The Structure of Diatom Communities in Similar Ecological Conditions

The University of Chicago

The Structure of Diatom Communities in Similar Ecological ConditionsAuthor(s): Ruth PatrickSource: The American Naturalist, Vol. 102, No. 924 (Mar. - Apr., 1968), pp. 173-183Published by: The University of Chicago Press for The American Society of NaturalistsStable URL: http://www.jstor.org/stable/2459084 .

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Vol. 102, No. 924 The American Naturalist March-April, 1968

THE STRUCTURE OF DIATOM COMMUNITIES IN SIMILAR ECOLOGICAL CONDITIONS

RUTH PATRICK

Department of Limnology, Academy of Natural Sciences of Philadelphia, Philadelphia, Pennsylvania 19103

During the last 150 years many people have been interested in diatom systematics, ecology, and distribution. Within the last 60 years considerable interest has arisen in the changes in the diatom floras which are indica- tive of climatic changes or of changes in the nutrient level (Cleve, 1899; Krieger, 1929; Hanna, 1933; Patrick, 1936, 1939, 1943, 1946; Pennington, 1943; Fjerdingstad, 1954). Recent workers have tried to express these changes in more precise ways. Nygaard (1949) and Foged (1954) have suggested that the changes in ratios of Pennales to Centrales might be used to indicate changes in the nutrient level of the water. Patrick and others (Patrick, Hohn, and Wallace, 1954; Patrick and Hohn, 1956; Pat- rick, 1963, 1964) has shown that the structure of a diatom community simulates a log-normal curve, and the structure of a large sample of the community can be expressed by a truncated log-normal curve. If the structure of the community changes, the structure of the curve is altered. Margalef (1958) has expressed the structure of phytoplankton communities in terms of diversity indices. More recently, he has used pigments in phytoplankton as a diversity index.

The purpose of this series of experiments was to determine under con- trolled conditions how various environmental factors might affect the structure of a natural community. Since no one has been able to grow diatom communities of a hundred or more species in strict laboratory conditions, semicontrolled natural conditions were set up.

Our first problem was to determine the degree and kind of variability in the structure of the community that one might expect under very similar ecological conditions; second, to determine which were the relative factors, such as invasion rate, species pool, and size of area, in maintaining a diversified community; and third, how the change in amount or quality of some physical or chemical factor would affect the structure of the community. This paper concerns itself with the similarities and differences among eight communities in 1965 and among four communities in 1966 set up under steady-state conditions which were as similar as possible.

METHODS AND PROCEDURES

In order to establish these natural communities of diatoms, part of the flow of Darby Creek, Pennsylvania, was diverted into a shallow pond and

173



174 THE AMERICAN NATURALIST

water from the pond was pumped into a small children's swimming pool in which the water was continually circulated. The pumps leading to the experimental boxes were placed in a circle in the center of the swimming pool. This was done to assure that the diatoms and water coming to each box would be as similar as possible. The water for each box was pumped into a mixing jar and from the jar through the experimental boxes. The rate of flow most suitable for diatom growth was found to be about 600 liters per hour; the water had only one pass through each box. The boxes were 1 X 2 inches in cross-section and 18 inches long. Four 1 X 3-inch glass slides were placed in each box with their length parallel to the direc- tion of flow. This positioning of slides has been found in previous experiments to be most suitable for diatom growth.

In this manner four similar slides would be obtainable for results from each experiment. Preliminary studies showed that the second, third, and fourth slides developed very similar communities. The slide in the first position, due to the variation in flow patterns, produced less reproducible results.

The slides were left in each box for two weeks. Previous experiments (Patrick et al., 1954; and unpublished work) have shown that this is usually the best time interval for diatoms to settle and grow on the slides and to produce a community characteristic of the natural stream.

A temperature probe which was hooked to a continuous recorder was placed in each box. The pH was continually monitored on the flow from each box. As the pH continuous-recording probes were found to drift at times in an unpredictable manner, spot checks by colorimetric methods were frequently made.

RESULTS AND CONCLUSIONS

The diatom communities which developed in each of the boxes exposed at the same time were very similar. As seen in Table 1, the structures of truncated curves developed from each of the communities were very similar. Also, the Shannon-Weaver diversity indices showed little variation.

