Background:

Termites are important ecosystem engineers in the tropics and sub-tropics, so understanding their diversity, particularly their functional diversity, across biogeographical scales is important for understanding where they alter theenvironment and deliver ecological services. Feeding groups combine phylogeneticand dietary information about termites into ecologically significant functional categories

Objectives:

To characterise termite feeding group prevalence, distribution and diversity in southern Africa and assess the effect of precipitation on termite diversity and assemblage composition.

Method:

Termite genus and species-level occurrence data were acquired from the South African Termite Database and classified into one of five feeding groups. We evaluated the prevalence of each feeding group and assessed species and feeding group richness and dominance. Linear regressions were performed to determine the relationship between 1) species richness and precipitation; and 2) feeding group richness and precipitation.

Results:

We find that southern Africa 1) is dominated by FG-IIw (feeding group – II, wood feeding) termites; 2) is occupied by multiple feeding groups across the entirety of the rainfall gradient; and that precipitation 3) influences feeding group species diversity variably; and 4) causes notable shifts in termite community structure.

Conclusion:

Our results indicate that termites likely make substantial contributionsto plant material decomposition across southern Africa and that while shifts in feeding group dominance are associated with rainfall gradients, the services unique to individual feeding groups are not isolated to certain regions, but ratherare widespread regardless of the amount of precipitation received.

Termite species data and study area

Termite presence-absence data were acquired from the South African Termite Database (SATD) maintained by the Biosystematics Division of the Plant Protection Research Institute at the Agricultural Research Council in Pretoria, South Africa. The SATD contains >35 000 occurrence records, mostly a product of the South African National Survey of Isoptera (NSI) led by Dr W.H.G. Co-aton and co-workers (Coaton & Sheasby 1972); some records were also gleaned from Mitchell (1980). The original survey was initially intended to include every quarter degree square (0.25° x 0.25°, or 50 x 50 km) of South Africa, but was later expanded to include surveys from Namibia, Zimbabwe and Eswatini. Unfortunately, no termite survey data is available from Botswana or Lesotho (Uys 2002; Figure 1).

The National Survey of Isoptera was conducted over two decades (~1960-1980). Termites were sampled mostly during the wet season (when they are most active), through active searching by trained termitologists at one or more locations within each sample area (Coaton & Sheasby 1972; Uys 2002). Multiple sample locations falling within the same quarter degree square were aggregated to reduce bias and location error and maintain consistent resolution. All termite specimens were identified by an expert taxonomist (Coaton and colleagues engaged by the NSI) to genus level and, time permitting, to species level. As many database entries were recorded only to genus, overall species-richness estimates likely underestimate true diversity (Meredith et al. 2019). We re-examined the SATD to correct minor spelling mistakes and antiquated species names. Ambiguous georeferences (e.g., points where latitude-longitude did not correspond with additional locality information on nearby towns or country name) were corrected where possible or removed. In so doing, the database was ultimately reduced to 26 968 reliable presence records that cover 1 952 grid cells) and includes 52 genera and 121 species (Supplementary Table S1).

Feeding group classification

Termites were classified into five feeding groups (FGs) based on their phylogeny and the level of decomposition of feeding substrate in their gut (Donovan et al. 2001). FG-I species are primitive termites belonging to families Kalotermitidae, Termopsidae, Hodotermitidae, Rhinotermitidae) and feed on non- or lightly decayed material including dead wood and grass, whereas FG-II through FG-IV species belong to the family Termitidae and feed on more decayed materials (Donovan et al. 2001). FG-II termites include species of the conspicuous mound-building genera (Macrotermes, Odontotermes), which have broad diet preferences including dead wood, grass, leaf litter and micro-epiphytes, and can be separated into fungus-feeders (FG-IIf) and wood-feeders (FG-IIw) (Jones & Eggleton 2011). FG-III termites feed on visible organic material in the soil, while FG-IV termites are known as 'true soil feeders' and feed on clay-bound proteins and peptides (Donovan et al. 2001; Ji & Brune 2005).

Precipitation Data

Annual cumulative precipitation data at a 0.5° x 0.5° resolution were acquired from the Climate Research Unit at the University of East Anglia, UK (Harris & Jones 2015), averaged for 1901-2014 into 0.5° x 0.5° and disaggregated to a 0.25° x 0.25° grid using bilinear resampling in ArcGIS 10.7.1. to match the resolution of the South African Termite Database (Figure 1, ESRI, 2020). Mean annual precipitation in the study region ranges from 50 to 2 100 mm/year, encompassing a wide range of biomes including deserts and semi-deserts, fynbos, temperate Afromontane forests, grasslands, savannas, and moist broad leaf forests (Olson et al. 2001).

Mapping and analysis

Termite feeding group distribution maps were generated in ArcGIS 10.7.1 (ESRI 2020). The maps depict the geographical extent of feeding groups in the nearly two thousand (n = 1 952) 50 x 50 km areas sampled as part of the SATD. Darker shades indicate higher numbers of species present in a sampled area (Figure 2, Figure 3). We calculated the prevalence of each feeding group as the percentage of sampled locations that had a positive occurrence record, where prevalence = (no. positive samples / 1952) x 100. We also assessed species richness, or the number of species present in a single 50 x 50 km sampled location, and feeding group richness, or the number of feeding groups present in a sampled location. While the SATD is composed of acquisitions identified to both the genus and species levels, we combined all acquisitions to a 'species richness' value by conservatively assuming that species richness equals one when only genus-level acquisition is present and otherwise using the number of species-level acquisitions.

Simple linear regressions were performed to assess the relationship between 1) species richness and precipitation; and 2) feeding group richness and precipitation. We define feeding group richness as the number of species present at a sample location belonging to the same feeding group. To interrogate the relationship between feeding groups and precipitation further, we first organised the data into eight precipitation bins, each representing roughly 200 sampling locations and a 150-250 mm increase in precipitation between bin categories, and then calculated feeding group dominance by summing occurrence records for each individual feeding group and then dividing by the total number of occurrences in that bin. This provided the relative percentage that each feeding group contributed to the entire assemblage across the precipitation gradient. Statistical analyses were performed in base R version 4.0.3. (R Core Team 2020).