Spell-Like Ability vs Concentration Check

[ckdragons]

Forgive me as I'm not able to find this in the current Pathfinder rules. Is a Concentration check required for spell-like abilities? Such as, when in a threatened square in comat, taking damage, or grappled? If this is required for spell-like ability, why is the modifier omitted on statistic blocks where it is listed in the block when the creature is a regular spell caster (i.e. wizard, cleric, etc.)? Just confused. Thanks.

[SlimGauge]

Using a spell-like ability is a standard action that provokes (Table 8-2 Actions In Combat).

From Page 186 of the core rules

Spell-Like Abilities (Sp): Using a spell-like ability works like casting a spell in that it requires concentration and provokes attacks of opportunity. Spell-like abilities can be disrupted. If your concentration is broken, the attempt to use the ability fails, but the attempt counts as if you had used the ability. The casting time of a spell-like ability is 1 standard action, unless the ability description notes otherwise.

Using a Spell-Like Ability on the Defensive: You may attempt to use a spell-like ability on the defensive, just as with casting a spell. If the concentration check (DC 15 + double the spell’s level) fails, you can’t use the ability, but the attempt counts as if you had used the ability.

[Grick]

Linkified: Spell-Like Abilities (Sp) in the Combat chapter.