The underappreciated role of rodent generalists in fungal spore dispersal networks

Abstract

Animals are often the primary dispersers of seeds and fungal spores. Specialist species that consume fruits or fungal fruiting bodies (sporocarps) as their main food source are thought to play a more important role in dispersal networks compared to generalist species. However, dispersal networks are often based on occurrence data, overlooking the influence of animal abundance and dispersal effectiveness on network interactions. Using rodent‐mycorrhizal fungi networks, we determined how diet specialization and abundance influence the role of rodent species in dispersing fungal spores in temperate forests of northern New Hampshire, USA. We tracked the interactions of five rodent species and 34 fungal taxa over a 3‐yr period across hardwood, mixed, and softwood forest stands. We accounted for fluctuations in rodent abundance and differences in the number of spores dispersed in rodent scat. Myodes gapperi, a fungal specialist, dispersed a more diverse spore community than rodent generalists and was consistently the most important disperser in forest types with high fungal availability. Nevertheless, during years when generalist species such as Tamias striatus and Peromyscus maniculatus reached high abundance, their relative importance (species strength) in networks approached or even surpassed that of M. gapperi, particularly in forest types where M. gapperi was less common and fungal availability was low. Increased numbers of generalists enhanced network interaction diversity and the number of fungal taxa dispersed, the timing of which was coincident with seedling establishment following masting, a stage when inoculation by mycorrhizal fungi is critical for growth and survival. Our findings suggest that although specialists play key roles in dispersing mycorrhizal fungal spores, generalists play a heretofore underappreciated role.

Signaling from below: rodents select for deeper fruiting truffles with stronger volatile emissions

“…For truffle selection, we focused on five rodents that are among the most common species in the Northeast (Stephens et al 2017 a ): woodland jumping mice ( Napaeozapus insignis ), white‐footed mice ( Peromyscus leucopus ), deer mice ( P. maniculatus ), eastern chipmunks ( Tamias striatus ), and southern red‐backed voles ( Myodes gapperi ). Although all five rodent species consume fungi during the summer, fungi only comprise about 15% of the diets of N. insignis , P. leucopus , P. maniculatus , and T. striatus whereas M. gapperi is a fungal specialist with over 60% of its diet from fungi (Stephens and Rowe, in press ). To determine consumption of Elaphomyces species by rodents, we collected scat samples in June, July, and August of 2013–2015 on each grid.…”

“…Although Elaphomyces spp. are among the most commonly consumed fungal taxa by rodents at Bartlett Experimental Forest, there are over 30 other fungal taxa consumed (Stephens and Rowe in press ). Additionally, fungi only comprise about 15% of the diet for most of the rodent species during the summer (Stephens and Rowe in press ).…”

“…are among the most commonly consumed fungal taxa by rodents at Bartlett Experimental Forest, there are over 30 other fungal taxa consumed (Stephens and Rowe in press ). Additionally, fungi only comprise about 15% of the diet for most of the rodent species during the summer (Stephens and Rowe in press ). Thus, because all four Elaphomyces species were rarely consumed on a daily basis by an individual rodent, and spores are expelled within 3 d (Cork and Kenagy , Danks ), it is difficult to determine selection for Elaphomyces spp.…”

“…f–h), subsequently passing spores in their scat. The abundance of spores in scat is a product of how many, and how often, truffles are eaten, and can be used as an index of truffle consumption (Stephens and Rowe ). Following methods in Stephens et al (2017 b ), we calculated the number of spores per gram of rodent scat for each Elaphomyces species.…”

Classifying rodent diets for comparative research

“…Frugivory is widespread among mammals, but is typically reported for primates, particular bat groups, and large herbivores (Bodmer & Ward 2006). We posit Frugivores as a cohesive set of plant‐eating rodents that also consume fungi, with often underappreciated roles as dispersers of seeds and fungal spores (Stephens & Rowe 2020).…”