Download Population studies of two colonial orb

ZoologicalJoumal ofthe Linnean Society, 70: 265-287. With 8 figures
November 1980
Population studies of two colonial
orb - weaving spiders
YAEL D. LUBIN
Smithsonian Tropical Research Institute,
P.O. Box2072, Balboa, Canal Zone, Panama"
Accepted for publication February I 9 8 0
Colonial spiders have individual capture webs (territories) within a tonimurlally \ h d i cti web
wucture. I describe here the life histories and colony population dynamics of two cr~nimunal
specks, Crrtophora moluccensts (Doleschalll (Araneidae) in Papua NCH Guitwa and Philoponella
repubkana !Simon) (Uloboridae) in the Panama Canal Zone. In both species, dispci.r,il and
foundation of new colonies are primarily by groups of immatures. Population gt-owth o f new
colonies w d s rdpid during the first generation, but then colony population sire clecrcdscd mar-kcdlv.
Colonies of P republicana rarely lasted more than one generation, whereas thow of C. molui<rrist,
.tttained an equilibrium population size and often persisted for many grnciations <it tlir \ m i c rite.
Reproduction occurred during the wet season in P . republiconu colonies and \ m i - I ound in colonies
o f C moluccen,iJ. Reproduction was synchronized in widely separ-ated colonio o f P. rt~picbi~cana
F d C t 0 l . S controlling population growth and survival of colonies are discuwxl. CvrloJihom mo/tcrcenri~
colonies were probably regulated by density dependant factors, especially predation and parasitism,
and perhaps a shortage of flying insects due to colony visibility. Philoponella republicana colonies were
most likely limited by climatic conditions and instability of the habitat (i.e. density independent
factors). Colonial social organization influences both dispersal and colony population growth.
Colonialin. is, however, compatible with various life history strategies.
K E Y WORDS:
-
colonial spiders
-
Cylophoru moluccensic
-
Phi/opurru/iu r~,tmh/rtnnri- lilt,
lii\tot\
p o p d i t i o i i cl\ iiaiiiic\.
CONTENTS
. . . .
. . . .
Cyrfophorii I U U ~ U L L ~ U M(Doleschall!
l'hdoponel/u republicana (Simon)
Mcthodr
. . . . . . .
Crrlophora nioluccen~i~
. .
P h i l o p o t d n republicma
. .
Rr\ull\
. . . . . . .
C yrtophora moluccensi\
. . .
Life histor)
. . . . .
Colony foundation
. .
Colonv growth
. . .
Phcllolop
. . . . .
Illtlo(iu(tloll
The \pidcrs
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"Prcascrlt addrcss: Wau Ecology Institute, P.O. Box 7 7 , Wau, Papua New Guirrca
0024-4082/80/110265
+ 23$02.00/0
265
0 1980 Thr I , I I I I I SIC
~ ~ ~l Ir tI\
of L o n d o l l
266
Y. D. LUBIN
Philoponella republicana
. . . . . . . . . .
Life history . . . . . . . . . . . . .
Colony foundation
. . . . . . . . . .
Colony growth and longevity . . . . . . . .
Phenology
. . . . . . . . . . . . .
Discussion
. . . . . . . . . . . . . . .
Dispersaland geographicdistribution
. . . . . .
Colony growth and survival . . . . . . . . .
Coloniality, life history strategies and population dynamics
Acknowledgements
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References
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INTRODUCTION
Colonial or communal spiders (Lubin, 1974; Shear, 1970, uses the term
‘semisocial’) are characterized by having individual territories within a
communal web structure. They generally lack cooperation in prey capture and in
the construction of individual capture webs, nor do they feed communally.
Certain behavioural adaptations, primarily involving tolerance of conspecifics
and reduced cannibalistic tendencies, are typical of colonial species (Buskirk, in
press, and references therein).
Ecological adaptations to communal living may include modifications in
patterns of dispersal, growth and reproduction. How do population processes in
communal species differ from those in solitary species? The life histories and
population dynamics of two colonial spiders, Cyrtophora moluccensis (Doleschall)
(Araneidae) and Philoponella republicuna (Simon) (Uloboridae), are examined here
in an attempt to answer this question. A third colonial species, Metabus grauidus
(Cambridge) (Araneidae), was investigated by Buskirk (1975a, b) and provides
additional data for comparison. All three of these colonial species spin orb-webs
and all are tropical in distribution. They are, however, phylogenetically
unrelated, they occur in different habitats and differ in many aspects of their
webs and colony structure. A comparison of these three species provides the basis
for broad conclusions concerning the relationship between communal social
organization, life history strategies and population processes.
T H E SPIDERS
Cyrtophora moluccensis (Doleschall)
Colonies of C. moluccensis were studied in Papua New Guinea. Descriptions of
web structure and colony social organization are given in Lubin (1973, 1974).
This species is common in open, secondary-growth habitats and around human
habitation where the communal webs are often strung between trees, on power
lines and telephone wires (Fig. 1A). Individual capture webs are non-sticky,
horizontal orb-webs; an irregular tangle of non-sticky threads above the orbweb (the barrier web) acts as a stopping maze for flying insects and a similar
tangle below the orb-web may provide protection against predators and
parasites. The entire structure is best described as a ‘knockdown trap’ for flying
insects (Lubin, 1973). In a colony, the individual capture webs are interconnected
through their barrier webs. Aggressive interactions between colony members
occur during prey capture and web construction, but fighting and cannibalism
are rare (Lubin, 1974).
COLOUIAL ORB-WEAVING SPIDERS
A
B
Figurc I . A , schematic drawing of a C . moluccensts colony showing horizontal, trnr-,ha@ ui.t)-wehs
( O W ) (in profile) suspended from communal frame threads (F). Webs of many differmt iri\tdr\ are
present. Egg sacs are suspended in chains above the hub of the orb-web. Drawn from a photogr-aph.
B, schcmatic drawing of a P. republzcuna colony. Orb-webs (OW) are plared at varying a n g l r ~in the
from
~ d
colony. Thc core area ( C ) is occupied by adult females with stellate egg sacs IES). D I - ~ w
photograph.
261
268
Y . D. LUBIN
Philoponella republicana (Simon)
Philoponella republicana was originally described by Simon ( 1891) who noted
that the spiders lived in colonies often numbering several hundred individuals.
Observations of Simon (1891) in Venezuela, Schwartz (1904) in Cuba, and
Hingston (1932) in Guiana (Hingston’s “Uloborus socialis” is presumed to be P.
republicana)constitute the only published notes on the biology of this species.
