Fav

Fig. 4.3.7. Population cycles of Canadian lynx and snow shoe rabbit. (After Holtmeier 1999)

Fig. 4.3.8. Schematic of a capercaillie biotope. (After Von Hessberg, unpubl. results); 1. beech buds as spring fodder for hens; 2. protected nesting site; 3. courtship display area (tree display); 4. grit removal from root holes of up-rooted trees; 5. high and vital blueberry bushes; 6. dead wood for wood-living insects; 7. ant heap; 8. courtship display area (ground display); 9. pine needles for winter food; 10. grazing area; 11. sheltered roost

Fig. 4.3.8. Schematic of a capercaillie biotope. (After Von Hessberg, unpubl. results); 1. beech buds as spring fodder for hens; 2. protected nesting site; 3. courtship display area (tree display); 4. grit removal from root holes of up-rooted trees; 5. high and vital blueberry bushes; 6. dead wood for wood-living insects; 7. ant heap; 8. courtship display area (ground display); 9. pine needles for winter food; 10. grazing area; 11. sheltered roost

Complex structured plants and types of vegetation offer numerous microhabitats for a species-rich fauna: similarly, stand mosaics are particularly important in satisfying demands of many birds. Birds require, in addition to food from plants and animals, nesting and breeding sites such as holes in trees, singing and hunting platforms, and mating and pairing sites, and they also require roosting sites and protection from enemies. For many species such a diverse environment is only available in a structure-rich landscape, where small vegetation units join up to form vegetation complexes. Kratochwil (1987) analysed habitats of the rock bunting (Emberiza cia) in the southern Black Forest and in Grau-biinden and showed that a very similar type of vegetation, particularly in its structure, was required. The demands of the capercaillie (Tetrao urogallus) demonstrate the great extent to which the floristic and structural characteristics of vegetation need to be interlinked to fulfil the bird's demands on the habitat (Fig. 4.3.8). Of the 11 habitat characteristics mentioned only three are linked to food and thus to particular plant species. The other characteristics refer to structural features of the vegetation required in the biotope for capercaillie.

Information

Plants can also inform animals about the state of available resources, the possible presence of a partner or enemy, and the suitability of the habitat for certain stages in the life cycle, for exam ple. Form, colour, smell and stage of development of plants are information carriers. Plants not only signal the current stage, but possibly also future development. Migratory birds breeding in meadows must know the future development of the vegetation when they arrive in spring, in order to be protected as much as possible during the breeding season. Many insect imagos are able to find the required type of vegetation early, to provide the habitat and food required for the later developmental stages of the larvae. Another example is the migratory locust in many dry regions of the Old World.

Effects of Animals on Vegetation The effects of animals on individual plants and vegetation units may be interpreted, in many cases, as a response to the resources provided by plants. Animals need particular species and amounts of plants for their food supply, thus affecting plants directly, perhaps decreasing the photosynthetically active surface and influencing reproduction via pollination and thus propagation. Ultimately, many animals are the only, or most important, vector for the dispersal of numerous plant species in all biomes (see Chap. 4.2.1.1).

The far-reaching influences of animals on the formation of vegetation becomes obvious from terms such as termite savannah or beaver meadow. In tropical mountains and in the Andes, animals which burrow and live below ground cause partial or even complete destruction of vegetation (Werner 1977). Bioturbation is only a side effect. Large mammals may contribute to soil compaction and, of course, to total destruction of vegetation.

In addition, organic substances are, in many cases, more easily degraded and the plant nutrition improved because of excretion by animals which changes the mineral status of soils. Research showed that 90% of the litter in tropical rain forests would not be degraded without invertebrates. Dung beetles are very important for such turnover. The widely occurring "fly pest" in Australia was only curtailed after introduction of dung beetles (species of Scarabaeus and Onto-phagus). Birds are responsible for considerable transport of material: Sea birds transport large amounts of nutrients from the sea to the mainland and greatly affect sites. Guano deposits in the North Chilean coastal regions are witness to this.

Animals are also important as 'switches' and 'amplifiers' in the ecosystem (Remmert 1992). If deer in deciduous forests eat buds, and small mammals destroy seeds and seedlings but also disperse fruiting bodies of mycorrhizae, and birds pollinate flowers, the consequences for ecosystems are decisive, even though the energy turnover is only small. Animals often only use 10% of the material available in the ecosystem in which they live, but regulate the most important system processes (e.g. pollination, dispersal of propagules) and thus contribute substantially to the ecological stability of these systems. This shows that ecosystems cannot be described and understood by energy and material fluxes alone.

Pollination by Animals

An important field for interactions between plants and animals is pollination biology. Most flowering plants are not able to propagate without visitors to the flowers. Trees of nemoral forests are, to a large extent, wind pollinated, but in the shrub and herbaceous layers entomoga-mous species dominate. Richards (1991) classified plant communities in western Ireland according to the plant succession and the occurrence of wind and insect pollination. Figure 4.3.9 shows that in almost all plant communities insect pollination dominates and that special pollination mechanisms have developed, particularly in "old" species-rich communities (e.g. Fes-tuco-Brometea and Sedo-Scleranthetea communities).

