Data from: Fire frequency drives habitat selection by a diverse herbivore guild impacting top–down control of plant communities in an African savanna

In areas with diverse herbivore communities such as African savannas, the frequency of disturbance by fire may alter the top–down role of different herbivore species on plant community dynamics. In a seven year experiment in the Kruger National Park, South Africa, we examined the habitat use of nine common herbivore species across annually burned, triennially burned and unburned areas. We also used two types of exclosures (plus open access controls) to examine the impacts of different herbivores on plant community dynamics across fire disturbance regimes. Full exclosures excluded all herbivores > 0.5 kg (e.g. elephant, zebra, impala) while partial exclosures allowed access only to animals with shoulder heights ≤ 0.85 m (e.g. impala, steenbok). Annual burns attracted a diverse suite of herbivores, and exclusion of larger herbivores (e.g. elephant, zebra, wildebeest) increased plant abundance. When smaller species, mainly impala, were also excluded there were declines in plant diversity, likely mediated by a decline in open space available for colonization of uncommon plant species. Unburned areas attracted the least diverse suite of herbivores, dominated by impala. Here, herbivore exclusion, especially of impala, led to strong declines in plant richness and diversity. With no fire disturbance, herbivore exclusion led to competitive exclusion via increases in plant dominance and light limitation. In contrast, on triennial burns, herbivore exclusion had no effect on plant richness or diversity, potentially due to relatively little open space for colonization across exclosure treatments but also little competitive exclusion due to the intermediate fire disturbance. Further, the diverse suite of grazers and browsers on triennial burns may have had a compensating effect of on the diversity of grasses and forbs. Ultimately, our work shows that differential disturbance regimes can result in differential consumer pressure across a landscape and result in heterogeneous patterns in top–down control of community dynamics.

在非洲稀树草原等草食动物群落多样的区域，火灾干扰频率可能会改变不同草食动物物种对植物群落动态的自上而下调控（top–down）作用。我们于南非克鲁格国家公园开展了一项为期七年的野外实验，探究了9种常见草食动物在年度火烧、三年火烧以及未火烧生境中的生境利用情况。同时，我们设置了两种类型的草食动物排除围栏（exclosures，辅以开放访问对照处理），以探究不同火干扰格局下，不同草食动物类群对植物群落动态的影响。全围栏可排除所有体重超过0.5千克的草食动物（如大象、斑马、黑斑羚），而半围栏仅允许肩高≤0.85米的动物进入（如黑斑羚、小羚羊）。年度火烧生境吸引了多样的草食动物类群，移除大型草食动物（如大象、斑马、角马）后，植物丰度显著提升。当连以黑斑羚为主的小型草食动物也被排除后，植物多样性出现下降，这一现象可能由可供稀有植物定植的开放空间减少所介导。未火烧生境的草食动物类群多样性最低，且以黑斑羚为绝对优势类群。在此类生境中，排除草食动物（尤其是黑斑羚）会导致植物物种丰富度与多样性大幅下降。在无火干扰的生境中，排除草食动物会通过提升植物优势度、加剧光照限制，引发植物物种间的竞争排除。与之相反，在三年火烧生境中，排除草食动物对植物物种丰富度与多样性无显著影响，这可能源于两方面原因：一是围栏处理下可供植物定植的开放空间相对匮乏，二是中等强度的火干扰降低了竞争排除的发生概率。此外，三年火烧生境中多样的牧食者与啃食者类群，可能对草本植物与杂类草的多样性起到了补偿调控作用。综上，本研究表明，差异化的干扰格局可使整个景观中形成差异化的消费者调控压力，进而导致群落动态的自上而下调控呈现异质性分布模式。