Taxonomic diversity gradients through geological time

first_imgThere is evidence from the fossil record to suggest that latitudinal gradients in taxonomic diversity may be time-invariant features, although almost certainly not on the same scale as that seen at the present day. It is now apparent that both latitudinal and longitudinal gradients increased dramatically in strength through the Cenozoic era (i.e. the last 65 my) to become more pronounced today than at any time in the geological past. Present-day taxonomic diversity gradients, in both the marine and terrestrial realms, are underpinned by the tropical radiations of a comparatively small number of species-rich clades. Quite why these particular taxa proliferated through the Cenozoic is uncertain, but it could be that at least part of the explanation involves the phenomenon of evolutionary escalation. This is, in essence, a theory of biological diversification through evolutionary feedback mechanisms between predators and prey; first one develops an adaptive advantage, and then the other. However, there may also have been some form of extrinsic control on the process of tropical diversification, and this was most likely centred on the phenomenon of global climate change. This is especially so over the last 15 my Various Late Cenozoic (Neogene) vicariant events effectively partitioned the tropics into a series of high diversity centres, or foci. It has been suggested that, in the largest of these in the marine realm (the Indo-West Pacific or IWP centre), a critical patterns of islands acted as a template for rapid speciation during glacioeustatic sea level cycles. The same process occurred in the Atlantic, Caribbean and East Pacific (ACEP) centre, though on a lesser scale. Tropical terrestrial diversity may also have been promoted by rapid range expansions and contractions in concert with glacial cycles (a modified refugium hypothesis). We are beginning to appreciate that an integrated sequence of Neogene tectonic and climatic events greatly influenced the formation of contemporary taxonomic diversity patterns.last_img read more

USS James E. Williams Transfers Mariners to Iranian Vessel in Gulf of Oman

first_img View post tag: Mariners Guided-missile destroyer USS James E. Williams transferred 10 Iranian mariners rescued from a burning dhow Aug. 8 to an Iranian vessel in the Gulf of Oman Aug. 10.Members of Williams’ visit, board, search and seizure (VBSS) team transferred the mariners from the destroyer to an Iranian-flagged dhow for repatriation.Williams (DDG 95) rescued the 10 mariners in the Gulf of Oman after they were forced to abandon their burning vessel.Following the rescue, the mariners were taken to Williams, where they received initial medical treatment for injuries sustained during the fire and subsequent evacuation.They were then transported to aircraft carrier USS Enterprise (CVN 65) for further medical treatment before being returned to Williams for today’s repatriation.The cause of the fire is under investigation.James E. Williams is currently deployed as part of the Enterprise Carrier Strike Group to the U.S. 5th Fleet area of responsibility conducting maritime security operations and theater security cooperation efforts.[mappress]Naval Today Staff, August 14, 2012; Image: US Navy View post tag: Transfers View post tag: James August 14, 2012 View post tag: € View post tag: Williams Training & Education View post tag: Iranian View post tag: Oman View post tag: USS View post tag: vessel View post tag: News by topic View post tag: Naval USS James E. Williams Transfers Mariners to Iranian Vessel in Gulf of Oman View post tag: Navy View post tag: Gulf Back to overview,Home naval-today USS James E. Williams Transfers Mariners to Iranian Vessel in Gulf of Oman Share this articlelast_img read more