Ecological affinity changes in a Sudano-Sahelian rodent community after slash-and-burn farming (Gonsé Forest, Burkina Faso)
Article first published online: 9 MAY 2008
© 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Ltd
African Journal of Ecology
Volume 46, Issue 3, pages 435–439, September 2008
How to Cite
Papillon, Y., Godron, M. and Delattre, P. (2008), Ecological affinity changes in a Sudano-Sahelian rodent community after slash-and-burn farming (Gonsé Forest, Burkina Faso). African Journal of Ecology, 46: 435–439. doi: 10.1111/j.1365-2028.2007.00828.x
- Issue published online: 26 AUG 2008
- Article first published online: 9 MAY 2008
- (Manuscript accepted 23 July 2007)
In undisturbed environments, Sahelian rodent population dynamics are determined by climatic (Hubert & Adam, 1985) and edaphic factors (Hubert, Leprun & Poulet, 1977). Demographic change is therefore relatively predictable (Hubert, 1982; Sicard, Diarra & Cooper, 1999). Such situations are rare in the Sahel, notably, because of the high incidence of natural or anthropic disturbances. The impact of such disturbances on rodent population dynamics has been confirmed by various workers (Duplantier, 1998; Granjon et al., 2005; Papillon, Godron & Delattre, 2006). However, to develop rodent control strategies, allowance must be made for the effects of disturbances on the spatial distribution of rodent communities in different habitats and these effects must be measured in the short and medium term.
This study investigates spatial distribution variations of a rodent community over four seasons (wet and dry) following burning and correlates these with population variations (analysed and described elsewhere; Papillon et al., 2006).
Materials and methods
The study site (Fig. 1), climate and rodent population dynamics have been described in detail elsewhere (Papillon et al., 2006). Nine landscape elements (LE) were identified and classified on the basis of three descriptors: (i) vegetation, defined by the dominant forest species, whether mixed or not with crops; (ii) soil typology and rooting conditions: pedo 1 – with mottled ferruginous, more or less hydromorphic concretions and good rooting conditions; pedo 2 – with mottled, lessivated of tropical ferruginous soil and moderate rooting conditions; pedo 3 – calco-alkaline granite and poor rooting conditions and (iii) the presence of termite mounds.
About half of the area was pedo 1 type and was used for crops [Sorghum bicolour and Penissetum glaucum on Parkia biglobosa and crops (PBC) an Acacia albida (AAC) facies] or was unburnt [Acacia nilotica (ANA) or PBC].
The occurrence of termitaries for each LE was evaluated with a chi-squared test. Overall, termitaries were distributed evenly over type 1 and 2 soils (chi-squared nonsignificant) but were under-represented on type 3 soils (chi-squared highly significant: 8.33 < 0.005).
Figure 2 illustrates the seasonal affinities of each species: Taterillus gracilis was regularly present on the site whatever the season. It was the first species to colonize the site after burning (Wl) and displayed an immediate positive affinity for ANT and grass covered buffer zone (PAS) that lasted through all seasons. The species also regularly frequented Acacia radiana (ARA) and ANA in Wl and Parkinsonia aculeata (PAC) in D2. During colonization (Wl), the preferred LE were associated with habitats featuring Acacia: ARA, ANT and ANA. At this period, the mostly adult T. gracilis population clustered on the soils that were best for digging. Over the following seasons (Dl, W2 and D2), their distribution became more even.
Nannomys sp. colonized the site from Wl and concentrated mostly in a grass-and shrub-rich corridor (PAS). Nannomys sp. deserted the site during Dl but recolonized it rapidly and massively during W2. This demographic explosion involved colonization of all LE and a very even distribution.
Tatera guineae colonized remained chronically low during the two wet seasons and fell even further during the two dry seasons. Spatial distribution was strongly clustered with Prosopis, Parkinsonia and ANA.
Mastomys erythroleucus did not colonize the plot until D1. Thereafter it spread rapidly throughout the LE (except for PBC), with a very strong affinity for PAS. It largely abandoned the plot during W2, but recolonized it during D2 preferentially repopulating PAS and ARA.
A single LE (PAS) was particularly attractive to rodents. By contrast, three LE were little frequented: AAC, PBC and PAC.
Figure 3 illustrates the apparently antagonistic relations identified among species. There are nine of them. Four concern T. gracilis, two of which are versus T. guineae, one versus M. erythroleucus and one versus Nannomys sp. Three ‘antagonistic’ relations concern T. guineae; all three versus T. gracilis. Lastly, two antagonistic relations concern M. erythroleucus versus Nannomys sp. and Nannomys sp. versus T. guineae.
Figure 4 shows the three clearest examples of potentially competitive relations for a given LE. They involve PAS, PAC and ANA. Potential competition is also expressed for ARA and PJM, respectively between T. gracilis (Wl) and M. erythroleucus (D2) and between Nannomys sp. (D2) and T. guineae (W1-W2).
After burning (Wl), spatial behaviour seemed selective – the presence of one species in one LE seemed to exclude others – and the number of apparently antagonistic relations was highest during this season. The succession of species over time favoured the progressive installation of populations and allowed mechanisms leading to highly selective spatial occupation, to be put in place.
With Dl, T. gracilis and M. erythroleucus developed a loose spatial behaviour with no antagonistic relations. This can be explained by M. erythroleucus arriving late on parcels occupied for several months by T. gracilis. Despite its greater reproductive capacities, the M. erythroleucus population was less competitive. Mechanisms dissuading the occupation of its preferred LE could not therefore have been fully in place.
During W2 and in the absence of M. erythroleucus, there was a resumption of selective behaviour among T. gracilis and T. guineae (as in Wl), associated with antagonistic relations between both species. Nannomys sp. alone occupied all LE with no antagonistic relations. Its behavioural and morphological characteristics probably facilitate its being maintained in the LE where it comes least into confrontation with M. erythroleucus.
With D2, M. erythroleucus was already present and actively breeding. It rapidly became dominant and developed selective spatial behaviour on the most favourable LE.
This process is accompanied by antagonistic relations. The prolific character of M. erythroleucus supposedly explains why its population increases earlier and more swiftly. It becomes dominant only when colonization coincides with its dispersion phases.
Fox (1982) and Fox, Taylor & Thompson (2003) show how the succession of rodent species after burning matches the plant stages favourable to them. They emphasize, although, that this is not a sufficient cause to explain colonization by these species. Other criteria such as the pattern of disturbance which must be analysed with the methods developed in landscape ecology, the mobility phase of each species and selective and aggregative occupation of LE are also decisive. By taking all these criteria into account we can better understand the colonizing mechanism affecting both outbreak risks and local biodiversity.
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