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Voysey MD, de Bruyn PJN, Davies AB. Are hippos Africa's most influential megaherbivore? A review of ecosystem engineering by the semi-aquatic common hippopotamus. Biol Rev Camb Philos Soc 2023; 98:1509-1529. [PMID: 37095627 DOI: 10.1111/brv.12960] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Revised: 03/30/2023] [Accepted: 04/03/2023] [Indexed: 04/26/2023]
Abstract
Megaherbivores perform vital ecosystem engineering roles, and have their last remaining stronghold in Africa. Of Africa's remaining megaherbivores, the common hippopotamus (Hippopotamus amphibius) has received the least scientific and conservation attention, despite how influential their ecosystem engineering activities appear to be. Given the potentially crucial ecosystem engineering influence of hippos, as well as mounting conservation concerns threatening their long-term persistence, a review of the evidence for hippos being ecosystem engineers, and the effects of their engineering, is both timely and necessary. In this review, we assess, (i) aspects of hippo biology that underlie their unique ecosystem engineering potential; (ii) evaluate hippo ecological impacts in terrestrial and aquatic environments; (iii) compare the ecosystem engineering influence of hippos to other extant African megaherbivores; (iv) evaluate factors most critical to hippo conservation and ecosystem engineering; and (v) highlight future research directions and challenges that may yield new insights into the ecological role of hippos, and of megaherbivores more broadly. We find that a variety of key life-history traits determine the hippo's unique influence, including their semi-aquatic lifestyle, large body size, specialised gut anatomy, muzzle structure, small and partially webbed feet, and highly gregarious nature. On land, hippos create grazing lawns that contain distinct plant communities and alter fire spatial extent, which shapes woody plant demographics and might assist in maintaining fire-sensitive riverine vegetation. In water, hippos deposit nutrient-rich dung, stimulating aquatic food chains and altering water chemistry and quality, impacting a host of different organisms. Hippo trampling and wallowing alters geomorphological processes, widening riverbanks, creating new river channels, and forming gullies along well-utilised hippo paths. Taken together, we propose that these myriad impacts combine to make hippos Africa's most influential megaherbivore, specifically because of the high diversity and intensity of their ecological impacts compared with other megaherbivores, and because of their unique capacity to transfer nutrients across ecosystem boundaries, enriching both terrestrial and aquatic ecosystems. Nonetheless, water pollution and extraction for agriculture and industry, erratic rainfall patterns and human-hippo conflict, threaten hippo ecosystem engineering and persistence. Therefore, we encourage greater consideration of the unique role of hippos as ecosystem engineers when considering the functional importance of megafauna in African ecosystems, and increased attention to declining hippo habitat and populations, which if unchecked could change the way in which many African ecosystems function.
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Affiliation(s)
- Michael D Voysey
- Department of Organismic and Evolutionary Biology, Harvard University, 22 Divinity Avenue, Cambridge, MA, 02138, USA
| | - P J Nico de Bruyn
- Department of Zoology and Entomology, Mammal Research Institute, University of Pretoria, Private Bag X20, Hatfield, 0028, South Africa
| | - Andrew B Davies
- Department of Organismic and Evolutionary Biology, Harvard University, 22 Divinity Avenue, Cambridge, MA, 02138, USA
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Pringle RM, Abraham JO, Anderson TM, Coverdale TC, Davies AB, Dutton CL, Gaylard A, Goheen JR, Holdo RM, Hutchinson MC, Kimuyu DM, Long RA, Subalusky AL, Veldhuis MP. Impacts of large herbivores on terrestrial ecosystems. Curr Biol 2023; 33:R584-R610. [PMID: 37279691 DOI: 10.1016/j.cub.2023.04.024] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Large herbivores play unique ecological roles and are disproportionately imperiled by human activity. As many wild populations dwindle towards extinction, and as interest grows in restoring lost biodiversity, research on large herbivores and their ecological impacts has intensified. Yet, results are often conflicting or contingent on local conditions, and new findings have challenged conventional wisdom, making it hard to discern general principles. Here, we review what is known about the ecosystem impacts of large herbivores globally, identify key uncertainties, and suggest priorities to guide research. Many findings are generalizable across ecosystems: large herbivores consistently exert top-down control of plant demography, species composition, and biomass, thereby suppressing fires and the abundance of smaller animals. Other general patterns do not have clearly defined impacts: large herbivores respond to predation risk but the strength of trophic cascades is variable; large herbivores move vast quantities of seeds and nutrients but with poorly understood effects on vegetation and biogeochemistry. Questions of the greatest relevance for conservation and management are among the least certain, including effects on carbon storage and other ecosystem functions and the ability to predict outcomes of extinctions and reintroductions. A unifying theme is the role of body size in regulating ecological impact. Small herbivores cannot fully substitute for large ones, and large-herbivore species are not functionally redundant - losing any, especially the largest, will alter net impact, helping to explain why livestock are poor surrogates for wild species. We advocate leveraging a broad spectrum of techniques to mechanistically explain how large-herbivore traits and environmental context interactively govern the ecological impacts of these animals.
