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Components of the Okavango ecosystem. (a) Hippo trail through flooded vegetation in seasonal swamp; (b) termite mound; (c) elephants in newly flooded seasonal swamp; and (d) experimental gill net catch of fish, showing the diversity of species. Photographs: Peter B. Moyle.
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Kalahari Desert of southern Africa, is an immense allu-vial fan created by the rivers that drain the highlands of An-gola (Mendelsohn and el Obeid 2004). It is perhaps most famous for its dense populations of African megafauna, from elephants to lions to crocodiles. However, it is also one of the largest intact wetlands in the world, which is refle...
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... a complex plant community dominated by sedges and grasses becomes dominant, similar to the plant community that emerges downstream as the channels become smaller (Ellery and McCarthy 1994, Ellery et al. 2003). From the panhandle region, the water moves through a reach of anas- tomosing channels, fed by a central, meandering, 26-km channel (Smith et al. 1997). Most of the side channels and lagoons in this area come and go in a dynamic equilibrium between sediment deposition and the action of large animals, especially hippos (figures 3, 4). The channels are lined with giant grasses ( Phragmites mauritanus and Miscanthus junceus ) or similar plants, with dominance determined by complex interactions of flow, soils, nutrients, and fire (Ellery et al. 2003). Generally, the walls lining the channels are not as dense with stems as are the papyrus stands of the panhandle. The river next bifurcates into three channels—the Thaoge, Jao, and the Nqoga—just below Seronga, and the waters spread into a vast area of seasonal swamp (figure 1). The Thaoge is currently inactive (Porter and Muzila 1989), so the Jao and Nqoga remain the main source of water for much of the delta, which is distributed through a series of large, semipermanent branch channels. These drainage channels are perennial where they begin, but at their lower ends, they are typically dry for much of the year. The main channels are con- nected to lagoons by smaller channels. The lagoons are large, open expanses of water of complex origin that contain dense growths of macrophytes (McCarthy et al. 1993). During wet periods, the more distal small drainage channels deliver water (and fish) to pools that otherwise depend on rain- water to be filled. These pools are important sources of water for wildlife. The geomorphology and ecology of ecosystems are tied to- gether under a framework of complexity through what Stallins (2006) terms “ecological memory.”A key concept for understanding the way floodwaters influence the delta’s ecosystem is to think of each region as having a memory of the extent and size of past floods. The memory is longest in the seasonal swamp, where extensive flooding in one year may fill clay- bottomed pools and river channels with enough water to keep them watered through one or more drier years, and where swamp vegetation will persist for decades even if the flood regime changes (Gumbricht and McCarthy 2003). In the panhandle, the memory is shorter because most of the region floods annually, but the extent of flooding influences the size of off-channel lagoons and the strength of their connections to the main river channel. Overall, the memory of wet years can sustain species and populations through dry years, while the memory of dry years can reduce the ecosystem effects of wet years, although potentially it can have positive effects on nutrient cycling (see the next section). Overall, the alterna- tion of wet and dry years in an irregular pattern very likely maximizes ecosystem productivity and diversity. The biophysical processes that occur in the delta also occur in other systems around the world, but the isolated desert location of the Okavango, combined with the strong biotic interactions described here, make it unique. The most similar systems are also in Africa. The Bangweulu Swamps (Zambia) is a system in which seasonal flooding creates dynamic habitats and dispersal pathways for fish (Kolding et al. 2003). This seasonal flood pulse, in a lagoon and river channel complex, is also present in the Central Barotse (Zambia) floodplain (Kelly 1968). Likewise, the Shire floodplain (Malawi) is driven by a flood pulse, which maintains an oxbow lake, lagoon, and island complex (Chimatiro 2004). Similar observations of the effect of the flood pulse on fish dynamics have been made in the Solimoes floodplains of the Amazon (Cox Fernandes and de Mérona 1988, Chernoff et al. 2004, Siqueira-Souza and Freitas 2004). The importance of the annual flooding regime to fish and other aquatic organisms is enhanced by a number of large- scale biological processes that link the terrestrial and aquatic ecosystems. Three that have been identified as particularly important are (1) the role of large animals, (2) the role of termites, and (3) the biotic mobilization of nutrients. The role of large animals. The conspicuous mammals, birds, and reptiles that attract so many tourists to the Okavango region are important players in determining the physical and biological structure of the delta’s ecosystem, as ecosystem engineers (as defined by Wright and Jones 2006). For physical