Where are all my monsters and animals?

I have noticed that I have close to no monsters or animals spawning on my server.
Could someone please help me increase the spawn rate?
These are my plugins (incase one decreases them):
AfkKick.jar
AlphaChest.jar
CFBanner.jar
ChatManager.jar
CommandBook.jar
CraftBukkitUpToDate.jar
HeroicDeath.jar
Honeypot.jar
JSONAPI.jar
LagMeter.jar
LogBlock.jar
LogBlockQuestioner.jar
LWC.jar
mcbans.jar
mcMMO.jar
MinecraftRKitPlugin.jar
MobArena.jar
Multiverse-Core.jar
Multiverse-Portals.jar
NoCheat.jar
OpenInv.jar
Permissions.jar
PermissionsEx.jar
playerScan.jar
proofBan.jar
rawcritics_ore_obfuscation_plugin_spout.jar
SimpleSkylands.jar
SkylandsPlus.jar
Spout.jar
SpyerAdmin.jar
SpyerAdminCommands.jar
WorldBorder.jar
WorldEdit.jar
WorldGuard.jar

 

You could get a plugin that lets you set the permission for animals spawning, and then increase it, but I do not think that any of those plugins decrease them, as I have most of the same permissions on my server.