Data from: Latitudinal and photic effects on diel foraging and predation risk in freshwater pelagic ecosystems

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.