Final answer:
Low competition between species is the least likely factor to increase the probability of speciation by adaptive radiation because it doesn't provide the environmental pressures that are necessary for rapid adaptation and differentiation in new ecological niches.
Step-by-step explanation:
The factor that is least likely to increase the probability of speciation by adaptive radiation is (c) Low competition between species. Adaptive radiation typically occurs when a single species or a small group of species evolves into several different forms that live in different ways. This is facilitated by factors such as the availability of diverse ecological niches, rapid environmental changes that create new opportunities for adaptation, and high reproductive isolation between populations, which prevents gene flow between them. Low competition, on the other hand, does not provide the pressure necessary for species to differentiate and adapt rapidly to new niches, making it the least likely factor to contribute to speciation in this context.
Another aspect contributing to speciation is allopatric speciation, which is more likely to occur quickly with (b) longer distances between divided groups, as geographic separation reduces gene flow and enables populations to diverge genetically. Necessary components for punctuated equilibrium, a pattern of speciation where there are long periods of stability interrupted by rapid evolutionary change, would include a division in populations and a change in environmental conditions; however, a stable and unchanging environment would be least likely associated with this mode of speciation. Genetic variation is crucial for speciation and can arise from mutations and sexual reproduction, which are two primary sources of genetic variation.