The Effects of Hippopotamus Grazing on Grasslands

Lock, J. M.

doi:10.2307/2258356

Cited by 112 publications

(92 citation statements)

References 13 publications

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“…Previous studies from disparate plant herbivore systems found similar asymmetries in the effect of exploitation of one herbivore on the other. Exploitative competition was suggested for hippopotamus (Hippopotamus amphibius L.) in Ugandan Queen Elizabeth Park, where it consumes large amounts of grass at night, therewith inhibiting exploitation of the same grasslands by day-feeders such as buffalo (Syncerus caffer Sparrman) (Lock 1972). Similarly, Fox (1996) reported Brent Geese (Branta bernicla (L.)) foraging on seagrass (Zostera spp.)…”

Section: Discussionmentioning

confidence: 99%

Compensatory growth in an aquatic plant mediates exploitative competition between seasonally tied herbivores

Hidding¹,

Nolet

Boer

et al. 2009

Ecology

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Abstract. The degree to which vertebrate herbivores exploitatively compete for the same food plant may depend on the level of compensatory plant growth. Such compensation is higher when there is reduced density-dependent competition in plants after herbivore damage. Whether there is relief from competition may largely be determined by the life-history stage of plants under herbivory. Such stage-specific compensation may apply to seasonal herbivory on the clonal aquatic plant sago pondweed (Potamogeton pectinatus L.). It winters in sediments of shallow lakes as tubers that are foraged upon by Bewick's Swans (Cygnus columbianus bewickii Yarrell), whereas aboveground biomass in summer is mostly consumed by ducks, coots, and Mute Swans. Here, tuber predation may be compensated due to diminished negative density dependence in the next growth season. However, we expected lower compensation to summer herbivory by waterfowl and fish as density of aboveground biomass in summer is closely related to photosynthetic carbon fixation. In a factorial exclosure study we simultaneously investigated (1) the effect of summer herbivory on aboveground biomass and autumn tuber biomass and (2) the effect of tuber predation in autumn on aboveground biomass and tuber biomass a year later. Summer herbivory strongly influenced belowground tuber biomass in autumn, limiting food availability to Bewick's Swans. In contrast, tuber predation in autumn by Bewick's Swans had a limited and variable effect on P. pectinatus biomass in the following growth season. Whereas relief from negative density dependence largely eliminates effects of belowground herbivory by swans, aboveground herbivory in summer limits both above-and belowground plant biomass. Hence, there was an asymmetry in exploitative competition, with herbivores in summer reducing food availability for belowground herbivores in autumn, but not the other way around.

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Section: Discussionmentioning

confidence: 99%

Compensatory growth in an aquatic plant mediates exploitative competition between seasonally tied herbivores

Hidding¹,

Nolet

Boer

et al. 2009

Ecology

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“…However, relatively little is known about the development of piosphere gradients in ecosystems supporting diverse assemblages of large wild herbivores, livestock and pastoralists, such as the semi-arid savanna ecosystems of East Africa. Riparian savanna habitats in such ecosystems, if also grazed heavily by hippopotamus (Hippopotamus amphibious, Linnaeus 1758) or livestock, may experience seasonal ecological stresses through the depletion of herbaceous vegetation and increased denudation (Thornton 1971;Lock 1972;Fleischner 1994;Eltringham 1999;Oba et al 2000). While most wild herbivores are highly mobile and distribute their grazing impacts more evenly over the landscape, hippos and pastoral livestock are typically central-place foragers, because hippos must leave and return to water, whereas pastoral livestock must leave and return to pastoral settlements daily.…”

Section: Introductionmentioning

confidence: 99%

“…This creates zones of attenuating impacts from water and settlements (Ogutu et al 2010), which, in turn, affect the use of riparian habitats and pastoral landscapes by other herbivores. Hippo grazing can be potentially destructive to vegetation due to a combination of their large daily food requirements and their characteristic grazing style of plucking grass (Lock 1972;Eltrigham 1974;Thornton 1971). Similarly, heavy livestock grazing can be detrimental to wildlife habitats (Jones 1981;Quinn and Walgenbach 1990;Fleischner 1994), except under well-managed grazing conditions (Vavra 2005).…”

