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\section{Introduction}  Molecular gas is the hosts of all known star formation in the local and distant Universe. The average properties of the star formation process point to roughly constant star formation rate per unit free fall time \citep[e.g.,][]{Krumholz_2007}. However, there is emerging evidence, particularly dense environments of variations in the molecular gas depletion timescale ($\tau_{\mathrm{dep}} \equiv \Sigma_{\mathrm{H2}}\Sigma_{\mathrm{H2}}$, where $\Sigma_{\mathrm{H2}}$ is the molecular gas surface density and $\Sigma_{\mathrm{H2}}$ is the star formation rate surface density). Recent work in the local \cite{Usero_2015,Bigiel_2015,Pereira_Santaella_2016,Bigiel_2016} and high-redshift \citep{Genzel_2015,Aravena_2016,Scoville_2016} universe point to significant variation in depletion times, converging to the sense that higher density environments have shorter depeletion times. Whether the changes in depletion time reflect a different mode of star formation or acontinuous  variation along a continuum \citep[e.g.,][]{Krumholz_2012} \citep[e.g.,][]{Krumholz_2011}  remains unsettled. Star formation is often parameterized as uniform mass rate of star production, but the organization of the resulting stellar structures also shows significant evolution with star formation rate, and by correlation, with the molecular gas (surface) density. In particular, the fraction of stars formed in bound clusters ($\Gamma$) is seen to correlate with star formation rate \citep{Larsen_2002,Bastian_2008}. The origin of this correlation has been attributed to the evolution of the underlying properties of the molecular (star forming) interstellar medium (ISM)  \begin{itemize}