Disruption of ecological networks in lakes by climate change and nutrient fluctuations

Abstract

Climate change interacts with local processes to threaten biodiversity by disrupting the complex network of ecological interactions. While changes in network interactions drastically affect ecosystems, how ecological networks respond to climate change, in particular warming and nutrient supply fluctuations, is largely unknown. Here, using an equation-free modelling approach on monthly plankton community data in ten Swiss lakes, we show that the number and strength of plankton community interactions fluctuate and respond nonlinearly to water temperature and phosphorus. While lakes show system-specific responses, warming generally reduces network interactions, particularly under high phosphate levels. This network reorganization shifts trophic control of food webs, leading to consumers being controlled by resources. Small grazers and cyanobacteria emerge as sensitive indicators of changes in plankton networks. By exposing the outcomes of a complex interplay between environmental drivers, our results provide tools for studying and advancing our understanding of how climate change impacts entire ecological communities.

Direct and indirect relationships of climate and land use change with food webs in lakes and streams

“…Thus, for both lakes and streams, we expected warming to decrease top consumer occurrence (Ho et al, 2022;Merz et al, 2023), increase herbivory and omnivory (O'Connor, 2009;Wootton, 2017) and reduce mean trophic levels within food webs (Jackson et al, 2020;O'Gorman et al, 2019). As in freshwater ecosystems, top predators can be large consumers with wider niche breadth (Ho et al, 2022), we expected connectance to decrease with warming in lakes (Merz et al, 2023) and streams (Ho et al, 2022;O'Gorman et al, 2019).…”

“…Another difference is their geological history: lakes can have diverse origins and ages, while rivers are more uniform in their formation and evolution (Allan & Castillo, 2009;Wetzel, 2001). These differences have implications for the ecology and biodiversity of these systems and influence how communities respond to environmental changes (Ho et al, 2022;Merz et al, 2023;Rosset et al, 2017).…”

“…We first tested the hypothesis that (H1) land use intensification favours generalist consumers in freshwater food webs due to ecosystem homogenization (Estes et al, 2011;Schürings et al, 2022). We expected a decrease in the number of top specialist consumers (Ho et al, 2022;Merz et al, 2023) and, consequently, an increase in herbivory and omnivory (Wootton, 2017), decrease in mean trophic levels and higher connectance values in both lake and streams, as generalists concentrate a higher number of links within few species (Riede et al, 2010;Tylianakis & Morris, 2017). However, (H2) the exclusion of top predators could also reduce connectance, as in cases where environmental changes caused the extinction of generalist top consumers with relatively broader diets in lakes (Merz et al, 2023) and streams (Ho et al, 2022).…”

“…Regarding temperature change, we tested the following hypothesis: (H3) warming increases the demand for food resources, selecting against large top predators and favouring omnivores and species at lower trophic levels (Jackson et al, 2020;Wootton, 2017). Thus, for both lakes and streams, we expected warming to decrease top consumer occurrence (Ho et al, 2022;Merz et al, 2023), increase herbivory and omnivory (O'Connor, 2009;Wootton, 2017) and reduce mean trophic levels within food webs (Jackson et al, 2020;O'Gorman et al, 2019). As in freshwater ecosystems, top predators can be large consumers with wider niche breadth (Ho et al, 2022), we expected connectance to decrease with warming in lakes (Merz et al, 2023) and streams (Ho et al, 2022;O'Gorman et al, 2019).…”

“…Regarding precipitation change, we tested the following hypothesis: (H5) water limits the flux of biomass across trophic levels and regulate the loss of species and interactions (Ledger et al, 2013;Rosenblatt et al, 2017). Thus, we expected reduced precipitation to decrease top consumers, mean trophic level and connectance in lakes and streams (Ho et al, 2022;Merz et al, 2023). However, (H6) physical aspects of ecosystems govern how precipitation change influences freshwater communities (Rosset et al, 2017).…”