The Influence of Interspecific Competition and Other Factors on the Distribution of the Stellatus Author(s): Joseph H. Connell Source: Ecology, Vol. 42, No. 4 (Oct., 1961), pp. 710-723 Published by: Ecological Society of America Stable URL: http://www.jstor.org/stable/1933500 . Accessed: 22/12/2010 13:41

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http://www.jstor.org 710 JOSEPH CONNELL H. Ecology, Vol. 42, No4 of Indian villagers toward monkeys, so that radiata Geoff roy). Jour. Bombay Nat. Hist. Soc. monkeys are no longer protected as extensively as 53: 177-184. in former years, (2) intensive trapping to obtain Pocock, R. I. 1929. The Fauna of British India. monkeys for export, (3) changing patterns of Mammalia. Vol. 1 Primates and Carnivora. Lon- don, Taylor and Francis, Ltd. land use, including the deterioration of roadside Prakash, I. 1958. The breeding season of the rhesus habitats, and commercial forest management. monkey Macaca tuldatta (Zimmermann) in Rajasthan.

REFERENCES Jour. Bombay Nat. Hist. Soc. 55: 154. Champion, H. G. 1936. A preliminary survey of the Prater, S. H. 1948. The Book of Indian Mammals. forest types of India and Burma. Indian Forest Bombay. The Bombay Natural History Society. Records (Silviculture Series), Vol. 1, No. 1. Ruch, T. C. 1959. Diseases of Laboratory Primates. Manson-Bahr, P. H. 1954. Manson's Tropical Dis- Philadelphia, W. B. Sauniders Company. eases. 14 Ed., London, Cassell and Co. Southwick, C. H., M. A. Beg and M. R. Siddiqi. Nolte, A. 1955. Field observations on the daily routine 1961. A population survey of rhesus monkeys in and social behavior of common Indian monkeys, with villages, towns, aild temples of northern India. special reference to the Bonnet monkey (Macaca Ecology 42: 538-547.

THE INFLUENCE OF INTERSPECIFIC COMPETITION AND OTHER FACTORS ON THE DISTRIBUTION OF THE BARNACLE CHTHAMALUS STELLA TUS

JOSEPH H. CONNELL Department of Biology, University of California, Santa Barbara, Goleta, Californ,iia

INTRODUCTION lower zone. It seemed probable that this Most of the evidence for the occurrence of was eliminated by the lower one, balan- interspecific competition in has been oides (L), in a struggle for a common requisite gained from laboratory populations. Because of which was in short supply. In the rocky inter- the small amount of direct evidence for its oc- tidal region, space for attachment and growth is currence in niature, competition has sometimes often extremely limited. This paper is an account been assigned a minor role in determining the of some observations and experiments designed composition of aniimal communities. to test the hypothesis that the absence in the lower Indirect evidence exists, however, which sug- zone of adults of Chthacalus was due to inter- gests that competition may sometimes be re- specific competition with Balanus for space. sponsible for the distribution of animals in na- Other factors which may have inifluencedthe dis- ture. The range of distribution of a species may tribution were also studied. The study was made be decreased in the presence of another species at Millport, Isle of Cumbrae, Scotland. with similar requirements (Beauchamp and Ull- I would like to thank Prof. C. M. Yonge and yott 1932, Endean, Kenny and Stephenson 1956). the staff of the Marine Station, Millport, for their Uniform distribution is space is usually attributed help, discussions and encouragement during the to intraspecies competition (Holme 1950, Clark course of this work. Thanks are due to the fol- anid Evans 1954). When animals with similar lowing for their critical reading of the manu- requirements, such as 2 or more closely related script: C. S. Elton, P. W. Frank, G. Hardin, species, are found coexisting in the same area, N. G. Hairston, E. Orias, T. Park and his careful analysis usually indicates that they are students, and my wife. not actually competing with each other (Lack 1954, MacArthur 1958). Distribution of the species of In the course of an investigation of the animals The upper species, , has of an intertidal rocky shore I noticed that the its center of distribution in the Mediterranean; adults of 2 species of barnacles occupied 2 sep- it reaches its northern limit in the Shetland Is- arate horizontal zones with a small area of over- lands, north of Scotland. At MIillport, adults lap, whereas the young of the species from the of this species occur between the levels of mean upper zone were found in much of the lower high water of neap and spring tides (M.H.W.N. zone. The upper species, Clhtharnlus stellatus and MI.H.W.S.: see Figure 5 and Table I). (Poli) thus settled but did not survive in the In southwest England and Ireland, adult Chtham- Autumn 1961 INTERSPECIFIC COM.PETITION 711 alIfs occur at moderate population densities other barnacle species present were Balanus cren- throughout the intertidal zone, more abundantly atu>sBrug and Verrucca stroemia (0. F. Muller), when Balanus balanoides is sparse or absent both found in small numbers only at and below (Southward and Crisp 1954, 1956). At Millport M.L. W.S. the larvae settle from the onto the shore To measure the survival of Chthamaluis, the m-iainlyin September and October; some addi- positions of all individuals in a patch were mapped. tional settlement may occur until December. The Any barnacles which were empty or missinig settlement is miost abundant between M.H.W.S. at the next examination of this patch must and nmeantide level (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. The mapping was done by placing Balanus, limpets, and otlher sedentary organisms. thin glass plates (lanterin slide cover glasses, Few of the Clhthamalis that settle below M.H. 10.7 X 8.2 cm, area 87.7 cM2) over a patch of W.N. survive, so that adults are found only oc- barnacles and marking the position of each casionally at these levels. Chthainalus oln it with glass-marking ink. The Balanuis balanoides is a boreal-arctic species, positions of the corniers of the plate were marked reaching its southern limit in northern Spain. by drilling small holes in the rock. Observations At Millport it occupies almost the entire inter- made in subsequent censuses were noted on a tidal region, from mean low water of spring tides paper copy of the glass map. (M.L.W.S.) up to the region between M.H.W.N. The study areas were chosen by searching and M.H.W.S. Above M.H.W.N. it occurs in- for patches of Chtham1taiUsbelow MI.H.W.N. in termingled with Chthamialusfor a short distance. a stretch of shore about 50 ft long. When 8 Balanits settles on the shore in April and May, patches had been found, no more were looked often in very dense concentrations (see Table for. The only basis for rejection of an area in IV). this search was that it contaiined fewer than 50 The main purpose of this study was to de- Chthamaius in an area of about 1/10 m2. Each termine the cause of death of those Chthamalus numbered area consisted of one or more glass that settled below M.H.\V.N. A study which was maps located in the 1/10 m2. They were mapped being carried on at this time had revealed that in March and April, 1954, before the main set- physical conditions, competition for space, and tlement of Balanus began in late April. predation by the snail Thais lapillits L. were Very few Chthauialius were found to have among the most important causes of mortality of settled below mid-tide level. Therefore pieces of Balanus balanoides. Therefore, the observations rock bearing Chthamtahis were removed from and experiments in the present study were de- levels above M.H.W.N. and transplanted to and signed to detect the effects of these factors on the below M.T.L. A lhole was drilled through each survival of Chtharnalus. piece; it was then fastened to the rock by a stainless steel screw driveni into a plastic screw METHODS anchor fitted ilnto a hole drilled into the rock. Intertidal barnacles are very nearly ideal for A hole ?4" in diameter and 1" deep was found the study of survival under natural conditions. to be satisfactory. The screw could be removed Their sessile habit allows direct observation of and replaced repeatedly and only one stone was the survival of individuals in a group whose po- lost in the entire period. sitions have been mapped. Their small size and For censusing, the stones were removed during on rocks at inter- dense conicentrations exposed a low tide period, brought to the laboratory for vals make feasible. In addition, experimentation examination, and returned before the tide rose they may be handled and transplanted without again. The locationis and arrangements of each injury on pieces of rock, since their opercular area are given in Table I; the transplanted stones plates remain closed when exposed to air. areas 11 to 15. The experimental area was located on the Isle are represented by for on the sur- of Cumbrae in the Firth of Clyde, Scotland. The effect of competition space Farland Point, where the study was made, com- vival of Chthamalus was studied in the following prises the southeast tip of the island; it is ex- manner: After the settlement of Balanus had posed to moderate wave action. The shore rock stopped in early June, having reached densities of consists mainly of old red sandstone, arranged 49/CM2 on the experimentalareas (Table I) a in a series of ridges, from 2 to 6 ft high, oriented census of the surviving Chthantalus was made at right angles to the shoreline. A more detailed on each area (see Figure 1). Each map was then description is given by Connell (1961). The divided so that about half of the number of 712 JOSEPH H. CONNELL Ecology, Vol. 42, No.4 TABLE I. Description of experimental areas*

