In the early days of highway development, they could follow the landscape, that is, along the edges of rivers or forests. But today, highways are omnipresent, and animal populations that could have wandered freely, such as wolves and bears, have been fragmented. Compared with large animal populations, smaller animal populations are more volatile in number and more prone to mischief. What is this passage about? ['Trends in road development.', 'Impact of roads on animals.', 'Changes in animal survival.', 'The different fate of different animals.']