BIODIVERSITY: STASIS, THE LOG SERIES AND GRADIENTS

Biodiversity stasis exists when stations along a traverse exhibit no change in diversity. For stasis, If N, the number of individuals, is constant at each station , then, S, species richness and H, the information function, will also be constant. Because rare species appear at only one or a few stations, as N and S are accumulated by station, the accumulated total number of species in a traverse will exceed the number at each station. The Log series distribution serves as a null model for this situation. For a Log series S increases with accumulating N at a semi-log rate, but H remains constant. The regression H = β_0H + β_1HlnN expresses the relationship of H with accumulating N where β_0H is a constant and β_1H is the regression coefficient expressing the rate of change between-station (habitat) diversity. At stasis β_1H = 0 and there is no biodiversity gradient. When β_1H is positive S accumulates at a higher rate than for a Log series and there is a positive gradient. Consequently, although two areas may contain the same number of species per station, the area with higher between-station diversity will contain more overall species. We divided the deep-sea into two categories: 200 – 1500 m and > 1500 m. The β_1H coefficient was examined for benthic foraminifera between 333 stations within 49 communities from New Zealand, the South Atlantic Ocean, Gulf of Mexico, Norwegian Sea and the Arctic Ocean. Β_1H-diversity exhibits no evidence of regional differences. Instead, higher values at shallower depths are observed world-wide. At depths > 1500 m the average β_1H is zero, indicating stasis or no biodiversity gradient. This difference in β_1H-diversity explains why, despite species richness often being greater per station at deeper depths, the total number of species is greater at shallower depths. The greater number of communities and higher rate of evolution resulting in shorter species durations at shallower depths is also consistent with higher β_1H values.