If you are really worried about the reducing number of your followers or if you want to be alerted if anybody unfollows you on twitter, then you can go for the following:
Follow Goodbyebuddy and it’ll send you a Direct Message when someone unfollows you. Easiest way to know who unfollowed you, no need to signup or register anywhere, just follow Goodbyebuddy on twitter.
Not only Twitter, Nutshell Mail can take care of Facebook and Myspace too. Nutshell Mail is not limited to unfollowers but provides a details information about your profile, it delivers you Saved Searches, Latest Tweets, @Replies, New Followers, Latest Quitters all in a single email. Signup is required, and you can also connect your other Social Network Accounts to it.
Qwitter e-mails you when someone stops following you on Twitter, the good feature which distinguishes Qwitter with others is that it also sends you the last tweet you posted before the user unfollowed you. To signup just enter your Twitter username and the email id where you wish to receive Qwitter emails.