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ecologia mediterranea, tome 29, fascicule 2, 2003, p. 153-164 INTERPRETING GERMINATION RESULTS BASED ON SEED SIZE, MASS AND ECOLOGICAL… ◆ firmed by Zahran (1975) in his studies on Juncus rigidus seeds that succeeded to germinate at salinity level of 3% NaCl solution. Accordingly, he reported that the success or failure of seed germination in saline soil might be an indicator for the success or failure of seed propagation of salt tolerant plant in saline soil. Annuals in desert ecosystems exploit top centimeters of the soil, and are abundant only when surface moisture is relatively high. Moisture conditions of the surface soil vary less spatially than they do temporally (Olsvig- Whittaker et al., 1983). Hence, spatial heterogeneity of annuals as a response to local environmental variation may be relatively low, although countered by biologically caused patterning. Baker (1972) compared seed weight of the California flora with moisture availability of each habitat. He reported that among herbaceous species there was a significant negative correlation between moisture availability and seed weight. Westoby et al. (1992) argued that Baker’s data should be regarded cautiously. However, in the present study, there was a highly significant correlation between seed weight, seed size of annuals and the moisture availability of the natural habitats they collected from as well as the water supply allowed in the laboratory experiments. This trend is disagreeing with Baker (1972). On the other hand, Mazer (1989) working on Indian Dunes flora reported no significant association between seed mass and moisture availability. This trend is also noted in this study where there is no significant correlation between moisture level and seed mass of the species collected from xeric and dried habitats, such as the inland plateau, saline depressions, sand dunes and rocky cliffs habitats (see values of correlation in table 1). Similarly, Telenius and Torstensson (1991) did not find any association between seed weight and moisture availability in 48 species from the genus Spergularia. However, the comparative evidence for an association between large seed mass and dry habitats is quite limited, despite its general acceptance in the literature. On the other hand, Guerrero-Campo and Fitter (2001) reported that plant species with shallow or thin main root had smaller seeds than plants with fibrous or other adventitious roots. They concluded that seed size was related to plant height, but this association was weaker than that between seed size and root depth. Their results suggested that traditional ecological explanation do not explain the relation between seed and adult plant size, and they proposed that deeprooted plants have large seeds because of allometric and developmental constraints, which means that only large seeds can produce the thick roots that can grow rapidly to depth. The abundant literature that demonstrates the adaptation of plants to the conditions prevailing in their habitats showed that natural selection operates, at a very fine level, genotypes that are most efficient at gathering the resources of the local habitats (Heslop-Harrison, 1964). The changes in moisture and salinity in different habitats are reflected in the changes of the produced progeny (seeds). It seems that with the greater austerity in available moisture resources most of the plant species directed to produce small seeds. As stated above larger seed size is not necessarily associated with larger mass. It is unlikely that the advantage of large seeds was due to the ability to emerge from greater depth in the soil, where soil moisture is more favorable. Experimentation on the behavior of the studied species should be the next step in clarifying the mode of that behavior and its relevant to the habitats. ACKNOWLEDGMENTS The author sincerely wishes to thank Dr. Nabil El- Hadidi, Professor of plant taxonomy and flora & the keeper of Cairo University Herbarium for the identification of the plant specimens. The author also acknowledges the valuable comments of Dr. M. Abdel-Razik & Dr. S. El-Darier, Professors of plant ecology and Dr. S.Y. Barakat, emeritus Professor of plant physiology, Faculty of Science Alexandria University. I wish to thank my colleague Dr. H. Deif for his kind help in preparing the photographs. References ALLEN S., GRIMSHAW H. M., PARKINSON J. A. & QUARMBY C., 1974. Chemical analysis of ecological materials: Blackwell Scientific Publications, Oxford and London. 565 p. Baker H.G., 1972. Seed weight in relation to environmental conditions in California. Ecology, 53: 997-1010. Baskin J.M. & Baskin C.C., 1992. Seed germination biology of the weedy biennial Alliaria pelidata. Nat. Areas J., 12: 191-197. Bl at e G.M., Pear t D.R. & Leight on M., 1998. Post-dispersal predation on isolated seeds: a comparative study of 40 tree species in a southeast Asian rainforest. Oikos, 82: 522-538. Boul os L., 1995. Flora of Egypt: Checklist. Al-Hadra Publishing, Cairo. 286 p. Chapin F.S. III., 1980. The mineral nutrition of wild plants. Annu. Rev. Ecol. Syst., 11: 233-260. 163
