Competitive Interference between the Puerto Rican Lizards, Anolis cooki and A. cristatellus

Abstract

Anolis cooki and Anolis cristatellus are sympatric lizards engaged in intense interspecific competition. We have identified and analyzed a critical area of competitive interference by measuring various niche dimensions and behavioral interactions under natural conditions. Four study areas of similar habitat composition were established within 5 km of each other: one allopatric for A. cooki, one allopatric for A. cristatellus and two sympatric areas. The variables of cloacal temperatures, perch height, perch diameter and habitat type were compared between lizards in and among the study areas. No significant differences in the variables were found between the sexes of a species or between species on the allopatric areas, nor were there differences between sympatric and allopatric A. cristatellus. Sympatric A. cooki males and females, however, exhibited a significant divergence from their allopatric counterparts by utilizing standing dead vegetation and small bushes rather than larger and more complex microhabitat. This shift was most likely in response to competitive interference from A. cristatellus. Except for sympatric A. cooki, adult males in both the allopatric and sympatric conditions showed a significant and positive correlation between snout-vent lengths and the relative complexity and height of their immediate microhabitat. This suggests that there is intraspecific competition among males, with the larger conspecific males controlling the taller and more complex habitat. Thus when the sympatric male A. cooki occupy small types of microhabitat, they are only likely to encounter the smaller size classes of A. cristatellus males. Intruder-release experiments showed that encounters between male A. cooki and A. cristatellus were very aggressive, similar in intensity to conspecific interactions. Less than one out of two times were resident A. cooki able to evict A. cristatellus intruders of similar size. Thus by occupying smaller habitat types, sympatric A. cooki appears to decrease the likelihood of interacting with large A. cristatellus, against whom they would have little chance of holding a disputed territory. From current evidence, A. cooki is under competitive pressure from the more ubiquitous A. cristatellus and has no apparent refugium.

Evidence for habitat partitioning based on adaptation to environmental light in a pair of sympatric lizard species

“…Moreover, the interspecific differences found in both visual system and signal design appear to be adaptations to the habitat spectral characteristics present at each microhabitat. Previous research suggested that competition between A. cristatellus and A. cooki is responsible for the present distribution of A. cooki (Ortiz & Jenssen 1982;Jenssen et al 1984). However, there is no clear empirical evidence demonstrating competitive exclusion between A. cooki and A. cristatellus in the wild.…”

“…Thus this species pair appears to coexist without clear niche differentiation. Due to the lack of clear evidence supporting niche partitioning, Jenssen et al (1984) proposed that this species pair represents an example of competitive interference, in which A. cooki has been displaced by A. cristatellus to less vegetated, and presumably less optimal, regions of the habitat.…”

Competing for crevices: interspecific conflict influences retreat-site selection in montane lizards

“…Remarkably, however, such interactions have attracted much less study in reptiles, especially squamates (lizards and snakes). Most published research on direct social competition between squamate species has focused on interactions between invading species and native fauna [geckos (Case et al 1994); lacertids (Downes and Bauwens 2002); anoline lizards (Rand 1969;Williams 1969;Jenssen 1973;Pacala and Roughgarden 1982;Jenssen et al 1984;Losos et al 1993;Leal et al 1998)]. In contrast, literature on habitat use in natural assemblages of reptiles has generally focused on the influence of habitat characteristics (including thermal environment and habitat structure), predation risk, and intraspecific territorial interactions (Heatwole 1977;Milton and Hughes 1986;Adolph 1990;M'Closkey et al 1990;Hertz et al 1994;Downes and Shine 1998;Howard and Hailey 1999;Kearney 2002).…”

Uso nocturno de perchas en dos especies de Anolis (Squamata: Polychrotidae) en un bosque Andino de Colombia

“…Diversos trabajos sobre uso de hábitat han demostrado que la segregación espacial parece ser un fenómeno recurrente en especies simpátricas de lagartijas (Jenssen et al, 1984;Reinert, 1984;Rummel & Roughgarden, 1985;Goto & Osborne, 1989). Los estudios que han considerado la percha como el criterio de segregación espacial, han evaluado principalmente el uso de determinadas especies vegetales, pero sus resultados han demostrado que no existen diferencias en su uso.…”

“…Los estudios que han considerado la percha como el criterio de segregación espacial, han evaluado principalmente el uso de determinadas especies vegetales, pero sus resultados han demostrado que no existen diferencias en su uso. Quizás, para las lagartijas es más importante la estructura física de la percha y la potencial protección que ésta pueda brindarles que la especie vegetal en particular (Jenssen et al, 1984;Kattan, 1984;Echeverry, 1996).…”