HL Paper 3
The worm Branchiobdella italica lives on the external surface of the freshwater crayfish Austropotamobius pallipes. A study was carried out in a river in central Liguria, north-western Italy, of the range of sizes of B. italica found on adult A. pallipes.
Describe the body length frequency of the B. italica worms collected in this study.
The relationship between A. pallipes and B. italica is mutualistic.
A. pallipes feeds on algae and another worm, B. exodonta, lives inside A. pallipes as a parasite. State the trophic level of B. exodonta in this food chain.
Distinguish between mutualism and parasitism, providing another example of mutualism and another example of parasitism.
Forest fires are very common in the Amazon forest. A study was performed to see the relationship between forest fragmentation, fire and management
Describe one method that could have been used to estimate the population size of a given tree in a forest after fire damage had occurred.
Outline how the edge effect can affect diversity in forests.
The number of plants in two fields of approximately the same size was counted.
Compare and contrast the richness and the evenness of the two fields.
An investigation into food web interactions was conducted in mesocosms in the Mediterranean Sea, off the coast of France. The effects of the addition of soil and fish on bacterial populations were tested.
Each of the mesocosms is an open ecosystem. State the property that makes the mesocosms open ecosystems.
Assuming that the populations of bacteria are under bottom-up control, identify the mesocosms in which the bacterial populations will be highest.
Outline top-down effects on the bacteria in the four mesocosms.
Suggest advantages of undertaking this experiment in the sea rather than in the laboratory.
Cryptococcus neoformans and the closely related species Cryptococcus gattii are human fungal pathogens. The reproduction of these yeast species on increasing concentrations of pigeon droppings (PD) was examined to determine whether they occupy the same or different ecological niches. The results for reproduction are expressed as a percentage relative to the control.
Suggest how this experiment shows that pigeon droppings represent a realized ecological niche for C. neoformans and a fundamental (but not a realized) niche for C. gattii.
State two bottom-up factors affecting algal blooms.
Explain how top-down factors control algal blooms.
The sketched map shows the density of microplastics and macroplastics found in a lake within a national park.
Predict one example of macroplastic pollution that is likely to be found in this lake.
State two possible effects on organisms of microplastic pollution.
Outline the effect of wind on the distribution of plastic pollution in this lake.
Suggest changes in the management of the national park that could reduce the amount of macroplastic pollution.
Zoos devote much effort to preserving and breeding elephants in captivity. Data for births resulting from artificial insemination in zoos in the United States from 1960 to 2012 are shown below.
54% of successful artificial inseminations have resulted in miscarriages, stillborn births or premature deaths.
Evaluate the success rate of breeding elephants by artificial insemination using these data.
Discuss two advantages of ex situ conservation measures.
State the two components needed to calculate the biodiversity of an area.
The predominant source of phosphorus is rock containing phosphate (phosphate rock). The graph below shows the world production between 1900 and 2009.
Some scientists estimate that available phosphorus reserves in the Earth will be completely depleted within approximately 100 years. Discuss the implications of these estimates.
The percentage of phosphorus in an ecosystem that is recycled per year is in most cases very small, and far smaller than the percentage of nitrogen that is recycled. Suggest reasons for this difference.
Define indicator species.
Indicator species may be affected by biomagnification. Discuss biomagnification using a named example of a pollutant.
Determine whether islands are open or closed ecosystems.
Most reef-building corals contain photosynthetic algae, called Zooxanthellae, that live in their cells. Coral bleaching can occur as a result of human-induced changes leading to the Zooxanthellae being ejected from the coral.
State the type of interaction that occurs between Zooxanthellae and reef-building corals.
State the trophic level of Zooxanthellae.
When coral is bleached, certain organisms become more common in the ecosystem such as the cnidarian Gorgonia, the echinoderm Diadema, other algae and certain sponges. State the term that is used for organisms whose presence provides evidence of the existence of a particular environmental condition.
A coat of algae builds up on coral reefs as a consequence of eutrophication. Explain the relationship between eutrophication and algal growth.
Explain how an excessive growth of algae on coral reefs can be controlled by top-down factors.
Sea urchins (Strongylocentrotus) are echinoderms that consume large quantities of algae. Sea otters (Enhydra lutris) feed on sea urchins.
The graphs show the biomass of sea urchins in an area of 0.25ām2 plotted against their size. Data were collected in two Aleutian Islands, Amchitka and Shemya. In Amchitka the sea otter population is high while at Shemya there are no sea otters.
[Source: From Estes, J.A. and Palmisano, J.F., 1974. Sea Otters: Their Role in Structuring Nearshore Communities. Science,
185(4156), pp.1058ā1060.16. DOI: 10.1126/science.185.4156.1058, https://science.sciencemag.org/content/185/4156/1058.
Reprinted with permission from AAAS. Readers may view, browse, and/or download material for temporary copying purposes
only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further
reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or in part, without prior
written permission from the publisher.]
Outline a method that could have been used in this study to measure the numbers of sea urchins per 0.25ām2.
Sea otters are considered keystone species in this environment. Suggest how the presence of sea otters could affect the algae population.
Sea urchins are destroying the giant kelp alga (Macrocystis pyrifera) marine forests of South East Australia. Suggest a reason that sea urchins might be an invasive species in this environment.
Define fundamental niche.
Outline a reason for organisms seldom occupying their entire fundamental niche.
Describe the relationship between Zooxanthellae and reef-building coral species.
The elimination of wolves (Canis lupus) from Yellowstone National Park in 1926 and their reintroduction in 1995 provided the opportunity to examine ecological interactions with elk (Cervus elaphus). The National Park Service made efforts between the 1920s and 1968 to reduce the size of elk herds by culling (selective killing) because of concerns about overgrazing.
