Reader Comments
Post a new comment on this article
Post Your Discussion Comment
Please follow our guidelines for comments and review our competing interests policy. Comments that do not conform to our guidelines will be promptly removed and the user account disabled. The following must be avoided:
- Remarks that could be interpreted as allegations of misconduct
- Unsupported assertions or statements
- Inflammatory or insulting language
Thank You!
Thank you for taking the time to flag this posting; we review flagged postings on a regular basis.
closeThis term already has a well-known definition
Posted by WardTesta on 01 May 2012 at 20:16 GMT
Corresponding numerical responses characterize absolute prey consumption numbers.
http://plosone.org/article/info:doi/10.1371/journal.pone.0030173#article1.body1.sec3.sec3.p1
The use of the term “numeric response” by Horning and Mellish to mean the number of prey killed as a logical consequence of multiplying the functional response (number of prey killed per predator) by the number of assumed predators is unfortunate. It contradicts the original definition of that term in predator-prey theory (Solomon ME, 1949. The natural control of animal populations. J. Anim Ecol 19:1-35) and in contemporary texts: changes in the growth rate of the predator population as a function of prey numbers. It also belies one of the flaws in that paper and others (e.g., Springer et al. 2003, Sequential megafaunal collapse in the North Pacific Ocean: an ongoing legacy of industrial whaling. Proc Nat Acad Sci 100:12223-12228 and related papers) concerning the possible role of predators, especially transient, or mammal-eating killer whales (Orcinus orca) in the northeast Pacific Ocean: no acknowledgement that a true numeric response of predators to the large declines in their mammalian prey populations might have occurred, as would be expected in most other predator-prey systems. This has taken a crucial element of “dynamics” out of consideration in the discussion about these marine mammal declines. Apart from adding to confusion in the literature, this new definition of “numeric response” obscures the assumption being made by Horning and Mellish of a constant number of predators in the course of an 80% decline in Steller sea lions. Their “numerical response” only rescales the functional response curve, and does not change its form in any way. We have no data on how predator numbers have changed, but from a theoretical perspective we expect predators to respond with negative growth when their prey base declines, even while they might still exert considerable, even magnified pressure on their prey (Holling CS, 1965, The functional response of predators to prey density and its role in mimicry and population regulation. Mem Ent. Soc. Can. 45:1-60; Messier F and Crete M, 1985, Moose-wolf dynamics and the natural regulation of moose populations. Oecologia 65:603-502; Walters et al. 1981, Simulation and optimization models for a wolf-ungulate system in Dynamics of Large Mammal Populations, CW Fowler and T.D. Smith eds, Wiley, NY). It is not a trivial assumption in the present context, because Horning and Mellish build an elaborate framework for predator behavior, sea lion vital rates, and the role of predators in the long-term sea lion decline that is based not on the functional response per se, but on this “numeric response”.