PoPuLATIoN DENSITY: NO./CM2 IN JUNE, 1954 Chthamalus, autumn 1953settlement Area no. Height %Oof All Remark in ft time Portion barnacles, from sub- Undisturbed without undisturbed M.T.L. merged portion Balanu.8 portion MHWS.+4.9 4 - -

1.+4.2 9 2.2 - 19.2 Vertical,partly protected 2 .+3.5 16 5.2 4.2 - Vertical,wave beaten

MHWN .+3.1 21 - _ - 3a.+2.2 30 0.6 0.6 30.9 Horizontal,wave beaten 3b . 0.5 0.7 29.2. ' i 4 .+1.4 38 1.9 0.6 - 30? to vertical, partly protected 5.+1.4 it2.4 1.2 - it it"i 6 ...... 0.... +1. O 42 1.1 1.9 38.2 Horizontal,top of a boulder, partly protected 7a.+0.7 44 1.3 2.0 49.3 Vertical,protected 7b U 2.3 2.0 51.7 it la.0.0 50 1.0 0.6 32.0 Vertical,protected llb 4( 0.2 0.3 -

12a . .0 100 1.2 1.2 18.8 Horizontal immersed in tide pool 12b . . 100 0.8 0.9 it a

13a .-1.0 58 4.9 4.1 29.5 Vertical, wave beaten 13b a 3.1 2.4 it " .

14a .-2.5 71 0.7 1.1 - 45? angle, wave beaten 14b 1.0 1.0 '- a U

MLWN .-3.0 77 - _ MLWS .-5.1 96 - _

15 .+1.0 42 32.0 _ JChthamalus of autumn, 1954 set- 7b.+0.7 44 5.5 3.7 l - tlement;densities of Oct.,1954.

* The letter "a" followingan area numberindicates that this area was enclosedby a cage; "b" refersto a closelyadjanent area which was not enclosed. All areas. facedeither east or south except7a and 7b, whichfaced north.

Chthanalus were in each portion. One portion betvxxeenthe 2 portions of each area can probably was chosen (by flipping a coin), and those Bal- be disregarded; intraspecific crowding was very anus which were touching or immediately sur- seldom observed. Censuses of the Chthamaius- rounidingeach Chthamnaluswere carefully removed were made at intervals of 4-6 weeks during the with a needle; the other portion was left un- next year; notes were made at each census of touched. In this way it was possible to measure factors such as crowding, undercutting or smoth- the effect on the survival of Chthamalus both of ering which had taken place since the last ex- intraspecific competition alone and of competi- amination. When necessary, Balanus which had tioln with Balanus. It was not possible to have grown until they threatened to touch the Chth- the nulmibersor population densities of Chthamna- amnaluswere removed in later examinations. lits exactly equal on the 2 portions of each area. To study the effects of different degrees of This was due to the fact that, since Chthamalus immersion, the areas were located throughout often occurred in groups, the Balanus had to be the tidal range, either in situ or on transplanted remnovedfrom around all the members of a group stolnes, as shown in Table I. Area 1 had been to einsure that no crowdinig by Balanus occurred. under observation for 112 years previously. The- The densities of Chthamialus were very low, effects of different degrees of wave shock could however, so that the slight differences in density not be studied adequately in such a small area Autumn 1961 INTERSPECIFIC COMPETITION 713