structure, hippo, elephant, and perhaps Nile crocodile ( Crocodylus niloticus ) are most important because of their size and abundance. Hippos are particularly important because their amphibious life style requires extensive daily movements between water and land (McCarthy et al. 1998a). These movements create incised, vegetation-free pathways through which water can flow during flooding (figure 4). These channels may become major river channels when the old channels fill with sand and avulse. In the panhandle and permanent swamp areas, hippos regularly break through the dense papyrus and reeds that form the stream banks, diverting water and sediment into adjacent areas. Because they favor deep lagoons for resting during the day, the hippo-created channels usually lead to lagoons. When these channels are re- captured by the main river, the lagoons fill with sediment (McCarthy et al. 1998a). These ever-changing channels and lagoons created by the actions of hippos are major habitats for fish. Elephants, with an expanding population of about 35,000 individuals in the delta (Mendelsohn and el Obeid 2004, Ramberg et al. 2006), also create channels, both by walking through flooded vegetation and through creation of de- pressed pathways during the dry season, which then serve as conduits for floodwater. Elephants also have major impacts on trees through their feeding activity; they kill and mangle the plants and disperse seeds through their dung. Extensive removal of trees by elephants on the largest island of the delta, Chiefs Island, and elsewhere may result in major rises in the salinity of the channels, through changes in water moved through transpiration. This observation is based on findings from McCarthy and Ellery (1994), who observed that large plants on islands act as “transpirational pumps” by removing water and leaving salts in the groundwater of islands. Subsequently, these islands act as salt sinks and hence assist in keeping the delta’s water less saline. Removing large trees from islands can stop this process, resulting in greater salinity of seasonal floodplain waters, with potential catastrophic effects on swamp vegetation and fish (Mendelsohn and el Obeid 2004). Elephants, hippos, buffalo, and other mammalian herbivores have exceptionally high densities in the Okavango Delta (Ramberg et al. 2006). They not only affect the structure and composition of delta vegetation, but presumably play a major role in converting vegetation biomass into forms that readily fertilize floodwaters, promoting fish production. The full importance of mammalian herbivores as a nutrient source for the aquatic ecosystem, compared with other sources (e.g., decaying vegetation), still needs to be determined (Hoberg et al. 2002). However, there is evidence that small and relatively shallow lagoons in the delta, which are most likely to be heav- ily fertilized by animal dung, sustain high fish production (Fox 1976). The role of piscivorous birds, mammals (e.g., two ot- ter species), reptiles (e.g., Nile crocodile, water monitor), and fishes in recycling nutrients in the system is also not well understood, but, given their abundance and diversity, it is bound to be considerable. The Nile crocodile in particular is often noted as a keystone predator and scavenger in African systems; its role in the Okavango is poorly understood, although fish (mainly catfishes and cichlids) and macroinvertebrates are major food items (Blomberg 1976). The impact of large herbivores, especially hippos, is some- what similar in other African floodplain systems. The activities of hippos and elephants in combination create many of the large pools in floodplain rivers, which provide refuges for fish during the dry season (Naiman and Rogers 1997). These pools and lagoons are subsequently fertilized by hippo dung, which promotes primary production, while the action of hippos in stirring the water prevents formation of anoxic conditions (Kilham 1982, Gereta and Wolanski 1998, Wolanski and Gereta 1999). The role of termites. Much of the upland topography of the delta is the result of the actions of a termite, Macrotermes michaelseni (Dangerfield et al. 1998). During dry periods, or when water shifts away from an area, termites colonize areas with suitable clay soils and vegetation and build subterranean nests, each topped by a large mound full of passages. The function of the mound is to ventilate the nest, into which vegetation is carried to support the gardens of fungi that the termites eat. The mounds can be up to 4 m high and cover 50 m 2 . When a termite colony is killed by inundation, the mound erodes, creating a small island, which then becomes a favorable site for recolonization by termites (Dangerfield et al. 1998). As this process repeats, the island grows in size. Because of the combination of elevation above low floods and nutrient-enriched soils, termite islands become colonized by trees and other plants (figures 3, 4). The islands then become favored places for living and feeding by mammals and birds, resulting in positive feedback loops that fertilize the soils and bring in seeds from other areas, contributing to successional processes (McCarthy et al. 1998b). With regard to fish, the 150,000 termite- derived islands not only determine the location of channels but also provide a source of complex cover and habitat ...
