Effects of differential habitat warming on complex communities

Hydrobiologia, 2017

Sustainable development of hydropower demands a holistic view of potential impacts of water level regulation (WLR) on reservoir ecosystems. Most environmental studies of hydropower have focused on rivers, whereas environmental effects of hydropower operations on reservoirs are less well understood. Here, we synthesize knowledge on how WLR from hydropower affects alpine lake ecosystems and highlight the fundamental factors that shape the environmental impacts of WLR. Our analysis of these impacts ranges from abiotic conditions to lower trophic levels and ultimately to fish. We conclude that the environmental effects are complex and case-specific and thus considering the operational regime of WLR (i.e., amplitude, timing, frequency, and rate of change) as well as the reservoir's morphometry, geology and biotic community are prerequisites for any reliable predictions. Finally, we indicate promising avenues for future research and argue that recording and sharing of data, views and demands among different stakeholders, including operators, researchers and the public, is necessary for the sustainable development of hydropower in alpine lakes.

Ecology and Evolution

The stability of complex ecosystems depends on the maintenance of the distinct properties of energy channels, such as different levels of productivity and turnover rate (McCann, Rasmussen, &

Scientific Reports

As agricultural regions are threatened by climate change, warming of high latitude regions and increasing food demands may lead to northward expansion of global agriculture. While socioeconomic demands and edaphic conditions may govern the expansion, climate is a key limiting factor. Extant literature on future crop projections considers established agricultural regions and is mainly temperature based. We employed growing degree days (GDD), as the physiological link between temperature and crop growth, to assess the global northward shift of agricultural climate zones under 21 st-century climate change. Using ClimGen scenarios for seven global climate models (GCMs), based on greenhouse gas (GHG) emissions and transient GHGs, we delineated the future extent of GDD areas, feasible for small cereals, and assessed the projected changes in rainfall and potential evapotranspiration. By 2099, roughly 76% (55% to 89%) of the boreal region might reach crop feasible GDD conditions, compared to the current 32%. The leading edge of the feasible GDD will shift northwards up to 1200 km by 2099 while the altitudinal shift remains marginal. However, most of the newly gained areas are associated with highly seasonal and monthly variations in climatic water balances, a critical component of any future land-use and management decisions.

Proceedings of the National Academy of Sciences, 2017

Significance Climate warming is having wide-ranging effects on aquatic ecosystems. Fish are believed to adapt their feeding behavior as temperatures change, but empirical evidence of this behavior in nature and its impacts on individual fitness are lacking. We monitored the feeding behavior and growth of a temperature-sensitive fish population in a pristine lake for 11 y. Fish adjusted their feeding behavior annually in response to differences in temperature. In cooler years, fish ate more large prey from shallow nearshore regions, resulting in higher growth and condition than in warmer years, when fish ate more small prey from deep offshore regions. This suggests that the impacts of warming on aquatic ecosystems can scale from the individual to the food web level.

PLOS Biology, 2019

Aquatic ecosystems worldwide continue to experience unprecedented warming and ecological change. Warming increases metabolic rates of animals, plants, and microbes, accelerating their use of energy and materials, their population growth, and interaction rates. At a much larger biological scale, warming accelerates ecosystem-level processes, elevating fluxes of carbon and oxygen between biota and the atmosphere. Although these general effects of temperature at finer and broader biological scales are widely observed, they can lead to contradictory predictions for how warming affects the structure and function of ecological communities at the intermediate scale of biological organization. We experimentally tested the hypothesis that the presence of predators and their associated species interactions modify the temperature dependence of net ecosystem oxygen production and respiration. We tracked a series of independent freshwater ecosystems (370 L) over 9 weeks, and we found that at higher temperatures, cascading effects of predators on zooplankton prey and algae were stronger than at lower temperatures. When grazing was weak or absent, standing phytoplankton biomass declined by 85%-95% (<1-fold) over the temperature gradient (19-30˚C), and by 3-fold when grazers were present and lacked predators. These temperature-dependent species interactions and consequent community biomass shifts occurred without signs of species loss or community collapse, and only modestly affected the temperature dependence of net ecosystem oxygen fluxes. The exponential increases in net ecosystem oxygen production and consumption were relatively insensitive to differences in trophic interactions among ecosystems. Furthermore, monotonic declines in phytoplankton standing stock suggested no threshold effects of warming across systems. We conclude that local changes in community structure, including temperature-dependent trophic cascades, may be compatible with prevailing and predictable effects of temperature on ecosystem functions related to fundamental effects of temperature on metabolism.

