Download The Influence of Interspecific Competition and Other Factors on the

The Influence of Interspecific Competition and Other Factors on the Distribution
of the Barnacle Chthamalus Stellatus
Joseph H. Connell
Ecology, Vol. 42, No. 4. (Oct., 1961), pp. 710-723.
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710
JOSEPH H . C O X N E L L
of J~itlian villagers tolvard monkeys, so that
~ i i o ~ i k e yare
s no longer protected as extensively as
i l l forliier years, ( 2 ) intensive trapping to obtain
n1onLeys for export, ( 3 ) changing patterns of
l;uitl use, inclueling the tleterinration of roadsicle
Iial)itats, ancl coni~iiercialforest managenlent.
REFERLSC
ES
Champion, H. G. 19311. .\ pre1in1i11al-y survey of the
forcyt t y l ~ c s o f India ant1 B u r m a . 111tlia11F o r e s t
IZecortls (Silviculture S e r i c s ) . Vol. 1, No. 1.
Manson-Bahr, P . H. 1954. Mall,on's Tropical Disca,c,. 14 1.:(1.. I.ontlon. Cassell a11t1 C ' o .
Nolte, A . 1955. 1;ield o t ) s e r v a t i o ~ ~o \n t l ~ edaily routine
a ~ ~social
tl
I ~ c l ~ a v i oofs common I n t l i a ~mollkeys,
~
with
sl)ecial r e i e r e ~ ~ c eto the 13onnet monkey (diacaca
Ecology, Val. 42, No. 4
radiatu Geoffroy). Jour. Bombay Nat. Hist. Soc.
5 3 : 177-184.
Pocock, R . I. 1929. T h e F a u n a of British India.
hZamtiialia. Vol. 1 l'rimates a l ~ t l Carnivora. Lontloli, Taylor and Francis, Ltd.
P r a k a s h , I. 1958. Thc 111-eetling season of the rhesus
n ~ o n k e y.2l~ri-ni-tri~~rrltrttcl(Zinimermann) in Rajasthan.
J o u r . R o n ~ l ~ aSya t . IIist. Soc. 5 5 : 154.
P r a t e r , S . H. 1948. T h e n o o k tti 111tlian hlatnmals.
1:oml)ay. T h e I3otnhay Satul-a1 H i s t o r y Society.
Ruch, T. C. 1959. I)i,cases of 1.al)oratory P r i m a t e s .
Philatlcll)l~ia.\V. I:. Sauntlers Company.
Couthwick, C. H., M. A. Beg a n d M. R. Siddiqi.
l')(Il. .\ ~)ol)ulation survey of rlicsus monkeys i n
\.illage\, t o w l ~ s , a ~ ~ ttetni~lcy
l
of ~ ~ o r t l ~ e Ir~ni d i a .
Ecology 4 2 : 538-547.
THE Isr:Lr1:scI:
01: INTERSPECII~IC COIIPETITION A N D OTHER
F-ACTORS ON TI-IE DISTRIBUTIOS O F TI-IE B-4RNACLE
CHTHAAIALGS S7'ELLA7'17S
] U S E I ~ I ~1 1.
CO'i
KELL
Uepnrt?ircrtt o f Biolo!gy, I'tlirrcrsitg o f Califorrria, Snnta Burbara, Goleta, Califoriiia
Nost of tlie eviclence for the occurrence of
interspecific coiiil,etition in aninials has been
gained froni lal~oratory populations. Recause of
tlie siiiall anioulit of direct evitlence for its occurrelice i l l nature, competition has sometimes
bee11 assignet1 a niinor role in cletermining tlie
coinl)obitio~ioi aninial communities.
Inclirect evitlence exists, lio\vever, \vhicli suggests that co11il)etition Iiiay sometin~es I)e resl)o~isil)lefor tlie tlistribution of animals in naturc. The range 11i distribution of a species may
I)e decreasetl in the presence of another species
ivith siniilar recjuirenients (l3eauclianip and U11yott 1932, Elitlean, Kenny and Stephenson 1956).
Uniform t1istril)ution is space is usually attributed
to intraspecies competition (Holtne 1950, Clark
and Evans 1954). IVhen aninials with similar
requireme~its, sucli as 2 o r more closely related
species, are found coexisting in tlie same area,
careful analysis usually indicates that they a r e
not actually conipeting with each other (Lack
1954, iLlac:lrtliur 1958).
I n the course of a n investigation of the animals
of an intertidal rocky shore I noticed that the
adults of 2 species of barnacles occupied 2 separate horizontal zones with a small area of overlap, whereas the young of the species from the
upper zone \\ere found in much of the lower
zone. T h e upper species, Clzthawmlus stellatz4s
(Poli) thus settled but did not survive in the
lower zone. It seenied probable that this species
\\-as eliminated by the lower one, Balanus balanoicics ( I ~ , ) ,in a struggle for a common requisite
which lvas in short supply. I n the rocky interticlal region, since for attachment aiitl groivth is
often extremely limited. This paper is an account
of sonie observations ant1 experiments designed
to test the hypothesis that tlie al~sencein the lower
zone of aclults of Chtlza~tlalzts was due to interspecific coi~ipetition lvith Balnnlrs for space.
Other factors lvhicli may have influei~cedthe distribution \\-ere also studied. T h e study was made
at Llillport, Isle of Cumbrae, Scotland.
I \voultl like to thank Ijrof. C. 12. Yonge and
the staff of the hlarine Station, Llillport, for their
help, discussions ant1 encouragen~ent during the
course of this \vork. Thanks are due to the folloiving for their critical reading of the manuscript: C. S. Elton, P. 12.. Frank, G. Hardin,
N. (;. Hairston, I<. Orias, T. Park and his
students, and my wife.
Distribution of the species of barnacles
The upper species, C l z t l z a ~ ~ ~ astellati(s,
l~~s
has
its center of d~stribution in tlie hlediterranean ;
it reaches its northern limit in the Shetland Islands, north of Scotland. .At Jlillport, adults
of this species occur bet~veen the levels of mean
high water of neap and spring tides (hl.H.\V.N.
and L1.H.W.S.: see Figure 5 and Table I ) .
In southn.est England and Ireland, adult Clztlln~t-
Autumn 1961
I N T E R S P E C I F I C COMPETITION
71 1
alrts occur at nloderate population densities other barnacle species present were Balanzis crenthroughout the intert~dalzone, more abundantly a t u s Brug and V e r r u c a s t r o e f ~ z i a( 0 .F Muller),
when B a l a n l ~ s ba1nnozdr.s is sparse or absent both found In small numbers only at and below
(Southward and Crisp 1954, 1956). - i t Mlllport hI L.11'S.
the larvae settle fro111 the plankton onto the shore
T o measure the survival of Chthanzalus, the
nlalnly In bepteml~er and Octol~er, some addi- positions of all ~ndividualsin a patch were mapl~ed
t ~ o n a lsettlement nlaq occur until December. T h e Any barnacles which were empty or missing
settleinent 1s tnost abundant between M.H.W.S. at the next examination of this patch must
ancl mean t~clelevel ( M . T . L . ) , in patches of rock have died in the interval, since emigration is
surface left bare as a result of the mortality of impossible. T h e mapping \ \ a s done by plac~ng
Bulanzds, litnpets, and other sedentary organisms. thin glass plates (lantern slide cover glasses,
Few of the C/ztlzn?tlalzts that settle below A1.H. 10.7 X 8.2 cm, area 87.7 cm2) over a patch of
\I7.N. s u r ~ i v e ,so that adults are found only oc- barnacles and marking the position of each
casionally at these levels.
Clzthar~~allts
on it \\ ith glass-marhing ink. T h e
Balaizrrc ba1anoidc.s is a boreal-arctic species, positions of the corners of the plate \vere marLed
reaching its southern limit in northern Spain. by drilling small holes in the rock. Observations
A t Alillport it occupies allnost the entire inter- made 111 subsequent censuses mere noted on a
tidal region, from inean lo\% v a t e r of spring tides paper copy of the glass map.
T h e study areas mere chosen by searching
( h l . I A . K . S . )up to the regio~ibetween 1I.H.TV.N.
and X . H . W . S . Above l I . H . \ \ T . N . it occurs in- for patches of Clztllalllcllus belom A1.H.W.N. in
termingled with Clltlzal~zalltsfor a short distance. a stretch of shore about 50 ft long. TVhen 8
Balanlts settles on the shore in *\pril and May, patches had been found, no more were looked
often in very dense concentrations (see Table for. T h e onlj basis for reject1011 of an area in
11')
this search 1vas that it contained femer than 50
T h e inain purpose of this study was to de- C1ztlla~~zalzr.sin an area of about 1/10 m2. Each
termine the cause of death of those Clztlza~~lalzrs numbered area consistetl of one o r more glass
lnaps located in the 1/10 m2. They were mapped
that settled belom \.f.H.\Y.N. A s t u d ~ % h i cwas
h
being carried on at this titne had revealed that in RIarch and April, 1954, before the main setphysical conditions, competition for \pace, and tlement of Balu~zzisbegan in late .April.
