Elephant-induced structural changes in the vegetation and habitat selection by large herbivores in an African savanna

Valeix, Marion; Fritz, Hervé; Sabatier, Rodolphe; Murindagomo, Felix; Cumming, David H. M.; Duncan, Patrick

doi:10.1016/j.biocon.2010.10.029

Cited by 91 publications

(81 citation statements)

References 52 publications

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“…However, Sinclair et al (2003) showed that predation is a factor defining herbivore densities on African savannas, particularly for small herbivores (<150 kg). The change in vegetation structure could affect the predation risk of a species; the opening up of the landscape increases the visibility and is expected to decrease the predation risk (Valeix et al 2011). The decrease in impala densities in our study is not easily explained by increased visibility as a consequence of the lower tree density, but predation could play a role here through a larger success of cursorial predators, such as the cheetah, in a more open landscape.…”

Section: Discussionmentioning

confidence: 62%

“…2 Relationship between the elephant density (N/km 2 ) and the overall tree stem density (N/km 2 ) (a), the number of stems per tree (b) and the estimated total consumption of browse (filled squares) and grass (open squares) of the relevant herbivores depicted as a percentage of the total consumption excluding elephants in Sabi Sand WildtuinMalaMala complex (c) (Fritz et al 2002;Kohi et al 2011;Valeix et al 2011;Kohi 2013). The impact of elephant may be site-or contextdependent (Guldemond and Van Aarde 2008) and varies spatially within KNP (Eckhardt et al 2000).…”

Section: Discussionmentioning

confidence: 99%

“…However, a decrease in tree cover can also increase the visibility for prey and predators, and thereby influence the predation risk (Valeix et al 2011).…”

Section: Introductionmentioning

confidence: 99%

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Elephant-mediated habitat modifications and changes in herbivore species assemblages in Sabi Sand, South Africa

Boer

Oort

Grover³

et al. 2015

Eur J Wildl Res

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Elephant Loxodonta africana conservation might indirectly influence the wider herbivore community structure, as elephants have the ability to significantly modify the savanna habitat. Uncertainty remains as to the consequences of these effects, as elephants might either compete with other species or facilitate foraging especially for grazers and smaller browsing species by increasing the amount of grass or the amount of browse at lower feeding heights. We studied these potential cascading effects of elephants by using 16 years of data (1992-2011) from the Sabi Sand Wildtuin, South Africa, which showed a steady increase in elephant densities from 0.12 to 2.03 elephants/km 2 over this period. We demonstrate that tree densities, and browse availability at feeding heights below 2 m, decreased with increasing elephant densities, and that there was no positive effect of elephants on browse availability. The changes in elephant densities were good predictors (R 2 adj >0.50) in explaining population fluctuations of other herbivore species. The total body mass of grazers increased more than that of the browsers, shifting the community toward a grazer and megaherbivore-dominated community. An increasing density of elephants changes the composition of the herbivore community, as mesobrowsers are unable to benefit from the impact of elephants on trees, but megagrazers show strong positive responses. Hence, changes in elephant densities as a result of poaching or conservation may trigger cascading community effects. These are neglected but important consequences of (negative or positive) human impacts on elephant numbers, especially in restricted areas such as reserves and national parks.

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Section: Discussionmentioning

confidence: 62%

Section: Discussionmentioning

confidence: 99%

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Elephant-mediated habitat modifications and changes in herbivore species assemblages in Sabi Sand, South Africa

Boer

Oort

Grover³

et al. 2015

Eur J Wildl Res

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“…Several studies have dealt with the distribution of grazers and browsers (e.g. Rodgers, 1984;Knight, 1991;Valeix et al, 2011). Due to their results, we expected that typical grazers would prefer the open bush-cleared areas, while typical browsers should prefer non-cleared sites.…”

Section: Impacts Of Bush Encroachment Management On Large Herbivore Dmentioning

confidence: 93%

Impact of bush encroachment management on plant response and animal distribution

Stolter¹,

Joubert²,

Schwarz³

et al. 2018

Biodivers. Ecol.