When one examines the species lists of diatoms composing the communities, the number of taxa observed in the various communities are very similar (Tables 2 and 3). Sixty-one of the taxa were common to all communities in 1965 study. Of those species not common to all communities, 70%o to 80% of these were represented by four specimens or less, in the sample of each community which averaged 4,509 specimens. The species not common to all communities composed about 4.5%o of all the specimens in the community. Thus, one could predict 95%o of the time the group of species a specimen would probably be in.

In the 1966 studies, 68 species were common to the four communities studied. Of those not common, 67%o to 72%o were represented by less than four specimens in communities which averaged 14,226 specimens. The species which were not common to all communities composed 1%o to 2%o of all the specimens counted in each community. Thus, one could probably



DIATOM COMMUNITIES 175

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TABLE 2 DIATOM COMMUNITIES IN BOXES, 1965

NUMBERS OF INDIVIDUALS

Box Box Box Box Box Box Box Box SPECIES 8 7 6 5 4 3 2 1

Nitzschia frustulum v. perminuta... 1,446 1,570 726 867 984 699 1,070 1,224 Synedra parasitica v. subconstricta.. 456 455 168 168 536 138 265 244 Navicula cryptocephala . ....... 450 455 141 210 604 161 435 262 Cyclotella stelligera. ............. . 330 295 162 126 200 159 305 248 Navicula minima. . 318 305 201 186 212 135 48 140 N. secrela v. apiculata . ....... 306 206 59 99 256 162 335 114 Nitzschia plea. .270 225 132 90 340 120 265 232 N. frustulum ......................... 162 325 120 194 160 126 155 112 Navicula luzonensis. . 132 78 46 51 81 36 54 50 Nitzschia frustulum v. indica..... . 126 180 71 43 136 81 124 87 Melosira variants. . 118 140 57 80 72 26 180 72 Nitzschia amphibia. . 93 95 63 65 87 33 88 76 Achnanthes lanceolata.......... . 75 275 123 105 126 177 165 180 Stephanodiscus hantzschii. . 74 59 33 51 80 75 70 75 Navicula lanceolata. . . 69 245 81 144 240 100 180 200 N. viridula. ..... . 68 72 36 47 72 42 53 65 Rhoicosphenia curvata v. minor . 61 121 84 59 54 70 75 91 Navicula minima v. atomoides. 59 47 11 14 10 8 17 14 N. pelliculosa. 54 19 15 25 7 10 95 10 Melosira granulate v. angustissima. 54 73 28 40 58 44 37 40 Navicula seminulum. . 52 36 93 111 45 19 155 124 N. gregaria. . 40 34 10 66 16 17 11 20 Nitzschia capitellata . ........ 40 16 11 10 1 * . ... Achnanthes subhudsonis v. kraeuselii 39 51 26 24 26 15 15 35 A. minutissima. .35 61 40 29 61 36 44 70 Nitzschia diserta. .35 53 35 28 46 27 10 10 Amphora ovalis v. pediculus . .... 33 53 43 40 28 23 41 45 Cymbella tumida . ..... .... 29 95 39 57 23 44 88 61 Synedra parasitica. ............. . 24 42 24 33 57 24 24 45 Cymbella ventricosa. .. . 21 27 7 9 18 13 10 20 Navicula paucivisitata . ....... 20 12 2 7 5 9 10 5 Nitzschia kutzingiana. . 19 70 54 38 34 10 19 12 Gomphonema parvulum. .. . 18 66 39 36 27 34 49 45 Rhoicosphenia curvata. .......... . 18 22 39 56 14 9 19 21 Synedra ulna........ 18 36 11 7 35 16 57 19 Surirella angustata . ........ 17 11 5 4 18 9 11 12 Synedra ulna v. danica. .. . 17 37 8 12 24 10 26 15 Navicula pupula. . 17 27 8 11 22 16 10 15 Achnanthes biporoma . .16 32 20 13 11 25 20 11 Stephanodiscus astraea v. minutula. 16 21 11 13 19 20 10 11 Navicula germainii... . 13 19 9 8 18 17 7 18 Denticula elegans. . . 12 4 4 3 3 4 5 ... Gomphonema sphaerophorum ...... 11 40 23 30 17 13 27 14 Synedra rumpens. . 11 13 10 * 7 9 13 12 S. vaucheriae. .... 11 14 9 8 13 17 39 11 Cocconeis placentula v. euglypta.. 10 5 5 4 9 11 9 8 Navicula menisculus........... . 10 5 5 11 * . - ... Nitzschia linearis . ......... 10 18 15 9 4 2 8 8 Stephanodiscus invisitatus . ..... 10 22 10 11 17 17 6 11 Amphora ovalis. .9 16 2 4 8 16 9 9 Cymbella sinuata. . 9 5 2 7 3 3 4 ... Gyrosigma wormleyii. . 9 5 7 6 16 19 9 10 Nitzschia fonticola. 9 6 5 . . - * ... N. bacata..9 7 12 2 5 10 ... ... Synedra rumpens v. meneghiniana. 9 17 6 15 25 16 37 17 Cyclotella meneghiniana small...... 8 4 ... ... ... ... ... ... Nitzschia gracilis v. minor . . 8 10 5 4 10 * 3 14 N. frustulum v. subsalina ......... 7 10 15 18 11 5 18 34 N. subtilis... 7 16 6 10 8 40 5 ... Cymbella affinis. .6 3 1 * 1 12 2 3 Cocconeis placentula v. lineata. 6 13 8 8 8 10 4 10




