Saturday, September 20, 2014

Side-blotch lizard thermoregulation & climate change

Top: A side-blotch lizard. Photo Credit M. Goller. Below 
Thermograms of temperature microhabitats in the overall 
landscape (A–B) and analysis of lizard and environmental
 temperature (C–D). Measurement of lizard average temperature
 (line) and perch temperature (outline) is seen in (C). (D) 
Determination of maximum lizard temperature (box) and 
environmental maximum and minimum from the entire visible 
substrate available to the lizard. Only the rock surface (arrows 
indicate rock outline) was included in environmental analyses.
Ectotherms are well known for using behavioral  thermoregulation  to optimize physiological processes. Thermoregulation is a complex problem because different physiological processes and behaviors achieve performance optima at different temperatures. Lizards usually  thermoregulate by choosing when to be active throughout the day and by shuttling between microhabitats of differing temperatures. Ectotherms usually follow a daily cycle of thermal microhabitat preference. Thus the potential for behavioral thermoregulation is limited by the available thermal niches, and the number of microhabitats available for regulating body temperatures.

In a recently published paper Goller et al. (2014) examined the impact of  habitat structural complexity on thermal microhabitats for thermoregulation using the side-blotch lizard, Uta stansburiana. Thermal microhabitat structure, lizard temperature, and substrate preference were simultaneously evaluated using thermal imaging.  Lizard thermal preference data were collected by measuring environmental and lizard temperatures simultaneously with an infrared camera.  The authors approached a lizard and either filmed at 10 frames/sec or photographed at 0.1 frames/sec for varying lengths of time (minimum of 10–25 min, up to several hours). The environment around the lizard was included in each frame, so that available thermal niches could be assessed.

They found a broad range of microhabitat temperatures was available (mean range of 11°C within 1–2 square meters) while mean lizard temperature was between 36°C and 38°C. Lizards selected sites that differed significantly from the mean environmental temperature, indicating behavioral thermoregulation, and they maintained a temperature significantly above that of their perch (mean difference of 2.6°C). Uta's thermoregulatory potential within a complex thermal microhabitat structure suggests that a warming trend may prove advantageous, rather than detrimental for this population.

A result of climate change will be greater variation and an increase in temperature across the range of Uta stansburiana. Although an increase in several degrees will probably provide a more optimal thermal environment for temperate species, it will also increase the chance of overheating, and rising temperatures may render habitats with less thermal heterogeneity unsuitable for Uta. An increase in temperature may not be detrimental to the study population. Higher thermal microhabitat diversity is important as it may allow behavioral thermoregulation to a preferred temperature in varying temperature conditions. Ability to thermoregulate by moving into shaded microhabitats can be an important buffer of climate change and complex habitats provide shade more reliably.

Goller M, Goller F,  French SS. 2014. A heterogeneous thermal environment enables remarkable behavioral thermoregulation in Uta stansburiana.  Ecology and Evolution 2014; 4(17): 3319–3329.

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