A new study may have solved the mystery of why Alaskan horses, hidden sea turtles and island lizards have shrunk in size over time. New theoretical research proposes that changes in animal size over time depend on two key ecological factors: the intensity of direct competition between species for resources and the risk of environmental extinction. Research has revealed a key factor behind changes in body size over time in some animals, with findings about how species change in size that challenge traditional theories of evolution.
Research results and ecological factors
The study, published today (Thursday, January 18) in the journal Communications Biology, used computer models that simulated evolution to find out why some species gradually became smaller in the fossil record.
Dr Shovonlal Roy, an expert in ecosystem modeling at the University of Reading, who led the study, said: "Our study shows that animals can become larger or smaller over time depending on their habitat or environment. In places and times where there is a lot of competition between different species for food and shelter, animals tend to become smaller as species spread out and adapt to the distribution of resources and competitors. For example, due to climate and vegetation Ponies living in Alaska during the Ice Age rapidly shrank in size as a result of changes in vegetation. Where there was less direct competition, animals tended to become larger, although large size and small numbers make animals more vulnerable to extinction - as was the case with the dinosaurs. "Changes in ecological factors help explain why the fossil record shows such a confusing mix of evolutionary patterns in body size, with some strains shrinking over time and others expanding."
The team conducted their research by questioning the contradiction between fossil evidence and "popular science rules." The popular science rule refers to the tendency of certain groups of animals to become larger over the course of tens or even millions of years of evolution. The law is named after 19th-century paleontologist Edward Cope, who is believed to be the first to discover it in the fossil record. For example, the ancestors of early horses were puppy-sized animals that gradually increased in size over evolutionary time, eventually forming the modern horse.
However, the fossil evidence shows apparently contradictory trends, with some groups increasing in size and others shrinking.
evolutionary pressure
The study used computer models to simulate evolution and identified three distinct patterns of body size changes that occur under different conditions:
Gradual increase in body size over time: This occurs when competition between species is determined primarily by relative body size rather than niche differences. For example, several genera of marine animal species, such as invertebrates, have gradually increased in size over millions of years.
Increased size is followed by extinction: in this case, the largest animals often die out, providing the opportunity for other species to take their place, evolve larger bodies, and the cycle continues. Mass extinctions hit large apex predators hardest. Very large mammals and birds, such as dinosaurs and giant flying reptiles, are particularly vulnerable to extinction.
Size reduction over time: The simulations also predicted the opposite of popular science's rule: species shrinking over time. This occurs when competition is intense and there is some degree of overlap in habitat and resource use. As species evolve into different ecological niches, they face evolutionary pressure to shrink in size. Reductions in body size have been reported in vertebrates, bony fishes, cryptoturtles, Alaskan Pleistocene horses, and island lizards.
Compiled source: ScitechDaily