Multiple stressors have mixed effects in an experimental Spartina alterniflora - herbivore system

Rachael E. Blake, Jill A. Olin


     This will say something brilliant about this experiment. 


          Stressors are threatening coastal ecosystems around the globe, yet their simultaneous impacts remain difficult to test and predict because multiple stressors can interact to produce ecologically surprising effects (Paine 1998).  A stressor is a factor that causes a species or population to vary significantly more than expected, with potential adverse effects on organisms or populations (Barrett 1976, Vinebrooke 2004).  Early on, stressors were primarily thought of as anthropogenic, whether chemical pollution, changes in oxygen levels, or physical alteration of habitats.  However, ecologists have recently been realizing that organisms also deal with biological or ecological stressors on a constant basis, such as predation, herbivory, and competition.  These biological stressors need to be studied in concert with anthropogenic or environmental stressors because potential interactions between stressors present some of the biggest uncertainties in understanding and predicting ecological change in coastal systems (Piggott 2015).     

        Stressor interactions are frequently assumed to be synergistic (Whitehead 2013), especially between anthropogenic stressors, and sometimes even between biotic and anthropogenic stressors (Ruiz 1999, Sih 2004).  However, this cannot be assumed to always be the case, and thus we need to test the effects of stressors simultaneously (Crain 2008).  The framework for assessing stressor interactions put forth by Crain et al. (Crain 2008) has been cited and used throughout the literature, including in our study.  However, recent theoretical work has focused on exactly how synergistic or antagonistic stressor interactions are defined operationally and calculated analytically (