Ground invertebrate biomass differs from one habitat to another, but may often exceed 0.5 tonnes ha_1 (Killham, 1994). Numerically, and in terms of ecosystem processes, the most important of these ground-dwelling invertebrates are the oligochaetes (the earthworms and enchytraeid worms), nematodes, arthropods (such as centipedes, millipedes, springtails and mites) and molluscs (including slugs and snails; Gange and Brown, 1997). Saprotrophic fungi, the primary agents of organic matter decomposition in most terrestrial ecosystems (Chapters 2, 3, 10-12, 14-16), may be affected by these invertebrates through a range of mechanisms; many are primarily mycophagous and possess chitinases in their guts for degrading fungal cell walls (Berg et al., 2004).

Invertebrates and fungi are affected by each other in both direct and indirect ways. Direct interactions largely comprise: (1) provision of a fungal food source or habitat for invertebrates (e.g. invertebrates directly grazing on mycelium or fruit bodies) or (2) basidiomycetes killing and then utilizing invertebrate body contents. General insect-fungus interactions, as understood then, were well covered by Carter (1973), Agrios (1980) and Wilding et al. (1989). Indirect effects of fungi on invertebrates include: (1) altering behaviour, by attraction, repulsion and arresting activity; and (2) improvement of the nutritional environment by enzymatically softening resources allowing easier feeding, destruction of inhibitory compounds in resources and decreasing carbon:nutrient ratio. Indirect effects of invertebrates on fungi largely relate to: (1) spread, including carriage to, inoculation into and facilitation of colonization of resources; (2) changes to the physical and chemical environment; (3) changes to the microbial community; and also (4) changes to physiology and metabolism. These aspects of fungus-invertebrate interactions, amongst others, were reviewed by Barbosa (1991), de Nooij et al. (1992) and Hatcher (1995), highlighting how over many millennia some have evolved into facultative or even obligate symbioses (Table 1). This review highlights the variety of interactions that occur, how these interactions affect ecosystem processes and the possible consequences of global environmental change on these interactions.

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