Competitive exclusion between insular Lacerta species (Sauria, Lacertidae)

Abstract

Competetive exclusion between Lacerta sicula and L. melisellensis characterizes the small islands of the Adriatic Sea.In 1958 and 1959 M. Radovanovié introduced Lacerta sicula or Lacerta melisellensis onto islands exclusively occupied by the other species. During the summer of 1971 follow-up observations were made on three of these islands, two of which completely lacked representatives of the introduced species. On the third island, the introduced species appears to be replacing the native form. Minor habitat differences permit coexistence, however the situation is dynamic and probably not at equilibrium. A reciprocal introduction involving the two species on the islands of Pod Kopiŝte and Pod Mrĉaru is announced.

Digit ratios in two lacertid lizards: sexual dimorphism and morphological and physiological correlates

“…Apparently, ecological selection pressures may override the developmental programme in some squamate groups. It seems unlikely, however, that ecological divergence is responsible for the differences in digit ratio observed in our study species, because Podarcis siculus and P. melisellensis resemble each other in almost every aspect of their ecology, including microhabitat use (Radovanovic 1959;Nevo et al 1972;Arnold 1987).…”

“…The two species occupy similar semi-open habitats (often stone walls or rocks surrounded by grassy vegetation and maquis) in the Mediterranean. This ecological similitude has been held responsible for the fact that on the smaller islands, almost invariably only one of both species is found (competitive exclusion hypothesis, Nevo et al 1972). Geographical and experimental evidence suggests that the more 'timid' endemic P. melisellensis is expelled from islands on which the more 'assertive' P. siculus gets a foothold (Radovanovic 1959;Vervust et al 2007).…”

Competition theory, evolution, and the concept of an ecological niche

“…The consequences of competition may include microhabit divergence (as in some pairs of flatworm (Planaria) species; Beauchamp and Ullyatt, 1932), or habitat shift (as in many related bird (Lack, 1971) and reptile (Schoener, 1977) species), competitive exclusion producing differentiation of geographic distribution (as in the Lactera lizard species studied by Nevo et aL, 1972), adaptive radiation (as in Darwin's finches: Lack, 1971;Grant, 1981), range restriction (as in several coexisting species of shorebirds that have similar diets but forage at different distances from shore; Cody, 1973a), ecological variation via polymorphism (as in many cases of sexual dimorphism; Selander, 1966), or the displacement (as in character displacement) or compression (see Christiansen and Fenchel, 1977;MacArthur, 1972) of econiches. Furthermore, increasing competition (either intraspecific or interspecific), insofar as it is density dependent, will tend to shift life-history strategies towards K selection (a strategy of producing offspring of high competitive ability [fitness] on the r-K continuum; in the (idealized) case of completely density independent population control in which there is no competition, r-selection (i.e., maximization of r, the intrinsic rate of natural increase) will be favored (MacArthur and Wilson, 1967;McNaughton, 1975;Pianka, 1970).…”

Genetic data reveal a multiple origin for the populations of the Italian wall lizardPodarcis sicula(Squamata: Lacertidae) introduced in the Iberian Peninsula and Balearic islands

“…Experimental results have demonstrated behavioural interference with P. melisellensis (Downes & Bauwens 2002), which has gone extinct after introduction of P. sicula in Adriatic islets (Nevo et al 1972). Furthermore, hybridization between P. sicula and other Podarcis species has been demonstrated by means of genetic data at least with the endemic Podarcis of Sardinia (P. tiliguerta, Capula 2002), of the Aeolian islands (P. raffonei, Capula et al 2002) and of Sicily (P. wagleriana, Capula 1993).…”