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Conflicts between the interests of agriculture and wildlife conservation are a major threat to biodiversity and human wellbeing globally. Addressing such conflicts requires a thorough understanding of the impacts associated with living alongside protected wildlife. Despite this, most studies reporting on human‐wildlife impacts and the strategies us...
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... The Okavango Delta, located in northern Botswana, is one of Africa's largest inland wetlands (Keddy et al. 2009) and offers a unique set of conditions to support aquatic biodiversity. For several millennia, the annual flood pulse together with the activity of ecosystem engineers (hippos, elephants, termites and plants) (Mosepele et al. 2009), have shaped a mosaic of habitats that is an oasis for biodiversity in an area that would otherwise have been a desert. ...
... It was not until the second half of the twentieth century that researchers started to study freshwater diversity of the Okavango Delta in more depth, focusing mainly on fish (Merron 1991(Merron ,1993Merron and Bruton 1995), plants (Ellery and Ellery 1997) and certain macroinvertebrate groups, including beetles (Bilardo and Rocchi 1987), dragonflies (Pinhey 1976), molluscs (Appleton 1979) and nematodes (Heyns and Coomans 1991). In the present century, the knowledge of aquatic diversity in the region has improved substantially, with more details about the processes that determine the distribution of macroinvertebrates Mosepele 2007, 2020; Davidson et al. 2012), fish (Mosepele et al. 2009) birds (Francis et al. 2021) and algae (Marazzi 2014(Marazzi , 2023. At species level, the composition and dynamics have been described in a comprehensive assessment by Appleton et al. (2003) and the reviews by Ramberg et al. (2006) and Mosepele and Mosepele (2021). ...
Freshwater organisms in the Okavango Delta and Lake Ngami (Botswana) provide direct and indirect benefits to people and the economy of the region. However, their existence could be potentially threatened by human activities (primarily, upstream water abstraction and planned hydropower structures) coupled with climate change. For their protection, it is essential to know their distribution, ecology, and status of the ecosystems that they inhabit. Publications that record taxa from the Delta at species level are scarce, particularly aquatic macroinvertebrates. Identifying organisms to species level can provide more accurate information for environmental monitoring and conservation programmes but requires significant training and expertise. Here, we present a comprehensive taxonomical review of 2204 freshwater species from the Okavango Delta and Lake Ngami, with additional 355 species found in other areas of Botswana that are likely to be present in the study region. We also compare the diversity of the Okavango Delta and Lake Ngami with two other tropical wetlands: the Pantanal (Bra-zil) and the Kakadu Region (Australia). We show that biodiversity in the Okavango Delta and Lake Ngami is higher than in previous estimates, with recorded species richness dominated by phytoplankton and macroinvertebrates. Most species are widespread across the system and southern Africa. The resulting database includes new records (Bryozoa, Porifera), information on species conservation status, habitat, ecology, distribution in continental Africa, site details and taxonomical notes. This will be an essential resource for researchers, conservation managers, policy makers and consultants investigating freshwater biodiversity in tropical wetlands in the region.
... Elephants are unique ecosystem engineers [25,26], able and willing to knock over large trees. They can convert a woodland into a glade. ...
Savanna landscapes are shaped by the interactions of disturbances with land use goals. Elephant hunting in a site in Botswana, and its consequences for wildlife, people, and landscapes, are described and discussed in order to make broader generalizations about the dynamics of savanna landscapes. Change comes from alterations in tree-grass interactions, fire regimes, predator-prey relations, livestock raising, and conservation goals. Some of these implications are specific to African landscapes, but others may be apt in global contexts.