2017

Ecological communities and their ecosystem functions are sensitive to temperature, and aquatic habitats worldwide continue to experience unprecedented warming. Understanding ecological effects of warming requires linking empirical evidence to theories that allow projection to unobserved conditions. Metabolic scaling theory and its tests suggest that warming accelerates ecosystem functions (e.g., oxygen flux), yet this prediction apparently contradicts community-level studies suggesting warming is a stressor that can reduce ecosystem function. We sought to reconcile these predictions with an experimental test of the hypothesis that cascading trophic interactions modify the temperature-dependence of community structure and ecosystem fluxes. In a series of independent freshwater ecosystems exposed to a thermal gradient, we found that warmer temperatures strengthened the trophic cascade increased and indirectly changed community structure by altering grazer species composition and phyto...

Diversity and Distributions, 2019

Aim: Understanding and quantifying the seasonal patterns in biodiversity of phytobenthos, macro-zoobenthos and fishes in Mediterranean coastal lagoons, and the species dependence upon environmental factors. Location: The study was carried out in the "Stagnone di Marsala e Saline di Trapani e Paceco," the largest coastal lagoon system in the central Mediterranean Sea (Sicily, Italy), a Special Protection Area located along one of the central ecological corridors joining Africa and Europe. Methods: The coastal lagoon system was selected as a model ecosystem to investigate the seasonal variations in biodiversity indices and dominance-diversity relationships in phytobenthos, macro-zoobenthos and fishes, and how seasonal variations in temperature, salinity, depth, inorganic and organic suspended matter affect the abundance of the species constituting these communities. Models of ecosystem structure, describing the interactions among functional groups and environmental variables, were also developed using confirmatory path analysis and artificial neural networks to exemplify their application in predicting temperature-driven alterations. Results: Wide seasonal variations in biodiversity indices and dominance-diversity relationships across the communities of the coastal lagoon system were observed, driven by the dynamics in climate and resource availability. The effects of the environmental variables on taxon abundances varied in relation to the community, with the widest responses elicited in phytobenthos and fishes. Temperature was the main variable affecting taxon abundances in macro-zoobenthos and was also the major driver of shallow water ecosystem structure. Main conclusions: This research shed light on the seasonal variations in biodiversity of Mediterranean coastal lagoons, elucidating also the tight dependence of phytobenthos, macro-zoobenthos and fish diversity upon environmental factors. The findings and the methodological approach proposed may be crucial in developing models able to predict future climate-driven alterations in communities inhabiting these important and threatened ecosystems.

Canadian Journal of Fisheries and Aquatic Sciences, 2018

We quantified production, biomass, and production to biomass (P/B) ratios for cisco (Coregonus artedi) in Trout Lake, Wisconsin, USA (2001–2015). Across all years, annual production, biomass, and P/B were variable ranging 0.6–30.2 kg·ha−1·year−1, 1.2–39.7 kg·ha−1, and 0.4–0.9·year−1, respectively. Cisco production exhibited obvious decline. However, neither biomass nor P/B changed significantly over time. Long-term patterns of environmental conditions remained unchanged during the study and were unrelated to cisco production. However, lake trout (Salvelinus namaycush) relative abundance showed a strong inverse relationship with cisco production and biomass. Intense lake trout stocking has occurred in this lake over time to conserve a genetically unique strain of the species. These management efforts may have had the unintended consequence of amplifying top-down predation on cisco. Since cisco P/B has gone largely unchanged, cisco production would be predicted to rebound quickly to a...

