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RESULTS
For comparison, an additional run was made on the set 1 (fully occupied) map. In this run, the organism followed a simple straight path. This is the case labeled "straight" in Table 1 and Figure 5. Moving in a straight path increases the gain per step over random movements because it does not revisit already harvested nodes.
Self-crossing is also infrequent on patchy resource maps. This is expected, since the simulated organisms will tend not to revisit regions that have already been harvested. When self-crossing does occur on the sparser maps, it is usually when the organism is out of sensory range of any resource and thus moves randomly in a small area.
This seeming conundrum can be understood by looking at the standard deviations of the mean resources gained at the end of the run. Every long-range run on the 20% map produced exactly the same path; because the detection-range was so long, it always located the "best" sites within this local range. Better sites in other parts of the map were missed. On the other hand, the shorter-range chemoreception produced a greater randomness to the search. As a result, parts of the map that had slightly higher levels of resource were encountered. Some randomness in a search may lead to greater efficiency of resource acquisition. This result is consistent with theoretical studies of search strategies during foraging (Viswanathan et al. 1999), which suggest random movements increase search efficiency when the desired objective is not in direct sight. Introducing currents had only a minor effect on the search efficiency (Figure 8.2). The probability of detecting "upstream" sites was increased, but potentially better sites perpendicular to the current direction were missed. |
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