TABLE 2 (continued)



Melosira italica v. valida. .... 6 1 5 3 ...... Navicula cryptocephala v. veneta. 6 6 2 2 1 1 4 5 7 Cymbella turgida.......... 5 8 9 5 9 7 8 15 Fragilaria intermedia. ............ 5 5 1 8 .. .. .. .. Gomphonema angustatum v. obesa. 5 1 6 6 5 4 5 1 0 1 0 G. angustatum v. producta. ..5 4 3 9 .. 5 1 3 G. longiceps v. subclavata. ..5 9 2 5 5 5 * 10 Meridion circular. 5 4 7 2 6 3 6 8 Melosira ambigua....... 5 ................ 3 Nitzschia acicularis. ............. 5 .. 8 5 4 5 ... ,Synedra rumpens v. familiaris. 5 37 5 8 27 12 1 1 17 Cyclotella meneghiniana. .......4 8 3 4 5 4 9 1 0 Gyrosigma spencerii. ..........4 2 2 5 5 5 3 2 Fragilaria construens v. venter. 3 ... .. ..... 2 .. .. Gomphonema gracile. 3 1 0 1. 0 2 .... 9 Navicula cincta .......... 3 2 1 3 1 . . N. gracilis fo. minor.3 .. .... . . Navicula decussis. .....3 2 2 3 .. 5 1 3 N. pupula v. capitata. 3 1 0 1 4 1 1 3 N. symmetrica.3.. 1 . ... 1 Nitzschia dissipate v. media . ... 3 4 3 1 5 5 3 N. tryblionella v. debilis. ....3 1 .. 1 2 2 2 1 N. 3igmodea.3 .. 2 .. 4 2 .. Anomoeoneis exilis......... 2 .. 1 1 .. .. .. Caloneis hyalina........2 2 2 7 6 3 3 6 Diatoma vulgare...2 ..... 2........ Eunotia pectinalis v. minor. 2 1 .. .. 1 .. 3 1 Fragilaria leptostauron. .....2 3 2. . .- 4 3 3 Gomphonema constrictum. .....2 .. 1 2 4 4 1 .

