Author Institution: Le Moyne, College, Memphis, Tenn

Gibson, Walter William

The Ohio Journal of Science

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AN ECOLOGICAL STUDY OF THE SPIDERS OF A RIVER-TERRACE FOREST IN WESTERN TENNESSEE1WALTER WILLIAM GIBSON,Le Moyne College,Memphis, Term.Studies dealing with the ecology of spiders are of two main types: (1) thosewhich give ecological consideration to the entire animal population of the habitatand the spiders incidentally as members of that population, Adams (1915), Weese(1924), Blake (1926), and (2) those which give intensive consideration to theecology of spiders exclusively of a particular habitat, Elliott (1930), Truman (1942).This study is of the latter nature.PROCEDURE AND SCOPE OF WORKSpiders were collected continuously every ten to fourteen days over a periodof twenty-two months in a River-Terrace forest located along the secondary terraceof the Wolf river, a tributary of the Mississippi, in the region of Memphis, Ten-nessee. The land adjacent to the Mississippi River and its tributaries is char-acterized by typical swamp forest vegetation. As the land rises from the floodplain level, a secondary terrace forest is apparent, composed essentially of anOak-Gum community along the lowland and Oak-Hickory along the upland,drier portion. Collections were made by beating branches of trees and shrubbery,sweeping herbage, sifting leaves and upper soil layer and removing the bark andwood from trees, stumps and logs. Species were identified by Dr. W. M. Barrows,of the Ohio State University.THE SPIDER POPULATION OF THE RIVER-TERRACE FORESTSpecies inhabiting the forest are listed alphabetically and numbered con-secutively in order that they may be referred to by their numerical position in thetable which appears below. The names given to the spiders are those, as far aspossible, listed in the synonymic Index-Catalogue of Spiders of North, Centraland South America (Petrunkevitch).1. Acacesia foliata Hentz.2. Agassa cyaena Hentz.3. Agelena americana Keyserling.4. Agelena emertoni Chamberlin & Ivie.5. Agelena naevia Walckenaer.6. Agroeca sp. ?7. Amourobius americana Keyserling.8. Antistea sp.?9. Anyphaena fraterna Banks.10. Anyphaena saltibunda Hentz.11. A raneus arenatus Walckenaer.12. Araneus benjaminus Walckenaer.13. Araneus marmoreus Clerck.14. Araneus miniatus Walckenaer.15. Araneus stellatus Walckenaer.16. Araneus thaddeus Hentz.17. Araneus tusus Petrunkevitch.18. Arctosa sp.?19. Argiope aurantia Lucas.20. Argiope trifasciata Forskal.21. Argyrodes trigonium Hentz.22. Argyrodes trituberculatus Becker.23. Ariadne bicolor Hentz.24. Aysha gracilis Hentz.25. Bathyphantes tnicaria Emerton.26. Callilepis imbecilla Keyserling.27. Castaneira longipalpis Hentz.28. Castaneira stupkai Barrows.29. Ceraticelus fissiceps Cambridge.30. Ceraticelus micropalpis Emerton.1A Digest for publication of Dissertation presented in Partial fulfillment of the Require-ments for the Degree of Doctor of Philosophy in the Graduate School of The Ohio StateUniversity.38No. 1 AN ECOLOGICAL STUDY OF SPIDERS 3931. Ceraticelus minutus Emerton.32. Ceratinopsis sp. ?33. Cesonia bilineata Hentz.34. Chiracanthium inclusum Hentz.35. Cicurina itasca Chamberlin & Ivie.36. Clubiona pattens Hentz.37. Crustulina guttata Wider.38. Cyclosa conica Pallas.39. Dendryphantes (P) audax Hentz.40. Dendryphantes (M) capitatus Hentz.41. Dendryphantes insignarius Koch.42. Dendryphantes (P) whitmanii Pecham.43. Dictyna armata Banks.44. Dictyna bicornis Emerton.45. Dictyna cruciata Emerton.46. Dictyna frondea Emerton.47. Dictyna sublata Hentz.48. Dictyna foliacea Hentz.49. Dictyna zaba Barrows and Ivie.50. Dipoena nigra Emerton.51. Dolomedes sp.?52. Drassodes sp.?53. Drasyllus aprilinus Banks.54. Drasyllus dixinus Chamberlin.55. Drasyllus fallens Chamberlin.56. Drexelia directa Hentz.57. Ebo latithorax Keyserling.58. Epeira juniperi