Table 2.

Glossary of widely used terms and concepts in multiple-stressor research; when multiple terms are grouped together we consider them synonyms.

terms/concepts	our definition	source
stressor factor driver	any natural or anthropogenic variable that causes a quantifiable change, irrespective of its direction (increase or decrease), in a biological response. However, many researchers associate the term ‘stressor’ with an anthropogenic variable that has a negative impact	[29]
multiple stressors	two or more co-occurring or sequential stressors	n.a.
combined effect cumulative effect net effect	the aggregate effect of multiple stressors and their interactions	n.a.
stressor interaction	modification of a stressor's intensity or the sensitivity of an organism or ecosystem towards this stressor by another stressor or multiple other stressors. Thus, the term refers to the interaction between stressors in the real world. By contrast, concepts such as the multiplicative null model rely on mathematical interactions that do not necessarily imply interactions in the real world. Not to be confused with biotic interactions among organisms	[27]
additive	when the combined effect of multiple stressors is equal to the sum of their individual effects, i.e. no interaction effect	[8]
antagonistic dampening counteracting	interactions between stressors that result in a lesser combined effect than that predicted by a null model (i.e. an interaction between stressors making their observed net effect less than expected)	[27]
synergistic amplifying	interactions between stressors that result in a greater combined effect than that predicted by a null model (i.e. an interaction between stressors making their observed net effect more than expected)	[27]
reversal	interactions that result in the combined effect of two stressors being opposite in the direction (negative or positive) from that of the sum of their single effects	[5]
null models	a model that predicts the combined effect of multiple stressors assuming the absence of interactions among stressors as defined above. However, some null models contain mathematical interactions to capture stochastic aspects in the action of two stressors, for example the multiplicative null model	[27]
ecological surprises	scenarios where the mechanisms of stressor interactions are not understood and predictions based on null models fail	[51]
discipline	a field of science that is represented by specific journals and conferences and consequently establishes a community of scientists. Disciplines are typically taught and researched separately as part of higher education	n.a.