1'ery few Clzthar~lnllts \\ere found to have
pretlation by the snail Tlznis lapilllts I,. were
among the inost ~ m p o r t a n tcauses of tnortality of settled belo\\ mid-tide level Therefore pieces of
Balanzts balanoides. Therefore, the observations rock bearing Clztllalizallts were removed fronl
antl experinlents in the present study were de- l e ~ e l sabove 1I.II.\\ .S. and transplanted to and
signed to detect the effects of these factors on the 11elom \.I 'T.T>. A hole \ \ a s drilled through each
survival of Clz tllat~lalus.
piece; it \\as then fastened to the rock by a
stainless steel screw driven into a plastic sere\%
Af ETIIODS
anchor fitted into a hole drilled into the rock.
Tntertidal barnacles are very n e a r 1 ideal for
hole %'' in diameter and 1" deep \%as found
the study of survival under natural conditions. to be satisfactory. The screw could be removed
Their s e d e habit allons direct observation of and replaced repeatedljr and only one stone was
the survival of individuals in a group whose po- lost in the entire period.
sitions have 1)een mapped. Their small size and
F o r censusing, the stones mere renloved during
dense concentrations on rocks exposed at intera low tide period, l~roughtto the laboratory for
vals make experimentation feasible. I n addition,
examination, antl returned before the tide rose
they tnay be handled and transplanted without
again.
The locations and arrangements of each
injury on pieces of rock, since their opercular
area
are
given in Table I ; the transplanted stones
plates remain closed \\hen exposed to air.
are
represented
by areas 11 to 15.
The experimental area was located on the Isle
T
h
e
effect
of
competitiotl for space on the surof Cumbrae in the Firth of Clyde, Scotland.
Clzthal~lalzdsmas
studied in the following
vival
of
Farland Point, n h e r e the study was made, com:
After
the
settlement
of Balanzls had
Inaniler
prises the southeast tip of the island; it is exstopped
in
early
June,
having
reached
densities of
posed to moderate mave action. T h e shore rock
cons~sts mainly of old red sandstone, arranged 49, cni' on the experimental areas (Table I ) a
in a series of ridges, from 2 to 6 ft high, oriented cerlsus of the surliving Clztlzawzalzts was made
at right angles to the shoreline. A more detailed on each area (see Figure 1 ) . Each tnap was then
description is given by Connell (1961). T h e divided so that about half of the number of
A \
712
Ecology, Vol. 42, No. 4
JOSEPH H. C O N N E L L
TABLEI. Description of experimental areas*
m a r r r no./cu2
1 POPIJLAT~ONDJUNE,
1954
:
Chthamalus, autumn
1953 settlement
Height
in ft
from
M.T.L.
Area no.
-
of
time
aubmerged
Undisturbed
portion
IN
--,
I'ortion
witliout
Balanus
All
barnacles,
undisturbed
portion
Itemarks
-
-
-
---
MHWS.. . . . . . . . . . .
+4.9
4
-
I... . . . . . . . . . . . . .
+4.2
9
2.2
-
19.2
2. . . . . . . . . . . . . . .
+3.5
16
5.2
4.2
-
MHWN. . . . . . . . . . . . . .
+3.1
21
-
-
--
3s. . . . . . . . . . . . . . .
3b . . . . . . . . . . . . . .
+:.2
30
,,
0.6
0.5
0.6
0.7
30.9
29.2
4.
. . . . . . . . . . . .
5. . . . . . . . . . . . . . . .
$1.4
+1.4
38
"
1.9
2.4
0.6
1.2
-
6 ...............
$1.0
42
1.1
1.9
38.2
Horizontal, top of a boulder,
partly protected
7a. . . . . . . . . . . . .
7b. . . . . . . . . . . . . . . .
+0.7
44
,'
1.3
2.3
2.0
2.0
49.3
51.7
Vertical, protected
11s... . . . . . . . . . . . . . .
l l b. . . . . . . . . . . . . . . .
0.0
50
u
1 .O
0.2
0.ti
0.3
82.0
-
Vertical, protcted
12a. . . . . . . . . . . . . . .
12b . . . . . . . . . . . . . . . .
0.0
100
100
1.2
0.8
1.2
0.9
18.8
Horizontal, immersed in tide pool
29.5
-
Vertical, wave beaten
-
45' angle, wave beaten
"
"
l3a. . . . . . . . . . . . . . . . .
13b . . . . . . . . . . . . . . . . .
-1.0
"
543
,'
4.9
3.1
4.1
2.4
14a . . . . . . . . . . . . . . . . .
14b . . . . . . . . . . . . . . . . .
-2.5
,,
71
0.7
1.0
1.1
1.0
MLWN.. . . . . . . . . . . . . .
MLWS.. . . . . . . . . . . . .
-3.0
-5.1
77
96
-
-
15 . . . . . . . . . . . . . . .
7b.
. . . . . . . .
$1.0
+0.7
.12
1
'
-
Vertical, partly protected
Vertical, wave beaten
Horizontal, wave beaten
,
,I
r
30" to vertical, pattly protected
,, ,'
u
(i
,,
"
"
,,
,'
,,
I6
"
,,
U
;
.
I- -
The letter "a" following an area [lumber indicates that this area
faced c~thereast or south except 7a and 7b, wh~chlaced 1101th.
i
-.
nay
11
'1
-
-.
-
3.7
,,
,,
-
32 .0
5 5
"
Chthamalua of autumn, 1954 settlement; densities of Oct., 19%.
-
--
--
-
-
enrlowd by a cage; "b" reIei-a to a closely adjave~ltarea whir,h x w not encloied. All area*
C'l~thu~~ztrlus
were in cach portion. One portion
\vas chose11 (by flipping a coin), and those Baltanlrs kvhich were touclii~ig or imniediately surru1111tli1igeacli C'l~tha~ricll~rs
\\.ere carefully removed
ivith a needle; the other l~ortionwas left untouchetl. 111 this \vay it \vas l~ossibleto measure
the effect 011 tlie .survival uf C'lttlztl~rltrl~ts
both of
intrasl~eciiic competition alone zund of competiti011 \\.ith Unlnnus. It was not possible to have
the 1111l1111ers
or population densities of Clztiza?~za1r1s rxactly eclual 011 the 2 portions of each area.
This \vas tlue to the fact that, since C'hthawmlus
ofcell occurred in groups, the Haltr~trrshad to he
removetl from around all the ~nenlbersof a group
to elisiire that 110 crowtling I)\- Bnltr?zlls occurred.
tvere very low,
The densities of Cl~tlzu~~tt~ltts
however, so that the slight differences in density
bet\\ eel1 the 2 portions of each area can probably
be disregarded; intraspecitic cro~vdingwas Yery
seltlon~ observed. Ce~isuses of the C'lzthar~~c~lzts
were made at intervals of 4-6 iveeks during the
next year; notes \vere ~iiadeat each census of
factors such as crowding, undercutting o r smothering which had taken place since the last ex:~niination. \Vhen necessary, Balanus which had
grown until they threatened to touch the Clltlza~naluswere removed in later examinations.
T o study the effects of different degrees of
immersion, the areas were locatetl tllroughout
the tidal range, either in situ o r on transplanted
stones, as shown in Table I. Area 1 had been
under observation for 1% years previously. T h e
effects of different degrees of wave shock could
no1 be studied adequately in s ~ ~ ca h small area
713
Autumn 1961
NOV 3, i954
MAY 13,1955
.4rca 711. 111 tlic fir\t ~~liotogral~ll
tllc largc I)ar~iaclcsare Ilcllnnrrs, tlic sniall o l i c c-ttcred
Ilarr l~;itcll.C /rtlrcrr~~(rllts.
-l'llc \\liitr line 1111 tlie \ccolitl ~ ~ h o t o ~ r a
tli\.itles
[ ~ l ~ tlic t~tltlirtc~rl)edportion
(rixlit) ~ I - ( ~ I I Itlic
I
llortio11 fl-0111 \\llicli / I ~ I ! ~ J I ~\\ere
~ ~ , Yr c ~ ~ ~ o v (lcft).
e(l
.4 li11111rt./~~7trl/(rT , I ~ / ! I ( I ~ ( I ,o ccurs 1111
the Icft, and prctlatc~rys~iails,7'1rrris Iirpillrts, arc tis~hle.
I;I(;. 1.
ill
the
of shore I ~ u ts u c l ~c l i f f c r e ~ ~ c;isc csibtctl a r e listc.tl nell 1901), sn1;iII 'l'llnis \\-ere csti~ilatrtlto have
in T a b l e I.
occr~rretlinsitle the cages a l ~ o r ~,3y
t of the time.
T h e effccts of tllc pretl;itor!. snail. 7'hnis lnpil.\I1 the areah ;inti hto~ies\\.ere c~sta1)lishctlI ~ e f o r e
O I I S .\'rtc~Ila o r ~ ' r o . p l { r n , the scttlrment of Rn1n~irt.s I)egan in late :\~>ril,
l t ~ , ( ~ ~ I I O I I ~ I I Iivitll
1954. T h u s the C'liflinlrralr(s \vhich hat1 settled
Clench 1 9 3 7 ) . \vere btr~tlic(l
follo\vs: ('ages
of stain1t.s~stet.1 wirv netting, X 111ebl1csper inch. tiaturally oti the shore \yere tlletl of the 1953
were attacl~e(lo\.er some of the areas. Tllis nlesli vear c1;iss ;ind all aljout 7 months oltl. S o m e
\vhicIi settletl in the a u t u m n of 1954
has an ope11 area of 60?, anlltl ljrevious ivork ('l~tl~c~riicrlits
\\-ere
follo\\.etl
until the stutly ivas entletl in June,
(C'onnell 1901) hat1 shoivn that it tlitl not in105.5.
