Contrasting responses of black fly species (Diptera: Simuliidae) to experimental whole‐stream warming
- As global temperatures continue to rise, assessment of how species within ecological communities respond to shifts in temperature has become increasingly important. However, such assessments require detailed long‐term observations or ecosystem‐level manipulations that allow for interactions among species and the potential for species dispersal and exchange with the regional species pool.
- We examined the effects of experimental whole‐stream warming on a larval black fly assemblage in southwest Iceland. We used a paired‐catchment design, in which we studied the warmed stream and a nearby reference stream for 1 year prior to warming and 2 years during warming and estimated population abundance, biomass, secondary production, and growth rates for larvae of three black fly species.
- Experimental warming by 3.8°C had contrasting effects on the three black fly species in the assemblage. The abundance, biomass, growth, and production of Prosimulium ursinum decreased in the experimental stream during the warming manipulation. Despite increasing in the reference stream, the abundance, biomass, and production of another species, Simulium vernum, decreased in the experimental stream during warming.
- In contrast, warming had an overall positive effect on Simulium vittatum. While warming had little effect on the growth of overwintering cohorts of S. vittatum, warming led to an additional cohort during the summer months and increased its abundance, biomass, and production. Overall, family‐level production was enhanced by warming, despite variation in species‐level responses.
- Our study illustrates that the effects of climate warming are likely to differ even among closely related species. Moreover, our study highlights the need for further investigation into the uneven effects of warming on individual species and how those variable effects influence food web dynamics and ecosystem function.
Nelson, D., J.P. Benstead, A.D. Huryn, W.F. Cross, J.M. Hood, P.W. Johnson, J.R. Junker, G.M. Gíslason, J.S. Ólafsson. 2020. Contrasting responses of black fly species (Diptera: Simuliidae) to experimental whole‐stream warming. Freshwater Biology, in press. doi.org/10.1111/fwb.13583
Thermal niche diversity and trophic redundancy drive neutral effects of warming on energy flux through a stream food web
Climate warming is predicted to alter routing and flows of energy through food webs because of the critical and varied effects of temperature on physiological rates, community structure, and trophic dynamics. Few studies, however, have experimentally assessed the net effect of warming on energy flux and food web dynamics in natural intact communities. Here, we test how warming affects energy flux and the trophic basis of production in a natural invertebrate food web by experimentally heating a stream reach in southwest Iceland by ~4°C for 2 yr and comparing its response to an unheated reference stream. Previous results from this experiment showed that warming led to shifts in the structure of the invertebrate assemblage, with estimated increases in total metabolic demand but no change in annual secondary production. We hypothesized that elevated metabolic demand and invariant secondary production would combine to increase total consumption of organic matter in the food web, if diet composition did not change appreciably with warming. Dietary composition of primary consumers indeed varied little between streams and among years, with gut contents primarily consisting of diatoms (72.9%) and amorphous detritus (19.5%). Diatoms dominated the trophic basis of production of primary consumers in both study streams, contributing 79–86% to secondary production. Although warming increased the flux of filamentous algae within the food web, total resource consumption did not increase as predicted. The neutral net effect of warming on total energy flow through the food web was a result of taxon‐level variation in responses to warming, a neutral effect on total invertebrate production, and strong trophic redundancy within the invertebrate assemblage. Thus, food webs characterized by a high degree of trophic redundancy may be more resistant to the effects of climate warming than those with more diverse and specialized consumers.
