Strong positive effects of termites on savanna bird abundance and diversity are amplified by large herbivore exclusion

Moe, Stein R.; Eldegard, Katrine; Rannestad, Ole Tobias; Okullo, Paul; Lindtjørn, Ommund; Støen, Ole‐Gunnar; Dale, Svein

doi:10.1002/ece3.3513

Cited by 5 publications

(8 citation statements)

References 48 publications

(85 reference statements)

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“…Large mounds (5–10 m in diameter) constructed by Macrotermes subhyalinus (Rambur) are conspicuous features in much of the park covering about 5% of the landscape (Moe et al. ). The tree communities on these mounds differ from those off‐mound, and tree densities and diversity are higher (Støen et al.…”

Section: Methodsmentioning

confidence: 99%

Wood decomposition is more rapid on than off termite mounds in an African savanna

2019

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Decomposition is important for nutrient cycling and the dynamics of soil organic matter. The factors that influence local decomposition rates in savannas dominated by Macrotermes mounds remain uncertain. Here, we experimentally assessed the effects of macro-and micro-detritivores, active and inactive mounds, and vegetation cover on wood decomposition rates for eight common woody plant species in Lake Mburo National Park, in Uganda. Five pairs of Macrotermes mounds, one active and one inactive per pair, were selected. Each mound provided two sample locations, one, the most shaded (with canopy cover), and one, the most open (without canopy cover) edge of mound. In addition, for each mound pair, one additional sample location was located off-mound, in an open level area between the mounds. After one, three, and 12 months, protected (wrapped in 1-mm mesh fiber-glass excluding macrodetritivores) and unprotected wood samples from each location were retrieved, brushed clean, oven-dried, and weighed. After 12 months, mean percentage mass loss was four times higher for unprotected than protected wood samples across all species located on mound sites (when decomposition in shaded and open microhabitats was combined). Mean percentage mass loss across all species combined was 1.2 times higher on active than inactive mounds. Across all mounds, decomposition was on average 1.1 times more rapid in the shaded than open mound parts. These differences were more pronounced on inactive mounds (1.3 times more rapid in the shaded than open parts). Percentage mass loss was markedly lower off-mound (12.6 AE 0.8%) than on active (25.9 AE 1.5%) or inactive mounds (19.7 AE 1.2%). Proportional mass loss for unprotected wood decreased with increasing wood density, but proportional mass loss of protected wood samples was not detectably influenced by wood density. Our study highlights the strong and locally contingent influence of termite mounds, termite activity, vegetation, and their interactions on wood decomposition rates within a savanna landscape. Furthermore, variation in per-species wood decomposition rates, including the negative correlation with wood density, depends on accessibility to macrodetritivores.

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Section: Methodsmentioning

confidence: 99%

Wood decomposition is more rapid on than off termite mounds in an African savanna

2019

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“…(), working in a Kenyan savanna, found that bird diversity and abundance increased in the savanna when ungulates were absent, which suggests that increased dispersal by birds is a possible explanation for our results. We know that birds use mound plots much more than off‐mound plots and that bird abundance increase on fenced mounds (Moe et al., ), but we do not know how important seed dispersal by birds is in the two habitats. It is also possible that small mammals and invertebrates move and scatter‐hoard seeds into off‐mound exclosures (Acanakwo, Sheil, & Stein, ).…”

Section: Discussionmentioning

confidence: 99%

“…In addition, increased tree cover is associated with higher biomass and enhanced sequestration of atmospheric carbon. While woody vegetation supports many organisms within the landscape (Moe et al., ), increasing tree cover may impact negatively on grass, grazers and other organisms which favour more open landscapes (Riginos, Grace, Augustine, & Young, ; Smit & Prins, ). With global increase in atmospheric CO 2 levels and changing fire regimes through much of the savannas (Bond, ; Bond & Midgley, ), we anticipate a continued increase in tree cover through the savanna landscape of Lake Mburo National Park.…”

Section: Discussionmentioning

confidence: 99%

“…and A. hockii De Willd. dominate off‐mound (Moe et al., ). Common grazing ungulates include topi ( Damaliscus lunatus Burchell, 1823), waterbuck ( Kobus ellipsiprymnus Ogilby, 1833), bushbuck ( Tragelaphus scriptus Pallas, 1766) and warthog ( Phacochoerus africanus Gmelin, 1788), while common mixed feeders include impala ( Aepyceros melampus Lichtenstein, 1812), zebra ( Equus q. burchelli Gray, 1824) and eland ( Taurotragus oryx Pallas, 1766).…”

