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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Central place foraging | 3/4 | https://en.wikipedia.org/wiki/Central_place_foraging | reference | science, encyclopedia | 2026-05-05T14:59:49.572605+00:00 | kb-cron |
=== Ethnoarchaeological case study: pickleweed and piñon === Barlow and Metcalfe (1996) address the issues of field processing of plant materials. Decisions of central place foragers may confound archaeological interpretations about the contribution plant material to the diet. Two interrelated issues are pertinent: the location of the central place, and field processing. Barlow and Metcalfe study archaeological materials from two sites, Danger Cave and Hogup Cave, in the area of the Great Salt Lake. These sites contain evidence for the use of piñon pine (Pinus monophylla) and pickleweed (Allenrolfea occidentalis). Samples were obtained for experimental processing from extant piñon groves and pickleweed patches in the vicinity as the cave sites. Piñon and pickleweed were harvested and processed in carefully timed and controlled stages. After each stage the useful, i.e. edible, portion of the remaining material was weighed and recorded before proceeding to the next stage. Stages consisted of: gathering, drying, and a variety of processes (parching, hulling, winnowing, etc.) to remove inedible constituents. Caloric values of the samples were then determined via laboratory analysis. These values, as well as assumed load sizes from 3 to 15 kg (based on ethnographic burden basket sizes) were then used to generate field processing model predictions. At a distance of 15 kilometers from the central place, the estimated net return rates for field processing loads of piñon and pickleweed are 3,000 and 190 calories per hour, respectively. Since piñon has higher overall return rates, field processing produces a higher rate of return. Because pickleweed has a lower rate of return, it is not worthwhile to spend the additional effort required for field processing. Therefore, the central place will be situated closer to pickleweed patches than to piñon in order to more effectively exploit the lower-ranked resource. These results imply that the archaeological evidence for pickleweed at the cave may over estimate its actual contribution to the diet. If foragers choose to reside closer to pickleweed patches and bring back largely unprocessed plants, a high density of pickleweed macrofossils will be incorporated into site deposits. However, the opposite is true for piñon, which is largely processed in the field. Thus, most sites will contain little macrofossil evidence of the inedible portions of piñon that could later be recovered by archaeologists. As such, the relative abundance of macrofossils in most cases does not directly translate into the relative contribution of those resources to the diet of central place foragers.
== The model ==
=== Basic math: single stage of processing ===
The goal of the field processing model is for a forager to maximize its return rate per roundtrip from home base to patch. The model typically solves for some amount of travel time that makes it worthwhile to process a resource to a certain stage. To determine this, we need to relate the benefit of processing and the time spent processing to the travel time. We let
z
=
{\displaystyle z=}
point on transport-time axis where field processing become profitable
x
0
=
{\displaystyle x_{0}=}
time to procure unprocessed resources
x
1
=
{\displaystyle x_{1}=}
time to procure and process a load of resources
y
0
=
{\displaystyle y_{0}=}
utility of load without field processing
y
1
=
{\displaystyle y_{1}=}
utility of load with field processing The relationship is then specified by:
With values for the utility and time of processed
(
y
1
,
x
1
)
{\displaystyle (y_{1},x_{1})}
and unprocessed loads
(
y
0
,
x
0
)
{\displaystyle (y_{0},x_{0})}
, we can solve for
z
{\displaystyle z}
. The right hand side of the equation is the proportion of relative utility*time to utility. Two conditions must be satisfied. First, the processed load must have higher utility than the unprocessed load. Second, the return rate of the unprocessed load must be at least as good as the return rate for the processed load. Formally,
=== Multiple components and multiple stages of processing === Many resources have multiple components that can be removed during processing to increase utility. Multistage field processing models provide a way to calculate travel thresholds for each stage when a resource has more than one component. As one increases the utility per load, the time needed to procure a complete load increases. The benefit of each stage of processing is:
where
A
j
=
{\displaystyle A_{j}=}
utility of resource component j
B
j
=
{\displaystyle B_{j}=}
proportion of package composed of resource component j prior to processing
y
j
=
{\displaystyle y_{j}=}
utility of load at field-processing stage j The cost in terms of time for each stage of processing is:
where
D
j
=
{\displaystyle D_{j}=}
time required to remove resource component j
L
=
{\displaystyle L=}
weight of optimal load size for transport
P
=
{\displaystyle P=}
weight of unmodified resource package
M
=
{\displaystyle M=}
time required to handle each resource package
x
j
=
{\displaystyle x_{j}=}
total handling and processing time required to reach each stage j of processing Now these values can be used to calculate
z
j
{\displaystyle z_{j}}
, which is the travel threshold for processing to stage j. In addition to a resource with multiple components, this same model generalizes to a resource with multiple stages, each of which is composed of multiple resources, each of which can be removed independently of each other (i.e., with no additional cost). This model can be further generalized to the case where multiple components with additional costs can be removed in multiple stages of processing through recursion.
=== Assumptions ===
This model rests on a number of assumptions. The most important are listed here.
Individuals attempt to maximize their rate of delivery per round trip * Packages have at least two components with different utilities The optimal load size is less than or equal to the resources available Time spent away from camp comes with an opportunity cost, but time spent in camp does not. So there is no cost to processing in camp.