Table 1. Definition and connection of commonly used terms in this paper.

Term	Definition
Impact	Impact is the proportion of the population parameter (in this study, growth rate and carrying capacity) that is reduced by the threat. This is sometimes investigated in experimental studies
Joint impact	Joint impact is the combined impact that two threats have on one of the population parameters.
Damage (D)	Damage is the change in the population equilibrium that is caused by one or more threats. A change in equilibrium population size is what is often approximated in long-term observational studies.
Joint damage (D1,2)	Joint damage is the reduction in population equilibrium size that can be measure after two threats have occurred.
Additivity index	The additivity index gives a characteristic of the joint damage in relation to the damages caused by a single threat. It ranges from -1 to 1 and can be categories as additivity types: superadditive (−1≤A<0), additive (A = 0) or subadditive (0<A≤1).