Opinions differ whether tail loss in lizards is mainly caused by predators or by intra-specific fighting. Recently this dilemma was investigated through a comparison of lizard tail loss rates between mainland populations in Greece and those on nearby islands harboring fewer predators. The higher tail loss rate on the islands was interpreted as due to the predation-free denser lizard populations having more intra-specific fighting (Itescu et al. 2017, Journal of Animal Ecology 86: 66–74). However, that analysis failed to exclude an alternative hypothesis which I propose and support with well documented circumstantial evidence: The lizards analyzed were Hemidactylus turcicus and Mediodactylus kotschyi (Gekkonidae), both relatively long-lived. On the predator-poor islands they could live longer due to the few predators and thus accumulate the low rate of tail loss. Moreover, both on the mainland and on the islands the tail loss rates are higher in M. kotschyi than in H. turcicus, although life spans are of similar order of magnitude, possibly longer in H. turcicus. But the latter is active at night whereas M. kotschyi is active also in daytime, exposed to more predators during more time. Thus also this inter-specific difference accords with the alternative hypothesis. The two processes are not mutually exclusive and both should be taken into account as potentially responsible for the rate of tail loss in lizards.
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