MODERN VARIATION IN PREDATION INTENSITY: CONSTRAINTS ON AND IMPLICATIONS FOR ESCALATION

Escalation, or the evolutionary “arms-race” which produces increased ornamentation and thicker shells in molluscs, has been emphasized as a dominant force in the evolution of life by Vermeij (1987). Drawing from the previous works of Vermeij and Dudley (1982) and Taylor and Taylor (1977), Vermeij (1987) concluded that the frequency of predation increases towards the lower latitudes. Therefore, in response to the increased interplay between predators and prey at increasing lower latitude, escalation should have resulted in more rapid evolutionary rates and potentially greater diversification in tropical habitats. Review of the previous works used by Vermeij (1987) to conclude that tropical fauna evolve "faster and better" produces limited spatial and temporal data points, and the hypothesis needs to be tested. This study tests the hypothesis that predation increases at lower latitude by using bore holes found in mollusks in modern beach deposits as a proxy for predation intensity. These single data points were analyzed along latitudinal, longitudinal, and provincial gradients. In addition, escalation in marine mollusks was examined by measuring and comparing predation at the genus level in single sample populations. Proposed paleoecologic relationships between predator and prey are oftentimes based on data from a single locality (i.e., Vermeij and Dudley, 1982). An analysis of over 50 sampling locations along the coastal plain of the southeastern United States did not provide a significant correlation of spatial position with predation intensity. Predation intensity varied from as 1.82 to 120.56 percent, with a vast majority between 5 to 35 percent. Results of this study imply that predation in marine gastropods are not correlated with latitude, suggesting that either a more complex interplay is at work or that the phenomenon may be random in nature.

Bibliography:

Taylor, J. D. and Taylor, C. N., 1977. Latitudinal distribution of predatory gastropods on the eastern Atlantic shelf. Journal of Biogeography (4): 73-81.

Vermeij, G. J., 1987. Evolution & Escalation, An Ecological History of Life. Princeton University Press, New Jersey.

Vermeij, G. J. and Dudley, E. C., 1982. Shell Repair and Drilling in Some Gastropods from the Ripley Formation (Upper Cretaceous) of the South-eastern U.S.A. Cretaceous Research (3): 397-403.