[tdwg-content] Abundance

Robert Stevenson Robert.Stevenson at umb.edu
Sun Sep 29 01:54:38 CEST 2013

Some thoughts about usage of some of the terms under discussion and the ultimate goals

I often use the term "abundance" as a refinement of the term "occurrence".

I say  "Species X occurs or does not occur at Location L.  This kind of statement is refined with a statement such as "Females are rare in March" or "Juveniles are common or very abundant in July".  The details of the life stage, timing and numbers of individuals or groups are more specific but still categorical.

I think of such statements as being derived from "expert opinion" or being summary statements based on enumerations from a series of samples taken during several field trips. I think these kinds of generalities are useful for policy making. 

In terms of data, the simplest category is "presence only" data. Some times this is referred to as occurrence data - some number of individuals are seen at a particular time and location. Many museum records fall into this category as there is no other information associated with the specimen.  Such records are equivalent to an incidental sighting by a field ecologist.

Today many biodiversity data are collect following a particular protocol. Here sampling effort is known.  A specific number of individuals seen in a "given area" and during a known time interval. From this information one can compute population densities.  

As several others have commented, the results are dependent on the particular protocols and it can be difficult to reconcile data from two different protocols.  How are data from pitfall traps equivalent to data from baits.....? This is an important challenge because we know that usually one and often two protocols are insufficient to characterize the presence of all members of a taxon 

If I am not mistaken, the goal is to establish terms that will let humans efficiently prepare data and write programs so that machines can reason with the data. If so, the key challenges seem to be 

1) Distinguishing presence-only data from data collected using known protocols 
2) Finding ways to reconcile data from different protocols

Rob Stevenson

Rob Stevenson 
Biology Department 
UMass Boston

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