Teleologically expressed, many animals 'expect' to obtain 'payment' from flowering plants

Ammophiletea Asplenietea rupestris Cakiletea maritimae Bidentetea tripartiti Plantaginetea majoris Littorelletea Montio-Cardaminetea Phragmitetea Juncetea maritimi

Puccinellion maritimae Armerion maritimae Sedo-Scleranthetea Molinio-Arrhenatheretea Festuco-Brometea

Scheuchzerio-Caricetea Moist moors Caricetalia davallianae Oxycocco-Sphagnetea Nardo-Callunetea Querco-Fagetea

□ Wind pollinated

General insect pollinated ¡3 Special Insect pollinated

Fig. 4.3.9. Plant communities (classes) from western Ireland and the proportions of different methods of pollination. (After Richards 1991)

for their contribution to pollination and plants 'expect' to obtain 'payment' for the supply of 'rewards'. Thus predominantly mutual relationships develop. Only in rare case are the 'expectations' of plants frustrated by pollen or nectar robbers or those of animals frustrated because flowers of plants mimic potential sexual partners (e.g. insect flowers such as various Ophrys species) or even flowers which keep visitors captive until the flower is pollinated (e.g. flowers that are insect traps such as Arum species).

In pollination symbiosis, pollen of a flower must stick to animals and should be transported to the stigma of the next flower. To enable this process to take place, plants must possess certain characteristics and provide 'payments' or 'services' (to use teleological expressions again). Animals are mainly attracted by various foods, but in arid regions a supply of water may also be important. The most important nutrients are energy-rich proteins and lipids in pollen, and nectar containing sugars, as well as oils and resins. The supply is often directed to particular

Plate/cup flowers

Bell/beaker flowers

Brush/broom flowers

Throat/lipped flowers

Flag/butterfly flowers

Tube/salver shaped flowers

Brush/broom flowers

Throat/lipped flowers

Flag/butterfly flowers

Coleoptera beetles

Hymenoptera wasps

Diptera flies

Chiroptera bats

Hymenoptera bees

Lepidoptera moths

Lepidoptera butterflies

Colibris humming birds

Coleoptera beetles

Hymenoptera wasps

Fig. 4.3.10. Interaction of flower types and pollinators. (After Hess 1990)

Diptera flies

Chiroptera bats

Hymenoptera bees

Lepidoptera moths

Lepidoptera butterflies

Colibris humming birds visitors, where the flowers of plants attract by colours, shapes and smells. Thus, bats and bees do not profit from the same species. Usually, the supply of individual flowers is so limited that animals need to visit other flowers and thus pollination is more likely to become successful.

Birds and insects are usually enticed by the colour of flowers whereas bats, which play an important role as pollinators in tropical communities, are attracted by smell. The structure of some flowers is such that many pollinators gain access, and guarantee success. In many cases, however, there is a special combination which is particularly reliable for considerably less pollen. In anemophilic species the relation of pollen grains to pollinated ovules is between 10:1 to 6:1, but the ratio may be 1:1 for highly specialised entomogamous species (e.g. orchids).

Special plant animal combinations can be recognised from the forms of the flowers. Hess (1990) grouped the proportions of different types of flowers in particular groups. They are shown, together with their faunistic partners, in Fig. 4.3.10. Amongst insects, beetles (Coleoptera) are regarded as the original, oldest groups of pollinators, followed by the Hymenoptera, which are the most important group now, then the

Diptera. Only relatively recently did Lepidoptera, and finally vertebrates, particularly humming birds and nectar birds as well as bats and flying foxes, develop as pollinators.

The many possible specialisations were seen as a solution to restrict the great competition for pollinators. This is also indicated by the fact that plants using the same pollinators flower at different times. In species-rich plant communities the number of species pollinated by insects increases, however, the number of pollinators also increases. As Boucher (1985) recognised, there is a relation between the density of plant species (and individual plants) and the available pollinators which plants attract (Fig. 4.3.11). With few flowers in an area, only few pollinators are attracted, with increasing numbers there are more, leading to mutualistic interactions. If the number of flowers increases further, a point is reached when the reservoir of pollinators is exhausted. There is, therefore, competition for pollinators.

Pollinators (and also herbivores) visit at a certain time and place flowers or plants which may be irregularly distributed. Such temporal and spatial scales have very rarely been considered in research into such plant-animal interactions.

Bronstein (1994) pointed out that the spatial relations between plants and their pollinators should be regarded quite differently from those between plants and herbivores. Plants need to attract pollinators, but at the same time need to avoid herbivores as much as possible, so time and space are important variables.

Many examples show that flowering periods of sympatric species competing for the same pollinators are shifted, particularly in regions without clearly differentiated seasons. Some species have very short flowering periods, others considerably longer. Flowering dates of individual flowers are not well synchronised. In regions without natural differences between seasons, temperature and photoperiod do not play an important role; species can flower once a year, as in temperate climates, or other flowering rhythms may occur. Bronstein (1994) distinguishes four different types: annual flowering, those that flower several times a year, those flowering at longer intervals, and those flowering continuously (Fig. 4.3.12 a-d).

Spatial aspects are linked to the number and distribution of potential food plants and pollinators. Theoretically, it might be assumed that animals gather food using the least possible energy. This is confirmed by systematic grazing and gathering, and limited maximum distances travelled, for example, by bees visiting sites of food and the nest (about 6 km). Tropical bats and flying foxes may cover many kilometres. Amongst birds there are real 'nomad' species that follow the regional gradient of flowering species, moving to different altitudes as required as their food species flower considerably later there. Others are aggressively "territorial"; e.g. some

Fig. 4.3.11. Relationship between pollinator visits and flower density. (After Boucher 1985)

a) Frequently in the year at different times

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