Anatomy of a RAMP curve

RAMP curves are different for each animal species. These differences are probably related to differing abilities for adaption to stress. Within a species, the RAMP curve is similar or identical among different  animal sizes and stages of ontogeny, assuming that the component reflex responses are developed.  In RAMP, individual reflex actions are scored as present or absent and then combined to express the proportion of reflex actions impaired. The presence-absence scoring factors out the effects of animal size and development. A different way to score would be to measure strength of reflex actions, but this would vary with animal size and would not independently measure vitality. Other ways of scoring for RAMP, which could include injury, will be discussed in a separate post.

RAMP data can be fitted to logistic curves to express the relationship between reflex impairment and delayed mortality.

Restrained Atlantic cod, Humborstad et al. 2009

 Restrained fish, Davis 2009

 Unrestrained fish, Davis 2009

Spot prawn, Stoner 2012

The RAMP curve begins with a control condition of no reflex impairment and no mortality. The left hand curve tail continues at no mortality as reflex impairment increase, i.e., the animal becomes less responsive and more lethargic, in a zone of sublethal stress effects. At the first inflection point, as reflex impairment increase, probability for mortality appears and rapidly increases with small increases in reflex impairment, in a mixed zone of sublethal stress effects and morbidity. Finally, a second inflection point is reached at the right hand curve tail and high probability for mortality is evident at high levels of reflex impairment. The RAMP curves vary among species while maintaining these logistic characteristics.

Tanner crabs and snow crabs, Stoner 2008

A study with crabs, in which injury was also scored, showed a family of RAMP curves that varied over injury intensity for Tanner crabs, but not for snow crabs. For Tanner crabs it is useful to include injury scoring in the RAMP calculations, as reflected in the surface response curve shown.