Nelson, D., J.P. Benstead, A.D. Huryn, W.F. Cross, J.M. Hood, P.W. Johnson, J.R. Junker, G.M. Gíslason, J.S. Ólafsson. 2020. Thermal niche diversity and trophic redundancy drive neutral effects of warming on energy flux through a stream food web. Ecology 101(4), e02952. doi.org/10.1002/ecy.2952
Increased resource use efficiency amplifies positive response of aquatic primary production to experimental warming
Climate warming is affecting the structure and function of river ecosystems, including their role in transforming and transporting carbon (C), nitrogen (N), and phosphorus (P). Predicting how river ecosystems respond to warming has been hindered by a dearth of information about how otherwise well‐studied physiological responses to temperature scale from organismal to ecosystem levels. We conducted an ecosystem‐level temperature manipulation to quantify how coupling of stream ecosystem metabolism and nutrient uptake responded to a realistic warming scenario. A ~3.3°C increase in mean water temperature altered coupling of C, N, and P fluxes in ways inconsistent with single‐species laboratory experiments. Net primary production tripled during the year of experimental warming, while whole‐stream N and P uptake rates did not change, resulting in 289% and 281% increases in autotrophic dissolved inorganic N and P use efficiency (UE), respectively. Increased ecosystem production was a product of unexpectedly large increases in mass‐specific net primary production and autotroph biomass, supported by (i) combined increases in resource availability (via N mineralization and N2 fixation) and (ii) elevated resource use efficiency, the latter associated with changes in community structure. These large changes in C and nutrient cycling could not have been predicted from the physiological effects of temperature alone. Our experiment provides clear ecosystem‐level evidence that warming can shift the balance between C and nutrient cycling in rivers, demonstrating that warming will alter the important role of in‐stream processes in C, N, and P transformations. Moreover, our results reveal a key role for nutrient supply and use efficiency in mediating responses of primary producers to climate warming.
Hood, J.M., J.P. Benstead, W.F. Cross, A.D. Huryn, P.W. Johnson, G.M. Gíslason, J.R. Junker, D. Nelson, J.S. Ólafsson, C. Tran. 2018. Increased resource use efficiency amplifies positive response of aquatic primary production to experimental warming. Global Change Biology 24(3):1069-1084. doi.org/10.1111/gcb.13912
Elemental content of stream biota
Measuring the elemental content of stream biota is a prerequisite to the application of ecological stoichiometry theory, which focuses on the balance of chemical elements in ecological interactions. In this chapter, we describe basic and advanced methods for the estimation of elemental content in frequently encountered compartments of stream food webs, concentrating on the measurement of carbon, nitrogen, and phosphorus. We also cover methods for measuring rates and stoichiometry of animal excretion and egestion, as these represent important terms in the elemental mass balance of feeding interactions that may control important ecosystem-level effects and feedbacks.
Benstead, J.P., M.A. Evans-White, C.A. Gibson, J.M. Hood. 2017. “Elemental content of stream biota.” In Methods in Stream Ecology, Volume 2: Ecosystem Function. Chapter 36, pp.255-273. Edited by G.A. Lamberti and F.R. Hauer. Academic Press, London United Kingdom. doi.org/10.1016/B978-0-12-813047-6.00014-0
Experimental whole-stream warming alters community size structure
How ecological communities respond to predicted increases in temperature will determine the extent to which Earth's biodiversity and ecosystem functioning can be maintained into a warmer future. Warming is predicted to alter the structure of natural communities, but robust tests of such predictions require appropriate large‐scale manipulations of intact, natural habitat that is open to dispersal processes via exchange with regional species pools. Here, we report results of a two‐year whole‐stream warming experiment that shifted invertebrate assemblage structure via unanticipated mechanisms, while still conforming to community‐level metabolic theory. While warming by 3.8 °C decreased invertebrate abundance in the experimental stream by 60% relative to a reference stream, total invertebrate biomass was unchanged. Associated shifts in invertebrate assemblage structure were driven by the arrival of new taxa and a higher proportion of large, warm‐adapted species (i.e., snails and predatory dipterans) relative to small‐bodied, cold‐adapted taxa (e.g., chironomids and oligochaetes). Experimental warming consequently shifted assemblage size spectra in ways that were unexpected, but consistent with thermal optima of taxa in the regional species pool. Higher temperatures increased community‐level energy demand, which was presumably satisfied by higher primary production after warming. Our experiment demonstrates how warming reassembles communities within the constraints of energy supply via regional exchange of species that differ in thermal physiological traits. Similar responses will likely mediate impacts of anthropogenic warming on biodiversity and ecosystem function across all ecological communities.
