Land‐use influences on New Zealand stream communities: Effects on species composition, functional organisation, and food‐web structure

Abstract

We used standardised techniques to assemble 18 food‐webs in streams subject to four land uses; exotic pasture, native tussock, native forest, and pine plantation. There were clear differences in the algal productivity and standing crops of organic matter between the forested (native and pine) and grassland (tussock and pasture), but not within each grouping. Algal productivity was more than twice as high in the grassland sites, whereas the converse was true for organic matter standing crop. These differences in energy resources were correlated with differences in community composition and food‐web structure. Although all streams had a generalist core of species, certain species of algae and invertebrates were predictably associated with either forested or grassland sites. Food‐web structure in the forested and grassland sites was also distinct. Grassland food‐webs were complex, highly internally connected, and typified by a “triangular” shape. Forested food‐webs in contrast were less highly connected, tended to have fewer trophic levels, and were “squarer” in shape. These results provide some support for the concept that energy supply may be an important contributing factor influencing stream community structure. In terms of riparian management, the results emphasise the importance of protecting representative vegetation around streams to protect stream communities.

Keywords:

• land‐use
• stream
• food‐web structure
• productivity