I studied this species in lowland monsoon rainforest on Barro Colorado Island
(BCI) in the Panama Canal Zone. Colonies are found in forest understorey,
spanning gaps between shrubs and saplings, rarely more than 2 m above ground
30-215, N=34).
level (mean colonyheight in BCI forest=89 cm, l s . ~ . = 3 5range
,
Colonies occur most frequently where gaps in the canopy cover allow
penetration of light flecks during much of the day.
The structure of the colony is essentially as described by Simon (1891).
Colonies are composed of two parts : individual orb-webs and a central core. The
orb-webs (“toiles orbiculaires, rayons et a cercles, qui ne sont alors habitukes
que par un seul individu”, Simon, 1891: 8) are typical uloborid orb-webs with a
sticky spiral made of cribellar silk (see Eberhard, 1972). The individual orbs are
placed at varying angles within a framework of non-sticky threads which suspend
the entire colony between its supports (Fig. 1B).The colony is roughly spherical;
most orbs are located around the periphery and especially at the upper edge of
the colony. The centre or core of the colony (“un rPseau central assez serri.”,
Simon, 189 1 : 8 ) is generally free of orb-webs, consisting of an irregular tangle of
non-sticky threads.
Prey capture takes place on the individual orb-webs. At night spiders leave the
orbs and sit in the core area. New orbs are constructed before dawn, though
some web building and strengthening of the frame threads continues throughout
the day. The colony framework and some orbs remain intact at the end of the day
and are re-used the following day. Not all individuals have orb-webs. Adult
females with egg-sacs and adult males do not construct orbs and tend to sit in the
core area. Courtship and mating generally take place in the core area.
An orb-web abandoned by its owner is often reoccupied by another individual
and a web occupant may be chased off its web by another spider. Adult males
sometimes displace females from their webs. I have seen aggressive interactions
during web construction, prey capture and web takeover. During an aggressive
encounter, the web occupant may jerk or shake the web or run out on the orb
toward the intruder; cannibalism was never observed.
METHODS
Cyrtophora moluccensis
I studied C. moluccensis at the Wau Ecology Institute (WEI, formerly the B. P.
Bishop Museum Field Station) in Wau, Morobe Province, Papua New Guinea
(7’19OS, 146’44OE; elevation c. 1200m) from May 1970 to August 1971. The
climate is tropical montane. Rainfall data were obtained from WE1 and a nearby
weather station.
Colonies of C. moluccensis on the grounds of WE1 were censused weekly. In the
censuses, individuals were grouped into the following size classes : immatures less
C O L O N I A L ORB-WEAVING SPIDERS
269
than 10 mni body length, including immature males with webs; subadult (last
instar) females and adult females without egg sacs; adult females with one or
more egg sacs. Adult females are approximately 25 mm body length. Adult males
were not censused since they lacked orb-webs and were difficult to see from a
distance. N o attempt was made to count newly emerged spiderlings that had not
yet constructed webs. These censuses provided data on colony population
dynamics : dispersal, foundation of new colonies, colony growth and longevity.
Life history data for individual spiders were obtained from studies of small
groups of spiders located in an abandoned citrus grove in the Wau valley and
from an experimental colony at WEI. I recorded the development from hatching
to adult, longevity of adult females, the presence of males in webs of females and
the intervals between successive egg sacs laid by individual females.
Twenty-five female C. moluccensis were marked in the abandoned citrus grove
and checked daily from November 1970 to February 197 1. New egg sacs and the
presence of males were noted for each female. When one female disappeared in
the course of the census, 1 marked another, so that in fact the total number of
spiders followed during the census was 54. Some spiders were subadults at the
beginning of the census and matured during the census period. From
observations of these individuals I determined the interval from the last molt t o
production of the first egg sac.
Since I was not able to follow each individual spider from its last molt to
death, I used an indirect method of estimating adult lifespan based on the
number of egg sacs produced and the average interval between succcssive egg
sacs. The following formula was used to calculate the adult lif&pan of 19
individuals :
adult lifespan (days)= interval between the first dated egg sac and death of the
spider + (average interval between successive egg
sacs x number of previous undated cgg sacs) + average
interval between the last molt and production of the
first egg sac.
The average interval between successive egg sacs was 27.0 days and from the final
molt to the first egg sac 34.5 days (see Table 1).
Philoponella republicana
Data on the life history of P . republicana and colony population dynamics were
obtained from censuses of colonies on Barro Colorado Island during 197 2- 1973.
Forty-two colonies were found during the period October 1972 to May 1973,
mostly along the edges of trails in approximately 70-year old forest in the central
part of the island. From March to October 1973 the study concentrated o n a
complex of nine colonies located in one area (area I ) of about 50 m2. Another
large colony was monitored from May to October 1973. Colonies along trails
were censused weekly. Colonies in area I were censused at irregular intervals.
In censusing P. republicana colonies, individuals were estimated by eye against a
millimetre scale and scored according to four size classes: ( 1 ) less than 2 nim
body length, corresponding to newly hatched spiderlings, ( 2 ) 2-3 mni, ( 3 )
4-5mm, and (4)greater than 5 m m , corresponding to the adult stage. Adult
females were further categorized by the presence or absence of egg sacs. Males
270
Y. D. LUBIN
Table 1. Life history data for C. moluccensis, in days
Stage
Egg sacs :
Production to emergence"?
Immatures:
Emergence to dispersal
from egg sac*
Emergence to adult female*
Adults :
Mating to 1st egg sac"
Final molt to 1st egg sac7
Interval between successive
egg sacs*
Interval between successive
egg sacst
Adult female lifespan
(estimated)?
N
Mean
4
38.0
1.50
Range
27-50
2 egg sacs
3-8
1
c. 120
1
2
15
34.5
7
30.4
18.6
11-58
29
27.0
11.8
10-56
19
106.2
28.6
64.5-153.0
27-42
See Methods for formula used to estimate adult lifespans. N=sample size. *Data from observations of an
experimental colony near amercury-vapour lamp. ?Data from a 4-month census of \mall colonies in an
abandoned citrus grove.
were recognizable when they reached a body length of about 4 mm, one or two
instars before the adult stage. Estimating population size in large colonies (more
than 100 individuals) and in colonies containing newly emerged spiderlings was
difficult; such estimates may contain a 10%error. Spiders sitting off their webs
were more difficult to detect and count than spiders sitting on orb webs. For this
reason, all censuses were conducted in the early morning, when most individuals
had orbs.