In
atltlition
some a d ~ ~ l tn-hicli,
s
judging
hibit groivth o r survival of the 1)arnacles. T h e
from
their
large
size
ant1
the
great
erosion
of
cages were about 3 X 6 inches, tlie roof \vas
1952
o
r
earlier,
their
sliells,
must
have
settled
in
allout an inch a l ~ o v ethe I~arnaclesatld the sides
were tittetl to the irregularitie. of the rock. T h e y ivere present on the transplantetl stones. T h u s
ivere heltl in place in the same m a n n e r ;is the recortls ivere made of a t least 3 year-classes of
C'l~tl~a~r~crlirs.
tratisl)l;inte(l s t o ~ l c s . Tile tr;lnsl)lanted stones n-ere
attachetl in [lair.;, one of each ljair I ~ e i n ge ~ ~ c l o s e t l
in a cage ( T a l ~ l eI ) .
These c;i:yes Lvere effective in exclutling all
T l l c c f f f r c f s of plzysical factors
but the st11;illest T h a i s . ()ccasionally smnll T h a i s ,
I n I<'igures 2 a n d 3, the tlashetl line indicates
J4 to 1 cnl in length, enterctl the cages through the survival of C - I i t l z a ~ ~ ~ agl rr~os ~ r i ~without
~g
congaps a t the line of juncture of netting ant1 rock tact with R a l a ~ ~ wT. h e suffix "a" indicates that
surface. In the concurrent study of h'nlanits ( C o n - tlie a r e a \\-as protected from T1lni.r by a cage.
7 14 Ecology, V O ~42,
. ,No. 4
JOSEPII H . C O N N E L L
In the absence of Rcrlanz4s ;ind Thais, ant1 protected 1)y the cages from damage by ivater-l~orne
objects, the survival of Cllthantnlus was gootl at
all levels. For those which had settled normally
011 the shore ( 1;ig. Z), the poorest survival was
(JII
the lowest area. 7a. ( I n the transplanted
sto~les ( Fig. .3, area 1 2 ) , constant imnlersion
i l l a title lmol resultetl in the 1)oorest sl~rvival.T h e
re;Lsolls for the trentl toward sliglltly greater
~llort:ility :is the degree of imlllersion increasetl
are u1lknou.11. 'I'he anlotult of att:~clletl;tlgae on
t l ~ rstones i l l the title 1)ool \v;~s 11lltc11greater
tl1;~11
011 tlie other areas. 'This I I I ; ~h;~veretlltcetl
~
the flax of \v;Lter a11tl footl o r havc interfered
tlirec.tly ~vitlifeetli~lgnlove~llc~nts.. \nother 110so t lthe
sil)le intlirect effect o f i~lcrrasetli n l ~ ~ ~ e r s iis
itlc~rr;~se
i l l ~)retl:~tiotl
I)y the s ~ l ; ~ iThcris
l,
Itrpillrt.~,
:it lower levels.
C'lrflrir~~~irl~rs
is toler;~~it
of ;i nlttc11 greater tlegrec of it~lmersiollt l n n it nornlally ellcotu~ters.
T l ~ i sis shown I)y the sl~rviv;~l
for ;L year on area
12 i t 1 :L title ~ ) o o l ,t ogetller with the findings of
I;iscller 1102X ) atltl I:arncs ( 1 0 5 0 ; ~ ) .ivho fottnd
witllstootl sul)tllersion for 12
tl1;~t C'lztlrtr~rlnlrt.~
: i ~ l t l 22 nlo~lths,resl)cctively. I t s :iI)sellce 1)elow
81.'r.1,. can ~)rol)al)lyI)e :iscril)ed either to ;i lack
of illitin1 settlcnle~ltor to poor survival of lle\vly
settletl larvae. I .ewis ant1 I'o\vrll (1960 j Ilave
suggestrtl that tllc surviv;il of C'lrtl1crrrrcrlu.s 1 1 1 ; ~l)e
60
-
40
-
I-
BILANUS
REYOVEO
f;~voretl 1)y increasetl light or \varmtli during
enlersion it1 its early life on the shore. These contlitions woultl tend to occur higher on the shore
i t 1 Scotla~ltlthali in southern I'nglantl.
7'11e effects of wave action on the survival of
('htlrc~r~rallts
;ire difficult to assess. T.ike the degree of imnlersion, the effects uf \\.n\.e aztion nlay
act intlirectly. 7'lie areas 7 ant1 12, where relatively poor survival was foun(l. \vere also the
:ire:is of Irnst \\.rive actioti. i\lthough Clltllnmalus
is usllally al)ttntl;int on Lvavr 1)eaten areas and
:il)se~ltfro111sl~elteretlhays in Scotlantl, Lewis and
I'o\vcll (1900) have slio\vn that in certain sheltcretl Inys it nlay I)e very ;il)undatit. l-Tatton
( 193%) fount1 that in ~lorthernf:rance, settlement
: ~ ~ l t gro\vth
l
rates were greater in wave-heaten
;ireas at .\I.T.l.., l ~ t at
, A/I,H.\V.X., greater in
sl~cltcretl:irta;is.
. \ t tlie ul)l)er shore nlargins of t1istril)ution
C'l~thirrr~trl~~.s
evitle~~tly
call cxist higher tliall I3alrzrlrrs 111;~inlyas a result of its greater tolerance
to heat a ~ ~ t l / oclesiccatioli.
r
'I'he evidence for this
\\.as g;~inctltlltring the s l ~ r i ~ iofg 1955. Recortls
frotll a title ;i11tl wave guage ol)erating at this
tinw ;il)ottt one-half mile 11ortIi of tlie study area
hllowetl tllnt ;i 1)eriotl of 11eal)titles hat1 coincitled
\vith :ill l u l ~ t s l ~ a~)eriotlof
l
Lvarln c;tlm iveather in
;\l)ril so that for several (lays no ~ v a t e r ,not even
\v;lves, re;iclictl the level of .\rea 1. 111 the 1)eriotl
---
UNMODlFlEO
.
UNY001FlED
\
:
2 0 . ----.----- -- - --a
W
BALANVS
BALANUS REMOVED
REMOVED
t.7
:
.
5
3b r 2 2' ----------_______
BALMUS
REMOVED
I 2'
- - -- - - - - - - -- -BALANUS
REMOVED
L
-------- - - - - _ _ _ _ _ _
BALAWUS
REMOVED
UNMODIFIED
W
a 1 10:
3 Z
-5
J J A S O ND
L~
J F M A M J
FIG. 2. Survivorship curves of Chthutilalits stellatzrs which had settled naturally on the shore in the
autumn of 1953. Areas designated "a" were protected from predation by cages. In each area the survival of Chthninolzts growing without contact with Ralunus is compared to that in the undisturbed area.
For each area the vertical distance in feet from M.T.L. is shown.
Autumn 1961
80
60
40
INTERSPECIFIC COMPETITIOK
-
IIO
.
0.0'
120
IN
.
130
TlOE POOL
0AUNUS
-14 a
.
2.5,
REYWED
-------_M L A N U S REMOVED
BALANUS
20
10
RCYWEO
---_-_
:
WYOOIFIED
UNYOOIFIED
'\-
+ - .
2
XW
%
.
5 .
.
a
2
4
UNMODIFIED
2 .
P
'
I
*80
'
a
'
Ilb
60
1 40
-
0.0'
3
4
IC
E
P
12b
.
20
- --
.r---.
0
I3 b
III TIDE POOL
'.---O&LA*US
,-
.----
--------___--_
MU*JI REMOVED
REMOVED
-.______----
UWODIfSO
MUNUS IEWEO
--.
'\
'\,
'.
I A L U U S REYQIIO
U*YOOIfIEO
\-
m
ft
14 b
-2.g
-LO'
--\,\\\\
5 :
UNYODDICO
\
2 .
J F ' M A 'M J
I955
I
IIJ*ISOIN J ' J A
I954
I955
'SO IUD JF'YA'MJ'
1954
I955
\
J~JA'SO'ND
1954
Frc. 3. Survivorship curves of Chthamelus stelltitlcs on stones transplanted from high levels. These
had settled in the autumn of 1953; the arrangement is the same as that of Figure 2.
betneen the censu5es of February and May, Balanus aged one year suffered a mortal~tyof 92%,
those 2 )ears and older, 5 1 % Over the same
p e r ~ o dthe n ~ o r t a l ~of
t j Chthanml~tsaged 7 months
was 6 2 2 , those 1 years ant1 older. 2% Records of the survival of Balallzds at sel era1 levels
belou t h ~ ssho\\ed that onlj those Balanzds in
the top quarter of the Intertidal reqion suffered
high mortal~tyduring this titile ( C onnell 1961) .
