Gradualism
Based on research and information, I concluded that the type of speciation that Struthioniformes follow is gradualism. They evolved slowly and continuously, without any sudden transitions, over a long period of time. The fossil record shows proof of these gradual changes by the lack of major, drastic changes between time periods. There are no sudden abruptions of species that appeared out of no where. Present day struthioniformes still have some similar traits to those of their ancestral origins.
Type of Evolution
Over time, Struthioniformes evolved by divergent evolution. Divergent evolution is when different species evolve from a common ancestor and accumulate changes that differentiates them from one another. These species have individualized themselves due to the process of natural selection and its environmental pressures. With the evidence of embryology, anatomy and physiology, chromosome analysis, and the fossil record, all struthioniformes can be traced back to a common ancestor from which they all descended from.
Evolutionary Mechanisms
Immigration and Emigration
Immigration and emigration does impact the genetic migration of species, such as ostriches and emus, in the Order Struthioniformes. Ostriches live in flocks that typically contain 10 birds. However, multiple flocks sometimes gather together to form a larger group, which helps them in defense and noticing danger. This along with straggling males that come and go between flocks during breeding season contributes to the gene flow. When the flocks regroup and males travels around to breed, there is a mix in the population, resulting in new and different alleles being presented into the flocks to be passed down to future offspring.
Although emus are often found in pairs, they can band together to form enormous flocks that migrate for necessities, such as food and water. During this long travel, emus can split from the group to create smaller flocks and mix up the possible mating options. Furthermore, female emus wander off after laying 5 to 15 eggs and leave incubating the eggs to the male. The female may find another male to mate with during this time or even find a different nest to lay her eggs and let that father do the incubating. These intermixing of organisms also mixes the genes and alleles within the gene pool.
Geographic Isolation
Geographic isolation played a large role in the evolution of struthioniformes and flightless birds. Struthioniformes descended from an ancestral bird that could fly; however, it is suggested that they lost their ability to fly due to becoming geographically isolated from their main predators. In a habitat isolated from predators, flight would have been unnecessary and struthioniformes would pass on more favorable traits like strong, swift legs. Being geographically isolated is a theory believed to have resulted in struthioniformes becoming flightless.
Furthermore, ratites have continued to differentiate into many subspecies due to geographic isolation. Ostriches are native to Africa in the savanna biome, kiwis are common in New Zealand and typically inhabits regions of grasslands and swampy forests, and emus are mainly found in Australia where there are grasslands and savannah forests. As islands rose and tectonic plates shifted, continents that were once together split apart, resulting in species becoming geographically isolated. The habitats changed as an effect of the moving plates and the species of struthioniformes had to adapt to their own unique environmental changes, successfully forming new subspecies in the process.
Order Struthioniformes 