Foraging Theory

Increasing diet breadth, a distinguishing characteristic of human foraging strategies at the end of the Pleistocene and in the early Holocene, is known to be a key development contributing to domestication and the spread of agriculture and pastoralism. Many scholars have focused on broad-spectrum foraging as a result of resource depression due to demographic stress and/or environmental degradation. However, these factors are absent in an increasing number of cases. New research in the Gobi Desert shows that a dramatic change in organizational strategies, including the intensified use of low-ranked foods from dune-field and wetland habitats, is closely correlated with the establishment of dispersed patches boasting high species diversity and a concentrated abundance of small prey. According to a global suite of paleoenvironmental and archaeological data, it appears that the fragmentation of more homogeneous grassland habitats coincided with the rise of broad-spectrum foraging and that these fragmented ecosystems were ideally suited to the unique set of foraging strategies employed by modern humans. This study shows how broad spectrum foraging, increased human population density, and the shift toward food production should be considered by-products of major environmental changes that created an ecological setting ideal for enhanced human reproduction.

A short review of current data regarding the landscape use in the Sierras of Córdoba Late Prehispanic Period (ca. 1500–300 BP) is presented in this article. Resulting expectation about residential mobility and subsistence are analyzed in light of new evidence and interpretative framework. The lack of substantial middens, few evidences of year-round residence and the low investment in farming fields support the inadequacies of the assumption that the agriculture led to the sudden dependence of crops and to the sedentary way of life in pit-house villages. Other archaeological indicators as the intensity of landscape use, the taxonomic richness of food residues, the abundance of projectile point-types and isotopic evidence reinforce these arguments. However, the evidence suggests that the Late Prehispanic peoples showed flexible subsistence and mobility patterns as one of their defining traits, where nuclear families moved around the landscape to take advantage of both agricultural and wild resources as available. Thus, farming was a fluctuating component in a mixed foraging and cultivation economy where wild animals and plants were intensively exploited through seasonal co-residential group fission–fusion mechanisms that follow the pre-existing Middle Holocene forager lifeways. Nevertheless, many variables can affect this equation, including regional population densities, social boundaries or annual variation in foraging opportunities and a mosaic of strategies combination is also predicted.

1. Olfactory predator search processes differ fundamentally to those based on vision, particularly when odour cues are deposited rather than airborne or emanating from a point source. When searching for visually cryptic prey that may have moved some distance from a deposited odour cue, cue context and spatial variability are the most likely sources of information about prey location available to an olfactory predator.

2. We tested whether the house mouse (Mus domesticus), a model olfactory predator, would use cue context and spatial variability when searching for buried food items; specifically, we tested the effect of varying cue patchiness, odour strength, and cue–prey association on mouse foraging success.

3. Within mouse- and predator-proof enclosures, we created grids of 100 sand-filled Petri dishes and buried peanut pieces in a set number of these patches to represent visually cryptic ‘prey’. By adding peanut oil to selected dishes, we varied the spatial distribution of prey odour relative to the distribution of prey patches in each grid, to reflect different levels of cue patchiness (Experiment 1), odour strength (Experiment 2) and cue–prey association (Experiment 3). We measured the overnight foraging success of individual mice (percentage of searched patches containing prey), as well as their foraging activity (percentage of patches searched), and prey survival (percentage of unsearched prey patches).

4. Mouse foraging success was highest where odour cues were patchy rather than uniform (Experiment 1), and where cues were tightly associated with prey location, rather than randomly or uniformly distributed (Experiment 3). However, when cues at prey patches were ten times stronger than a uniformly distributed weak background odour, mice did not improve their foraging success over that experienced when cues were of uniform strength and distribution (Experiment 2).

5. These results suggest that spatial variability and cue context are important means by which olfactory predators can use deposited odour cues to locate visually cryptic prey. They also indicate that chemical crypsis can disrupt these search processes as effectively as background matching in visually based predator–prey systems.