CHECKLIST

 

Spiders (Arachnida: Araneae) of a wildlife and cattle savanna ranch in South-Western Zimbabwe

 

 

Sicelo Sebata^{I, II}; Charles R. Haddad^II; Moira J. FitzPatrick^III; Stefan H. Foord^IV

^IDepartment of Crop and Soil Sciences, Faculty of Agricultural Sciences, Lupane State University, Lupane, Zimbabwe, South Africa
^IIFaculty of Natural and Agricultural Sciences, University of Free State, Bloemfontein, South Africa
^IIINatural History Museums of Zimbabwe, Bulawayo, Zimbabwe
^IVNRF-SARChI Chair in Biodiversity Value and Change, University of Venda, Thohoyandou, South Africa

Correspondence

 

 

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ABSTRACT

In order to contribute to spider diversity distribution records within Zimbabwe, spiders were sampled at a mixed wildlife and cattle ranch using pitfall traps and sweep-netting. Sampling was conducted from June 2017 to April 2018. A total of 2328 spiders representing 25 families, 94 genera, and 166 species were recorded. The most species-rich families were Salticidae (33 spp.), followed by the Gnaphosidae (28 spp.) and Lycosidae (20 spp.), while eight families were represented by a single species. Pitfall traps accounted for 1857 individuals overall, with the ground-dwelling fauna dominated by Stenaelurillus guttiger (37.86% of the total abundance). Sweep-nets accounted for 471 individuals overall, with the grass-dwelling fauna dominated by Thyene thyenioides (15.29% of the total abundance). The most abundant functional group was the free-living ground-dwellers (n = 1809, 77.71%), followed by free-living plant-dwellers (n = 266, 11.43%) and orb-web builders (n = 186, 7.98%). The current study contributes to the knowledge of a megadiverse group of predatory arthropods in the region.
CONSERVATION IMPLICATIONS: Sampling and monitoring of rangelands is essential, as the former aids in the identification of new species not previously recorded, as well as increasing knowledge on the distribution of spider species, which if not adequately conserved could face significant threats to their survival even before their documentation.

Keywords: conservation planning; invertebrates; monitoring; rangelands; spider biodiversity; surveys.

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Introduction

With roughly 51 000 described species (World Spider Catalog 2023), spiders are found in almost all terrestrial biotopes, are easy to collect, and are essential predators (Turnbull 1973). According to the African Arachnological Database, there are presently 454 species known from Zimbabwe (Dippenaar-Schoeman et al. 2015), representing 0.89% of the global species richness (World Spider Catalog 2023). This is far below the 2253 species recorded from the neighbouring country of South Africa (Foord et al. 2020). In contrast, it is higher than the 250 species from the neighbouring Botswana and 183 from Malawi (Jocqué, Alderweireldt & Dippenaar-Schoeman 2013). Despite that within the Afrotropical region, Zimbabwe is amongst the top 10 countries in terms of the highest spider species richness (Jocqué et al. 2013), its known richness can be regarded as low compared to the rest of the region. Jocqué et al. (2013) suggest that the documented spider species richness of any country more strongly reflects the effort placed on studying its fauna than its size, mainly because countries with approximately similar sizes have recorded very contrasting levels of species richness (Jocqué et al. 2013).

The inclusion of spiders into conservation programmes requires correct and regularly updated checklists (Dippenaar-Schoeman et al. 2015). The latter expedited the inclusion of South African spiders in the National Spatial Biodiversity Assessment (NSBA) in 2010 (Dippenaar-Schoeman et al. 2015) and the subsequent preparation of a National Red List (Foord et al. 2020). However, in Zimbabwe, limited checklists (FitzPatrick 2001) and partial surveys have contributed distribution data on species (Cumming & Wesołowska 2004; Wesołowska & Cumming 2011), which unfortunately have not yet been included in any Government of Zimbabwe National Reports on biodiversity and conservation. Additionally, vast areas of the country are still poorly sampled, thus limiting the knowledge of distribution records and the identification of endemic species. Therefore, there is a need to document more species distributions within Zimbabwe. Furthermore, the augmentation of spider biodiversity information, particularly species richness, can also be applied through activities that include the examination of unidentified material in museums and increasing awareness through engagement with the public (Dippenaar-Schoeman et al. 2015). Such activities encourage interest and research on invertebrates, such as spiders.

As part of the PhD study of the first author, spiders were sampled in several biotypes as part of two kraaling impact studies. Sampling proceeded over a period of approximately 1 year, using mainly two methods (pitfall traps and sweep netting). Detailed information on the response of spiders to short-duration kraaling has been published (Sebata et al. 2022), and this article provides an annotated checklist of the spiders sampled at the Debshan Ranch.

 

Materials and methods

The study was conducted at a mixed cattle and wildlife ranch called Debshan (29º 15ʹ E, 19º 35ʹ S), located 100 km north-east of Bulawayo along the Bulawayo-Harare road in the Insiza district, Matabeleland North Province. Rainfall falls between October and April, with an annual average of 639 mm (Dunham et al. 2003). Average daily humidity is 55% and the annual average temperature is 18°C, with the hottest month being October (average 21°C) and the coldest being July (average 12.4°C). The ranch lies at an elevation of between 1230 m and 1414 m above sea level (Dunham et al. 2003).

The landscape of the ranch is moderately undulating, with coarse-grained, yellowish-brown loamy sands. Some sections have ultramafic or mafic rocks that that give rise to productive red and dark brown clayey soils (Robertson 2013). The soils support floral types that are normally dispersed in a chain-like pattern (Dunham et al. 2003), including Colophospermum bushlands, Julbernadia-Stereochlaena woodland, Combretum hereroense-Hyparrhenia mixed bushlands, dominated by Combretum hereroense and other species of Combretum mixed with Vachellia species, Terminalia-Schizachyrium bushlands, and wooded grasslands (Robertson 2013).