Emerton.59. Erigone autumnalis Emerton.60. Eperigone maculata Banks.61. Ero (furcatus?) Villers.62. Euryopis funebris Hentz.63. Eustalia anastera Walckenaer.64. Fuentes lineatus Koch.65. Gea heptagon Hentz.66. Gnaphosa bicolor Hentz.67. Hahnia brunnea Emerton.68. Harbrocestum pulex Hentz.69. Hentzia basilica McCook.70. Herpyllus vasifer Walckenaer.71. Hyctia sp.?72. Kaira alba Hentz.73. Lepthyphantes sabulosa Keyserling.74. Leucage venusta Walckenaer.75. Linyphia communis Hentz.76. Linyphia lineata Linnaeus.77. Litopyllus rupicolens Chamberlin.78. Loxosceles (rufescens?) Dufour.79. Lycosa avara Keyserling.80. Lycosa punctulata Hentz.81. Lycosa rabida Walckenaer.82. Maevia vittata Hentz.83. Mangora gibberosa Hentz.84. Mangora placida Hentz.85. Mar pis sa undata DeGeer.86.87,88.89,90.91.92.93.94.95.96.97.98.99.100.101.102.103.104.105.106.107.108.109.110.111.112.113.114.115.116.117.118.119.120.121.122.123.124.125.126.127.128.129.130.131.132.133.134.135.136.137.138.139.Micaria sp. ?Micrathena gracilis Walckenaer.Micrathena reduviana Walckenaer.Microneta cornupalpis Cambridge.Microneta latidens Emerton.Mimetus sp. ?Misumenops asperatus Hentz.Misumenops celer Hentz.Misumenops oblorlgus Keyserling.Oedothorax sp. ?Originates rostratus Emerton.Oxyopes aglossus Chamberlin.Oxyopes salticus Hentz.Pachylomerus sp.?Pardosa nigropalpis Emerton.Pechamia scorpionea Hentz.Pallenes sp. ?Philodromus minutus Banks.Philodromus pernix Blackwell.Phlegra fasciata Hahn.Phrurolithus alarius Hentz.Phrurolithus divinulus Gertsch.Phrurolithus dulcineus Gertsch.Pirata arenicola Emerton.Pirata minutus Emerton.Pisaurina mira Walckenaer.Sergolius variegatus Hentz.Schizocosa crassipes Walckenaer.Scoloderus tuberculifer Cambridge.Sittious cursor Barrows.Synaema parvulum Hentz.Tapinopa bilineata Banks.Tetragnatha laboriosa Hentz.Thanatidius dubius Hentz.Theridion differ ens Emerton.Theridion dulcineum Gertsch & Archer.Theridion frondeum Hentz.Theridion globosum Hentz.Theridion kentuckyense Keyserling.Theridula opulenta Walckenaer.Theridion studio sum Hentz.Theridion waliacii Gertsch & Archer.Thiodina sylvana Hentz.Tmarus (angulatus?) Walckenaer.Tmeticus {asetivalis?)Trachelas tranquillas Hentz.Uloborus americanus Walckenaer.Wala mitrata Hentz.Wala palmarium Hentz.Xysticus ferox Hentz.Xysticus funestus Keyserling.Zelotes hentzi M.S.S. W. M. BarrowsZygoballus bettini Pecham.Zygoballus sexpunctatus Hentz.40 WALTER WILLIAM GIBSON Vol. XLVIIECOLOGY OF THE RIVER-TERRACE FOREST SPIDERSA summary of the findings with reference to ecological factors is given belowin tabular form. Blank spaces in the table indicate insufficient data for thedetermination required. The symbols used in the table are as follows:COLUMN I—Species as indicated by numbers given in the taxonomies listing on pages 38 and 39.A " D " alongside of the number representing the species indicates that the speciescharacteristically inhabits the more moist lowland portion of the forest.COLUMN II—The number of individuals collected of a particular species.COLUMN III—Specific relation of the species to the forest. These determinations are basedupon a comparative study made between species of spiders inhabiting this forest and thoserecorded for vegetational associations such as Oak-Hickory, Beech-Maple, Elm-Maple,Wet and Dry Prairie, etc. Also upon numerous collections made along the margins of theforest, the adjacent fields and meadows and other similar forests of the region. Symbolsused in column III are:R—Species typical of the River-Terrace forest.E—Species usually found along the forest border or in regions where cutting of treeshas resulted in a mixed grassland-forest community.F—Field spiders, those found most often and in greatest numbers in cultivated areas,meadows or grassland.Fo—Species reported for all forests on which data have been compiled and thereforeexhibiting no habitat specificity in this