At each census notes were made for indilitlual
barnacles of any crowding nhich had occurred
since the last census. T h u s when one barnacle
started to grow u p over another this fact was
noted and at the next census 4-6 weeks later the
progress of this process was noted. I n this way
a detailed description was built up of these gradually occurring events.
Intraspecific competition leading to mortality
in Clztlza~ltalltswas a rare event. F o r areas 2
to 7, on the portions from which Balanus had
been removed, 167 deaths were recorded in a
year. Of these, only 6 could be ascribed to
crowding between individuals of Chthamahrs. O n
the undisturbed portions no such crowding was
observed. This accords with Hatton's (1938)
o1)servation that he never saw crowding between
individuals of Clztlzattzulrrs as contrasted to its
frecluent occurrence I~etiveen individuals of Bala11ZIS.
Interspecific competition between Balanus and
Chthatnalus was, on the other hand, a most irnportant cause of death of Chthawtalus. This is
sho\\n both by the direct observations of the
process of crowding at each census and by the
differences hetween the survival curves of Chtharnalus with and ~ i t h o u t Balanzds. From the
periodic observations it \\.as noted that after the
first month on the undisturbed portions of areas
3 to 7 about 10% of the Clztlztrl~lalltswere being
covered as Balatzzts grew over them; about 3%
were being undercut and lifted by growing Balanzas; a few had died without cro\vditlg. By the
end of the 2nd month about 20% of the Chtha11lali4s were either wholly or partly covered by
Balanus; about 4% had been undercut; others
were surrounded by tall Balanus. These processes
continued a t a lower rate in the autumn and
almost ceased during the later winter. I n the
spring Balanus resumed growth and more crowding was observed.
COX NELL
Ecoiog?, Val. 42, KO. 4
that uf tlie I~ase. It \ \ a s ol~vious that extreme
cro~vding occurretl under these circumstances,
Ilut the exact cause of the mortality of the C'htllairitrl~is caught in this crush \vas difficult to ascertain.
111 conil~aring the sur\.iv;~l curves oi I-igs. 2
alid 3 ~vitliineach area it is evident tliat Clztllnll~ir1li.r 1,ellt free of 13alanlts survi\-etl Iletter than
tliow in tlie adjacent ul~tlisturl)etl areas on all
I ~ u tarcas 2 ant1 13a. Area 2 Ivas in the zone
\\.here atlults of I3alanlts and Clltl~a~l~nllrs
\yere
~iormally mixed; at this high level Ralarltas evitlently has 110 influence on the survival of Clltlla~lzal~rs. (-111 Stone 13a, the survival of Cllthai~rallts
ivithout Rnlan~ts was much better ~ l n t i lJanuary
I S entered the
\vhen a starfisll. Ast~ritrs ~ I I ~ I E ) I,.,
cage and ate the barnacles.
T.~H
E I1 I . Tlie cause.\ 11i mortality oi L'lttltntrli~llrsstcl/atns
~ , ithe 1053 )car group un the utl(1i~turbed portions of
,\Iuch variation occurred on the other 13 areas.
each area
\\.hen the C'lzthtr~llalits gro\ving \vithout contact
\vith Bnlanrts are compared \vith those on the
adjacent undisturbed portion of the area, the
survival ivas very much better 011 10 areas and
. k r a no.
motlerately better o n 4. I n all areas, some
C'l1fhtr~1lalltsin the undisturbed portions escaped
severe cro\vding. Someti~nes no Bnlanlcs hapor somepenetl to settle close to a Clztha~~zulzis,
times those Ivhich did died soon after settlement.
111 some instances, Clzthat,lallrs \vhich Ivere being
undercut by Balatltrs attached themselves to the
Balnnlrs and so survi\-ed. Some C'lztlralnnlus \vere
partly covered by Balatl1rs I ~ u tstill survivetl. I t
seems 1)rol)al~lethat i11 the 4 areas, nos. 1. 6, l l a ,
and 1 l b , where C'hfhnnmlits survived well in the
presence of Halanzts, a higher proportion of the
y.0
21
13
54
8
0
!
38
1 . . .
l l b . .. . . . . .
10
5 1 40
0 1
0 1 6 0
Clltlltrnltrlus escaped death in one of these nays.
T h e fate of very young C'hthanzallts which settletl in the autumn of 1951 \\.as follo\ved in detail in 2 instances, on stone 15 and area 7b. T h e
Chtllai~~trlus
on stone 15 hat1 settled in an irregular
14a. . . . . . .
-2.5
space
surrountletl
by large Ilalanlts. Most of the
'
14b.
.
mortality occurred around the edges of the space
Total, 2 - 7 . .
as the Ralanlts undercut and lifted the small
C-lltllci~~lalrcs
nearl,-.
T h e follo\ving is a tal)ulaI9
1 ?I
Total. 11-14 1 J01
271
-tion of all the deaths of young Chthantnlus be-tbveen Sei)t. 30, 1953 and Feb. 14, 1955, on Stone
I n Table TI untler the term "other cro\\tllng"
IS, \vith the associated situations :
have been placed all instances \\here Clzthanlolus Liftetl by Balanus
: 29
\\.ere cruslied laterally between 2 o r more Balanus, Cruslietl 1)y Bolanus
: 4
or where Chtlrailtallts disappeared in an interval Smothered by Balanlts and Clltlta)?talns
: 2
during which a dense population of Balarllts grew Cruslietl between Balanlis and Chthawlalzts : 1
rapidly. F o r example, in area 7a the Balat1its, Lifted by Chtha.~zulus
: 1
which were at the high lmpulation density of cruslietl betbveen two other Chthntilaltts
: 1
48 per cm2, had no room to expand except up- U1lkno\\-11
: 3
bvard and the barnacles very quickly grew into
the form of tall cylinders or cones with the This list shows that crowding of newly settled
diameter of the opercular opening greater than Clltllamalus by older Balanlrs in the autumn main-
111l'al~ie 11, these ol)hervatiolia are sum~iiarized
for the un(1istril)uted l~ortionh of all the areas.
. l l ~ o v ehZ.T.I,., the ISalanlts tended to overgrow
the C.'llt/ttr~nallts,Lvhereas at tlie lower levels,
u~itlercutting was more conimon. This same
t r e ~ i d \vas evitlent rvithin each groul) of areas,
ulidercutting I~eing more l~revalent on area 7
than on area 3, for examl~le. 'I'he faster growth
of Ra1ant;s at lo\ver levels ( 1 latton 1938, l3arnes
ant1 l'owell 195.3) may have resultetl in more
untlercutting. \\Tlien Clrtlla111al1ts\vas coml)letely
co\.eretl 1)y Uaicrtzl(.s it was recorded a s d e a d ;
even though death may not have occurred imthe 1)urietl I~arnacle\vas obviously not
n~etliatel~.,
a functioliing ~ i i e m l ~ eofr the l ~ o l ) ~ ~ l a t i o n .
,
1
1
i
)
1
~
1
--
Autumn 1961
717
INTERSPECIFIC COhIPETITION
1y takes the form of undercutting, rather than of
s l ~ ~ o t l i e r i nags was the case in the spring. T h e
reason for thib tlifferellcc is proljal~ly that t h e
('1rthtrlrralu.s a r e m o r e tirmly attached in t h e spring
s o that the fast gro\ving youllg llalirnus g r o w u p
over them when they lllake contact. In the
autuliili tlle reverse is tlle case, the Ilalanzts being
kveakly so.
firmly attached, tile C-lrtlral~ztrl~ts
on
r \ l t h o l ~ ~ htlie bcttlcliicnt of Clltllt~~l~(zlrts
Stone 15 in the a u t u m n of 1954 was very tle~lse,
.32/c1ii2, so that ~iiobtof then1 were touching allother, olily 2 of tllc 31 tlc:~ths Lvcre catlsetl by
intr:~sl)ecitic cro~vtling a m o n g the Clltllal~tnltts.
,.
I his i:, in i~ccortl\\.it11 the tintliligs from the 1953
settlcliie~itof C'lzt/rarrlnlrts.
r.
I he ~iiortalityrates for tlie young C'lltllatnalus
011 area 71) sliou.ctl seasol~alvariations. I3etween
O c t o l ~ e r10, 19.34 a11tl 11; ~ y15, I955 the relative
mortality rate l)er (lay X 100 was 0.13 on the
untlisturl)etl area ant1 0.13 whcre I~alanus had
bcen removetl. ( ) v c r the next ~ n o n t h ,the rate
increasctl to 1.39 o n the untlisturl)ed area a n d
0.22 \vherc Ijtrltrnrcs \v;~s absent. T h u s the increase in nlort;llity of young Chtlln~~~ct1rr.s
in late
sprillg \vas also associated ~vitlithe llresellce of
Ilultrn~ts.
S o ~ u eof tlic stolies t r a n s l ~ l n ~ l t e tfrom
l
high t o
low 1cvel.s i l l the sllring of 1954 bore adult
C'1rflrnlr~crlrr.s. O n ,Z stones, recortls \verc k e l ~ tof
the .s~lrvivalof these atltllts, \vliicl~Ii:~tl scttletl in
the ;1uttul111 of 19.52 o r i l l ~)reviotlsyears and
\Yere a t least 20 ~ i i o l ~ t hold
s at tlle start of tlie
c s l ) c r i ~ i ~ e l ~'l'lleir
t.
