Symbolism, Imagery, Allegory
Lions, tigers, and bears: oh my! This play is full of beasts; in fact, the word "beast" shows up in this play more than any other Shakespeare play (source).
First, Apemantus notices, "[T]he strain of man's bred out into baboon and monkey" (1.1.254-255). He can't believe that men are no longer courteous to each other; instead, they're acting like animals (baboons and monkeys, to be exact, neither of which are famous for their genteel manners). That's our first clue that there will be loads of beastly imagery in this play.
We know we can always count on Timon for some animalistic imagery. He laments that "the unkindest beast more kinder than mankind" (4.1.36). Sadly, it's true in this play: everyone treats everyone else savagely, and no one really seems to care about anyone but himself. Don't believe us? Take a look at that Senate scene again to see just how savage the Senators are when a guy's life is at stake.
When Apemantus tells Timon "Athens is become a forest of beasts" (4.3.350), we have to wonder where the real wilderness is: outside the city, or inside the city?