regard.O—Spiders which though present in the River-Terrace forest are more typical ofOak-Hickory.Pw—Species characteristically inhabiting the wet prairie.Pd—Species characteristically inhabiting the dry prairie.Be—Spiders more typical of Beech-Maple and River-Terrace forest.COLUMN IV—Characteristic stratal position of the spider population within the forest duringthe warm part of the year. Symbols used in column IV are:G—Ground stratum.H—Herb stratum.S—Shrub stratum.A—All strata.U—Upper strata (herb-shrub-tree).B—Species found characteristically under or in the crevice of bark.COLUMN V—Approximate hatching periods for the species. (Suggested periods are good onlyfor the vicinity of Memphis, Tennessee.) The determinations were made by comparingyounger and younger stages of various species and by keeping the egg sac of others untilhatching occurred. Though the suggested hatching Deriods are approximations in certaininstances, the list is presented in the hope that it will stimulate further investigation onthe part of those ecologically minded with resulting verification and necessary correction.Symbols: The months are numbered according to their occurrence in the year.E—indicates the first half of the month.M—indicates the mid-portion of the month.L—indicates the last half of the month.COLUMN VI—Period during which species matures. Symbols are the same as in Column V.COLUMN VII—Hibernation stage of the species. In general the determination of the hiberna-tion stage rests upon the mid-winter collection of spiders. Symbols used in ColumnVII are:I—spiders that hibernate in immature or adult form.E—spiders that overwinter in the egg sac as eggs or very young.TABLE II12D34567II161214208213IIIERFFFFoIVHGAAAH?GV9E9E9E9E6MVI7L7M7M7M5EVIIEWWWII891011121314II2613237151812IIIREFo0FoRIVG?AATSSsV6M6M8L8LVI5M5E6L6LVIIiIIIEIN o . 1 AN ECOLOGICAL STUDY OF SPIDERS 41TABLE I—(Continued)42 WALTER WILLIAM GIBSON Vol. X L V I ITHE HABITATThe River-Terrace forest, like the Deciduous forest in general, presents welldefined strata. These are forest floor, herb layer, shrub layer and forest crown.Because of the influence of the forest crown and the absence of conditions suchas exist in associations like arctic tundra and desert, environmental conditions aremore uniform. Habitat situations within the forest, as pertaining to spiders,primarily reflect differences associated with the various vegetational strata fromforest floor to forest crown. It is axiomatic that soil temperatures in general andespecially forest soil temperatures are more stable than the overlying atmospherictemperature. Periodic checks of temperature, light and humidity in the strataof the forest under investigation substantiated the observations made by Weese,Blake and others that the forest floor has the lowest temperature of the stratagenerally during the summer, and highest during the winter. Humidity is greatestand light intensity lowest at the forest floor. The rate of evaporation was notchecked, but it may be assumed that the evaporation rate is least at the ground-leaflayer. Weese (1924) has given proof of this for the Elm-Maple forest which heinvestigated. From the forest floor upward light intensity, temperature andevaporation increases while humidity decreases. Fluctuations in these physicalfactors of the environment occurs least in the ground-leaf layer and most* in theforest crown, the reasons for this have been fully explained by Adams (1915),Weese (1924) and Blake (1926).Spiders inhabiting the ground-leaf layer are species tolerant of little light,comparatively low temperature, a fair degree of moisture and low evaporation.The population of this stratum is the most constant of all the strata except duringthe winter months when migrants characteristic of other situations hibernatein it. This constancy of population is associated with physical factor gradientswhich exist