Are Termite Mounds Always Grazing Hotspots? Grazing Variability with Mound Size, Season and Geology in an African Savanna
Foraging site selection by large herbivores is influenced by multiple factors varying across landscapes and spatial scales. Termite mounds harbour highly nutritious plants compared with the savanna matrix, making them preferred foraging patches in many savannas. However, it is unknown whether termite mounds equally influence herbivore grazing intensity across geological substrates and mound sizes. These knowledge gaps hamper our ability to draw general trans-ecosystem conclusions about the effect of termite mounds for savanna herbivores. We measured grazing intensity on mounds of three different size classes (small, medium and large) across two geologies with differing soil nutrition (granite and basalt) in Gonarezhou National Park, Zimbabwe. We recorded measurements across three seasons (hot wet, cool dry and hot dry), and at multiple distances from mounds. Grazing intensity on mounds was higher on nutrient-poor granite than nutrient-rich basalt, and termite mounds of all sizes had a significant effect on grazing on granite during the cool dry season. Grazing was highest on large mounds on both geologies throughout the year. Large mounds also had the largest spatial influence on grazing in the cool dry season, up to 8 m beyond the mound edge on granite and 2 m on basalt. When scaled up to the landscape level, mounds influenced about 15% of the granite landscape, but only about 0.5% of the basalt landscape. Our results show that the positive effects of mounds on grazing intensity were pronounced on nutrient-poor soils but negligible on nutrient-rich soils, and that the magnitude of these effects varied across seasons and with mound size.
Keywordsbasalt granite grazing intensity landscape large herbivore nutrient hotspots semi-arid savannas
- Anderson DR, Link WA, Johnson DH, Burnham KP, Press A. 2001. Suggestions for presenting the results of data analyses invited paper: the results of data analyses suggestions. J Wildl Manag 65:373–8. http://www.jstor.org/stable/3803088.
- Anderson JM, Ingram JSI. 1993. Tropical soil biology and fertility: a handbook of methods. second. Wallingford: CABI.Google Scholar
- Barton K. 2016. MuMIn: multi-model inference. R package Version 1156, www.r-project.org.
- Bates D. 2007. nlme: Linear and Nonlinear Mixed Effects Models. R package version 31-128, www.r-project.org.
- Davies AB, Robertson MP, Levick SR, Asner GP, van Rensburg BJ, Parr CL. 2014. Variable effects of termite mounds on African savanna grass communities across a rainfall gradient. Journal of Vegetation Science 25:1405–16. https://doi.org/10.1111/jvs.12200.
- Fox J, Weisberg S, Adler D, Bates D, Baud-Bovy G, Ellison S, Firth D, Friendly M, Gorjanc G, Graves S, Heiberger R, Laboissiere R, Monette G, Murdoch D, Nilsson H, Ogle D, Ripley B, Venables W, Winsemius D, Zeileis A. 2015. CAR: companion to applied regression. R package version 21-2, www.r-project.org.
- Genz A, Bretz F, Miwa T, Mi X, Leisch F, Scheipl F, Bornkamp B, Maechler M, Hothorn T. 2016. Multivariate normal and t distributions. R package version 10-5: www.r-project.org.
- Holt J, Coventry R. 1990. Nutrient cycling in Australian savannas. Journal of Biogeography 17:427–32. http://www.jstor.org/stable/2845373.
- Hothorn T, Bretz F, Westfall P, Heiberger RM, Schuetzenmeister A, Scheibe S. 2016. Simultaneous inference in general parametric models. R package version 14-4: www.r-project.org.
- Kartzinel TR, Chen PA, Coverdale TC, Erickson DL, Kress WJ, Kuzmina ML, Rubenstein DI, Wang W, Pringle RM. 2015. DNA metabarcoding illuminates dietary niche partitioning by African large herbivores. Proc Natl Acad Sci: 6.Google Scholar
- Knox NM, Skidmore AK, Prins HHT, Asner GP, van der Werff HMA, de Boer WF, van der Waal C, de Knegt HJ, Kohi EM, Slotow R, Grant RC. 2011. Dry season mapping of savanna forage quality, using the hyperspectral Carnegie Airborne Observatory sensor. Remote Sens Environ 115:1478–88. https://doi.org/10.1016/j.rse.2011.02.007.
- Kruckeberg AR. 1986. An essay: the stimulus of unusual geologies for plant speciation. Syst Bot 11:455–63. http://www.jstor.org/stable/2419082.
- Lagendijk DDG, Davies AB, Eggleton P, Slotow R. 2016. No evidence for an elephant-termite feedback loop in Sand Forest, South Africa. Biol Conserv 203:125–33. http://linkinghub.elsevier.com/retrieve/pii/S0006320716303317.
- Mobæk R, Narmo AK, Moe SR. 2005. Termitaria are focal feeding sites for large ungulates in Lake Mburo National Park, Uganda. J Zool Lond 267:97–102. https://doi.org/10.1017/s0952836905007272.
- Muvengwi J. 2016. Relationships between termite (Macrotermes) mound distribution, plant diversity and large mammalian herbivory patterns in Gonarezhou National Park, Zimbabwe.Google Scholar
- Muvengwi J, Davies AB, Parrini F, Witkowski ETF. 2018b. Geology drives the spatial patterning and structure of termite mounds in an African savanna. Ecosphere 9:e02148. https://doi.org/10.1002/ecs2.2148.
- Muvengwi J, Mbiba M, Nyenda T. 2013. Termite mounds may not be foraging hotspots for mega-herbivores in a nutrient-rich matrix. J Trop Ecol 29:551–8. http://www.journals.cambridge.org/abstract_S0266467413000564.
- Muvengwi J, Ndagurwa HGT, Nyenda T, Mbiba M. 2016. Nutrient dynamics and plant assemblages of Macrotermes falciger mounds in a savanna ecosystem. Acta Oecol 76:13–21. http://linkinghub.elsevier.com/retrieve/pii/S1146609X16301722.
- Muvengwi J, Ndagurwa HGT, Nyenda T, Mlambo I. 2014. Termitaria as preferred browsing patches for black rhinoceros (Diceros bicornis) in Chipinge Safari Area, Zimbabwe. J Trop Ecol 30:591–8. http://www.journals.cambridge.org/abstract_S0266467414000480.
- Naiman R, Braack L, Grant C, Kemp A, Du Toit J, Venter F. 2003. Interactions between species and ecosystem characteristics. In: Du Toit JT, Rogers KH, Biggs HC, Eds. The Kruger experience, ecology and management of savanna heterogeneity. Washington: Long Island Press. p 221–41.Google Scholar
- Okalebo JR, Gathma KW, Woomer PL. 2002. Laboratory methods of soil and plant analysis: a working manual. second. Soil Science Society of East Africa, Nairobi.Google Scholar
- Scholes RJ, Bond WJ, Eckhardt HC. 2003. Vegetation dynamics in the Kruger ecosystem. In: du Toit JT, Rogers KH, Biggs HC, Eds. The Kruger experience: ecology and management of savanna heterogeneity. Washington: Island Press. p 242–62.Google Scholar
- Venter FJ. 1990. A classification of land use for management planning in the Kruger National Park.Google Scholar
- Venter FJ, Scholes RJ, Eckhardt HC. 2003. The abiotic template and its associated vegetation pattern. In: Du Toit JT, Biggs HC, Rogers KH, Eds. The Kruger experience: ecology and management of savanna heterogeneity. Washington: Island Press. p 81–129.Google Scholar