The pyrodiversity–biodiversity hypothesis: a test with savanna termite assemblages

Abstract

Summary 1.Fire is an important disturbance in African savannas where it is generally assumed that high levels of pyrodiversity (variation in aspects of the fire regime) are necessary to maintain high levels of biodiversity. There is, however, little empirical evidence in support of this hypothesis for animals. Furthermore, the relationship between pyrodiversity and biodiversity may vary with different savanna types, shaped by mean annual precipitation. 2. We made use of a long-term burning experiment to investigate the effect of interactions between precipitation and pyrodiversity on biodiversity. We sampled termites (major ecosystem engineers in savannas) within experimental plots involving a range of fire seasons and frequencies. Sampling was conducted in three distinct savanna types along a rainfall gradient in South Africa. We explored how termite diversity varied with mean annual precipitation and whether faunal responses to fire regimes varied with rainfall. Termites were sampled comprehensively during the wet season using cellulose baits and active searching in order to sample a variety of functional groups. 3. Assemblages differed significantly across savanna types with higher levels of diversity in the wetter site using the active searching method. Diversity was lowest at the most arid site but certain feeding groups (FGs) peaked in the savanna with intermediate rainfall. Differences between these savannas are attributed to broad underlying changes in net primary productivity and temperature, with mammalian herbivores thought to generate a peak in diversity of some faunal groups at the intermediate savanna through their role in facilitating nutrient cycling. 4. Overall, termites were highly resistant to fire in all savanna types with little difference between fire regimes (season and frequency), but assemblage composition and some FGs were affected by burning. Differences between fire regimes were more pronounced with increasing rainfall. These differences are likely to be linked to changes in vegetation structure caused by fire, which are more significant in wet savannas. 5. Synthesis and applications. Our findings, along with those for other insect taxa, indicate limited support for the pyrodiversity-biodiversity hypothesis; this suggests that, at least for invertebrates, management regimes can be flexible, although more caution is advisable in wetter savannas.

Seasonal activity patterns of African savanna termites vary across a rainfall gradient

“…Although soil feeders are likely to respond in similar ways because of their dependence on moisture and malleable soil (Bignell and Eggleton, 2000;Davies et al, 2012), grass harvesters may well be active in drier months as recorded in previous studies (Ohiagu, 1979;Braack, 1995), possibly substantiating claims that termites complement other taxa through the ecosystem functions they provide.…”

“…The drier sites differ further by having higher activity levels during the dry season than the wetter sites, with a peak in activity and species density at the intermediate rainfall site, Satara. This unimodal peak in diversity is unusual given the strong dependence of most termite groups on soil moisture and is attributed to factors related to the relatively high mammalian herbivore abundance here (see Davies et al, 2012) and fungusgrowing termites (which are attracted to cellulose baits) being able to out compete fungi in semiarid environments (see Aanen and Eggleton, 2005;Davies et al, 2013b) …”

“…The four in each set of plots form part of a burning experiment, but are representative of 6 each savanna type and its fire regimes. Fire effects were not expected to influence sampling because both termite diversity (Davies et al, 2012) and mound distributions (Davies et al, 2014) display remarkable resistance to fire. Furthermore, the same four burning regimes were sampled in each habitat, thus controlling for any potential fire effects.…”

“…Tables 1 and 2 in Results) and can therefore be validly compared. This study forms part of a larger programme investigating aspects of savanna termite diversity (see Davies et al, 2012Davies et al, , 2013a and sampling in KNP was subsequently carried out across a series of experimental burning plots (see Biggs et al, 2003;van Wilgen et al, 2007).…”

Pyrodiversity promotes avian diversity over the decade following forest fire

“…Evaluations of the pyrodiversity-biodiversity hypothesis, however, have been equivocal, with different studies showing weak responses of species to pyrodiversity [11][12][13], strong responses to pyrodiversity [14,15] or no response [16,17]. Pyrodiversity-biodiversity tests have almost universally been conducted as tests of fire age structure, in which pyrodiversity is defined in terms of the diversity of differently aged post-fire patches across a landscape [11,13] or as spatial variation in the frequency or seasonal timing of fire [14].…”