APRIL 16,1954 JUNE 11, 1954

NOV 3, 1954 MAY 13,1955

FIG. 1. Area 7b. In the first plhotograph the large barnacles are Balanlus, the small ones scattered in the bare patch, Chtha,nialis. The wlhite line on the second photograph divides the undisturbed portion (right) from the portioli from which BalanuVs were removed (left). A limpet, Patella vTlgata, occurs on the left, and predatory snails, Thlais lapdillus, are visible. of shore but such (lifferenlces as existed are listed nell 1961), small Thais were estimiiatedto have in Table I. occurred inside the cages aboout3% of the time. The effects of the predatory snail, Thais lapil- All the areas ancdstones were established before lus, (synonymous wNith Nit cella or Purpura, the settlemilenitof Balanits began in late April, Clench 1947), were studied as follows: Cages 1954. Tlhus the Chltha.malutswhich ha(l settled of stainless steel wire netting, (S miieslhesper inich. naturallv oni the slhore were theni of the 1953 were attached over some of the areas. This mlesh year class and all about 7 months old. Some has ani open area of 60%o and previous w ork C/ht/ianial/s wlhich settled in the autumn of 1954 (Connell 1961) had shown that it did not in- were followed unitil the study was ended in June, hibit growth or survival of the barnacles. The 1955. In additioin somue adults w hich, judging fromii their large size and the great erosion of cages were about 4 X 6 inches, the roof was about an inclh above the barnacles and the sides their shells, must have settled in 1952 or earlier, were were fitted to the irregtularities of the rock. They present on the transplanted stones. Thus records were made of at least 3 year-classes of were lheld in place in the samiie manner as the Chtha,ntalhs. transp)lallted stonies. The transplanted stonies w ere attached in pairs, onle of each pair being eniclosed RESULTS in a cage (Table I). These cages w ere effective in excluding all The effects of physical factors but the smiiallest Thais. Occasionally small Thais, In Figures 2 and 3, the dashed line indicates 2 to 1 cIml in lenigtlh, enitered the cages through the survival of Chthamnaltis growing without con- gaps at the linie of juncture of netting and rock tact with Balanus. The suffix "a" indicates that surface. In the concurrenit study of Balamns (Con- the area was protected fronm Tliais bv a cage. 714 JOSEPH H. CONNELL Ecology, Vol. 42, No. 4 In the absence of Balanus and Thais, and pro- favored by increased light or warmth during tected by the cages from damage by water-borne emersion in its early life on the shore. These con- objects, the survival of Chthamalus was good at ditions would tend to occur higher on the shore all levels. For those which had settled normally in Scotland than in southern England. on the shore (Fig. 2), the poorest survival was The effects of wave action on the survival of on the lowest area, 7a. On the transplanted Chthamnalusare difficult to assess. Like the de- stones (Fig. 3, area 12), constant immersion gree of immersion, the effects of wave action may in a tide pool resulted in the poorest suirvival. The act indirectly. The areas 7 and 12, where rel- reasons for the trend toward slightly greater atively poor survival was found, were also the mortality as the degree of immersion increased areas of least wave action. Although Chthamalus are unknown. The amount of attached algae on is usually abundant on wave beaten areas and the stones in the tide pool was much greater absent from sheltered bays in Scotland, Lewis and than on the other areas. This may have reduced Powell (1960) have shown that in certain shel- the flow of water and food or have interfered tered bays it mav be very abundant. Hatton directly with feeding movements. Another pos- (1938) found that in northern France, settlement sible indirect effect of increased immersion is the and growth rates were greater in wave-beaten increase in predation by the snail, Thais lapillus, areas at M.T.L., but, at M.H.W.N., greater in at lower levels. slhelteredareas. Chthamaalutsis tolerant of a much greater de- At the upper shore margins of distribution gree of immersion than it normally encounters. Chthamnalusevidently can exist higher than Bal- This is shown by the survival for a year on area ants mainly as a result of its greater tolerance 12 in a tide pool, together with the findings of to heat and/or desiccation. The evidence for this Fischer (1928) and Barnes (1956a), who found was gained during the spring of 1955. Records that Chthamalmuswithstood submersion for 12 from a tide and wave guage operating at this and 22 months, respectively. Its absence below time about one-half mile north of the study area M.T.L. can probably be ascribed either to a lack showed that a period of neap tides had coincided of initial settlement or to poor survival of newly with an unusual period of warm calm weather in settled larvae. Lewis and Powell (1960) have April so that for several days no water, not even suggested that the survival of Chthamialusmay be waves, reached the level of Area 1. In the period

4 7a 120 2 3o .12' +0.7' I00 + 3.5' +2.2 - 80 REMOVED BALANUS 60

_\UNMODIFIEDUNMODIFD REMOVED. 40UMDII ALANUS 20 BALANUSREMOVED _ ALANUS REMOVED

UNMODIFIED 7AAUREOb 4 0 UNM-IFIE - 5-. 0 22 .';+O7 w 605 +.

60

480 -6AANU 5EMOVE

z 0

It UNMODIFIED FIED~~~~~~~~~~~~~~~~~~~BLAU RMOE

3o40 J J A S O N D | J f M A " J J J A S BALANUDS|J REMOVEDF A MJAASONMS RDEVFED UJS NMDIJFI 2 0

1954 11955 1954 1955 1954 1 1955 1954 1 1955 on the shore in the FIG. 2. Survivorship curves of Chthantahus stellatits wiiiclh had settled naturally In each area the sur- autumn of 1953. Areas designated "a" were protected froni predation by cages. that in the undisturbed area. vival of Chthamaltis growing without colitact with Balc nus is compared to For each area the vertical distance in feet fromsIoEn. M.T.L. is Autumn 1961 INTERSPECIFIC COMPETITION 715

80 Ila 12G 13o 14:a 60 IN TIDE POOL \ ALANUS REMOVED

40 -1.0

\ ALANUS REMOVED 20 REMOVED BALANS \ALANUS REMOVED

10 UNMODI UNMODIFIED UNMODIFIED z

WL [[k [ [ STONE 2 r \ [ UNMODIFED LOST

.4 , 60 llb *12b 13b < -14b O~~~~~.0O 0.0' -LO' - 2.5 2 40 IN TIOE POOL -- ANU__ _ S ts ' I^LANUS REMOVED B REMOVED x to0 2ALANUS

O | ---. _S ALANUSREMOVED

10 UNMODIFIED SALANUS REMOVED

NMODIFIEDUNMODFIED

J JA F MA M J J JF MA J J A SO D MA SO SO NDJ IJA SO5N N1 JFF J JJA NDJJF M MJ 1954 1955 1954 1955 1954 1955 1954 1955 FIG. 3. Survivorship curves of Chthanalus stellatus on stones transplanted from high levels. These had settled in the autumn of 1953; the arrangement is the same as that of Figure 2. between the censuses of February and May, Bala- observed. This accords with Hatton's (1938) nus aged one year suffered a mortality of 92%, observation that he never saw crowding between those 2 years and older, 51 %. Over the same individuals of Chthamalus as contrasted to its period the mortality of Chthamalus aged 7 months frequent occurrence between individuals of Bala- was 62%, those 112 years and older, 2%o. Rec- fius. ords of the survival of Balanus at several levels Interspecific competition between Balanus and below this showed that only those Balanus in Chthamalus was, on the other hand, a most im- the top quarter of the intertidal region suffered portant cause of death of Chthamalus. This is high mortality during this time (Connell 1961). shown both by the direct observations of the process of crowding at each census and by the Comlpetition for space differences between the survival curves of Chtha- At each census notes were made for individual malis with and without Balanus. From the barnacles of any crowding which had occurred periodic observations it was noted that after the since the last census. Thus when one barnacle first month on the undisturbed portions of areas started to grow up over another this fact was 3 to 7 about 10% of the Chthamalus were being noted and at the next census 4-6 weeks later the covered as Balanus grew over them; about 3%o progress of this process was noted. In this way were being undercut and lifted by growing Bala- a detailed description was built up of these grad- nus; a few had died without crowding. By the ually occurring events. end of the 2nd month about 20% of the Chtha- Intraspecific competition leading to mortality malus were either wholly or partly covered by in Chtha.malus was a rare event. For areas 2 Balanus; about 4% had been undercut; others to 7, on the portions from which Balanus had were surrounded by tall Balanus. These processes been removed, 167 deaths were recorded in a continued at a lower rate in the autumn and year. Of these, only 6 could be ascribed to almost ceased during the later winter. In the crowding between individuals of Chthamalus. On spring Balanus resumnedgrowth and more crowd- the undisturbed portions no such crowding was ing was observed. 716 JOSEPH H. CONNELL Ecology, Vol. 42, No. 4 In Table II, these observations are summarized that of the base. It was obvious that extreme for the undistributed portions of all the areas. crowding occurred under these circumstances, Above M.T.L., the Balanus tended to overgrow but the exact cause of the mortality of the Chtha- the Chtzamalus, whereas at the lower levels, malus caught in this crush was difficult to as- undercutting was more common. This same certain. trend was evident within each group of areas, In comparing the survival curves of Figs. 2 undercutting being more prevalent on area 7 and 3 within each area it is evident that Chthania- than on area 3, for example. The faster growth lus kept free of Balanus survived better than of Balanus at lower levels (Hatton 1938, Barnes those in the adjacent undisturbed areas on all and Powell 1953) may have resulted in more but areas 2 and 14a. Area 2 was in the zone undercutting. When Chthamalus was completely where adults of Balanus and Chthamalus were covered by Balanus it was recorded as dead; normally mixed; at this high level Balanus evi- even though death may not have occurred im- dently has no influence on the survival of Chthan- mediately, the buried barnacle was obviously not alus. On Stone 14a, the survival of Chthlamnalus a functioning member of the population. without Balanus was much better until January when a starfish, Asterias rubens L., entered the TABLE II. The causes of mortality of Chthamnalusstellatus cage and ate the barnacles. of the 1953 year group on the undisturbed portions of Much variation occurred on the other 14 areas. each area When the Chthamalus growing without contact

