In his lectures my teacher Karl Mägdefrau used to say that one only becomes a real plant scientist when one enters a tropical rainforest. For me this initiation occurred in 1969 in northern Queensland, Australia, and was associated with the greatest excitement. On another level it received confirmation when I set out in 1983 together with some friends and colleagues for the first detailed ecophysiological studies of epiphytes in the wet tropics in situ in the island of Trinidad and later for similar work in Venezuela. This then promoted the idea of organizing a special symposium on "The evolution and ecophysiology of vascular plants as epiphytes" during the XIV International Botanical Congress in luly 1987 in Berlin, and to ask some of the speakers to produce chapters for a small monograph on the interesting ecologically defined group of plants "epiphytes" as presented in this volume of "Ecological Studies". The enthusiasm of the participants of the symposium giving reports and adding to the discussion was most stimulating, and it appears that epiphytes might gain well-deserved, wider consideration in the future. The cooperation with the authors of this book was very pleasant and I appreciated the new contacts established with adepts of the "epiphyte community". The chapters were organized and arranged covering first more gen­ eral aspects with setting the scene in Chapter 1, the evolution of epi­ phytism in Chapter 2 and the role of CO -concentrating mechanisms in 2 Chapter 3.

Inhalt

1 Vascular Epiphytes: Setting the Scene.- 1.1 The Conquest of Space.- 1.2 Life-Forms.- 1.3 Importance: Biomass Production, Taxonomic Diversity, Economic Use.- 1.4 Stress.- 1.4.1 Environmental Gradients Along Stratum Heights in Rainforests.- 1.4.2 Stress Driving Evolution.- 1.4.3 Stress and Ecophysiology.- 1.4.4 Stress Determining Floristic Diversity.- 1.5 Interactions with Other Non-Host Organisms.- 1.6 Curiosity.- References.- 2 The Evolution of Epiphytism.- 2.1 Ancestral Habitats: Dark and Moist or Exposed and Dry?.- 2.2 The Geologic Record of Epiphytism.- 2.3 The Systematic Occurrence of Epiphytes.- 2.4 Epiphytism as a Coherent Ecological Category.- 2.5 Classification of Epiphytes.- 2.6 Continuously-Supplied Versus Pulse-Supplied Epiphytes . ..- 2.7 Patterns of Origin.- 2.8 Predisposition and Phylogenetic Constraints.- 2.9 Historical Basis for Canopy Dependence.- 2.9.1 Ferns.- 2.9.2 Liliopsida as a Whole.- 2.9.3 Nonorchid Monocotyledons.- 2.9.4 Orchids.- 2.9.5 Dicotyledons.- 2.9.6 Ancestral Habitats.- References.- 3 Carbon Dioxide Concentrating Mechanisms and the Evolution of CAM in Vascular Epiphytes.- 3.1 Introduction.- 3.2 Evolution and Characteristics of Biochemical and Biophysical C02 Concentrating Mechanisms.- 3.2.1 Carboxylase and Oxygenase Functions of RUBISCO ..- 3.2.2 C4 Photosynthesis as a C02 Concentrating Mechanism.- 3.2.3 CAM as a C02 Concentrating Mechanism.- 3.2.4 C02 Concentrating Mechanisms in Aquatic Plants.- 3.3 Ecophysiological Interactions in the Development of C02 Concentrating Mechanisms.- 3.3.1 Efficiency of Water Use.- 3.3.2 Carbon Economy.- 3.3.3 Nitrogen Economy.- 3.3.4 Responses to Photosynthetically Active Radiation.- 3.4 Phylogenetic Distribution of CAM in Vascular Epiphytes.- 3.4.1 Evolution of Epiphytism and CAM in the Polypodiaceae.- 3.4.2 Evolution of Epiphytism and CAM in the Monocotyledons.