Applying Economic Principles to Other Studies I was recently reading this article about some research that was done concerning the illegal killing of elephants.  There were two quotes that caught my attention: 


  ...illegal killing [of the elephants] increased markedly after 2008 and was correlated strongly with the local black market ivory price and increased seizures of ivory destined for China...


and 


  ...Illegal killing rates were strongly correlated with black market ivory prices in the Samburu ecosystem...


In the article, the correlation is treated as a previously unknown fact that was "discovered" by the research team and appears to be one of the major finds of the study.  

However, it does not seem like the researchers can take credit for this "discovery."  It seems that an economist can reach the same conclusion by a much simpler method: 


Increased seizures of ivory reduce the supply of ivory on the market.  
Since the supply of ivory has decreased and the demand has remained constant, the price of ivory will increase.  
The higher price will motivate individuals to enter the ivory market as suppliers (which, therefore, will lead to more elephants being killed).  


Is there a particluar reason as to why the economic principles of supply and demand were not applied to this study in order to more rapidly reach this result?
This paper seems to be about practical policy. It seeks to understand what drives the killing of elephants. While what you write makes sense in theory, there might be some hidden factor that we do not perceive that has a much bigger effect (for example the actors of the market may not be rational) so looking at the data is always welcome.

I would also say that your economic reasoning is not the only possible one. I could also provide a line of reasoning reverses causality 


More elephants are killed (this may be random, or it may be a result of unemployment in other sectors).
Because demand is unchanged, prices fall. 
Since authorities always seize half of the ivory contraband, more contraband is seized.


If this is true then the seizures and the price change is a result, implying a different market dynamic. Unfortunately the paper only tested correlation, not causality, but this highlights that there can be more than one explanation to a phenomenon. In fact it is even possible to argue that the price of ivory and the number of elephants killed is negatively correlated:


More elephants are killed (this may be random, or it may be a result of unemployment in other sectors). 
The authorities, who until now looked the other way, notice this and start seizing ivory, leaving almost none on the market. 
The price of ivory rises.


Which of these explanations you find logical is somewhat subjective. Because there can more than one, a logical explanation may not be the right one. That is why econometric papers (could) provide useful insights.