Latitudinal and photic effects on diel foraging and predation risk in freshwater pelagic ecosystems.

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Latitudinal and photic effects on diel foraging and predation risk in freshwater pelagic ecosystems.

J Anim Ecol. 2014 Sep 29;

Authors: Hansen AG, Beauchamp DA

Abstract
1. Clark & Levy (1988) described an antipredation window for smaller planktivorous fish during crepuscular periods when light permits feeding on zooplankton, but limits visual detection by piscivores. Yet, how the window is influenced by the interaction between light regime, turbidity and cloud cover over a broad latitudinal gradient remains unexplored. 2. We evaluated how latitudinal and seasonal shifts in diel light regimes alter the foraging-risk environment for visually-feeding planktivores and piscivores across a natural range of turbidities and cloud covers. Pairing a model of aquatic visual feeding with a model of sun and moon illuminance, we estimated foraging rates of an idealized planktivore and piscivore over depth and time across factorial combinations of latitude (0-70º), turbidity (0.1-5 NTU) and cloud cover (clear to overcast skies) during the summer solstice and autumnal equinox. We evaluated the foraging-risk environment based on changes in the magnitude, duration and peak timing of the antipredation window. 3. The model scenarios generated up to 10-fold shifts in magnitude, 24-fold shifts in duration, and 5.5 h shifts in timing of the peak antipredation window. The size of the window increased with latitude. This pattern was strongest during the solstice. In clear water at low turbidity (0.1-0.5 NTU), peaks in the magnitude and duration of the window formed at 57-60º latitude, before falling to near zero as surface waters became saturated with light under a midnight sun and clear skies at latitudes near 70º. Overcast dampened the midnight sun enough to allow larger windows to form in clear water at high latitudes. Conversely, at turbidities ≥ 2 NTU, greater reductions in the visual range of piscivores than planktivores created a window for long periods at high latitudes. Latitudinal dependencies were essentially lost during the equinox, indicating a progressive compression of the window from early summer into autumn. 4. Model results show that diel-seasonal foraging and predation risk in freshwater pelagic ecosystems changes considerably with latitude, turbidity and cloud cover. These changes alter the structure of pelagic predator-prey interactions, and in turn, the broader role of pelagic consumers in habitat coupling in lakes. This article is protected by copyright. All rights reserved.

PMID: 25266197 [PubMed – as supplied by publisher]

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Developing a broader scientific foundation for river restoration: Columbia River food webs.

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Developing a broader scientific foundation for river restoration: Columbia River food webs.

Proc Natl Acad Sci U S A. 2012 Nov 28;

Authors: Naiman RJ, Alldredge JR, Beauchamp DA, Bisson PA, Congleton J, Henny CJ, Huntly N, Lamberson R, Levings C, Merrill EN, Pearcy WG, Rieman BE, Ruggerone GT, Scarnecchia D, Smouse PE, Wood CC

Abstract
Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure-without explicitly considering food webs-has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.

PMID: 23197837 [PubMed – as supplied by publisher]

via pubmed: school of aquatic an… http://www.ncbi.nlm.nih.gov/PubMed/23197837?dopt=Abstract