Chemoreception, Odor Landscapes, and Foraging in Ancient Marine LandscapeS
For many organisms, chemoreception is critical for activities such as foraging, the detection of potential mates, and the avoidance of possible predators. The spatial pattern of odors, the odor landscape, is a function of the distribution of the odor sources and of fluid dynamics. Microscopic organisms, and probably most infaunal organisms, are in a physical realm where the detection of distant odor sources is controlled by diffusion and movement that takes place in response to chemical gradients. For larger organisms, chemical detection of distant sources is largely controlled by turbulence and thus by spatially and temporally complex odor plumes.
An individual-based, spatially explicit movement model allows the examination of the importance of contact and distant chemoreception for foraging movements in spatially heterogeneous and patchy environments. Gain curves allow the importance of sensory range in settings of differing degrees of patchiness to be compared. As patchiness increases, distant chemoreception becomes increasingly important for efficient foraging.
Movement patterns within patches are different from those between patches. The spatial distribution of resources, therefore, should be a major control of trace geometry.
During the Ediacaran-Cambrian interval, the spatial complexity and patchiness of the marine odor landscape may have increased due to disruption of Neoproterozoic-style microbially bound substrates and the packaging of biomass into spatially discrete carcasses and fecal pellets. At the same time, larger and non-infaunal mobile bilaterians would have entered a fluid regime dominated by turbulence. These changes may be partially responsible for the evolution of external bilateral sensory organs.
Paleontological Society April 2007