USING BIOPHYSICAL ECOLOGY TO PREDICT OVERLAP IN ACTIVITY PERIODS OF MOUNTAIN ANDEAN sympatric LIZARDS

AGUILAR, ROCÍO; KEARNEY, MICHAEL RAY

Congreso; IX Congreso Argentino de Herpetología; 2013

Lizards often rely on thermoregulatory behaviour to maintain physiologically optimal body temperatures in thermally heterogeneous environments. The effectiveness of this behaviour depends on the microclimates available in a species? habitat, and on how microhabitat use is conditioned by interspecific interactions. Closely related species occupying the same habitat might be expected to have different thermal niches, such that overlap in the use of space and time is reduced. We integrated physiological measurements of thermal biology and thermal tolerance with a biophysical modelling system (Niche Mapper) to assess the extent of thermal niche overlap between two species of high mountain lizards, Phymaturus roigorum and Phymaturus payuniae, in Payunia Nature Reserve, Mendoza, Argentina. We studied lizards from two sites, one where only P.roigorum occurs and another where, P.roigorum is sympatric with P.payuniae. Thermal gradient studies show that P. roigorum has higher thermal preferenda than P. payuniae in allopatry (30.5 ±3.2ºC and 28.7 ±1.9 ºC, respectively), and an even higher preferenda when it occurs in sympatry (35±3.5 ºC). Calculations of potential body temperatures and activity periods were made using Niche Mapper, with measured thermal preferences and a global climatic database as inputs. These analyses showed that environments where P. roigorum occurs in allopatry impose a more pronounced bimodal activity pattern than do environments where it lives in sympatry with P. payuniae. The environment of P. roigorum in allopatry also permits a greater annual activity time. Overlap of activity time is evident for the species living in sympatry mostly between 10:00 to 17:00 h, which represents more than 75% of total activity exhibited by P. payuniae. The model predicts that P. payuniae is active earlier in the morning and during colder months than sympatric P. roigorum, whose thermal thresholds for activity are considerably higher. These data are consistent with the hypothesis that coexistence among these closely related species has been facilitated by thermal niche shifts.