January, 1954 NOTES AND COMMENT 97 rating mechanism can be introduced to permit a stable more complex function such as the second power term point on the left side of the hump. suggested by Hutchinson (1947) for social animals. The absence of a stable point on the left side of the In man's evolution, we have apparently had continual curve helps to explain why cooperation among organisms shiftingof the stable point to the right as man's coopera- is often overlooked. The importantquestion arises: why tion increased. The great question before us all is not inevitable is cooperation so widely distributed in the living king- how to increase cooperation or how to avoid the disoperationbut what formof disoperation will ultimately doms even though populations are rarely found in the determine our stable point and at what density will this correspondingto predominantlycooperative density range take place. interaction? It is suggested that the presence of coopera- tion in a species has the functionof raising the density REFERENCES of the stable point thus giving a species an edge in com- Allee, W. C. 1931. Animal aggregations. A study in petition with other species. In terms of the equation general sociology. Univ. of Chicago Press, Chicago. above, the cooperative term illustrated in Figure 3B 431 p. when added to the remainder of the equation in Figure . 1940. Concerning the origin of sociality in 3A produces a curve in Figure 2 whose stable point animals. Scientia, 1940: 154-160. is shifted to the right. Thus, other things being equal, 1951. Cooperation among animals with hu- cooperative animals have higher densities in their stable man implications. Schuman, New York. 233 p. population levels than non-cooperativeanimals. But in all Allee, W. C., A. E. Emerson, 0. Park, T. Park, and cases, the stable point is characterized by an excess of K. P. Schmidt. 1949. Principles of animal ecology. disoperative competition over cooperation. The intra- Saunders, Phila. 837 p. specificcooperative effectabove may be either linear or a Gause, G. F. 1935. Verifications experimentales de la theorie mathematique de la lutte pour la vie. Paris. Actualites scientifiques et industrielles. 277 p. Holmes, S. J. 1948. The principle of stability as a FCOOPERATION cause of evolution. A review of some theories. TERMS Quart. Rev. Biol. 23: 324-332. b. Hutchinson, G. E. 1947. A note on the theory of com- petition between two social species. Ecology 28: 319- 321. dN Ludwig, Wilhelm, and Charlotte Boost. 1939. fYber Ndt? o das Wachstum von Protisten Populationen und den allelokatalytischen Effekt. Archiv Protistenkunde A 92: -453-484. DISOPERATION TABLE TERMSa b POINTS Odum, H. T. 1951. The stability of the world stronti- um cycle. Science 114: 407-411. HOWARD T. ODUM W. C. ALLEE - N DEPARTMENT OF BIOLOGY, FiG. 3. Survival curve and components for a species UNIVERSITY OF FLORIDA, with a survival rate that is positive at minimumdensities. GAINESVILLE, FLORIDA

