Which ecosystem would you find this food chain in: leaves, beetle, bat, and boa constrictor?

To identify the ecosystem, we should investigate the range and habitat types of the species listed in the food chain. 'Range' refers to the geographic distribution of the species. Once we have found a place where the range and habitat overlap, we can make some suppositions about the type of ecosystem. 

The most basic division of ecosystems is between terrestrial and aquatic ecosystems. Leaves can be found on land and in water. There are also land and aquatic beetles. Bats are terrestrial. Snakes can be aquatic or terrestrial, but the boa constrictor falls into the latter of the two categories.

So we now know we are looking for a terrestrial ecosystem.

Bats and beetles are found nearly everywhere on earth (except polar areas), so this does not help us narrow down the ecosystem any further. Leaves are present in most places, except very harsh polar or desert areas. 

Thus the range and preferred habitat of the boa constrictor is likely to be our most important clue. The boa constrictor is a snake present in the Americas which resides in a variety of habitats, but prefers rainforests. 

Thus, we can conclude that the food chain described is present in a rainforest ecosystem.