Abstract
Ecological regime shifts typically result in abrupt changes in ecosystem structure through several trophic levels, which leads to rapid ecosystem reconfiguration between regimes. An interesting aspect of the impact of regime shift is that alternative regimes may induce distinct shifts in energy pathways; these have been less tested than structural changes. This paper addresses this by using stable isotopes to establish the energy pathways in fish communities. We specifically focus on the impact of regime shift on changes of the energy pathways, and how the magnitude and direction of these changes affect the local community. We found that energy pathways significantly varied among the planktivorous, benthivorous, and piscivorous trophic guilds as a result of the alternative regimes. The regime shift from a clear to a turbid state altered the food web towards planktonic energy pathways and truncated food chain length, which is indicative of less ecological efficiency. This was confirmed by the adaptive foraging strategies of prevalent omnivores in the current communities. These structural and functional characteristics of trophic interactions might not facilitate classic trophic cascading effects in such a turbid regime and suppress the system’s response to environmental changes, e.g., nutrient loading, and restoration efforts in turbid to clear water regime shifts.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-013-2878-2) contains supplementary material, which is available to authorized users.
Highlights
Differences in δ13C and δ15N of fish species by regimes were complex, and it was difficult to identify patterns of food web change from these isotopic signatures. Some species, such as those belonging to the planktivorous trophic guild, had clearly shifted in isotopic niche space by regimes (Fig. 1)
Shallow lakes are the typical example of ecosystems with alternative regimes
The regimes are commonly categorized as the clear water regime with abundant submersed macrophytes and the turbid regime with few submersed macrophytes (Jeppesen et al 2007; Scheffer and Carpenter 2003)
Summary
Shallow marine systems can shift between coral- and macroalgae-dominated structures and grazers (McCook 1999), and shallow lakes can shift between clear, macrophyte-dominated and turbid, phytoplankton-dominated regimes (Scheffer et al 1993) Understanding variations in these alternative regimes is of importance for understanding responses to environmental changes and ecosystem management. Despite the general pattern of benthic and planktonic energy pathways, our knowledge about the effects of energy pathways in alternative regimes on fish communities remains negligible, especially for eutrophic subtropical shallow lakes dominated by omnivorous fish species. With respect to such subtropical lakes, the following questions remain unanswered: 1. We illustrate the manner in which alternative ecosystem regimes can affect the energy pathways of fish communities, giving insight into the causes and patterns, as well as fundamental stability properties, of this ecosystem
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