~iiortality is sliokvn in T a l ~ l e
111 ; it was : ~ l w a y smuch g r a t e r when Rnlnnrts
\\-;~s~ i o t renlovetl. ( In 2 of tlie 3 s t o ~ l e sthis
nlortalit!. rate Lvas ; ~ l m o s ta s high a s that of the
,.
yollllger grorll). I liese results s ~ l g g e s t that any
C'lrflrn~ricrlrt.~
that nianagetl to survive tile conll)etition for sl)ace \vitli Bnlanus (luring tlie first year
\vo~lltl11rol)aI)ly I J V eliminated in the 211tl year.
Cclisuses of IIt~l(l)zlts\vere not m a d e on t h e
exl)erin~elital areas. I Iokvever, on nlany o t h e r
areas i l l tlie sanie stretch of shore the survival
of Hnln~lrts \!-as Ijeing studietl d u r i n g the same
periotl (C'olinell 1 9 0 1 ) . I n T a h l e IV some mortality r a t r s meas~lre(1in that stutly a r e listed; the
Rtrlcl~rrs \\-ere m e m l ~ e r s of the 1954 settlement
at ~ ~ o l ) ~ ~ densities
l a t i t ~ ~ant1
~ shore levels sitnilar to
those of t h e present stutly. T h e mortality rates
of Hn1n~zt.s \\-ere allout the same a s those of
C'htlrn1lrnlrr.s in similar situations except at the
highcst level, n r r a 1. where Bnlanrts suffered much
greater mort;tlity than Cllthalrzc~lzts. M u c h of this
mortality lvas carlsetl 1)y intraspecific crowding
a t all levels I)eloiv area 1.
~ Smortality
OII
rates of young
T~ti1.1..
111. C O I ~ ~ ~ Iof~ ~the
ant1 oltler C h t h t i ) t ~ i ~ l .ctrlluttr.r
~is
on transplantetl stones
Yumher of Chlho- 7, mortal~tyover
rnalup prrsent In one year (or for 0
months for 14a)
June. 1951
o f Chlharnalua
No.
I
-
I:ib
' 1 0 ft below
, LlTI,
---
A
~
Ralanus rcnroved
-
51
-. - -
~
Ralanus removed
hfTL. In a
t ~ d elwol,
raged
-
-
or older
1053
year
group
50
lJt~d~sturbcd
60
~-
-
~ ~ - - -
36
2 5 ft below
MTL, caned
'I'AIII.E
I V . C ~ I I ~ ~ I ; of
I ~ ~~ I ~I I IOI I ;ILI~111ortality rates of
Chthnmalus strllntirs ant1 Bulanirs hnlanoides*
I
Chthamalun tella at us, autumn 1053
srttlement
l'opulation
Ilcight in ft
density:
from M.T.1,. no./cm2
June, 1954
Area no.
128 . . . . . . . .
1
(tide pool)
76 mortality
in the next
year
19
Oh
Balan~tsbalanoides, spring 1954 settlement
1 (top). . . . . .
1.;\fiddle C a ~ e1
1 .lIiddle Cage 2
Stone 1
Stone 2
1
I
+21
1
1
I
- 0 9 1
8.5
25
20
69
1
i
X6
94
Population density,includes hoth species. The mortality rat- of Chthamalua
refer to those on thp und~sturhedpnrtioni, of each arpa. Thp data and arpa des~anations for Balanna were taken from Connell(1961); the present area 1 is the same as
that designated 1 (top) in that p a p r .
In the ohser\ations m a d e a t each census it
appeared that Balnnzts was grobving faster than
Chthnnznlzts. hleasurelnents of growth rates of
the 2 species were niatle from photographs of
Ecology, V O ~42,
. NO. 4
CON S E L L
the areas taken in J u ~ l eant1 Sovemher, 1954.
Barnacles growing free of contact with each other
were measured; the results are given in Table V.
T h e growth rate uf I?trlntl.u.s ivas greater than
that of Cllt/lawzallrs in the experimental areas;
this agrees lvith the tintlings of I latton (1938)
on the shore in 1;rallce :11ltl of 1:arlles ( 1956a)
for collti~lr~al
sul)~llerge~lce
on a raft at illillport.
'~AIII.V
~ .
(irowtli r a t c of C l r t l r i ~ r ~ ~ c ~.cti~ll~rfrcs
l~ts
and
I~trlnriris hc~li~troitlrs. .\lcasurcr~lcr~tswere lllatlc of unof areas 3a, 31) and
crowtletl illdivitluala oli ~~llotogr;ll)hs
7h. l'liose of C'l~fl~irrrrirlrtswcrc ni;~tlr OII tlie carlle intlivitlual:, or1 I)otli tl;rtcs; I J I llirl~rr~rr.r,
rcl)r-csctrt;ctiw ; ~ r n l ) l e s
\\.ere c h o w r ~
-
- . -- -
.\vrraqe
-
-
-
--
sir? ill tit,, ~ u t c r v a l. .
i
I
.\l~x,lutc yrowtil r;il<. llcr day x 100,
creases in the growth rate of Balanus. T h e
correlat~on ivas tested using the Spearman rank
correlation coefficient. T h e absolute increase in
diameter of Balanus in each month, reat1 from
the curve of growth, was conll>aretl to the percentage mortality of C'1zfhar11nllt.s in the same
month. For the 13 months in which tlata for
C'hthnri~rrlrrs was ava~lalde, the correlation was
highly significant, I' = .01.
GROWTH OF BALANUS
--:j
1 21
;liter a year of cro\\-(ling the average 1)ol)ulation de~lsities of Bafan~r.s a11tl C'lztlza?ttnlus re111ainetl i l l the s;l~lle rcslativc, l ) r u l ) o r t i o ~as
~ tlley
hat1 Ijee~i at tllc start, s i ~ ~ cthe
c ~llortality r:ltes
\\.ere about the sa111c. I lo\vevcr, 1)ec;luse of its
faster growtll, 1 ~ ~ ~ l ~ occ111)i~iI
r n ~ r . s ;L rc1:~tivelygrc3ater area a ~ l t l , presunlal~ly, ~)ossessetl ;I greater
I~iomass relative to tllat oi C'lltlln&~lnlzr.cafter a
vear.
T h e faster gro\vtIi of Ilal(ltlrr.s prol)al)ly ;lc\vere
co1111tsfor tile maliner ill \vllich C'lztl~nrr~nlrrs
crowtletl by Bn1atzlr.s. It also accounts ior the
sinuosity of the st1rviv:11 curves of C'lltlrtrrrrc1l~rs
growing in contact \\.it11 Ral(1nzrs. T h e mort:~lity
rate of these C l z t l ~ n ~ ~ ~ aas
l ~ rintlicated
s,
1)y the
s l o l ~of the curves in Figs. 2 ant1 3,
greatest
in suliuiier, tlecreasetl in winter ant1 increased
again ill spring. T h e survival curves of C'lltlrnlrzalzrs growing \vithout contact ~ v i t hBalntzlrs tlo
not show these seasonal variatiolls which, therefore, cannot he the result of the tlirect action of
physical factors such as temperature. \vave action
or rain.
Seasonal variations in gro\vth rate of Ra1nnzl.c
correspond to these changes in mortality rate of
Clzthamalus. I n Figure 1 the growth of B a l a n l ~ s
throughout the year as studied on an intertidal
pa11el at ilIillport. , 1 Barnes and I'owell (1953), is compared to the survival of Clrtllnrr~nl~rsa t
about the same intertidal level ill the present
study. T h e increased mortality of Clltlln~r~alits
\\-as
foulld to occur in the same seasons as the in-
MONTHS
1-1(,.1. . \ coml~arisoliof the \casorial c l l a n g e ill the
groikt11 of Ilillrr~t~rsI1cilanordc.r aritl i l l the survival of
C'l~tl~c~rriirlrcs
.rtrllirtri.r I ~ c i t ~ crowtlctl
g
I)y Rala)tus. T h e
x r o \ \ t l ~ of 1jnlirri1r.c was that of ~)ariel 3, I<ar~iesand
I'owcll (19.53), just a l ~ o v c M.T.1-. on Kcppcl I'ier,
.\tilll)ort, tluritig 1051-52. T h e C'lztllc~tnalus were or1 area
.la of tlic 1)rc~crltstutly, orie-lialf mile soutli of Keppcll
I'icr, tlut-irig 1051-55.
I;ro111 :ill these o1)scrvations it appears tllat
tlie 1)oor sl~rvivalof C-lrtlrnltzn1rr.c 11elo\v R1. t L.\\..N.
is a result n ~ a i ~ l lof
y cro\vtli~ig11y dense ~)opulatio~isof faster gro\ving llnlnnlrs.