Section: Introductionmentioning

confidence: 99%

Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya

et al. 2011

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Riparian savanna habitats grazed by hippopotamus or livestock experience seasonal ecological stresses through the depletion of herbaceous vegetation, and are often points of contacts and conflicts between herbivores, humans and their livestock. We investigated how hippopotamus and livestock grazing influence vegetation structure and cover and facilitate other wild herbivores in the Mara region of Kenya. We used 5 km-long transects, each with 13 plots measuring 10 9 10 m 2 , and which radiate from rivers in the Masai Mara National Reserve and adjoining community pastoral ranches. For each plot, we measured the height and visually estimated the percent cover of grasses, forbs, shrubs and bare ground, herbivore abundance and species richness. Our results showed that grass height was shortest closest to rivers in both landscapes, increased with increasing distance from rivers in the reserve, but was uniformly short in the pastoral ranches. Shifting mosaics of short grass lawns interspersed with patches of medium to tall grasses occurred within 2.5 km of the rivers in the reserve in areas grazed habitually by hippos. Hence, hippo grazing enhanced the structural heterogeneity of vegetation but livestock grazing had a homogenizing effect in the pastoral ranches. The distribution of biomass and the species richness of other ungulates with distance from rivers followed a quadratic pattern in the reserve, suggesting that hippopotamus grazing attracted more herbivores to the vegetation patches at intermediate distances from rivers in the reserve. However, the distribution of biomass and the species richness of other ungulates followed a linear pattern in the pastoral ranches, implying that herbivores avoided areas grazed heavily by livestock in the pastoral ranches, especially near rivers.

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“…Examples of this aggregation and its subsequent effects on nutrient regimes abound in terrestrial systems. The effects on nutrient regimes include, but are not limited to herbivory (Day and Detling 1990, Frank and McNaughton 1992, Lock 1971, removal or accumulation of organic matter (Lal 1998), and nutrient deposition via defecation (Joblin 1981). Of these processes, defecation has been shown to produce greater changes in nutrient concentration in substrates and among primary producers.…”

Section: Introductionmentioning

confidence: 99%

“…Of these processes, defecation has been shown to produce greater changes in nutrient concentration in substrates and among primary producers. Quantification and analysis of the impact of concentrated animal feces has been recorded for such diverse animals such as colonial birds (Lindeboom 1984, Bildstein et al 1992, Post et al 1998, Powell et al 1991, Hayes and Caslick 1984, Allaway and Ashford 1984, McColl and Burger 1976, herding bison (Day and Detling 1990, Frank and McNaughton 1992, Lock 1971) and nesting ants (Wagner 1997, Lugo et. al 1973, Frouz et al 2002, Wagner and Jones 2004.…”

Section: Introductionmentioning

confidence: 99%

Artificially induced aggregation of fauna and their effects on nutrient regimes and primary producers in an oligotrophic subtropical estuary

Dewsbury¹

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Dewsbury, Bryan M., "Artificially induced aggregation of fauna and their effects on nutrient regimes and primary producers in an oligotrophic subtropical estuary" (2006 In order to investigate the role of faunal aggregations in concentrating nutrients in the oligotrophic landscape of Florida Bay, I manipulated faunal densities in Florida Bay sea grass beds by constructing artificial reefs. The effects of reefs and faunal aggregations on nutrient availability and benthic community structure were assessed.Over a year-long sampling period, artificial reefs had an average population of 50 fishes and crustaceans of various species. Faunal aggregation resulted in significant sediment organic matter decreases and sediment phosphorus increases. Plots with high fauna populations also had shorter seagrass blades presumably due to the effects of grazing.Chlorophyll-a concentrations in the sediment and periphyton samplers were mainly affected by reef presence or exclosure type and not due to the presence of aggregating fauna. Our results suggest that faunal aggregation may have more top-down effects on primary producers than bottom-up effects over smaller temporal scales.111

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The Effects of Hippopotamus Grazing on Grasslands

Cited by 112 publications

References 13 publications

Compensatory growth in an aquatic plant mediates exploitative competition between seasonally tied herbivores

Compensatory growth in an aquatic plant mediates exploitative competition between seasonally tied herbivores

Hippopotamus and livestock grazing: influences on riparian vegetation and facilitation of other herbivores in the Mara Region of Kenya

Artificially induced aggregation of fauna and their effects on nutrient regimes and primary producers in an oligotrophic subtropical estuary

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