Return rates from plant foraging on the Cape south coast: Understanding early human economies

Quaternary Science Reviews xxx (xxxx) xxx

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Return rates from plant foraging on the Cape south coast: Understanding early human economies M. Susan Botha a, Richard M. Cowling a, Karen J. Esler b, Jan C. de Vynck a, Naomi E. Cleghorn c, Alastair J. Potts a, * a b c

African Centre for Coastal Palaeoscience, Botany Department, Nelson Mandela University, South Africa Conservation Ecology & Entomology, Stellenbosch University, South Africa Department of Sociology and Anthropology, University of Texas at Arlington, Arlington, TX, 76019, USA

a r t i c l e i n f o

a b s t r a c t

Article history: Received 5 September 2019 Received in revised form 6 December 2019 Accepted 6 December 2019 Available online xxx

The Cape south coast of South Africa has attracted significant archaeological research because it hosts the earliest evidence of human cultural and material complexity. Furthermore, the now-submerged PalaeoAgulhas Plain provided habitat and resources for humans during the emergence of modern behavioural traits. Using a human behavioural ecology approachdoptimal foraging theorydwe sought to understand how this region’s flora may have contributed to the existence of early humans along the Cape south coast. We conducted monthly plant food foraging excursions over a two-year period in the seven main vegetation types that occur within the study area. Two (rarely three) local inhabitants harvested indigenous edible plant parts in 30-min foraging bouts. A total of sixty-eight participants (of Khoe-San descent), with knowledge on edible indigenous flora, contributed to 451 bouts. This study thus provides the largest published actualistic dataset on plant foraging returns. Without any prior knowledge of spatial resource density, the foragers harvested a total of 90 different edible species and obtained an overall mean (±SD) hourly return of 0.66 ± 0.45 kg/h or 141 ± 221 kcal/h. Apart from renosterveld, where winter returns were higher compared to summer, all other vegetation types showed no seasonal difference in return rates. Plants, therefore, most likely played an important role as fall-back or reliable staple food in the Cape south coast. Edible resources were unevenly distributed spatially, with calorific returns ranging from 0 to 2079 kcal/h, with fewer d but productive d high-density areas or “hotspots”. Sand fynbos (246 ± 307 kcal/h) and dune fynbos-thicket mosaic (214 ± 303 kcal/h) yielded significantly higher returns than other vegetation types (except for riparian). Prior knowledge of such hotspots, both within and amongst vegetation types, would have offered a significant foraging advantage. Finally, we provide the first quantified evidence that forager-extracted plant returns are significantly higherdnearly three times higherdin recently burnt sand and limestone fynbos vegetation. This supports Deacon’s hypothesis that hunter-gatherers could have improved their return rates by purposely burning Cape vegetation (i.e. “fire-stick farming”) to give them access to temporally abundant geophyte "hotspots". We also demonstrate the current challenges when comparing plant return rates across different studies and discuss the benefits of using participants that are not full-time hunter gatherers. © 2020 Elsevier Ltd. All rights reserved.

Keywords: Plant foraging Cape south coast Fire-stick farming Hunter-gatherer Underground storage organs

1. Introduction The earliest proxy evidence for human cognitive development is found along South Africa’s Cape south coast (Brown et al., 2009, 2012; Henshilwood et al., 2002, 2011; Marean et al., 2007, 2014), making this area a crucial paleoanthropological focus for the study

* Corresponding author. E-mail addresses: [email protected], [email protected] (A.J. Potts).

of the origins of modern humans (Compton, 2011). The PalaeoAgulhas Plain (PAP), now submerged off the Cape south coast, would have been exposed during glacial periods due to lowered sea levels (Fisher et al., 2010), creating a very different environmental setting to that characteristic of the Cape today (Cowling et al., this issue). Marean (2010) has hypothesised that the Cape south coast may have been a refugium for early hominids because of the unique array of resources which could have supported their persistence during strong glacial environments. Associated with the PAP were

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Please cite this article as: Botha, M.S et al., Return rates from plant foraging on the Cape south coast: Understanding early human economies, Quaternary Science Reviews, https://doi.org/10.1016/j.quascirev.2019.106129

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abundant marine (Marean et al., 2007) and terrestrial sources of protein in the form of shellfish and a game fauna (Helm et al., 2018, Helm et al., 2019, this issue; Henshilwood et al., 2001; Klein, 1972; Klein, 1976; Venter et al., this issue) associated with the extensive and relatively fertile landscape of this drowned feature (Cawthra et al., 2019, this issue). It has been hypothesised that plant carbohydrates in the form of underground storage organs (USOs; i.e. geophytes) would have been a predictable and reliable component of forager resources (de Vynck et al., 2016b; Deacon, 1993; Klein, 2001; Singels et al., 2016). The diversity of taxa with USOs in the Greater Cape Floristic Region (GCFR) is unparalleled globally (~2100 species, ~17% of total flora; Proches¸ et al., 2005). Furthermore, historical and archaeological evidence suggests that a large proportion of this plant diversity is edible (Botha et al., 2019; Welcome and Van Wyk, 2019). Either as “fall-back” food or as a reliable staple, this USO diversity and abundance likely played a key role in the Late Pleistocene human resourcescape, and would have impacted forager mobility, density, and dispersal on the PalaeoAghulhas Plain. The purpose of this study is to explore the potential return rate of plant carbohydrate resources directly from the perspective of hunter-gatherers. Does the exceptionally high USO plant diversity of this region equate to an abundant carbohydrate resource for consumption by modern humans? In a similar approach, recent marine intertidal foraging experiments with local inhabitants of the Cape South coast (Khoe-San descendants) quantified the potential size of the marine ‘protein’ resource, with returns equal or exceeding intertidal calorific returns from other hunter-gatherer studies (de Vynck et al., 2016a). In addition to shellfish foraging, local people living in rural areas of the Cape south coast can also still identify 58 different indigenous edible plants with 69 uses (de Vynck et al., 2016c). Although this knowledge has declined because of European colonization, a subsequent shift to an agriculturallybased diet, and restricted access to much of the landscape, the local people in this region still recognise more edible plant species than many extant hunter-gatherer communities (de Vynck et al., 2016c). de Vynck et al. (2016b) noted in our study area that several of the 52 carbohydrate-rich edible plant species are visible to foragers at any given time of the year, suggesting that this resource base could have potentially provided a reliable, yearround source of calories for early hunter-gatherers. This is corroborated by Singels et al. (2016) who found that 83 of 100 randomlyselected plots of 25 m2 within the study area contained edible biomass. She further tested the harvest-rate of foragers on specific target plant species and found that hunter-gatherers could potentially meet their daily calorific demands within a few hours of foraging. Instead of an ecological sampling approach din which all possible edible plants are extracted in defined areas at randomlyassigned locations and then extrapolated to a larger region (as used to assess plant biomass and phenology by Singels et al. (2016) and de Vynck et al. (2016b), respectively) d in this study we use a forager-driven, ethnoarchaeological and actualistic approach in which foraging returns were recorded. Ethnoarchaeology, the observational study of “living cultures from archaeological perspectives” (David et al., 2001), and other types of actualistic studies (sensu Gifford-Gonzalez, 1991) have a deep history in African archaeology (MacEachern, 1996; Yellen, 1977), including studies focused on foraging returns from both animal and plant resources (Bartram, 1997; Lupo, 2001; O’Connell et al., 1991; Vincent, 1985). There are few such studies that focus on plant resources south of the Kalahari, and this is a novel approach for the Cape south coast: for the first time in this region, and in South Africa, we employ local people (who are of Khoe-San descent) to harvest plant food on a monthly basis over two years to determine the potential returns of

