Asymmetric assimilation of an anthropogenic resource subsidy in a freshwater food web

McMeans

Guzzo

et al. 2020

Preprint

Self Cite

Global change is fundamentally altering flows of natural and anthropogenic subsidies across space and time. After a pointed call for research on subsidies in the 1990s, an industry of empirical work has documented the ubiquitous role subsidies play in ecosystem structure, stability and function. Here, we argue that physical constraints (e.g., water temperature) and species traits can govern a species’ accessibility to resource subsidies, and that these physical constraints have been largely overlooked in the subsidy literature. We examined the input of a high quality, point-source anthropogenic subsidy into a recipient freshwater lake food web (i.e., released net-pen aquaculture feed in Parry Sound, Lake Huron), to demonstrate the importance of subsidy accessibility in governing recipient whole food web responses. By using a combined bio-tracer approach, we detect a gradient in accessibility of the anthropogenic subsidy within the surrounding food web driven by the thermal tolerances of three constituent species. This thermally-driven accessibility gradient drives asymmetrical changes in food web structure, effectively rewiring the recipient lake food web and altering patterns in secondary production with yet unknown stability consequences. Since aquaculture is predicted to increase significantly in coming decades to support growing human populations, and global change is altering temperature regimes, then this form of food web alteration may be expected to occur frequently. We argue that subsidy accessibility is a key characteristic of recipient food web interactions that must be considered when trying to understand the impacts of subsidies on ecosystem stability and function under continued global change.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Subsidy Accessibility Drives Asymmetric Food Web Responses

McMeans

Guzzo

et al. 2020

Preprint

Self Cite

“…Escape was due to a 2018 fall storm that damaged growing pens and led to the escape of tens of thousands of fish into the lake. A baseline for comparison with escapees relied on sampling of captive trout directly from growing pens in 2019 as well as in prior years (2015)(2016)(2017), part of a study of resource subsidies of the farming operation into the Parry Sound food web (Johnson et al, 2018). The use of fish sampled over multiple years was needed to establish a reliable baseline of captive fish.…”

Section: Sampling and Preparationmentioning

confidence: 99%

“…We compared damage to the caudal fins on photographs of rainbow trout and lake trout sampled in Parry Sound using available photographs of lake trout sampled for purposes other than the present study (e.g. Johnson et al, 2018). A scale of caudal fin damage adapted from Petersson et al (2013) was established with the lower erosion level 1 (little to no erosion) what is typically seen in wild fish, intermediate erosion level 2 (clear erosion on less than 50% of the fin), and advanced erosion level 3 (fin more than 50% eroded) (Figure 1B).…”

Section: Fin Erosionmentioning

confidence: 99%

Increased brain growth in escaped rainbow trout

Laberge

McCann

2021

Preprint

Self Cite

Recent examples of rapid brain size plasticity in response to novel laboratory environments suggest that fish brain size is a flexible trait, allowing growth or shrinkage of brain tissue based on short term needs. Nevertheless, it remains to be seen if plasticity of fish brain size is relevant to natural environmental conditions. Here, using rainbow trout escaped from a farming operation as a natural experiment, we demonstrate that adult fish brain size can change rapidly in response to life in a natural lake environment. Specifically, escaped trout had on average 15% heavier brains relative to body size than captive trout after living for about 7 months in the lake. Because relative brain size of most escaped trout fell above the range of variation seen within the captive trout population, we conclude that increased brain size was achieved by plasticity after escape. Brain morphology analysis showed that the most anterior regions (olfactory bulbs and rest of telencephalon) contributed most to the increase in overall brain size in escaped trout. Relative size of the heart ventricle, another organ which can be subject to plastic changes under variable environmental conditions in fish, did not differ between escaped and captive trout. Massive and selective brain growth under the changed environmental conditions associated with escape from holding pens highlighted the plastic potential of fish brain size and suggests that a shift to increased complexity of life in the wild setting of a lake imposed greatly increased cognitive requirements on escaped trout.

“…Akin to natural subsidies, anthropogenic subsidies also have the potential to influence recipient food web dynamics (DeBruyn et al, 2004;Rodewald et al, 2011;Newsom et al, 2015;Singer et al, 2016;Lee et al, 2018;Johnson et al, 2018;DeBruyn et al, 2020). As food web dynamics govern whole ecosystem stability and function (de Ruiter et al, 1995;Neutel et al, 2002), it is imperative to understand how recipient food webs respond to both natural and anthropogenic subsidies under continued global change.…”

Section: Introductionmentioning

confidence: 99%

Subsidy accessibility drives asymmetric food web responses

McMeans

Guzzo

et al. 2022

Ecology

Self Cite

Global change is fundamentally altering flows of natural and anthropogenic subsidies across space and time. After a pointed call for research on subsidies in the 1990s, an industry of empirical work has documented the ubiquitous role subsidies play in ecosystem structure, stability and function.Here, we argue that physical constraints (e.g., water temperature) and species traits can govern a species' accessibility to resource subsidies, and that these physical constraints have been largely overlooked in the subsidy literature. We examined the input of a high quality, point-source anthropogenic subsidy into a recipient freshwater lake food web (i.e., released net-pen aquaculture feed in Parry Sound, Lake Huron), to demonstrate the importance of subsidy accessibility in governing recipient whole food web responses. By using a combined bio-tracer approach, we detect a gradient in accessibility of the anthropogenic subsidy within the surrounding food web driven by the thermal tolerances of three constituent species. This thermally-driven accessibility gradient drives asymmetrical changes in food web structure, effectively rewiring the recipient lake food web and altering patterns in secondary production with yet unknown stability consequences.Since aquaculture is predicted to increase significantly in coming decades to support growing human populations, and global change is altering temperature regimes, then this form of food web alteration may be expected to occur frequently. We argue that subsidy accessibility is a key characteristic of recipient food web interactions that must be considered when trying to understand the impacts of subsidies on ecosystem stability and function under continued global change.