| Fig. 4.3.14. A specific and well-known example of "indirect" herbivory between different types of trees and the leaf cutter ants (Atta of diverse species), often considered as symbiosis. The insects provide their symbiont fungus (e.g. Rho-zites of diverse spp.) with chewed leaf material cut from leaves, as substrate (A), and often carried considerable distances to their nests (B). (Photo K. Müller-Hohenstein)
eluding effects beyond phytophagy. Consumption of phytomass (e.g. leaves, but also seeds) is a direct effect of herbivores and is important, but also the indirect effect, e.g. on the site and also on competition and vegetation dynamics, etc., must be considered.
In the following, various forms of herbivory are explained together with the possible responses of plants as well as the most important consequences.
Herbivores which only take pollen have little influence on plants and communities, but the influence of herbivores eating seed and seedlings is much greater. The particular demands of animals need to be known before their influence can be assessed.
The most important herbivores, because they are also the most well known, are the large vertebrates, for example in savannahs of semiarid tropical Africa and man-made vegetation in temperate climates. There are also many invertebrate species using vegetation and their herbivory need not only relate to eating leaves. Particularly invertebrates have found ways of using plant resources, and suck sap, eat pollen or seeds, or target other organs, such as buds or young shoots. It therefore seems useful to make a distinction between vertebrates and invertebrates.
In all vertebrate groups there are phytophagous species. Most important are, without doubt, mammals, followed by frugivorous birds. Insects are the most important phytophagous group within the invertebrates, with molluscs and nematodes of lesser importance. They affect leaves, flowers, seeds and roots by eating, mining, boring and burrowing, sap-sucking, and forming galls. Reichelt and Wilmanns (1973) showed the different effects of guilds of phytophages on nemoral forest ecosystems and the different extent to which they are able to use resources from plants (Table 4.3.1).
Vertebrates and invertebrates are able to disturb growth of plants in very similar ways, affecting their regeneration and contributing to early death. However, there are differences; different types of metabolism and mobility, and thus access to the required resources. Vertebrates are mostly polyphagous, with the exception of such specialists as the panda and koala which consume bamboo and eucalyptus species, respectively. Invertebrates are oligo- to mono-phage, thus their effects are much more selective than those of vertebrates. Vertebrates consume much more biomass because they are usually larger, sometimes consuming whole plants in one go. However, their populations are much smaller than those of invertebrates.
Tscharntke (1998) describes three possible interactions between plants and herbivores: (1) there is no damage to the plants as they are re-
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