edible plant resource across different vegetation types, seasons and sites. Although not reliant on foraging for subsistence, our subjects nonetheless possess both lifelong experience with these plant taxa and vegetation types and have access to a deep multi-generational cultural knowledge of wild food resources in these environments. Thus, the local people (of Khoe-San descent) living in this region today provide the best-available analogue for past foragers on the Cape south coast. This ethnoarchaeological approach to data collection allows us to develop return rates on plants incorporating a forager-based cost perspective. To our knowledge, this study is extraordinary among plant foraging actualistic studies in both scale (i.e., number of foraging bouts observed and vegetation types explored) and the multi-seasonal scope of data collection. We adopt a behavioural ecology approach to this study by using optimal foraging theory (Stephens and Krebs, 1986; Winterhalder, 1981) as our theoretical framework. We anticipate that in each foraging bout, agents will exploit a patch e in our case e of vegetation in such a way as to maximise return rates of edible plant parts (underground storage organs, fruit, shoots) by focusing on items that are most apparent and easiest to harvest (Hill et al., 1987). While we did, to a limited degree, take forager search times into account, we did not consider transport and processing times in this study. By sampling across different vegetation types and seasons, our study produces data that can be used to inform ecological models of the past, i.e. the palaeoscape (sensu Marean et al., 2015). In addition, we recognise that fire can impact both plant productivity estimates as well as human behaviours, including landscape engineering behaviours. Australian Aboriginals, for example, used and continue to use fire to gain access to food resources in the post-fire environment, and this practice has shaped the heterogeneity of vegetation on a landscape-scale (Bird et al., 2008). Deacon (1983) hypothesised that Stone Age people in the Cape would have employed fire (e.g. “fire-stick farming”: Jones, 1969) to increase USO returns because many USOs are more prolific and apparent after fire (Lamont and Downes, 2011; Le Maitre and Brown, 1992). Hominins have known how to use fire for the past one million years or more (Bentsen, 2013; Berna et al., 2012; Hlubik et al., 2019). Historical accounts of the human use of fire to burn natural vegetation on a landscape scale is scant, but early travellers (from about 1400 AD) to the Cape noted Khoe-khoe pastoralists burning vegetation to improve pasture quality for livestock (Skead, 2009). Our study area comprises mostly fire-prone vegetation, so it was possible to locate sites spanning a wide range of post-fire ages within which to conduct foraging bouts. Consequently, it was possible to test a key prediction of the ‘fire-stick farming’ hypothesis (Bird et al., 2008), specifically that returns would be highest in the early phases of post-fire succession (Deacon, 1993). The aim of our study was to estimate the return rate on plant resource foraging for the Cape south coast via the implementation of experimental foraging bouts by people who are knowledgeable about the region’s natural vegetation and plant resources. It is important to note this is not an extant hunter-gatherer system and this study is not conducted in a pristine environment. Thus, we provide baseline return rates across the landscape. In this context, ours is not a strictly optimal foraging study (i.e. not explicitly forager-centred) as participating foragers have not had to forage on this landscape for their survival. Rather, it is an exploration on the potential return rates from different vegetation types from a forager perspective (e.g., what is the range of values that one could obtain at different localities in different seasons). Thus, we asked the following questions: what are the plant food resources available, how abundant (and extractable) are these resources, and to what extent is a human forager on this landscape able to meet daily caloric needs (with an incomplete knowledge of the landscape)?

Please cite this article as: Botha, M.S et al., Return rates from plant foraging on the Cape south coast: Understanding early human economies, Quaternary Science Reviews, https://doi.org/10.1016/j.quascirev.2019.106129

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We addressed these questions by employing people living in local rural contexts to conduct monthly plant food foraging bouts across the dominant vegetation types over a period of two years (451 bouts in total). The results show that carbohydrate returns are patchily distributed across sites within all vegetation types, and that sand fynbos and dune fynbos-thicket mosaic are the vegetation types where it is easiest to harvest 2000 kilocalories in a 9-h day, this being an estimate of daily calorific requirement to support a hunter-gatherer person of small stature and high physical activity (e.g. Hurtado and Hill, 1989; Lee, 2017; Speth and Spielmann, 1983). Apart from renosterveld, no other vegetation type showed significant seasonal fluctuations, suggesting that plant carbohydrates comprise a reliable year-round resource. We found that return rates were nearly three times higher in recently burnt than mature vegetation, suggesting that humans would have profited if they utilised “fire-stick farming” for improving return rates. In addition, we summarise the return rates from available plant foraging studies and discuss these in the context of our results.

2. Methods 2.1. Environment of the study area The study area forms part of the coastal forelands of the Cape south coast of South Africa. It is located between Blombos Cave in the west and Pinnacle Point in the east and extends inland to the foothills of the Langeberg-Outeniqua Mountains (similar to de Vynck et al., 2016b and Singels et al., 2016). The study area has all-year rainfall, with a small peak observed in MarcheApril, and more pronounced peaks during August and October (average 80 mm rainfall for each peak) (Engelbrecht et al., 2014). The mean annual rainfall ranges from 300 to 500 mm (Engelbrecht et al., 2014). Although rain occurs year-round, evaporation stress is highest in summer (de Vynck et al., 2016b) and mean temperatures increase from the coast inland. Maximum summer temperatures average about 27
C in January and February, with minimum winter temperatures averaging 5
C in July (South African Weather Service). Vegetation of the Cape coastal lowlands is under strong edaphic control (Cowling et al., 2015, this issue; Rebelo et al., 1991; Thwaites et al., 1988) and the study area has a wide range of geologies which

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generate different soil types (Cawthra et al., 2019, this issue) (Table 1). Table Mountain Group sandstones are exposed as a narrow band on the coast whilst aeolian sands of marine origin mantle much of the immediate coastal hinterland. Here pH varies with sediment age: older sands are leached and acidic, while younger sands, which contain a high content of shell grit, are alkaline (Rebelo et al., 1991). Cemented aeolianites (calcarenites) are widespread inland of the coastal margin; soils are shallow and highly alkaline. Calcareous sands associated with limestone, calcrete and coastal dunes are relatively infertile due to their high alkalinity and subsequent low levels of plant-available phosphorous (Thwaites et al., 1988). Leached sands are highly infertile. Bokkeveld (Devonian) shales and Enon (Cretaceous) mudstones are exposed on the inland margin of the study area; these geologies yield moderately fertile loams. The area falls within the Greater Cape Floristic Region (GCFR), an intensively studied megadiversity centre (Allsopp et al., 2014). The GCFR contains 11,423 species, and 1119 genera of which 77.9% and 22.2% are endemic, respectively (Snijman, 2013). This makes it the richest concentration of extratropical plant diversity and endemism (Colville et al., 2014). Three of the GCFR’s biomes occur in the study area, namely Fynbos, Renosterveld and Subtropical Thicket (Bergh et al., 2014). Fynbos is an evergreen, fire-prone ‘heathland’ characterised by the presence of restiods (wiry, evergreen graminoids of the Restionaceae and Cyperaceae), fine-leaved ericoid shrubs and shrublets (Ericaceae, Asteraceae, Rutaceae, Thymelaeaceae) and proteoid shrubs (exclusively Proteaceae) (Bergh et al., 2014). The core distribution of the Fynbos is along the spines of the Cape Fold Belt mountains, from the Bokkeveld Plateau at Niewoudtville south to the Cape Peninsula and then eastwards on the inland mountains, and along the coast to Port Elizabeth (Bergh et al., 2014). The occurrence of Fynbos correlates strongly with nutrient-poor (low availability of phosphorous and nitrogen) sandy soils, either acidic sands of quartzite origin or calcareous or leached coastal sands (Cowling, 1984; Cramer et al., 2014). Renosterveld is also a fineleaved, evergreen, fire-prone shrubland where the heathlandtype taxa (Ericaceae, Proteaceae, Restionaceae) are rare or absent, and having a grass-dominated herbaceous layer and high diversity and abundance of USOs (Cowling, 1990). It occurs on soils that are generally more fertile and finer-grained compared to Fynbos (Bergh et al., 2014; Cowling, 1984). Subtropical Thicket (including valley thicket: Vlok et al., 2003) possesses a large diversity of growth

Table 1 Geology and soils, fire frequency and dominant plant species that occur in each of the dominant vegetation types within the study area (compiled from Rebelo et al., 1991 and Mucina and Rutherford, 2006). Vegetation

Soils and geology

Fire frequency (years)

Dominant species

Subtropical Thicket

Dune fynbos-thicket mosaic

20e50

Fynbos

Subtropical thicket (“valley thicket”) Sand fynbos

Alkaline (white to grey) to neutral (red to grey), deep sands; moderately fertile; Late PleistoceneHolocene (white to grey) and Early to MidPleistocene (red to grey) Weakly acidic, mostly deep loams; moderately fertile; Devonian shale sand Cretaceous mudstones Acid (red to grey), deep sands; infertile; Early to Mid-Pleistocene