Nelson, D. J.P. Benstead, A.D. Huryn, W.F. Cross, J.M. Hood, P.W. Johnson, J.R. Junker, GM. Gislason, J.S. Ólafsson. 2017. Experimental whole-stream warming alters community size structure. Global Change Biology 23(7):2618-2628. doi.org/10.1111/gcb.13574
Shifts in community size structure drive temperature invariance of secondary production in a stream-warming experiment
A central question at the interface of food‐web and climate change research is how secondary production, or the formation of heterotroph biomass over time, will respond to rising temperatures. The metabolic theory of ecology (MTE) hypothesizes the temperature‐invariance of secondary production, driven by matched and opposed forces that reduce biomass of heterotrophs while increasing their biomass turnover rate (production : biomass, or P:B) with warming. To test this prediction at the whole community level, we used a geothermal heat exchanger to experimentally warm a stream in southwest Iceland by 3.8°C for two years. We quantified invertebrate community biomass, production, and P : B in the experimental stream and a reference stream for one year prior to warming and two years during warming. As predicted, warming had a neutral effect on community production, but this result was not driven by opposing effects on community biomass and P:B. Instead, warming had a positive effect on both the biomass and production of larger‐bodied, slower‐growing taxa (e.g., larval black flies, dipteran predators, snails) and a negative effect on small‐bodied taxa with relatively high growth rates (e.g., ostracods, larval chironomids). We attribute these divergent responses to differences in thermal preference between small‐ vs. large‐bodied taxa. Although metabolic demand vs. resource supply must ultimately constrain community production, our results highlight the potential for idiosyncratic community responses to warming, driven by variation in thermal preference and body size within regional species pools.
Nelson, D. J.P. Benstead, A.D. Huryn, W.F. Cross, J.M. Hood, P.W. Johnson, J.R. Junker, GM. Gislason, J.S. Ólafsson. 2017. Shifts in community size structure drive temperature invariance of secondary production in a stream-warming experiment. Ecology 98(7):1797-1806. doi.org/10.1002/ecy.1857
A global database of nitrogen and phosphorus excretion rates of aquatic animals
Animals can be important in modulating ecosystem‐level nutrient cycling, although their importance varies greatly among species and ecosystems. Nutrient cycling rates of individual animals represent valuable data for testing the predictions of important frameworks such as the Metabolic Theory of Ecology (MTE) and ecological stoichiometry (ES). They also represent an important set of functional traits that may reflect both environmental and phylogenetic influences. Over the past two decades, studies of animal‐mediated nutrient cycling have increased dramatically, especially in aquatic ecosystems. Here we present a global compilation of aquatic animal nutrient excretion rates. The dataset includes 10,534 observations from freshwater and marine animals of N and/or P excretion rates. These observations represent 491 species, including most aquatic phyla. Coverage varies greatly among phyla and other taxonomic levels. The dataset includes information on animal body size, ambient temperature, taxonomic affiliations, and animal body N:P. This data set was used to test predictions of MTE and ES, as described in Vanni and McIntyre (2016; Ecology DOI: 10.1002/ecy.1582).
Vanni, M.J., P.B. McIntyre, … J.M.Hood and 72 others. 2017. A global database of nitrogen and phosphorus excretion rates of aquatic animals. Ecology 98(5):1475. doi.org/10.1002/ecy.1792
Bridging food webs, ecosystem metabolism, and biogeochemistry using ecological stoichiometry theory
Although aquatic ecologists and biogeochemists are well aware of the crucial importance of ecosystem functions, i.e., how biota drive biogeochemical processes and vice-versa, linking these fields in conceptual models is still uncommon. Attempts to explain the variability in elemental cycling consequently miss an important biological component and thereby impede a comprehensive understanding of the underlying processes governing energy and matter flow and transformation. The fate of multiple chemical elements in ecosystems is strongly linked by biotic demand and uptake; thus, considering elemental stoichiometry is important for both biogeochemical and ecological research. Nonetheless, assessments of ecological stoichiometry (ES) often focus on the elemental content of biota rather than taking a more holistic view by examining both elemental pools and fluxes (e.g., organismal stoichiometry and ecosystem process rates). ES theory holds the promise to be a unifying concept to link across hierarchical scales of patterns and processes in ecology, but this has not been fully achieved. Therefore, we propose connecting the expertise of aquatic ecologists and biogeochemists with ES theory as a common currency to connect food webs, ecosystem metabolism, and biogeochemistry, as they are inherently concatenated by the transfer of carbon, nitrogen, and phosphorous through biotic and abiotic nutrient transformation and fluxes. Several new studies exist that demonstrate the connections between food web ecology, biogeochemistry, and ecosystem metabolism. In addition to a general introduction into the topic, this paper presents examples of how these fields can be combined with a focus on ES. In this review, a series of concepts have guided the discussion: (1) changing biogeochemistry affects trophic interactions and ecosystem processes by altering the elemental ratios of key species and assemblages; (2) changing trophic dynamics influences the transformation and fluxes of matter across environmental boundaries; (3) changing ecosystem metabolism will alter the chemical diversity of the non-living environment. Finally, we propose that using ES to link nutrient cycling, trophic dynamics, and ecosystem metabolism would allow for a more holistic understanding of ecosystem functions in a changing environment.