PERCENTAGE OF DEATHS RESULTING with Balanus are compared with those on the FROM: adjacent undisturbed portion of the area, the No. of survival was very much better on 10 areas and Area no. Height No. at deaths Smoth- Under- Other in ft start in the ering cutting crowding Un- moderately better on 4. In all areas, some from next by by by known M.T.L. year Balanus Balanius Balanus causes Chthamalus in the undisturbed portions escaped

2 ...... +3.5 28 1 0 0 0 100 severe crowding. Sometimes no Balanuts hap- pened to settle close to a Chthawluss, or some- 3a ...... +2.2 111 81 61 6 10 23 i 3b ...... 47 42 57 5 2 36 times those which did died soon after settlement. In some instances, Chthamalhiswhich were being 4 ...... +1.4 34 14 21 14 0 65 undercut by Balanus attached themselves to the 5 ...... +1.4 43 35 11 11 3 75 Balanus and so survived. Some Chthamalus were 6 ...... +1.0 27 11 9 0 0 91 partly covered by Balanus but still survived. It 7a ...... +0.7 42 38 21 16 53 10 seems probable that in the 4 areas, nos. 4, 6, 1la, 7b. 51 42 24 10 10 56 and llb, where Chthamilus survived well in the l1a ...... 0.0 21 13 54 8 0 38 presence of Balanus, a higher proportion of the l1b ...... 10 5 40 0 0 60 Chthamalus escaped death in one of these ways. 12a...... 0.0 60 57 19 33 7 41 The fate of very young Chthamalus which set- 12b ...... a 39 34 9 18 3 70 tled in the autumn of 1954 was followed in de- 13a...... -1.0 71 70 19 24 3 54 tail in 2 instances, on stone 15 and area 7b. The 13b ...... 69 62 18 8 3 71 Chthaiialus on stone 15 had settled in an irregular 14a...... -2.5 22 21 24 42 10 24 space surrounded by large Balanus. Most of the 0 0 0 100 14b ...... 9 9 mortality occurred around the edges of the space Total, 2- 7.. - 383 264 37 9 16 38 as the Balanus undercut and lifted the small Total, 11-14.. - 301 271 19 21 4 56 Chthainalus nearby. The following is a tabula- tion of all the deaths of young Chthamalus be- tween Sept. 30, 1954 and Feb. 14, 1955, on Stone In Table II under the term "other crowding" 15, with the associated situations: all instances where Chthacmalus have been placed Lifted by Balanus : 29 between 2 or more Balanus, were crushed laterally Crushed by Balanus : 4 in an interval or where Chthamalus disappeared Smothered by Balanus and Chthamalus : 2 during which a dense population of Balanus grew Crushed between Balanus and Chthamalus: 1 the rapidly. For example, in area 7a Balanus, Lifted by Chthamalus : 1 of which were at the high population density Crushed between two other Chthamalus : 1 48 per cm2, had no room to expand except up- Unknown 3 ward 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 Chthamalus by older Balanutsin the autumn main- Autumn 1961 INTERSPECIFIC COMPETITION 717 ly takes the form of undercutting, rather than of TABLE III. Comparison of the mortality rates of young smothering as was the case in the spring. The and older Chthamalus stellatus on transplanted stones reason for this difference is probably that the Number of Chtha- % mortality over Chthamalhs are more firmly attached in the spring malus present in one year (or for 6 June, 1954 months for 14a) so that the fast growing young Balanus grow up of Chthamalus over them when they make contact. In the Stone' Shore level Treatment No. 1952 1952 autumn the reverse is the case, the Balanus being 1953 or older 1953 or older year year year year firmly attached, the Chthamalus weakly so. group groups group groups the settlement of Chthamalus on Although 1.0 ft below Balanus removed 51 3 35 0 Stone 15 in the autumn of 1954 was very dense, 13b MTL 32/cm2, so that most of them were touching an- Undisturbed 69 16 90 31 other, only 2 of the 41 deaths were caused by MTL, in a Balanus removed 50 41 44 37 intraspecific crowding among the Chthamalus. 12a tide pool, 71 This is in accord with the findings from the 1953 caged Undisturbed 60 31 95 settlement of Chthamialus. 2.5 ft below Baianus removed 25 45 40 36 The mortality rates for the young Chthamalus 14a MTL, caged Undisturbed 22 8 86 78 on area 7b showed seasonal variations. Between October 10, 1954 and May 15, 1955 the relative rate per day X 100 was 0.14 on the mortality TABLE IV. Comparison of annual mortality rates of undisturbed area and 0.13 where Balanus had Chthamalus stellatus and Balanus balanoides* been removed. Over the next month, the rate increased to 1.49 on the undisturbed area and Chthamalus stellatus, autumn 1953 0.22 where Balanus was absent. Thus the in- settlement crease in mortality of young Chthamalus in late Population spring was also associated with the presence of Area no. Height in ft density: % mortality from M.T.L. no./cm2 in the next Balanus. June, 1954 year Some of the stones transplanted from high to low levels in the spring of 1954 bore adult 1 ...... +4.2 21 17 Chthamalus. On 3 stones, records were kept of 3a ...... +2.2 31 72 the survival of these adults, which had settled in 89 the autumn of 1952 or in previous years and 3b ...... 29 were at least 20 months old at the start of the 6 ...... +1.0 38 41 experiment. Their mortality is shown in Table 7a ...... +0.7 49 90 III; it was always much greater when Balanus 7b ...... 52 82 was not removed. On 2 of the 3 stones this lia ...... O.00 32 62 mortality rate was almost as high as that of the younger group. These results suggest that any 13a ...... -1.0 29 99 to survive the competi- Chthamahis that managed 12a ...... (tide pool) 19 95 tion for space with Balanus during the first year would probably be eliminated in the 2nd year. Balanus balanoides, spring 1954 settlement Cetnsuses of Balanus were not made on the 1 (top) . +4.2 21 99 experimental areas. However, on many other Cage 1 .. +2. 1 85 92 1:Middle cc areas in the same stretch of shore the survival 1 :Middle Cage 2. 25 77 of Balanis was being studied during the same I :Low Cage 1 l. . + 1 .5 26 88 period (Connell 1961). In Table IV some mor- tality rates measured in that study are listed; the Stone 1...... -0.9 26 86 Stone 2 ...... it 68 94 Balanus were members of the 1954 settlement to at population densities and shore levels similar * Population density includes both species. The mortality rates of Chthamalus The mortality rates refer to those on the undisturbed portions of each area. The data and area designa- those of the present study. tions for Balanutswere taken from Connell (1961); the present area 1 is the same as of Balanus were about the same as those of that designated 1 (top) in that paper. Chthamalus in similar situations except at the highest level, area 1, where Balanus suffered much In the observations made at each census it greater mortality than Chthamalus. Much of this appeared that Balanus was growing faster than mortality was caused by intraspecific crowding Chthamalus. Measuremnentsof growth rates of at all levels below area 1. the 2 species were made from photographs of 718 JOSEPH H. CONNELL Ecology, Vol. 42, No. 4 the areas taken in June and November, 1954. creases in the growth rate of Balanus. The Barnacles growing free of contact with each other correlation was tested using the Spearman rank were measured; the results are given in Table V. correlation coefficient. The absolute increase in The growth rate of Ba/anus was greater than diameter of Balanus in each month, read from that of Chthamalus in the experimental areas; the curve of growth, was compared to the per- this agrees with the findings of Hatton (1938) centage mortality of Chthantalus in the same oIn the shore in France and of Barnes (1956a) month. For the 13 months in which data for for continual submergence on a raft at Millport. Chthamiiailuswas available, the correlation was highly significant, P .01. TABLE V. Growth rates of Chthamnalusstellatus and Balanus balanoides. Measurements were made of un- 120 24 crowded individuals on photographs of areas 3a, 3b and 110 C22 7b. Those of Chthamalus were made on the same indi- z 100 \20 viduals on both dates; of Balanuis, representative samples 90g > 18 . GROWTH Of BALANUS were chosen 80 1: 6

