Savanna ecosystems are vital for both economic and biodiversity values. In savannas worldwide, management decisions are based on the concept that wildlife and livestock compete for grassland resources[1-4], yet there are virtually no experimental data to support this assumption[1]. Specifically, the critical assessment of whether or not wild ungulates alter livestock performance (e.g., weight gain, reproduction or survival) has rarely been carried out, although diminished performance is an essential prerequisite for inferring competition[1]. Here we use a large-scale experiment in a semi-arid savanna in Kenya to show that wild ungulates do depress cattle performance (weight gain) during the dry season, indicating a competitive effect, but enhance cattle performance during the wet season, signifying facilitation. This is the first experimental demonstration of either competitive or facilitative effects of an assemblage of native ungulates on domestic livestock in a savanna ecosystem, and a unique demonstration of a rainfall-dependent shift in competition-facilitation balance within any herbivore guild. These results are critical for better understanding and management of wildlife-livestock coexistence in savanna ecosystems globally, and especially in the African savanna biome which crucially hosts the last remnants of an intact large herbivore fauna.

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The impacts of wild herbivores on cattle diet selection were investigated in an East African rangeland during August 2001 and February 2002. The study compared cattle diets in plots exclusively accessible to cattle (C) and those accessible to megaherbivores (elephants and giraffes), non-megaherbivore wild herbivores. 15 kg (zebras, hartebeests, Grant's gazelles, oryx, elands, and buffaloes) and cattle (MWC); or non-megaherbivore wild herbivores and cattle (WC). There were no treatment differences in selection of most grass species in either sampling period (P. 0.05). However, selection of forbs differed among treatments during February when conditions were relatively dry and percent of bites taken by cattle on this forage class increased (P , 0.005) from 1.8% 6 0.3 to 7.7% 6 1.6 (mean 6 SE). During this period, cattle took a lower percent of bites on forbs in MWC (4.3% 6 1.7; P ¼ 0.01) and WC (5.9% 6 2.2; P ¼ 0.03) than in C (12.9% 6 0.9). These patterns were generally driven by Commelina spp., which comprised 65% 6 9.4 of total bites on forbs. Notably, these differences were associated with differences in cover of forbs, which was positively correlated with percent of bites on forbs (r 2 ¼ 0.86, P , 0.01). Because forbs may be critical components of cattle diets in such rangelands during relatively dry periods, these dietary changes may indicate potential seasonal costs of wildlife to cattle production. Looking for ways to offset such costs may be worthwhile for livestock properties that accommodate wildlife. Resumen Los impactos de los herbívoros silvestres sobre selecció n de la dieta del ganado fueron investigados en un pastizal del este de Á frica de Agosto del 2001 a Febrero del 2002. En el estudio se compararon las dietas del ganado en potreros accesibles exclusivamente al ganado (C) y en potreros accesibles a megaherbívoros (elefantes y jirafas), herbívoros silvestres mayores de 15 kg (zebras, ñ us, gacelas, oryx, alce africano y bú falos) y ganado (MWC) y en potreros accesibles a no-mega herbívoros silvestres y ganado (WC). En ninguna de las épocas de muestro hubo diferencia entre tratamientos en la selecció n para la mayoría de especies de zacates (P. 0.05). Sin embargo, en Febrero, cuando las condiciones fueron relativamente secas, la selecció n de hierbas difirió entre tratamientos y el porcentaje de mordidas efectuadas por el ganado en esta clase de forraje aumentó (P , 0.005) de 1.8% 6 0.3 a 7.7% 6 1.6. Durante este periodo, el ganado registró porcentajes de mordidas de hierbas má s bajos en los potreros MWC (4.3% 6 1.7; P ¼ 0.01) y WC (5.9% 6 2.2; P ¼ 0.03) que en los accesibles solo al ganado (12.9% 6 0.9). estos patrones generalmente estuvieron regidos por las plantas del género Commelina spp., las cuales comprendieron 65% 6 9.4 del total de las mordidas de hierbas. Estas diferencias estuvieron notablemente asociadas con diferencias en la cobertura de hierbas, la que fue positivamente correlacionada con el porcentaje de mordidas (r 2 ¼ 0.86, P , 0.01). Debido a que las hierbas pueden ser un compo...

Although livestock and wildlife share most of their ranges worldwide, little controlled experimental research has been done on their interactions. Since 1995 we have been manipulating the presence of cattle and large wild ungulates in a Kenyan savanna rangeland in order to better understand the nature of competition and coexistence between these two guilds of herbivores and how they affect biodiversity. In a replicated experiment in which different combinations of cattle and wild herbivores are allowed access to large-scale plots, we have been monitoring the impacts of these herbivores on vegetation, on the wild herbivores, and cattle themselves, and on a variety of other taxa. We have also been conducting experimental research to examine other ways in which livestock management in eastern Africa might affect biodiversity. These include studies on the impacts of fire, livestock corrals, and changes in tree density. This research has revealed the following patterns. (1) Cattle suppress many species of wild herbivores, presumably through competition for their shared resources. The nature of this competition, however, is contingent on rainfall and the presence of other herbivores. (2) Wild herbivores both compete with and facilitate cattle, depending on rainfall. (3) The pastoral practice of housing livestock nightly in protective corral enclosures ("bomas") over time produces long-lived nutrient hotspots preferred by both livestock and wild herbivores. (4) Fire, frequently used by pastoralists in the past, is valuable for improving grass quality, with benefits for many species of wild herbivores. (5) Pastoral practices that reduce woody cover, including burning and boma construction, create local habitat patches that are preferred by wild herbivores, apparently for their greater anti-predator visibility. (6) Despite competition between livestock and wild herbivores, coexistence between these two guilds can be managed, and there are several positive (facilitative) pathways between livestock husbandry and wild herbivores and other biodiversity.