Egg sacs produced in area I colonies were marked with dots of enamel paint
and the fate of some of these was followed until they hatched or disappeared.
This method provides a minimum estimate of the number of egg sacs produced
by the colony since some egg sacs may have been abandoned (and therefore
missed) in the interval between successive censuses. In censuses of other colonies,
the maximum number of unmarked egg sacs recorded during the census period
again provided a minimum estimate of egg sac production. Development from
hatching to adult and adult longevity were determined from censuses of colonies
in area I . Since there was little overlap in generations, it was possible to do this
without marking individual spiders.
RESULTS
Cyrtophora moluccensis
L f e history
During their lifetime, C. moluccensis females may produce 1-6 egg sacs, each
containing 87 7 f 299 eggs on average ( N = 4 ) . Spiderlings emerge en m s s e from the
egg sac after a proximately 38 days (Table 1) and remain near the empty egg sac
for 3-8 days, Erming a dense cloud of spiderlings embedded in a loose matrix of
silk. After this period they disperse and construct tiny orbs that are perfect
replicas of the adult web. Development of females from hatching to adult
27 1
COLONIAL ORB-WEAVING SPIDERS
requires about four months. This figure is derived from studies of a colony
located next to a mercury-vapor lamp which attracted insects, thereby providing
the colony with abundant prey. Growth rates in ‘natural’ colonies may be
somewhat slower. The adult female lifespan was calculated at about 3.5 months
(Table 1).
Males of C. moluccensis are small, about l/lOth the weight of adult females
(adult females weigh c. 1.4g; Lubin, 1973) and almost certainly mature more
rapidly than females. The tendency for males of species with strong sexual size
dimorphism to mature in fewer instars than the females has already been noted
in several spiders (Levy, 1970; Robinson & Robinson, 1976; B. Robinson &
M. H. Robinson, 1978).
Immature and subadult males construct typical Cyrtophora webs, often near o r
within the barrier web o r frame threads of the female’s web. Adult males sit in
the upper or lower barrier webs o r on frame threads of webs of subadult o r adult
females. As many as twelve males were seen in the web of a single last instar
female. Females possibly mate more than once, as evidenced by the presence of
males and courtship sequences observed in webs of females that had already
produced one or more egg sacs (Table 2). Nonetheless, males spent more time on
webs of adult females that had just reached maturity than on webs of either last
instar females (t= 2.60, P < 0.05) or of adult females that had already produced an
egg sac (t= 1.47, P < 0.1). This suggests that females are most attractive during the
period just after maturation and before laying the first egg sac.
Table 2. Occurrence of males in webs of female C. moluccensis: mean number of
web-da s (t1 S.D. and range) and percent of total web-days with males resent in
webs o last instar (subadult) females and of adult females before an after the
production of the first egg sac. Data for last instar females include only those
individuals monitored for more than ten days prior to the final moult. N = number
of females
r
Stage
Last
K
.V
Total no.
web-days
N o . web-davs with mnle\
Mean
SD
Rangc
%> \ \ d - d a v \
wich itinles
illsldl-
(subadultI
Adult
Before 1st egg \ d C
After 1st egg sac
5
73
8.6
8.6
0-20
58.9
3
16
94
453
24.7
13.8
8.1
12.2
20-34
78.7
kX.6
1-37
Colonyfoundation
Three natural colonies ( l a , Ib and 3a) were observed in early stages of colony
growth. All three were located near larger colonies and were almost certainly
derived from them. Colonies l a and l b were respectively five and ten metres
away from colony 1, a colony about 1-year old at the beginning of the study.
Colony 3a was about ten metres from colony 3, a mature colony more than
1-year-old at the start of the study.
Colony l a was founded by 3-5 mm long immatures, probably derived from
colony 1. Immatures of C. moluccensis were seen in the location of colon) l a from
the beginning of the study period in May 1970, but were not observed
272
Y. D. LUBIN
systematically until the first adults appeared in December, eight months later.
The site may have been colonized several times and immatures from previous
colonizations died out, or perhaps the original colonizing immatures took 2-3
times longer than average to reach maturity (see Table I). The first egg sacs
appeared in early February 197 1 and a total of five egg sacs were produced over a
period of seven months. At least two of these egg sacs hatched, but the
spiderlings either died or dispersed, as the number of immatures in the colony
did not increase. N o more than 16 individuals with webs (adults and immatures)
were observed at this location in a period of 15 months.
I do not know whether Ib was established initially by immatures or by adults
or subadults since the first records of this colony in September 1970 were o f two
adults (one with an egg sac) and several newly emerged spiderlings (Fig. 2).
Colony growth was slow for four and a half months, until mid-January 197 1,
when the number of individuals increased sharply with the hatching of two egg
sacs.
Colony 3a was formed by dispersing immatures. Three immatures were
present on 1 September 1970; of these, two females matured and laid two egg
sacs each. Only one egg sac hatched and the spiderlings disappeared within a
week. With the exception of these newly emerged spiderlings, no more than three
immatures and two adults were present at any one time at this location. After
eight months the colony disappeared altogether.
Although I never recorded a case of dispersal and colony foundation by
adults, it is at least theoretically possible. Certainly adult females moved websites
within colonies. Web locations of 26 adult females in colony 1 were noted over a
period of one month (21 April-22 May): 16 females moved their webs at least
once, eight remained at the same website for the entire month and two
individuals died. During this period two new adults appeared on previously
abandoned websites, but I do not know if they came from within or outside the
colony. It is significant that both immatures and adults of C. moluccensis tend to
aggregate. When spiders are removed from a colony and released at a new site
they group to form a new colony. Three separate releases of 4-10 spiders each
(adults and immatures) on the grounds of WE1 resulted in three new colonies at
these locations.
Colony growth
The growth curves of colonies Ib, 1 and 3 illustrate three different phases of
colony development (Figs 2, 3 & 4 respectively). In general terms, colonies ( 1 )
increase their population rapidly in the first generation, then ( 2 )undergo a period
of decline in population size, finally (3) equilibrating at a population size
considerably lower than that reached during the growth stage. Although the
three stages grade into one another, the population processes in each are
different enough to justiftr the distinction.