Ecography, 2016

Present-day tests of the niche conservatism hypothesis are complicated, however, by the multidimensional nature of the niche concept. Hutchinson (1957) originally defined species' niche as the hyper-volume in the ecological space where a species can persist with permissive conditions and requisite resources as its axes (Colwell and Rangel 2009). Since then, literature has repeatedly emphasized the need to distinguish between these two articulations of species' niche, commonly referred to as the Grinellian (abiotic) niche and the Eltonian (biotic or trophic) niche (Soberón 2007, Devictor et al. 2010). While the distinction between Grinnellian and Eltonian niches has set a meaningful heuristic basis to understand species spatial distributions, it is also relevant to better understanding the patterns of niche conservatism (Wiens et al. 2010). Indeed, the context in which niche evolution or conservatism occurs can depend upon different abiotic and biotic niche axes (Holt 2009). For instance, changes in abiotic conditions promote the selec tion and evolution of physiological characteristics through differential survival, reproduction and growth (Davis and Shaw 2001, Bradshaw and Holzapfel 2006). Similarly, trophic interactions, such as predation and competition,

Oecologia, 2018

Habitat coupling is a concept that refers to consumer integration of resources derived from different habitats. This coupling unites fundamental food web pathways (e.g., cross-habitat trophic linkages) that mediate key ecological processes such as biomass flows, nutrient cycling, and stability. We consider the influence of water transparency, an important environmental driver in aquatic ecosystems, on habitat coupling by a light-sensitive predator, walleye (Sander vitreus), and its prey in 33 Canadian lakes. Our large-scale, across-lake study shows that the contribution of nearshore carbon (δ 13 C) relative to offshore carbon (δ 13 C) to walleye is higher in less transparent lakes. To a lesser degree, the contribution of nearshore carbon increased with a greater proportion of prey in nearshore compared to offshore habitats. Interestingly, water transparency and habitat coupling predict among-lake variation in walleye relative biomass. These findings support the idea that predator responses to changing conditions (e.g., water transparency) can fundamentally alter carbon pathways, and predator biomass, in aquatic ecosystems. Identifying environmental factors that influence habitat coupling is an important step toward understanding spatial food web structure in a changing world.

Ecology of Freshwater Fish, 2020

Water temperature affects many of the physiological and biochemical processes performed by fish (Kitchell, Stewart, & Weininger, 1977; Magnuson, Crowder, & Medvick, 1979). Thus, changes in the thermal environment would be expected to alter fish performance and survival (Whitney et al., 2016). Water temperatures are anticipated to increase under climate change, which should in turn cause major shifts in species abundance and distribution (see Comte, Buisson,

PLOS ONE, 2018

Global environmental change has the potential to disrupt well established species interactions, with impacts on nutrient cycling and ecosystem function. On coral reefs, fish living within the branches of coral colonies can promote coral performance, and it has been hypothesized that the enhanced water flow and nutrients provided by fish to corals could ameliorate coral bleaching. The aim of this study was to evaluate the influence of small, aggregating damselfish on the health of their host corals (physiology, recovery, and survival) before, during, and after a thermal-bleaching event. When comparing coral colonies with and without fish, those with resident fish exhibited higher Symbiodinium densities and chlorophyll in both field and experimentally-induced bleaching conditions, and higher protein concentrations in field colonies. Additionally, colonies with damselfish in aquaria exhibited both higher photosynthetic efficiency (F V /F M) during bleaching stress and post-bleaching recovery, compared to uninhabited colonies. These results demonstrate that symbiotic damselfishes, and the services they provide, translate into measureable impacts on coral tissue, and can influence coral bleaching susceptibility/resilience and recovery. By mediating how external abiotic stressors influence coral colony health, damselfish can affect the functional responses of these interspecific interactions in a warming ocean.

