1. The graph below shows how a population changes over time.

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1 1. The graph below shows how a population changes over time. Based on the graph, which statement best explains how the population is changing? (A) The population is growing at a constant rate because it is not restricted by limiting factors. This answer suggests the student understands that population growth tends to involve slight fluctuations, that the population is increasing at a relatively constant rate, and that the population does not appear to be affected by limiting factors. (B) The population is growing at an increasing rate because it is not experiencing densitydependent limiting factors. This answer suggests the student may understand that populations typically experience initial exponential growth due to abundant resources and that the population is growing, but does not understand that population growth tends to involve slight fluctuations, and that the graphical data do not show an increasing (exponential) rate of population growth. (C) The population is growing at a decreasing rate, and it will reach equilibrium at about 120 individuals due to the effects of limiting factors. This answer suggests the student may understand that populations typically reach carrying capacity due to density-dependent limiting factors, but does not understand that population growth tends to involve slight fluctuations, and that the slope of the graph is not flattening out to indicate that the population is reaching equilibrium (carrying capacity). Page 1 of 8

2 (D) The population is growing at a constant rate, but density-independent factors are preventing the population from reaching its carrying capacity of 120 individuals. This answer suggests the student may understand that the graph shows fairly constant growth, but does not understand that population growth tends to involve slight fluctuations, that density-independent factors are not limiting growth, or that the carrying capacity is not 120 individuals. 2. The graph below shows how a population changed over time. Which statement best explains the data? (A) The population experienced exponential growth due to unlimited resources, and then experienced a decrease in growth due to a change in limiting factors that reduced the death rate. This answer suggests the student may understand that a population will experience exponential growth when no limiting factors are present, but may not understand that this population experienced limiting factors that resulted in a logistical growth curve and that the limiting factors increased the death rate until the population reached the carrying capacity for the environment. (B) The population experienced logistical growth due to density-dependent factors, and then decreased because it exceeded the carrying capacity of the environment. Page 2 of 8

3 This answer suggests the student understands that the population experienced logistical growth due to density-dependent factors that prevented the population from being stable beyond a certain size, and that once the population exceeded the certain size (carrying capacity), the population declined due to density-dependent factors, such as the competition for limited resources in the environment causing reduced birth rates and increased death rates. (C) The population experienced exponential growth due to density-independent factors, and then decreased due to the immigration of a competitive species to the same area. This answer suggests the student may understand that density-independent factors will maximize reproduction and may lead to exponential growth, but may not understand that the population experienced limiting factors and that once the population exceeded the carrying capacity of the environment, the population decreased due to competition for resources among individuals within the species. (D) The population experienced logistical growth due to pressures from competition, and then decreased because of a disease in the dense population. This answer suggests the student may understand that the population follows a logistical growth pattern, which may be caused by increasing competition for resources, but may not understand that a disease would likely cause only a temporary decrease in a population and the population should increase to reach carrying capacity once survivors begin reproducing. Page 3 of 8

4 3. The graph below shows the population of Asian carp in each of three equal-sized ponds over a 20-month period. Based on the graph, which statement best explains the differences in the carp populations in the three pond communities? (A) The carp populations in all three ponds have reached carrying capacity; pond 1 has the largest carrying capacity, pond 2 has a smaller carrying capacity than pond 1, and pond 3 has the smallest carrying capacity. This answer suggests the student may understand that introduced populations often reach their carrying capacity after a time period, but does not understand that the graph does not show any pond reaching carrying capacity. (B) Pond 1 has the most species that compete with the carp for food, pond 2 has fewer competing species than pond 1, and pond 3 has the least number of competing species. This answer suggests the student may understand that competition with other species for resources will slow the growth rate of a population, but does not understand that the population growth rate in pond 1 is highest, so it would have the least competition, and pond 3 would have the most competition. (C) Pond 1 has the fewest producers, pond 2 has more producers than pond 1, and pond 3 has the most producers of the three ponds. Page 4 of 8

5 This answer suggests the student may understand that the number of producers in a community will affect the biotic potential, but does not understand that since pond 1 has the greatest carp population, it likely has the greatest number of producers, and pond 3, with the lowest carp population, likely has the least number of producers. (D) Limiting factors are affecting the carp populations in all three ponds; pond 1 has the fewest limiting factors, pond 2 has fewer limiting factors than pond 3, and pond 3 has the most limiting factors. This answer suggests the student understands that the carp populations in the ponds have not reached carrying capacity, as evidenced by the shapes of the lines on the graph; however, many limiting factors (e.g., competition, space, available free energy, predation) are affecting population growth in each pond and accounting for the differences in the rates/curves of population growth among the ponds. 4. The table below shows the species richness (total number of species) and the relative abundance of each species (total number of organisms in a species) found in a rocky intertidal community. Which statement best predicts and explains how the species diversity of the community will be affected if the population of purple sea urchins increases to 50 and the other populations remain the same? Page 5 of 8

6 (A) Species diversity will decrease because the species richness will decrease if sea urchins become the dominant species. This answer suggests the student may understand that there is a positive correlation between species richness and diversity, but does not understand that the relative abundance of sea urchins will increase, not species richness (there are still five species). (B) Species diversity will increase because the total number of organisms in the community will increase. This answer suggests the student may understand that the total number of organisms in a community can affect species diversity, but does not understand that species richness will not change (there are still five species), that the relative abundance for four of the five species will decrease as the sea urchin population increases, and that the species diversity of the community will decrease. (C) Species diversity will decrease because the relative abundance of sea urchins will increase compared to that of other species. This answer suggests the student understands that as the relative abundance of sea urchins increases, the species diversity in the community will decrease because the community is becoming dominated by sea urchins and the relative abundance of each species, except for sea urchins, will decrease. (D) Species diversity will increase because the species richness of the community will increase. This answer suggests the student may understand that there is a positive correlation between species richness and species diversity, but does not understand that species richness will not change (there are still five species), or that species diversity will decrease due to an increase in relative abundance of sea urchins. Page 6 of 8

7 5. The graph below shows the birth and death rates for a human population over time. Which statement best describes how this human population changed over time? (A) The birth and death rates for the population decreased over time, which caused the overall population size to decrease, and the smaller population stabilized when birth and death rates equalized. This answer suggests the student understands that a declining birth rate and a declining death rate may indicate a decrease in the overall population size, but may not understand that the birth rate was higher than the death rate, which caused the population to increase (but at a declining rate) and then the population decreased slightly before it stabilized when the birth rates and death rates were equal. (B) The death rate decreased faster than the birth rate, which caused the population to increase in size, but then the death rate exceeded the birth rate, which caused the population growth rate to stabilize at a slower rate. This answer suggests the student understands that a population will increase when the death rate is less than the birth rate, but may not understand that when the death rate exceeds the birth rate, the population growth is negative (it decreases in size) rather than increasing at a slower rate of growth, or that the population will remain stable in size if the birth and death rates are equal. (C) The birth and death rates for the population both decreased over time, which caused the growth rate of the population to increase over time and the overall population size to increase at a stable rate. Page 7 of 8

8 This answer suggests the student may understand that the birth rate and the death rate decreased over time, but may not understand that the population will not experience growth if the birth rate and the death rate are equal. (D) The birth rate decreased more slowly than the death rate, which caused the population to increase at a decreasing rate, then the population decreased slightly before the birth rates and death rates equalized and the population stabilized. This answer suggests the student understands that the population increased, but at a declining rate, when the birth rate was higher than the death rate, that the population decreased slightly when the death rate exceeded the birth rate, and that the population stabilized when the birth rate and death rate were equal. Page 8 of 8