( 1) Early growth. Colony l b increased in number of individuals over a period of
seven months as the first generation of young matured and laid eggs and the
second generation of spiderlings emerged. The growth curve of the total
population is roughly sigmoid (Fig. 5). Since maturation, egg laying and
hatching of spiderlings were not synchronized, the population increase was
gradual. There was little evidence of predation, parasitism or large-scale
emigration during this stage of colony growth. The maximum number of pre-
C O L O N I A L ORB-WEAVING SPIDERS
273
I
Months
Figui-e 2 . Cri w v t h curves ot' C. moluccensii colony Ib. Numbers of immatur-rs 1 dotrrd line), \ul)ndul!
lrniaie5 and adult fernales without egg sacs (solid line) and adult femalry \vith ~ g \at$
g i b r o h linel,
rxpre\,ed a \ averages of four weekly censuses per month from Septembcl- 1970 t o A ~ i g t ~ 197
\ t 1 mo11e
ccnsii\ o n l r i n August).
L
i
z
\
\
\
\
\
\
\
\
\
I sI '~ o ~ ~ e
Figui-r 3 . Growth curves of C. moluccenszs colony 1, censused from May 1970 t o A ~ ~ L197
census in Augu\t 197 1). Lines as in Fig. 2.
Y. D. LUBIN
274
.
2
..
2 '50
0
E:
z
10-
0)
n
5
z
5-
Flgure 4 Growth curves of C . molurcrnszs colony 3, censused from July 1970 to August 1971 (two
censuses in July and one in August). Lines as in Fig. 2.
reproductive individuals recorded in the colony was 57 in May (38 immatures
and 19 subadult and adult females without egg sacs). At the end of the study,
there were 39 adult females, i.e. about as many adult females as there were
immatures at their peak (assuming that roughly half of the immatures were
males).
(2) Transition. Growth curves of colonies 1b and 1 illustrate the transition stage.
At the end of the study period, second generation females in colony l b were
maturing and beginning to reproduce (Fig. 2). Nonetheless, the number of
immatures in the colony continued to decline. Possibly hatching of egg sacs was
delayed or egg sacs failed to hatch due to predation or parasitism, or if they did
hatch, the spiderlings emigrated from the colony. The net result was a decrease in
total colony population (Fig. 5).
Colony 1 was about a year old at the beginning of the study and at the same
stage of development as colony l b at the end of the study, i.e. reproducing
females were increasing in number while immatures were decreasing (Fig. 3). At
the peak of its growth (September 19701, colony 1 contained 73 adult females and
9 1 egg sacs. Colony size then declined dramatically from September to December
as the adults died off. Although immatures began to appear in the colony in
September, their numbers fell far short of the total production of eggs by females
of the previous generation. The population of colony 1 equilibrated at 25-30
individuals and stayed at this level throughout the remaining nine months of the
study (December to August).
(3) Equilibrium. Colonies 1 and 3 appeared to reach an equilibrium population
size that was maintained with less than three-fold variation for a period of many
months (Figs 3, 4).Colony 3 contained 12-34 spiders over a period of 14 months
(mean+ 1 S . D . = 23.2 5- 5.1, 5 1 censuses). Numbers of adult and subadult females
varied from 5-20 (12.4_+3.9) and immatures from 3-19 ( 1 1 . 3 5 5 . 1 ) .Females with
egg sacs were present throughout the study and accounted for more than 50%of
the adult population at any one time.
Growth curves of colonies Ib and 1 indicate that it takes about 18 months for a
colony to reach the equilibrium stage. Although the exact age of colony 3 was not
known, it was at least a year old at the beginning of the study (information from
local sources). With a generation time of 5-6 months (Table 11, colonies of C.
moluccensis can produce approximately two generations per year.
COLONIAL ORB-WEAVING SPIDERS
215
Phenology
The rainfall pattern at Wau is seasonal only to the extent h a t o n e can
distinguish wetter and drier periods (Fig. 5 ) . The dry period gener-allv lasts fi-om
May through August, but is variable both in timing and in its sevei,ity'(Brookfield
& Hart, 1966). In 1970, a relatively dry year, the four-month dry period had
28.94 cm of rain, almost 14% of the total annual rainfall (Mav 197o-April 197 1).
Data are not available on other climatic variables.
Colonies of C. moluccensis were present year-round and individual colonies
persisted for more than one year. One colony in the Wau valley was known t o
60
VI
L
al
E
-
m
a
p
40-
0,
n
5
z
20 -
FiguIe 5 . GI-owth curves, all age classes combined, o f C moluccenczr co1oritc.s 1. 1.1. IIi . i t i ( i 3 (1111 ttig
1970-197 1 and monthly rainfall data for Wau. Rainfall data fronl WE1 rle\.. 1:'OO 1111 r ~ ~ 1(1'1 o 1 1 t h l 1
totals f o r the census period May 1970-July 197 1. Rainfall data fot Gcildrii Ridg,c,\ G R ' ( , l c ~
1190 nil o i i the mine side of the Wau valley as WEI, are monthly awragc.5 t i d v d 0 1 1 1'2 ~ r d\t 01 ILILI
froin 1951-1963 (Brookfield & Hart, 1966).
have occupied the same site for 12 years. Adults and immatures wcre present at
any time of year (except in incipient colonies) and reproduction occurred yearround (Figs 2-4). I do not know if colony foundation is seasonal : colonies l a and
3a were started in December and September respectively. Colony Ib was tirst seen
in May, but may have been founded earlier.
Although growth and reproduction occurred throughout t h c y c a ~ - ,certain
aspects of colony dynamics did show weak seasonal trends. These n w e most
obvious in colonies 1 and 3 in the equilibrium phase. Number-s o f i-cproducing
females were at their lowest at the end of the dry period (July-August) in b o t h
colonies. Numbers of immature spiders in these colonies dropped b o t h at the
end of the dry period (July-August) and at the end of the major rainy period
(December-January). A decline in numbers of immatures occurI-ed at th'c cnd of
the dry period in the incipient colonies la and Ib as well.
276
Y. D. LUBIN
Philoponella republicana
Ltje histo7y
Philoponella republicana females guard a single egg sac at a time; rarely, two egg
sacs are attached together end-to-end. The egg sacs are flattened, 17-23 mm long
and 5-6 mm wide, dark brown and roughly rectangular in shape with angular
projections along the edges. Egg sacs were guarded for 13-21 days (mean= 18
days, N=5) and hatched after 18-21 days (mean=20, N = 5 ) . There were an
average of 121 hatchlings per egg sac (range 88-155, N = 5 ) . One female may
produce 1-3 egg sacs in her lifetime.
