RESUMEN
Association analyses by contingency tables and generalized linear modeling were compared to infer relationships among hypogeous (belowground-fruiting) ectomycorrhizal fungi and potential host tree species from 136 study plots in forested habitats in southeastern mainland Australia. Results from both types of statistical approaches were highly congruent. As with previous experimental studies, no exclusive fungus-host tree associations were identified. However, the likelihood of occurrence of some species of fungi increased significantly in the presence of particular host tree species, suggesting fungal host preference or shared habitat preferences. Similarly, while most associations among fungal species were nonsignificant, a few taxa were more likely to be found in the presence of certain others. These were termed positively associated and are thought to share common climatic and microhabitat requirements or host preferences. In contrast, other combinations of fungal species were negatively associated with one another, perhaps indicating different habitat preferences. Furthermore, the finding that some fungi occurred more frequently in the presence of certain tree species provides a starting point for selection of compatible host-fungus combinations that could be used for forest nursery and restoration applications.
RESUMEN
We evaluated the nutritional value of sporocarps of Rhizopogon vinicolor, a common hypogeous fungus in the coniferous forests of North America, for two small mammal species: the Californian red-backed vole (Clethrionomys californicus) and the northern flying squirrel (Glaucomys sabrinus). Although the nitrogen concentration of sporocarps was high, much of it was in non-protein form or associated with cell walls, suggesting that it may be of low nutritional value or protected from mammalian digestive enzymes. Sporocarps also had high concentrations of cell wall constituents, indicating low availability of digestible energy. When fed a diet of this fungus alone in a controlled feeding experiment both mammal species lost a small amount of body mass. Digestibilities of dry matter, nitrogen, cell wall constituents and energy from sporocarps by both species were lower than the digestibilities of other food types by other similarly sized small mammals. Red-backed voles digested the various components of sporocarps at least as well as the flying squirrels, even though they were almost six-fold smaller in body mass. This observation supports the notion that red-backed voles, like other microtine rodents, have morphological and physiological adaptations of the digestive system that are postulated to permit greater digestion of fibrous diets than predicted on the basis of body size. Despite this, our results re-affirm previous conclusions that hypogeous fungi are only of moderate nutritional value for most small, hindgut-fermenting mammals. Future studies should focus on the importance of mixed-species of fungi in the diet of small mammalian mycophagists.