Welti, N., M. Striebel, A.J. Ulseth, W.F. Cross, S. DeVilbiss, P.M. Gilbert, L. Guo, A.G. Hirst, J.M. Hood, J.S. Kominoski, K.L. MacNeill, A.S. Mehring, J.R. Welter, and H. Hillebrand. 2017. Bridging food webs, ecosystem metabolism, and biogeochemistry using ecological stoichiometry theory. Frontiers in Microbiology 8:1298. doi.org/10.3389/fmicb.2017.01298
Full publication list
- Nelson, D., J.P. Benstead, A.D. Huryn, W.F. Cross, J.M. Hood, P.W. Johnson, J.R. Junker, G.M. Gíslason, J.S. Ólafsson. 2020. Contrasting responses of black fly species (Diptera: Simuliidae) to experimental whole‐stream warming. Freshwater Biology, in press. doi.org/10.1111/fwb.13583
- Nelson, D., J.P. Benstead, A.D. Huryn, W.F. Cross, J.M. Hood, P.W. Johnson, J.R. Junker, G.M. Gíslason, J.S. Ólafsson. 2020. Thermal niche diversity and trophic redundancy drive neutral effects of warming on energy flux through a stream food web. Ecology 101(4), e02952. doi.org/10.1002/ecy.2952
- Hood, J.M., J.P. Benstead, W.F. Cross, A.D. Huryn, P.W. Johnson, G.M. Gíslason, J.R. Junker, D. Nelson, J.S. Ólafsson, C. Tran. 2018. Increased resource use efficiency amplifies positive response of aquatic primary production to experimental warming. Global Change Biology 24(3):1069-1084. doi.org/10.1111/gcb.13912
- Benstead, J.P., M.A. Evans-White, C.A. Gibson, J.M. Hood. 2017. “Elemental content of stream biota.” In Methods in Stream Ecology, Volume 2: Ecosystem Function. Chapter 36, pp.255-273. Edited by G.A. Lamberti and F.R. Hauer. Academic Press, London United Kingdom. doi.org/10.1016/B978-0-12-813047-6.00014-0
- Nelson, D. J.P. Benstead, A.D. Huryn, W.F. Cross, J.M. Hood, P.W. Johnson, J.R. Junker, GM. Gislason, J.S. Ólafsson. 2017. Experimental whole-stream warming alters community size structure. Global Change Biology 23(7):2618-2628. doi.org/10.1111/gcb.13574
- Nelson, D. J.P. Benstead, A.D. Huryn, W.F. Cross, J.M. Hood, P.W. Johnson, J.R. Junker, GM. Gislason, J.S. Ólafsson. 2017. Shifts in community size structure drive temperature invariance of secondary production in a stream-warming experiment. Ecology 98(7):1797-1806. doi.org/10.1002/ecy.1857
- Vanni, M.J., P.B. McIntyre, … J.M.Hood and 72 others. 2017. A global database of nitrogen and phosphorus excretion rates of aquatic animals. Ecology 98(5):1475. doi.org/10.1002/ecy.1792
- Welti, N., M. Striebel, A.J. Ulseth, W.F. Cross, S. DeVilbiss, P.M. Gilbert, L. Guo, A.G. Hirst, J.M. Hood, J.S. Kominoski, K.L. MacNeill, A.S. Mehring, J.R. Welter, and H. Hillebrand. 2017. Bridging food webs, ecosystem metabolism, and biogeochemistry using ecological stoichiometry theory. Frontiers in Microbiology 8:1298. doi.org/10.3389/fmicb.2017.01298