Newly emerged spiderlings remain aggregated near the egg sac for approximately three days before dispersing and building their first webs. Adult type
orb-webs are constructed only after the first molt outside the egg sac. Prior to
this, spiderlings lack a functional cribellum (Wiehle, 1931) and thus cannot
produce the cribellar silk spiral. The hatchling web is a dense sheet of fine, nonsticky threads arranged in a radial pattern, similar to the first webs of Uloborus
plumipes (Szlep, 1961)and U . diwersus (Eberhard, 1977).
Development from emergence to adult female required a minimum of 28-66
days (mean=41, 7 colonies). The lifespan of adult females, from the date of their
first appearance in a colony to disappearance, was 35-57 days (mean=45, 3
colonies). Adult males are smaller than females (males: 3.8-4.6 mg body weight,
N=3; females: 12.2-19.4 mg, N=4) and probably mature before females of the
same brood. In nine out of 11 colonies, adult males appeared one week or more
(maximum 28 days) before adult females. Males that mature and remain in the
colony, however, overlap with females of the same generation. The extent of
migration of males between colonies is not known.
The adult sex ratio (male/female)was variable between colonies, ranging from
0.43-2.93, but was not significantly different from 1 : 1 when data from all
colonies were pooled (18 colonies: 366 males, 350 females). Adult males tended
to be more abundant in colonies with last instar females than in colonies with
adult females with egg sacs. The causes of their disappearance, whether migration
or mortality, are not known.
Colonyfoundation
New colonies are started by groups of 2-3 mm spiderlings that move away
from the parent colony en masse. At this stage, the spiderlings are already
constructing adult-type webs. Of the eight groups which formed the colony
complex in area I, six were clearly founded by groups of spiderlings budding off
the main colony (Fig. 6). The formation of colonies 2 and 3 was correlated with
the emergence of spiderlings from egg sacs produced in April-May, whereas
colonies 4, 4a, 5 and 6 appeared after a massive emergence of spiderlings from
egg sacs produced during June-August.
In August, colony 1 had approximately 1500 immatures less than 3 mm long
(Fig. 6). In September, about 1000 spiderlings split off from colony 1 to form
colony 4. Colonies 4a and 5 were founded by groups of c. 200 and 40 spiderlings
respectively. Both colonies 1 and 4 suffered substantial losses of spiderlings
during this period. Colony 1 died out at the end of September, but the same
location was recolonized by a group of c. 245 spiderlings 4 mm and less (colony
6) which had split off colony 4.
COLONIAL ORB-WEAVING SPIDERS
c-
2500
211
56
9
A
C
1000
\,":
50
+5
L
0
I
I
I
5
10
l
M
l
A
I
1
M
I
15
20
Weeks
I
J
I
J
A
Months
I
I
25
30
I
1
S
I
I
O
N
Figut-e 6. GI-owth curves of P. republicam colonies in area I from Mar-ch to No\,crriber- 1973. A,
colony 1 : numbers of imrnatures of all size classes (solid line) and numbers of adult females Iklotted
line). B. colonies 2 , 3 and 4: 2 and 3, all size classes combined; 4, immatures (solid line) arid adult
females (dotted line). C, colonies 5 , 6 and 7 : all size classes combined. The preseric-r o f rgg 5acs in
c-oloiiie5 I and 4 is indicated by horizontal bars; the maximum number of egg sacs obwrvrd I \ 5 t i o w i
above each bar. The arrow in colony 4 indicates the fusion of colonirs 4 and 4a. Colonic\ th,it dicd
offdui-ingthe census period are indicated by a star.
Spiderlings colonizing a new site may be derived from a single egg sac o r
group of egg sacs laid at the same time. More than 50% of the colonies observed
(24 out of 43) were, at the first census, composed of immatures of a 5ingle age
class and 20 of these colonies had fewer than 100 immatures at the start of the
census.
New colonies may also arise from single adult females which lay their eggs
away from the parent colony. Solitary females with egg sacs were observed on
only three occasions. Admittedly, solitary spiders are more difficult to spot,
particularly if they do not have an orb-web; dispersal and colonization by gravid
females may be more widespread than my observations indicated (see
Discussion).
278
Y . D. LUBIN
Colony growth and longevity
Colonies increased in size and numbers of individuals by means of ( 1 ) the
recruitment of spiderlings from egg sacs laid in the colony, (2) immigration of
immatures or adults and (3) fusion with nearby groups. The first of these modes
of growth was the best documented and probably accounted for most of the
observed growth in the colonies I studied.
Colony 1 in area I had 27 individuals at the beginning of the study. Thirteen
females matured, but only eight (62%)laid eggs, producing ten egg sacs. Four of
the egg sacs hatched (four were parasitized and two were removed from the
colony), yielding approximately 290 spiderlings. Of these, 83 females and 26
males matured within the colony. Using figures for adult females alone, the
population of colony 1 increased by about 200% from the first to the second
generation. Of the remaining spiderlings that disappeared from colony 1,
approximately 170 (94%)emigrated and formed colonies 2 and 3. Thus, only 6%
of the first generation offspring in colony 1 were unaccounted for and probably
represent losses to predators or parasites. Of the second generation females, 68
(82%) laid 73 egg sacs. At least 2000 spiderlings emerged, most of which dispersed
to found colonies 4, 4a and 5 (see previous section). Colony 1 lasted only two
generations, but the same location was recolonized by colony 6, which consisted
primarily of 2-4 mm immatures, within a week of the disappearance of colony 1.
Immigration may play an important role in colony population increase. Ten
of the 43 colonies which were censused more than once, were augmented
between censuses by ten or more individuals of 3rd or later instars (more than
2 m m long) at a time when no egg sacs were present in the colonies. These
immatures must have immigrated into the colonies.
I observed fusion of two colonies on one occasion only. Colonies 4 and 4a
were less than 1 m apart and fused as individuals within the colonies grew and
their web spaces overlapped (Fig. 6).
Fewer than one-third of the colonies censused produced egg sacs, at least
within the colony framework, and only one colony persisted for more than one
generation (Table 3). Twenty colonies with adult females did not produce egg
sacs, although ten of these had adult females in them during periods when other
colonies were producing egg sacs.
Colonies that produced egg sacs had a significantly higher maximum number
of adult females in them than did colonies with adults that did not reproduce
(reproducing colonies: mean fS.D. = 26.3 f 20.4, N = 1 1 ; non-reproducing:
6.9k6.1, N = 2 0 ; t=3.79, P<O.OOl). The total population of adult females and
immatures greater than 2 mm long, i.e. all individuals constructing adult- type
webs, was greater in reproducing colonies than in non-reproducing colonies
(reproducing: 51.8 k 40.4; non-producing: 16.0+ 13.8, sample sizes as above;
t=3.64, P(0.01). The sex ratios in reproducing and non-reproducing colonies
were not significantly different, or even consistently biased in one direction.
