Many commodities are prices in US dollars. If the Dollar strengthens, then commodities (in non-US countries) will become more expensive. From the consumers' (suppliers') point of view, this should be a move along the demand (supply) curve, not a shift since nothing has inherently changed in their demand or supply of the actual commodity. For a stronger dollar, a consumer will simply demand less.
Then why is it that a strong US dollars is highly correlated with low commodity prices? Is the efficient market adjusting to pre- strong dollar levels?