ABSTRACT
Many organisms live in advective media, defined as media possessing either a net unidirectional flow or a complex velocity field with local unidirectional flow due to
features such as vortices. Examples include drifting macroinvertebrates in rivers and streams, marine organisms whose larvae are dispersed in local longshore currents, and plants with wind or waterborne seeds. If the directional bias in dispersal is strong, the theory underpinning many fundamental questions in population ecology may no longer hold, or at least requires careful re-interpretation. Our aim in this essay is to review recent developments concerning population dynamics in advective media, with particular focus on two issues: conditions for population persistence and biotic responses to abiotic forcing. Although we hope that the new theory will have broad applicability, our primary emphasis is on population dynamics in rivers and streams.
We pay particular attention to the interrelationship between processes operating at multiple spatial and temporal scales. Establishing such links empirically is commonly impossible, even with large quantities of data and sophisticated statistical approaches (Diehl et al. 2008). Our essay rests on the premises that determining the underlying ecological mechanisms is an essential prerequisite to understanding these links, and that simple mathematical models can help elucidate the broader implications of mechanisms found to occur at one particular scale in space or time.