Most P. republicana colonies were short-lived, lasting less than 40 days on
average (Table 3, Fig. 7). Colonies declined in population as a result of both
emigration and mortality. Dispersing immatures that did not join another
colony probably rarely survived. I saw only three solitary immatures and three
solitary adults during the entire study. Seven colonies which were increasing in
size disappeared suddenly, leaving not a trace of the colony web structure.
I saw predators at colonies on several occasions. Wasps (Trypoxylon sp. and two
219
COL ONIAL ORB-WEAVING SPIDERS
Table 3 . Number of generations of P. republicana colonie, and
their longevity, calculated as the interval in days between the
first and last sightings of a colony. Seven colonies seen on o n h
one occasion each are not included
Number of generations
I
2
-
< I
N u n i l x i - ofc.olonirs
31
%
72.1
DLll~'lll01l (tdVS!
\ICdIl*
R,ingc
I
5 11
I
2.3
11
25.6
7 1.4 k 47.4
24-162
28.2-C 19.5
6-84
1O l d l
43
39 9 k 3 5 . 3
A
-
P < 0.001
t=4.347
unidentified species) were observed taking an adult female and two inimatures
from colon): 1 and searching the same colony on two other occasions. Immature
P. republicana sitting on orb-webs responded to wasps by dropping off their webs.
Emisine bugs (Hemiptera: Reduviidae) which live as kleptoparasites in the
colonies, a pholcid spider, and two species of damselflies (Anisoptera) werr seen
feeding on spiderlings of P. republicana. In addition, 1 found parasitic wasps in
four egg sacs from colony 1.
Phenology
On BCI, the dry season is clearly more severe for forest understorey
arthropods than the wet season. Less than 4% of the total yearly rainfall occurred
during the four-month period January-April 1973. Average wind velocity
increased two-fold, from 1.85 to 3.95 km/h, average relative humidity dropped
from 9 1 to 8 1% and air temperatures inside the forest were higher during the dry
season (Smvthe, 1974).
Colonies of P. republicana were found throughout the year, from October 1972
to November 1973. Colonies censused during the wet season months October to
December did not persist any longer than those censused during the dry season
months January to March. However, eight of the 24 (33.3%)wet season colonies
persisted into the dry season, whereas only one of the 18 (5.6%) dn. season
colonies persisted into the following wet season.
Reproduction occurred in three periods, corresponding to early, mid, and late
wet seasons (Figs 6 , 7 ) . Colonies censused from October 1972 to May 1973
exhibited a major egg-laying peak in the late wet season of 1 9 7 2
(November-December, eight colonies) and a second period in early wet season of
1973 (April-May, two colonies). The colonies in area I had three periods of
reproductive activity: colony 1, in early wet season (April-May) and mid-wet
season (June-August); colony 4, which was founded by the June-August brood
of colony 1, in the late wet season (October). Individual females laid egg sacs
during only a single period of reproductive activity. Females which laid eggs in
June-August were the offspring of individuals that laid their eggs in April-May.
Thus, given a total individual lifespan of 3.5-4 months, P. republicana can
produce three generations a year.
280
Y. D . LUBIN
I
I3
I
I
I
-
I
I
I
I
I
13
3
59
31
13-
16
l7-
24
23-
23
3
34-
60
18
22
I02
102
5
8237
82
37
3
32
40
22
22
II
11-
32
-
14-
32
14
7
62
231
52-
52
8
43
36
43
-
36
2
84
84-
52
52
23
23
48
48
-
34
35
50
50
81
81
68
68
58 -
74
13-
13
I
34
74
l5-
19
52
I
I
O
I
N
I
D
I
1
J
-
F
I
M
52
I
I
A
M
Months
Figure 7. Occurrence of 32 colonies of P. republicma censused along trails on BCI during Octoher
1972-May 1973. Colonies seen on only one or two occasions are not included. Shown arc the
duration of each colony (horizontal line), periods of egg sac production (horizontal bar), maximum
nuniber of egg sacs observed (number above horizontal bar), initial colony population at first
sighting (number to left of each line) and maximum population of each colony (number to right of
each line).
In general, reproduction occurred sporadically throughout the wet season and
appeared to be loosely synchronized in different and widely separated colonies.
None of the census colonies had females with egg sacs during the dry season.
First stage spiderlings did, however, appear in area I in early April, suggesting
that either some egg sacs were, in fact, laid during the dry season or that
emergence of spiderlings from late wet season egg sacs was delayed until the
following wet season.
C O L O N I A L ORB-WEAVI N G SPIDERS
28 1
Colonies were not precisely synchronized in their development ; imniatures of
all sizes and adults could be found in some colonies at almost any time during
the census. Two general trends, however, were observed: ( 1 ) first instar
spiderlings were rare during the dry season, occurring in only 13.3% of the
colonies in February and completely absent in March; (2) relatively fe\v colonies
contained adults during the transition from wet to d n season (15.8% in
December and 16.7%in January).
The development of immatures may be slower in the dry season than in the wet
season. Three broods emerging in January developed to maturity in 41-48 days
(mean 45.6) and two others took 34+ and 63+ days. Two broods which emerged
in November developed in 28 days. Clearly more data are needed t o vcr-ifi. this.
DISCUSSION
Dispersal and geographic distribution
New colonies of C. moluccensis and P. republicana were founded by groups of
spiderlings dispersing from the parent colony, and perhaps by groups splitting
off the parent colony or by emigrating adults. The first of these was probablv the
predominant method in the two species studied here. The latter two nietliods
have been recorded in other colony-dwelling spiders : in the colonial arancid,
Eriophora bistriata, adult females leave the colonial web to lay their eggs (Fowler &
Diehl, 1978); new colonies of the social agelinid, Agelena consociata, are formed
when the parent colony breaks up during the dry season (Darchen, 1976).
Long-distance dispersal in many temperate region spiders is accomplished b y
‘ballooning’ of spiderlings (Bristowe, 1931, 1939: 187-201). Ballooning ivas not
observed in either species studied here; indeed, I know of no record of
ballooning in tropical spiders. Dispersing immatures of the colonial species C.
citricola produced floating silk threads and walked out on them after they became
attached to a substrate (Blanke, 1972). Cyrtophora citricola spiderlings mo\kd only a
short distance from the parent web o r release site (Blanke, 1972; Kullniann,
1958).
