Disentangling how climate change can affect an aquatic food web by combining multiple experimental approaches

Abstract

Predicting the biological effects of climate change presents major challenges due to the interplay of potential biotic and abiotic mechanisms. Climate change can create unexpected outcomes by altering species interactions, and uncertainty over the ability of species to develop in situ tolerance or track environmental change further hampers meaningful predictions. As multiple climatic variables shift in concert, their potential interactions further complicate ecosystem responses. Despite awareness of these complexities, we still lack controlled experiments that manipulate multiple climatic stressors, species interactions, and prior exposure of species to future climatic conditions. Particularly studies that address how changes in water availability interact with other climatic stressors to affect aquatic ecosystems are still rare. Using aquatic insect communities of Neotropical tank bromeliads, we combined controlled manipulations of drought length and species interactions with a space-for-time transplant (lower elevations represent future climate) and a common garden approach.Manipulating drought length and experiment elevation revealed that adverse effects of drought were amplified at the warmer location, highlighting the potential of climatic stressors to synergistically affect communities. Manipulating the presence of omnivorous tipulid larvae showed that negative interactions from tipulids, presumably from predation, arose under drought, and were stronger at the warmer location, stressing the importance of species interactions in mediating community responses to climate change. The common garden treatments revealed that prior community exposure to potential future climatic conditions did not affect the outcome. In this powerful experiment, we demonstrated how complexities arise from the interplay of biotic and abiotic mechanisms of climate change. We stress that single species can steer ecological outcomes, and suggest that focusing on such disproportionately influential species may improve attempts at making meaningful predictions of climate change impacts on food webs. K E Y W O R D S

Temperature but not nutrient addition affects abundance and assemblage structure of colonizing aquatic insects

“…However, the ability to mediate negative effects of warmer water through habitat selection may result in more complex interactions with other species and habitat types across a landscape (Amundrud and Srivastava 2019). In a scenario where changing environmental conditions increase patch temperature above the optimum for thermally sensitive species, greater colonization rates in cooler patches leads to increased density.…”

Extreme rainfall events alter the trophic structure in bromeliad tanks across the Neotropics

“…This implies that organisms from lower trophic levels may be more susceptible to rainfall changes in certain geographic regions, and may be restricted to the most stable ecosystems in the near future. As the manipulated changes in extreme rainfall were within predictions for the next few decades [1][2][3][4] , we can predict strong changes in food web structure and dynamics in the near future [5][6][7][8]15,37 . In transient water bodies, such as small streams, pools, ponds or phytotelmata, this may intensify trophic interaction and result in less stable ecosystems 21 .…”

Cascading effects of predators on algal size structure

“…The extent to which these factions operate in the future is uncertain and will likely depend on the timing of hydrologic regimes associated with climate change (e.g., Douglas et al 2020, Euskirchen et al 2020. While extended wet periods will likely increase trophic regulation, including the indirect effects of predators, more intermittent periods of drought may restrict top-down forces by limiting the development of higher trophic levels (Marks et al 2000, Amundrud andSrivastava 2019).…”