.840
13
2
2.090
.790
14
2.190
.745
15
2.140
.699
16
0
1.960
.654
[,
17
1.690
.610|
18
0
1.38
.570t,
19
1.06
.530
20
0
"78
I
2.28
"49
1
>20
7
1.50
5.95
21
34.06
.005
1.46
1.89
1.95
1.80
1.63
1.44
1.26
1.10
6.44
1979]
Uetz
&
Burgess
Behavior
in
M.
spinipes
85
spiders
were
aggregated
in
any
way
in
the
willow
shrub
area,
thus
a
social
aggregation
hypothesis
is
supported.
The
colonial
web
of
Metepeira
spinipes
is
a
permanent
aggrega-
tion
of
individual
prey
catching
orb
webs
in
a
matrix
of
communal
space
web.
Burgess
(1978)
has
suggested
that
cooperative
behavior
of
"Social"
spiders
consists
of
simultaneous
coordination
of
individ-
ual
effort
on
a
task,
like
web-building.
In
M.
spinipes
the
colonial
web
would
appear
to
arise
as
the
result
of
simultaneous
or
sequen-
tial
(but
not
coordinated)
individual
efforts
at
web
building,
rather
than
cooperative
behavior.
Prey
catching
orbs
are
spaced
apart
and
each
spider
inhabits
its
own
retreat.
Although
individuals
may
coex-
ist
at
short
distances,
intruders
on
the
spiral
are
met
with
agonistic
behavior
(Web
shaking,
chasing,
etc.).
In
many
solitary
and
aggre-
gated
spider
species,
maintenance
of
a
personal
space
or
territory
by
aggressive
behavior
has
been
shown
(Buskirk
1975
and
in
press,
Riechert
1978,
Burgess
1978).
The
combination
of
solitary
and
colonial
behaviors
exhibited
by
this
species
suggests
that
it
repre-
sents
an
intermediate
stage
in
the
evolution
of
social
behavior
in
spiders.
In
a
colonial
web
like
that
of
M.
spinipes,
where
space
webs
are
three-dimensional
and
highly
interconnected,
it
is
not
possible
to
discern
clearly
the
space
web
made
by
one
individual
vs.
another.
We
measured
the
dimensions
of
polygonal
colonial
webs
and
counted
individuals
and
orbs
in
the
field,
and
from
these
we
have
estimated
how
the
volume
of
the
colonial
web
is
subdivided
by
individuals
(Fig.
2).
The
amount
of
space
per
individual
in
a
colon-
ial
web
decreases
dramatically
as
colony
size
increases
from
2-10
individuals.
However,
in
larger
colonies,
there
appears
to
be
a
lower
limit
on
the
amount
of
space
per
individual.
The
asymptote
in
figure
2
possibly
reflects
the
minimal
individual
space
requirements
of
M.
spinip’es.
These
values
are
probably
underestimates
of
the
actual
amount
of
individual
space,
since
there
are
often
more
individuals
in
a
colony
than
there
are
orbs.
The
compressibility
of
individual
space
in
aggregations
of
varying
size
shown
by
this
species
indicates
a
degree
of
tolerance
of
conspecifics
beyond
that
expected
if
individu-
als’
webs
were
merely
attached
to
one
another.
Riechert
(1978
and
personal
communication)
has
found
that
terri-
tory
size
in
a
desert
sheet
web
spider
(Agelenopsis
aperta
(Gertsch))
decreases
with
increased
habitat
quality
over
a
wide
range
of
areas.
The
size
of
the
area
occupied
by
an
individual
Agelenopsis
spider
is
86
Psyche
[March
Table
3.
Frequency
distribution
of
group
size
in
Metepeira
spinipes
colonies
in
low
willows
(Salix
sp.).
Truncated
Observed
Truncated
Negative
Group
Size
Frequency
Poisson
Binomial
8
2
2
33
4
0
5
3
6
2
7
83
9
0
10
0
11
0
12
13
14
0
15
16
0
17
0
18
0
19
0
20
0
20
6
31
0.58
I
.244 2.43
.686
1.44
2.42
3.39
4.080
4.285
4.000
3.360
2.57
1.00
1.16
.69
1.51
5.16
3.26
2.42
1.93
1.60
1.36
1.19
1.04
.93
.83
"75
.68
.62
.57
.53
.48
.45
.42
.39
.36
6.06
79.36
X
16.02
.005
.4
<
p
<
.5
1.76
1.43
1.19
1.46
1.17
related
to
its
energy
needs
and
to
the
accessibility
of
prey
(based
on
prey
abundance
and
microclimatic
stress
limits
on
prey
catching
time)
in
a
habitat.