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Affiliation(s)
- Robert M Pringle
- Department of Ecology & Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
| | - Joel O Abraham
- Department of Ecology & Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA
| | - T Michael Anderson
- Department of Biology, Wake Forest University, Winston Salem, NC 27109, USA
| | - Tyler C Coverdale
- Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA; Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Andrew B Davies
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | | | | | - Jacob R Goheen
- Department of Zoology & Physiology, University of Wyoming, Laramie, WY 82072, USA
| | - Ricardo M Holdo
- Odum School of Ecology, University of Georgia, Athens, GA 30602, USA
| | - Matthew C Hutchinson
- Department of Life & Environmental Sciences, University of California Merced, Merced, CA 95343, USA
| | - Duncan M Kimuyu
- Department of Natural Resources, Karatina University, Karatina, Kenya
| | - Ryan A Long
- Department of Fish and Wildlife Sciences, University of Idaho, Moscow, ID 83844, USA
| | - Amanda L Subalusky
- Department of Biology, University of Florida, Gainesville, FL 32611, USA
| | - Michiel P Veldhuis
- Institute of Environmental Sciences, Leiden University, 2333 CC Leiden, The Netherlands
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Inundation area drives hippo group aggregation and dispersal in a seasonal floodplain system. Mamm Biol 2022. [DOI: 10.1007/s42991-022-00286-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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Masese FO, Fuss T, Bistarelli LT, Buchen-Tschiskale C, Singer G. Large herbivorous wildlife and livestock differentially influence the relative importance of different sources of energy for riverine food webs. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 828:154452. [PMID: 35278569 DOI: 10.1016/j.scitotenv.2022.154452] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 03/05/2022] [Accepted: 03/06/2022] [Indexed: 06/14/2023]
Abstract
In many regions of the world, large populations of native wildlife have declined or been replaced by livestock grazing areas and farmlands, with consequences for terrestrial-aquatic ecosystem connectivity and trophic resources supporting food webs in aquatic ecosystems. The river continuum concept (RCC) and the riverine productivity model (RPM) predict a shift of energy supplying aquatic food webs along rivers: from terrestrial inputs in low-order streams to autochthonous production in mid-sized rivers. In Afromontane-savanna landscapes, the shifting numbers of large mammalian wildlife present a physical continuum whose ecological implications for rivers is not clearly understood. Here, we studied the influence of replacing large wildlife (mainly hippos) with livestock on the fractional contribution of C3 vegetation, C4 grasses and periphyton on macroinvertebrates in the Mara River, which is an African montane-savanna river known to receive large subsidy fluxes of terrestrial organic matter and nutrients mediated by large mammalian herbivores (LMH), both wildlife and livestock, in its middle and lower reaches. Using stable carbon (δ13C) and nitrogen (δ15N) isotopes, we identified spatial patterns in the fractional contribution of allochthonous organic matter from C3 and C4 plants (woody vegetation and grasses, respectively) and autochthonous energy from periphyton for macroinvertebrates at various sites of the Mara River and its tributaries. Potential energy sources and invertebrates were sampled at 80 sites spanning stream orders 1 to 7, various catchment land uses (forest, agriculture and grasslands) and different loading rates of organic matter and nutrients by LMH (livestock and wildlife, i.e., hippopotamus). The fractional contribution of different sources of energy for macroinvertebrates along the river did not follow predictions of the RCC and RPM. First, the fractional contribution of C3 and C4 carbon was not related to river order or location along the fluvial continuum but to the loading of organic matter (dung) by both wildlife and livestock. Notably, C4 carbon was important for macroinvertebrates even in large river sections inhabited by hippos. Second, even in small 1st -3rd order forested streams, periphyton was a major source of energy for macroinvertebrates, and this was fostered by livestock inputs fuelling aquatic primary production throughout the river network. Importantly, our results show that replacing wildlife (hippos) with livestock shifts river systems towards greater reliance on autochthonous sources of energy through an algae-grazer pathway as opposed to reliance on allochthonous inputs of C4 carbon through a detrital pathway.
