Territoriality evidenced by asymmetric intruder-holder motivation in an amblypygid

Territoriality has an extensive and thorough history of research, but has been difficult to impossible to test empirically in most species. We offer a method for testing for territoriality by measuring the motivation of territory intruders to win contests in controlled trials. We demonstrated this approach by staging paired trials of the Amblypygi Phrynus longipes (Chelicerata: Arachnida). Amblypygids engaged in agonistic interactions after the opportunity to establish a putative territory on one side of an arena. We found that intruders of putative territories had lower motivation to win contests, thus evidencing territoriality. Physical components of individuals (i.e. energy stores) increased the probability of winning the contest for holders but not intruders, thereby providing insight into the differing decision rules opponents use in territory contests. We discuss why alternative hypotheses, including loser-initiator covariation and home field bourgeois advantage, fail empirical tests. We demonstrated that analyzing animal motivation in territorial contests is tractable even for animals where territories are inconspicuous and cues are outside the normal perceptions of researchers.