Interactions between fire, mycophagous mammals, and dispersal of ectromycorrhizal fungi in Eucalyptus forests

Abstract

Several species of marsupials in Eucalyptus forests in Australia feed predominantly on the sporocarps of hypogeous fungi. This feeding is apparently beneficial to the fungi as it results in dispersal of spores. As these fungi are in almost all cases ectomycorrhiza-forming species, mycophagy by mammals may play an important role in the maintenance of mycorrhizal symbiosis in Eucalyptus forests. Fire is frequent and a dominant ecological factor in these forests, and this study tested the hypothesis that fire triggers both increased sporocarp production by some hypogeous ectomycorrhizal fungi associated with eucalypts, and increased mycophagy by mammals. Three experimental burns were set in E. tenuiramus forest in southeastern Tasmania. Digging activity (which reflects feeding on hypogeous fungi) by a mycophagous marsupial, the Tasmanian bettong Bettongia gaimardi, increased up to ten-fold after fire, with a peak about 1 month post-fire. This was associated with a similar pattern of increase in sporocarp production, which was due to species in the family Mesophelliaceae (especially Castoreum tasmanicum and Mesophellia spp.). This family appears to have radiated in association with eucalypts and has an exclusively Australasian distribution, unlike many of the other ectomycorrhizal fungi collected in this study which are cosmopolitan and have broad host ranges. No B. gaimardi were killed by fire, and there was no increase in mortality following fire. Population density increased after fire as a result of immigration of adult males. However, body condition and fecundity of individual B. gaimardi were maintained at pre-fire levels. This suggests that the availability of energy to B. gaimardi increased as a result of fire, and the fact that the contribution of fungus to the diet of B. gaimardi was high on burnt relative to control sites suggests further that this increase in energy availability was provided by hypogeous fungi. Effects of fire on hypogeous fungi and B. gaimardi were short-lived; all measured variables returned to control values about 4 months after fire. The capacity of B. gaimardi to survive fire and to harvest the increased sporocarp production triggered by fire provides a mechanism for the rapid dispersal of spores after fire. This should result in the establishment of ectomycorrhizae very early in post-fire succession. Because only some species of ectomycorrhizal fungi fruited in response to burning, fire probably has a strong influence on community structure among ectomycorrhizal fungi.