Trophic Transfer Efficiency in Lakes

Abstract

Trophic transfer efficiency (TTE) is usually calculated as the ratio of production rates between two consecutive trophic levels. Although seemingly simple, TTE estimates from lakes are rare. In our review, we explore the processes and structures that must be understood for a proper lake TTE estimate. We briefly discuss measurements of production rates and trophic positions and mention how ecological efficiencies, nutrients (N, P) and other compounds (fatty acids) affect energy transfer between trophic levels and hence TTE. Furthermore, we elucidate how TTE estimates are linked with size-based approaches according to the Metabolic Theory of Ecology, and how food-web models can be applied to study TTE in lakes. Subsequently, we explore temporal and spatial heterogeneity of production and TTE in lakes, with a particular focus on the links between benthic and pelagic habitats and between the lake and the terrestrial environment. We provide an overview of TTE estimates from lakes found in the published literature. Finally, we present two alternative approaches to estimating TTE. First, TTE can be seen as a mechanistic quantity informing about the energy and matter flow between producer and consumer groups. This approach is informative with respect to food-web structure, but requires enormous amounts of data. The greatest uncertainty comes from the proper consideration of basal production to estimate TTE of omnivorous organisms. An alternative approach is estimating food-chain and food-web efficiencies, by comparing the heterotrophic production of single consumer levels or the total sum of all heterotrophic production including that of heterotrophic bacteria to the total sum of primary production. We close the review by pointing to a few research questions that would benefit from more frequent and standardized estimates of TTE in lakes.

Autochthonous production sustains food webs in large perialpine lakes, independent of trophic status: Evidence from amino acid stable isotopes

“…We found that trout showed non‐discrete TPs, ranging from secondary consumers to TP of 4.5, half a trophic step higher than most of lake ecosystems that are composed of four trophic levels (Jake Vander Zanden & Fetzer, 2007) This supported the top consumer position of trout in the food webs, and so the fact that they integrate the OC and energy that flows up the food chain (Mehner et al, 2022).…”

“…Autochthonous production that we found in trout could come from either benthic (biofilm) or pelagic (phytoplankton) energy channels (Mehner et al, 2022), two sources that we could not distinguish in our model. However, samples of primary consumers (i.e.…”

“…It is worth noting that trout do not represent the complexity of the whole lake food web (e.g., insectivore specialists or aquatic birds feeding on macrophytes). Rather, we used trout as an integrative tool, because as top consumers they integrate the OC that flows up the food chains (Mehner et al, 2022). By looking at EAAs in trout (see below), we could therefore describe the OC at the base of the food web that is effectively transferred up food chains, and so the source of OC TA B L E 1 Summary of study sites.…”

“…The relative importance of one pathway or the other depends on the characteristics of the OC Terr and the recipient ecosystems. In general, OC Terr is believed to subsidise aquatic consumers mainly through the assimilation of either dissolved OC (Karlsson et al, 2012) or particulate OC (Cole et al, 2006) by bacteria and protists (Mehner et al, 2022). However, there are also specific instances of fish being supported by subsidised terrestrial prey (e.g.…”

Cascading impacts of changes in subsidy quality on recipient ecosystem functioning

“…Our study was also novel in that we focused on how subsidy quality affected recipient ecosystem functions (i.e., production, recycling, and efficiency), thereby providing model predictions in metrics that are often measured by empiricists (Mehner et al, 2022). Hence, we improved on the connections or testability of existing theory, which tends to focus on measures of stability (e.g., leading eigenvalue of Jacobian matrix), a metric that is not often measured empirically.…”