‘Moving South’: Late Pleistocene Plant Exploitation and the Importance of Palm in the Colombian Amazon

The role of plants in early human migrations across the globe has received little attention compared to big game hunting. Tropical forests in particular have been seen as a barrier for Late Pleistocene human dispersals due to perceived difficulties in obtaining sufficient subsistence resources. Archaeobotanical data from the Cerro Azul rock outcrop in the Colombian Amazon details Late Pleistocene plant exploitation providing insight into early human subsistence in the tropical forest. The dominance of palm taxa in the assemblage, dating from 12.5 ka BP, allows us to speculate on processes of ecological knowledge transfer and the identification of edible resources in a novel environment. Following the hypothesis of Martin Jones from his 2009 work, “Moving North: archaeobotanical evidence for plant diet in Middle and Upper Paleolithic Europe”, we contend that the instantly recognizable and economically useful palm family (Arecaceae) provided a “gateway” to the unknown resources of the Amazon forest

The <i>Surales</i>, Self-Organized Earth-Mound Landscapes Made by Earthworms in a Seasonal Tropical Wetland

<div><p>The formation, functioning and emergent properties of patterned landscapes have recently drawn increased attention, notably in semi-arid ecosystems. We describe and analyze a set of similarly spectacular landforms in seasonal tropical wetlands. <i>Surales</i> landscapes, comprised of densely packed, regularly spaced mounds, cover large areas of the Orinoco Llanos. Although descriptions of <i>surales</i> date back to the 1940’s, their ecology is virtually unknown. From data on soil physical and chemical properties, soil macrofauna, vegetation and aerial imagery, we provide evidence of the spatial extent of <i>surales</i> and how they form and develop. Mounds are largely comprised of earthworm casts. Recognizable, recently produced casts account for up to one-half of total soil mass. Locally, mounds are relatively constant in size, but vary greatly across sites in diameter (0.5–5 m) and height (from 0.3 m to over 2 m). This variation appears to reflect a chronosequence of <i>surales</i> formation and growth. Mound shape (round to labyrinth) varies across elevational gradients. Mounds are initiated when large earthworms feed in shallowly flooded soils, depositing casts that form ‘towers’ above water level. Using permanent galleries, each earthworm returns repeatedly to the same spot to deposit casts and to respire. Over time, the tower becomes a mound. Because each earthworm has a restricted foraging radius, there is net movement of soil to the mound from the surrounding area. As the mound grows, its basin thus becomes deeper, making initiation of a new mound nearby more difficult. When mounds already initiated are situated close together, the basin between them is filled and mounds coalesce to form larger composite mounds. Over time, this process produces mounds up to 5 m in diameter and 2 m tall. Our results suggest that one earthworm species drives self-organizing processes that produce keystone structures determining ecosystem functioning and development.</p></div

Influence of topographical depressions on <i>surales</i> development.

<p>Small basin containing <i>surales</i> in Site 1. Photo Doyle McKey 2012.</p

Summary diagram of phytolith morphotype composition in soils of Sites 1–3 and in earthworm casts.

<p>Horizontal bars represent percentages of phytolith morphotypes for each soil layer.</p

Earthworm biomass for ecological groups.

<p>Fresh earthworm biomass (g*m^-2) for ecological groups (endogeics and epigeics), <i>Andiorrhinus</i> sp. and the total of all species in mound and inter-mound habitats in <i>surales</i> field sites (Sites 1–3) and the control site (Site 4).</p

Main soil characteristics in the field sites.

<p>Main soil characteristics in the field sites.</p

Aerial photograph of Site 2 showing the same sequence of change in surales mound patterning—from spots to labyrinth and gaps, happening at the scale of a hundred meters—predicted by models of self-organization developed for other ecosystems.

<p>Photograph taken using Pixy^™ drone, Delphine Renard 2012.</p

Aerial and terrestrial images of the three field sites bearing <i>surales</i>.

<p>A. Site 1, B. Site 2, C. Site 3. Aerial images were taken using the Pixy^™ drone, Delphine Renard 2012. A(i), B(i): Photo Doyle McKey 2012; C(i), C(ii): Photo José Iriarte 2012.</p

Accumulation of a freshly emitted cast (still moist) and an older cast (dried) over the opening of a burrow of <i>Andiorrhinus</i> sp.

<p>Photos Doyle McKey 2012.</p

Plant community composition in <i>surales</i> landscapes and its seasonal variation.

<p>NMDS performed on the abundances of plant species collected during the dry (A) and the rainy (B) seasons. Plant life forms during the dry (C) and rainy (D) seasons. NB: For Site 3, where trees dominate on mounds, only the herbaceous substratum is represented here.</p