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Abstract:The transformation of grassland by bush encroachment causes socioeconomic problems in arid and semi-arid regions. At the moment, de-bushing is the only way to control bush encroachment. In this context, we conducted two independent projects within SASSCAL. First, in a greenhouse experiment, we investigated the morphological plant response to damage of four diff erent bush encroacher species in order to understand if intervention in the plants' early life stage may reasonably fi ght bush encroachment and if treated plants are used diff erently by livestock (e.g., sheep and goats). In a second project, we investigated the infl uence of bush clearing on the habitat utilisation of diff erent large herbivores (e.g., greater kudu, warthog, and gemsbok). Specifi cally, we wanted to know if typical grazers (e.g., warthog and gemsbok) are found at open cleared sites and typical browsers (greater kudu) in encroached regions and if vegetation parameters (e.g., grass cover) drive this distribution. For our greenhouse experiment, we found that all seedlings reacted morphologically to the damage of top-shoots, but to diff erent extents. Damaged plants show species-specifi c responses, like diff erences in branching and thorn sizes and survival rates. In contrast to sheep, goats were not absolutely deterred by mechanical defences of the off ered plant species. Therefore, we assume that under controlled grazing regimes, goat feeding could be a useful tool to interfere with the establishment of large numbers of seedlings. In our second project, the animal distribution did not consistently match our expectations. While warthog and cattle shared open bush-cleared sites, we found gemsbok utilising non-cleared sites with high thornbush cover of medium height, which was similar to patterns shown by greater kudu. The results are discussed in light of competition, risk avoidance, and habitat heterogeneity.Resumo: A transformação dos prados pela densifi cação de plantas lenhosas causa problemas s ocioeconómicos em regiões áridas e semi-áridas. De momento, a remoção de plantas lenhosas é a única maneira de controlar a sua densifi cação. Assim, conduzimos dois projectos independentes no contexto do SASSCAL. Numa experiência numa estufa, investigámos a resposta morfológica a danos de quatro espécies invasoras diferentes, de modo a compreender se a intervenção no estádio inicial de vida é razoável para combater a invasão das lenhosas, bem como se estas plantas tratadas são usadas de forma diferente pelo gado (ovelhas e cabras). Num segundo projecto, investigámos a infl uência do desmatamento na utilização do habitat por diferentes grandes herbívoros (cudo, javali-africano e órix). Especifi camente, queriamos saber se típicos herbívoros de pasto (e.x.: javali-africano e órix) eram encontrados em locais abertos, e típicos browsers (cudo) em regiões invadidas, e se os parâmetros da vegetação (e.x.: cobertura de gramíneas) conduzem esta distribuição. Na nossa experiência na estufa, descobrimos que todas as plântulas reagiram morfologic...

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“…However, Rutina et al [45] found that the converted woodland to shrubland by elephants improved the dry-season browse availability for impalas, which increased in numbers as a result. Valeix et al [46] also reported that elephant-induced vegetation changes influenced selection by browsers for microhabitats with modified vegetation. Similarly, Stokke et al [47] found that small/medium sized mammals and gallinaceous birds in Chobe may have benefited from impacts of elephants, through increasing the shrubland habitats.…”

Section: Impacts Of Woodland Conversion By Elephantsmentioning

confidence: 98%

Woodland Conversion by Elephants in Africa: The Search for Causal Factors, Processes, Mechanisms and Management Strategies

Zyambo¹

2016

OJE

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The impacts of elephants on woodlands have triggered concerns that elephants were converting woodlands to grasslands in African savannas leading to the loss of biodiversity. Therefore, the objectives of the study are to identify the causes, processes and impacts of woodland conversion by elephants and thereby propose a guideline for formulating management strategies. The study is conducted through reviewing published documents on elephant-woodland interaction, factors, mechanisms and processes of woodland conversion to grasslands and impacts on biodiversity have been identified. The study reveals that: 1) the large nutritional and energetic requirements by elephants and high elephant population densities are two driving forces that may cause elephants to convert woodlands to grasslands; 2) the process of woodland conversion is not just elephant-tree interaction, but usually included other agents such as fires, droughts or other herbivores. Woodlands are converted to grasslands or scrublands because elephants, fires, droughts and other herbivores prevent recruitment of tree to larger class sizes and regeneration of seedlings of woody plants; 3) whereas there are few studies that support biodiversity decline due to impacts of elephants on woodlands, there are studies that indicate woodland disturbance by elephants have benefited and increased diversity of other species. It is concluded that woodland disturbance by elephant is not always detrimental to biodiversity, but may create heterogeneity and suitable habitats for other species. In formulating management strategies, considerations must be made to elephant densities, other agents that interact or work with elephants in woodland conversion and the benefits of woodland changes to biodiversity due to elephants.

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Elephant-induced structural changes in the vegetation and habitat selection by large herbivores in an African savanna

Cited by 91 publications

References 52 publications

Elephant-mediated habitat modifications and changes in herbivore species assemblages in Sabi Sand, South Africa

Elephant-mediated habitat modifications and changes in herbivore species assemblages in Sabi Sand, South Africa

Impact of bush encroachment management on plant response and animal distribution

Woodland Conversion by Elephants in Africa: The Search for Causal Factors, Processes, Mechanisms and Management Strategies

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