Department of Forest Sciences
3041-2424 Main Mall, UBC
Vancouver, B.C. V6T 1Z4
Position: Ph.D. Candidate
Study Area: Community ecology and forestry impacts on complex systems
Project: Linking stream and forest food webs: the effects of aquatic insects on riparian predators and their terrestrial prey.
Previous studies have often argued that riparian forests generally support greater species diversity and population abundance of terrestrial consumers than adjacent upland habitats although the mechanisms responsible for this effect have remained poorly understood. In attempting to ascertain the factors that promote biodiversity in both streams and their riparian forests it is vital to determine the importance of streams to biodiversity in the riparian forests they traverse and the strength of the food web linkages between the two habitats. Forest and stream food webs are widely viewed as energetically coupled, particularly with respect to the contributions of riparian forests to stream ecosystems. Inputs of particulate organic matter from riparian forests represent an important energy source of stream production [1, 2] while accidental inputs of terrestrial invertebrates are known to be a major prey category directly available for stream consumers such as fish [3, 4]. Conversely, the importance of cross-boundary subsidies from streams to riparian forest communities has only recently been emphasized. Researchers have begun to quantify the importance of nutrients from salmon carcasses in riparian forest growth [5, 6], nutrient supplements to terrestrial consumers  and subsidies of emergent aquatic prey to terrestrial predators . As yet, little is known about the effects of these links on terrestrial consumer performance and fitness or direct and indirect influences on local resources, competitors or prey species.
I propose to advance our understanding of these interactions by experimentally testing the effect of river-derived insects on the growth rate of 2-3 key terrestrial predators (e.g. spiders, centipedes, carabids) and the alternate, ground-dwelling prey of these terrestrial consumers. I am interested in distinguishing between several hypotheses: · multiple predators are maintained at high densities by aquatic prey subsidies and thus have a negative indirect effect on terrestrial invertebrate prey; · intraguild competition or predation reduces the overall effectiveness of individual predators and results in a non-additive predation load and thus positive indirect effects on terrestrial prey densities; · seasonality (times of maximum terrestrial vs aquatic productivity) is the determinant of direction for these interactions. The general approach will be to experimentally manipulate the flux of aquatic subsidies (emergent insects) to large enclosures to evaluate the effects of subsidies on the growth of various combinations of predators and associated terrestrial insect abundance.
In order to develop a general theory of natural community structure and dynamics, we need to understand the mechanisms of direct and indirect effects of different species. This is particularly critical as we struggle to develop an understanding of the measures required to conserve diversity within riparian zones. This study will contribute to our understanding of cross-ecosystem fluxes and connections through close attention to the phenology, diet and behaviour of the species mediating interactions at the edges of ecosystems.
References  Wallace, J.B., et al. 1997. Science 277:102. Vannote, R.L., et al, 1980. Canadian Journal of Fisheries and Aquatic Sciences 37:130.  Nakano, S., et al. 1999. Ecological Research 14:351.  Wiplfi, M.S. 1997. Canadian Journal of Fisheries and Aquatic Sciences 54:1259.  Wipfli, M.S. 2000. Bulletin of the North American Benthological Society. 17:106.  Ben-David, M. et al. 1998. Oikos 83:47.  Bastow, J.L., et al. 2002. Oecologia 131:261.  Sabo, J.L. and M.E. Power. 2002. Ecology 83:1860.
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