.\t the clitl of the cxl)eri~lle~it
in June, 19.5.5,
tlle survivil~gC'lltllc~irrnlr~s
\\.ere collected iron1 5 of
tlie ;tre:is. ;Is s l i o \ v ~in
~ Table V I , the a\,crage
size u as greater in the Clltllnrr!cllirs a hich hatl
grolvn free of contact with Bnlnillrs; ill every
case the tlifference \\-as significant (P < .01,
~ l a ~ ~ ~ ~ - \ \ ~V.
l i test.
i t ~ ~Siege1
e y 1956). T h e stirvivors on the undisturhetl areas Jvere often misshapen, in some cases as a result of being lifted
011 to the sitle of an underct~ttingBnlnnr(s. T h u s
the smaller size of these barnacles may have been
tlue to disturbances in the normal pattern of
gro\vth while they were I~eingcro\\ detl.
These Cllflza~llalzrs\vere examined for the presence of developing larvae in their mantle cavities.
. I s sho\vn in Tahle \-I, in every area the prowith larvae
portion of the ~uncro\vtledCl~thn~lrnllrs
\\-as equal to o r more often slightly greater than
on the cro\vtletl areas. The reason for this may
11e related to the smaller size of the crowtled
It is not due to separation, since
('l~tl~a~rrnl~is.
Clztharrlali~s can self-fertilize ( Barnes and Crisp
Autumn 1961
TABI.EL-I T h e effect of c r o ~ + d i n ogn the size and presence of lar\ae In C ' l ~ t h t l ~ ~ i~t t~cl /~l ~( ~s t fcollected
(s,
in June,
1955
1
4rra
1 ik
TABLI-\ 11. T h e effect of predation by Thois lapillus
on the annual mortality rate of Ci~thcl~~rollts
stcllatirs in
tlie experimental areas*
1%
Number ' D I A M ~ TI EN IYM
~
of lndiv~dof
I uals whirh
Chhhad larvae ~n
rnaius
Average Range J m a n t ~ravity
e
I,evel,
Trratmet
719
INTERSPECIFIC C O h i P E T I T I O S
1
%, mortality o i Chlhamnlus over a year (The initial Inlmbers are given In parentheses)
(
..
- --
--
--
-
a Protected from predatlotl
by a cagr
Arra
--.
-----
". .
Baianur removed
"
!-6 . . . Undisturbed
'. .
' Baianus removed
1 . 0
"
-
--
II Und~qturhed
i a b- b
"
.
Balariu3rernoved(
13
11
O.i
"
(
10
23
Arra
Area
Area
Arra
Arra
:i
i
1l
I2
1.i
-
-
--
- ---
b Unproterted, oprn to predatlnn - - - ---...- - - -
( l l t i r o u t I DC
1 f eDifr e n ~ e Rni,,nu* Ralntius ( f e r ~ n c e
Wth
Rninn,ts
Without
Ralanur
73 (112)
90 ( 42)
62 ( 21)
100 ( 60)
98 i 72)
25 (96)
47 (40)
18
43
18 (18)
31
53 (501
4 (7i)
li
89
~
WI~II
----.
.- -
'The records for 12a extend over only 10 months; for purlwses of compar~sol~
the mortality rat? for 12a hss been nrultiplied by 1.1.
tTide pool.
at loiver levels greater outside. Densities of Tlzais
tend to be greater at and below h1.T.L. so that
this trentl in the mortality rates of Chthawialus
may he ascril~edto a n increase in predation by
Thais :it lower levels.
Mortality of Clzthavttalz4s in the absence of
lialaltus was appreciably greater outside than
insitle the cage only on area 13. I n the other 4
areas it seems evident that few Chthat+zalus were
1)eing eaten by Thais. In a concurrent study of
the I)ehavior of Thais in feeding on Balanzts
it was foulid that Tlza,is selected the
bala~~oidrs,
larger i~ldividualsas prey ( Couuell 1961 ) . Since
Bnlalrlls after a few month's growth was usually
larger thali Chthanzalzcs, it might he expected that
7'hnis would feed on Balanus in preference to
C'lltllc~ir~alus.In a later study (unpublished)
made at Santa Uarbara, California, Thais entarginata Ueshayes were enclosed in cages on the shore
\vith mixed pol)ulations of Balanus ylandula Dar7'11~effrc-t of prctintiovt b y l'hnis
\vin and Clztha~wzllrsfissus Darwin. These species
C'ages which exclutled Thais liad been attached \Yere each of the salne size range as the corre011 6 areas (indicated l)y the letter "a'' following
sl~ontlingsl~eciesat Millport. It was fount1 that
tlie number of the a r e a ) . .\rea 14 was not in- Tlza,is emarginata fed on Balanus glandula in
cluded in the folio\\-ing analysis since many star- preference to Chthamulus fissus.
A s has k e n indicated, much of the ~nortality
fish \\.ere ol~servetlfeeding on the 1)arnacles at this
level ; one entered the cage in January, 1955, and of Clzfl~amalusgrowing naturally intermingled
ate most of the barnacles.
with Bala~tuswas a result of direct crowding by
Tlzais ivere common in this locality, feeding Ralanrts. I t therefore seemed reasonable to take
on barnacles and mussels, and reaching average the difference between the ~nortality rates of
with and without Balanus as an index
l)olx~lation densities of 2 0 0 / r n V e l o w M.T.L. Clztl~art~al~ts
(C'onnell 1961). T h e mortality rates for C'lztlza~rt- of the degree of c ~ m . ~ t i t i obetween
n
the species.
nllrs in cages and on adjacent areas outside cages This difference was calculated for each area and
(indicated l ~ ythe letter "h" after the number) is included in Table V I I . If these differences
are sho\vn on T a l ~ l eV I I .
are compared between each pair of adjacent areas
If the mortality rates of Clztllanznllcs growing in and out of a cage, it appears that the difference,
\vitliout contact with Balanz4.s are compared in and therefore the degree of competition, was
and out of the cages, it can be seen that at the greater outside the cages at the upper shore levels
upper levels mortality is greater inside the cages, and less outside the cages at the lower levels.
1050). ,\loore ( 1935) and t h r n e s (1953) have
sho\v11 that the number of larvae in an individual
of Bala~lusDala~roidcs i~zcreases\\.it11 increase in
volunle of the parent. Co~npariso~z
of the cube of
the diameter, which is proportional to the volume,
of Chtha~~zaln.s\vitIi and without l'alanus sholvs
lnormal
that the volume may I)e decreased to
size ivllen cro\vtlitng occurs. .lssuming that the
.
relation l~etn-eenlarval numljers and volume 1x1
C/~thailralrlsis similar to that of Balt-rnus, a decrease ill I)c>thfrecluency of occurrence ant1 abunresults fro111 corndance of larvae in Clltl~a~tzalus
petition bvith Balavtrls. T h u s the 1)rocess described
in this l>al)er satisties I)oth asl~ectsof intersl~cific
IClto~i alitl lliller
competition as tlefinetl 11).
(19.54) : "in ~vhich one sl~ecicsaffects the population uf another 1)y a process of interference,
i.e., 1)y reducing the reprotluctive efficiency or increasing the mortality of its conq)etitor."
720
JOSEI'II
.I.h u h
11. COX SELL
Ecology, Vol. 42, 'No. 4
a~ltl3 ) , and these survivors n-ere oftell misshapen
antl smaller than those \vhicli had not been
crowdetl (Table V I ) . rldults on the transplanted
stones had suffered high mortality in the previous
year (Table 111).
:\nother diftictllty was tliat C71tllai1zal~tswas
rarely found to have settled belo\v mid tide level
at hlilll~ort. Tlie reasons for this are unknown;
it survived lvell if transplanted I)elo\v this level,
".\ltllough animal communities appear cluali- ill the absence of Balanz~s. I n other areas of the
tatively to be constructetl as if competition ivere British Isles (in soutli\vest 1:ngland and Ireland,
regulating their structure, even in the I~eststudied ior example) it occurs I)elo\v mid tide level.
cases there are nearly al~vaysdifficulties antl unT h e 1)ossi11ility that ClztJznlitall(s might affect
exl~loretlpossil~ilities" ( Hutchinson 1957).
h'ala111ts deleteriously remains to be considered.
I n the present study direct ol~servationsat in- I t is unlikely that Cl1tlzair1alitscould cause much
tervals sho\vetl tliat couipetitio~i \vas o c c u r r i ~ ~ gmortality of Ilalanl(s 1,- direct cro\vding; its
untler natural co~itlitions. I n addition, the evi- growth is n~ucli sloiver, and cro\vtling I~etween
dence is strollg that the observed competition with intlivitluals of Clitllainalrrs seltlom resulted in
Ilaln/ll(s \vas the l~rincipalfactor determining the tleath. .\ dense ~)olj~ilation
of Chthiri>zallts tnight
local distril~ution of C l l t l ~ a ~ ~ ~ a l Chtl1irirltrlz(s
~rs.
delxive larvae of Balanzts of space for settlethrived at lower levels when it \vas not grobving ment. .ilso, C'lztlznirtallls might feed on the plankin contact witli Balnn14s.
tonic larvae of Bnlanus; however, this \vould oclIowever, there remain unexplored possibilities. cur in March and April \vhen 110th the sea \vater
T h e elitilitiation of C'lztlzainal~(srequires a dense teml~erature and rate of cirral activity (pre1101~1lationof lialon~rs,yet the settlenlent of Ra- sunia1)ly correlated with feeding activity), \vould
lirnlis varied from year to year. :It Alilllmrt, the he near their minima (South\\,ard 1955).
settlement density of Hnlarz~ts bnlirttoitirs \vas
Tlie itldication from the caging experiments
nleasuretl for 9 years I)et\veen 1914 a~ltl 195s that predation decreased interspecific competi( Iiarnes 195hl). Co~inell 1961 ) . Settlemelit \vas tion suggests that the action of such additional
light in 2 years, 19-16 antl 1958. I11 tlie 3 seasons factors tentls to reduce the intensity of such
of Hala~l~(.s
settlemelit stutlietl in tlctail, 1C)j.Z-55, interactions in natural conditio~ls. ;I11 adtlitional
there \vas a vast oversul)l)ly of larvae reatly for suggestion in this regartl timy 1)e made consettlement. It thus seelils 1,rol)al)le that most of cerni~lg parasitism. C'risp ( 1960) found that
the Chtlzai/~nlz~s
\vhich survivetl in a year of poor the growth rate of Balanzcs bnlnfzoidcs was desettlement of Haln~zltsivould he liilletl in competi- creased if indivitluals were infected with the isotion with a normal settlement the follo\ving !.ear. ~ ) o dparasite IIc~t~ionisrzrs
balnni ( Spence R a t e ) .
