Populations and “Packing Thresholds”
The lower Bosque River basin covers 2,351 km2, or ca. 235,130 hectares, and includes the South and Middle Bosque Rivers, Hog Creek, and the lower North Bosque River from its merger with the South Bosque to ca. 65 km upstream to the vicinity of Meridian, Texas. The lower Bosque River basin contains vital resources that were exploited by hunters and gatherers, a few of which were heavily or commonly used at all three sites and many other sites throughout the area. These include white-tailed deer, geophytes (roots, bulbs, and tubers), freshwater mussels, firewood, and lithic raw materials.
Access to these resources was assured through mobility. In his 2001analysis of modern-day hunters and gatherers, archeological theorist Lewis Binford found that residential mobility was the key mechanism that assured groups access to resources. Hunters and gatherers, particularly those that exploit large mammals, tend to use relatively narrow environmental niches and face constricted mobility as regional populations grow. Based on ethnographically known hunters and gatherers largely dependent on large terrestrial game such as deer, he found that “packing” of the landscape begins at about 1.6 persons per 100 km2. At this point the regional population of large mammals declines, and hunting as a major subsistence strategy decreases. Hunting of large mammals will continue to decrease as population densities increase to a “packing threshold” of 9.1 persons per 100 km2. At this point mobility becomes severely constrained, and groups are forced to broaden their diet through new subsistence strategies. Depending on environmental parameters, this may include intensified use of aquatic resources such as fish and shellfish, intensified use of plants, or the adoption of horticulture.
Based on evidence recovered from the Britton, McMillan, and Higginbotham sites, subsistence patterns, and hence mobility, appear unchanged over the last few millennia in the lower Bosque basin. Because there is no indication of intensified use of aquatic or plant resources or the use of horticulture, we assume that the “packing threshold” of 9.1 persons per 100 km2 was never exceeded during the Late Archaic and Late Prehistoric periods. A broad-spectrum foraging pattern focused on deer, geophytes, mussels, and small mammals and reptiles suggests that the initial “packing” point of 1.6 persons per 100 km2 was exceeded and that mobility was not unrestrained. In a broad sense, this subsistence pattern predates the time frame represented by these sites and represents an unchanging, successful way of life that had its genesis nearly 9,000 years ago in the region. In his 1995 overview of central Texas archeology, archeologist Michael Collins states that “there are distinctive changes to be seen within the Archaic archeological record, but it is not clear how significant these really were at the times they occurred.” We assume that sometime around 9,000 years ago, Binford’s initial packing threshold (1.6 person per 100 km2) was reached. At this point exploitation of large mammals, primarily deer, started to decline, resulting in subsistence and dietary adjustments such as increasing the diet breadth. Overall, the subsistence pattern remained relatively stable over the time frame represented by the Britton, McMillan, and Higginbotham sites, but mobility appears to have become more constricted. The formation of burned rock middens at McMillan, Higginbotham, and other sites of the same time period in the region is evidence of this, because the accumulation of burned rock hearth and oven debris represents more frequent reuse of various locales.
So how did the subsistence pattern remain relatively unchanged for several millennia, with mobility becoming more constrained? The answer must be that, although human population densities increased, the resource base was rich enough and/or acquisition and use was efficient enough to support hunting and gathering groups in increasingly smaller spaces. This is not to say that hunters and gatherers did not experience periodic food shortages. On average, though, there were plenty of resources that, when used efficiently, could support a foraging way of life in the lower Bosque basin. This suggests that, throughout the Archaic and subsequent Late Prehistoric periods, population densities far exceeded the initial packing point of 1.6 persons per 100 km2 but did not ever exceed the packing threshold of 9.1 persons per 100 km2.
Given this, we estimate that up to 9.1 persons per 100 km2 inhabited the lower Bosque River basin—an estimate that equates to 214 people. We assume that groups and group membership were dynamic and fluid and that the 214 individuals living in the lower Bosque basin may have at times comprised either many small groups or a few larger groups. Based on the division of labor and labor schedules of ethnographically known hunters and gatherers, Binford suggests that a minimal group size of 18 to 20 people could be maintained throughout most of the year. Based on a producer/dependent member ratio of 1.75, this minimal group would consist of 10 to 11 food producers (both male and female) and 7 to 10 dependents (e.g., children). Groups as small as 9 people could be maintained, but only for relatively short periods of time.