Impacts on Stream Food Webs of Native and Exotic Forest: An Intercontinental Comparison

Native pine-forest streams from Maine and North Carolina, USA, and exotic pine-forest streams from New Zealand were compared to assess the effects of geographic location on three aspects of community structure: (1) taxonomic composition, (2) trophic structure (summarized in terms of functional feeding groups), and (3) food web structure (as connectivity food webs). In addition, pine-forest assemblages in New Zealand were compared to assemblages from New Zealand native forest and grassland streams. Taxonomic similarity was, as expected, low for invertebrates, but there were strong similarities in the algal assemblages in different geographic locations. Trophic structure analysis was unable to distinguish either geographic or land-use effects. Food web analysis revealed structural similarities between the pine-forest streams, regardless of location, but there were clear differences among land uses in New Zealand. Pine-forest streams were typified by food webs with few algal species, low internal connectance and a relatively square shape. Grassland food webs were more triangular in shape and exhibited high internal connectance, while native forest food webs had intermediate characteristics. The results show that the native stream biota, despite a distinct species composition, can adapt to a novel riparian vegetation type and produce trophic and food web structures that are difficult to distinguish from those in the country of origin.