70- 14 (CHTHAMALUS BALANI!S 60 12

50 / O No. Average No. Average measured size, mm. measured size, mm. I , < L X SURVIVAL OF CHTHAMALUS June 11, 1954 ...... 25 2. 49 39 1.87 November 3, 1954...... 25 4.24 27 4.83 t lo- 2C2O Average size in the interval ...... 3.36 3.35 AS 0 N' D S Absolute growth rate per day x 100 1.21 2.04 MONTHS Fi (;. 4. A comparison of the seasonal changes in the growth of Balanuis balanoides and in the survival of After a year of crowding the average popula- Chtham-nalusstellatuts being crowded by Bala-nus. The tion densities of Balanus and Chthamalus re- growth of Balainus was that of panel 3, Barnes and mained in the same relative proportion as they Powell (1953), just above M.T.L. on Keppel Pier, Millport, during 1951-52. The Chthamaluswere on area had been at the start, since the mortality rates 3a of the present study, one-half mile south of Keppell were about the samne. However, because of its Pier, during 1954-55. faster growth, Balanits occupied a relatively great- er area and, presumably, possessed a greater From all these observations it appears that biomass relative to that of Chthamcalusafter a the poor survival of Chthamalusbelow M.H.W\.N. year. is a result mainly of crowding by dense popula- The faster growth of Balanus probably ac- tionls of faster growing Balanus. counts for the manner in which Chthanialulswere At the end of the experiment in J une, 1955, crowded by Balanus. It also accounts for the the surviving Chthaiialius were collected from 5 of sinuosity of the survival curves of Chthamtaluts the areas. As shown in Table VI, the average growing in contact with Balanus. The mortality size was greater in the Chthanmaluswhich had rate of these Chthanmalus,as indicated by the growxn free of contact with Balanus; in every slope of the curves in Figs. 2 and 3, was greatest case the difference was significant (P < .01, in summer, decreased in winter and increased Mann-\Whitnev U. test, Siegel 1956). The stur- again in spring. The survival curves of Chtha- vivors on the undisturbed areas were oftenl mis- mnalusgrowing without contact with Balanus do shapein, in some cases as a result of being lifted not show these seasonal variations which, there- onl to the side of an undercutting Balanits. Thus fore, cannot be the result of the direct action of the smaller size of these barnacles may have been plhysical factors such as temperature, wave action due to disturbances in the normal pattern of or rain. growtlh while they were being crowded. Seasonal variations in growth rate of Balanuts Th-ese Chthamalits were examined for the pres- correspond to these changes in mortality rate of ence of developing larvae in their mantle cavities. Chtha.nmlus. In Figure 4 the growth of Balanuts As shown in Table VI, in every area the pro- throughout the year as studied on an intertidal lportion of the uncrowded Chthaniaius with larvae panel at Millport by Barnes and Powell (1953), was equal to or miore often slightly greater than is compared to the survival of Chthaintahts at oni the crowded areas. The reason for this mlay about the same intertidal level in the l)resent be related to thie smaller size of the crowded study. The increased mortality of Chthamtaluswas C(hthamaius. It is not due to se)aration, sinice found to occur in the same seasons as the in- Chtharnalus can self-fertilize (Barnes and Crisp Autumn 1961 INTERSPECIFIC COMPETITION 719 TABLE VI. The effect of crowdingon the size and pres- TABLE VII. The effect of predation by Thais lapillus ence of larvae in Chthainalusstellatus, collected in June, on the anniiualmortality rate of Chthamnalussteellatus in 1955 the experimental areas*