Olea exasperata, Euclea racemosa, Restio eleocharis, Metalasia muricata, Salvia africana-lutea, Pterocelastrus tricuspidatus, Sideroxylon inerme, Thamnochortus erectus Euclea undulata, Pappea capensis, Searsia glauca, Schotia afra, Aloe ferox Protea susannae, Leucadendron galpinii, L. eucalyptifolium, Leucospermum praecox, L. muirii, Thamnochortus insignis Protea obtusifolia, Leucadendron meridianum, Acmadenia densifolia, Thamnochortus muirii, Agathosma spp. Elytropappus rhinocerotis, Oedera genistifolia, Capeochloa stricta, Themeda triandra Vachellia karoo, Zygophyllum morgsana, Lycium spp, Cynodon dactylon, Eragrostis spp. Prionium serratum, Berzelia spp, Cyclopia maculata

Biome

No fire 10e20

Limestone fynbos

Alkaline, shallow sands on calcrete and calcarenite; moderately fertile; Plio-Pleistocene

10e20

Renosterveld

Renosterveld

10e20

Azonal

Floodplain woodland

Weakly acidic, moderately deep loams; moderately fertile; Devonian shale and Cretaceous mudstones Neutral loams; highly fertile; Quaternary alluvium

20e50

Riparian

Hydromorphic alluvium

10e20

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forms, creating a dense canopy of largely evergreen, broadleaved, sclerophyllous, spiny and/or succulent shrubs and low trees up to 3 m (Bergh et al., 2014). Dune fynbos-thicket mosaic, found close to the sea on aeolianites, forms part of Subtropical Thicket but includes a matrix of lower shrubs dominated by Fynbos taxa. 2.2. Foraging locations and sampling procedures Following Cowling et al. (this issue), we identified seven major vegetation types in the study area, namely: dune fynbos-thicket mosaic, sand fynbos, limestone fynbos, subtropical thicket, renosterveld, floodplain woodland and riparian. Note that this vegetation terminology differs from Singels et al. (2016), who used “strandveld” and “dune cordon” (now merged into dune fynbos-thicket mosaic), “valley thicket” (now subtropical thicket), and “riparian vegetation” (now floodplain woodland); note that Singels et al. (2016) erroneously used “riparian” to describe a terrestrial vegetation type. Experimental foraging bouts were conducted in each of the seven major vegetation types. Locations to conduct foraging experiments were based on several considerations, specifically ease of access to the site, landowner permission, and the presence of pristine or near-pristine vegetation representative of a particular type. Note that much of the Cape south coastal lowlands has been converted to agriculture or has been invaded by alien plant species that change the diversity, physiognomy and ecology of the native plant communities (Kemper et al., 2000; Rouget et al., 2003). Thus, site selection was limited within this fragmented landscape and finding a sufficient range of pristine sites within each vegetation type to conduct foraging bouts necessitated extensive travelling to new sites. Thus, foragers would be familiar with plant species or genera that occur within a vegetation type, but not necessarily a particular site. Throughout this manuscript we define a ‘foraging bout’ (or ‘bout’) as a 30-min period during which a forager searches for and harvests edible plant carbohydrates in a particular patch of vegetation d irrespective of the number of foragers participating in the bout. Note that by this definition, patch size is not fixed but depends on the density, accessibility and apparency of the “prey” or edible plant parts in that patch, thus patch size was defind by the agents’ foraging strategy. Bouts were conducted within each of the targeted vegetation types on a monthly basis from November 2014 to December 2016 (over 25 months). The first visit to a site was predominantly exploratory, i.e. the foragers had no prior knowledge of the locality. In rarer instances, word-of-mouth recommendations led us to explore sites that had potential to deliver high yields. Foragers were instructed to harvest all the edible parts of species in a bout (underground storage organs, fruits, shoots etc.). At the end of a bout, non-edible parts were removed, and the fresh edible biomass was weighed in the field using a spring-scale. 2.3. Foragers Foragers were recruited informally via researchers who were familiar with inhabitants of some areas, through foragers’ acquaintances, and by word of mouth. The subjects resided in different rural localities, from formal villages (e.g. Melkhoutfontein) to small clusters of staff cottages on commercial farms. Ethical permission for this study was granted by the research ethics committee of Nelson Mandela University (H15eSCI-BOT001) and Arizona State University (IRB Protocol 1301008742). In total, sixty-seven foragers (58 females, 9 males, mean age ¼ 35) residing in nine different localities within the study area, contributed to a total of 451 foraging bouts over 25 months. For each bout, the total harvest was then divided by the number of participating foragers to obtain an average return rate per forager

per hour (kg/hr). Note that ~95% of bouts involved only two foragers, whereas the remainder involved three foragers. The foragers were given no instructions on where to forage within a location and how to forage in a patch. Four foragers each participated in over 90 bouts (maximum ¼ 170), and 51 foragers in less than ten bouts (Fig. S1), i.e. forager participation was not randomised but based on availability, knowledge and enthusiasm of local community members. The total “person bouts” (i.e. an individual foraging for 30 min) was 991. Ad hoc behavioural observations of forager activities were also recorded. For a subset of foraging bouts (n ¼ 249), the distance each forager walked during a bout was recorded uisng an attached GPS device. Soil hardnessdas a proxy for the difficulty involved in extracting USOsdwas estimated by pushing a plastic ruler into the soil at four random locations within each foraging bout area. The deeper the ruler can be pushed in, the softer the soil. 2.4. Nutrient analyses Edible plant parts of the species foraged in each bout were dried and stored. Some of this material (see below for details) was analysed for nutrient content, specifically the percentage of sugar, starch, protein, moisture, fat, ash and dry matter. These analyses were conducted at Quantum Analytical Services lab in Malmesbury (South Africa) following the official methods of analysis published by the Association of Official Analytical Chemists (Nielsen, 2003). We calculated energy content from wet weight (kcal/100 g) using the Atwater general factor system (Atwater and Woods, 1896), specifically calculated as: (fat%  9) þ (protein %  4) þ (carbohydrates%  4) (http://www.fao.org). Note that this system does not distinguish between sugars and starch, which are readily metabolised, and unavailable carbohydrates such as dietary fibre; thus, in the case of plant material with high fibre content, this method will provide an overestimate of energy available to foragers (Conklin-Brittain, 2006). We conducted nutrient content analysis for only the most commonly foraged species from each vegetation type (48 in total). Data from another member of the genus (or average of multiple members) was used as an energy content proxy for 27 of the remaining species, and for the rest (15 species), return rates were set to zero. However, the zero return-rate assignment had a negligible effect on the results as these species were rarely collected and their collective weight across all bouts was 3.7% of the total harvested edible weight. The energy yield for each species within a bout was determined by multiplying the relevant (uncooked) energy content value by the edible harvested wet weight (g) divided by 100. The nutrition values are available in Table S1, and how these were used within each bout to calculate return rates are provided in Table S2. 2.5. Meeting daily calorific demands A diet of 1900e2000 kilocalories per day is regarded as sufficient to support hunter-gatherer people of small stature and high physical activity (Hurtado and Hill, 1989; Lee, 2017; Speth and Spielmann, 1983). To estimate the time it would take to reach the threshold of 2000 kcal within each vegetation type, the foraging data were randomly sampled by bout (without replacement) until the 2000 kcal threshold was exceeded. This provides an estimated minimum time that a naïve forager (i.e. a forager that was not familiar with the whereabouts of high-density populations, i.e. hotspots, of target species) would take to fulfil his/her daily requirements; an experienced forager who knows the whereabouts of hotspots in the landscape is likely to exceed this minimum time. This analysis was conducted in the base package in R (R Development Core Team, 2017), and the random sampling (of bouts) procedure was repeated (n ¼ 10,000) to obtain the

Please cite this article as: Botha, M.S et al., Return rates from plant foraging on the Cape south coast: Understanding early human economies, Quaternary Science Reviews, https://doi.org/10.1016/j.quascirev.2019.106129