Philoponella republicana occurs from Panama to northern South America [ Opell,
1979), but is restricted in habitat to forest understorey and small treefall gaps.
From my observations of colonies in Panama, Colombia and Venezuela, it
appears to be patchily distributed, but locally abundant. Although dispersal
within patches may be accounted for by ‘overland’ group migration, thc question
of long-range dispersal remains problematical.
Cyrtophora moluccensis is widely distributed throughout the South Pacific, India,
Malaysia and southern Japan, suggesting a capacity for long-range dispersal. I t is
a clearing and forest edge species, both common and abundant throughout its
range. In New Guinea, I found colonies associated with human habitation
ranging from the coast to remote villages in the mountainous interior, hut never
in densely forested areas undisturbed by man. This association with villages may
be partly due to the fact that human disturbance creates conditions favourable to
the spiders (i.e., favourable websites, abundant insect prey). Additionallv, New
Guinea villagers transplant ornamental shrubs and fruit trees when a new hamlet
is established; spiders o r egg sacs in these trees might be transplanted as well.
Transplantation of colonies may also be deliberate. In a description o f the Dani
282
Y . D. LUBIN
tribes of’ the Baliem valley, Irian Jaya, Gardner 8c Heider (1968) show a
photograph of a C . moluccensis colony, captioned ‘Spiders are collected in the
forests and brought to the compounds where they weave elaborate webs. These
webs are compressed into magically protective strips which hang from the throat
or, more rarely, are formed into hats’. Silk from C. moluccensis colonies in
Liptimin (West Sepik Province) is used in making ceremonial headdresses (pers.
obs.). I t would be interesting to know what role man has played in the longdistance dispersal of this species.
Colony growth and survival
Following an initial phase of rapid population expansion, colonies of both C.
moluccensis and P . republicana experienced a sharp decrease in population size.
Colonies of P. republicana generally dispersed or died out at this stage. Cyrtophora
moluccensis colonies appeared to reach an equilibrium population size that was
considerably lower than the maximum population size during the growth phase.
In both species, the decline occurred when the adults of the previous generation
died and their eggs either failed to hatch, or the spiderlings that did emerge died
or emigrated from the colony. Causes for the decline in colony population size
must be sought in changes in the physical and/or biotic environment of the
colony, i.e. physical changes in colony websites, increased predation or
parasitism on eggs or spiderlings, or decreased food supply or food quality. The
immediate results of such changes might be increased mortality and a greater
tendency to disperse from the colony. Finally, there remains the possibility of
long-term rhythms of colony growth over many generations which could not be
detected in the duration of the study.
Physical changes in websites were not responsible for the decline in
populations of C. moluccensis colonies 1 and 1b. There were no marked changes
over the year in the structural supports of either colony (the upper branches of
large pine trees in both cases). Rain and falling branches or leaves are unlikely to
damage the strong, durable webs of this species (Lubin, 1973).This is not the case
in P. republicana colonies. Webs of this species are fragile and easily destroyed by
rain, strong winds, falling leaves and branches and mammal activity on the forest
floor (agoutis, pacas, coatis and many other common mammals are active in
light-gap areas on BCI and might easily blunder through a colony). Such natural
disasters may have accounted for the disappearance of apparently thriving
colonies.
Large colonies are conspicuous targets for predators, parasites and
kleptoparasites. Incipient colonies may go unnoticed by predators and parasites,
but as they grow larger, these influences will increase. Colonies of C . moluccensis
are particularly vulnerable : webs of Cyrtophora are renewed infrequently (Lubin,
19 73) and colony websites are occupied continuously for several generations.
Thus, these colonies are a year-round and fixed resource for predators and
parasites alike. Colonies 1 and 3 were visited by a tachinid fly (misidentified as a
sarcophagid fly in Lubin, 1974) egg parasite and there was a high incidence of
egg parasitism by both tachinids and scelionid wasps in other mature colonies
(Lubin, 1974). Kleptoparasitic theridiid spiders (Argyrodes spp.), which steal prey
from their hosts and also feed on newly emerged spiderlings, were abundant in
these colonies. The impact of kleptoparasites may be particularly great on the
COLONIAL ORB-WEAVING SPIDERS
283
immature stages of C. moluccensis which are about the same size as Argyrodes.
(Vollrath, pers. commn, presents evidence for the impact of prey theft o n the host
energy budget.)
Predation and parasitism may reduce colony growth rates indirectly, by
influencing spiderlings to emigrare from the parent colony. Incipient colonies of
both species were derived from spiderlings that had dispersed from colonies
undergoing rapid expansion and population growth. Adults, too, may change
websites within colonies o r even emigrate as a result of predator and' parasite
activity.
Relatively few P. republicana colonies yielded mature females which reproduced
within the colony. Those colonies in which egg laying did occur were significantly
larger (in numbers of adults and total population) than colonies with adult
females that did not lay eggs. The colony provides a protective matrix for females
guarding their egg sacs; perhaps colonies with few individuals provide
inadequate protection against parasites and predators. Adult females in such
colonies may choose to lay their eggs away from the colony. This hypothesis
implies the existence of a feedback mechanism between colony size and
reproductive behaviour of females. A similar sort of feedback mechanism was
demonstrated between the density of insect prey and movement of web location
by spiders (Turnbull, 1964).
Large colonies are conspicuous not only to predators and parasites, but also to
flying insects. Between 30 and 50% of the insects flying toward C. moluccensis
colonies 1 and 3 avoided them by flying over o r around them (Lubin, 1974).Web
avoidance bv potential prey will increase with colony size and may cause both
increased mortality and tendencies to emigrate.
Food supply has been shown to influence growth rates of spiders (Turnbull,
1962, 1965; Wise, 1975) and their fecundity (Wise, 1975). There is no direct
evidence that colonies of either C. molucceniis o r P. republicana experienced a
shortage of prey. Records of flying insects caught in window-traps and stickytraps at WE1 and captured by C . moluccensis colonies themselves (as estimated by
prey remains which fell into sheets placed under the colonies) showed that there
was little seasonal variation in insect abundances (Robinson & Robinson, 1973;
pers. obs.). On BCI, however, the numbers of insects caught in light-traps in the
forest understorey showed strong seasonal fluctuations (Smythe, 1974; Wolda,
1978). Many groups of flying insects were less abundant during both the late dry
and late wet seasons. Other forest-understorey species of web-building spiders
similarly declined in numbers during these months, perhaps due to a shortage of
prey (Lubin, 1978).
