Agriculture and Mining Contamination Contribute to a Productivity Gradient Driving Cross-Ecosystem Associations Between
Stream and riparian ecosystems can be strongly connected via the emergence of adult aquatic insects, which form an important prey subsidy for a wide range of terrestrial consumers. Consequently, human perturbations affecting stream ecosystems may propagat
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strong insight for applied ecology is that the dynamics of seemingly distinct systems are intimately linked by spatial flow of matter and organisms. [P]rocesses and policies in aquatic systems…affect both aquatic and terrestrial systems Polis et al. (1997)
1 Introduction The reciprocal flow of resource subsidies from one habitat to another can strongly influence the structure and dynamics of food webs in a wide range of ecosystems (Polis et al. 1997). This pattern challenges ecologists to redefine interaction webs to include strong links both within and across traditional habitat and ecosystem boundaries (Sabo and Power 2002). For example, stream and terrestrial ecosystems can be highly connected via reciprocal subsidies that include exchanges of organic matter and prey (Power and Rainey 2000; Nakano and Murakami 2001). In particular, the emergence of adult aquatic insects forms an important prey subsidy for a wide range of riparian consumers that include spiders, birds, lizards, and bats (Baxter et al. 2005). However, human pressures from activities such as mining and agriculture frequently degrade stream ecosystems (Allan 2004), with potential consequences
F. J. Burdon (*) School of Biological Sciences, University of Canterbury, Christchurch, New Zealand Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden e-mail: [email protected] © Springer Nature Switzerland AG 2020 J. M. Kraus et al. (eds.), Contaminants and Ecological Subsidies, https://doi.org/10.1007/978-3-030-49480-3_4
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for cross-habitat linkages through impacts on stream assemblages (Baxter et al. 2005). Food web theory suggests that productivity gradients in both recipient and donor habitats can drive the magnitude of subsidy influences across habitats (Polis et al. 1997). The strength of this influence may also depend on the trophic level at which the subsidy is received, with effects generally greater on detritivores than higher trophic levels (Marczak et al. 2007). Moreover, the magnitude of indirect effects resulting from subsidies may decrease as the trophic level of resource and consumer fluxes increases (Allen and Wesner 2016). However, resource quality should also be considered in combination with the magnitude of subsidy fluxes between ecosystems, because many consumers preferentially favor low-flux, high-quality resources (Marcarelli et al. 2011). For example, stream insects can be an important source of essential, highly unsaturated fatty acids (HUFAs), which may disproportionately mediate their effects on receiving food webs (Twining et al. 2016a). Thus, the quality and quantity of aquatic-derived prey subsidies should influence communities of terrestrial consumers, and their importance may be greatest where in situ prey production and quality is low in the receiving habitat, such as resource-scarce riparian gravel bars (Naiman et al. 2005)
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