between the ground-leaf layer and the adjacent herb layer. Spiderspassing from one of these strata to the other undergo marked and sometimesvery sharp changes.Similar differences exist with regards to herb, shrub and tree strata but thegradients are not as steep nor as controlling in their effect.The transitional nature of the forest under investigation affords a more variedhabitat than more homogeneous vegetational associations such as Oak-Hickoryor Beech-Maple forests because the River-Terrace Forest gradually changes fromthe more dense humid and shady forest of the lowland to the drier, more openOak-Hickory association of the upland. Also, the presence of prairie vegetation incertain regions of the area adds further to the diversified nature of the habitat.Correlated with these varied biotic and physical features, there is much diversifica-tion in the spider population.DISCUSSIONThe stratal and habitat relations given above are not intended to indicatethat the spiders are limited to the designated situations, but that the particularspecies are found most often and in greatest numbers in the micro-habitat orhabitat suggested. Some of the spiders are apparently tolerant of a wide varietyof conditions and can be found virtually in all situations in substantial numbers.Comparative abundance alone cannot be used as a criterion for determining habitatpreferences,' as the table shows, it often happens that a species characteristicof one habitat is numerically dominant in another; for example, Agelena naevia—>a field form—and Pisaurina mira—a transitional form—are among the mostnumerous in the River-Terrace forest.Physical factors are the dominant forces in the activities of the spiders duringthe winter. The habitat is essentially reduced to a single layer, the ground-leafstratum. In southern Tennessee, however, a few species can be collected fromNo. 1 AN ECOLOGICAL STUDY OF SPIDERS 43the remnant herb layer throughout the winter. As pointed out by Weese (1924),preceding hibernation there is a general downward migration of the spiders butcertain species such as Clubiona pollens and Ariadna bicolor move upward with theadvent of winter and hibernate under the bark of trees. Activity is reduced to aminimum during hibernation except on warm days when certain species move abouton the dead leaves and herbs but even then evidence of predatory activity islacking.The mass hatchings indicated in the table during the late spring and the latesummer result in two population peaks in the population density of the spiderswhen the young hatched at these periods mature. The fact that the hatching periodand time of maturity of the species given above are somewhat earlier than publishedreports in this regard for the same species farther north, and that species reportedas overwintering as eggs or egg-sized spiders in the north are readily collectedfrom one-fourth to one-half grown in the Memphis area indicate the effect ofenvironment on the reproductive and developmental processes of the spiders.SPECIES DIAGNOSTIC OF THE HABITATOnly thirty species were represented by fifty individuals or more in the col-lections. The total number of individuals of these thirty species constitute morethan three-fourths of the 5,090 spiders taken. Among these principal or numeri-cally dominant groups were some more typical of other habitats as the tableshows. However, it is interesting to note that certain of these principal speciesoccur in great abundance in this forest while being very scarce or absent in othervegetational communities studied. Further, according to published reports andinformation gained from collectors, one of the species (Oxyopes aglossus) thoughwidely distributed, seems to be found in large numbers only in this type of habitat.Species of this nature are: Oxyopes aglossus, A nyphaena fraterna, Thiodina sylvana,Mangora placida, Dictyna cruciata, Theridion