Section: Methodsmentioning

confidence: 99%

“…We also predicted that excluding ungulates would result in larger effects on tree species composition on‐mound than off‐mound, because (a) the effect of herbivory on species richness can increase with resource availability (Chase, Leibold, Downing, & Shurin, ); and (b) competitive dominance occurs sooner in more productive sites (Hautier, Niklaus, & Hector, ). Finally, we predicted that in fenced treatments (a) the per‐plot proportion of fleshy‐fruited tree species would increase because the majority of these trees are dispersed by frugivorous birds, and these birds have been observed to become more abundant, particularly on‐mounds, in the absence of ungulates (Moe et al., ; Ogada, Gadd, Ostfeld, Young, & Keesing, ); (b) the per‐plot proportion of armed (i.e., spine‐ or thorn‐bearing) trees would decline because the relative benefits of these defences are removed; (c) the proportion of evergreen trees would increase due to release from dry season browsing and trampling (Moe, Rutina, et al., ); and (d) mean bark thickness would be greater off‐mound than on‐mound and increase after ungulate exclusion because of differences in fuel load and the resulting fires.…”

Section: Introductionmentioning

confidence: 99%

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Termites confer resistance to changes in tree composition following reduced browsing in an African savanna

Acanakwo

Okullo²,

Sheil

et al. 2018

J Vegetation Science

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Questions Ungulates affect plant community structure and composition. Vegetation response to these effects are variable. Wild large herbivore populations are declining globally, but how tree communities respond to this change is not clear. We experimentally examined how tree communities respond to changes in ungulate abundance in a heterogeneous landscape. Location Lake Mburo National Park, Uganda. Methods We recorded tree species in nine replicate sites each with four treatment plots: fenced off‐mound (excluding ungulates), unfenced off‐mound, fenced and unfenced on‐mound. Each species was assessed for fruit type, leafing strategy, spinescence and bark thickness. We compared tree communities on‐ and off‐mound, with and without ungulates using PERMANOVA, and the effects of habitat, fencing and time on stem density and traits using generalized linear mixed effects model. Results Stem density increased by 88% off‐mound and 138% on‐mound (p = 0.005) with fencing, between 2006 and 2015. Whether tree communities occurred on‐ or off‐mound determined species composition, but fencing had little effect. Tree traits were not markedly altered by fencing on‐mound. Off‐mound, fencing was associated with a 38% increase in the proportion of fleshy‐fruited tree stems (p < 0.001), 18% decline in armed tree stems (p = 0.035) and a 44% reduction in mean bark thickness (p = 0.001). Conclusion Our study highlights the important role mounds play in maintaining tree community composition with declining ungulate abundance. While ungulates influence tree communities off‐mounds they have little effect on tree composition and traits of mound‐borne trees. Thus, Macrotermes mounds support distinct tree communities that are robust to exclusion of ungulates.

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Termites and large herbivores influence seed removal rates in an African savanna

Acanakwo

Sheil

Moe

2017

Ecology

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Seed removal can influence plant community dynamics, composition, and resulting vegetation characteristics. In the African savanna, termites and large herbivores influence vegetation in various ways, likely including indirect effects on seed predators and secondary dispersers. However, the intensity and variation of seed removal rates in African savannas has seldom been studied. We experimentally investigated whether termites and large herbivores were important factors in the mechanisms contributing to observed patterns in tree species composition on and off mounds, in Lake Mburo National Park, Uganda. Within fenced (excluding large herbivores) and unfenced termite mound and adjacent savanna plots, we placed seeds of nine native tree species within small open "cages," accessed by all animals, roofed cages that only allowed access to small vertebrates and invertebrates, and closed cages that permitted access by smaller invertebrates only (5 mm wire mesh). We found that mean seed removal rate was high (up to 87.3% per 3 d). Mound habitats experienced significantly higher removal rates than off-mound habitats. The mean removal rate of native seeds from closed cages was 11.1% per 3 d compared with 19.4% and 23.3% removed per 3 d in the roofed and open cages, respectively. Smaller seeds experienced higher removal rates than larger seeds. Large herbivore exclusion on mounds reduced native seed removal rates by a mean of 8.8% in the open cages, but increased removal rates by 1.7% in the open cages when off-mound habitats were fenced. While removal rates from open cages were higher on active mounds (30.9%) than on inactive mounds (26.7%), the removal rates from closed cages were lower on active vs. inactive mounds (6.1% vs. 11.6%, respectively). Thus, we conclude that large herbivores and Macrotermes mounds influence seed removal rates, though these effects appear indirect.

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Strong positive effects of termites on savanna bird abundance and diversity are amplified by large herbivore exclusion

Cited by 5 publications

References 48 publications

Wood decomposition is more rapid on than off termite mounds in an African savanna

Wood decomposition is more rapid on than off termite mounds in an African savanna

Termites confer resistance to changes in tree composition following reduced browsing in an African savanna

Termites and large herbivores influence seed removal rates in an African savanna

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