Concept explainers
Peter and Rosemary Grant of Princeton University have studied the ecology and evolution of finches on the Galápagos Islands since the early 1970s. They have shown that finches with large bills (as measured by bill depth; see Figure) can eat both small seeds and large seeds, but finches with small bills can only eat small seeds. In 1977, a severe drought on the island of Daphne Major reduced seed production by plants. After the birds consumed whatever small seeds they found, only large seeds were still available. The resulting food shortage killed a majority of the medium ground finches (Geospizafortis) on Daphne Major; their population plummeted from 751 in 1976 to just 90 in 1978. The Grants’ research also documented a change in the distributions of bill depths in the birds from 1976 to 1978, as illustrated in the graphs to the right. In light of what you now know about the relationship between bill size and food size for these birds, interpret the change illustrated in the graph. What type of natural selection does this example illustrate?
Source: P. R. Grant. 1986. Ecology and Evolution of Darwin’s Finches. Princeton University Press.
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Chapter 21 Solutions
Biology: The Dynamic Science (MindTap Course List)
- Say that you had only the Florida example for the graph. Would it necessarily be true to claim that natural selection was acting on the beak length of the insect when the introduced host plant species became the abundant feeding site? Or could natural selection be acting on a character that is correlated with beak length? Why or why not?arrow_forwardWhich of the following best explains the connection between increased competition and the evolution of a species by natural selection? Individuals migrate to another area in order to avoid competition for limited resources in the current ecosystem. Individuals that have traits that allow them to outcompete others survive better and produce more offspring. Individuals must become stronger to compete for resources, and this increased strength is passed on to the next generation. Individuals that must compete for limited resources are more likely to have diseases that cause mutations.arrow_forwardResearchers have characterized the niches of Darwin’s finches by beak size (which correlates with diet) and the niches of parasitoids by size of caterpillar. How would you characterize the niches of sympatric canid species such as red fox, coyote, and wolf in North America? Or felids, such as ocelots, pumas, and jaguars in South America? What characteristics or environmental features do you think would be useful for representing the niches of desert plants? Or the plants in temperate forest or prairie?arrow_forward
- After the drought of 1977, researchers hypothesized that on the Galapagos Islands’ Daphne Major, medium ground finches with large, deep beaks survived better than those with smaller beaks because they could more easily crack and eat the tough Tribulus cistoides fruits. A tourist company sets up reliable feeding stations with a variety of bird seeds (different types and sizes) so that tourists can get a better look at the finches. Which of these events is now most likely to occur to finch beaks on this island? Why? * Increased variation in beak size and shape over time No answer No change in beak size and shape over time. Evolution of yet larger, deeper beaks over time, until all birds have relatively large, deep beaks. Evolution of smaller, pointier beaks over time, until all birds have relatively small, pointy beaksarrow_forwardThe graph in Figure 3 represents the beak sizes of the offspring of the birds that survived the drought of1977. (The survivors were represented by the black bars in Figure 2, and this graph shows the beak depth distribution of their offspring in 1978.) Explain the observed change in beak characteristics using the following concepts in your answer: competition, survival of the fittest, inheritance.arrow_forwardHow does an individual with a competitive advantage lead to the evolution of an entire species? Individuals that survive due to their competitive advantage are able to expand their range, similar to how the finches radiated out from one common ancestor on the mainland. Traits that are advantageous help certain individuals reproduce at higher rates, so those traits are more common within the population. Some individuals are better at competing for resources, and that allows them to survive droughts or other major ecological events, leading to the extinction of certain species and the survival of others. Those who have traits that help them survive are able to reproduce, and their offspring have those traits, leading to a change in the species over time.arrow_forward
- In crossbill birds the beaks have a specialized shape to allow the crossbills to extract pine seeds out of cones. Crossbills in one forest feed on two different pine species. For one kind of cone a long thin beak is most efficient while in the other type of cone a short thick beak is most efficient. Birds with shapes in between these two shapes are not good at feeding on either type of cones. What evolutionary force is likely happening on beak shape? Group of answer choices A. disruptive (natural) selection B. intersexual selection C. intrasexual selection D. stabilizing (natural) selection E. directional (natural) selectionarrow_forwardOne way to prevent a small population of a plant or animal species from going extinct is to deliberately introduce some individuals from a large population of the same species into the smaller population. In terms of the evolutionary mechanisms discussed in this chapter, what are the potential benefits and drawbacks of transferring individuals from one population to another? Do you think biologists and concerned citizens should take such actions?arrow_forwardTests on wild cheetahs have shown that there is low genetic diversity among individuals. Wildlife biologists and conservationists are worried about what this means for the survival of this species. Why is low genetic variability a big problem when it comes to a species survival in a changing habitat?arrow_forward
- For various reasons, some species prefer to live on the edge of a habitat patch while others fare better if they stay near the middle of a patch. In areas with a mosaic of grassland and woodland, warbler fledglings are more likely to survive when their parents nest in the core rather than the ecotone, because the ecotone is also habitat for brown-headed cowbirds. What is the name for the behavior of cowbirds that poses a risk to warblers? Give typing answer with explanation and conclusionarrow_forwardIf natural selection has no foresight,how can it explain features that seem to prepare organisms for future events? For example, deciduous trees at high latitudes drop their leaves before winter arrives, male birds establish territories before females arrive in the spring, and animals such as squirrels and jays store food as winter approaches.arrow_forwardEVOLUTION LINK Biologists have wondered how introduced species that would probably have limited genetic variation (due to the founder effect) survive and adapt so successfully that they become invasive. Part of the answer may be that invasive species are the result of multiple introductions instead of a single one. Explain how multiple introductions from a species native area to an introduced area could increase that species invasion success.arrow_forward
- Biology: The Dynamic Science (MindTap Course List)BiologyISBN:9781305389892Author:Peter J. Russell, Paul E. Hertz, Beverly McMillanPublisher:Cengage LearningBiology (MindTap Course List)BiologyISBN:9781337392938Author:Eldra Solomon, Charles Martin, Diana W. Martin, Linda R. BergPublisher:Cengage Learning