TESTING FOR ESCALATION ACROSS SPATIAL SCALES DURING THE MIDDLE JURASSIC: DISCORDANT OCCURRENCE AND ABUNDANCE PATTERNS ACROSS LOCAL, REGIONAL, AND GLOBAL SCALES

Biotic interactions are evolutionarily important at the community level, but their effects at larger scales are poorly understood. Here, the escalation hypothesis is tested over local, regional, and global spatial scales to determine if evidence consistent with escalatory interactions occur during the Middle Jurassic, a crucial interval of the Mesozoic marine revolution. Local ecological patterns from the Middle Jurassic (Bajocian to Bathonian) Carmel Formation in east-central Utah, USA are compared with regional and global data from the Paleobiology Database. Because the Carmel Formation is characterized by low biological productivity, it is expected that evidence consistent with escalation should be rare or lacking. Frequency distributions of six escalation-sensitive traits (epifaunal, shallow infaunal, cementing, sessile, facultative mobile, and mobile) were generated, using occurrence and abundance data of species, to test for temporal shifts consistent with escalation.

Results reveal weak support for escalation in Utah (as predicted), with increases in the occurrences and abundance of shallow infaunal, mobile, and sessile species providing the strongest support for escalation; similar trends are also present in global data. Ecological trends vary markedly across spatial scales, with the increase in occurrences of mobile species being the only consistent trend at all three scales. Furthermore, patterns in occurrence data at the global scale conflict with those of abundance data for five of the six traits. The disparities between occurrences and abundance of some of these ecological groups cannot be explained by lags between the appearance of species with certain traits and their proliferation, which would support escalation. This study suggests that while few local ecological patterns are reflected regionally and globally, the conflicting patterns across all scales indicate that local patterns may not be manifested at higher spatial scales, and vice versa. As such, the results do not support a major role for escalation on macroevolutionary patterns across the Bajocian-Bathonian interval stemming from patterns at the local scale.