... In Africa, elephants and hippopotamus are among the largest of the herbivores (Ripple et al., 2015). While these species differ considerably in their behaviour, feeding and landscape exploitation, they are similar in that both have an affinity for water (Mosepele et al., 2009;Owen-Smith, 1992). Hippopotamus are considered semi-aquatic and diurnally, spend their time in aquatic environments such as rivers, lakes and impoundments, and thus utilise water not only for drinking purposes but also as habitat (Coughlin & Fish, 2009;Field, 1970;McCarthy et al., 1998). ...
... At night, hippopotamus leave their aquatic environments to forage in surrounding terrestrial habitats (Field, 1970). While elephants utilise water primarily for hydration purposes, these mega-herbivores also exploit water extensively for non-drinking activities such as mud-bathing and swimming (Mosepele et al., 2009;Owen-Smith, 1992;Vanschoenwinkel et al., 2011). As such, both hippopotamus and elephants regularly move between terrestrial and aquatic environments (Loarie et al., 2009;McCauley et al., 2015;Mosepele et al., 2009). ...
... While elephants utilise water primarily for hydration purposes, these mega-herbivores also exploit water extensively for non-drinking activities such as mud-bathing and swimming (Mosepele et al., 2009;Owen-Smith, 1992;Vanschoenwinkel et al., 2011). As such, both hippopotamus and elephants regularly move between terrestrial and aquatic environments (Loarie et al., 2009;McCauley et al., 2015;Mosepele et al., 2009). In this research note we discuss hypothetical means by which elephants and hippopotamus could alter the limnology and ecology of water bodies. ...
Large herbivores have been described as agents of change in terrestrial habitats. Their effect on aquatic ecosystems are, however, underexplored. We raise the question of whether elephants and hippopotamus have the potential to significantly alter limnological properties and, indirectly, primary and secondary productivity within small and shallow freshwaters in arid and semi-arid African landscapes. In this note we discuss hypothetical means by which elephants and hippopotamus alter shallow freshwater bodies. We further assimilate this with known ways by which these mega-herbivores alter aquatic environments giving an overview of their potential functional role in structuring aquatic habitats.
... Hippos are considered important ecosystem engineers in African landscapes, because their large body size necessitates the consumption of substantial quantities of grass, thereby altering ecosystem processes such as fire regimes and nutrient transport. Hippos are also central place foragers (Lewison & Carter, 2004), making routine visits between grazing grounds and their aquatic habitat, spending most of the daytime wallowing, which can lead to considerable geomorphological change (McCarthy, Ellery & Bloem, 1998a;Bakker et al., 2016), profoundly altering the environment and impacting a host of co-occurring species (Mosepele et al., 2009). Moreover, hippos often congregate in large numbers (Fig. 3A) (Chomba, Simpamba & Nyirenda, 2013;Dutton et al., 2018b;Fritsch, Plebani & Downs, 2022), extenuating and amplifying their individual engineering impacts. ...
... (3) Hippo influences on geomorphology, both on land and in water Hippo trail formation represents an important geomorphological process ( Fig. 3E; McCarthy et al., 1998a;Deocampo, 2002;Mosepele et al., 2009). Over time, hippo trails become free of vegetation, resulting in the development of scoured pathways that can be up to 5 m wide and 1 m deep ( Fig. 3F; McCarthy et al., 1998a;Deocampo, 2002), which can lead to the development of new river channels (Fig. 3G, H). ...
... Although hippos are widely considered pivotal in determining fluvial characteristics of wetlands (e.g. McCarthy et al., 1998a;Mosepele et al., 2009), little empirical support is available. A more comprehensive understanding of their impact in comparison with other important hydrological determinants is required. ...
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.
... The latter case may also exemplify a situation in which a moving animal acts as a keystone species/ecosystem engineer that increases landscape connectivity by either removing physical obstacles or building structures that allow the other animals to cross the barrier. Ecosystem engineers are ubiquitous in terrestrial and wetland habitats around the world [10], yet documentation of their function as providers of movement corridors for other species is surprisingly scarce [11]. ...
