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Graphopterus exclamationis Chrysomela bicolor Scaurus dubius Julodis manipularis Mylabris brevicollis Mylabris baulnyi Acinopus sabulosus Aethiessa floralis Zophosis ghilianii

Pimelia gibba

Graphopterus exclamationis Chrysomela bicolor Scaurus dubius Julodis manipularis Mylabris brevicollis Mylabris baulnyi Acinopus sabulosus Aethiessa floralis Zophosis ghilianii

Beetles were caught in the same area at approximately monthly intervals between October 1973 and June 1974 (• = only one, 1 =several, 2 = many)

communities (see Chap. 3). There is a certain selection and patterns become visible as a result of conditions at the site (exogenic) or by competition (endogenic). They are interlinked by coexistence as is clearly visible.

Competition and coexistence are two important forms of interaction between plants. There are, of course, other forms of interaction (also with animals, see Chap. 4.3.2) contributing to the formation of patterns of plant communities in space and time. However, the long-established idea that the phenomenon of competition alone is the decisive interaction between plants must be corrected.

It became obvious in the discussion of temporal vegetation dynamics (Chap. 4.1.1.1) that interactions may stimulate succession: They may be neutral or without influence, or they may be inhibitory (Connell and Slatyer 1977). Neutral coexistence of two species (in different ecological niches) may occur after competition over time.

According to Wilson (1969), there is an early pioneer stage in primary succession where there are no contacts between individual plants, the so-called non-interactive species equilibrium. Then the spaces fill in and there are interactions, the so-called interactive species equilibrium. After competition and occupation of space, and formation of niches, the assortative species equilibrium follows with relatively stable self-renewal and maintenance of the community until the next disturbance, the so-called evolutionary species equilibrium. The word "equilibrium" is used here to mean balance of species.

Plants may have very different functions in the biocenose from the point of view of their plant or animal partners. Mistletoes are parasites for trees on which they grow, hosts for some plant-eaters and have mutualistic relations with birds. Some species live during their early development in symbioses with others, but later behave antagonistically. For herbaceous species shade trees are not competitors for light, but partners providing protection against climatic extremes and allowing coexistence.

Interactions become even more complicated when not two but several partners participate, with different effects on each other, or if the interactions at the level of plant communities and vegetation mosaics are studied. They are subjected to temporal dynamics and thus cause changes in the spectrum of interactions.

Possibilities outlined here show that it is difficult, because of the temporal change of interactions, to find a comprehensive typology of interactions. However, to gain an overview of minimum order, the attempts of Glavac (1996) and Schubert (1991) are discussed. Table 4.3.4 summarises current concepts.

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