- Given your familiarity with the extinctions and subsequent radiations of the cartilaginous fishes, what do you believe would happen to the abundance and diversity of the sharks, rays, and chimaeras if the climate warms in the future? (Kimley, P. 2013).
Radiation refers to divergence from an ancestral animal (in this case Chondrichthyes) into a variety of new forms. In this case, evolution is a process of radiation not progression. Radiational evolution can be exhibited as related to external forces rather than internal forces.
On a rudimentary level, the role of mass extinction in evolution can reduce diversity by killing off specific lineages. In turn, any species that may have been produced. On the other hand, a mass extinction can impact evolution in an opposing way, stimulating growth to other branches that may not have had an opportunistic ability to thrive previously. Therefore, on a granular scale, extinction, or singular extinction, or a smaller scale extinction can have a chain reaction as well, impacting and upsetting the current ecosystem of that given time period. What once may have been a marine keystone species of cartilaginous fish, may now be of the past, giving rise to predecessor who may have a slightly different diet, creating an imbalance in that current ecosystem.
As far as evolutionary radiation and an increase in climates are concerned, rising temperatures have an adverse effect on biodiversity and can cause small scale extinctions and mass extinctions. Perhaps a rise in temperature yields an algae bloom, subsequently suffocating a small species of fish, that happens to make up the majority of our keystone species diet. The result is another ecosystem upset and imbalance that may or may not recover. Most marine ecosystems can be easily unbalanced or upset by the slightest rise in temperature. In 2017 the Texas Flower Gardens incurred a mass coral bleaching event after a rise in temperature of between +3-8 degrees of its highest threshold, and it only took a matter of weeks (Piccitto, R. 2019).
In conclusion, based on past data and events, as the climate warms, the abundance of Chondrichthyes will fade away. We will start to notice varieties of species and sub-species will have a smaller range than previously, and we will see less of these species within their ranges. A shark that was previously of least concern may drop to a threatened status. Sensitive species will disappear, and the most hearty and resilient ones will survive, and either flourish, or will be at risk depending on the result of its dietary sources. Coupled with environment degradation and fishing (legal, illegal, commercial, sport), we may see drastic changes over a short period of time. The results could be shocking.