• to start by depicting habitats and plants physiognomically,
• to deduce problems from such observations in the field as are suited for physiological, biochemical and biophysical and perhaps even molecular experimentation in the laboratory, and
• to return from the laboratory to the field with increasingly sophisticated technologies for measurements and analyses applicable to field conditions.
With this we follow a great tradition, which was begun early in the last century, and which we may retrace from Mägdefrau's History of Botany (1992) as follows.
The title of one of the best-known essays (1806) by Alexander von Humboldt is Ideas for a Physiognomy of Plants ("Ideen zu einer Physiognomik der Gewächse"). He realized that the physiognomy of vegetation is determined by environmental conditions and that the distribution of plants depends on the climate and, thus he became the founder of plant geography (von Humboldt ed 1989). The selective pressure exerted by variation in environmental factors then also became the most essential aspect for explanation of natural selection in
Charles Darwin's theory of evolution (Darwin 1859). However, it was Ernst Haeckel who coined the term ecology in 1866. Stephen J. Gould (1977), the sharp American essayist in phylogeny, caricatured it as follows:
"Ernst Haeckel, the great popularizer of evolutionary theory in Germany, loved to coin words. The vast majority of his creations died with him half a century ago, but among the survivors are 'ontogeny', 'phylogeny', and 'ecology'. The last is now facing an opposite fate - loss of meaning by extension and vastly inflated currency. Common usage now threatens to make 'ecology' a label for anything good that happens far from cities or anything that does not have synthetic chemicals in it".
However, Ernst Haeckel's own original definition of ecology was already wide and may, in fact, encompass much of the current application of the term, since he
wrote that ecology is "... the entire science of the relations of the organism to its surrounding environment, comprising in a broader sense all conditions of its existence".1
Andreas Franz Wilhelm Schimper (1856-1901) founded Plant Geography on a Physiological Basis with this title of his famous text published in 1898, and he coined the term tropical rainforest. Simon Schwendener (1829-1919) suggested that the relations between the environment and the morphological traits of plants are best studied in areas providing extreme conditions. His advice has found many followers to date. It was, however, Ernst Stahl (1848-1919) who introduced experimentation to ecological research and thus founded physiological ecology. He also discovered the role of stomata in transpiration and photosynthesis. Among the late scientists of the twentieth century Arthur George Tansley (1871-1955), Otto Stocker (1888-1979), Arthur Pisek (1894-1975), Heinrich Walter (1898-1989), Bruno Huber (1899-1969) and Michael Evenari (1904-1989) all stimulated the development of physiological ecology. Physiological ecology primarily addresses itself to aute-cology, i.e. ecological relations of properties and performance of individual plants or species, but must also develop with synecology, i.e. consideration of integration of plant functions at the community level (Luttge and Scarano 2004), which was already made clear by the early pioneers such as Arthur George Tansley who
1 "... die gesamte Wissenschaft von den Beziehungen des Organismus zur umgebenden Außenwelt, wohin wir im weiteren Sinne alle Existenzbedingungen rechnen können."
"made it clear that synecology and autecology are subsumed in the study of the community by methods firstly descriptive and appreciative, and secondly, analytic and experimental" (quoted from Godwin 1977).
Applying the approach of physiological ecology to understanding ecological functions and relationships in the tropics requires that we first must define what we mean by tropics.
Fig. 1.2A,B Diurnal (A) and annual temperature cycles (B) at a station in the warm tropics (Manaos at the Amazonas, Brazil) and in the cold tropics (Quito at 2,660 m a.s.l. in the Andes, Ecuador) and at stations in the temperate zone (Paris and Milan, respectively). The diurnal cycles in A are given for the warmest months as indicated by solid lines (July, September and July for Manaos, Quito and Paris) and the coldest months are depicted by dotted lines (June, November and January for Manaos, Quito and Paris). (After Lauer 1975)
Volkmar Vareschi (1980) has listed several possible definitions of the tropics, which partially overlap but give different emphasis:
• geodetically the tropics are limited by the lines of latitude 23 0 27' north and south of the equator, i.e. the Tropic of Cancer and the Tropic of Capricorn respectively;
• climatologically the tropics are the zones of equal day and night length; they are not basically characterized by high temperature and moisture; depending on altitude, warm and cold tropics can be distinguished, and depending on the precipitation regimes in the region between the equator and the two lines of latitude at 230 27' north and south, wet and dry tropics can be distinguished (Lauer 1975; Fig. 1.1);
Fig. 1.3A-C Global distribution of savannas (A) and tropical rainforest (B) and optimum carbon fixation (C). (After Vareschi 1980, A, C with permission of R. Ulmer; Walter and Breckle 1984, B with permission of S.-W. Breckle and G. Fischer-Verlag)
• phyto-geographically the tropics are indicated by the distribution of palms;
• eco-geographically the tropics are the zone in which the climatic effects of day-night cycles are far more important than those of seasonal cycles; day-night cycles of temperature are much larger than in the temperate zone in both the coldest and the warmest months, but annual cycles of mean monthly temperature are almost absent in the tropics (Fig. 1.2);
• botanically the tropics are contained in a well-separated pantropical floristic province;
• in terms of the biology of productivity, the tropics are the zones of optimal carbon fixation and photosynthetic capacity with > 600gm-2 year-1, which globally corresponds well to the occurrence of tropical rainforest in a broader sense (Fig. 1.3).
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