Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

The reproductive effort of 49 Angiosperms from the herb layers of Oak-Hornbeam forest, Black Pine forest, rock steppe andBromus erectus meadow was determined on a dry weight basis. The average reproductive effort of these communities appears to depend on habitat factors and competition (e.g. water, temperature and light) and not on the position within the successional position. The general validity of the r- and K-selection concept therefore is questioned.

Der Reproduktionsaufwand in vier mitteleuropäischen Pflanzengemeinschaften

The present study reveals a variety of competitive interactions between the two species ofEuphorbia—Euphorbia hirta andEuphorbia thymifolia depending upon the calcium status of the soil. In general,Euphorbia thymifolia suffered high mortality in low calcium soils as compared toEuphorbia hirta. The former, however, showed better survival in high calcium soils. This was more pronounced in mixtures than in pure stands. A similar pattern of behaviour though not so pronounced was also recognised with respect to the growth performance of the two Species in low and high calcium soils. The significance of these results is discussed.

Comparative biology of two closely related species ofEuphorbia — Competitive relationships

The present studies indicate that the differentiation of ecotypes inEuphorbia hirta into erect and prostrate forms as related to soil moisture and compaction is not complete and often they may be merely plastic modifications. Besides, the reproductive strategies of the two ecotypes and different in that the prostrate form has greater reproductive effort compared to vegetative growth. It was also shown that the two populations show differences in their abundance at different seasons of the year.

P. S. Ramakrishnan

Papers

Reproductive strategies within the speciesEuphorbia hirta L. related to soil moisture and compaction