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TYBIRK, K., 1993. Pollination, breeding system and seed abortion in some African acacias. Studies of the flower visitors and pollination ecology of Acacia albida Del., A . nilotica (L.) Willd. ex Del. A . tortilis (Forssk.) Hayne and A . senegal (L.) Willd. in Senegal and Kenya showed a high diversity of floral foragers. One hundred and eighteen taxa of insects mainly from Hymenoptera, Lepidoptera, Coleoptera and Diptera were collected. The most important pollen vectors were bees from the families Megachilidae and Halictidae, and wasps from the families Scoliidae and Eumenidae. Beetles, flies and butterflies were secondary pollen vectors. Diversity and frequency of flower visitors of species with floral nectar ( A . senegal and A . albida) were not clearly different from species without floral nectar ( A . tortilis, A . nilotica). Acacia tortilic was almost exclusively outcrossed (Index of Self Incompatibility = 0.2), with 5.5% of the inflorescences (0.13% of the flowers) developing fruits. The number of seeds per pod was positively correlated with dispersal type. Wind dispersed species had fewer seeds per pod than animal dispersed species. About 5% of the seeds were aborted in A . fortilis and A . nilotica, while 2211.8% of the seeds were aborted in A . senegal, A . ataxacantha DC. and A . polyacantha Willd. Most abortions in the latter three species occur in the proximal end of the pods, indicating selective seed abortion.

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TYBIRK, K., 1993. Pollination, breeding system and seed abortion in some African acacias. Studies of the flower visitors and pollination ecology of Acacia albida Del., A . nilotica (L.) Willd. ex Del. A . tortilis (Forssk.) Hayne and A . senegal (L.) Willd. in Senegal and Kenya showed a high diversity of floral foragers. One hundred and eighteen taxa of insects mainly from Hymenoptera, Lepidoptera, Coleoptera and Diptera were collected. The most important pollen vectors were bees from the families Megachilidae and Halictidae, and wasps from the families Scoliidae and Eumenidae. Beetles, flies and butterflies were secondary pollen vectors. Diversity and frequency of flower visitors of species with floral nectar ( A . senegal and A . albida) were not clearly different from species without floral nectar ( A . tortilis, A . nilotica). Acacia tortilic was almost exclusively outcrossed (Index of Self Incompatibility = 0.2), with 5.5% of the inflorescences (0.13% of the flowers) developing fruits. The number of seeds per pod was positively correlated with dispersal type. Wind dispersed species had fewer seeds per pod than animal dispersed species. About 5% of the seeds were aborted in A . fortilis and A . nilotica, while 2211.8% of the seeds were aborted in A . senegal, A . ataxacantha DC. and A . polyacantha Willd. Most abortions in the latter three species occur in the proximal end of the pods, indicating selective seed abortion.

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ABSTRACT. Nature quality in relation to farming is a complex field. It involves different traditions and interests, different views of what nature is, and different ways of valuing nature. Furthermore there is a general lack of empirical data on many aspects of nature quality in the farmed landscape. The present paper looks at nature quality from the perspective of organic farming, which has its own values and goals in relation to nature -the "Ecologist View of Nature." This is in contrast to the "Culturist View" characteristic of much conventional agriculture and the "Naturalist View" characteristic of the traditional biological approach to nature quality. This threefold distinction forms a framework for exploration of nature quality criteria in the farmed landscape. The traditional work on nature quality has mainly focused on biological interests based on a Naturalist View of Nature. In this paper we will explore how criteria for nature quality based on the Ecologist View can be developed and thereby feed into the ongoing discussion of the development of the organic farming practices. We suggest additional criteria for nature quality based on an Ecologist View of Nature: biodiversity; habitat diversity, extent and structure; functional integrity of habitats and agroecosystems; and landscape integrity, accessibility, and experientiality. The larger set of Naturalist and Ecologist criteria can provide a wider and more balanced basis for developing nature quality indicators that are relevant in the farmed landscapes. This broader approach to nature quality is also expected to benefit the general societal discussions and decisions on farming and nature.