Termites create spatial structure and govern ecosystem function by affecting N₂ fixation in an East African savanna

Abstract

. 2010. "Termites create spatial structure and govern ecosystem function by affecting N-2 fixation in an East African savanna." Ecology 91(5): 1296-1307. Ecology, 91(5), 2010Ecology, 91(5), , pp. 1296Ecology, 91(5), -1307Ecology, 91(5), Ó 2010 Abstract. The mechanisms by which even the clearest of keystone or dominant species exert community-wide effects are only partially understood in most ecosystems. This is especially true when a species or guild influences community-wide interactions via changes in the abiotic landscape. Using stable isotope analyses, we show that subterranean termites in an East African savanna strongly influence a key ecosystem process: atmospheric nitrogen fixation by a monodominant tree species and its bacterial symbionts. Specifically, we applied the 15 N natural abundance method in combination with other biogeochemical analyses to assess levels of nitrogen fixation by Acacia drepanolobium and its effects on co-occurring grasses and forbs in areas near and far from mounds and where ungulates were or were not excluded. We find that termites exert far stronger effects than do herbivores on nitrogen fixation. The percentage of nitrogen derived from fixation in Acacia drepanolobium trees is higher (55-80%) away from mounds vs. near mounds (40-50%). Mound soils have higher levels of plant available nitrogen, and Acacia drepanolobium may preferentially utilize soilbased nitrogen sources in lieu of fixed nitrogen when these sources are readily available near termite mounds. At the scale of the landscape, our models predict that termite/soil derived nitrogen sources influence .50% of the Acacia drepanolobium trees in our system. Further, the spatial extent of these effects combine with the spacing of termite mounds to create highly regular patterning in nitrogen fixation rates, resulting in marked habitat heterogeneity in an otherwise uniform landscape. In summary, we show that termite-associated effects on nitrogen processes are not only stronger than those of more apparent large herbivores in the same system, but also occur in a highly regular spatial pattern, potentially adding to their importance as drivers of community and ecosystem structure.

Pathways for Positive Cattle–Wildlife Interactions in Semiarid Rangelands

“…Furthermore, spatial heterogeneity in soil and plant nutrients in African rangelands can strongly influence the distribution of wild herbivores at multiple spatial scales (McNaughton, 1988(McNaughton, , 1990Blackmore et al, 1990;Ben-Shahar and Coe, 1992;Murray, 1995;Muchiru et al, 2008). Natural sources of soil nutrient heterogeneity include termites Fox-Dobbs et al, 2010) and tree canopies (Riginos et al, 2009). Here we discuss a major anthropogenic source of landscape heterogeneity: livestock corrals.…”

Conserving Wildlife in African Landscapes Kenya’s Ewaso Ecosystem

“…Furthermore, spatial heterogeneity in soil and plant nutrients in African rangelands can strongly influence the distribution of wild herbivores at multiple spatial scales (McNaughton, 1988(McNaughton, , 1990Blackmore et al, 1990;Ben-Shahar and Coe, 1992;Murray, 1995;. Natural sources of soil nutrient heterogeneity include termites Fox-Dobbs et al, 2010) and tree canopies ). Here we discuss a major anthropogenic source of landscape heterogeneity: livestock corrals.…”

Lower ant Diversity on Earth Mounds in a Semi-Arid Brazilian Ecosystem: Natural or a Sign of Degradation?

“…in African savannas have shown that active termite mounds in the otherwise relatively flat homogeneous landscapes increased nitrogen availability by supporting nitrogenfixing plant species, resulting in significantly higher nutrient concentrations than those resulting from droppings of herbivorous ungulates (Fox-Dobbs et al, 2010). Similarly, semi-arid environments in Asia possess high spatial variability in soil nutrient and vegetation properties, where organic matter and nutrients were shown to contribute to the islands of fertility phenomenon (Chen et al, 2006), what is also registered for desert ecosystems (Ganer & Steinberg, 1989).…”