Research methods in ecology

Preface

The present volume is intended as a handbook for investigators and for advanced students of ecology, and not as a text-book of the subject. An elementary text-book covering the same field, but adapted to the needs of undergraduate students, is in preparation. The handbook is essentially an account of the methods used by the author in his studies of the last eight years, during which a serious attempt has been made to discover and to correlate the fundamental points of view in the vast field of vegetation. No endeavor is made to treat any portion of the subject exhaustively, since a discussion of general methods and general principles is of much greater value in the present condition of ecology. The somewhat unequal treatment given the different subjects is due to the fact that it has been found possible to develop some of these more rapidly than others. Finally, it must be constantly kept in mind that ecology is still in a very plastic condition, and in consequence, methods, fundamental principles, and matters of nomenclature and terminology must be approached without prejudice in order that the best possible development of this field may be attained.

Grateful acknowledgment for criticisms and suggestions is made to Professor Doctor Charles E. Bessey and Professor Doctor Roscoe Pound, who have read the text. The author is under especial obligations to Doctor Edith S. Clements for the drawings of leaf types, as well as for reading and criticising the manuscript. Professor Goodwin D. Swezey, Professor of Astronomy in the University of Nebraska, has kindly furnished much material for the determination of the sun's altitude, and consequent light intensities, and has read the section devoted to light. Mr. George A. Loveland, Director of the Nebraska Section of the U. S. Weather Bureau, has contributed many helpful suggestions to the discussion of meteorological instruments. To Nella Schlesinger, Alice Venters, and George L. Fawcett, advanced students in experimental ecology, the author is indebted for many experiments which have been used in the discussion of adjustment and adaptation.

Acknowledgment is also made to the following for various cuts : Henry J. Green, Brooklyn, New York ; Julien P. Friez, Baltimore, Maryland ; C. H. Stocking Co., Chicago, Illinois ; Draper Manufacturing Co., New York city ; Gundlach-Manhattan Optical Co., Rochester, New York; Rochester Optical Co., Rochester, New York; Bausch and Lomb Optical Co., Rochester, New York.

FREDERIC EDWARD CLEMENTS.

The University of Nebraska, May, 1905.

Chapter I. The Foundation of Ecology THE NEED OF A SYSTEM

1. The scope of ecology

2. Ecology and physiology Historical Development

3. Geographical distribution

4. The plant formation

5. Plant succession

6. Ecological phytogeography

7. Experimental ecology

Ecology of the habitat

IT.

9. The evidence from historical development Present Status of Ecology

10. The lack of special training Descriptive ecology The value of floristic Reconnaissance and investigation Resident investigation The dangers of a restricted field Applications of Ecology

16. The subjects touched by ecology

17. Physiology and pathology

19. Taxonomy ....

20. Forestry Physiography Soil physics Zoogeography Sociology

THE ESSENTIALS OF A SYSTEM

25. Cause and effect: habitat and plant

26. The place of function

PAGE

5 6

7 8

9 9

10 11 11 12

15 16

16 17

VI

Chapter II. The Habitat CONCEPT AND ANALYSIS

2.J. Definition of the habitat

28. Factors

Classification of Factors

29. The nature of factors

30. The influence of factors Determination of Factors

31. The need of exact measurement

32. The value of meteorological methods

33. Habitat determination

34. Determinable and efficient differences Instrumentation

35. Methods

36. Method of simple instruments

37. Method of automatic instruments

38. Combined methods ....

PAGE

18 18

19 19

20 20 21 21

22 22

23 23

CONSTRUCTION AND USE OF INSTRUMENTS

39. The selection of instruments Water-content

40. Value of different instruments .

Geotome methods

41. The geotome ....

42. Soil borers ....

Taking samples of soil Weighing Computation ....

46. Time and location of readings

47. Location of readings Depth of samples . .

Check and control instruments

Physical and Physiological Water 50. The availability of soil water Terms .....

Chresard determination under control Chresard readings in the field .

Chresard values of different soils

43- 44- 45-

48. 49-

5*.

53- 54-

25 26

29 30 30

Vll

Records and Results

55. The field record

56. The permanent record

57. Sums and means

58. Curves Humidity

59. Instruments Psychrometers

60. Kinds

61. The sling psychrometer

62. Readings

63. Cog psychrometer

64. Construction and use

65. Hygrometers Psychrographs

66. The Draper psychrograph

67. Placing the instrument

68. Regulating and operating the instrument

69. The weekly visit Humidity Readings and Records

70. The time of readings

71. Place and height

72. Check instruments 7^. Humidity tables

74. Sums, means, and curves

Conversion scale for temperatures

75. Records

PAGE

76. Methods ....

The Photometer

77. Construction

78. Filling the photometer

79. Making readings

80. The Dawson-Lander sun recorder

81. The selagraph Standards

83. Making a standard

84. Kinds of standards Readings

85. Time

Chart for determining sun's altitude

35 36 36 37

37 38 39

39 40

43 44

45 46

47 48

53 53 54

0/

Vlll

86. Table for determining apparent noon

87. Place

Table of intensity at various angles Reflected and Absorbed Light •

88. The fate of incident light

89. Methods of determination

90. Leaf and epidermis prints Expression of Results

91. Light records ....

92. Light sums, means and curves

95- 96.

