The natural history of biotic interactions, highlighting nutrient uptake mutualisms, pollination, seed protection and viability threats in a nutrient-impoverished biome

Abstract

I give a short account of the development of natural history and the concepts of environment, ecology and ecosystem. Biotic interactions are a component of biodiversity and largely revolve around the concept of symbiosis, with lichens the earliest example of mutualisms. Biotic interactions between plants, animals and fungi are particularly well developed and understood in the Mediterranean-type-climate region of Southwestern Australia. Renowned for its nutrient-impoverished soils, nutrient cycling between biotic components of ecosystems in this biome are expected to be exceptionally tight. Among the 10 case studies outlined here, nutrient conservation adaptations were most notable at the levels of (a) efficient nutrient uptake via such biotic interactions as mycorrhizas and plant carnivory, and (b) protection of the nutrient-enriched seeds from granivores. Hakeas have evolved self-mimicry and woody fruits that deter granivory by black cockatoos, spiny leaves that deter herbivory by kangaroos, and prominent inflorescences that attract bird pollinators. The caterpillar fungus Drechmeria parasitises larvae of the ghost moth Oxycanus. Many non-rewarding orchids mimic the appearance of co-occurring nectar/pollen-rewarding herbs such that native bees are deceived into pollinating both groups. The orchid Rhizanthella relies on a mycorrhizal fungus for both its organic and inorganic nutrient requirements that in turn receives organic nutrients from its host shrub. The invasive weevil Euwallacea is now widespread in some Mediterranean-climate regions of the world. Its obligate relationship with a Fusarium mould makes control of this polyphagous pest difficult. The small burrowing marsupial Bettongia disperses spores of underground fungi in its faeces, as a necessary germination pretreatment, that form mycorrhizas which increase growth of their host shrubs and trees manyfold. The carnivorous plant Cephalotus produces pitcher-shaped leaves that attract many insects, especially ants and a wingless, ant-mimicking fly, Badisis, whose larvae feed on carrion in the ‘soup’ supported by the vessel. The shrub Adenanthos produces extrafloral nectaries on reaching maturity that attract a parasitoid wasp and scores of ant species that not only deter insect herbivores but collect seeds held on the plant and carry them to their nests, thus escaping ground-dwelling granivores, where they are ideally placed for later germination. I finish by noting that these examples demonstrate that each species in the trophic web has specific roles as partner or prey and that the loss of any one may have rippling effects through the web, leading in some cases to a more nutrient-leaky ecosystem. Steps are being taken by naturalists and natural resource managers to adopt the emerging approach of ‘reciprocal contributions’ to facilitate these interactions, rather than the one-way justification of ‘ecosystem services’.

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