Physical obstacles within animal habitats create barriers to individual movements. To cross those barriers, specific corridors are used, some of them created by keystone species such as Eurasian beavers (Castor fiber). Their dams on rivers may also increase habitat connectivity for terrestrial mammals, but the significance of that function has never been quantified. To investigate this, we placed tracking tunnels on beaver dams, fallen trees, and—as a control—on floating rafts. Additionally, we tested kinetic sand as a novel substrate for collecting tracks and found the paws of small mustelids precisely imprinted in that medium, allowing easy identification. However, we needed to lump all shrews and rodents smaller than water voles (Arvicola amphibius) into one category as they can only be detected but not identified. The highest mammalian activity was observed on dams, as they may provide shelter, offering protection from predators during a river crossing or permanent residence, and even the opportunity to hunt invertebrates. Slightly higher diversity was found on logs because of a higher proportion of mustelids, which select exposed locations for scent marking. Our results increase our body of knowledge about the beaver as an ecosystem engineer and provide a novel tool for the monitoring of mammal activity.
... Although the Oromeng et al. (2021) and Ramatlapeng et al. (2021) studies have provided insights on the role of hydrology and evapotranspiration in controlling solute behavior at the inlet and outlet of the Delta, there is still a lack of understanding of the processes driving the variations in river solute concentrations both in space and time for the nearly 450 km river distance between the Delta inlet and outlet (e.g., Letshele et al, 2023). The Delta serves as an important source of potable water and food (fish, water lily) to the riparian communities (Mosepele et al., 2006(Mosepele et al., , 2009Kgathi et al., 2006) and therefore, studying the processes that may affect the solute behavior in the Delta is crucial for water quality monitoring and ecological sustainability. ...
... Lastly, note that similarly to L. Africana and S. caffer, H. amphibius plays a key role in the habitat it belongs to. In its daily routine in and out of the water, H. amphibius opens and clears paths that when flooded, create most of the water lagoons and side pools that many small organisms use especially during drought conditions (Mason, 2013;Mosepele et al., 2009). ...
Among the large herbivores that inhabit the Mozambican Limpopo National Park are the elephant (L. africana), the buffalo (S. caffer), and the hippo (H. amphibius). Although since the moment of declaration of the territory as a National Park in 2001 the existing population within the park and adjoining areas have been relocating outside of it, the negative human interaction with the species continue to occur, a conflict exacerbated by drought and increasing pressure on freshwater resources. In this work, we approach this conflict through ensemble modeling of species and interactions, exploring the statistics to eventually provide heat maps of potential conflict areas in and around the park. The ensemble statistics showed in general good results in TSS (0.72-0.78), ROC (0.91-0.95), and Kappa (0.4-0.65) values. RF, Maxent, and GAM show better performance, with the variables of most importance in the models being altitude and mean temperature of the warmest month for L. africana; altitude and annual precipitation for S. caffer; and the dry season NDWI and annual precipitation for H. amphibius. Potential conflict points are found around the park, mainly distributed in the western half of it, if we consider the probability gradient of occurrence of the species. Our results illustrate the potential application of habitat distribution models in the study of human-wildlife conflicts. *Work subject to license CC BY 4.0
... This really is lower than the concentrations described by other studies from various nations (Adedire et al., 2015;Phuong et al., 1999;Wenlock et al., 1979). Mn content in fish varies greatly depending on environment and season (Table 1) (Mosepele et al., 2009). According to the current study, Scomberomorus commerson and Tilapia fish have the greatest Mn concentration rather than other food items (14.6 and 11.2 µg/g, respectively). ...
The current study was conducted to measure the manganese content in nine different food groups. A cross-sectional study was designed; a total of 89 food items were randomly purchased from the main markets and hypermarkets in Alexandria Governorate, then digested by wet ashing procedure and finally analyzed using ICP-OES. The highest mean Mn value was obtained in the fat group (6.75 µg/g) compared to the other eight groups, followed by nuts (4.64 µg/g) and the protein-rich food group (4.52 µg/g), while meat and its products have the lowest mean of Mn (0.53 µg/g). Manganese content in food groups is strongly correlated with the food matrix, soil composition, and fortification process. Local butter, margarine, sunflower oil, corn oil, Scomberomorus commerson, poulty fish, pistachio, and walnuts had the highest content of manganese.
