No abstract

Central-place foragers need to explore their immediate habitat in order to reach food. We let colonies of the individually foraging desert ant Cataglyphis niger search for a food reward in a maze. We did so for three tests per day over two successive days and an additional test after a time interval of 4–20 days (seven tests in total). We examined whether the colonies reached the food reward faster, consumed more food and changed the number of workers searching over time, within and between days. Colonies’ food-discovery time shortened within and between days, indicating that some workers learnt and became more efficient in moving through the maze. Such workers, however, also forgot and deteriorated in their food-discovery time, leveling off back to initial performance after about two weeks. We used mazes of increasing complexity levels, differing in the potential number of wrong turns. The number of workers searching increased with colony size. Food-discovery time also increased with colony size in complex mazes but not in simple ones, perhaps due to the more frequent interactions among workers in large colonies having to move through narrow routes. Finally, the motivation to solve the maze was probably not only the food reward, because food consumption did not change over time.

Carrying capacity has multiple definitions, but nowadays, it is mainly referred to as the maximum number of individuals of a particular species sustained by the environment. We examined whether multiple populations of two flour beetle species grown under controlled laboratory conditions reach similar asymptotic population sizes when provided with similar amounts of food resources. We demonstrate that the variation in the asymptotic population sizes was considerably larger than that of the initial food resources and that the latter had no significant effect on the former. Our results experimentally contribute to past literature criticizing the carrying capacity concept, demonstrating that there is no single carrying capacity even under strict laboratory conditions. Therefore, we should not expect to often find “carrying capacities” in nature, where resources fluctuate over time, and interspecific interactions are ubiquitous. We suggest that the classic meaning of carrying capacity should be revisited or saved chiefly for didactic purposes.