Letter Aquatic Predators provide a fascinating mechanism for satisfy- and potentially limiting organic compounds, ing EFA demands of some consumers [5]. including amino acids, sterols, and vita- Influence Future EFA research can increase its impact mins, that remain understudied in natural Micronutrients: on research across ecological subdisci- ecosystems. For example, thiamine (vita- plines by including a broader set of taxa min B1)deficiency is also known to impair Important but within aquatic systems and by moving be- neurological function, which can result in yond the water’s edge to examine linkages high mortality of early life stages in fishes Understudied between aquatic and terrestrial systems. [10], and has been hypothesized as a driver Moreover, most experimental studies evalu- of extirpation of some predators [11]. Alexander S. Flecker,1,*,@ ating EFA limitation on consumer growth Nevertheless, there are still remarkably Cornelia W. Twining,2,3,@ and productivity have been conducted in large knowledge gaps about thiamine in Oswald J. Schmitz,4 laboratory settings, and ecologists should ecosystems, starting with the range of work to link analogous effects on organism natural concentrations found in most Steven J. Cooke,5,@ and 6,7,@ performance in nature, with studies that natural waters, thiamine requirements of Neil Hammerschlag quantify natural EFA sources and fluxes. aquatic predators from wild populations, For example, recent work by Twining and especially those found high in food chains, colleagues [6,7] on aquatic sources of and how thiamine deficiency can affect EFAs as food web subsidies for riparian predator secondary production [12]. In a recent paper on ecosystem function bird species illustrates some of the exciting and services of aquatic predators in the insights as well as the challenges of thor- Závorka et al. [2] correctly emphasize Anthropocene [1], Hammerschlag and col- oughly understanding complex interactions how the decline of predators in aquatic leagues highlight a set of 16 outstanding involving EFAs and aquatic predators. food webs has critical implications for fi research needs, including strengthening Through integrated laboratory and eld human health through the loss of vital our understanding of the mechanisms studies based on bulk and compound- sources of micronutrients such as EFAs. fi and extent to which aquatic predators speci c isotope analyses, this work demon- Indeed, aquatic predators represent a key influence micronutrient and trace element strated how EFA sources for tree swallows provisioning ecosystem service via linkages fluxes within ecosystems. Závorka et al. (Tachycineta bicolor)andEasternphoebes with human nutrition, which serves as a [2] persuasively point out that within the (Sayornis phoebe) originate from aquatic pri- major rationale as to why further research realm of micronutrients, there is strong mary producers, with emerging aquatic in- aimed at elucidating mechanisms and ex- fl evidence that aquatic predators play a sects enriched in EFAs serving as tent to which aquatic predators in uence fl central role in the transfer of essential fatty micronutrient conveyor belts to riparian con- micronutrients and trace element uxes acids (EFAs) such as docosahexaenoic sumers [6,7]. Moreover, controlled diet ex- within ecosystems is an urgent priority [1]. periments revealed that chick growth acid (DHA, 22:6ω3) and eicosapentaenoic 1Department of Ecology and Evolutionary Biology, Cornell rate and condition were substantially im- acid (EPA, 20:5ω3) in food webs, and University, Ithaca, NY, 14853, USA proved when diets were supplemented 2Limnological Institute, University of Konstanz, 78464 Konstanz, that EFAs are vitally important neuro- Germany by EFAs [6], and extensive field observa- 3 logically for many consumers including Max Planck Institute for Animal Behavior, 78315 Radolfzell, tions over a 24-year period suggested Germany humans. We agree that EFAs are an 4School of Forestry and Environmental Studies, Yale University, that EFA-rich aquatic insects are funda- exciting and significant area of research, New Haven, CT, 06511, USA mental to bird population success [7]. 5Fish Ecology and Conservation Physiology Laboratory, and we embrace their suggestion to Carleton University, Ottawa, ON, K1S 5B6, Canada extend the social and ecological framework 6Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, 33149, USA presented in [1] to incorporate what is known 7 Even with recent progress in EFA studies, Leonard and Jayne Abess Center for Ecosystem Science and about fluxes of EFAs as micronutrients. Policy, University of Miami, Coral Gables, FL, 33146, USA micronutrients remain highly understudied in food webs, and our knowledge about *Correspondence: interactions involving many key elements, [email protected] (A.S. Flecker). EFAs have been studied in aquatic systems @Twitter: @DrNeilHammer (N. Hammerschlag), @SJC_Fishy from a variety of perspectives [3].Linkages including predator effects, is woefully inade- (S.J. Cooke), @SchmitzLab (O.J. Schmitz), @Cornell (A.S. between photoautotrophs and lower trophic quate, despite their importance as vital Flecker), and @twisci1 (C.W. Twining) levels have been studied for some time [4], building blocks for life [8,9]. Fatty acids are https://doi.org/10.1016/j.tree.2019.07.006 and recent work on egg-rafts in the ocean just one of many physiologically important © 2019 Elsevier Ltd. All rights reserved.
