Animals in the wild constantly face choices about where to find their next meal. Sometimes, the safest option is not always the most rewarding. Picture a gecko in your room with two potential food sources: a small snack of spiders in the corner of the room and another big feast that requires it to venture out into danger. Which one would it choose? According to a hypothesis, the answer depends on how hungry they are.
According to the ‘risk-sensitive foraging hypothesis’, well-fed animals preferred the safe bet, which was a constant but smaller food reward. But when they are starved, they become risk-takers, opting for the chance of a larger, though less certain, meal. In short, satiated animals were risk-averse, while starved ones were risk-prone. Researchers at the Indian Institute of Science (IISc) set out to test this hypothesis by studying how rock agamas (Psammophilus dorsalis) make foraging decisions. Although birds and mammals have been shown to behave this way earlier, the same has not been reported in reptiles yet.
“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. 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,” explains Maria Thaker, a professor at the Center for Ecological Sciences at IISc.
The researchers captured adult lizards from rocky habitats in Karnataka and housed them in individual glass terrariums with controlled temperature and light cycles. To conduct the experiment, the researchers split the lizards into two groups: a 'satiated' group that was fed daily and a 'starved' group that experienced a 48-hour starvation period between feeding opportunities.
The lizards then went through a training phase where they learned to associate the colour of a Petri dish with a specific food reward. One colour (assigned randomly) always contained two mealworms (the constant reward), while the other colour contained either zero or four mealworms (the variable reward). The colours of the dishes were gradually made more opaque. This ensured that the lizards chose the dishes depending on the colour they were presented with instead of the visual cues of the food.
To test the hypothesis, the lizards were presented with a choice between the two coloured dishes. The researchers recorded which dish the lizard approached first, indicating its foraging choice. By analysing the lizards' choices, the researchers were able to determine whether the lizards preferred the constant or variable food option based on their energetic state (satiated or starved).
Their study confirmed the hypothesis that
“well-fed lizards played it safe, opting for the guaranteed two mealworms option. On the other hand, starved lizards took greater risks, frequently choosing the variable option, which has the potential to get them four mealworms.” says Avik Banerjee, PhD student at CES and co-author of the paper. “Remarkably, both groups of lizards ended up with similar net food gains by the end of the trials, indicating that the different strategies worked.” He adds.
This behaviour suggests that animals don't just focus on the average amount of food available. They also consider the variability and predictability of their options. When an animal is well fed (positive energy budget), it can afford to be picky and avoid risk. Choosing a constant food source ensures a steady supply of energy, minimising the chance of starvation. However, when an animal is starving (negative energy budget), it needs to take a chance on the variable food source, even if it means risking going hungry because the potential payoff of a large meal could be the difference between life and death.
Optimal foraging models suggest that animals will forage in a way that maximises the net rate of energy gain from a food source. The energy budget rule provides an explanation for risk-sensitive foraging, where animals at a positive energy budget are risk averse while those at a negative energy budget are risk prone.
By understanding how these animals weigh risks and rewards, we can gain a deeper appreciation for the challenges they face in the wild and the strategies they use to survive.
“We think that humans have an excellent ability to assess our environment and take calculated risks when needed. But lizards can too! 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.” concludes Prof Thaker.
Based on a Press Release from Indian Institute of Science