Level, Number DIAMETERIN MM % of individ- % mortality of Chthamalusover a year (The initial num- feet of uals which Area Treatmenit above Chtha- hadlarvae in bers are given in parentheses) Mf L malus Average Range mantlecavity a: Protected from predation b- Unprotected, open to 3a... Undisturbed 2.2 18 3.5 2.7-4.6 61 by a cage predation Height a ... Balanusremoved 50 4.1 3.0-5.5 65 A ,__ __ Area in ft from With Without Dif- With Without Dif- 4.... Undisturbed 1.4 16 2.3 1.8 3.2 81 M.T.L. Balanuts Balanus ference Balainus Balanus ference a ... Balanusremoved 37 3.7 2.5-5 1 100 Area 3.. +2.2 73 (112) 25 (96) 48 89 (47) 6 (50) 83 5.... Undisturbed 1.4 7 3.3 2.8-3.7 70 Area 7.. +0.7 90 ( 42) 47 (40) 43 82 (51) 23 (47) 59 Area ' ... Balanusremoved " 13 4.0 3.5-4.5 100 11.. 0 62 ( 21) 28 (18) 34 50 (10) 25 (16) 25 Area 12 Ot 100 ( 60) 53 (50) 47 87 (39) 59 (32) 28 6.... Undisturbed 1.0 13 2.8 2.1-3.9 100 Area 13. - 1.0 98 ( 72) 9 (77) 89 90 (69) 35 (51) 55 .....Balanus removed 14 4.1 3.0-5.2 100 *The records for 12a extend over only 10 months; for purposes of comparison 7a & b. . Undisturbed 0.7 10 3.5 2.7-4.5 70 the mortality rate for 12a has been multiplied by 1. 2. Balanusremoved 23 4.3 3.0-6.3 81 tTide pool.

1956). Moore (1935) and Barnes (1953) have at lower levels greater outside. Densities of Thais shown that the number of larvae in an individual tend to be greater at and below M.T.L. so that of Balanus balanoides increases with increase in this trend in the mortality rates of Chthamalus volume of the parent. Comparison of the cube of may be ascribed to an increase in predation by the diameter, which is proportional to the volume, Thais at lower levels. of Chtharnalus with and without Balanus shows Mortality of Chthamcalus in the absence of Balanus was that the volume may be decreased to '4 normal appreciably greater outside than size when crowding occurs. Assuming that the inside the cage only on area 13. In the other 4 relation lbetween larval numbers and volume in areas it seems evident that few Chthamlus were Chthaiial-is is similar to that of Balanuis, a de- being eaten by Thais. In a concurrent study of crease in both frequency of occurrence and abun- the behavior of Thais in feeding on Balanus dance of larvae in Chthamalus results from com- balanoides, it was found that Thais selected the larger petition with Balanus. Thus the process described individuals as prey (Connell 1961). Since Balanus after in this paper satisfies both aspects of interspecific a few month's growth was usually larger than competition as defined by Elton and Mliller Chthamalus, it might be expected that Thais would feed (1954): "in which one species affects the pop- on Balanus in preference to Chthamv.talus. In a later study ulation of another by a process of interference, (unpublished) made at Santa i.e., by reducing the reproductive efficiency or in- Barbara, California, Thais emargin- ata creasing the mortality of its competitor." Deshayes were enclosed in cages on the shore with mixed populations of Balanus glandula Dar- The effect of predation by Thais win and Chthamnlus fissus Darwin. These species Cages which excluded Thai's had been attached were each of the same size range as the corre- on 6 areas (indicated by the letter "a" following sponding species at Millport. It was found that the number of the area). Area 14 was not in- Thais emarginata fed on Balanus glandlda in cluded in the following analysis since many star- preference to Chthamalus fissus. fish were observed feedin-igon the barnacles at this As has been indicated, much of the mortality level; one entered the cage in January, 1955, and of Chthawlus growing naturally intermingled ate most of the barnacles. with Balanus was a result of direct crowding by Thais were common in this locality, feeding Balanuts. It therefore seemed reasonable to take on barnacles and , and reaching average the difference between the mortality rates of population densities of 200/M2 below M.T.L. Chthacnalus with and without Balanus as an index (Connell 1961). The mortality rates for Chtham- of the degree of competition between the species. alus in cages and on adjacent areas outside cages This difference was calculated for each area and (indicated by the letter "b" after the nuimber) is included in Table VII. If these differences are shown on Table VII. are compared between each pair of adjacent areas If the mortality rates of Chthawmalusgrowing in and out of a cage, it appears that the difference, without contact with Balanus 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. 720 JOSEPH H. CONNELL Ecology, Vol. 42, No.4 Thus as predation increased at lower levels, the anid 3), and these survivors were often misshapen degree of competition decreased. This result and smaller than those which had not been would have been expected if Thais had fed upon crowded (Table VI). Adults on the transplanted Balanus in preference to Chthamalus. The gen- stones had suffered high mortality in the previous eral effect of predation by Thais seems to have year (Table III). been to lessen the interspecific competition below Another difficulty was that Chthamalus was M.T.L. rarely found to have settled below mid tide level at Millport. The reasons for this are unknown; DISCUSSION it survived well if transplanted below this level, "Although communities appear quali- in the absence of Balanus. In other areas of the tatively to be constructed as if competition were British Isles (in southwest England and Ireland, regulating their structure, even in the best stuidied for example) it occurs below mid tide level. cases there are nearly always difficulties and un- The possibility that Ch.thawalus might affect explored possibilities" (Hutchinson 1957). Balanus deleteriously remains to be considered. In the present study direct observations at in- It is unlikely that Chthamalus could cause much tervals showed that competition was occurring mortality of Balanus by direct crowding; its tinder natural conditions. In addition, the evi- growth is much slower, and crowding between denice is strong that the observed competition with individuals of Chthamalus seldom resulted in Balanus was the principal factor determining the death. A dense population of Chthamalus might local distribution of Chthanmalts. Chthatmalus deprive larvae of Balanus of space for settle- thrived at lower levels when it was not growing ment. Also, Chthamalus might feed on the plank- in contact with Balanus. tonic larvae of Balanus; however, this would oc- However, there remain unexplored possibilities. cur in March and April when both the sea water The elimination of Chth-amalusrequires a dense temperature and rate of cirral activity (pre- population of Balanus, yet the settlement of Ba- sumably correlated with feeding activity), would lanus varied from year to year. At Millport, the be n-eartheir minima (Southward 1955). settlement density of Balanus balanoides was The indication from the caging experiments measured for 9 years between 1944 and 1958 that predation decreased interspecific competi- (Barnes 1956b, Connell 1961). Settlement was tion suggests that the action of such additional light in 2 years, 1946 and 1958. In the 3 seasons factors tends to reduce the intensity of such of Balanis settlement studied in detail, 1953-55, interactions in natural conditions. An additional there was a vast oversupply of larvae ready for suggestion in this regard may be made con- settlement. It thus seems probable that most of cerning parasitism. Crisp (1960) found that the Chthamalus which survived in a year of poor the growth rate of Balanus balanoides was de- settlement of Balacus would be killed in competi- creased if individuals were infected with the iso- tion with a normal settlement the following year. pod parasite (Spence Bate). A succession of years with poor settlements of In Britain this parasite has not been reported Balanus is a possible, but improbable occurrence from Chthamalus stellatus. Thus if this parasite at Millport, judging from the past record. A were present, both the growth rate of Balanus, very light settlement is probably the result of a and its ability to eliminate Chthamalus would be chance combination of unfavorable weather cir- decreased, with a corresponding lessening of the cumstances during the planktonic period (Barnes degree of competition between the species. 