Canadian Journal of Fisheries and Aquatic Sciences, 2020

As the global human population grows, it remains a top priority for communities, managers, policymakers, and stakeholders to maintain healthy, sustainable, and productive fisheries under continued global change. Here we used a dataset consisting of fish and lake characteristics for 536 lakes across Ontario, Canada, to test whether multiple climate, human, and biological factors differentially affect fish production (i.e., population biomass per hectare per year). We tested the hypothesis that temperature is the key driver of fisheries production by testing for the effects of multiple factors on the production of three top predatory fish species: cold-water lake trout (Salvelinus namaycush), cool-water walleye (Sander vitreus), and warm-water smallmouth bass (Micropterus dolomieu). Using boosted regression tree analyses, we found that lake trout production was most influenced by the volume of hypolimnetic habitat, walleye production was related to other climatic variables, and smallmouth bass production was most influenced by sampling day of the year followed by Secchi depth. Our results suggest that current fish production modelsthat only include temperature and body sizemay oversimplify important ecological complexities and thus misinform management decisions because species respond differently to environmental drivers. Résumé : Pour faire face à la croissance démographique mondiale, les communautés, gestionnaires, décideurs et parties prenantes doivent continuer de prioriser le maintien de ressources halieutiques saines, durables et productives dans un contexte de changements climatiques. Nous avons utilisé un ensemble de données constitué de caractéristiques de poissons et de lacs pour 536 lacs en Ontario (Canada) pour vérifier si divers facteurs climatiques, humains et biologiques exercent différents effets sur la production de poissons (c.-à-d. la biomasse de la population par hectare par année). Nous avons vérifié l'hypothèse voulant que la température soit le principal facteur qui module la production des pêches en examinant les effets de différents facteurs sur la production de trois espèces de prédateurs de niveau trophique supérieur, à savoir le touladi (Salvelinus namaycush), une espèce d'eau froide, le doré jaune (Sander vitreus), une espèce d'eau fraîche, et l'achigan à petite bouche (Micropterus dolomieu), une espèce d'eau chaude. En utilisant des analyses par arbre de régression augmenté, nous constatons que le volume des habitats hypolimnétiques exerce la plus forte influence sur la production des touladis, que la production de dorés jaunes est associée à d'autres variables climatiques et que la date d'échantillonnage, suivie de la profondeur mesurée par le disque de Secchi, influencent le plus la production d'achigans à petite bouche. Nos résultats donnent à penser que les modèles de production de poissons actuels, qui n'intègrent que la température et la taille du corps, pourraient trop simplifier d'importantes complexités écologiques et ainsi produire des décisions de gestion non optimales découlant du fait que les espèces ne répondent pas toutes de la même manière à différents facteurs environnementaux. [Traduit par la Rédaction]

Ecosphere, 2018

The need to protect biostructure is increasingly recognized, yet empirical studies of how human exploits affect ecological networks are rare. Studying the effects of variation in human disturbance intensity from decades past can help us understand and anticipate ecosystem change under alleviated or amplified disturbance over decades to come. Here, we use stable isotopes and an innovative analytical approach to compare the food webs of two akin lake ecosystems subject to disparate water use regimes, a pervasive, yet unappreciated stressor. We show that intensive water use (persistent, early season, rapid lake-level drawdown) can compress trophic diversity by 46%, necessitating reorganization of biostructural elements configuring lake food webs. Compression occurred over the d 13 C axis indicating erosion of basal trophic diversity, but food chain length remained intact over the period and intensity of disturbance examined. This study demonstrates the potential for water use, like other disturbances (warming, eutrophication, and invasive species), to mute opportunity for benthic-pelagic coupling and benefits to lake food webs and the inherent capacity of lake ecosystems to adapt to stress. Trophically compressed lakes may be less able to adapt to intensified water use.

Ecology Letters, 2019

From clear lakes to murky waters : tracing the functional response of high-latitude lake communities to concurrent 'greening' and 'browning'