Coloniality, l f e history strategies and population dynamics
The life histories and colony population dynamics of C. moluccensis and P.
republicana are different in several important respects. Cyrtophora moluccensis has
long-lived colonies with overlapping generations and year-round reproduction.
Philoponella republicana has short-lived colonies, little generation overlap and
distinctly seasonal reproduction and development. Another colonial orb-weaver
found in Costa Rica, Metabus gravidus (Araneidae) has a social organization
similar to that of P. republicana (Buskirk, 1975a) and exhibits a third pattern of
284
Y . D. LUBIN
long-lived colonies with overlapping generations and a seasonal peak in
reproduction and abundance (Buskirk, 197513).
These different patterns may be understood in the context of climatic
seasonality and characteristics of the habitat and colony websites. BCI had a
marked dry season lasting about four months and strong fluctuations in insect
abundances. The New Guinea site had a less distinct dry period and insect
abundances did not fluctuate strongly. The Costa Rican study site, at
1540-1560 m elevation, had a four-month dry season, but insect abundances
fluctuated only three-fold and peaked in the late dry and early wet seasons
(Buskirk 8e Buskirk, 1976). Seasonal reproduction, synchronous development
and little generation overlap are to be expected in P. republicana, but not in M .
gravidus or C . moluccensis. Another communal orb-weaver, Eriophora bistriata,
which occurs in the dry, seasonal parts of Paraguay, Brazil and Argentina, has
non-overlapping generations and highly synchronous seasonal development and
reproduction (Fowler & Diehl, 1978). Colonies of M . grauidus and C. moluccensis
were located in relatively permanent sites, the former attached to rock
outcroppings over fast-running streams (Buskirk, 1975131, the latter in large gaps
between trees (Lubin, 1974). Colonies of P. republicana were attached to shrubs
and saplings near the forest floor, i.e. sites that are temporary and easily
disturbed. Whereas websites of M . gravidus and C . moluccensis could be occupied
for many generations, those of P. republicana remained suitable for only a short
period of time, often less than a generation.
Levy (1970) suggested that spider life histories could be divided into two basic
types: those in which males and females matured at the same rate and mating
occurred within the brood of a single generation, and those in which males
matured at a variable rate, mating with females from a different (previous)
generation. Both types of life cycle occur in colonial spiders. Philoponella
republicana and M . gravidus both have relatively large males and undoubtedly have
the first type of life cycle. This is particularly evident in P. republicana which also
has discrete generations. This life history strategy would appear successful in
seasonal environments where reproduction and development are synchronized
by climate. Robinson 8c Robinson (1978) argued that the second strategy, of
which C. moluccensis is an example, is favoured in tropical climates that are
relatively non-seasonal, where reproduction and development can proceed yearround.
Life histories and phenology of P. republicana and C. moluccensis are basically
similar to those of other non-social species occurring in the same habitats. Three
patterns of seasonal abundance were evident in the web-building spiders
censused in forest understorey on BCI and along roadside-second growth
ecotone in Wau (Robinson et al., 1974; Lubin, 1978): (1) species which reproduce
seasonally with relatively little overlap of generations; (2) species which
reproduce seasonally, but have overlapping generations; (3) species with yearround reproduction and overlapping generations. Most orb-weavers on the
roadside transects in Wau were present year-round and probably represent the
third pattern of seasonality, although some had peaks of abundance in either the
wet or the dry period. Cyrtophora moluccensis clearly falls into this category (as do
other species such as Argiope picta L. Koch and Leucuuge pupuana Kuluynski). The
majority of orb-weavers in the forest understorey on BCI, however, fell into the
first two categories. Reproduction appeared to be limited to the wet season and
285
C O L O N I A L ORB-WEAVING SPIDERS
many species became rare o r disappeared altogether during the drv season.
Philoponella republicana belongs to the first category which includes other spiders
found in open forest understorey, e.g. Pronous tuberculfer Kevserling, Micrathena
duodecimspinosa ( 0.P. -Cambridge) and Aruneus tuonubo (Chamberlin 8c Ivie).
Population dynamics of C. moluccensis and P. republicana are characterizcd bv ( 1 )
group dispersal and group colonization of new websites and ( 2 ) initial rapid
growth and expansion of colonies. Group colonization may offer several
advantages : protection from predators, the ability to colonize websites that are
unavailable to solitary spiders and construction of a more efficient prey trap
(Lubin, 1974). Once the colony is established, these same advantages operate to
allow rapid population growth within the colony. The risk in obligatorv group
colonisation lies in the fact that if conditions become unfavourable or the. habitat
is unsuitable, the entire colony may die out. This is clearly demonstrated in data
on survival of P. republicana colonies. A corollary of group dispersal and
colonization is the close relatedness of individuals within colonies, facilitating kin
selection and evolution of traits which further enhance communal behaviour.
Web-building spiders, by virtue of their dispersal methods, are considered to
be good colonizers (Bristowe, 1939). While both communal species discussed
here are colonizers of light gaps and clearings and may be considered typically rselected (MacArthur 8c Wilson, 1967), they differ somewhat in their long-term
strategies. Philoponella republicana is a fugitive species : local populations
(=colonies) are limited primarily by density-independent factors (climate and
habitat instability) and are consequently short-lived. Cjrtophom moluccensis
populations are limited by density-dependent factors (predation, parasitism,
prey) ; once established, these colonies are long-lived and K-selection factors
predominate.
In conclusion, the relationship between life history, population dynamics and
coloniality is both variable and complex (Fig. 8). On the one hand, coloniality
appears to be compatible with different life history strategies. These may be
determined primarily by local climate and habitat. On the other hand, dispersal
M a t u r a t i o n rate
SEASONAL1 I
----7
i
Generation overlap
H A B I T A T STRUCTURE
Website stability
A
Survival to egg-laying
BIOTIC FACTORS
Predation
Parasitism
Prey
SOCIAL ORGANISATION
-
-
COLONY
POPULATION
DYNAMICS
Dispersal
Figure 8. Schematic diagram of the relationship between environment, lile hiscot) stracrglrs.
population dynamics and social organization of communal spiders.
286
Y . D. LUBIN
and colony growth and survival are clearly influenced by the communal social
organization. The population dynamics of spider colonies reflect the combined
influences of life history pattern and the colonial social organization.
ACKNOWLEDGEMENTS
I thank F. Vollrath and M. H. Robinson for reading and criticizing earlier
drafts of the manuscript. The study was made possible by Smithsonian Tropical
Research Institute pre-doctoral and post-doctoral fellowships. A . Mahler assisted
in the field work on BCI.
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