Animals have to make strategic decisions when foraging, especially when they are very hungry. One of these decisions includes choosing between predictable (less risky) and unpredictable (more risky) sources of food, especially if the latter promises greater reward. A recent study led by Maria Thaker, Professor at the Centre for Ecological Sciences (CES), Indian Institute of Science (IISc), shows that when some reptiles are starving, they take greater risks to achieve greater food rewards.
The idea that animals are able to evaluate the predictability and quantity of food sources, and make decisions based on how hungry they are is the essence of the “risk-sensitive foraging hypothesis”. According to this hypothesis, when animals have a choice between a constant food source (which provides a fixed amount) and a variable food source (which provides potentially higher amounts), animals prefer the constant food option when their energy levels are high (less hunger), and the variable option when their energy levels are low (more hunger). Scientists have tested this behaviour in birds and mammals earlier, but not in reptiles.
“Reptiles can slow down their metabolism a lot. So, in food-scarce times like winter, they go into torpor (hibernation) to avoid starving to death,” explains Thaker. “In the tropics, however, reptiles are exposed to warm temperatures all year round and cannot slow their metabolism down enough to get through tough (food lean) times. We expected that lizards in the tropics should have evolved the ability to assess food options, because if they don’t, they may risk starving to death.”
In the current study, the researchers focused on tropical lizards called rock agamas (Psammophilus dorsalis). These lizards are also city-dwellers, found in and around urban areas like Bengaluru.
The team manipulated the energy levels of these lizards by either keeping them well-fed or starving for 48 hours. Then, they provided both sets of lizards with two food options to choose from: a constant reward of two mealworms or a variable reward of either zero or four mealworms.
“We found that well-fed lizards played it safe, opting for the guaranteed two mealworms option,” says Avik Banerjee, PhD student at CES and co-author of the paper. “On the other hand, starved lizards took greater risks, frequently choosing the variable option which has the potential to get them four mealworms. Remarkably, both groups of lizards ended up with similar net food gains by the end of the trials, indicating that the different strategies worked.”
The study provides new understanding on how tropical lizards could adjust their foraging behaviour based on food resource uncertainty. For reptiles in the tropics, where it is warm and energy demands are high all year around, this flexible approach could be key to thriving in unpredictable conditions.
“We think that humans have an excellent ability to assess our environment and take calculated risks when needed. But lizards can too,” says Thaker. “The fact that the rock agamas can remember different options and make appropriate choices to secure their survival is rather cool. We are surrounded by very clever and calculating animals.”
