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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. Stable URL: http://links.jstor.org/sici?sici=0012-9658%28196110%2942%3A4%3C710%3ATIOICA%3E2.0.CO%3B2-U Ecology is currently published by Ecological Society of America. Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/about/terms.html. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/journals/esa.html. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. The JSTOR Archive is a trusted digital repository providing for long-term preservation and access to leading academic journals and scholarly literature from around the world. The Archive is supported by libraries, scholarly societies, publishers, and foundations. It is an initiative of JSTOR, a not-for-profit organization with a mission to help the scholarly community take advantage of advances in technology. For more information regarding JSTOR, please contact [email protected]. http://www.jstor.org Mon Aug 13 18:31:58 2007 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. 20: 263-277. -. 1936. T h e biology of Balar~zts /~a/aitoidcs. 1.. r)istrihution in t h e Plymouth a r e a . J. M a r . Biol. .\ss. U. I<. 20: 701-716. Siegel, S. 1956. Nonparametric statistics. New Y o r k , l\lcGraw Hill. Southward, A. J. 1955. O n the behavior of barnacles. I. T h e relation of c i r r a l a n d other activities t o 34: 403-422. temperature. J. Liar. Biol. .Ass. U. K'. -- and D. J. Crisp. 1954. Recent changes in t h e distribution of the intertidal harnacles CJttJtamallts stt~llat~tsPoli and Ralatrzts h(11a1roidcs L. in t!ie I:ritish Isles. J . Anim. Ecol. 23: 163-177. , 1956. Fluctuations in t h e distribution a n d abundance of intertidal harnacles. J . M a r . Biol. . \ s s . U. k.35: 211-229.