Temperature sensitivity of vertical distributions of zooplankton and planktivorous fish in a stratified lake

Abstract

Recent studies have indicated that temporal mismatches between interacting populations may be caused by consequences of global warming, for example rising spring temperatures. However, little is known about the impact of spatial temperature gradients, their vulnerability to global warming, and their importance for interacting populations. Here, we studied the vertical distribution of two planktivorous fish species (Coregonus spp.) and their zooplankton prey in the deep, oligotrophic Lake Stechlin (Germany). The night-time vertical centre of gravity both of the fish populations and of two of their prey groups, daphnids and copepods, were significantly correlated to the seasonally varying water temperature between March and December 2005. During the warmer months, fish and zooplankton occurred closer to the surface of the lake and experienced higher temperatures. The Coregonus populations differed significantly in their centre of gravity; hence, also, the temperature experienced by the populations was different. Likewise, daphnids and copepods occurred in different water depths and hence experienced different temperatures at least during the summer months. We conclude that any changes in the vertical temperature gradient of the lake as a result of potential future global warming may impact the two fish populations differently, and may shape interaction strength and timing between fish and their zooplankton prey.

Adaptive Phenotypic Diversification along a Temperature-Depth Gradient

“…Figure 4B shows the depth distributions of the two morphs after dimorphic evolution has come to a halt and compares their average depths with the year-round average depths observed for the coregonids in Lake Stechlin. This comparison shows that the model-predicted average depths of the populations at the endpoint of dimorphic evolution match very well those observed in the field (Helland et al 2007). Figure 5 displays the evolutionary outcome for the sexual model in dependence on the functions describing assortative mating and segregation/recombination.…”

“…B, Depth distributions at the evolutionary endpoint (solid and dashed curved lines) for the two populations. The resultant model-predicted average depths (solid and dashed horizontal lines) are compared with the average depths observed for the Lake Stechlin coregonids (dotted lines), showing very good agreement (at 17 and 24 m, respectively; Helland et al 2007). : Evolutionary outcomes of the sexual model (white for monomorphic, gray for dimorphic), depending on the widths of the assortative-mating kernel (j a ) and of the segregation-recombination kernel (j sr ).…”

“…ciation drive the ecological differentiation that enables the coexistence of closely related species in sympatry (Schluter 2000;Coyne and Orr 2004). Previous empirical studies on the species pair in Lake Stechlin had revealed that the two coexisting coregonids have diverged with respect to their vertical distribution in the lake (Helland et al 2007(Helland et al , 2009), the temperature dependence of their metabolisms (Ohlberger et al 2008b), and their associated thermal preferences (Ohlberger et al 2008c). The concordance in the ecological, physiological, and behavioral differentiation of the species with respect to temperature suggests thermal specialization as the main driver of their eco-evolutionary divergence.…”

“…The species differ in their average population depths within the pelagic zone, with C. fontanae being found deeper in the water column than C. albula throughout the year. This difference in depth distribution is associated with a difference in mean experienced water temperature (Helland et al 2007;Mehner et al 2010a).…”

“…This parameter measures the degree to which individuals forage at their temperature optimum. In order to estimate the degree of foraging optimality in the natural system, we ran our model without evolutionary dynamics for the empirically determined temperature optima as fixed trait values and compared the resulting average depths with the measured year-round average depths of the Lake Stechlin coregonids (Helland et al 2007). Figure B1 shows, as a function of a, the sum of absolute values of the deviations of the two modeled population depths from the two observed average population depths in the natural system.…”