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distribution of time (in hours) it would take to harvest 2000 kilocalories within each vegetation type. 2.6. Fire and foraging return rates Of the study area’s vegetation types, sand fynbos and limestone fynbos offered the best opportunities to test whether foraging return rates would be highest in the early phases of post-fire succession. This is because these two vegetation types burn more frequently than the others, and because it is possible to estimate post-fire vegetation age with reasonable accuracy. We were able to estimate post-fire vegetation age across a range of sand and limestone fynbos patches using node counts on fire-killed Proteaceae (Bond et al., 1984). Note that all of these locations were embedded in a large area (>50 ha) of vegetation of the same post-fire age. Following fynbos fire ecology principles (Kruger and Bigalke, 1984), we binned post-fire age as follows: 0e2 years (youth phase: low [0e0.5 m], open structure, post-fire flowering flush, maximum species apparency); 3e8 years (ericoid shrub phase: mid-high [0.5e1.5 m], mid-dense structure, reduced apparency, dominated by small-leaved shrubs); >8 years (proteoid shrub phase: tall [>2.0 m], dense structure, much reduced apparency, dominated by an overstorey of Proteaceae shrubs). Foraging bouts (n ¼ 42 for sand fynbos, n ¼ 32 for limestone fynbos; within each post-fire age category for sand or limestone fynbos: n ¼ 6e21) were conducted in the same way as for the other vegetation types. 2.7. Statistical analyses An analysis of variance (Anova) was performed to test for significant differences in foraging return rates (edible weight and kilocalories per hour) amongst vegetation types and seasons. Where assumptions of normal distribution of data (tested using the Shapiro test) and homogeneity of variance (tested using the Levene test) were violated, a non-parametric Kruskal-Wallis rank sum test was used, followed by the post-hoc Dunn test. A Kruskal-Wallis rank sum test, and the post-hoc Dunn test, were used to assess for significant differences in foraging return rates (kg/hr and kcal/ hr) amongst the three post-fire vegetation age categories. All analyses described above were completed in R v3.5.1 (R Team, 2017) using the car and FSA libraries (Fox and Weisberg, 2011 and Ogle et al., 2018, respectively). 3. Results 3.1. Forager behaviour, movement within patches, and application of prior knowledge Generally, foragers chose to dig with a wooden stick ~30 cm long, which was acquired at the foraging location; in some cases they were used for only one bout, whereas in others for all bouts in a day, before being discarded. Due to the generally high shrub density of the vegetation in the study area, during experimental bouts agents foraged along animal paths and in more open areas and, therefore, often together. Exceptions to this occurred when the vegetation was low and sparse, e.g. early post-fire fynbos. Foragers shared information on the localities of target species in a patch. The most well-known USO by the majority of foragers was Cyphia digitata, a creeper whose tuber can be eaten without any processing (de Vynck et al., 2016c). Foragers would not taste plant parts from species they did not know with certainty were edible. Foragers often demonstrated area-specific, and vegetation-specific, ethnobotanical knowledge. For example, inhabitants of Soetmelkfontein who live adjacent to an extensive stand of Prionium serratum (locally known as palmiet) had intimate knowledge on how to

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harvest and eat this species, whilst foragers of Melkhoutfontein and Bietoe Dorp did not. Bietoe Dorp foragers knew that the green seeds of Schotia afra were edible and knew how to ‘peel’ these. This species is more common around Bietoe Dorp than Melkhoutfontein, and few of the Melkhoutfontein foragers knew this species at all, let alone that it was edible. 3.2. Resource return rates The total edible weight harvested was 203 kg (mean ± SD per bout ¼ 0.45 ± 0.66 kg/h) and 96.3% of this harvested material could be converted into calorific data. The summed energetic return across all bouts from the total convertible edible weight was 59,631 kcal (or 245,870 kJ). Across all bouts, the mean and standard deviation values were 141 ± 221 kcal/h (n ¼ 422). The distribution of kilocalories per bout is shown in Figs. 1 and S2. In total, 90 edible plant species (Fig. 2, Table S3) from 33 families (24% of all species were from Iridaceae which only contains geophytes) were harvested during the study period, of which 20 species comprised 91% of all edible weight harvested. Initial site selection was based on human choice (both forager and researcher [MSB]); however, for most sites there was no prior knowledge on the first visit, and thus no way to predict the return rate. Since patches that would yield highest return rates (hotspots) occur sporadically and unpredictably in the landscape (at least in terms of vegetation, terrain and soil type) (Singels et al., 2016), foragers were most likely to find themselves in low- or averagecalorific locations for all the vegetation types (Fig. 1). The best chance of a naive forager coming across hotspots was in sand fynbos and dune fynbos-thicket mosaic, yielded significantly higher returns than the rest of the vegetation types except riparian (H(6) ¼ 68.22, p ¼ 0.001; Table 2). Due to a single species, Prionium serratum, which was harvested year-round, riparian vegetation yielded significantly higher edible weight per hour (mean ± SD ¼ 1.23 ± 1.0 kg/h) than any other vegetation type (H(6) ¼ 96.85, p ¼ 0.001; Table 2; Fig. 3). Despite being a reliable source, the low calorific content of P. serratum (mean ¼ 17 kcal/ 100 g) substantially reduces the hourly kilojoule potential for this vegetation type (Fig. 4). Among vegetation types, only renosterveld showed significant seasonal differences in foraging returns, with lower edible weight (H(3) ¼ 10.16, p ¼ 0.016; Fig. 3) and calorific returns (H(3) ¼ 10.3, p ¼ 0.02; Fig. 4) in summer (0.04 kg/h; 17 kcal/ h, respectively) compared to winter (0.24 kg/h; 78 kcal/h) (Fig. 4 Table S4). Simulations show that the 2000 kcal target is most frequently reached in the shortest time in sand fynbos, followed by dune fynbos-thicket mosaic (Fig. 5); the majority of simulations for the other vegetation types indicated more than 10 h of foraging required to obtain 2000 kcal. Even the 90th percentile, here used as a proxy for the likely return rates achieved by a forager knowledgeable about the location of hotspots, indicates that achieving this threshold would take >9 h per day in most of the vegetation types. Return rates among vegetation types were likely affected by soil hardness, which differed significantly (H(5) ¼ 58.11, p ¼ 0.001; note that riparian vegetation was excluded in this test) dthe softest soils were found in dune fynbos-thicket mosaic and sand fynbos, and the hardest soils in renosterveld. In addition, the return rates were also influenced by the geophyte species and densities which varied in the different vegetation types (e.g. large, apparent stands of easy-to-harvest Watsonia were largely absent from renosterveld). Foragers walked on average 707 m (SD ¼ 419 m) per foraging bout, and there was a negative correlation between distance travelled and edible plant weight harvested (Fig. S3), as well as a statistically significant difference in distance travelled per hour among vegetation types (H(6) ¼ 38.85, p ¼ 0.001), with the shortest distances covered per hour in renosterveld and riparian vegetation

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M.S. Botha et al. / Quaternary Science Reviews xxx (xxxx) xxx

Fig. 1. The distribution of (A) bout localities within each vegetation type, and (B) bout return rates for each locality across four calorific return rate categories. Foraging bouts were conducted between Nov 2014 and Dec 2016 across the study region on the south Cape coast of South Africa. A 10 km scale bar is included in the bottom right of each map.

(Table 2). 3.3. Fire and foraging return rates Consistent with the fire-stick farming hypotheses, both currencies for return rates d edible weight and calories d declined

with increasing post-fire vegetation in sand fynbos and limestone fynbos (Fig. 6). However, results were significantly different only between the youth phase (i.e. 0e2 years) and the older phases (see statistics in Fig. 6 legend). This implies that the benefits for return rates are restricted to the early post-fire years.

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M.S. Botha et al. / Quaternary Science Reviews xxx (xxxx) xxx

7

Fig. 2. The range of search and harvesting rates of edible weight (kg/hr) per plant species across foraging bouts. The number of foraging bouts in which a species was harvested is shown in brackets. For species with a sample size of five bouts or less, the values of each harvesting rate are shown (stars) instead of boxplots. The following species were collected by foragers, but never had a bout total greater than 200 g (and summed across all bouts totalled <400 g): Albuca fragrans, Albuca juncifolia subsp. juncifolia, Annesorhiza nuda, Babiana ambigua, Babiana patula, Babiana sp., Babiana tubulosa, Cassine peragua, Colpoon compressum, Cyperus esculentus, Cyphia pheutema, Cyrtanthus fergusoniae, Disa bracteata, Euclea racemosa, Euphorbia ecklonii, Ferraria crispa, Freesia alba, Freesia caryophyllacea, Freesia leichtlinii, Freesia sp., Gladiolus carinatus, Gladiolus floribundus, Gladiolus sp., Gladiolus teretifolius, Grewia occidentalis, Lauridia tetragona, Ledebouria revoluta, Lycium ferocissimum, Microloma sagittatum, Microloma sp., Moraea sp., Ornithogalum dubium, Osteospermum monilifera, Osyris compressa, Othonna undulosa, Pelargonium carneum, Pelargonium pinnatum, Satyrium longicolle, Satyrium sp., Searsia glauca, Searsia lucida, Trachyandra divaricata, Tritonia squalida, Tulbaghia capensis, Viscum capense, Viscum rotundifolium, Wachendorfia paniculata, Watsonia aletroides.