- Demars, B.O.L., G.M. Gíslason, J.S. Ólafsson, J.R. Manson, N. Frieberg, J.M. Hood, J.J.D. Thompson, T.E. Freitag. 2016. Impact of warming on CO2 emissions from streams countered by aquatic photosynthesis. Nature Geoscience 9:758-761. doi.org/10.1038/ngeo2807
- Williamson, T.J., W.F. Cross, J.P. Benstead, G.M. Gíslason, J.M. Hood, A.D. Huryn, P.M. Johnson, J.R. Welter. 2016. Warming alters coupled carbon and nutrient cycles in experimental streams. Global Change Biology 22(6):2152-2164. doi.org/10.1111/gcb.13205
- Cross, W.F., J.M. Hood, J.P. Benstead, A.D. Huryn, D. Nelson. 2015. Interactions between temperature and nutrients across levels of ecological organization. Global Change Biology 21(3):1025-1040. doi.org/10.1111/gcb.12809
- Sterner, R.W., J.M. Hood, M.R. Kearney, D. Raubenheimer, J. Urabe. 2015. Couples that have chemistry: When ecological theories collide. Oikos 124(7):917-919. doi.org/10.1111/oik.02672
- Welter, J., J.P. Benstead, W.F. Cross, J.M. Hood, A.D. Huryn, P.M. Johnson, T. Williamson. 2015. Does N2 fixation amplify the temperature dependence of ecosystem metabolism? Ecology 96(3):603-610. doi.org/10.1890/14-1667.1
- Benstead, J.P., J.M. Hood, N.V. Whelan, M.R. Kendrick, D. Nelson, A.F. Hanninen, L.M. Demi. 2014. Coupling of dietary phosphorus and growth across diverse fish taxa: a meta-analysis of experimental aquaculture studies. Ecology 95:2786-2777. doi.org/10.1890/13-1859.1
- Hood, J.M., C. McNeely, J.C. Finlay, R.W. Sterner. 2014. Selective feeding determines patterns of nutrient release by stream invertebrates. Freshwater Science 33(4):1093-1107. doi.org/10.1086/678693
- Hood, J.M., R.W. Sterner. 2014. Carbon and phosphorus linkages in Daphnia growth are determined by growth rate, not species or diet. Functional Ecology 28(5):1156-1165. doi.org/10.1111/1365-2435.12243
- O’Gorman, O., J.P. Benstead, W.F. Cross, N. Friberg, J.M. Hood, P.M. Johnson, B. Sigurðsson, G. Woodward. 2014. Climate change and geothermal ecosystems: natural laboratories, sentinel systems, and future refugia. Global Change Biology 20(11):3291-3299. doi.org/10.1111/gcb.12602
- O’Gorman, D.E. Pichler, G. Adams, J.P. Benstead, H. Cohen, N. Craig, W. Cross, B.O. Demars, N. Friberg, G. Gíslason, R. Gudmundsdóttir, A. Hawczak, J.M. Hood, L.N. Hudson, L.S. Johansson, M.P. Johansson, J.R. Junker, A. Laurila, J.R. Manson, E. Mavromati, D. Nelson, J. Ólafsson, D.M. Perkins, O.L. Petchey, M. Plebani, D.C. Reuman, B.C. Rall, R. Stewart, M.S.A. Thompson, G. Woodward. 2012. Impacts of warming on the structure and function of aquatic communities: individual-to ecosystem-level responses. Advances in Ecological Research 47:81-176. doi.org/10.1016/B978...
