Always On or On Demand

Defense is expensive, so plants split the bill two ways. Constitutive defenses stay switched on all the time — the thorns and stored toxins an attacker meets the moment it arrives. Induced defenses stay dormant until damage is detected, then ramp up fast.

The tradeoff is simple. Always-on protection wastes energy when no one is eating, while on-demand defense saves resources but takes a day or two to kick in. Most plants run both, leaning harder on induced defenses when attacks are rare.