4. Discussion The aim of this study was to determine the foraging return rates from the indigenous vegetation of the Cape south coast in the context of meeting the calorific requirements of hunter-gatherers. The results of our foraging experiments suggest that a forager naïve to the distribution of resources in the landscape (i.e. without prior knowledge of hotspots) could attain a mean ± SD of 141 ± 221 kcal/h. Quite obviously, daily calorific returns would increase if efforts were focused on hotspots in specific vegetation types, especially in the sand fynbos and dune fynbos-thicket mosaic. Specific plant species returns were generally lower than those reported for other studies but differences in study design need to be considered (Tables 3e5). Studies of plant foraging returns of hunter-gatherer societies such as the Batak, Alyawara and Hadza (Table 3) have employed foragers that are intimately familiar with their natural environment. Their landscape is not exploited haphazardly; instead foraging is for specific plant species in known hotspots at appropriate times, e.g. when target plant apparency is high. Local people (Khoe-San descendents) of the Cape south coast

are very knowledgeable about useful plants (de Vynck et al., 2016c), but do not actively exploit these plants as essential foodstuffs, i.e. these foragers are not reliant on harvesting plant foods from the environment for their day-to-day survival and likely lack the necessary experience to forage optimally in this landscape. Thus, the experimental design followed here was to assess the baseline foraging potential, with the help of knowledgeable participants, of a large and vegetationally complex landscape. Foraging sites were initially identified without any prior knowledge of the potential return they could yield and were also chosen to ensure the range of vegetation types could be sampled monthly. As the study progressed, foragers chose to return to the vicinities of hotspots and eschewed low-yielding locations. The results allow inferences to be made about what plant species and vegetation types a forager would potentially select to optimise energetic returns (Pyke et al., 1977). The highest plant calorific returns were derived from sand fynbos (mean ± SD ¼ 246 ± 307 kcal/h), dune fynbos-thicket mosaic (214 ± 303 kcal/h) and riparian (147 ± 104 kcal/h) vegetation, but only in the first and second could foragers readily reach their daily calorific requirements (here set at 2000 kcal/day) in less

Please cite this article as: Botha, M.S et al., Return rates from plant foraging on the Cape south coast: Understanding early human economies, Quaternary Science Reviews, https://doi.org/10.1016/j.quascirev.2019.106129

b a b a a a e

Sig

20 15 19 20 2 20 e

Max

c a,b a,b a,c a a,b b 5 6 7 7 5 5 2

20 9 18 8 2 13 e

90th

3 3 2 3 3 3 1

10 0 11 1 0 1 e

25th

1 1 1 1 1 1 1 1 1 1 1 1 1 1

6 0 6 0 0 0 e

Min

2 1 1 1 1 1 1 1.05 1.23 0.87 1.04 1.00 0.96 0.22

5 4 4 5 1 7 e 14 3 14 4 0.4 6 e 11 16 25 16 20 7 e b b a,c a,b c a,b c 2300 2300 1898 1800 1534 1568 1360 1306 1391 1133 1206 920 1361 744

Max 90th

546 681 331 443 272 473 342

25th

112 271 58 98 52 73 234

Min

741 942 578 859 438 684 416 439 434 404 391 309 438 271 850 944 642 775 507 740 490 57 31 39 41 41 21 17

M SD

Distance Travelled (m/hr)a

u

Dune fynbos-thicket mos. Subtropical thicket Sand fynbos Limestone fynbos Renosterveld Floodplain woodland Riparian

Vegetation Type

Dune fynbos-thicket mos. Subtropical thicket Sand fynbos Limestone fynbos Renosterveld Floodplain woodland Riparian

95 53 75 67 70 49 42

n

0.60 0.19 0.44 0.16 0.18 0.57 1.23

u

Soil hardness (cm)b

Sig

n

u

SD

c a c a a a,b b,c 2079 1140 1611 449 680 484 385 474 178 565 201 143 244 295 56 0 34 14 9 14 72 0 0 0 0 0 0 0 124 20 176 39 33 57 128 303 180 307 101 99 116 104 214 78 246 77 60 99 147 a b a b b a c 4.35 2.54 3.37 0.94 1.45 3.32 4.51 1.44 0.33 0.90 0.41 0.50 1.50 2.48 0.15 0.00 0.01 0.03 0.03 0.03 0.51 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.40 0.07 0.29 0.07 0.07 0.22 1.03

Sig Max 90th 25th Min SD

M Vegetation Type

0.68 0.39 0.56 0.20 0.28 0.78 1.01

u n

SD

Calories (kcal/hr) Edible weight (kg/hr)

M

Min

25th

90th

Max

Sig

M

12 2 13 3 0 3 e

2 2 1 2 2 1 1

90th 25th Min M SD u

No. of plants species per foraging bout

Max

Sig

M.S. Botha et al. / Quaternary Science Reviews xxx (xxxx) xxx Table 2 Summary statistics for 30-minute foraging bouts conducted monthly from Nov 2014 to Dec 2016 per vegetation type. The mean, standard deviation (SD), median (M), minimum (Min), maximum (Max) and 25th and 90th quantiles are shown for: edible weight, calories and number plant species harvested, and also distance travelled (averaged for two foragers per bout) and soil hardness (depth to which a plastic ruler could be easily pushed into soil). The non-parametric Post-hoc Dunn test shows significant differences between vegetation types for the different measurements (significant differences, at the p < 0.05, between vegetation types is indicated using dissimilar letters).

8

than 9 h of foraging. The median kg/hr and kcal/hr returns for all vegetation types fell below the mean values, suggesting the occurrence of fewer high-yielding sites, i.e. hotspots, inflated the mean. Optimal foraging theory predicts that a forager should choose hotspots to maximise energetic returns (Charnov, 1976; Hawkes et al., 1982; Pyke, 1984). In this study, given the choice, many foragers preferred to return to hotspots. Using the 90 percent quantile of calorific values in this study as a proxy for hotspot foraging alone, the return rate for all bouts across the study region increases to 330 kcal/h, and the highest calorific hotspots occur within dune fynbos-thicket mosaic (2079 kcal/h) and sand fynbos (1611 kcal/h). These two vegetation types also have softer soils compared to limestone fynbos and renosterveld, where considerable effort is required to dig up USOs, which contributes to the lower yield in these vegetation types. The fact that foragers covered the shortest distances in patches of renosterveld and limestone fynbos is suggestive of the difficulties in harvesting USOs in their respective soils. Only renosterveld had significantly lower calorific returns in summer vs. winter, which is likely because of fewer sources of aboveground carbohydrates in this vegetation type and the marked summer deciduousness (or lack of apparency) of the many iridaceous geophytes that grow there (de Vynck et al., 2016b). Like de Vynck et al. (2016b), this research supports the availability of some carbohydrate-rich plant species year-round for most vegetation types. The productive and high yielding intertidal resource (de Vynck et al., 2016a) is intermittently available, depending on tidal and weather conditions. In contrast, terrestrial plants provide a year-round resource, making it a readily available fall-back and, very likely for some species, a staple food resource for Stone Age people in this region (Laden and Wrangham, 2005). Comparing these results with foraging returns found in other systems is constrained by substantial differences in sampling strategies (Table 4). Some studies estimate resource density, either in hotspots for specific plant species (Vincent, 1985; Youngblood, 2004), or across a study area (not just hotspots) on particular species (Sato, 2001) or all species (Singels et al., 2016). In these studies, travelling time to foraging areas and search time within areas were not included, and, importantly, harvesting was done in an ecologically-designed manner e that is, all possible edible plants were included in the analysis (Table 4). In contrast, Eder (1978) and O’Connell and Hawkes (1981) adopted a forager-driven approach: yields are based on weights gathered by informed gatherers returning from foraging excursions. These studies also include a cost travel time to the locality and processing times, something our study did not. These differences in approach and design make it difficult to compare return rates among studies. Nonetheless, a broad-stroke comparison suggests that the return rates (kg/hr and kcal/hr) for the top fifteen plant species gathered during this study generally fall below those found in other systems and studies (Table 3). We speculate that the wide geographic scope, haphazard selection of sites and considerably longer time over which this study was conducted influenced the mean calorific return reported here. A prior knowledge and focus on hotspot locations, as well as a focus on seasonally available, high-yielding plant species, would increase substantially the mean foraging returns reported here. Although only 20 species comprise the bulk of the total harvested weight in this study (and could be construed as staples), 90 edible plant species were harvested by foragers. This is an extraordinarily high number of species and is consistent with evidence from the contemporary and archaeological literature, which show that early humans utilised a diversity of plants in the GCFR (Botha et al., 2019). The relationship between overall diversity and the species harvested remains to be explored. In extant hunter-