... The hierarchical cluster analysis revealed that the area had three large herbivore functional groups. The first group comprised ecosystem engineers such as elephant (Mosepele et al. 2009, Sidle & Ziegler 2010 and hippopotamus (McCarthy et al. 1998, Deocampo 2002, McCauley et al. 2015. The third group comprised megaherbivores such as giraffe and buffalo, while the middle group contained small herbivores such as duiker and impala. ...
covers broad environmental areas of ecology, agriculture, forestry, agro-forestry, social science, economics, water and energy, climate change, planning, land use, pollution, strategic and environmental assessments and related fields. The journal addresses the sustainable development agenda of the country in its broadest context. It publishes four categories of articles: Section A: Research articles. High quality peer-reviewed papers in basic and applied research, conforming to accepted scientific paper format and standards, and based on primary research findings, including testing of hypotheses and taxonomical revisions. Section B: Research reports. High quality peer-reviewed papers, generally shorter or less formal than Section A, including short notes, field observations, syntheses and reviews, scientific documentation and checklists. ABSTRACT Functional diversity is a component of biodiversity that includes the range of roles that organisms perform in communities and can explain and predict the impact of organisms on ecosystems. Mudumu National Park is an important ecosystem that acts as a wildlife corridor for migratory fauna moving between Botswana, Namibia, Angola and Zambia. Thus, a thorough understanding of the functional diversity of large herbivores would assist with the management of the park. The present study examined large herbivore species contribution to total large herbivore biomass; dominant species' functional similarities; and whether or not functional diversity is affected by increasing distance from the Kwando River. A total of twenty-two roads were selected that provided good coverage of the park and were surveyed using the line transect distance sampling method. All large herbivores seen on either side of the transects were identified to species level and recorded. The hierarchical cluster analysis in SPSS was used to classify the herbivores into functional groups. Only a small number of species were found to be dominant in both numbers and biomass. Furthermore, dominant species were found to be functionally distinct, and functional dominance changed with respect to season and distance from the river.
... Rivers that drain these landscapes show differing connectivity with the terrestrial environment depending on the density and types of LMH present. Mega-herbivores including hippos (Hippopotamus amphibius), elephants (Lexodonta Africana), buffalo (Syncerus caffer), and other ungulates, such as wildebeest (Connochaetes taurinus), transfer substantial amounts of terrestrial organic matter and nutrients to entire river networks (Naiman and Rogers, 1997;Mosepele et al., 2009;Hulot et al., 2019) with higher amounts in lowland rivers (Subalusky et al., 2015(Subalusky et al., , 2018, challenging the applicability of existing models of river ecosystem functioning in savannas. Notably, this potential source of allochthonous energy is mainly derived from C4 plants in surrounding grasslands and seems to require grazing LMH as subsidy vectors (Marwick et al., 2014). ...
... While increasing livestock density increased both the fractional contribution of periphyton and C4 carbon for macroinvertebrates in the river, hippo populations only increased that of C4 carbon and reduced that of periphyton (Fig. 3). Although hippo dung has been reported to fertilize aquatic ecosystems, and increase primary and secondary production (Grey and Harper, 2002;Mosepele et al., 2009), other studies have shown that large particles in hippo dung can have detrimental effects on benthic production, especially during the dry season when they settle at the bottom of hippo pools and downstream sections of rivers (Dawson et al., 2016;Dutton et al., 2018aDutton et al., , 2018b. Hippos also spend long periods in the water for thermoregulation, approximately 12 h of daytime (Subalusky et al., 2015), and their wallowing activity is known to increase turbidity that can further limit primary production (Dutton et al., 2018a(Dutton et al., , 2018b. ...
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 (δ 13 C) and nitrogen (δ 15 N) 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.
