Seasons of Change Activity Worksheet—Disappearing
Marine Iguanas Case Study
Instructions: Complete the lab report below while you explore the impact the events have on the
Marine Iguana population in the Seasons of Change Activity—Disappearing Marine Iguanas Case
Study. You will submit your completed activity worksheet.
(20 points possible)
Part One
1. Using the map and the minimal knowledge that Liz has at this point, propose three different
hypotheses regarding the sudden high mortality of marine iguanas. Post your hypotheses
to the discussion board before proceeding to the next question. (3 points possible)
Hypotheses One: Climate change and temperature increase could be causing
them to die faster because the heat is getting to be too much for them.
Hypotheses Two: Increased tourism and human activity in the area is increasing
pollution and ruining their natural habitat.
Hypotheses Three: Some kind of natural disaster like volcanic activity happened
in the area and their habitat has been damaged.
2. Look at your classmates’ hypotheses on the discussion board. Choose one hypothesis that
seems most likely to you. Provide the student name and hypothesis and tell what evidence
you would need to support (or refute) it.
I think that the most likely hypothesis is Derick Hernandez’s third hypothesis about volcanic
activity, and it can be supported by finding research about volcanic activity in the area and a
chart showing if there has been any and how much. They would also need to find information
on how previous volcanic activity has affected the iguana population.
Part Two
3. Given what you know at this point about marine iguanas and the abiotic effects of ENSO,
develop two possible directions of research that Liz should pursue to understand exactly why
the iguanas suffered such a high mortality. Keep in mind that you need to consider indirect
effects. While environmental temperature does change metabolic rates of ectotherms, the
iguanas are exposed to a wide range of temperatures as they feed and bask on the lava.
Direct mortality in response to a temperature change of a couple of degrees is unlikely. (3
points possible)
Possible Research Direction One: The El Niño climate event caused more
rainfall, which then raised the overall sea level around the island. This increase
caused the algae to now be inaccessible to the hungry iguanas, causing them to
starve and die out.
Possible Research Direction Two: The elevated temperatures caused by the El
Niño climate event caused the iguanas to adsorb more heat, making them more
sluggish and unable to avoid being attacked by predators.
4. Choose one of those directions of research and determine what data you would need to find
to support your ideas.
Data needed to support research direction one would be specific data on rising sea levels in
the Galapagos, and on the algae/ seaweed population during the El Niño event and during
normal years. Calculations relating the correlation between the algae/ seaweed population
and the marine iguana population, and Information on how the algae/seaweed population is
affected by rising sea levels. Lastly, I need data illustrating that the changes in the
algae/seaweed population are correlated to the marine iguana decline and the El Niño event.
5. Design an experiment that would help you collect the data you have identified in question
four. Identify your independent variable(s), dependent variable(s), treatments, and control.
Give a short explanation of how you would test your idea.
Independent variable: Amount of algae available above sea level during the El Niño season.
Dependent variable: Marine Iguana population numbers during the El Niño season.
Treatments: Find data on the marine iguana population during the El Niño season and
compare it to data found on the algae population during this time. Compare this data to
information from years without El Niño events.
Control: Marine Iguana population during normal climate conditions.
I would test my idea by trying to recreate the El Niño events and the iguanas habitat on a
small scale to see how it would affect the algae .
6. What conclusions do you think Liz made about the cause of population declines in marine
iguanas?
The conclusion Liz probably made about the cause of the population declines is that the
ENSO of 1982-1984 severely decreased the population of the green and red algae, which
are the two types of algae that the iguanas prefer and consume most. As a result, the iguana
population also decreases, however, as the algae population rebounds, there is a dramatic
spike in the iguana population. It is therefore very likely that because the green and red
algae were no longer available in the quantities needed to support the increased iguana
population, many starved and died, causing the massive dip in the population. Furthermore,
even those who did eat the brown algae probably didn’t get the same nutritional benefits they
would from the green and red algae because it is not as digestible.