- 3.4.3 Evolution of Epiphytism and CAM in the Dicotyledons.- 3.5 Regulation and Expression of CAM in Vascular Epiphytes ..- 3.5.1 Constitutive CAM.- 3.5.2 C3-CAM Intermediates.- 3.6 Cost-Benefit Relationships of C02 Concentrating Mechanisms.- 3.6.1 Energetics of C02 Concentrating Mechanisms.- 3.6.2 C3 and CAM Epiphyte Habitat Preference.- 3.7 Evolution of CAM and the Epiphytic Habit: Conclusions.- References.- 4 Gas Exchange and Water Relations in Epiphytic Tropical Ferns.- 4.1 Introduction.- 4.2 The Ecophysiological Problem.- 4.3 Nest Ferns.- 4.3.1 Morphology.- 4.3.2 Gas Exchange of Nest Ferns in Situ.- 4.4 Xeromorphic Ferns.- 4.4.1 Anatomical and Physiological Adaptations.- 4.4.2 Performance of CAM Ferns Under Laboratory Conditions.- 4.4.2.1 Water Deficiency.- 4.4.2.2 Temperature Requirements.- 4.4.2.3 Light Requirements.- 4.4.3 Performance of CAM Ferns in Situ.- 4.5 Water Use Efficiency of Epiphytic Ferns.- 4.6 Conclusions.- References.- 5 Epiphytic Bromeliads.- 5.1 Ecological Range and Diversity of the Bromeliaceae.- 5.2 Bromeliad Systematics and Life-Forms.- 5.2.1 Systematics.- 5.2.2 Life-Forms.- 5.3 Carbon Assimilation.- 5.3.1 Occurrence of Crassulacean Acid Metabolism (CAM) and C3 Photosynthesis.- 5.3.2 Gas Exchange and Photosynthesis in CAM and C3 Bromeliads.- 5.3.3 Photosynthetic Responses to Light Intensity.- 5.3.4 Photosynthetic Ecology.- 5.4 Water Relations.- 5.5 Phylogenetic Ecology.- References.- 6 Gas Exchange and Water Relations in Epiphytic Orchids.- 6.1 Introduction.- 6.2 Terrestrial and Epiphytic Orchids.- 6.3 Growth Habit.- 6.4 The Epiphytic Habitat of Orchids.- 6.5 Gas Exchange Patterns as Related to Succulence in Epiphytic Orchids.- 6.6 In Situ Studies of CAM in Epiphytic Orchids.- 6.7 Light Requirements.- 6.8 Water Relations in Epiphytic Orchids.- 6.9 The Physiology of Aerial Roots.- 6.9.1 Water Relations.- 6.9.2 Gas Exchange.- 6.9.3 Mode of Photosynthesis.- 6.10 The Evolution of Epiphytism in Orchids.- References.- 7 The Mineral Nutrition of Epiphytes.- 7.1 Introduction.- 7.2 Nutrient Sources in Forest Canopies.- 7.2.1 Atmospheric Input.- 7.2.2 Bark and Other Solid Media.- 7.3 Nutritional Modes.- 7.3.1 Mutualism.- 7.3.2 Hemiepiphytism.- 7.3.3 Humus-Based Nutrition.- 7.3.4 Unequivocal Carnivores.- 7.3.5 Carnivorous Bromeliads.- 7.3.6 Animal Assistance to Noncarnivores.- 7.3.7 Atmospheric Nutrition.- 7.4 Does Scarcity of Nutrient Ions Limit Epiphyte Vigor?.- 7.5 Effects on Forest Economy.- 7.5.1 Nutritional Piracy.- 7.5.2 Relationship to Other Environmental Factors.- 7.6 Conclusions and Outlook.- References.- 8 Epiphytic Associations with Ants.- 8.1 Ubiquity and Sociality of Ants: Diversity of Ant-Epiphyte Relations.- 8.2 Opportunistic Associations of Epiphytes and Ants.- 8.2.1 Carton as Epiphyte Substrate.- 8.2.2 Fitness Outcomes and Limits to Specialization and Abundance.- 8.3 Myrmecophytic Epiphytes.- 8.3.1 Benefits to Ants.- 8.3.2 Benefits to Plants.- 8.3.3 Complex Interaction Networks.- 8.3.4 Epiphytes, Ants and Host Trees.- 8.3.5 Habitat Quality and Ant-Epiphyte Assocations.- 8.4 Origins of Myrmecophytic Epiphytes.- 8.5 Summary and Conclusions.- References.- 9 The Systematic Distribution of Vascular Epiphytes.- 9.1 Introduction.- 9.2 Sources of Compilation and Methods of Classification of Epiphytes.- 9.3 Numbers of Epiphytes and Taxonomic Distribution.- 9.4 Our Knowledge of Epiphytes and Perspectives.- References.