AN EARLY VIEW OF THE RELATION BETWEEN PLANT DISTRIBUTION AND ENVIRONMENTAL FACTORS A featureof ecologyin recentyears has beenthe drift a series of conclusions concerning the factors controlling away from mono-climaxconcepts of vegetationand plant distribution. Since these anticipate present-day toward a factorial approach, which emphasizes that principles of plant geography and ecology, it may be plant distributionis conditionedby interactionsbetween worthwhile to quote them in full, as follows:- severalenvironmental factors capable of independentvari- "I. The principal conditions of vegetable distribution ation (Cain 1947,Major 1951,Billings 1952). Modern should be arranged in the following order; the first- ecologistsmay, therefore,be interestedto learn of a named being of greater sway than those which succeed, parallel situationexisting in Britainover a centuryago. and consequently a small difference in the former op- Duringthe earlypart of the nineteenthcentury a num- erating more change than a great dissimilarity in the ber of articles were publishedascribing differences in latter:-1. Temperature; 2. Moisture; 3. Configuration plantdistribution mainly to singlefactors, such as differ- of surface (chieflywith relation to shelter and exposure); encesin rocksor climate. In an attemptto reconcilethe 4. The mechanical and chemical properties of the sur- variousopinions on thismatter, H. C. Watson published face soil; 5. The mechanical and chemical properties in 1833 a paper entitled"Observations on the Affinities of the subjacent rocks. betweenPlants and subjacentRocks," wherehe stated: "II. The combined influenceof these, with some minor -"It is . . . necessary that all conditions of vegetation conditions, determines the flora and vegetation of coun- distributionbe studiedin connection.He who neglects tries. any, will so far fail in his generalizations."After a "III. As to comparative influence,these conditions are brief illustrationof this pointof view, he proceededto not always in equal ratio or proportion; but, when the 98 NOTES AND COMMENT Ecology,Vol. 35,No. 1 more potent condition or affinityis in its full play, the affected thereby, though the vegetation of small tracts feebler one is less apparent; and vice versa. Thus, when may evidentlybetray it." the temperatureis best suited to any given species, soil is of little moment; but when the temperature barely REFERENCES suffices,then soil may determine even the existence of Billings, W. D. 1952. The environmental complex in the species. relation to plant growth and distribution. Quart. "IV. Comparing these conditions with each other, the Rev. Biol. 27: 251-265. influence of temperature (being less local) is chiefly Cain, S. A. 1947. Characteristics of natural areas and shown in the flora of a country; while other conditions factors in their development. Ecological Monog. 17: (often partial in their sway) may not at all affect the 185-200. flora of a considerable tract, and yet greatly modify its Major, J. 1951. A functional, factorial approach to vegetation; the latter term having referenceto the com- plant ecology. Ecology 32: 392-412. parative prevalence, the formerto the mere existence, of Watson, H. C. 1833. Observations on the affinities the species. between plants and subjacent rocks. The Magazine "V. Comparing one species with another, some are of Natural History 6: 424-427. (This journal was more influenced by one, some by another of the above begun by J. C. Loudon, and is continued today as The conditions. Some, for example, have a wide range of Annals and Magazine of Natural History). temperature,others are indifferentto soil or moisture. EVILLE GORHAM "VI. With regard to subjacent rocks, their influence BOTANY DEPARTMENT, is so frequentlyveiled by the other conditions,that for UNIVERSITY COLLEGE, the most part the flora of a country is not obviously LONDON, ENGLAND

THE OCCURRENCE OF A MAYFLY NYMPH IN BRACKISH WATER

Circumstantial evidence has been available for some 10 parts per thousand. Dissolved oxygen ranged from a time indicating that the nymphs of Callibaetis floridanus minimumof 4.62 to a high of 7.02 parts per million. Banks may inhabit brackish water (Berner 1950) ; how- The nymphs were found on the leaves of the aquatic ever, no salinity determinationswere made to substanti- plants Potomogeton pectinatus L. and Vallisneria neo- ate this evidence. In 1949, the senior investigator col- tropicalis M.-V. No other mayflyspecies were encoun- lected nymphs of this species of mayflyfrom around the tered although nymphs of the damselflies Ischnura ram- roots of the red mangrove, Rhizophora mangle L., south burii (Selys), Enallagma durum (Hagen) and E. pol- of Homestead, Florida. Because of the flooded conditions lutum (Hagen), larvae of Tendipedidae and Heleidae, in the Florida Everglades, the water around the tree at and the water striders Trochopus plumbers (Uhler), that time was definitelyfresh. Mesovelia mulsanti White, Trepobates floridensisDrake The junior investigator, while studying the insect and Harris, and Rheumatobates ten *pes Meinert were fauna of Homosassa Springs, which empties into the found associated with the mayflynymphs. Gulf of Mexico north of Tampa, Florida, found that the nymphs of this species were present in water which ap- REFERENCE peared to be definitelybrackish. Further investigation Berner,Lewis. 1950. -The mayfliesof Florida. Univ. and analysis of the water proved that the insect can of Fla. Studies, Biol. Sci. Series 4: 1-267. tolerate rather high salinities. LEWIS BERNER The collecting stations from which the nymphs came WILLIAM C. SLOAN' are approximately one mile inland from the Gulf and DEPARTMENT OF BIOLOGY, are subject to tidal fluctuations. At low tide, chloride UNIVERSITY OF FLORIDA, values in parts per thousand at the collecting sites were GAINESVILLE. FLORIDA 2.13 (3.92 total salinity) and at three hours past high tide 4.43 (8.15 total salinity). It is estimated that at I The studies of the junior investigator were aided by a contract between the Office of Naval Research, Department of the Navy, the peak of high tide the salinity must be somewhere near and the University of Florida (NR 163-106).