When sister species live together, Tegu lizards in Argentina

Two Tegus, Salvator merianae and S. rufescens JCM
When two closely related species live side by side it is generally assumed that they have some way of dividing the resources so that they are not in direct competition with each other. The large terrestrial lizards the Black and White Tegu, Tupinambis (=Salavator) merianae, and the Red Tegu, T. (=Salvator) rufescens provide a model system to examine the role of life history factors in trophic niche divergence because they share several bioecological traits. They have similar body sizes and share external morphology and generalized foraging habits. Phylogenetic studies suggest the two species are sisters. In Argentina, they occur in parallel allopatric zones from approximately 10–40°S. Tupinambis rufescens occurs further west than T. merianae. However, they both occupy a large contact zone. These species differ in habitat requirements in allopatric areas, but in the contact zone the species use the same landscape and habitat resources. Moreover, T. merianae and T. rufescens select landscapes with a large proportion of forest and shrubs than the mean landscape availability in contact zones.
In a new paper López Juri et al. (2015) evaluate the trophic niche segregation between merianae and rufescens in a contact zone to understand how life history traits (body size, sexual body size dimorphism, sexual maturity and reproductive activity) might influence the feeding ecology of these lizards and lead to trophic niche differentiation between species. Their results suggest that, although both species are omnivorous, they exhibit a tendency to specialize, with arthropods being dominant in the diet of merianae and fruits and seeds being dominate in the diet of rufescens. The two species have broad trophic overlap, however, while both species share several prey items, the relative importance of each item varied between them. These differences may be important for niche segregation, mainly because the prey items considered fundamental were different between species, suggesting a differential use of certain resources. T. merianae is often associated with anthropogenic areas with cultural vegetation and remnant shrub lands where few vertebrate species remain which may explain the low diversity of food items and the dominance of arthropods and some rodents in the diet composition. Their results indicate that body size, sexual maturity and reproductive activity are relevant factors influencing the diet of these species. Life history traits of these two species of Tupinambis are important because they shape diet composition, contributing to interspecific segregation of the trophic niche and, therefore, allowing species coexistence.

López Juri G, Naretto S, Mateos AC, Chiaraviglio M, Cardozo G. 2015. Influence of life history traits on trophic niche segregation between two similar sympatric Tupinambislizards. South American Journal of Herpetology, 10(2): 132–142.

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