164 ◆ L. M. M. BIDAK CHAPIN F.S. III., 1991. INTEGRATED RESP ONSES OF PLANTS TO STRESS. BioScience, 41: 29-36. Chapman, V.J. 1966. Vegetation and Salinity. In: Salinity and Aridity. Dr.W Junk, The Hague, pp. 23-42. Cook R.E., 1980. Germination and size-dependent mortality in Viola blanda. Oecologia, 47: 115-117. Gr ime J.-P., 1974. Vegetation classification by reference to strategies. Nature, 250:26-31. Gr ime J.-P., 1977. Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory. Am. Nat., 111: 1169-1194. Guer r er o-Campo J. & Fit t er A. H., 2001. Relation between root characteristics and seed size in two contrasting floras. Acta Oecol., 22: 77-85. Har per , J.L., 1977. Population biology of plants. Academic Press, New York, USA. Har per J.L., Lovel l , P.H. & Moor e, K.G., 1970. The shapes and sizes of seeds. Annu. Rev. Ecol. Syst., 1: 327-356. Hesl op-Har r ison J., 1964. Forty years of genecology. Adv. Ecol. Res., 2: 159-247. Jackson K. L., 1973. Soil chemical analysis. Constable and Co. Ltd., London. 394 p. Jur ado F. & West oby M., 1992. Seedling growth in relation to seed size among species of arid Australia. J. Ecol., 80: 407- 416. Lindsay A.T, Mar k R. & Michael J.C., 1999. Seed mass and competition / colonization trade-off: a sowing experiment. J. Ecol., 87: 899-912. Mayer A.M. & Pol jakof f -mayber A., 1982. The Germination of seeds. 3rd edition. Pergamon Press, 211 p. Mazer S.J., 1989. Ecological, taxonomic and life history correlates and seed mass among Indian dune angiosperms. Ecol. Monogr., 59: 153-175. Mogie M., Lat ham J.R. & War man E.A., 1990. Genotypeindependent aspects of seed ecology in Taraxacum. Oikos, 59: 175-182. Mot t , J.J., 1972. Germination studies on some annual species from an arid region of Western Australia. J. Ecol. 60:293- 304. Ol svig-Whit t aker , L. Shachak, M. & Yair , A., 1983. Vegetation patterns related to environmental factors in a Negev Desert watershed. Vegetatio, 54: 153-165. Par ker , M.A., 1982. Association with mature plants protects seedlings from predation in an arid grassland shrub Gutierrezia microcephala. Oecologia, 53: 276-280. Pat e J.S. & Mccomb A.J., 1981. The Biology of australian plants. Univ. of Western Australia. Perth. Sal isbury E.J., 1975. Seed size and mass in relation to environment. Proceed. Royal Soc. London, B. 186: 83-88. Schimpf D.J., 1977. Seed weight of Amaranthus retroflexus in relation to moisture and length of growing season. Ecology, 58: 450-453. Sil ver t own J., 1989. The paradox of seed size and adaptation. Trends Ecol. Evol., 4: 24-26. Smit h C.C. & Fr et wel l S.D., 1974. The optimal balance between size and number offspring. Am. Nat., 108: 499- 506. Sol br ig O.T., Bar bour M.A., Cr oss J., Gol dst ein G., Lowe C.H., Mor el l o J. & Wang T.W., 1977. The strategies and community patterns of desert plants. In: G.H. Orians & O.T. Solbrig (eds.). Convergent evolution in warm deserts. US/IBP Synthesis Series 3, Dowden, Hutchinson and Ross, Inc. Stroudsberg, 67-106. Sor enson F.C. & Mil es R.S., 1978. Cone and seed weight relationships in angiosperms. II. Seeds and seedlings. Annu. Rev. Ecol. Syst., 2: 237-260. St r onber g J.C. & Pat t en D.T., 1990. Variation in seed size of a southwestern riparian tree. Arizona Walnut (Juglans major). Am. Midland Nat., 124: 269-277. Täckhol m V., 1974. Student’s flora of Egypt. Cairo University Press, Cairo. 888 p. Tel enius A. & Rst ensson P., 1991. Seed wings in relation to seed size in the genus Spergularia. Oikos, 61: 216-222. Tur nbul l L. A., Rees M. & Cr awl ey M.J., 1999. Seed mass and the competition / colonization trade-off: a sowing experiment. J. Ecol., 87: 899-912. West oby M. & Leishman M.R., 1994. The role of seed size in seedling establishment in dry soil conditions; experimental evidence from semi-arid species. J. Ecol., 82: 249-258. West oby M., & Saver imut t u T., 1996. Seedling longevity under deep shade in relation to seed size. J. Ecol., 84: 681- 689. West oby M., Jur ado E. & Leishman M.R., 1992. Comparative evolutionary ecology of seed size. Trends Ecol. Evol., 7: 368- 372. West oby M., Leishman M. & Lor d J., 1997. Comparative ecology of seed size and dispersal. In: J. Silvertown, M. Franco & J.L. Harper (eds.). Plant life histories, ecology, phylogeny and evolution. Cambridge University Press, Cambridge, 143-162. Zahr an M.A., 1975. On the germination of seeds on Juncus rigidus C.A. Mey and J. acutus L. Bull. Fac. Sci. Mansoura Univ., 3: 75-84. ecologia mediterranea, tome 29, fascicule 2, 2003
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