A demographic approach for predicting population responses to multifactorial stressors

Abstract

Populations face a suite of anthropogenic stressors acting simultaneously, which can combine additively or interact to have complex effects on population persistence. Yet we still know relatively little about the mechanisms underlying population-level responses to multifactorial combinations of stressors because multiple stressor impacts across organisms’ life cycles have not been systematically considered in population models. Specifically, different anthropogenic stressors can have variable effects across an organism’s life cycle, resulting in non-intuitive results for long-term population persistence. For example, synergistic or antagonistic interactions might exacerbate or alleviate the effects of stressors on population dynamics, and different life-history stages or vital rates might contribute unequally to long-term population growth rates. Demographic modeling provides a framework to incorporate individual vital rate responses to multiple stressors into estimates of population growth, which will allow us to make more informed predictions about population-level responses to novel combinations of anthropogenic change. Without integrating stressors' interactive effects across the entire life cycle on population persistence, we may over- or underestimate threats to biodiversity and risk missing conservation management actions that could reduce species’ vulnerability to stress.

The impact of multifactorial stress combination on plants, crops, and ecosystems: how should we prepare for what comes next?

“…While the cause of these reductions is unknown at present, two possible models/scenarios can explain it: (i) A 'cumulative effect' occurs between the same or different low-level impacts of each different stress (that compose the MFSC) on plant physiology, metabolism, and molecular responses, causing an overall reduction in growth, yield, and survival. Thus, while each different stress has a small (similar or different) effect on plant physiology and metabolism when applied individually, when the different stresses are combined during MFSC, their effects are cumulative, and the more stresses combined the stronger the effect will be (Zettlemoyer, 2023;Figure 2b); and (ii) a 'conflicting interaction effect' between different physiological, metabolic, and/or molecular responses during two or more specific stresses (that are part of the MFSC) are dominating the impacts of MFSC and causing an overall reduction in growth and yield, as plants are unable to balance their metabolism and energy flow through the different pathways that should be coordinated (Figure 2c). It is of course highly likely that, under natural conditions, or in the field, a combination of the two scenarios/models outlined above (i.e., conflicting versus cumulative models; Figure 2b) occurs in plants subjected to MFSC.…”