TESTING THE ASSUMPTION OF NEUTRALITY WITHIN THE LATE CRETACEOUS HOLZ SHALE, SANTA ANA MOUNTAINS, CALIFORNIA

Recent theory suggests that biodiversity is controlled predominantly by species abundance. Hubbell (2001) bases his theory on two assumptions: first, that species are interchangeable (i.e. neutral) and second, that the number of individuals increases linearly with area. The Unified Neutral Theory of Biodiversity (UNTB) is controversial because it contradicts the traditional idea that competition and specialization, such as the ability to exploit specific ecological niches, influence the survival of species. UNTB provides many testable theoretical models that have been tested in the modern record, but its primary assumptions have yet to be extensively tested within the fossil record. The Holz Shale of Silverado Canyon in Irvine, California provides an ideal site to test the assumptions of neutrality and the linear relationship of abundance and area because well-preserved and abundant fossils are exposed in a complete section. The communities present contain more than 100 congeneric species, species belonging to a single genus, with similar life modes and trophic levels. We hypothesize that 1) a linear relationship exists between the number of individuals (i.e., abundance) in a community and area; 2) congeneric species in the fossil record exhibit the same abundance patterns as non-congeneric species, indicating that species are interchangeable or neutral. To test hypothesis #1, fossil faunal specimens will be sampled laterally along a single bedding plane. Three samples will be collected from areas of increasing size: 0.5 m² area, 1.0 m² area, and 1.5 m² area. Each fossil will be counted and identified to the species level by comparison to the Sundberg Fossil Collection at California State University Fullerton and with literary sources. Linear change in abundance patterns between samples will be examined using a statistical technique called “RELATE”. This technique searches for correlations between sample site ordinations. The program PRIMER will be used to calculate the multivariate statistics. To test hypothesis #2: species taxonomic relationships will be determined using the Paleobiology Database and thus congeneric and non-congeneric species will be defined. Rank abundance curves will be generated for all the congeneric and non-congeneric species and compared with one another.