G. intricatum v. pumila. ......2 1 0 6 5 8 1 0 7 1 Navicula hungarica v. capitata. 2 5 2 4 3 5 3 1 1 N. protracta....2 3.. ...... .. .. ~Synedra acus v. angustissima .... 2 .. .. 1 1 1 5 1 Bacillaria paradoxa. ............. 1 .. 2....... 5 1 Cyclotella kutzingiana.1 1.. . .... . . Cymbella triangulum.1...... .... . . . . Cocconeis sp.1......... . . . Caloneis bacillum.1 3 3 3 1 2 2 ... Fragilaria bicapitata.1.... .... . . . . Frustulia vulgaris.1 .. .. 2 1 2 .. 2 Gomphonema carolinense...... 1 1 3 1 1 1 3 G. sp. [MH IV Ridley].1..... . 2 1. 1 . . Navicula capitata v. hungarica..1 1 .. 3 2 2 2 4 N. contenta f. biceps.1....1 2 2 4 2 ... 1 N. cincta v. rostrata.1 .. .. .. 1 1 .. .. .. N. americana.1........ .1... . . Nitzschia hungarica.1..1... 2.... N. sinuata v. tabularia.1......1 .

N. confinis.1 5 ...... ... 5

Synedra puichella v. lacerata. . 1 .1 .. .. 3 6 3 1 Surirella ovata.1 ..3 6 6 10 10 5 5 Achnanthes cleveii.. ..2 1 ...... .. .. A mphora submontana. . .....1 .. 2 5 3 3 5 Caloneis silicula v. ventricosa. . .3 2 1 2 .. 6 ... Eunotia lunaris. . ..2.... 1...... E. tenetta ........ .1... . 1 1.... .. Fragilaria pinnata. . ....3 .. 2 .... .. .. Gyrosigma scaiproides. . ..1 ........ Gomphonema sparsistriata. ... ............1 ..... Meridion circular v. constricts.. ... 3.......... 1 Navicula tenera.. .3........... 2 N. omissa.. . . .1........ .. ..




TABLE 2 (continued)



N. vetai.14 1 1 .. .. N. m.tica.. 1...... N. sp. [LL 30].. 1.... ...... 1 2 N. mutica v. cohnii......... ............ Nitzschia brevissima........ . 1 . . 1 .. 2 ..

N. frequens... 1~~........ Achnanthes pinnata...........4 .. .... .. .. A. lanceolata v. fossilis. ......... .. ... 1 .. .... .. .. A. exigua v. heterovalvata. ....... .. .. 2 2 1 1 Amphora veneta....*...... . 1 ... 3 .. .. .. Cocconeis placentula. .. ... 3 .......... Gomphonema afn.1 4 1 3 3 ... G. afflne v.insigne.......3 2 2 ...... Achnanthes deflexa......... .. .. .. . 1 .. .. .. .. A. clevei v. rostrata ........ .. .... 1 .... . . . 1 Cyclotella aliquantula. .. .. .. 3 3 .. .. 5 Fragilaria virescens v. cla'vata'' . . . . . . 1 .. .. .. .. Navicula carminata. ...... ...2 ...... N. texana........... .. 1 ........ N. sp. [photo 157] ... . .1 .. .. .. .. N. pygmaea.......... .... .. 1 ........ N. convergens........ .. 1 .... N. dicephala v. elginensis. ... .. ..1 .. .. .. .. Cymbella naviculiformis. ...... .. ..... 1 .. .. 1 Diatoma vulgare v. producta.... .. .... . . . . 1 .. .. .. Fragilaria brevistriata v. inflata ...... .. .... 1 .. .. .. Hantzschia amphioxys. ...........1 1 ..... Melosira italica. ..... ........5 17 6 3 Navicula integra....... .... 1...... N. wittrockii... ..........1 2 1. N. pupula v. rectangularis..... ..... 1 .. .. 3 N. notha. ........... 2 .... 1 Surirella ovata v. subsalina . . ..... .. .. .... 1 1 3 1 S. tenera v. nervosa. . . 3 .. 3 2 1 3 S. ovata v. pinnata..... ......2 3 ...... Caloneis lewisii.... ..... 1 .