studiosum and Ebo latithorax. Col-lectively, they are diagnostic of the River-Terrace forest.SUMMARY AND CONCLUSIONAlthough a great variety of species inhabit the forest, a comparatively fewspecies make up the largest part of the total number of individuals collected.One hundred and thirty-nine species of spiders are reported for the forest. Thirtyspecies, or approximately one-fifth of the total number, constitute 4,007 individualsor over three-fourths of the 5,090 individuals collected.Principal species numerically are not always spiders typical of the forest, butmay be forms more characteristic of other situations such as the forest border orfield.Of the spiders whose habitat relations were determined, 46 were typical River-Terrace forest spiders; 24 were forest spiders but more typical of other forests(Beech-Maple, Oak-Hickory, Elm-Ash-Maple, etc.); 33 were transitional formsand 11 were field spiders.Seven species which we consider particularly diagnostic of the River-Terraceforest have been listed.During the warm part of the year vertical distribution of the species is char-acterized by stratal communities. Stratification is associated with the physicalfactors and the vegetation.Species composition of the stratal communities is not constant but showsseasonal variation.Horizontal distribution is largely associated with varying moisture contentof the soil.44 WALTER WILLIAM GIBSON Vol. X L V I IMost of the spiders hibernate as immature forms or adults. Only 14% of thespiders whose hibernation stage was determined overwinter as eggs or egg-sizespiders.Over 90% of the species hibernate in the ground-leaf stratum, thus precedinghibernation there is a general downward migration. Apparently temperature isthe chief factor affecting this vertical shifting.The spiders exhibit two major hatching periods, late spring and late summer.The mass hatchings of late spring and late summer result in two populationpeaks of adults when the spiders hatched at these times have matured.REFERENCES*Adams, C. C. 1915. An Ecological Study of Prairie and Forest Investebrates. Bull. 111.State Lab. Nat. Hist., 11: 33-360.Barrows, W. M. 1918. A List of Ohio Spiders. Ohio Jour. Sci., 18: (8) 297-318.Barrows, W. M. 1940. New and Rare Spiders from the Great Smoky Mountain NationalPark Region. Ohio Jour. Sci., 40: (3) 130-138.*Blake, Irving H. 1926. A Comparison of the Animal Communities of coniferous andDeciduous Forests. 111. Biol. Mono., 10: (4) 7-17.Blake, Irving H. 1931. Further Studies on Deciduous Forest Animal Communities. Ecol.,12: (3) 508-527.Brown, Mary Jane. 1931. Comparative Studies of the Animal Communities of Oak-HickoryForests in Missouri and Oklahoma. Pub. Univ. Okla. Biol. Survey, 3: (2) 23-261.Comstock, J. H. 1940. The Spider Book. Doubleday Doran and Co.*EUiott, Frank R. 1930. An Ecological Study of the Spiders of the Beech-Maple Forest. OhioJour. Sci., 30: (1) 1-22.*Petrunkevitch, A. 1911. A Sysnonymic Index-Catalogue of Spiders of North, Central andSouth America, etc. Amer. Mus. Nat. Hist., Vol. 29.Petrunkevitch, A. 1928. Systema Aranearum. Trans. Conn. Acad. Sci., Vol. 29.Sampson, Homer C. 1930. Succession in the Swamp Forest Formation of Northern Ohio.Ohio Jour. Sci., 30: (5) 340-357.Smith, V. G. 1928. Animal Communities of a Deciduous Forest Succession. Ecol. 9: (4)479-500."Truman, Lee C. 1942. A Taxonomic and Ecologic Study of the Spider Fauna of PresqueIsle. Bull. Pitts. Univ., 38: (2) 404-411.*Weese, A. O. 1924. Animal Ecology of an Illinois Elm-Maple Forest. 111. Biol. Mono.,9: (4) 1-91.•References starred are those specifically cited in the manuscript.

An Ecological Study of the Spiders of a River-Terrace Forest in Western Tennessee

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An Ecological Study of the Spiders of a River-Terrace Forest in Western Tennessee

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