1956b). Also, after a light settlement, survival cautses zonation on the shore is improved, owing principally to The of the reduction in intraspecific crowding (Connell The evidence presented in this paper indicates 1961); this would tend to favor a normal settle- that the lower limit of the intertidal zone of ment the following year, since barnacles are stim- Chthamalus stellatus at Millport was determined ulated to settle by the presence of members of by interspecific competition for space with Bala- their own species already attached on the surface nus balanoides. Balanus, by virtue of its greater (Knight-Jones 1953). population density and faster growth, eliminated The fate of those Chthamalus which had sur- most of the Chthamalus by directing crowding. vived a year on the undisturbed areas is not At the upper limits of the zones of these known since the experiment ended at that time. species no interaction was observed. Chthamalus It is probable, however, that most of them would evidently can exist higher on the shore than have been eliminated within 6 molnths; the mor- Balanuis mainly as a result of its greater tolerance tality rate had increased in the spring (Figs. 2 to heat and/or desiccation. Autumn 1961 INTERSPECIFIC COMPETITION 721 The upper limits of most intertidal animals at one locality, Brixham. After 1951, Balanus are probably determined by physical factors such began to return in numbers, although by 1954 as these. Since growth rates usually decrease with it had not reached the densities of 1934; Chtha- increasing height on the shore, it would be less malus had declined, but again not to its former likely that a sessile species occupying a higher densities (Southward and Crisp 1956). zone could, by competition for space, prevent a Since Chthamalus increased in abundance at lower one from extending upwards. Likewise, the lower levels vacated by Balanus, it may there has been, as far as the author is aware, previously have been excluded by competition no study made which shows that predation by with Balacifs. The growth rate of Balanus is land species determines the upper limit of an greater than Chthamalus both north and south intertidal animal. In one of the most thorough (Hatton 1938) of this location, so that Balanus of such studies, Drinnan (1957) indicated that would be likely to win in competition with intense predation by birds accounted for an an- Chthanalus. HoweverYchanges in other environ- nual mortality of 22% of cockles (Cardiumstedule mental factors such as temperature may have L.) in sand flats where their total mortality was influenced the abundance of these species in a 74% per year. reciprocal manner. In its return to southwest In regard to the lower limits of an animal's England after 1951, the maximum density of zone, it is evident that physical factors may act settlement of Balanus was 12 per cm2; compe- directly to determine this boundary. For example, tition of the degree observed at Millport would some active amphipods from the upper levels of not be expected to occur at this density. At a sandy beaches die if kept submerged. However, higher population density, Balanus in southern evidence is accumulating that the lower limits England would probably eliminate Chthlmalus of distribution of intertidal animals are deter- at low shore levels in the same manner as it did mined mainly by biotic factors. at Millport. Connell (1961) found that the shorter length In Loch Sween, on the Argyll Peninsula, Scot- of life of Balanus balanoides at low shore levels land, Lewis and Powell (1960) have described could be accounted for by selective predation by an unusual pattern of zonation of Chthamalus stel- Thais lapillus and increased intraspecific com- latus. On the outer coast of the Argyll Penin- petition for space. The results of the experiments sula Chthamalus has a distribution similar to that in the present study confirm the suggestions of at Millport. In the more sheltered waters of other authors that lower limits may be due to in- Loch Sween, however, Chthamalus occurs from terspecific competition for space. Knox (1954) above M.H.W.S. to about Mi.T.L., judging the suggested that competition determined the dis- distribution by its relationship to other organisms. tribution of 2 species of barnacles in New Zealand. Balanus balanoides is scarce above M.T.L. in Endean, Kenny and Stephenson (1956) gave Loch Sween, so that there appears to be no pos- indirect evidence that competition with a colonial sibility of competition with Chthamalus, such as polychaete worm, (Galeolaria) may have de- that occurring at Millport, between the levels termined the lower limit of a barnacle (Tetra- of M.T.L. and M.H.W.N. clita) in Queensland, Australia. In turn the In Figure 5 an attempt has been made to lower limit of Galeolaria appeared to be deter- summarize the distribution of adults and newly mined by competition with a tunicate, Pyura, or settled larvae in relation to the main factors which with dense algal mats. appear to determine this distribution. For Ba- With regard to the 2 species of barnacles in lanus the estimates were based on the findings the present paper, some interesting observations of a previous study (Connell 1961); intraspecific have been made concerning changes in their competition was severe at the lower levels during abundance in Britain. Moore (1936) found that the first year, after which predation increased in southwest England in 1934, Chthamalutsstella- in importance. With Chthamalus, it appears that tus was most dense at M.H.W.N., decreasing in avoidance of settlement or early mortality of numbers toward M.T.L. while Balanus balanoides those larvae which settled at levels below M.T.L., increased in numbers below M.H.W.N. At the and elimination by competition with Balanus of same localities in 1951, Southward and Crisp those which settled between M.T.L. and M.H. (1954) found that Balanus had almost disap- W.N., were the principal causes for the ab- peared and that Chthanialus had increased both sence of adults below M.H.W.N. at Millport. above and below M.H.W.N. Chthamalfs had not This distribution appears to be typical for much reached the former densities of Balanus except of western Scotland. 722 JOSEPH H. CONNELL Ecology, Vol. 42, No. 4

