Iguanas get used to their environment and weather. They were a large number of size and their feeding was good; All this changed when "el nino" appeared...
When "el nino" appeared it got warm and the plants were starting to dry up this was affecting affect the Iguanas
Then the Iguanas began to die because the environment changed and their sizes got smaller "el nino" began to change Iguanas and their environment
You ask me "How can my species become resistant to antibiotics over time?"
Thank to those antibiotics which acts the role of selection.