The effects of meal size and feeding frequency on digestion in common wall lizards (Podarcis muralis)

Understanding the interplay between feeding, energetics and temperature in ectotherms is essential, particularly regarding introduced species and responses to climate change. Despite its importance, how feeding regimes - including meal timing and size - affect digestion has been underexplored. Previous research suggests that digestion is thermally dependent, with warm temperatures promoting quick digestion, and that consuming smaller meals results in slower digestion. However, empirical evidence is limited. Our study quantified digestive passage time, energy budgets, and fecal and urate production in the introduced common wall lizard (Podarcis muralis) relative to meal size and timing under a naturalistic temperature cycle (warm days at 34°C and cool nights at 25°C). We implemented four treatment groups based on meal size (large or small) and timing (morning only or morning and afternoon). While lizards consuming less food took significantly longer to completely pass food items, energy budgets and fecal and urate production did not differ among treatments. Our findings suggest that feeding regime may have some influence on digestive processes, but not to the extent of regulating energetics in the common wall lizard. Consistent energy budgets, despite variable meal sizes and timing of food consumption in relation to temperature, may contribute to wall lizard invasion success. Digestive processes play a critical role in regulating population persistence and expansion. The results of this study highlight the importance of quantifying feeding regimes and natural temperature cycles, with implications for invasion biology and predicting responses to climate change.