Cross-ecosystem effects of a large terrestrial herbivore on stream ecosystem functioning

Large
terrestrial consumers have direct and indirect effects on forest ecosystem
function, but few studies have investigated the impacts of terrestrial
consumers on freshwater ecosystems. In the Cape Breton Highlands of Nova
Scotia, browsing by hyper-abundant moose has transformed boreal forest into
grasslands. We investigated the potential for cross-ecosystem effects of hyper-abundant
moose on small boreal stream ecosystem structure and function. We predicted that
watersheds with higher levels of moose-mediated grasslands in their sub-basins would
have higher stream temperatures, total nitrogen, electrical conductivity,
periphyton biomass, and macroinvertebrate abundances. We found evidence of
higher stream temperature range, total nitrogen, electrical conductivity and
relative abundance of predatory inverts in streams with high moose impacts in
their watersheds. However, we found little evidence of moose impacts on average
daily maximum, average, maximum and minimum stream temperatures, periphyton
biomass and the abundance of shredders, filterers, gatherers, and grazers. This
empirical study fills a key gap in our understanding of meta-ecosystem ecology
by providing insight into the effects of large terrestrial consumers across
ecosystem boundaries with potential implications for landscape-scale management
of hyper-abundant ungulates.