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Nanyuki, Kenya

Ogada D.L.,Mpala Research Center | Keesing F.,Bard College
Journal of Raptor Research | Year: 2010

Raptors were monitored monthly over a three-year period in a protected area in central Kenya. The number of raptors declined more than 40 per year. Scavenging birds accounted for most of the decline; sightings decreased by 70 during our surveys, although these declines were not statistically significant. During the time of the study, the overall populations of large wild herbivores showed little change, whereas domestic herbivores, particularly sheep and goats, increased markedly, suggesting that food limitation was not the cause of the vulture declines at the study site. Possible causes of raptor decline include the consumption of poisoned baits, which are placed by pastoralists to kill large predators that attack livestock. Scavenging birds provide one of the most important yet underappreciated ecosystem services of any avian group. The rapid decline of scavenging birds, especially vultures, in central Kenya warrants additional population monitoring to understand whether declines are local or regional, and to elucidate causes of population decreases. © 2010 The Raptor Research Foundation, Inc. Source

Sensenig R.L.,University of California at Davis | Sensenig R.L.,Mpala Research Center | Sensenig R.L.,Goshen College | Demment M.W.,University of California at Davis | Laca E.A.,University of California at Davis
Ecology | Year: 2010

The high herbivore diversity in savanna systems has been attributed to the inherent spatial and temporal heterogeneity related to the quantity and quality of food resources. Allometric scaling predicts that smaller-bodied grazers rely on higher quality forage than larger-bodied grazers. We replicated burns at varying scales in an East African savanna and measured visitation by an entire guild of larger grazers ranging in size from hare to elephant. We found a strong negative relationship between burn preference and body mass with foregut fermenters preferring burns to a greater degree than hindgut fermenters. Burns with higher quality forage were preferred more than burns with lower quality forage by small- bodied grazers, while the opposite was true for large-bodied grazers. Our results represent some of the first experimental evidence demonstrating the importance of body size in predicting how large herbivores respond to fire-induced changes in plant quality and quantity. © 2010 by the Ecological Society of America. Source

Veblen K.E.,University of California at Davis | Veblen K.E.,Mpala Research Center
Journal of Arid Environments | Year: 2012

In African savannas, abandonment of traditional livestock corrals (bomas) creates long-term mosaics of nutrient hotspots embedded in a lower-nutrient matrix. It is unclear how plant communities develop over time on these sites in clay-rich "black cotton" soils or how herbivores attracted to these sites affect vegetation development. I first examined whether treeless "glades", derived from abandoned bomas, function as nutrient and herbivore hotspots. Soil, vegetation, and herbivore data were collected on glades of varying ages. The results indicated that glades persist as long-term (≥four decades) patches (0.25-1.0 ha) of improved soil texture and increased nutrient levels, palatable grasses, and herbivore use. Glade vegetation also appears to undergo succession from Cynodon plectostachyus to Pennisetum stramineum dominance. Based on these patterns, exclusion cages were used to test herbivore effects on glade vegetation development. I found that large herbivores may retard succession by suppressing invasion of P. stramineum into C. plectostachyus-dominated areas. These results provide evidence that abundant anthropogenic glades function as long-term nutrient and wildlife hotspots in black cotton soils, distinct from similar hotspots in other soil types. The findings provide evidence that large herbivores can exert control over development and persistence of glades through their effects on plant community dynamics. © 2011 Elsevier Ltd. Source

Porensky L.M.,University of California at Davis | Porensky L.M.,Mpala Research Center
Journal of Ecology | Year: 2011

1.Ecological edges (zones separating ecosystems or land cover types) can function as active boundaries, unique habitats and dynamic transition zones. Abiotic factors, species and species interactions exhibit strong responses to edges, and these responses - edge effects - can profoundly impact ecosystem structure and function. 2.Edge effects may be altered by the presence or proximity of other nearby edges. This phenomenon - edge interaction - is poorly understood, though its importance is increasingly recognized. Edge interactions are likely in fragmented or patchy landscapes that contain many edges. In such landscapes, understanding how nearby edges interact may be critical for effective conservation and management. 3.I examined edge interactions in an East African savanna. In this landscape, abandoned cattle corrals develop into treeless, nutrient-rich 'glades' that persist as preferentially grazed areas for decades to centuries. Glades represent important sources of structural and functional landscape heterogeneity and have major impacts on distributional patterns of plant and animals. 4.I used existing variation in inter-glade distance to investigate the importance and strength of glade edge interactions for plants, Acacia ants and large herbivores. Specifically, I compared response patterns obtained from transects that extended outward from isolated glades (>250m from another glade) and non-isolated glades (<150m from another glade). 5.Edge effect patterns between nearby glades differed significantly from patterns around isolated glades. When compared to areas outside isolated glades, areas between glades had almost twice the density of trees, half as much large herbivore use, reduced cover of glade-dominant grasses, and different Acacia ant communities. Many of the edge effects observed between non-isolated glades could not be inferred from effects around isolated glades. 6. Synthesis. These findings suggest that edge interactions can alter plant and animal distributions in patchy landscapes. Edge effects near multiple edges can be stronger, weaker or qualitatively different from those near isolated edges. Such edge interactions can increase or decrease structural and functional continuity between nearby patches. Appropriate extrapolation of local edge effects in complex and fragmented landscapes will require greater understanding of edge interactions. © 2011 The Author. Journal of Ecology © 2011 British Ecological Society. Source

Odadi W.O.,Mpala Research Center | Karachi M.K.,Egerton University | Abdulrazak S.A.,National Council for Science and Technology | Young T.P.,Mpala Research Center | Young T.P.,University of California at Davis
Science | Year: 2011

Savannas worldwide are vital for both socioeconomic and biodiversity values. In these ecosystems, management decisions are based on the perception that wildlife and livestock compete for food, yet there are virtually no experimental data to support this assumption. We examined the effects of wild African ungulates on cattle performance, food intake, and diet quality. Wild ungulates depressed cattle food intake and performance during the dry season (competition) but enhanced cattle diet quality and performance during the wet season (facilitation). These results extend our understanding of the context-dependent-competition-facilitation balance, in general, and are critical for better understanding and managing wildlife-livestock coexistence in human-occupied savanna landscapes. Source

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