BALANUS CHTHAMALUS A

MAtW.S.____

* k B C | | t ~~~~~~~~~~~B ~ C

M.H.W.NS.- -

ADULTS LARVAE DESICCATION INTRASPECIFIC ADULTS LARVAE OESICCATION INTE RSPECIFIC B COMPETITION B COMPETITION PREDATION PREDATION WITH BY BY BALANUS THAIS THAIS

DISTRIBUTION RELATIVE EFFECTS DISTRIBtUTION RELATIVE EFFECTS OF THESE FACTORS OF THESE FACTORS FIG. 5. The intertidal distribution of adults and newly settled larvae of Balanus balanoides and Chthawnalusstellatus at Millport, with a diagrammatic representation of the relative effects of the princi- pal limiting factors.

SUM MARY undercut, or crushed the Chthamcalus;the greatest Adults of Chthamnalusstellatus occur in the mortality of Chthamalus occurred during the marine intertidal in a zone above that of another seasons of most rapid growth of Balanus. Even barnacle, Balanus balanoides. Young Chthamalus older Chthawialustransplanted to low levels were settle in the Balanus zone but evidently seldom killed by Balanus in this way. Predation by survive, since few adults are found there. Thais tended to decrease the severity of this The survival of Chthainahlus which had settled interspecific competition. at various levels in the Balanuts zone was fol- Suirvivors of Chtharnalusafter a year of crowd- lowed for a year by successive censuses of mapped ing by Balanus were smaller than uncrowded individuals. Some Chthamalus were kept free onles. Since smaller barnacles produce fewer off- of contact with Balanius. These survived very spring, competition tended to reduce reproductive well at all intertidal levels, indicating that in- efficiency in addition to increasing mortality. creased time of submergence was not the factor \iortality as a result of intraspecies competition of Chthamcalusat low responsible for elimination for space between individuals of Chthamalus was shore levels. Comparison of the survival of un- only rarelv observed. protected populations with others, protected by The evidence of this and other studies indicates enclosure in cages from predation by the snail, that the lower limit of distribution of intertidal Thais lapilius, showed that Thais was not greatly is determined the action affecting the survival of Chthaialhts. orgalnisms mainly by of for or Comparison of the survival of undisturbed pop- biotic factors such as competition space ulations of Chthanialufs with tlhose kept free of predation. The upper limit is probably more often contact witlh Balanuls indicated that Balanus set by phvsical factors. could cause great mortality of Chtha1maius. Ba- References and lanus settled in greater population densities Barnes, H. 1953. Size variations in the cyprids of grew faster than Chthamnalus. Direct observations some common barnacles. J. Mar. Biol. Ass. U. K. 32: at each census showed that Balanus smothered, 297-304. Autumn 1961 METABOLIC CHARACTERISTICS OF PEROMYSCUS 723

1956a. The growth rate of Chthamalus stel- Hatton, H. 1938. Essais de bionomie explicative sur latus (Poli). J. Mar. Biol. Ass. U. K. 35: 355-361. quelques especes intercotidales d'algues et d'animaux. . 1956b. Balanus balanoides (L.) in the Firth Ann. Inst. Oceanogr. Monaco 17: 241-348. of Clyde: The development and annual variation Holme, N. A. 1950. Population-dispersion in Tellina of the larval population, and the causative factors. tenuis Da Costa. J. Mar. Biol. Ass. U. K. 29: 267- J. Anim. Ecol. 25: 72-84. 280. - ~~ and H. T. Powell. 1953. The growth of Ba- Hutchinson, G. E. 1957. Concluding remarks. Cold lanus balawioides (L.) and B. crenatus Brug. under Spring Harbor Symposium on Quant. Biol. 22: 415- varying conditions of submersion. J. Mar. Biol. 427. Ass. U. K. 32: 107-128. Knight-Jones, E. W. 1953. Laboratory experiments and D. J. Crisp. 1956. Evidence of self-fer- on gregariousness during setting in Balan-us balan- tilization in certain species of barnacles. J. Mar. oides and other barnacles. J. Exp. Biol. 30: 584-598. Biol. Ass. U. K. 35: 631-639. Knox, G. A. 1954. The intertidal flora and fauna of Beauchamp, R. S. A. and P. Ullyott. 1932. Competi- the Chatham Islands. Nature Lond. 174: 871-873. tive relationships between certain species of fresh- Lack, D. 1954. The natural regulation of animal num- water Triclads. J. Ecol. 20: 200-208. bers. Oxford, Clarendon Press. Clark, P. J. and F. C. Evans. 1954. Distance to nearest Lewis, J. R. and H. T. Powell. 1960. Aspects of the neighbor as a measure of spatial relationships in intertidal ecology of rocky shores in Argyll, Scot- populations. Ecology 35: 445-453. land. I. General description of the area. II. The Clench, W. J. 1947. The genera Purpura and Thais distribution of Chthamrnlus stellatus and Balanus in the western Atlantic. Johnsonia 2, No. 23: 61-92. balanoides in Kintyre. Trans. Roy. Soc. Edin. 64: Connell, J. H. 1961. The effects of competition, preda- 45-100. R. H. 1958. Population ecology of some tion by Thais lapil/us, and other factors on natural MacArthur, forests. populations of the barnacle, Balanus balanoides. warblers of northeastern coniferous Ecology Ecol. Mon. 31: 61-104. 39: 599-619. Moore, H. B. 1935. The biology of Balnus balan- Crisp, D. J. 1960. Factors influencing growth-rate in III. The soft Mar. Biol. Ass. U. K. Balanus balanoides. J. Anim. Ecol. 29: 95-116. oides. parts. J. 20: 263-277. Drinnan, R. E. 1957. The winter feeding of the oyster- - . 1936. The biology of Balanus balanoides. V. catcher ostralegus) on the edible (Haematoppus Distribution in the Plymouth area. J. Mar. Biol. cockle (Cardiun edul/c). J. Anim. Ecol. 26: 441-469. Ass. U. K. 20: 701-716. Elton, Charles and R. S. Miller. 1954. The ecological Siegel, S. 1956. Nonparametric statistics. New York, of animal communities: with a practical survey McGraw Hill. scheme of classifying habitats by structural char- Southward, A. J. 1955. On the behavior of barnacles. acters. J. Ecol. 42: 460-496. I. The relation of cirral and other activities to Endean, R., R. Kenny and W. Stephenson. 1956. The temperature. J. Mar. Biol. Ass. U. K. 34: 403-422. ecology and distribution of intertidal organisms on - and D. J. Crisp. 1954. Recent changes in the the rocky shores of the Queensland mainland. Aust. distribution of the intertidal barnacles Chthama/ts J. mar. freshw. Res. 7: 88-146. stellatus Poli and Balanus balanoides L. in the Fischer, E. 1928. Sur la distribution geographique de British Isles. j. Anim. Ecol. 23: 163-177. quelques organismes de rocher, le long des cotes . 1956. Fluctuations in the distribution and de la Manche. Tray. Lab. Mus. Hist. Nat. St.- abundance of intertidal barnacles. J. Mar. Biol. Servan 2: 1-16. Ass. U. K. 35: 211-229.

METABOILIC CHARACTERISTICS OF MOUNTAIN, DESERT AND COASTAL POPULATIONS OF PEROMYSCUS

MARTIN MURIE MIuseumn,of Vertebrate Zoology, University of California, Berkeley

INTRODUCTION bolic rate, body temperature and pelage insula- Because of its rich taxonomic diversity the deer tion were made in order to evaluate the selective mouse, Peromyscuis, has been used for many stud- roles that might be played by the enviromental ies of speciation and natural selection. These have variables: oxygen tension, temperature and arid- accord- focused mainly on the evolutionary implications ity. Many of the data were organized in et al. (1950) of variations in morphology, pelage color, behavior ance with the model of Scholander be- and reproductive biology. Progress along these which formulates the expected relationships lines has been reviewed by Blair (1950). The tween ambient temperature, body temperature, experiments reported here are a contribution to metabolism and insulation. These relationships, the investigation of physiologiCal aspects of evo- in non-laboratory mammals, have also been studied luction within this . Measurements of meta- by Griffin et al. (1953), Hart and Heroux (1953),