The basic feaures of an intensive study on the various stages o f a secondary succession, from fallow lield to birch woodland, are described. The a+ diversities of the green plants, and two orders of insects, Heteroptera and adult Coleoptera, are described. For the vegetation, in addition to taxonoinic diversity, structural diversity, with both spatial and architectural components, was recognized. It was found that up to a successional age of 16 months, the taxonomic diversities of plants and insects rose; therealter the diversity o l t h e plant species declined far more than the insect species diversity. I t was concluded that in the later successional stages the maintenance ofa high level 01' taxonomic diversity of these orders of insects is correlated with the rising structural diversity of the green plants, which virtually compensates for their falling taxonomic diversity. The larger fungi appear t o sliow a similar trend to the insects.
Observations on leaves from plants with a wide range of life-forms, ruderals to trees, indicate that palatability to insect herbivores is strongly correlated with the life-expectancy of the leaves. The amount of damage suffered in the field is however inversely correlated with palatability; although the rate of damage is less on unpalatable leaves, their longer life means that they accumulate damage over a longer period. It is only with extremely well-defended evergreen leaves, that the total damage is less than that experienced by less palatable (but short-lived) leaves. These observations are related to the current theories on relative palatability (the apparency theory and the resource availability theory), within the framework of the habitat templet.
The palatability of common plants from three stages of secondary sere have been assessed by a bioassay method. Foliage was exposed to five taxonomically very different herbivores (Agriolimax, Schistocera, Spodoptera, Myzus and Trialeurodes). Palatability was measured by foliage consumption or, for sap suckers, by survival and reporduction. The results of these experiments supported the predictions of Feeny's 'Apparency theory', but indicated considerable variations in palatability within plant communities and between herbivores.
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