Sex, Age, and Population Density Affect Aggressive Behaviors in Island Lizards Promoting Cannibalism

Abstract

Island populations may evolve distinct behavioral repertoires as a response to the conditions of insular life. Strong intraspecific competition is typical in insular lizards and may include cannibalism. In this study, we investigated sexual and age patterns of aggression in two populations of the Skyros wall lizard (Podarcis gaigeae), one from the main island of Skyros (Aegean Sea, Greece) and another from the satellite islet Diavates. The latter is terrestrial predator‐free biotope, hosting a dense population of large‐bodied lizards that have been reported to exert cannibalism. In staged encounters, we examined the aggressive propensities of adult male and female lizards against their age‐peers and juveniles. Males from both populations were much more aggressive than females toward juveniles and other adults. Males from Diavates were more frequently aggressive to juveniles and other male lizards than males from Skyros. Diavates cannibals also captured their targets at shorter latency. We ascribe this distinct behavioral pattern to the high population density. Infanticide and intramale aggressiveness confer two great advantages to cannibals: food and elimination of future rivals.

The fast‐slow life‐history continuum in insular lizards: a comparison between species with invariant and variable clutch sizes

“…Lower predation pressure is likely to result in increased population density on islands. The resulting higher intraspecific competition and the cannibalistic behaviour towards hatchlings that may ensue could select for larger offspring in order to increase hatchling survival (Case, ; Cooper et al., ; Meiri, ). For species that cannot increase their egg, hatchling or clutch size, i.e.…”

“…in the mostly arboreal anoles and geckos (Andrews & Rand, ; Kratochvil & Kubicka, ), and some of the leg‐reduced fossorial skinks and gymnophthalmids. Under some selection pressures, such as resource limitation and predation (especially by conspecifics), increasing hatchling size may be key to increasing survival (Ashton, ; Cooper, Dimopoulos, & Pafilis, ; Kratochvil & Kubicka, ). Consequently, there is an interplay between the need to produce small or large hatchlings.…”

Feed or fight: testing the impact of food availability and intraspecific aggression on the functional ecology of an island lizard

“…), performance (Pafilis, Foufopoulos & Poulakakis ; Vervust, Grbac & Van Damme ; Pafilis et al . ), and behavioural (Cooper & Pérez‐Mellado ; Cooper, Dimopoulos & Pafilis ) differences relative to mainland populations, and even populations on larger islands (Runemark et al . ; Pafilis et al .…”

A case of limb regeneration in a wild adult Podarcis lilfordi lizard

“…In such conditions, insular Podarcis individuals tend to be aggressive towards conspecifics, particularly adult males towards juveniles, with tail and toe amputation and even cannibalism tending to be common (Castilla and Van Damme, 1996;Cooper et al, 2015). Here we report a case of limb regeneration in one of these microinsular populations.…”

“…Under the insular conditions of the population, with few terrestrial predators and high densities, higher intraspecific competition would be expected (Whittaker and Fernández-Palacios, 2007; for lacertids, see Castilla and Van Damme, 1996;Carretero, 2004;Raia et al, 2010;Cooper et al, 2015). Thus, the amputation of the limb was most likely suffered by the lizard when it was still a juvenile and was likely due to an episode of conspecific aggression, triggered either by dominance behavior or a cannibalism attempt, which has already been recorded in this species (Salvador, 1986).…”