Data from: Intraspecific competition, not predation, drives lizard tail loss on islands

Tail autotomy is mainly considered an antipredator mechanism. Theory suggests that predation pressure relaxes on islands, subsequently reducing autotomy rates.

Intraspecific aggression, which may also cause tail loss, probably intensifies on islands due to the higher abundance.

We studied whether tail autotomy is mostly affected by predation pressure or by intraspecific competition. We further studied whether predator abundance or predator richness is more important in this context.

To test our predictions, we examined multiple populations of two gecko species: Kotschy's gecko (Mediodactylus kotschyi; mainland and 41 islands) and the Mediterranean house gecko (Hemidactylus turcicus; mainland and 17 islands), and estimated their abundance together with five indices of predation.

In both species, autotomy rates are higher on islands and decline with most predation indices, in contrast with common wisdom, and increase with gecko abundance. In M. kotschyi, tail-loss rates are higher on predator and viper-free islands, but increase with viper abundance.

We suggest that autotomy is not simply, or maybe even mainly, an antipredatory mechanism. Rather, such defence mechanisms are a response to complex direct and indirect biotic interactions and perhaps, in the case of tail autotomy in insular populations, chiefly to intraspecific aggression.

尾部自切（tail autotomy）通常被视为一种反捕食防御机制（antipredator mechanism）。相关理论认为，岛屿上的捕食压力会有所减弱，进而降低尾部自切率。种内攻击（intraspecific aggression）同样可能导致尾部断落，而由于岛屿上种群丰度更高，种内攻击的强度可能会加剧。本研究旨在探讨尾部自切主要受捕食压力还是种内竞争的影响，并进一步明确捕食者丰度（predator abundance）与捕食者丰富度（predator richness）何者在该研究情境中发挥更为关键的作用。为验证研究假设，我们选取两种壁虎的多个种群开展研究：分别为科奇趾虎（Kotschy's gecko，学名Mediodactylus kotschyi，采样覆盖大陆及41个岛屿）与地中海家壁虎（Mediterranean house gecko，学名Hemidactylus turcicus，采样覆盖大陆及17个岛屿），同时估算其种群丰度与五项捕食压力指数。与主流认知相悖的是，两种壁虎的尾部自切率在岛屿上均更高，且随多数捕食压力指数的升高而降低，同时随壁虎种群丰度的提升而上升。在科奇趾虎（M. kotschyi）中，无捕食者与无蝰蛇的岛屿上尾部断落率更高，但该率随蝰蛇丰度的增加而升高。本研究表明，尾部自切并非单纯，甚至可能并非主要的反捕食防御机制。相反，这类防御机制是对复杂直接与间接生物交互作用的响应；而就岛屿种群的尾部自切而言，其主要驱动因素或许是种内攻击行为。