Gomphonema acuminatum. . . . ... ... 1 ..... Navicula pupula v. mutata. ... ... ...... 1 .. .. Navicula paratunkae.... ..... 4 .. 3 N. subtilissima ............... ......1 1 ... N. asymbasia.......... ... 2 ..... Nitzschia sp. [11.11~. 8] ...........5.. Synedra ulna v. oxyrhynchus. ..... ... .. ..... 1 .. .. Gomphonema acuminatum v.

coronatum.... ..:II,,,-IIII .. .. ...... ..1 ... Melosira italica v. tenuissima. ..... .. .. ........ ... 2 6 Navicula protracted. .............. .. .. ...... ..1 ... N. gracilis v. schizonemoides. ... ... ...1.... . Nitzschia intermedia. . . . . ....... 2 6 NV. tryblionella v. victories. ..... .. .. ...... ... ...I Pinnularia molaris. .............. 1 1 P. braunii v. amphicephala. ...... ......... ... 1 Synedra minuscule. .................. 1 S. nana.......... ... 8 A chnanthes linearis............ ... .

Navicula canalis. ............... 1 N. exigua v. capitata. ........... ... .. 1 Nitzschia sigmoidea ... .. .......... ... 4 N. sigma. . . . . . 1 Neidium sp...... ... .......... 1




TABLE 3 DIATOM COMMUNITIES FOUND IN BOXES, 1966

NUMBER OF INDIVIDUALS

SPECIES B-6-3 B-7-2 B-8-3 B-5-3

Fragilaria crotonensis v. oregona. 5,295 3,032 3,552 5,580 Navicula luzonensis. 495 184 300 - 372 N. minima.105 272 660 360 N. secreta v. apiculata .495 408 792 648 Nitzschia amphibia.294 147 432 480 N. frustulum v. subsalina. 4,365 124 4,196 4,020 N. frustulum v. perminuta. 55 32 276 1,392 N. pal e a.1,050 640 984 1,188 N. tropical. 1,410 2,960 768 936 Synedra delicatula "type".112 192 240 276 Synedra una. 99 33 66 117 Synedra parasitica v. subconstricta 100 82 86 101 Navicula seminulum. 360 20 41 33 Nitzschia kutzingiana. 106 272 50 564 N. frustulum. 164 33 23 33 Stephanodiscus invisitatus. 176 110 176 105 Achnanthes lanceolata. . 51 36 66 65 Melosira varians.96 33 106 206 Navicula cryptocephala. 94 62 92 108 Nitzschia diserta. 61 67 25 45 Achnanthes minutissima. 34 24 34 26 Cyclotella stelligera.27 20 34 34 Cymbella tumida. 26 33 43 35 Gomphonema parvuum. 34 23 60 41 Melosira granulate v. angustissima 33 17 38 25 Navicula lanceolata. 32 38 41 23 N. viridula.40 20 49 41 Nitzschia frustulum v. indica .40 36 17 60 Rhoicosphenia curvata.28 19 25 19 Surirella angusta.25 11 21 17 Synedra parasitica. 33 17 23 26 S. rumpens v. familiaris. 34 * 33 Stephanodiscus hantzschii.26 26 20 33 Achnanthes subhudsonis v. kraeuselii 18 19 6 13 A. exigua v. heterovalvata.a 5 .. 1 1 Amphora ovalis. 5 5 9 8 A. ovalis v. pediculus. 24 9 2 14 A. veneta. 5 ... 4 Cocconeis placentula v. euglypta 6 * ... 4 C. placentula v. lineata. 17 10 33 14 Cyclotella florida .11 2 2 4 C. aliquantula.q 5 Cymbella turgid. 10 2 18 2 C. ventricosa.13 11 11 17 C. sinuata. 5 8 5 7 Caloneis bacillus. 9 2 3 5 Diatoma vulgare v. brevis. e5 * . 10 18 Denticula elegans.5 6 7 4 Eunotia lunaris. 4 * ... Frustulia vulgaris. 4 2 ... 1 Fragilaria leptostauron. 5 3 5 4 F. construens. 9 . 2 5 Gyrosigma wormleyii.18 9 10 19 Gomphonema angustata v. obesa 9 10 17 17 G. affne. 9 .. 9 4 G. angustata v. producta.9 9 8 9 G. sp. [MH Ridley]. 5 10 10 G. intricatum v. pumima 5 ... 5 8 G. commutatum. 4 1 - Melosira italica v. valida. 10 21 11 3 Meridion circular .9 2 9 8 Navicula paucivisitata.10 17 5 8 N. hungarica. 9 ... 5




