Density of Cape porcupines in a semi-arid environment and their impact on soil turnover and related ecosystem processes

Cape porcupines (Hystrix africaeaustralis) appear to have an important influence on landscapes through both biotic (foraging) and abiotic (soil turnover) impacts. Porcupine abundance and abiotic effects across the landscape were investigated in Nieuwoudtville, South Africa, a semi-arid area characterized by an extraordinary diversity and abundance of geophytes. Porcupine numbers were measured in 50 burrows, and the number of burrow entrances was a good predictor of the number of porcupines it contained (r2=0.76). Occupied burrow density was estimated to be 2.6 burrows km−2 and porcupine density on the study farm was estimated to be 8 animals km−2, which is high relative to other Hystrix populations in semi-arid environments. This can probably be attributed to the high abundance of geophytes in the region. Annually, porcupines disturb 0.34% of the soil surface and 1.6 m3 ha−1 yr−1 of soil is displaced across the landscape, through the excavation of 160-3463 diggings per hectare. Up to 2.2 m3 of soil is displaced per hectare per year in the natural Dolerite Plains vegetation, but very little foraging activity occurs in previously or currently ploughed lands. The extent of disturbance in Nieuwoudtville is on a par with or higher than that recorded for other porcupine populations in arid or semi-arid regions. Other studies have shown that porcupine diggings disturb plant community structure and create fertile sites for plant germination and recruitment. Porcupine diggings in Nieuwoudtville contained significantly more seedlings than adjacent areas. Thus, through widespread foraging pits, soil turnover, and numerous burrows, porcupines modulate the availability of resources to other organisms. Therefore, Cape porcupines are likely to act as ecosystem engineers in this landscape. Porcupines should be included in any conservation actions involving the unique geophyte flora of Nieuwoudtville.