The establishment of a territory: Effects of food and competitors on movement patterns in patella caerulea limpets

Foragers which recruit or immigrate into a new area explore it, and thereby gradually establish a home-range or territory. We hypothesized that the rate of area acquisition is determined by the costs of movement relative to its benefits. To test this hypothesis, we explored the movement patterns of Patella caerulea limpets, transplanted onto panels in a fully crossed, replicated laboratory experiment. Experimental treatments were high and low food, high and low limpet density. The limpets gradually increased their home-ranges during the 14 days of experiment. In spite of only few observed aggressive encounters, the home ranges were largely exclusive, hence constitute territories. Territories increased faster at high than at low food densities. At low food densities territories increased faster with high than with low limpet density. Territory formation was slowest in low food-low limpet densities. We propose that the limpets mark territories with mucus trails. When food is abundant, the benefit of foraging is higher than the costs of locomotion and marking, favouring high movement rates and large territories. When food is scarce but competitors are many, limpet movement leads to marking rather than foraging, and they monopolize prospective resources by increasing their territories. When both food is scarce and competitors are few, the reward of either foraging or marking is low, making for slow territory-formation rates. Thus, prospective benefits are involved in the determination of territory-formation rates. Previous studies proposed that the benefit of movement in low-food patches is acquisition of information on food distribution in changing environments. We suggest that an additional benefit lies in the exclusion of competitors for prospective resources.