97- 98.

Thermometers

94. Air thermometers Soil thermometers Maximum-minimum thermometers Radiation thermometers Thermographs Readings

100. Place and height Expression of Results

101. Temperature records

102. Temperature sums and means

103. Temperature curves

104. Plant temperatures

Precipitation

105. General relations

106. Tile rain gauge

107. Precipitation records . '

Wind

108. Value of readings

109. The anemometer no. Records

Soil

"3-

11=;.

Soil as a factor The value of soil surveys The origin of soils The structure of soils Mechanical analvsis

PAGE

59 60

60 61 62

63 63

64 64

65 67

69 70

70 70

7i 7i

73 74

75 76

77 77 78 79

IX

116. Kinds of soils

117. The chemical nature of soils Physiography

118. Factors . .

Altitude

119. Analysis into factors

120. The barometer Slope

122. The clinometer

123. The trechometer Exposure

124. Exposure

125. Surface

126. Record of physiographic factors

127. Topography Biotic Factors

128. Influence and importance

129. Animals

130. Plants

PAGE

79 80

83 83 84

85 86

87 87

METHODS OF HABITAT INVESTIGATION

Expression

Factor 138.

Factor

142.

Factor

Simple Instruments

Choice of stations

Time of readings

Details of the method .

Records Ecograph Batteries

of Physical Factor Results The form of results Records

Curves

Plotting

Kinds of curves .

Combinations of curves

The amplitude of curves

Means and Sums

89 89 9 1

95 96

98 98

Chapter III. The Plant STIMULUS AND RESPONSE

General Relations

144. The nature of stimuli

145. The kinds of stimuli .

146. The nature of response

147. Adjustment and adaptation

148. The measurement of response

149. Plasticity and fixity

150. The law of extremes .

151. The method of working hypotheses Hydroharmose

Adjustment

152. Water as a stimulus

153. The influence of other factors upon water .

154. Response

155. The measurement of absorption .

156. The quantitative relation of absorption and transpiration

157. Measurement of transpiration

158. Field methods ......

159. Expression of results ....

160. Coefficient of transpiration Adaptation

161. Modifications due to water stimuli

162. Modifications due to a small water supply

163. The decrease of water loss .

164. The increase of water supply

165. Modifications due to an excessive water supply

166. Plant types

167. Xerophytic types

168. Types of leaf xerophytes .

169. Types of stem xerophytes .

170. Bog plants ....

171. Hydrophytic types Photoharmose

Adjustment

172. Light as a stimulus

173. The reception of light stimuli

174. The response of the chloroplast

175. Aeration and translocation .

PAGE

100 100

I07 I07 I08 IO9 III

113 114

Il6

125 126 127

131 132

XI

176. The measurement of responses to light Adaptation

177. Influence of chloroplasts upon form and structure

178. Form of leaves and stems

179. Modification of the epidermis ....

180. The differentiation of the chlorenchym ,

181. Types of leaves .......

182. Heliophytes and sciophytes ....

PAGE

138 139

140 142

183. 184.

185. 186.

195. 196.

Scope . . .

Fundamental lines of inquiry

Ancestral form and structure

Variation and mutation

Methods Natural Experiment

Selection of species .

Determination of factors

Method of record Habitat Cultures

Scope and advantages

Methods

Transfer .

Modification of the habitat Control Cultures

Scope and procedure .

Water-content series .

