The figure below illustrates the age structure of humans in two different countries, labeled X and Y. Age classes are in 10-year intervals (e.g., 09 = 0-9 years, 1019 = 10-19 years, etc.). Both countries currently have approximately the same total population size. In comparing the populations of countries X and Y, a demographer would predict that the

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To analyze the two age-structure pyramids, I will examine what the width of each age class represents and what that implies about future population trends.

Option 1: "population size of X will continue to decrease, while that of Y will increase to its carrying capacity." This would be expected if X were aging-and-depleting while Y was expanding toward a carrying capacity. However, in the diagram, country X has a broad base (large number of youngsters) and a pyramidal shape indicating a young, growing population. Country Y shows a narrow base with relatively larger numbers in older age groups, indicating limited growth or potential decline, not rapid approach to carrying capacity. Therefore this option mischaracterizes both pyramids.

Option 2: "population size of X is growing logistically, whereas that of Y is growing exponentially." A logistic growth pattern typically applies to a population approaching a carrying capacity with a slowing growth rate, which would be reflected by an S-shaped curve and a less pronounced, not broad, base. The X pyramid does not show signs of rapid saturation; it shows many young individuals suggesting potential for continued growth rather than a near-carrying-capacity approach. The Y pyramid does not reflect classic exponential growth (which would feature broadening at multiple age classes rather than a compressed youth cohort). Thus this option is not supported by the depicted structures.

Option 3: "population size of X will increase, while that of Y will decrease." This aligns with the observed shapes: X has a wide base with many young cohorts (09, 19, 29, etc.), indicating a high proportion of children and potential for rapid population growth in the near future. Y, by contrast, shows relatively fewer young children and a larger share in older age groups, implying slower or negative growth and a tendency to decline as those cohorts age and are not fully replaced. This option correctly interprets the age-structure signals for X increasing and Y decreasing.

Option 4: "per capita death rate is lower in X than it is in Y." Per capita death rate cannot be directly inferred from the shape alone without additional data on age-specific mortality and total births. While the pyramids provide age structure, concluding a lower death rate in X than Y over all ages would require mortality data; the pyramid alone does not justify this statement. Therefore this option is not reliably supported by the given figure.

In summary, the most consistent interpretation of the two pyramids is that country X, with its broad base of young individuals, is set to experience population growth, while country Y, with a relatively narrow base and more top-heavy distribution, is more likely to experience a decline or slower growth. The other options incorrectly apply growth patterns or draw conclusions not warranted by the visual evidence of the age structures.

BIOL 1009 (001-006/050-055) Final Exam

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