Making Significant the Significant Portion of Range

The Endangered Species Act provides numerous ways to protect species.  First they can be listed as full species or as subspecies.  Second, two protected classes exist: endangered or threatened.   Third, a species can be listed if it is at risk in either all or a “significant portion of its range.”    On top of this framework, in 1988 Congress added the ability to protect a “distinct population segment” of animals and fish, but not invertebrates or plants.  Since 1996, the U.S. Fish and Wildlife Service and National Marine Fisheries Service (Services) have had a policy in place that created a framework for the use of distinct population segments in listing. (Congress gave direction for that authority to be ‘used sparingly’ and yet the majority of NMFS species are now listed as DPS populations but that is a story for another day.)  The authority to protect distinct populations means that we can list populations that are at risk even if the whole species isn’t.  

Given the DPS authority created in 1988, it becomes very difficult to determine how to use the other authority in the law – that of protecting a species that is only at risk in a ‘significant portion of its range.’  Distinct population authority already allows the agencies to protect a species at risk on just one side of an international border.  In many other cases where a population is at risk, those risks can already be said to jeopardize the species throughout its range so no additional analysis is needed to use this significant portion of range authority.  Indeed, it was rarely if ever used in the process of listing species over 40 years.    

In December 2011, the Services proposed a new policy that would add meaning to the term and allow it to apply in a limited set of circumstances.  First, they appropriately proposed listing the whole species if a significant portion were at risk.  Second, the draft policy allowed for such listings only in a very limited set of circumstances.  

It did this in a couple of ways.  The significance of a population was defined in terms of its contribution to the viability of a species – the ability of the species to persist.  In addition, the test asks whether if the population were to disappear tomorrow, would the species be in danger of extinction?  This is a very specific way to set up an analysis and as a biologist, it’s possible to imagine how to carry out the analysis.  For example, using a technique called Population Viability Analysis (PVA) one could simple run a model to look at extinction risk with and without that population included.  The result is a very narrow set of circumstances in which a species would be listed throughout its whole range because it is at risk in just a portion of the range.  The problem is, it is too narrow.

 

Why?

Surely any species that is in danger of extinction after the presumed disappearance of a significant population would already meet the test of being a threatened species.  It is almost impossible to think of a single realistic scenario where that is not the case.  

Another problem exists with the Services’ proposal for dealing with Distinct Population Segments and Significant Portion of Range.  The Services proposed that whenever a population simultaneously met both the Distinct and the Significant Portion criteria, they would list it as a Distinct Population and not list the whole species (or subspecies).  In any formulation, it should probably be a narrow set of circumstances that result in listing a full species when only a portion is endangered, but this approach is probably short-sighted.  If the full species is imperiled by the hypothetical loss of a population and that population is itself at risk, the Services should provide the entire range of the species.