A succession of years \vitli poor settlemelits of In I3ritain this l~arasite has not l~een reported
Bnln~lcsis a possil)lc, I ~ u tit~ll~robable
occurrence from C'htl~n~lzal~rs
stcllntlrs. T h u s if this parasite
at Millport, judging from the past record. A \Yere l~resellt. 110th the groivth rate of Balnnlrs,
very light settlement is l>rol)ably the result of a ant1 its al~ilityto eliminate Clztlzarl~alltswould I)e
chance cotubination of unfavorable \veather cir- decreasetl, ivith a corresl)onding lessening of the
cumstances (luring the l~lanktoniclxriod (Uarnes tlegree of coml~etition het\veen the species.
1956h). A-41so, after a light settlement, survival
011 the shore is iti~ljroved, o\ving l)rit~cipallyto
The evitlence prese~itedin this paper indicates
the reductio~lin intraspecitic crobvdiug (C'onnell
that
tlie lower limit of the intertitlal zone of
1961) ; this ivoultl tend to favor a normal settlement the folloiving year, since 1)arnacles are stim- Chtlln~lrnlusstcllntlls at A1illl)ort \vas tletermined
ulated to settle 1)y the presence of niemhers of 1)y intel-specific coml)etition for space \\.it11 Bnlntheir o\vn species already attached 011 the suriace ~ z t sOnlnnoidrs. Bnlnnzts, by virtue of its greater
p o ~ ~ u l a t i odensity
n
and faster gro\vth, eliminated
(Knight-Jones 1953).
Tlie fate of those Chtllniilal/ts \I-liich had sur- niost of tlie Clzthnnlnllts by directing cro\vding.
At the upper limits of the zones of these
vived a year on tlie undisturbed areas is not
knobvn since the experiment ended at that titile. species no interaction bvas observed. Chtllnii~nl~ts
It is probable, I:obvever, that most of them ivould e ~ , i d e t ~ t l cyan exist higher on the shore than
have been elit~~inated
within 6 tl~ontlis;the mor- Bnla)llrs mainly as a result of its greater toleratice
tality rate had increased in the spring (Figs. 2 to heat and/or desiccation.
as l)rc(l:itio~l illcreased at lo\ver levels, the
degrce of competition decreased. This result
ivoultl Ilave heen expected if Tllais had fed upon
Ba1a~lr.s in preference to C'lltha~tlnllrs. T h e general effect of lIretlatio11 by Thais seenls to have
Iwen to lessen the interspecific com11etition I~elow
1 1 ,T,I
>.
Autumn 1961
I N T E R S P E C I F I C COMPETITIOS
T h e u ~ l limits
~ r
of most intertidal animals
are 1xo11al)ly determined 11y physical factors such
as these. Since growth rates usually decrease ~ v i t h
increasing height on the shore, it bvould be less
likely that a sessile species occupying a higher
zone could. by competition for space, prevent a
lo\ver one from extending up\\-ards. 12iliea.ise,
there has heen, as far as the author is aivare,
no study made \\-hich sholvs that predation
land species tletermines the upper limit of an
intertidal animal. I n one of the most thorough
of such studies, Ilrinnan ( 1957) indicated that
intense predation I)y 1)irtls accounted for an anl
nual mortality of 225% of cockles ( c a r d i l r ~ ~edrrlc
I>.j in sand flats hvhere their total tniortality ivas
74% per year.
I n regard to the lo\ver li~nits of an animal's
zone, it is evident that physical factors may act
directly to determine this boundary. F o r example,
some active arnphipods from the upper levels of
sandy beaches die if kept submerged. However,
evidence is accumulating that the lower limits
of tlistribution of intertidal animals are determined mainly by biotic factors.
Connell ( 1961 ) found that the shorter length
of life of Bczlnn~rsbalanoides at low shore levels
could 1)e accounted for by selective predation l)y
Thnis lapillzts and increased intraspecific cornpetition for sllace. T h e results of the experiments
in the present study c o ~ ~ f i r the
m suggestions of
other authors that lower limits may be due to interspecific competition for space. Knox ( 1 9 5 4 )
suggested that competition determined the distriljution of 2 species of I~arnaclesin New Zealand.
I<ntlean, Kenny and Stephenson ( 1956) gave
indirect evidence that competition with a colonial
polychaete n.orm, ((;aleolaritr) may have determined the lower limit of a I~arnacle (Tetraclitcz) in Queensland, .Australia. In turn the
lon.er limit of (;trlcolczricz appeared to he deter~ n i n e dby competition with a tunicate, Pyztra, o r
~ v i t hdense algal mats.
\lrith regard to the 2 species of 1)arnacles in
the present paper, some interesting ol)servations
have heen made concernitng changes in their
abundance in Britain. l r o o r e ( 1 9 3 6 ) found that
stellain southtvest England in 1933, Chtha~~lal~cs
trts Lvas most dense at M.H.\V.N., decreasing in
numbers toward M.T.L. while Balanlrs halanoidrs
increased in numbers below M . H . \ l r . S . - I t the
same localities in 1951, Southward and Crisp
( 1 9 5 3 ) fount1 that Balanl(s had alrnost disaphad increased both
peared and that Clztl~a~~ral~ts
ahove and below hI.H.\V.N. Chtlla~nallrshad not
reached the former densities of Bala~tits except
72 1
at one locality, Erixham. ,After 1951, Bnlan~as
I~egan to return in numl~ers,although by 1954
it had not reached the densities of 1934; Clztha~rznlrrs had declined, 1)ut again not to its former
densities (Southward and Crisp 1956).
Since C'l~thairlalus increased in al~mndance a t
the lower levels vacated by Balanlrs, it may
lxeviously have I~een excluded by con~l~etition
with Balarllrs. T h e grolvth rate of Balanl4s is
greater than Clztlln~izalus both north and south
(Hatton 1938) of this location, so that Balanus
would be likely to \\-in in con~petition with
Chthn~italrrs. However, changes in other environmental factors such as temperature may have
influenced the abundance of these species in a
reciprocal manner. I n its return to southwest
I?ngland after 1951, the maxinlum density of
settlement of Balanlrs \vas 12 per cm2 ; competition of the degree observed at llillport would
not he expected to occur at this density. A t a
higher population density, Balattns in southern
England n.ould prohaldy eliminate Chtha~~talzts
at low shore levels in the same manner as it did
at llillport.
I n I.och Sween, on the Argyll Peninsula, Scotland, I>e\vis and Powell ( 1 9 6 0 ) have described
an unusual pattern of zonation of Clzthamalz~sstellatlts. On the outer coast of the Argyll Peninsula Clztlza~~tal~rs
has a distribution sitnilar to that
at YIillport. 111 the tnore sheltered waters of
1.och Sxveen, holvever, Chtlza~+znluso ccurs from
above YI.1 T.\\-.S. to about hI.T.T2., judging the
distril~utionI)y its relationship to other organisms.
finlatlrrs htrlanoides is scarce above h1.T.L. in
Loch S ~ v e e n ,so that there appears to he no possuch as
sil~ility of competition with Chtl~a~nalus,
that occurring at Millport, between the levels
of lI.T.1,. and 1I.H.\lT.N.
I n Figure 5 an attempt has been made to
summarize the distribution of adults and newly
settled larvae in relation to the main factors which
appear to determine this distribution. F o r Balanzrs the estimates were based on the findings
of a previous study (Connell 1961) ; intraspecific
conllxtition Lvas severe at the lower levels during
the first year, after which predation increased
in importance. \f'ith Chthamalzas, it appears that
avoidance of settlement or early mortality of
those larvae which settled at levels below M.T.L.,
and elimination by competition with Balatzzts of
those which settled between M.T.L. and M . H .
W.N., were the principal causes for the absence of adults below M.H.\lT.N. at Millport.
This distribution appears to be typical for much
of western Scotland.
