Abstract
AbstractEcosystem engineers can have diverse and conflicting effects on their ecosystems, and the balance between these effects can depend on the physical environment. This context dependence means that environmental variation can produce large differences in engineer effects through space and time. Here, we explore how local variability in environmental conditions can lead to large spatiotemporal variation in the effect of tube‐building midges on benthic ecosystem metabolism in a shallow subarctic lake. Using field experiments, we found that midge engineering increases both gross primary production (GPP) and respiration (RESP) in the sediment. Gross primary production and RESP have opposing influences on net ecosystem production, and the net effect of midges on the benthic ecosystem depends on the balance between their effects on GPP and RESP. Variation in light mediates this balance—under high light conditions, primary producers are able to exploit the structural benefits provided by midges, while in the dark, the elevation of respiration from midge engineering predominates. Benthic light levels vary spatially and temporally due to episodic cyanobacterial blooms that prevent almost all light from reaching the benthos. By quantifying the nonlinear relationship between midge engineering and light, we were able to project ecosystem‐wide consequences of natural variation in light conditions across the lake. Our results illustrate how the sign and magnitude of ecosystem‐wide effects of ecosystem engineers can vary through space and time.
Highlights
Ecologists have long been interested in the potential for single populations to have disproportionate influences on their ecosystems (Paine 1966)
We examined midge effects on net ecosystem production (NEP), which equals gross primary production (GPP) minus respiration (RESP; Lovett et al 2006, Chapin et al 2006)
Gross primary production was higher in the presence of midges (F1,24.78 = 6.34, P = 0.019) and silk (F1,25.64 = 6.83, P = 0.015) than in their absence, and these effects were of comparable magnitudes (Fig. 3a, b)
Summary
Ecologists have long been interested in the potential for single populations to have disproportionate influences on their ecosystems (Paine 1966). Scaling small-scale engineering to ecosystem-wide effects requires (1) modeling the functional response of engineering to continuous variation in the environment and (2) quantifying the spatial and temporal variation in the environment within the region of interest (Wright et al 2006, Hastings et al 2007). This is important because responses of engineering to environmental conditions are likely nonlinear (as is true for many ecological processes) and the shape of this nonlinearity could have large consequences for the overall effects of engineering in variable environments (Ruel et al 1999)
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