Underground storage organs of plants as a food source for Pleistocene hunter-gatherers in the southern Cape

Singels, Elzanne (2013-12)

Thesis (MSc)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: The abundance and diversity of carbohydrate and protein resources in the southern Cape of South Africa may well have aided the survival of modern humans through the harsh climatic conditions of the late Pleistocene. Until now, the carbohydrate resources, in particular the underground storage organs (USOs) of some plant species have not been described from a forager’s perspective. This is baffling when one considers that the Cape Floristic Region of South Africa harbors the highest diversity of geophyte (herbaceous plants which possess USOs) species in the world. I report on USO distribution and abundance in the southern Cape of South Africa and on the effort, nutritional return and energetic return rates of harvesting these USOs. To determine their distribution and abundance, I assessed identity and abundance in a hundred 25m2 plots. These data, along with biomass data of every species sampled, allowed me to quantify the variation of this potential food source over different habitat types in the southern Cape landscape. Furthermore, I observed the time it took for human subjects to gather a sample of six USO species in three different vegetation types and in two seasons. Proximal analyses of the nutritional content of each of these species provided data which, when combined with foraging time, enabled a basic quantification of the return rate of energy (in calories) per time unit. There is high variability in the distribution of edible USO abundance and biomass across the study area, with some sites having very high biomass. Such biomass hotspots are likely to have been targeted by foragers, returning biomass values comparable to other studies which have been conducted on extant hunter-gatherer communities. Due to considerable variation over the landscape, the hotspots of biomass did not correlate significantly with any abiotic variables we measured. This suggests that hotspots of high biomass may have been challenging to find, unless the cognitive skills required to locate such patches were sufficiently developed – certainly excellent knowledge of the landscape and botany would have been crucial if survival depended on locating these diet items. USO species belonging to the Iridaceae family had the highest overall and average biomass in the area, so it is not surprising that this family is best represented amongst USO plant remains found in the archaeological record. Little effort (time) was required to obtain the six species of USOs we observed, although the weights obtained were also low. The nutritional returns of the six test species were higher than in other studies. The return rates per simulated foraging event in this study therefore compare favorably to the anthropological observations of extant hunter-gatherer communities. The lines of evidence presented in this thesis therefore lend support to the hypothesis that the USO resources of the southern Cape would have provided a large component of the carbohydrate requirements for sustaining hunter-gatherer communities. The data set presented in this thesis can be considered a baseline for future studies.

AFRIKAANSE OPSOMMING: Die digtheid en diversiteit van koolhidraat- en proteïenhulpbronne in die Suid-Kaap van Suid-Afrika mag die oorlewing van die moderne mens beïnvloed het tydens die ongunstige klimaatstoestande wat geheers het deur die laat Pleistoseen. Tot op hede is die koolhidraathulpbronne in die area nie beskryf vanuit ‘n kosversamelaar se perspektief af nie, spesifiek nie die koolhidrate wat deur ondergrondse stoororgane (OSO's) van sommige plantspesies verskaf kan word nie. Dié feit is verstommend as mens in ag neem dat die Kaapse Floristiese Streek van Suid-Afrika die hoogste geofietspesies (kruidagtige plante met OSO's) diversiteit ter wêreld het. Ek rapporteer oor die verspreiding en digtheid van OSO's in die Suid-Kaap en op die inspanning, voedingswaarde en energie-opbrengskoerse verbonde aan die oes van dié OSO's. Verspreiding en digtheid is bepaal oor ʼn honderd 25m2 plotte. Dié data, saam met die biomassa-data van elke spesie wat geïdentifiseer was, is gebruik om potensiële voedselbronne te kwantifiseer in verskillende habitattipes in die Suid-Kaap. Ek het verder die tyd wat dit neem vir mense om die ses geïdentifiseerde OSO-spesies te oes in drie verskillende habitatte en twee seisoene waargeneem. Voedingswaarde-data, tesame met OSO-oestyd-data, is gebruik vir die basiese berekening van energie-opbrengskoerse van spesies deur middel van proksimale analises. Daar is hoë variasie in die verspreiding, digtheid en biomassa van eetbare OSO's gevind in die studie-area, met sommige plotte wat baie hoë biomassa bevat het. Hierdie areas van hoë biomassa sou heel waarskynlik deur kos-versamelaars geteiken gewees het, en gevolglik hoë opbrengste van biomassa bied, wat vergelykbaar is met die biomassa-waardes wat waargeneem word binne areas waar huidige jagter-versamelaar-gemeenskappe tans oorleef. As gevolg van die aansienlike variasie wat waargeneem is oor die landskap het die hoë-biomassa-areas nie beduidend gekorreleer met enige abiotiese veranderlikes wat gemeet is nie. Dit dui daarop dat hoë-biomassa-areas moeilik kan wees om te vind, tensy kognitiewe vermoëns wat noodsaaklik is om kolle van hoë biomassa te vind ontwikkel was. OSO-spesies wat aan die Iridaceae-familie behoort het die hoogste algehele en gemiddelde biomassa in die area gehad. Dit is dus nie verbasend dat dié familie die beste verteenwoordig word in die argeologiese rekord van OSO-plantoorskot nie. Min inspanning (tyd) was nodig om die OSO's van die ses geïdentifiseerde spesies te bekom, alhoewel die massa wat bekom is ook laag was. Die voedingswaarde-opbrengs (per eenheidsmassa) van die ses toetsspesies was hoër as in ander studies. Die energie-opbrengskoers per versamelingsgebeurtenis het gevolglik ook gunstig vergelyk met die antropologiese waarnemings wat van huidige jagter-versamelaars gemeenskappe gemaak is. Die resultate van hierdie studie ondersteun die hipotese dat die OSO-hulpbronne in die Suid-Kaap 'n groot komponent van die koolhidraat-vereistes van jagter-versamelaar-gemeenskappe sou gewees het. Die datastel wat in dié tesis aangebied word kan as 'n basisverwysing dien vir toekomstige studies.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95475
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