TABLE 3 (continued)


SPECIES B-6-3 B-7-2 B-8-3 B-5-3

N. sp. [RLD #4].20 7 11 N.\ pupula ...... ... ........................ 11 4 22 10 N. menisculus.18 9 3 17 N. pelliculosa.20 75 17 65 N. germainii.17 20 23 19 N. gregaria.9 19 4 14 N. pygmaea.5 ... ... ... N. mutica v. cohni9 4 ... 1 N. capitata v. hungarica................. 8 5 5 6 N. biconica.10 *-- 20 27 N. minima v. atomoides................. 5 10 ... 1 N. mutica.4 1 3 9 Nitzschia tryblionella v. debilis . 4 4 ... 2 N. subtilisi1 ...1 2 N. hungarica.7 3 4 15 N. bacata4 ... ... ... N. dissipate v. media.5 10 2 10 Rhoicosphenia curvata v. minor. 13 4 17 25 Surirella ovata.17 17 12 14 S. ovata v. sana.8 9 S. ovata v. pinnata.4 * - .* 3 Synedra rumpens v. meneghiniana. 11 37 15 24 S. vaucheriae.10 5 10 10 S. pulchella v. lacerata... 9 10 11 35 Stephanodiscus astraea v. minutula. 9 11 10 8 Achnanthes biporoma.2 4 4 2 Anomoeoneis exilis.2 5 ... 4 Amphora submontana.................... 1 2 2 Cocconeis placentula..................... 1 ... ... Cymbella naviculiformis. . 1 C. affinis. 2 2 ... 2 Caloneis hyalina ... ... Diatoma vulgare.3 5 6 Eunotia exigua. . 2 * - ... Fragilaria virescens. ... .3 .. ... Frustulia rhomboides v. crassinervia. 1 * - ... Gyrosigma spencerii.2 * 5 9 G. scalproides .....1 Gomphonema carolinense. 1 * . 3 G. constrictum.............. 2 3 8 4 G. affine v. insigne.............1... Navicula wittrockii. .......... 1 N. schroeteri v. escambia ... 31 N. gracilis.......... 2 1 1 5 N. tenera.1 ... 1 3 N. exigua v. capitata...... 1 N. cryptocephala v. veneta .....3... N. sp. [NAR 2]... 3 5 3 N. decussis.3 2 ... 8 N. americana. 1 N. accomoda..1 ... ... ... N. paratunkae........ 1 1 ... ... Nitzschia frequens . 2 1 ... 4 N. capitellata......... 2 10 2 N. acicularis............. 1 17 1 Opephora martin ...y......1 Pinnularia braunii v. amphicephala . ..... 2 ... ... 1 P. mesolepta... ...... .. 1 ... - ... Meridion circular v. constrict. 2 4 . 4 Navicula pupula v. capitata . 3 .. ... Achnanthes clevei v. rostrata....... * . 1 * Cymatopleura solea.... 1 * . 1 Cyclotella meneghiniana.... 2 2 5 Cymbella scotica. . 4




TABLE 3 (continued)