The graphs provide the trends for the numbers of wolves and elk in Yellowstone National Park from 1900 to 2004.
[Source: Ripple, W.J. and Beschta, R.L., 2004. Wolves and the Ecology of Fear: Can Predation Risk Structure Ecosystems?
BioScience, 54(8), pp.755ā766 by permission of Oxford University Press on behalf of the American Institute of Biological
Sciences. Translated and reprinted by permission of Oxford University Press on behalf of the American Institute of Biological
Sciences. Please visit: https://academic.oup.com/bioscience/article/54/8/755/238242.]
Outline the changes in elk population between the years 1930 and 2004.
List two biotic factors, other than wolf predation or culling, that could affect the elk population.
1.
2.
Wild turkeys (Meleagris gallopavo) once inhabited most forested areas of North America. As an important food source for early European settlers, the population of M. gallopavo seriously decreased. Due to recent conservation efforts, population numbers are increasing.
[Source: https://commons.wikimedia.org/wiki/File:A_wild_turkey_in_Middleboro,_Massachusetts.jpg]
![https://commons.wikimedia.org/wiki/File:A_wild_turkey_in_Middleboro,_Massachusetts.jpg]](https://commons.wikimedia.org/wiki/File:A_wild_turkey_in_Middleboro,_Massachusetts.jpg]){kind=link}
The curve shows a population of M. gallopavo from 2000 to 2015 in Ohio in the mid-western USA.
State the range of years when exponential growth of the M. gallopavo population occurred.
Suggest factors that could account for the growth curve of the M. gallopavo population.
State how the population of M. gallopavo may have been determined.
Hunting of M. gallopavo is currently regulated. Predict what would happen if the hunting regulations were removed.
Suggest how nitrogen and phosphate cycles can be disrupted by humans or extreme weather events.
The graph shows a theoretical model that divides species into five ecological groups (I to V) related to the degree of tolerance to an increasing pollution gradient.
[Reprinted from Marine Pollution Bulletin, 40, A. Borja, J. Franco and V. Perez, 'A marine biotic index to establish the ecological quality of soft-bottom benthos within European estuarine and coastal environments', pp. 1100ā1114, Copyright (2000), with permission from Elsevier. https://www.sciencedirect.com/journal/marine-pollution-bulletin]
The biotic index is calculated using the formula shown.
BI=Ī£(niĆai)N
Identify the group that is most intolerant to pollution.
Deduce the meaning of ni in this formula.
Deduce the meaning of ai in this formula.
Outline how organisms in Group V could be used to measure pollution in an environment.
To assess the impact of introduced cats (Felis silvestris) that prey on native species, a study was carried out on 120 islands around the world. The graph shows the impact of F. silvestris on reptiles, birds and mammals.
[Source: A global review of the impacts of invasive cats on island endangered vertebrates, F. M. Medina et al. (2011) Global Change Biology, 17, pp. 3503ā3510. Reproduced with permission from John Wiley and Sons.]
The āUaāu petrel (Pterodroma sandwichensis) is considered to be an indicator species in the Hawaiian Islands.
[Source: https://commons.wikimedia.org/wiki/File:Oestrelata_phaeopygia_AvesHawaiienses00Wils_0382.jpg]
Identify how the pattern in mammals is different from reptiles and birds.
Describe how invasive species such as F. silvestris can have a significant impact on native species.
Suggest a method to limit the impact of F. silvestris on native species.
State the role of an indicator species.
Identify possible approaches to maintain the population of P. sandwichensis.
Outline three issues arising from the release of pollutants into the environment.
The pie chart shows the world demand for phosphorus in 2010. The fraction used as detergents and in industries has decreased in recent years in response to evidence that phosphate pollution of surface waters causes eutrophication.
Describe reasons that the availability of phosphates may become limiting to agriculture in the future.
Explain how eutrophication can occur from the excessive use of phosphates.
Explain how an ecological community structure could be affected by the removal of a keystone species.
A retreating glacier leaves an environment of lifeless glacial deposits, including sands and gravels. Retreating glaciers often offer suitable sites for primary succession.
State one abiotic factor that will determine the type of ecosystem in a succession.
A retreating glacier leaves an environment of lifeless glacial deposits, including sands and gravels. Retreating glaciers often offer suitable sites for primary succession.
Predict the process of succession that takes place on exposed bare ground as the glacier retreats.
Compare and contrast food chains and food webs.
Discuss the factors affecting population growth that can result in an exponential growth curve.
Distinguish between tropical rainforest and taiga in terms of nutrient stores, nutrient flows and climate. Gersmehl diagrams can be used to support your answer.
A type of ecosystem in Brazil is tropical rainforest. Construct a Gersmehl diagram on the outline provided, to show flows of nutrients between stores in tropical rainforests.
Discuss how crop plants obtain the phosphorus that they need to grow and whether the supply of phosphorus to crops is sustainable.
Discuss the causes and consequences of eutrophication.
The model describes the fundamental and realized niches of a species of microscopic marine arthropod in the Northern hemisphere with respect to two different factors (X and Y). The abundance of the species is shown over twelve months. The fundamental niche is separated into five zones ranging from critical to optimal conditions. The population of the species in its realized niche each month is represented by an oval. The size of each oval shows the population abundance.
Distinguish between fundamental niche and realized niche.
State the month where the population reaches its maximum.
Outline how factor Y affects the species from January to April.
Suggest, with a reason, what factor Y could be.