Diversity and composition of flightless arthropods on rock outcrops and adjacent vegetation in the savannah, Mpumalanga Province, South Africa.

Abstract

Savannah vegetation is characterised by structural complexity, greater plant species richness and a variety of environmental conditions (Botha, Siebert, & Berg, 2016). Fire determines plant species richness and composition in the savannah (Bond & Parr, 2010). Savannah is a continuous grassland with trees scattered and/or dense woodland patches (Bond & Parr, 2010). The nature of the savannah increases arthropod heterogeneity (Botha et al., 2016) because different arthropods require different habitats and environmental conditions (Yekwayo, Pryke, Roets, & Samways, 2017). Anthropogenic activities, such as disturbance through residential development, invasion by exotic species and conversion to agricultural land (Mauda, Joseph, Seymour, Munyai, & Foord, 2018; Veldman & Putz, 2011), decrease plant diversity, thereby reducing arthropod diversity because of their positive association with plants (Rhoades, Davis, Tinkham, & Hoffman, 2018). Furthermore, high plant diversity increases availability of mesofilters, such as leaf litter and logs, which serve as nesting sites and/or food for some arthropods (Loyola, Brito, & Ferreira, 2006; Uno, Cotton, & Philpott, 2010). Transformation of natural landscapes because of residential development decreases specialist arthropods while increasing generalists (Magura, Horváth, & Tóthmérész, 2010; Vergnes, Pellissier, Lemperiere, Rollard, & Clergeau, 2014). Generalists increase because of being adapted to a variety of habitats and environmental conditions (Bizuet‐Flores, Jiménez‐Jiménez, Zavala‐Hurtado, & Corcuera, 2015). Arthropods, particularly with limited dispersal abilities, such as millipedes, are affected because residential development leads to habitat fragmentation. Benítez‐Malvido et al. (2016) reported that fragments are unfavourable habitat for beetles compared to continuous forests. In addition, flightless arthropods are restricted to specific habitats in which resources are available (Yekwayo et al., 2017), hence the greater sensitivity to habitat modification. In South Africa, impact of rockiness on arthropods has been investigated in grassland (Crous, Samways, & Pryke, 2013,2014) and fynbos (Yekwayo, Pryke, Gaigher, & Samways, 2018), which is dominated by small leaves and evergreen shrubs (Mucina & Rutherford, 2006). Although Crous et al. (2013) reported an increase in grasshopper and butterfly diversity with increasing rockiness, Yekwayo et al. (2018) observed that rockiness did not affect arthropod diversity. There is little information known about the influence of rockiness on arthropods in the savannah, yet small features within the landscape serve as mesofilters, which are important for arthropod conservation (Hunter, 2005). Furthermore, rockiness increases heterogeneity in the landscapes, which is consistent with Crous et al. (2014) observation of different butterfly composition in rocky and nonrocky areas. Here we compared species richness, abundance and composition of flightless arthropods between rocky and nonrocky sites and investigated also the effect of disturbance on flightless arthropods in the savannah.