An
energy-based
territorial
system
might
be
part
of
a
hypothesis
generated
to
explain
the
evolution
of
social
phenom-
ena
in
spiders
like
M.
spinipes.
In
habitats
where
accessibility
to
prey
is
high,
territory
size
and
inter-individual
distance
would
be
reduced,
and
populations
would
be
large.
If
available
web
sites
(providing
architectual
support
for
a
3
dimensional
webas
in
soli-
tary
Metepeira)
were
limited,
selection
would
favor
individuals
ca-
pable
of
living
in
an
aggregated
state.
Behaviors
favoring
group
occupation
of
web
sites
(increased
tolerance
of
conspecifics,
interat-
traction)
would
be
selected
for,
although
behaviors
associated
with
1979]
Uetz
&
Burgess
Behavior
in
M.
spinipes
87
maintenance
of
individual
space
(web
defense
etc.)
would
be
retained.
There
are
many
other
selective
advantages
to
group
living
that
might
also
apply
to
the
evolution
of
coloniality
in
M.
spinipes.
By
locating
space
webs
together,
spiders
gain
additional
"knock-down"
structures
which
may
serve
to
increase
prey
taken.
The
colonial
space
web
creates
a
stronger
foundation
on
which
to
build
individ-
ual
orbs,
and
may
allow
energy
savings
in
web
maintenance
costs.
The
colonial
web
also
transmits
vibrations,
and
may
be
an
impor-
tant
means
of
communication
of
predator
attack
or
prey
availabil-
ity.
Prey
stealing
and’web
take-over
are
often
seen
in
M.
spinipes
and
other
species,
and
suggest
that
spiders
may
benefit
from
living
in
an
aggregation
without
building
a
web.
The
mate
selection
pro-
cess
is
facilitated
by
group
living,
and
males
may
increase
their
fitness
by
"attending"
a
female
(we
have
observed
this)
before
she
molts
to
adulthood.
Colonies
of
spiders
like
M.
spinipes
can
monopolize
larger,
or
better
quality
web
sites,
while
solitary
species
20.0
>
I0.0
>..
z
0
o
o
o
o-IN
AGAVE
SP.
e-IN
WILLOW
SHRUBS
o
0
0
0
0
oO
0
O0
0
0
16
PLo
NO.
OF
INDIVIDUALS
/
COLONY
Figure
2.
Amount
of
colony
volume
per
individual
M.
spinipes
over
a
range
of
colony
sizes.
(Colony
volume
in
cm
is
expressed
as
a
cube
root
for
linear
comparison
with
number
of
individuals.)
88
Psyche
[March
may
not.
(For
more
detailed
discussion
see
Shear
1970;
Kullman
1972;
Lubin
1974;
Burgess
1978;
Buskirk,
in
press).
Hopefully,
future
research
on
this
species
and
other
group
living
spiders
will
shed
more
light
on
the
evolution
of
sociality
in
an
otherwise
asocial
group
of
animals.
SUMMARY
Data
on
habitat
preference
and
group
size
in
Metepeira
spinipes
F.
P.-Cambridge,
a
colonial
orb
weaving
spider
from
Central
Mex-
ico,
are
presented.
M.
spinipes
colonies
are
associated
with
micro-
habitats
of
permanent
structure,
and
occur
most
frequently
in
maguey
plants
(Agave
sp.).
Colony
size
appears
to
be
independent
of
microhabitat
structure.
Distribution
of
group
size
in
two
con-
trasted
habitats
(Agaves
and
willows)
showed
a
significant
differ-
ence
from
a
zero-truncated
Poisson
distribution
and
a
good
fit
to
a
zero-truncated
Negative
Binomial
distribution,
indicating
a
ten-
dency
to
aggregate
independently
of
habitat.
Amount
of
individual
space
decreased
with
increased
colony
size,
indicating
a
tolerance
of
conspecifics
greater
than
expected
if
spiders
merely
attached
indi-
vidual
webs
together.
The
combination
of
solitary
and
colonial
behaviors
exhibited
by
this
species
suggests
that
it
may
represent
an
intermediate
stage
in
the
evolution
of
social
behavior
in
orb-
weaving
spiders.
Possible
selective
advantages
to
group-living
in
this
species
and