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9

Fig. 3. The weight per hour (kg/hr) of edible plants foraged for each bout across vegetation type and season. The edible weight harvested per bout was averaged amongst the foragers. The number of foraging bouts is shown in brackets. Only renosterveld yielded significantly different returns between seasons (see text). Two events had values greater than 3.5 kg/h and are not shown in the figure: Riparian in winter (4.5 kg/h) and Dune fynbos-thicket mosaic in spring (4.3 kg/h).

gatherer societies, a handful of species, often from the same genus (e.g. Dioscorea), are utilised as staples (Eder, 1978; Sato, 2001; Vincent, 1985). We surmise that hyper-diversity of edible plants reduces search costs overall, in such a way that lower ranked species (based on handling cost) are selected occasionally but without particular focus, while higher ranking plants are more often selected. This is consistent with our results where just 20 of the 90 species harvested comprised 90% of the biomass returned by harvesters. Ours is the first study to show that return rates from fynbos are significantly elevated in recently burnt compared to mature vegetation, something that was predicted by Hilary Deacon in the 1980s (Deacon, 1983, 1993). Plants with edible underground storage organs (e.g. Watsonia spp.) and leafy edibles (e.g. Trachyandra spp.) are most apparent and abundant in the youth phase of fynbos postfire succession (Kruger and Bigalke, 1984; Le Maitre and Brown, 1992). The archaeological record for the GCFR suggests that Watsonia (Iridaceae) was one example of a widely utilised genus that ranks high among edible plants (Botha et al., 2019). Similarly, in this

study, foragers achieved high returns for Watsonia fourcadei. This species is evergreen, has a large corm, reaches a height up to 2 m (Manning and Goldblatt, 2012), grows in bunches, and flowers prolifically after fire making it easy to notice and obtain high returns from a small space in a short time. Watsonia is also the genus Deacon (1993) referred to when he proposed that high, postfire apparency of high-yielding underground storage organs may have been an important incentive for early humans to burn Cape vegetation. This supports the suggestion that there could have been strong incentive for intentional burning of the land, i.e. fire-stick farming. If used, it required managing the scale and timing of the areas burned, since yields decrease to near-zero the first few months post-fire, before rapidly increasing after the first growing season. Frequent fires would also have likely reduced the spread of fierce wildfires (cf. Bird et al., 2012) that might have rendered large areas without plant resources, albeit for a short time, but also maintained a mosaic of different aged vegetation that benefitted other prey, namely reptiles and mammals (Kruger and Bigalke, 1984).

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Fig. 4. The kilocalories per hour (kcal/hr) for each foraging bout of edible plants across vegetation type and season. The total kcal/hr harvested per bout was averaged amongst the foragers. The number of foraging bouts is shown in brackets. Four events had values greater than 1000 kcal/h and are not shown in the figure: Sand fynbos in spring (1006 and 2084 kcal/h), and Dune fynbos-thicket mosaic in spring (1429 kcal/h) and autumn (1237 kcal/h).

Fig. 5. Violin plots summarising simulations (n ¼ 10,000) of random draws (without replacement) of recorded bout return rates to determine the distribution of time (to the closest hour) it would take to reach 2000 kcal. In addition, the times to reach 2000 kcal using the maximum and 90th percentile kcal/hr values recorded within each vegetation type are shown (star and diamond, respectively). Note that the x-axis is an exponential scale.

Watsonia fourcadei and some other high-return USOs (e.g. Pelargonium lobatum, Pelargonium triste, Chasmanthe aethiopica)

require lengthy processing to render edible as they are fibrous and bitter (i.e. peeling, grinding and leaching) (Botha et al., 2019;

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Fig. 6. The harvest rate of edible weight (kg/hr) and kilocalories (kcal/hr) at different post-fire vegetation age intervals for two fire-prone vegetation types. A Kruskal-Wallis rank sum test indicated significant differences for both kg/hr and Kcal/hr across postfire categories within each vegetation type (across all comparisons [i.e. return rate and vegetation type combinations]: H(2) ¼ 7.09 to 14.93, p ¼ 0.028 to <0.001). A post-hoc Dunn Test established the significance amongst vegetation ages for each combination of kg/hr or kcal/hr and vegetation type d significant differences are indicated by dissimilar characters (at the p < 0.05 level). Note that two outliers occur beyond the yaxis limits in the sand fynbos 0e2 category (6.7 and 3.9 kg/h; 2084 and 939 kcal/h). In addition, one bout in limestone fynbos (k/hr > 0.5 and kcal/hr > 400) has high return rates as this was from fruit of Carpobrotus acinaciformis (i.e. was harvested aboveground, not underground storage organs).

Headland, 1987; Johns and Kubo, 1988; Leopold and Ardrey, 1972; Stahl, 1984; Wandsnider, 1997) compared to other species (e.g. Babiana spp., Freesia spp., Conicosia pugioniformis, Ferraria crispa, Cyphia digitata) that can be eaten raw or cooked without pretreatment (Botha et al., 2019). Factoring processing time into foraging return rates will influence the net energetic return rate per species. It also has implications for the foraging choices huntergatherers would have made (Ames and Marshall, 1981). For example, plant species that can be eaten unprocessed will satisfy immediate food requirements. Gathering plant species that require time to render edible would be indicative of humans interested in investing for future returns (Woodburn, 1982). It also has

11

implications for forager mobility patterns, guarding resources during the processing time (Eder, 1978) and pair-bonding (Wrangham et al., 1999). Humans survived by harvesting a wide range of foodstuffs available on the Cape south coast (e.g., honey, insects, mammals, marine foods) (Avery, 1987; Henshilwood et al., 2001; Jerardino and Marean, 2010; Klein, 1976; Marean et al., 2007; Matthews et al., 2009). Like plants, each of these resources require planning for optimal utilisation. Hunting mammals would have been influenced by both the contraction and expansion of the Palaeo-Agulhas Plain as well as the migratory patterns of the mammalian fauna associated with it (Compton, 2011; Copeland et al., 2016; Marean et al., 2014). de Vynck et al. (2016a) showed that intertidal resources can only be harvested for a few hours a day for a maximum of ten days per month. Within this limited window for foraging, the intertidal zone is, however, a high-yielding resource, with the overall mean caloric return of 1492 kcal/h (de Vynck et al., 2016a). Foragers could thus achieve their daily calorific requirements in a short time. However, mean energetic returns of intertidal resources are highly impacted by factors such as tidal level, forager’s gender, habitat type, and especially weather conditions, resulting in variable yields (Bird and Bird, 2000; de Vynck et al., 2016a). Harvesting of shellfish is arguably a more difficult and dangerous activity than plant harvesting (Marean et al., 2014). In this study, plant harvesting appeared to be a very easy skill to master. Although experienced plant foragers yielded highest returns, inexperienced foragers were generally able to start digging for USOs quite easily. Since this skill is readily acquired, it is likely that older adults and young children could have readily participated in plant foraging. A more specialized skill required whilst plant foraging would have been the ability to differentiate between poisonous and nonpoisonous plants, which is a topic that requires more research (Provenza et al., 1998). Foragers in our study were reluctant to taste plants species with which they were not familiar, thus highlighting the forager’s reliance on traditional cultural knowledge (Zarger and Stepp, 2004). This suggests that knowledge of edible and otherwise useful plant resources is conservative, and unlikely to be acquired or expanded on in the absence of traditional knowledge. Therefore, access to this knowledge would provide a selective advantage to individuals. Also, individual memory or cultural knowledge of the location in space and time of resource hotspots would have offered a selective advantage (New et al., 2007). One potential driver that may influence the return rates from plant foraging, which couldn’t be explored in this study, is the role of lowered atmospheric [CO2] during past period (e.g. the Last Glacial Maximum). As discussed in Cowling et al. (this issue), lower [CO2] reduces the water use-efficiency of C3 plants (almost all plants in this study use this photosynthetic pathway). Thus, plant growth rates may have declined. Faltein et al., 2019 (this issue) demonstrate that there is a significant decline in bulb biomass of Oxalis pes-caprae under lowered atmospheric [CO2] conditions. This requires further investigation, and the return rates here may require an adjustment (sensu precipitation thresholds used in the expert vegetation model of Cowling et al., this issue). Another influence is the additional processing time (leaching, cooking etc.) that may be required for some plant species d much of this knowledge has been lost (Botha et al., 2019) and so could not be included in this study. For certain species, and bouts, this would decrease the overall return rate. 5. Conclusion The Cape south coast provides a rich mix of vegetation types, with high numbers of endemic plant species that could have provided foragers with a species-rich, year-round food resource. These

