van der Waal Cornelis, de Kroon Hans, van Langevelde Frank, de Boer Willem F, Heitkönig Ignas M A, Slotow Rob, Pretorius Yolanda, Prins Herbert H T
Resource Ecology Group, Wageningen University, Droevendaalsesteeg 3A, 6708 PD, Wageningen, The Netherlands.
Agri-Ecological Services, PO Box 28, Omaruru, Namibia.
Oecologia. 2016 Aug;181(4):1173-85. doi: 10.1007/s00442-016-3627-0. Epub 2016 Apr 19.
The scale of resource heterogeneity may influence how resources are locally partitioned between co-existing large and small organisms such as trees and grasses in savannas. Scale-related plant responses may, in turn, influence herbivore use of the vegetation. To examine these scale-dependent bi-trophic interactions, we varied fertilizer [(nitrogen (N)/phosphorus (P)/potassium (K)] applications to patches to create different scales of nutrient patchiness (patch size 2 × 2 m, 10 × 10 m, or whole-plot 50 × 50 m) in a large field experiment in intact African savanna. Within-patch fertilizer concentration and the total fertilizer load per plot were independently varied. We found that fertilization increased the leaf N and P concentrations of trees and grasses, resulting in elevated utilization by browsers and grazers. Herbivory off-take was particularly considerable at higher nutrient concentrations. Scale-dependent effects were weak. The net effect of fertilization and herbivory was that plants in fertilized areas tended to grow less and develop smaller rather than larger standing biomass compared to plants growing in areas that remained unfertilized. When all of these effects were considered together at the community (plot) level, herbivory completely eliminated the positive effects of fertilization on the plant community. While this was true for all scales of fertilization, grasses tended to profit more from coarse-grained fertilization and trees from fine-grained fertilization. We conclude that in herbivore-dominated communities, such as the African savanna, nutrient patchiness results in the herbivore community profiting rather more than the plant community, irrespective of the scale of patchiness. At the community level, the allometric scaling theory's prediction of plant-and probably also animal-production does not hold or may even be reversed as a result of complex bi-trophic interactions.
资源异质性的规模可能会影响资源在稀树草原中共存的大型和小型生物（如树木和草本植物）之间的局部分配方式。与规模相关的植物反应可能反过来影响食草动物对植被的利用。为了研究这些与规模相关的双营养级相互作用，我们在完整的非洲稀树草原进行了一项大型田间试验，对小块区域施加不同的肥料（氮（N）/磷（P）/钾（K）），以创造不同规模的养分斑块（斑块大小为2×2米、10×10米或整块地50×50米）。斑块内的肥料浓度和每块地的总肥料负荷是独立变化的。我们发现施肥增加了树木和草本植物叶片中的氮和磷浓度，导致食叶动物和食草动物的利用率提高。在较高的养分浓度下，食草动物的采食量尤其可观。与规模相关的影响较弱。施肥和食草的综合影响是，与未施肥区域生长的植物相比，施肥区域的植物往往生长较慢，现存生物量较小而不是较大。当在群落（地块）水平上综合考虑所有这些影响时，食草作用完全消除了施肥对植物群落的积极影响。虽然所有施肥规模都是如此，但草本植物往往从粗粒度施肥中获益更多，而树木则从细粒度施肥中获益更多。我们得出结论，在以食草动物为主的群落中，如非洲稀树草原，养分斑块化使食草动物群落比植物群落受益更多，而与斑块化的规模无关。在群落水平上，异速生长比例理论对植物（可能还有动物）产量的预测不成立，甚至可能由于复杂的双营养级相互作用而逆转。