Light series

145 146

147 149

153 153 154 156

157 158 160

Chapter IV. The Formation METHODS OF INVESTIGATION AND RECORD

198. The need of exact methods .

Quadrats

200. Possible objections Kinds of Quadrats and Their Use

201. Size and kinds .

202. Tapes and stakes

203. Locating quadrats

161 163

164 164

Xll

The List Quadrat

204. Description

205. Manner of use .

206. Table of abundance .

The Chart Quadrat

207. Description and use .

208. The chart .

209. Mapping

210. Factors and photographs The Permanent Quadrat

211. Description and uses .

212. Manner of use .

The Denuded Quadrat

213. Description

214. Methods of denuding and recording

215. Physical factors .

Aquatic Quadrats

Transects

217. The transect The Line Transect

218. Description and method

219. The location and size .

The Belt Transect

220. Details ....

The Permanent Transect

221. Advantages

222. Details .

The Denuded Transect

The Layer Transect

Ecotone Charts

The Migration Circle

226. Purpose

227. Location and method .

228. The denuded circle

229. Photographs

Cartography

230. Value of cartographic methods

PAGE

166 166

167 168 168 170

170 172

173 174 175

176 177

179 179

180 180

182 182

. 183

Xlll

231. Standard scale

232. Color scheme

233. Formation and vegetation maps

234. Continental maps Photography

"235

236. The camera and its accessories

237. The choice of a camera

238. The use of the camera

239. The sequence of details

240. The time of exposure .

241. Developing ....

242. Finishing Formation and Succession Herbaria

243. Concept and purpose .

244. Details of collecting

245. Arrangement

2a6. Succession herbaria .

PAGE

184 184 185 187

188 188 190 191 192

193 194

196 197 197 198

DEVELOPMENT AND STRUCTURE

247. Vegetation an organism

248. Vegetation essentially dynamic

249. Functions and structures .

Association

252. Aggregation Kinds of Association

253. Categories ....

254. Stratum association

255. Ground association

256. Species guild association

257. Light association

258. Water-content association .

THE DEVELOPMENT OF THE FORMATION p 2 59- • Invasion

Migration

199 199 199

200 201 203

204 204 205 206 206 208

210 210 210

XIV

262. Mobility • .

263. Organs for dissemination

264. Contrivances for dissemination

265. Position of disseminules . 266. Seed production .

267. Agents of migration .

268. The direction of migration Ecesis

270. Germination of the seed

271. Adjustment to the habitat Barriers

2J2. Concept

273. Physical barriers

274. Biological barriers

275. Influence of barriers .

Endemism

277. Causes

278. Significance Polyphylesis and Polygenesis

280. Proofs of polygenesis

281. Origin by polyphylesis Kinds of Invasion

282. Continuous and intermittent invasion

283. Complete and partial invasion

284. Permanent and temporary invasion Manner of Invasion

285. Entrance into the habitat

286. Influence of levels Investigation of Invasion

289. Kinds of succession .

Primary Successions

29 1. Succession through elevation

292. Succession through volcanic action

293. Weathering ....

PAGE

211 21 £ 212 214

215 216

220 221 223

225 225 226

227 228 228

230 231 232

234 235 235

236 238

239 240

241 241 242

XV

300. 301. 302.

305. 306.

3"- 312.

294. Succession in residuary soils

295. Succession in colluvial soils

296. Succession in alluvial soils

297. Succession in aeolian soils

298. Succession in glacial soils Secondary Successions

299. .

Succession in eroded soils Succession in flooded soils Succession by subsidence Succession in land slips Succession in drained or dried soils Succession by animal agency Succession by human agency Succession in burned areas .

308. Succession in lumbered areas

309. Succession by cultivation .

Succession by drainage Succession by irrig-ation Anomalous successions Perfect and imperfect successions Stabilization ....

Causes and Reactions

316. Succession by preventing weathering

317. Succession by binding aeolian soils

318. Succession by reducing run-off and erosion

319. Succession by filling with silt and plant remains

320. Succession by enriching the soil .

321. Succession by exhausting the soil

322. Succession by the accumulation of humus .

323. Succession by modifying atmospheric factors Laws of Succession

3 2 4

Classification and Nomenclature

326. Nomenclature

327. Illustrations

Investigation of Succession

328. General rules ......

329. Method of alternating stages

PAGE

245 246 247

2 53 253 253 254

254 255

259 260

267 267 270

270 271

XVI

330. The relict method

THE STRUCTURE OF THE

332. Concept Causes of Zonation

334. 335- 336.

Growth Reactions .

Physical factors .

Physiographic symmetry

Kinds of Zonation

337- 338. 339-

34i.

Alternation

343- 344- 345-

Radial zonation .

Bilateral zonation Vertical zonation Vegetation zones

FORMATION

Causes Competition Kinds of alternation The Formation in Detail

346. The rank of the formation

347. The parts of a formation

348. Nomenclature of the divisions

349. The investigation of a particular formation Classification and Relationship

350. Basis .....

Plabitat classification .

2. Nomenclature 353. Developmental classification Regional classification Mixed formations

EXPERIMENTAL VEGETATION

356. Scope and methods Method of Natural Habitats

357. Natural experiments .

Method of Artificial Habitats

358. Modification of habitat

PAGE

275 276

279 280 280 280 281

284 285 289

295 299

299 300

304 304 304

307 307

CONTENTS XV11

PAGE

359. Denuding 308

360. Modification of the formation by transfer .... 309 Method of Control Habitats

361. Competition cultures . . . .. . . . .310

362. Details of culture methods . . . . ... 311

RESEARCH METHODS IN ECOLOGY