In populations of red crossbills (Loxia curvirostra), some individuals have beaks crossing to the right and others have beaks crossing to the left. Birds with left- and right-crossing beaks occur in the population at a proportion of ~1:1.
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Lien L.
Red crossbills (Loxia curvirostra species complex) are small finches specialized for eating seeds pried out of the cones of conifer trees. They fly thousands of kilometers each year in search of productive cone crops. Despite their mobility, crossbills have diverged into several "types" that differ in bill shape, body size, and vocalizations. Each type prefers to feed on a different species of conifer, and each species of conifer is found only in certain forests. Bill size and shape affect how efficiently a bird can open cones of a certain conifer species. Explain how a highly mobile animal such as the red crossbill could have diverged into different types in the absence of any geographic barrier. If crossbills could not fly, do you think speciation would occur more quickly or more slowly? If conifer species were not patchily distributed (i.e., in different forests $),$ do you think crossbill speciation would occur more quickly or more slowly? Compare your answers to the analyses and data presented in Benkman (2003)
Crossbill finches have beaks that overlap with the top beak to the lower beak. Most of the populations have a 50:50 ratio of "right-handed" and "left-handed" beaks, and the handedness of the beaks is thought to be randomly determined, so we see equal numbers of right-beak and left-beak finches. Consider a survey of 140 right beaks and 56 left beaks. What is the two-sided binomial test using the normal distribution to approximate the conclusion? Fail to reject null hypothesis, we lack evidence that the handedness of the beaks is non-random.
Sri K.
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