Please cite this article as: Botha, M.S et al., Return rates from plant foraging on the Cape south coast: Understanding early human economies, Quaternary Science Reviews, https://doi.org/10.1016/j.quascirev.2019.106129

12

M.S. Botha et al. / Quaternary Science Reviews xxx (xxxx) xxx

Table 3 A summary of all return rates (kcal/hr and kg/hr) from different plant foraging studies. (All values in italics were calculated using data available in the papers). Species People/Place

Batak, Philippines (Eder, 1978) Alyawara, Central Australia (O’Connell and Hawkes, 1981)

Dioscorea hispida Dioscorea luzoniensis Ipomoea costata

Growth Form

Collected Plant kcal/hr Part u SD

pc pc USO

Tuber Tuber Tuber

1739 484 2653

Zeekoe valley, South Africa (Youngblood, 2004)

Local residents of the southern Cape (of Khoe-San descent), South Africa (Singels et al., 2016)

Local residents of the southern Cape (of Khoe-San descent), South Africa (this study)

90th Min-Max n

a a

1360

2866

759 e5210 (805 e7815)a

(3392)a (2192) (2866) a

Hadza, Tanzania (Vincent, 1985)

kg/hr M

Vatovaea pseudolablab Vigna frutescens var frutescens Vigna frutescens var frutescens Vigna macrorhyncha Pelargonium sidoides Albuca canadensis Talinum caffrum Cyperus usitatus Chasmanthe aethiopica

pc pc

Tuber Tuber

1816 1077

a

pc

Tuber

3240

pc USO USO USO USO USO

Tuber Root Bulb Tuber Bulb Corm

Cyphia digitata

USO

Pelargonium lobatum

a

u

SD

M

90th MinMax

11 1.85 8 0.52 7 1.7 0.9 7

n

0.5e3.3 7

(2.2) (1.4)a (1.5)a

(0.55.0)

a

7

14 3 9 1.7

14 9

a

12 5.4

12

1967 3449 2438 222 391 2991

a

5

5

Tuber

146

55

1513 e4443 77e227

USO

Tuber

1737

Ferraria crispa

USO

Corm

2460

Watsonia meriana

USO

Corm

1876

Cyanella lutea

USO

Bulb

Carpobrotus edulis

pss

Watsonia fourcadei

a

3

4.7 3.3 9.2 2.5 1.7 1.07

7

0.41 0.09

1290

545e3569 4

1.53 0.85

1571

565e4760 5

1.2

3

0.89 0.41

276

183

1480 e2662 146e537

4

0.13 0.08

Fruit

387

448

158

1050 9e1140

24 0.86 1

0.35

2.54

USO

Corm

356

358

271

804

8e1961

55 0.6

0.45

1.35

Pelargonium lobatum

USO

Tuber

275

436

133

495

7e2814

54 0.58 0.91 0.28

1.03

Pelargonium triste

USO

Tuber

240

313

121

526

9e1804

76 0.5

1.1

Prionium serratum

Shrub

Meristem

184

143

143

350

12e769

48 1.08 0.84 0.84

2.06

Pelargonium rapaceum

USO

Tuber

148

212

76

451

7e762

17 0.31 0.44 0.16

0.94

Tetragonia decumbens

Shrub

Leaves

104

63

101

170

17e277

18 1.26 0.76 1.22

2.05

Conicosia pugioniformis USO

Root

99

105

72

243

2e567

51 0.64 0.67 0.46

1.56

Chasmanthe aethiopica USO

Corm

98

90

58

233

6e368

39 0.21 0.19 0.12

0.49

Cynanchum obtusifolium Carpobrotus acinaciformis Eriospermum paradoxum Typha capensis

pc

Seedpod

98

148

19

351

5e440

25 0.13 0.2

0.03

0.48

pss

Fruit

93

92

55

237

1e403

54 0.21 0.21 0.12

0.53

USO

Tuber

92

98

57

202

3e329

12 0.5

0.53 0.31

1.09

hp

Meristem

82

59

60

169

10e268

38 1.78 1.28 1.29

3.65

Vachellia karroo

pt

Pods

70

78

40

169

4e295

26 0.16 0.17 0.09

0.38

Trachyandra ciliata

USO

Flower

69

68

39

106

24e261

12 0.32 0.31 0.18

0.49

Cyphia digitata

USO

Tuber

57

53

35

139

4e203

79 0.19 0.18 0.12

0.47

Ferraria crispa

USO

Corm

54

39

44

97

18e160

16 0.07 0.05 0.05

0.12

Schotia afra

pt

Pods

51

55

42

111

1e228

39 0.21 0.22 0.17

0.45

Oxalis pes-caprae

USO

Corm

41

26

35

66

1e111

16 0.13 0.08 0.11

0.21

a a a a

a a a a

0.77

0.6

0.65 0.25

0.7 e1.37 0.26 e0.56 0.6 e2.62 0.36 e2.17 0.52 e1.34 0.07 e0.23 0.02 e2.54 0.01 e3.29 0.01 e5.89 0.02 e3.77 0.07 e4.53 0.01 e1.59 0.21 e3.34 0.01 e3.64 0.01 e0.78 0.01 e0.6 0.01 e0.9 0.01 e1.78 0.22 e5.81 0.01 e0.66 0.11 e1.2 0.01 e0.68 0.02 e0.2 0.01 e0.93 0.01 e0.34

3 7 4 5 3 4 24 55 54 76 48 17 18 51 39 25 54 12 38 26 12 79 16 39 16

See Table 4. Values in brackets only include search and gathering times only, whereas values above are calculated using search, gathering and processing times. a Not reported, hp ¼ herbaceous perrenial, pc ¼ perrenial climber, pt ¼ perrenial tree, pss ¼ perrenial succulent shrub.

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13

Table 4 Comparative methodology of the studies reported in Table 3. People/Place

Comparative Methodology

Batak, Philippines (Eder, 1978)

Weighed the tubers brought back daily to the village (over period of a month) after foraging by the Batak. Estimates include travelling and processing time. Kilocalories per hour calculated from data provided in Table 1 (p. 62) and Table 2 (p. 67). Note that kcal/hr for D. luzoniensis is based on calorific values reported for D. hispida. Tubers that Alyawara foragers collected were weighed after each foraging event. Travel, search and gathering and processing times were recorded. In Table 3, we report two values for kcal/hr and kg/hr: (1) relative to search, gathering and processing times (i.e. Ts, Tg & Ts in Table 5A2, p. 118), and (2) relative to search and gathering times only (i.e. Ts and Tg; values shown in brackets). Hotspots of species of interest were surveyed by standard botanical methods and digging experiments conducted to estimate tuber density per ha. Estimated general size of hotspots of each plant species and quantified plant density by counting plants in demarcated (1 m2) quadrats. Dug up one m2 and weighed edible portion. (Weight)  (plant density) used to extrapolate to hectare (ha). The foraging efficiency (kg/hr) was performed by the researcher and an assistant, but “experienced natives of the Zeekoe Valley could have significantly outperformed two inexperienced diggers” (p. 57). Kilocalories per hour were calculated here using the foraging efficiency and nutritional data provided. The kg/ha was calculated from plant surveys one hundred 25m2 randomly located plots. Mean weight per species was calculated from 10 to 15 excavated individuals. Singels et al. (2016) reported the six species with highest biomass and the extrapolated kg/ha (Table 3, p. 86). The kcal/hr estimates were calculated from variable time (7e121 min; median ¼ 25) directed (i.e. focused on one species at a time) foraging bouts. Here we used the data reported in the supplementary Table C1 to calculate the kcal/hr and kg/hr summary statistics. Note that the density estimate is not from hotspot surveys (sensu Youngblood, 2014 and Vincent, 1985), but randomly placed plots in which the species occurred. Found sites to forage across study area with generally no a priori knowledge of what plant species were present or in what density. Time included search and gathering within a 30-minute bout. Some highyielding sites, once identified, were returned to over a 25-month period. Further summary statistics for additional species are reported in Table S2.

