Biodiversity & Disruptions to Ecosystems (College Board AP® Biology)

Sand lances of the genus Ammodytes are small fish that function as keystone organisms in several coastal ecosystems. These sand lances are prey fish that support organisms at higher trophic levels. Scientists performed experiments to examine how sand lance populations are likely to be affected by the rising temperatures and CO₂ levels associated with climate change.

Sand lance embryos typically develop and mature into adult fish at low temperatures (approximately 5^oC) and stable, low CO₂ levels (approximately 400 µatm). Over the course of two years, the scientists measured the survival rate of sand lance embryos allowed to develop and mature in a laboratory at three different temperatures, 5^oC, 7^oC, and 10^oC with the level of CO₂ maintained at 400 µatm, 1,000 µatm, and 2,100 µatm for each temperature.

Describe the effect of increased biodiversity on the resilience of an ecosystem in a changing environment.

Justify the scientists' selecting 5^oC as the lowest temperature and 400 µatm as the lowest CO₂ level in their study of sand lance embryo survival.

State a null hypothesis for the experiment.

The scientists claim that a reduction in the population size of the Ammodytes sand lances will affect the stability of the entire coastal ecosystem. Provide reasoning to support the scientists' claim.

As part of a new suburban development, a sports complex consisting of athletic fields and buildings is constructed in a formerly wooded area.

Predict ONE ecological consequence on the local plant community that is likely to result during the site preparation and construction of the sports complex. Justify your prediction.

To maintain the playing fields, large quantities of water and chemicals are applied regularly to the grass- covered areas. Predict ONE effect on the local animal community that might result from regular use and maintenance of the playing fields. Justify your prediction.

Annual plants complete their life cycle, including germination, seed production, and death, within one year. Ambrosia trifida (giant ragweed) is an annual plant that readily colonizes any land that has had a disturbance such as plowing. The plant is considered an invasive species in regions outside of its native range. In a particular region, the seeds of A. trifida germinate from early March through the end of the summer, while the seeds of other annual plants require warmer soil temperatures and thus germinate from late April through the end of the summer.

Researchers studied the influence of A. trifida on the biodiversity of other annual plant species that grow in the same field. In early spring, the researchers marked off identical plots of land in a field that had been plowed the previous fall and not replanted with new crops. All plants that grew on one half of the plots were left untouched (Figure 1A), while all germinating A. trifida seedlings were removed from the other half of the plots throughout the spring and summer (figure 1B). In late summer, the researchers counted and identified all plants that grew in the plots. The distribution of plants is represented by the symbols in figures 1A and 1B.

Figure 1. Representations of plant identity and distribution in experimental plots in late summer. Each box represents one typical experimental plot, and each symbol represents 10 individual plants.

Describe a cause of logistic growth of the ragweed population.

Based on the representation in Figure 1, explain why the scientists claim that plot B would be more resilient than plot A in response to a sudden environmental change.

In a third group of plots, the researchers removed all seedlings of all plants that germinated before June 1. All plants that germinated after June 1 were left untouched. Using the template in the space provided for your response and the symbols shown in Figure 1, represent the expected plant species that would be found in this third group of plots three months later. Draw no more than 12 symbols. Assume all other environmental conditions are the same as for the initial study described.

Explain how an invasive species such as ragweed affects ecosystem biodiversity, as illustrated in Figure 1.