In this sentence, if you take away "because they have shorter lives", the sentence will sound natural. When you speak/write in English, you can add details in commas to give a little more description to your sentence. For example: Tomatoes are in season and very popular in this country. Tomatoes are in season and, because they are so healthy, are very popular in this country. I hope this helps

It's just makes the two sentences one. You could just say "Such little animals are easy to take care of. Because they have shorter lives, you don't have to take care of them for as long as a dog or cat."

Hello Tomomi "And" is connecting the two part of the sentence together, and providing additional information relating to "the small animals", I hope this helps

'And' is used to join multiple sentances or subjects together. Example: The boy and the girl walked to the shop. In the sentance there it does not read correctly, it works but reads strange; Such little aimals are easy to take care of and because they ahve shorter lives. Could be changed to; Such little animals are easy to care for as they have shorter lives, so you don't have to care for them as long as a dog or cat.