Now we make our way back to reviewing a new question for AP Environmental Science. The AP exams are approximately a month away, therefore practice is essential for your success. AP Environmental Science is one of those subjects that require you to know a lot of information, so the more often you see a question, the more likely you will see that concept or even question pop on on the day of the exam. For extra review, we previously covered a review of a question dealing with methane gas generation in landfills. That being said, let's look at another questions below:
A battery manufacturing plant accidentally leached cadmium into a local lake. Ecologists sampled various species from the lake and determined the cadmium concentration in the tissues of each organism. The data are shown below
Which species is most likely the second-order consumer?
The following answer choices for this question are:
- Species C
- Species E
- Species D
- Species B
- Species A
The answer to this question is Species C. This question evaluates your knowledge of biomagnification (aka bioaccumulation) within the foodchain. The concept of biomagnification states that any concentration of a pollutant introduced into an ecosystem scales as it moves up the food chain, meaning that the highest order consumer will contain the highest concentration of that pollutant within it's tissue.
The way we can determine the order of the consumers is by reordering the Cadmium concentration for each species from lowest to highest like so:
- Species B = 10 mg/kg
- Species E = 20mg/kg
- Species C = 30 mg/kg
- Species D = 65 mg/kg
- Species A =100 mg/kg
Seeing this list, you automatically think that Species E is the answer because it's ranked number 2. False! Remember that the question asks for the second-order consumer. In the biomagnification model, the species with the lowest concentration (Species B) is assumed to be the producer (not consumers) of the ecosystem. As the next level up the food chain consumes the producers, known as the first-order consumer, the concentration increases, which is the case with Species E. The second-order consumer is assumed to consume the lower level species as you move up the food chain, therefore having the next highest concentration in it's tissure. With Species C having the next highest concentration in its tissue, it must be the second-order consumer.
If we were to change the question and ask which species is most likely to be the final-order consumer, what would the answer be? If you answered Species A, then you are correct. Since Species A has the highest concentration of Cd in their tissue, it must be the highest predator in the food chain and will be the highest order consumer.
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Image Source: http://sustainable-nano.com/2013/12/17/the-cautionary-tale-of-ddt-biomagnification-bioaccumulation-and-research-motivation/