Spider sampling was conducted from June 2017 to April 2018 utilising pitfall traps and sweep netting following the sampling design reported in Sebata (2020), which was part of a PhD study on the kraaling impact on spider diversity that focused on only ground-dwelling and grass-dwelling spiders. At the end of the collecting period, the contents were collected and emptied into plastic bottles with 70% ethanol for sorting in the laboratory. All adult specimens were sorted to morphospecies and identified to species level, where possible. Voucher specimens were deposited in the Arachnology collection of the Natural History Museum in Bulawayo, Zimbabwe.

Ethical considerations

This article does not contain any experimental studies with human or animal participants, and informed consent is not applicable.

 

Results and discussion

A total of 2328 spiders representing 25 families, 94 genera, and 166 species were recorded during the study (Table 1). The most species-rich families were Salticidae (33 spp.), followed by the Gnaphosidae (28 spp.) and Lycosidae (20 spp.), while eight families were represented by a single species (Table 2). Overall, pitfall traps accounted for 1857 (79.77%) individuals, and the ground-dwelling fauna was dominated by Salticidae (n = 703; 37.86%), Gnaphosidae (n = 494; 26.26%), and Lycosidae (n = 275; 14.81%) with the jumping spider, Stenaelurillus guttiger (Salticidae; 37.86%) being the dominant species. Sweep-nets accounted for 471 (20.23%) individuals, and the grass-dwelling fauna was dominated by Araneidae (n = 175; 37.58%), Salticidae (n = 136; 28.88%), and Thomisidae (n = 70; 14.86%) with Thyene thyenioides (Salticidae; 15.29%) being the dominant grass-dwelling species. The most abundant functional group was the free-living ground-dwellers (n = 1809, 77.71%), dominated by S. guttiger and Asemesthes paynteri (Gnaphosidae), followed by the free-living plant-dwellers (n = 266, 11.43%), which were dominated by T. thyenioides and Runcinia flavida (Thomisidae). The dominant web-building group was the orb-web builders (n = 186, 7.98%). The remaining functional groups were mostly different web-builders that together constituted less than 2.87% (n = 67) of the total spider fauna, individually contributing less than 2% (Figure 1).

 

 

 

 

The dominant ground-dwelling families at Debshan Ranch are also fairly similar to those found in earlier studies in African grasslands (Haddad et al. 2015) and savannas (Haddad 2022). They are usually generalist predators, with some species having evolved specialised diets on termites, ants, mosquitoes, and other spiders (Pekár et al. 2012). They are also common epigeal species in agroecosystems in South Africa (Dippenaar-Schoeman et al. 2013) and Zimbabwe (Mashavakure et al. 2019), and are considered an important group in pest control. In this study, the grass-dwelling fauna was dominated by Araneidae (n = 175; 37.16%), Salticidae (n = 136; 28.88%) and Thomisidae (n = 70; 14.86%); however, Oxyopidae (n = 5; 0.12%) was not as common in this study as in other savanna biotypes (Foord et al. 2002, 2016). In order to enhance their chances of survival within their ideal habitats, some grass-dwelling species have evolved elongate, pale bodies, while ground-dwelling species are cryptically coloured (Dippenaar-Schoeman et al. 2013), for example, in Salticidae (Haddad & Wesolowska 2011).

 

Conclusion

This study contributes to our knowledge of the geographical distribution of Zimbabwean spiders. The baseline information on the spider assemblages of Debshan Ranch provides a list of 166 species. However, in order to improve on the distributions and the diversity of the spider fauna, inventories should be conducted in all floral biomes in the country, using not only pitfall traps and sweep nets, but a variety of active search methods, that is, hand collecting, beating sheets amongst others. This will ensure that all spider taxa, including those in trees and bushes (left out in the sampling design of this study) are also included. This will allow researchers to determine the species that are endemic and threatened.

 

Acknowledgements

The authors thank the Oppenheimer family and the Debshan Ranch staff for funding the fieldwork and for their logistical support during this research. Thanks are due as well to the Natural History Museum staff for assistance with fieldwork, sorting invertebrate samples and taxonomic inputs.

This article is partially based on the author's thesis entitled 'Spider ecology in southwestern Zimbabwe, with emphasis on the impact of holistic planned grazing practices' toward the degree of Philosophiae Doctor (Zoology and Entomology) in the Department of Zoology and Entomology, University of the Free State, South Africa, with supervisor(s) Prof. Charles R. Haddad, Prof. Stefan H. Foord and Dr Moira FitzPatrick, received January 2020, it is available here: http://hdl.handle.net/11660/10945.

Competing interests

The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this article.

Authors' contributions

S.S. undertook and conducted the survey, commenced the sorting and identification of sampled materials, and wrote the first draft of the manuscript. C.R.H. assisted in the identification of the sampled materials and in editing the manuscript. M.J.F. is the curator of the Natural History Museums of Zimbabwe and assisted with the sorting, identification & curation of the sampled material, and assisted in the editing of the manuscript. S.H.F. assisted in the editing of the manuscript.

Funding information

This research received a grant from N.F. Oppenheimer and was facilitated by Duncan MacFadyen.

Data availability

The data that support this study will be shared upon reasonable request from the corresponding author.

Disclaimer

The views and opinions expressed in this article are those of the authors and are the product of professional research. It does not necessarily reflect the official policy or position of any affiliated institution, funder, agency, or that of the publisher. The authors are responsible for this article's results, findings, and content.

 

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Correspondence:
Sicelo Sebata
sicelosebata@gmail.com

Received: 24 Jan. 2023
Accepted: 22 Sept. 2023
Published: 20 Dec. 2023