Vitality, stress, and survival (Update 9/6/2024)

Update from published review paper (validation of impairment method for survival prediction). Presents a useful method for evaluating relationships among stressors, impairment, physiology, and survival. Stressors can be adjusted to increase survival. R.J. Lennox, et. al. 2024. Conservation Physiology 12.

Image: Cleveland Clinic; vitality distinguishes characteristics of survival (heart beat and stroke volume, nerve, muscle, and organ function).

In our efforts to promote health and well-being in ecosystems and their components, we test hypotheses about the causes for impairment by assessing stress resulting from stressors (injury, hypoxia, pressure, xenobiotic, temperature, capture, hunger, fatigue, and disease).  Typically, individual biomarkers (genetic, physiological, and behavioral) are measured and assumed to be correlated with survival.  Vitality is a biomarker that reflects the whole animal condition after stress induction.  Full vitality is characterized by consistently present defined reflex actions and is the constant control for hypothesis testing. Impairment is measured as loss of reflex action traits. The relationship between reflex impairment and survival is weighted by sequence of impairment.  Sensitive reflex actions are impaired by low levels of stressors (sublethal).  More resistant reflex actions become impaired at higher levels of stressors (lethal). 

    
Vitality can be a subjective score for animal condition based on observation of injury, activity, and reflex action impairment.  These vitality scores are correlated with survival and delayed mortality; where size and taxa sensitivity to stressors interact to control impairment.  Levels of vitality can be indicated by condition class impairment; excellent, fair, poor, moribund, based on evaluation of activity and injury (Benoît et al. 2015, Morfin et al. 2017).   

A vitality heuristic based on trait classes of injury and reflex impairment (see tables) can be correlated with survival and delayed mortality. The index replicate is calculated as the number of impaired classes / total number of classes (ranges from 0 to 1).  This index is a combination of individual injury types and reflex actions with differing statistical distributions. As such it cannot supply a precise parametric estimate for vitality described above.  Instead the index is a summary expression (see below) of whole animal reactivity and impairment that is useful for rapid in-situ determination of stress levels and adjustment of experimental conditions for hypothesis testing (Brownscombe et al. 2017, Meeremans, et al. 2017).