882 Trends in Ecology & Evolution, October 2019, Vol. 34, No. 10 Trends in Ecology & Evolution
References adaptive pressures. The nature, fects of variations in the wider environment; 1. Hammerschlag, N. et al. (2019) Ecosystem function and an example is temperature regulation of the services of aquatic predators in the Anthropocene. Trends scale, and speed of such modifi- Ecol. Evol. 34, 369–383 cations have potential ill effects nestsofbeesandwasps. 2. Závorka, L. et al. (2019) Aquatic predators influence flux of These processes of niche construction lead essential micronutrients. Trends Ecol. Evol. 34, 880–881 that need to be addressed with 3. Arts, M.T. et al., eds (2009) Lipids in Aquatic Ecosystems, multilevel societal initiatives. to the attainment of equilibrium between Springer the organism’s constructed niche and its re- 4. Brett, M.T. and Müller-Navarra, D.C. (1997) The role of highly unsaturated fatty acids in aquatic foodweb pro- Humans as Niche Constructors – Is action norm of phenotypes. They thus confer cesses. Freshw. Biol. 38, 483–499 a Rethink Needed? an adaptive benefit. As Laland and Brown [3] 5. Fuiman, L.A. et al. (2015) Egg boons: central compo- nents of marine fatty acid food webs. Ecology 96, The concept of the Anthropocene has fo- pointed out, niche construction can serve to 362–372 cused attention on the far-reaching impact reduce the ‘adaptive lag’ that would other- 6. Twining, C.W. et al. (2019) Aquatic and terrestrial resources fi are not nutritionally reciprocal for consumers. Funct. Ecol. of human activity on many aspects of the wise challenge tness due to the time re- Published online June 27, 2019. https://doi.org/10.1111/ planetary environment. In this forum we quired for a new genotype to evolve 1365-2435.13401 7. Twining, C.W. et al. (2018) Aquatic insects drive breeding discuss the evolutionary implications of following substantial environmental change. success in a riparian aerial insectivore. Ecol. Lett. 21, contemporary human–environment inter- Humans are often considered an example 1812–1820 8. Jeyasingh, P.D. et al. (2017) Ecological stoichiometry actions, not only in terms of our unique ca- of niche constructors [4]. The question we beyond Redfield: an ionomic perspective on elemental pacity to change our environment, but also ask is: to what extent do modern human ac- homeostasis. Front. Microbiol. 8, 722 in terms of the possible effects of the envi- tivities relating to the Anthropocene present 9. Kaspari, M. and Powers, J.S. (2016) Biogeochemistry and geographical ecology: embracing all twenty-five ronment on our biology and culture. a challenge to this viewpoint? elements required to build organisms. Am. Nat. 188, A widely accepted and important concept in S62–S73 10. Kraft, C.E. and Angert, E.R. (2017) Competition for vitamin evolutionary biology is that of niche con- Humans as Niche Modifiers in the B1 (thiamin) structures numerous ecological interactions. struction [1] – the process whereby organ- Anthropocene Quart. Rev. Biol. 92, 151–168 11. Ketola, H.G. et al. (2000) Effects of thiamine on repro- isms actively construct environments that We argue that humans are not just counter- duction of Atlantic salmon and a new hypothesis for establish an evolutionary equilibrium by sus- active niche constructors, but rather now their extirpation in Lake Ontario. Transact. Am. Fisheries Soc. 129, 607–612 taining their fitness. Frequently cited exam- cumulative and progressive niche modifiers, 12. Harder et al. (2018) Thiamine deficiency in fishes: causes, ples of niche-constructing species are continually changing their environment irre- consequences, and potential solutions. Rev. Fish Biol. Fisheries 28, 865–886 beavers (Castor spp.) and termites (Isoptera) spective of adaptive need or pressures [5] [2]. Niche construction may involve the pro- (Table 1). Our evolution, and in particular active initiation of changes in the immediate our cultural evolution, is characterized by environment by the organism, or the reactive unique innovative capacities, including our Forum changing of the niche in direct response to manual dexterity and ability to learn and to prior environmental changes. The latter communicate through complex language, Niche Modification, strategy, termed counteractive niche con- building expertise cumulatively over time struction, stabilizes local environments in [5]. Thus, our environments in the world Human Cultural an adaptive way and buffers against the ef- change dramatically, unlike the relatively Evolution and the Anthropocene Table 1. Relative Differences between Niche Construction and Niche Modification Niche construction Niche modification Felicia M. Low,1,2 Biologically heritable Yes Not necessarily phenotype/genotype Peter D. Gluckman,1,2,*,@ 3 Enhances or Yes Not necessarily and Mark A. Hanson sustains fitness Behavioral Stereotyped Innovative Niche-constructing organisms ac- characteristics tively modify their environments Effectively creates Yes No environmental with adaptive consequences, sus- equilibrium taining a new equilibrium. Modern Relative pace Slow Rapid humans are instead niche modi- Relative impact Small (local) – generally the Large (even global) – wider populations, fiers, continually changing their subpopulations that engaged in including those far removed from actual environments irrespective of niche construction niche modifiers
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