SPECIES B-6-3 B-7-2 B-8-3 B-5-3

Eunotia polydentula v. perpusilla ......... ... 1 * ... E. tenella...... 4 ... 1 Fragilaria capucina v. mesolepta... 1 3 4 F. pinnata. ... 1 1 Gomphonema longiceps v. subclavata* 4 .11 Navicula symmetrica 3............ 3 * ... N. dicephala.**. 1 2 1 N. tripunctata v. schizonemoides.... 9 ... ... N. protracta ..................*- 1 1 * N. convergens.... 4 2 2 N. atomus ... ..... .. 5... N. contenta f. biceps....... 2 1 5 Nitzschia cnfis... 17 1 N. gracilis v. minor ..................... ... 8 * ... N. sigmoidea.... 10 N. tarda....... 3 ... N. Iinearis.... 1 ... 17 N. stagnorum.... 1 ... .. N. constrict v. subconstricta....... * . 1 N. tryblionella v. levidensis ....... 1 N. sigma.... . 1 1 . Pinnularia subcapitata .....* 4 Synedra rumpens.. * 10 * ... S. ulna v. danica.. 5 ... 24 Surirella tenera v. nervosa... 2 Achnanthes hungarica . ... ... 3 ... Caloneis silicula v. truncata ....... .... . .. ... 3 1 Gomphonema braziliense.... ... 1 2 G. sparsistriata.... ....... 1 Navicula graciloides. ... ... 1 1 N. cuspidata. ... ... 1 N. pupula v. minor.... ... 2 Nitzschia sinuata v. tabellaria ........... ... ... 1 1 N. brevissima.... ... 1 Pinnularia borealis. Stauroneis smithii....................... ... ... 1 Synedra ulna v. impressa f. contract. 76 21 69 314 S. rumpens v. scotica.... ... 5 40 Surirella sp. [SW 6]. ... ... 1 1 ... Achnanthes pinnata. ... ... ... 2 Bacillaria paradoxa. ... ... ... 3 Cocconeis diminuta .. ... ... ... 1 Eunotia pectinalis v. minor. ... ... ... 1 Hantzschia amphioxys. ............. ... * * 2 Melosira italica v. tenuissima .... ... ... ... 9 Meridion circular v. constrict ......... . ... ... ... 5 Navicula pupula v. mutata. ... ... ... 2 N. canalis..... ... ... 1 N. rhynchocephala....1... ... 1 N. ventralis... ... ... ... 1 Nitzschia intermedia....... ... ... ... 1 Pinnularia obscura.......... ... ... 2 P. interrupt. ... ... ... 1

predict 98% of the time that a specimen would belong in one of the species common to all four communities studied.

When one examines each community, the patterns of distributions of the species among the various taxa will be found to be very familiar. This is also indicated by the similarity of the diversity indices.




These results indicate that, under very similar ecological conditions, steady-state communities with great similarity can be produced. Their variation is mainly due to the species represented by very small popula- tions which have invaded, but in most cases are probably not established in, the community. Other studies (Patrick, 1967) have shown that, if the invasion rate is cut down, the numbers of these rare species are greatly reduced. Thus, it would appear that the high invasion rate, while it enhances the diversity of a community, is probably responsible for its small but non- predictable variation. Whether these rare species are always rare or are common in other communities is yet to be determined. The possible im- portance of these rare species in a community has been previously dis- cussed (Patrick, 1967).

SUMMARY

These experiments were designed to determine the degree and kind of variability in the structure of the community that one might expect under very similar ecological conditions.

The results of these experiments show that 95.5% to 98.0% of the specimens composed the same species in the eight communities. About 5%o of the specimens were in the remaining species in one series of experiments and 1% to 2%o of the species in the second series. The Shannon-Weaver diversity indices and the structures of the truncated log-normal curves representing the communities in a given series were also very similar.

ACKNOWLEDGMENTS

This work was accomplished with the aid of the U.S. Public Health grant WP-00475, for which the author is deeply grateful. She also wishes to express her thanks to Dr. Robert MacArthur for his constructive advice; to Miss Noma Ann Roberts, Mr. John Coles, Mr. Roger Daum, and Mr. Jesse Weinberger for their assistance in carrying out the research program; and to Dr. Jack McCormick, director of the Waterloo Mills Field Research Station of the Academy of Natural Sciences, where the research program was carried out.

LITERATURE CITED

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Fjerdingstad, E. 1954. The subfossil algal flora of the lake B0lling S0 and its limno- logical interpretation. Kongelige Danske Videnskabernes Selskab, Biol. Skrifter 7(6): 1-56.

Foged, N. 1954. On the diatom flora of some Funen lakes. Folia Limnol. Scand. No. 6: 1-75.

Hanna, G. D. 1933. Diatoms of the Florida peat deposits, p. 65-120. In Florida State Geol. Surv. 23d-24th Annu. Rep. 1930-1932.

Krieger, W. 1929. Algologisch-monographische Untersuchungen uber das Hochmoor am Diebelsee. Beitr. zur Naturdenkmalpflege 13(2): 233-300.




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The Structure of Diatom Communities in Similar Ecological Conditions