Alyawara, Central Australia (O’Connell and Hawkes, 1981)

Hadza, Tanzania (Vincent, 1985) Zeekoe valley, South Africa (Youngblood, 2014)

Local residents of the southern Cape (of KhoeSan descent), South Africa (Singels et al., 2016)

Local residents of the southern Cape (of KhoeSan descent), South Africa (this study)

Table 5 Study design of investigations that have explored human plant foraging (y ¼ yes; n ¼ no). Study design

Definition

Sub-sample of plants are generally extracted in a defined space (e.g. one m2) and extrapolated to landscape-scale Forager-driven Free-harvesting in a space done by foragers with knowledge of their environment The harvesting costs Travelling time Travelling to and from a residential location to a harvesting area Search time Looking for plants within a harvesting area Harvesting Time taken to harvest the desired plant foods time Gross Removing inedible plant parts processing Fine processing Time taken to render the harvested food edible (e.g. leaching, soaking, cooking)

This study

O’Connell and Hawkes (1981)

Eder (1978)

Ecologicallydriven

a

Vincent (1985)

Youngblood (2004)

Singels et al. (2016)

Sato (2001)

y

y

y

y

y

y

y

n

n/ya

y

n

n

n

n

y y

y y

y y

n n

n n

n n

n n

Y

y

y

n

n

n

n

n

y

y

n

n

n

n

O’Connell and Hawkes (1981) conducted analyses with travel time included (e.g. Table 5A2, pp 118e119) and excluded (e.g. Table 5A3, p. 121).

vegetation types often occur within short distances of each other, meaning that typical hunter-gatherers would have been able to traverse many types within their daily range. However, biomass is patchily distributed in the landscape; high-yielding hotspots were most frequently found in sand fynbos and dune fynbos-thicket mosaic. In fire-prone fynbos shrublands, highest returns were recorded in the immediate post-fire years, declining significantly with increasing vegetation age, the first evidence in the GCFR of the hypothesised benefits of ‘fire-stick’ farming. The mean plant calorific return for the entire study area was much lower than that mean obtained for intertidal foraging. However, the year-round availability of the terrestrial plant resource (in comparison to the tidal-driven availability of intertidal resources), implies that terrestrial plants could have been a critical fall-back food, or for some species, a staple. Foragers most likely utilised a range of resource types to meet their energetic requirements year-round. This study, unique within the GCFR, provides the largest

published actualistic dataset on plant foraging returns (see sample sizes reported in Table 3 for comparisons). These data directly support the creation, testing, and iterative refinement of palaeoscape and the early modern human resourcescape models such as those developed in this special issue (e.g. by Wren et al., this issue). Declaration of competing interest None. Acknowledgements We are exceptionally grateful to the resident people of the southern Cape who shared their natural heritage with us and to the property owners who granted us access to their natural veld. This study would not have been possible without these resources. This work is based on the research supported, in part, by the National

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M.S. Botha et al. / Quaternary Science Reviews xxx (xxxx) xxx

Research Foundation of South Africa (Grant number 93487), Department of Environment Affairs: Oceans and Coast Research, National Science Foundation (BCS-0524087, BCS-1138073 and BCS1460376), Hyde Family Foundations, the Institute of Human Origins (IHO) at Arizona State University, and the John Templeton Foundation to the Institute of Human Origins at Arizona State University. The opinions expressed in this publication are those of the author(s) and do not necessarily reflect the views of any of these funding organizations. We acknowledge Maxine Smit who commented on an early draft of this manuscript. We also thank three reviewers who provided detailed comments that substantially improved this manuscript. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.quascirev.2019.106129. References Allsopp, J.C., Colville, J., Verboom, G.A., 2014. Fynbos, Ecology, Evolution and Conservation of a Megadiverse Region. Oxford University Press, Oxford. Ames, K.M., Marshall, A.G., 1981. Villages, demography and subsistence intensification on the southern Columbia plateau. North Am. Archaeol. 2, 25e52. Atwater, W.O., Woods, C.D., 1896. The Chemical Composition of American Food Materials. Bulletin, vol. 28. Government Printing Office, Washington. USDA. Avery, D., 1987. Late pleistocene coastal environment of the southern cape province of South Africa: micromammals from Klasies river mouth. J. Archaeol. Sci. 14, 405e421. Bartram, L.E., 1997. A comparison of Kua (Botswana) and Hadza (Tanzania) bow and arrow hunting. In: Knecht, H. (Ed.), Projectile Technology. Springer, pp. 321e343. Bentsen, S.E., 2013. Using pyrotechnology: fire-related features and activities with a focus on the African Middle Stone age. J. Archaeol. Res. 22, 141e175. Bergh, N.G., Verboom, G.A., Rouget, M., Cowling, R.M., 2014. Vegetation types of the greater cape Floristic region. In: Allsopp, J.C., Colville, J., Verboom, G.A. (Eds.), Fynbos Ecology, Evolution and Conservation of a Megadiverse Region. Oxford University Press, Oxford. Berna, F., Goldberg, P., Horwitz, L.K., Brink, J., Holt, S., Bamford, M., Chazan, M., 2012. Microstratigraphic evidence of in situ fire in the Acheulean strata of wonderwerk cave, northern cape province, South Africa. Proc. Natl. Acad. Sci. 1215e1220. Bird, D.W., Bird, R.B., 2000. The ethnoarchaeology of juvenile foragers: shellfishing strategies among Meriam children. J. Anthropol. Archaeol. 461e476. Bird, R.B., Bird, D.W., Codding, B.F., Parker, C.H., Jones, J.H., 2008. The "fire stick farming" hypothesis: Australian Aboriginal foraging strategies, biodiversity, and anthropogenic fire mosaics. Proc. Natl. Acad. Sci. 105, 14796e14801. Bird, R.B., Codding, B.F., Kauhanen, P.G., Bird, D.W., 2012. Aboriginal hunting buffers climate-driven fire-size variability in Australia’s spinifex grasslands. Proc. Natl. Acad. Sci. 109, 10287e10292. Bond, W.J., Vlok, J., Viviers, M., 1984. Variation in seedling recruitment of Cape Proteaceae after fire. J. Ecol. 209e221. Botha, M., Cowling, R.M., Esler, K.J., De Vynck, J.C., Potts, A.J., 2019. Have humans living within the Greater Cape Floristic Region used the same plant species through time? South Afr. J. Bot. 122, 11e20. Brown, K.S., Marean, C.W., Herries, A.I., Jacobs, Z., Tribolo, C., Braun, D., Roberts, D.L., Meyer, M.C., Bernatchez, J., 2009. Fire as an engineering tool of early modern humans. Science 325, 859e862. Brown, K.S., Marean, C.W., Jacobs, Z., Schoville, B.J., Oestmo, S., Fisher, E.C., Bernatchez, J., Karkanas, P., Matthews, T., 2012. An early and enduring advanced technology originating 71,000 years ago in South Africa. Nature 491, 590e593. Charnov, E.L., 1976. Optimal foraging, the marginal value theorem. Theor. Popul. Biol. 9, 129e136.  , S., Marean, C.W., 2019. Geological and soil maps Cawthra, H.C., Cowling, R.M., Ando of the Palaeo-Agulhas Plain for the Last Glacial Maximum. Quat. Sci. Rev. https://doi.org/10.1016/j.quascirev.2019.07.040. Colville, J.F., Potts, A.J., Bradshaw, P.L., Measey, G.J., Snijman, D., Picker, M.D., Proches¸, S¸., Bowie, R.C.K., Manning, J.C., 2014. Floristic and faunal cape biochoria: do they exist?. In: Fynbos Ecology, Evolution and Conservation of a Megadiverse System. Oxford University Press, UK, pp. 73e92. Compton, J.S., 2011. Pleistocene sea-level fluctuations and human evolution on the southern coastal plain of South Africa. Quat. Sci. Rev. 30, 506e527. Conklin-Brittain, N.L., 2006. Energy intake by wild chimpanzees and orangutans: methodological considerations and a preliminary comparison. In: Hohmann, G., Robbins, M.M., Boesch, C. (Eds.), Feeding Ecology in Apes and Other Primates. Cambridge University Press, New York, pp. 445e471. Copeland, S.R., Cawthra, H.C., Fisher, E.C., Lee-Thorp, J.A., Cowling, R.M., le Roux, P.J., Hodgkins, J., Marean, C.W., 2016. Strontium isotope investigation of ungulate movement patterns on the pleistocene paleo-Agulhas Plain of the greater cape

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Please cite this article as: Botha, M.S et al., Return rates from plant foraging on the Cape south coast: Understanding early human economies, Quaternary Science Reviews, https://doi.org/10.1016/j.quascirev.2019.106129