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Affiliation(s)
- Frank O Masese
- University of Eldoret, Department of Fisheries and Aquatic Science, P.O. Box 1125-30100, Eldoret, Kenya; Department of Ecohydrology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.
| | - Thomas Fuss
- Department of Ecohydrology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany; Department of Ecology, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Lukas Thuile Bistarelli
- Department of Ecohydrology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany; Department of Ecology, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
| | - Caroline Buchen-Tschiskale
- Thünen Institute of Climate-Smart Agriculture, Bundesallee 65, 38116 Braunschweig, Germany; Leibniz Centre for Agricultural Landscape Research (ZALF), Eberswalder Straβe 84, 15374 Müncheberg, Germany
| | - Gabriel Singer
- Department of Ecohydrology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany; Department of Ecology, University of Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria
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Dutton CL, Subalusky AL, Sanchez A, Estrela S, Lu N, Hamilton SK, Njoroge L, Rosi EJ, Post DM. The meta-gut: community coalescence of animal gut and environmental microbiomes. Sci Rep 2021; 11:23117. [PMID: 34848778 PMCID: PMC8633035 DOI: 10.1038/s41598-021-02349-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Accepted: 11/08/2021] [Indexed: 01/04/2023] Open
Abstract
All animals carry specialized microbiomes, and their gut microbiota are continuously released into the environment through excretion of waste. Here we propose the meta-gut as a novel conceptual framework that addresses the ability of the gut microbiome released from an animal to function outside the host and alter biogeochemical processes mediated by microbes. We demonstrate this dynamic in the hippopotamus (hippo) and the pools they inhabit. We used natural field gradients and experimental approaches to examine fecal and pool water microbial communities and aquatic biogeochemistry across a range of hippo inputs. Sequencing using 16S RNA methods revealed community coalescence between hippo gut microbiomes and the active microbial communities in hippo pools that received high inputs of hippo feces. The shared microbiome between the hippo gut and the waters into which they excrete constitutes a meta-gut system that could influence the biogeochemistry of recipient ecosystems and provide a reservoir of gut microbiomes that could influence other hosts. We propose that meta-gut dynamics may also occur where other animal species congregate in high densities, particularly in aquatic environments.
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Affiliation(s)
- Christopher L Dutton
- Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect St., New Haven, CT, 06511, USA.
- Department of Biology, University of Florida, Gainesville, FL, USA.
| | - Amanda L Subalusky
- Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect St., New Haven, CT, 06511, USA
- Department of Biology, University of Florida, Gainesville, FL, USA
| | - Alvaro Sanchez
- Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect St., New Haven, CT, 06511, USA
- Microbial Sciences Institute, Yale University, New Haven, CT, USA
| | - Sylvie Estrela
- Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect St., New Haven, CT, 06511, USA
- Microbial Sciences Institute, Yale University, New Haven, CT, USA
| | - Nanxi Lu
- Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect St., New Haven, CT, 06511, USA
- Microbial Sciences Institute, Yale University, New Haven, CT, USA
| | - Stephen K Hamilton
- W.K. Kellogg Biological Station and Department of Integrative Biology, Michigan State University, Hickory Corners, MI, USA
- Cary Institute of Ecosystem Studies, Millbrook, NY, USA
| | | | - Emma J Rosi
- Cary Institute of Ecosystem Studies, Millbrook, NY, USA
| | - David M Post
- Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect St., New Haven, CT, 06511, USA
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