- Finlay, J.C., J.M. Hood, M. Limm, M.E. Power, J. Schade, J.R. Welter. 2011. Light-mediated thresholds in stream-water nutrient composition in a river network. Ecology 92(1):140-150. doi.org/10.1890/09-2243.1
- Sterner, R.W., G.E. Small, and J.M. Hood. 2011. The conservation of mass. Nature Education Knowledge 2(1):11.
- Hood, J.M. and R.W. Sterner. 2010. Diet mixing: Do animals integrate growth or resources across temporal heterogeneity? The American Naturalist 176(5):651- 663. doi.org/10.1086/656489
- Persson, J., P. Fink, A. Goto, J.M. Hood, J. Jonas, S. Kato. 2010. To be or not to be what you eat: regulation of stoichiometric homeostasis among autotrophs and heterotrophs. Oikos 119(5):741-751. *Authors contributed equally. doi.org/10.1111/j.1600-0706.2009.18545.x
- Schade, J.D., K. MacNeill, S.A. Thomas, F.C. McNeely, J.R. Welter, J.M. Hood, M. Goodrich, M.E. Power, J.C. Finlay. 2010. The stoichiometry of nitrogen and phosphorus spiraling in heterotrophic and autotrophic streams. Freshwater Biology 56(3):424-436. doi.org/10.1111/j.1365-2427.2010.02509.x
- McIntyre P.B., A.S. Flecker, M.J. Vanni, J.M. Hood, B.W. Taylor, S.A. Thomas. 2008. Fish distributions and nutrient recycling in a Neotropical stream: can fish create biogeochemical hotspots. Ecology 89(8):2335-2346. doi.org/10.1890/07-1552.1
- Sterner, R.W., T. Andersen, J.J. Elser, D.O. Hessen, J.M. Hood, E. McCauley, J. Urabe. 2008. Scale-dependent carbon:nitrogen:phosphorus seston stoichiometry in marine and freshwaters. Limnology and Oceanography 53(3):1169-1180. doi.org/10.4319/lo.2008.53.3.1169
- Hood, J.M., S. Brovold, R.W. Sterner, M. Villar-Argaiz, K.D. Zimmer. 2006. Near-infrared spectrometry (NIRS) for the analysis of seston carbon, nitrogen, and phosphorus from diverse sources. Limnology and Oceanography: Methods 4(4):96-104. doi.org/10.4319/lom.2006.4.96
- Hood, J.M., M.J. Vanni, A.S. Flecker. 2005. Nutrient recycling by two phosphorus rich grazing catfish: the potential for phosphorus-limitation of fish growth. Oecologia 146(2):247-257. doi.org/10.1007/s00442-005-0202-5
- Elser J.J., K. Acharya, M. Kyle, J. Cotner, W. Makino, T. Markow, T. Watts, S. Hobbie, W. Fagan, J. Schade, J.M. Hood, R.W. Sterner. 2003. Growth rate – stoichiometry couplings in diverse biota. Ecology Letters 6(10):936-943. doi.org/10.1046/j.1461-0248.2003.00518.x
- Flecker A.S., B.W. Taylor, E.S. Bernhardt, J.M. Hood, W.K. Cornwell, S.R. Cassatt, M.J. Vanni. 2002. Interactions between herbivorous fishes and limiting nutrients in a tropical stream ecosystem. Ecology 83(7):1831-1844. doi.org/10.1890/0012-9658(2002)...
- Vanni M.J., A.S. Flecker, J.M. Hood, J.L. Headworth. 2002. Stoichiometry of nutrient recycling by vertebrates in a tropical stream: linking species identity and ecosystem processes. Ecology Letters 5(2):285-293. doi.org/10.1046/j.1461-0248.2002.00314.x
- Frost T.M., J.P. Descy, B.T. DeStasio, G. Gerrish, J.M. Hood, J.P. Hurley and A. L. St. Amand. 1998. Evaluations of phytoplankton communities using varied techniques: A multi-media comparison of lakes in northern Wisconsin USA. Verh. Internat. Verein. Limnol. 27(2):1023-1030. doi.org/10.1080/03680770.1998.11901393