Ecology, Vol. 42, No. 4
JOSEPII H . C O N K E L L I
BALANUS AWLTS LARVAE
XSlCCATlON
<
DISTRIBUTION PREDATION
BY
TH*IS Y
-
ADULTS LARVAE
INTRASPECIFIC
COMPETITION
RELATIVE EFFECTS
OF THESE FACTORS
CHTHAMALUS
J
I
D1sTR'BUTIO*
DfSICCATION
INTERSPECIFIC
g
COMPETITION
PREDATION
WITH
BALANUS
BY
THAIS
-
RELATIVE EFFECTS
OF THESE FACTORS
F-IG. 5. T h c intertidal distribution of adults and newly settlctl larvae of Balanus bnlanoides and
C'l~tl~czr~~i~lzcs
stclltitus a t Millport, \\.it11 a diagrammatic representation of the relative effects of the principal limiting factors.
SL-Jl Jl .\UY
u~itlercut,or crushed the C l r t h a ~ ~ ~ a lthe
u s ; greatest
occurred during the
Atlults of Cl~fllczrrrulrc.cstcllatz(s occur in the ~nortality of C'l~tlza~~~alzrs
tnarine i~itertidali l l a zone al~ovethat of another seasons of most rapid g r o ~ v t hof Balanzts. Even
Clltlltr~~rczl~rs
transplanted to low levels were
s
barnacle, I,'trlarr~r.s l~czlczt~oitlc.s,1 - o u ~ i gC l ~ t h a i ~ ~ a l t tolder
settle in tlie R a l c ~ t ~ l tzone
s
I)ut evitlently seldom killetl 11y I1nlnnrl.s in this \vay. Predation l ~ y
survive, since fen. adults are fount1 there.
7'lznis tended to decrease the severity of this
The survival of C'lrtlrn~rrnl~rslvhich had settled interspecific competition.
at various le\.els in the Rn1nt1lr.s zone \vas folSurvivors of Clzthniirnl~tsafter a year of crowdlo\vetl for a year 11y successive censuses of rnal~ped ing I)!.
Rnlnj11r.s \\.ere smaller than uncrowded
~ l ~ r . kept
s
indivitluals. Some C ' l ~ t l : n ~ ~ ~ i\\.ere
free ones. Since smaller barnacles l~rotlucefewer offof contact \vith ljnlnj~rcs. These sur\.ived \.cry >Iring, coml~etitiontentletl to reduce reproductive
\\-ell at all intertidal le\.els, indicating that in- efficiency in addition to increasing mortality.
creased time of sul~merg-ence\\.as not the factor
llortality as a result of intraspecies competition
resl~onsil~le
for elimination of Chtllnl~ralztsat low
for sllace I)et\\-een indivitluals of Cl1thalrzallts was
shore levels. Comparison of the sur\.ival of unonly r a r e l ~ .ol~servetl.
lx-otectetl 1~1pulations \vith others, l~rotectecl by
T h e evidence of this and other studies indicates
enclosure in cages from predation I)!. the snail,
that
tlie lo\ver limit of tlistribution of intertidal
Tllnis lnpilllrs, sho\vetl tliat Tllnis \\.as not greatly
organisnls
is mainly tleterminecl by the action of
affecting the survival of C l ~ t l ~ n ~ ~ r n l ~ ~ s .
biotic
factors
such as cornl~etition for space or
Comparison of the survi\.al of untlisturbed populations of C'htha~rrcrl~cs\\.ith those kept free of pretlation. T h e ul1l)er limit is prol~ahlymore often
contact \vith Hnln)lrrs intlicatetl tliat Rnlnl~zrs set 1)y ph'sical factors.
could cause great mortality of Clltlrn~llnlrrs. 1jaReferences
on
and Barnes, H . 1953. Size variations in t h e cyprids of
lanlts settled in greater p o l ~ ~ ~ l a t idensities
.
observations
grew faster that1 C h t h n l ~ r a l ~ r sDirect
some common barnacles. J . M a r . Biol. .Ass. C . K . 32:
at each census sho\vetl that Ralant(s smothered,
297-304.
Autumn 1961
AIETABOLIC C l l h K A C T E R I S T I C S 0 1 1'1 RO i l k \ ( 1'3 723
. 1956a. T h e gro\\:th rate of Chthai~zalus stelIatlts ( P o l i ) . J . M a r . Biol. .Ass. U. K . 35: 355-361.
-.
1956b. Balartlts bala,loides (L.) in the F i r t h
of C l y d e : T h e development a n d a n n u a l variation
of the larval Donulation.
a n d the causative factors.
..
I. . h i m . Ecol. 25: 72-84.
and H. T. Powell. 1953.
T h e growth of Bala~~zdsl~alarloidcs ( L . ) and B . crerzatus Brug. under
varying conditions of suljtnersion. J. M a r . Biol.
Ass. U. K. 32: 107-128.
---- and D. J. Crisp. 1956. Evidence of self-fertilization in certain species of barnacles. .I.M a r .
Biol. .Ass. U. K. 35: 631-639.
Beauchamp, R. S. A. and P. Ullyott. 1932. Competitive relationships between certain species of freshw a t e r Triclads. J. Ecol. 20: 200-208.
Clark, P . J. and F . C. Evans. 1954. Distance t o nearest
neighbor a s a measure of spatial relationships in
populations. Ecology 35: 445-453.
Clench, W. J. 1947. T h e genera I ' I I ~ ~ I Iand
Y L IThais
in the western .Atlantic. Johnsonia 2, S o . 23: 61-92.
Connell, J. H . 1961. T h e effects of competition, predation by 7'Jtais lapillzls, and other factors on natural
populations of t h e I~arnacle, Balanlts baltrnoidcs.
Ecol. Man. 31: 61-104.
Crisp, D. J. 1960. F a c t o r s influencing growth-rate in
Balatlns balan,oidcs. J . .Anim. Ecol. 29: 95-116.
Drinnan, R. E . 1957. T h e winter feeding of the oystercatcher (I-lac~rrntop~lsostralcgzts) 011 the edible
cockle (C'ardiltrt~cdrtlt~). J . Anim. Ecol. 26: 441-469.
Elton, Charles and R. S. Miller. 1954. T h e ecological
survey of animal c o m n ~ u n i t i e s : with a practical
scheme of classifying habitats by structural c h a r acters. J. Ecol. 42: 460-496.
Endean, R., R. Kenny and W. Stephenson. 1956. T h e
ecology a n d distrihutiotl of intertidal organisms on
the rocky shores of the Queensland mainland. Aust.
J. m a r . freshw. Res. 7 : 88-146.
Fischer, E . 1928. S u r la distrihution geographique de
cluelc~ues organismes de rocher, le long des cotes
de la Manche. T r a v . Lab. Xlus. H i s t . N a t . St.S e r v a n 2: 1-16.
Hatton, H . 1938. E s s a i s d e bionomie explicative s u r
quelques especes intercotidales d'algues e t d'animaux.
.Ann. Inst. Oceanogr. Monaco 17: 241-348.
Holme, N. A. 1950. Population-dispersion in Tcllina
totrris D a Costa. J . Liar. Biol. Ass. U. K. 29: 267280.
Hutchinson, G. E. 1957. Concluding remarks. Cold
S p r i n g H a r b o r Symposium on Quant. Biol. 22: 415-
1N T R O D U C T I O N
Because of its rich taxonomic diversity the deer
mouse, P P Y O I I I ~ Shas
C ~heen
I S , used for many studies of speciation and natural selection. These have
focused mainly on the evolutionary iml~lications
of variations in morphology, pelage color, hehavior
and reproductive biology. Progress along these
lines has been reviewed I)y Blair (1950). T h e
ex~)eriments relmrtetl here are a contril~ution to
the investigation of physio'ogical aspects of evoluction within this genus. R4easurements of meta-
holic rate, body temperature and pelage insulation were made in order to evaluate the selective
roles that might be played 11y the enviromental
variables : oxygen tension, temperature and aridity. 11any of the data were organized in accordance with the model of Scholander ct al. (1950)
which formulates the expected relationships between ambient temperature, body temperature,
metabolism and insulation. These relationships,
in non-laboratory mammals, have also been studied
by Griffin ct al. (1953), H a r t and Heroux ( 1953 ) ,
---
.
*"
4L/.
Knight-Jones, E . W. 1953. Laboratory experiments
on gregariousness during setting in Balar~rts balunoidcs and other harnacles. J . E x p . Biol. 30: 584-598.
Knox, G. A. 1954. T h e intertidal flora a n d f a u n a of
the C h a t h a m Islands. N a t u r e Lond. 174: 871-873.
Lack, D. 1954. T h e n a t u r a l regulation of a n i m a l n u m bers. O x f o r d , Clarendon Press.
Lewis, J. R. and H. T. Powell. 1960. :\spects of the
intertidal ecology of rocky shores in .Argyll, Scotland. I. (;enera1 description of t h e a r e a . 11. T h e
distribution of Chtlra,t~alzrs stcllntrrs and Rala~~rrs
in Kintyre.
li~~ltr~loidrs
T r a n s . Roy. Soc. E d i n . 64:
4.5-100.
MacArthur, R. H . 1958. Population ecology of some
warblers of northeastern coniferous forests. Ecology
39: 599-619.
Moore, H . B. 1935.
T h e biology of Bal~lzts balanoidcs. 111. T h e soft parts. J. Mar. Biol. Ass. U. K.
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