Assumptions for use of RAMP

Loggerhead sea turtle escaping trawl, NOAA

Here is a list of key assumptions for the use of RAMP. The list is probably not exhaustive and can be added to as new perspectives and research warrant. These assumptions have been experimentally tested and validated to various degrees by peer-reviewed published research. Further validation is useful and helps to better define possible error terms in RAMP curves. Healthy, control animals are assumed to have a full complement of reflex actions present. See choices for reflex action testing. 

Vitality is inversely related to reflex impairment. Animal vitality is an abstract concept for which we have strong intuitive notions related to observing absence of injury and presence of behavior, including activity and responsiveness. Reflex actions are fixed response patterns to stimuli that clearly reflect internal state without confounding factors. By using reflex actions to quantitatively measure vitality, the confounding effects of volitional behavior and motivation that are often more related to external conditions can be eliminated. Also animals may not be injured, yet show reflex impairment and reduced vitality associated with other factors (e.g., temperature, exhaustion, hypoxia, and xenobiotics).

Reflex impairment is directly related to stressor types and intensities.  Stressors have been shown to induce reflex impairment, interpreted as symptoms of stress. Therefore reflex impairment is a useful measure of stress. Reflex impairment integrates the effects of stress in whole animal responses that are ecologically meaningful for vitality and fitness outcomes. An impaired animal can have morbidity or decreased predator avoidance, feeding, sheltering, migrating, and reproducing.

Reflex impairment occurs immediately after exposure to stressors. Time course studies for several species have shown immediate impairment after exposure to stressors.  Animals with lower levels of stress can then recover full reflex actions hours to days after exposure to stressors. Reflex actions are sensitive measures of sublethal acute and chronic stress as well as predictors of delayed mortality.    

RAMP curve is different for each species and related to stressor sensitivity. Each species has reflex responses that are evolved for habitat types in which they occur. Differences in reflex types and responsiveness among species are apparent in body types, predator avoidance, habitat choices, and feeding strategies. Some species are easily injured and reflex impaired, while others resist injury or are relatively insensitive to environmental insults (e.g., temperature, hypoxia, and hydrostatic pressure).

RAMP curve used for a species is experimentally derived by inclusion of appropriate types of stressors and animal sizes, ages, and sex. RAMP curves must be derived from reflex impairment observed in animals experimentally exposed to combinations of stressors present in systems of interest. Also animals representing size, age, and sex of interest should be included in impairment experiments. The experiments should result in animals with reflex impairment that ranges from 0 to 100%, with accompanying mortality. The curve must include the complete range of impairment and mortality to avoid extrapolation beyond available data. 

RAMP curve is stable for a species and comprehensive experimentally tested conditions. The stable RAMP curve, with defined conditions of reflex types and testing, can be used among widely different situations for measuring animal vitality, survival, and delayed mortality. Exceptions have been noted for larvae or juveniles with ontogenetically delayed development of reflex actions and spawning anadromous adults which show altered sensitivity to stressors.

Reflex actions in RAMP are given equal weighting rather than weighted differently. Reflex impairment used in a RAMP curve is the result of summing several reflex actions. This approach views the whole animal as the important entity of vitality and fitness. Different reflex actions may be affected by different stressor types. In stressor systems of interest, there are relatively unlimited sets of stressor combinations. Therefore, no a priori expectations of importance for specific reflex actions are made and all measured reflex actions can be equally important. However, the order of reflex action impairment relative to stressor intensity can give valuable information about species sensitivity and associated life history characteristics. 

Observers are assumed to objectively score presence or absence of reflex action in a replicable manner. This assumption is satisfied by using the “rule of doubt”. If any doubt exists about the presence of a reflex action, the action is scored as absent. If the reflex action is present without a doubt, it is scored as present. Further controlled comparisons of reflex scoring among observers is warranted to better define possible observer error terms.

RAMP mortality and survival predictions are dependent on the accuracy of captive holding, tagging, and biotelemetry experiments. To calculate RAMP curves, animals are observed for delayed mortality after initial exposure to experimental stressors. Mortality observed with captive holding is simply related to initial stress, assuming that holding conditions are not stressful.  Mortality observed with tagging or biotelemetry includes sources other than initial stress (e.g., additional stressors, predation, disease, and food limitation)(Thorsteinsson 2002).

Sedna, mother of all sea creatures, K. Sagiatok