The emergence of aquatic
insects from streams is a reliable, annual event. Some aquatic
adults are eaten by terrestrial predators while others return to the
aquatic system to lay eggs or be consumed by aquatic predators. This
exchange of prey between aquatic and terrestrial systems can affect the complexity and
structure of food webs. The flow of energy between systems can
increase production of consumers to levels more than terrestrial
production alone would support.
As part of a larger effort characterizing food chains in
hardwood- and conifer-dominated riparian systems, our study
examines linkages between emergent aquatic insects and predatory
spiders. Predators might be present in riparian areas because
of specific habitat requirements, or because particular food
resources, unique to these habitats, are available. Predatory
web-spinning spiders, such as those belonging to the families
of Tetragnathidae, Araneidae, Linyphiidae, and Uloboridae,
prey on a myriad of insects. In riparian areas emergent aquatic
insects may be limited to short distances from the stream;
these aquatic prey may influence how predators, such as spiders,
are distributed.
The objectives of this study are to describe riparian spider
habitat and to examine the prey base of spiders both seasonally
and by riparian vegetation type. The main questions we address
are 1) whether spider size and abundance depends on the availability
of aquatic emergents (as measured by distance from the stream);
2) whether emergent availability varies between alder- and
conifer- dominated reaches; and 3) whether emergent availability
varies between wet (~ May-June) and dry (~August-September)
seasons. By examining the availability and use of aquatic
prey in riparian zones of varying composition, this will be
a detailed study of an important interaction between stream
and terrestrial communities.
