C.5 Population ecology Questionbank

In 1789 Gilbert White, a naturalist, observed eight breeding pairs of swifts (Apus apus) in the English village of Selborne. On average, each pair of swifts produces two offspring per year. This would allow the population to rise to 1030 swifts over 200 years. A bird survey carried out in 1983 revealed only 12 breeding pairs in this village.

What could have prevented the numbers rising to 1030?

I. The number of nesting sites remained the same.

II. The food supply of the swifts remained constant.

III. Predatory birds in the area were exterminated.

Near the middle of pregnancy in humans, the placenta begins to secrete a hormone called corticotrophin-releasing hormone (CRH). CRH influences the production of hormones which stimulate the development of the fetus. A study was carried out to determine if levels of CRH were correlated with the timing of the baby's delivery. Blood samples were taken from 500 women during their pregnancies and the concentration of CRH was measured. The women were then divided into three groups according to whether their baby was delivered prematurely, at full-term (about 40 weeks) or late. The graph below shows how the concentration of CRH varied in the mothers' blood (maternal blood) in each of the three groups during pregnancy.

What do the graphs below show?

Global warming threatens the survival of Arctic foxes. Which of the following factors could be involved?

I. Competition with other fox species spreading north

II. Reduction in numbers of prey species of Arctic foxes

III. Decrease in oxygen availability to Arctic foxes

Sockeye salmon (Oncorhynchus nerka) spend the first years of their lives in the freshwater lakes of Alaska before migrating to marine waters. Their first months in marine waters are spent foraging and growing near the shore line. They then move to offshore regions of the North Pacific Ocean for 2 to 3 years. [Source: "Oncorhynchus nerka" by Timothy Knepp of the Fish and Wildlife Service. US Fish and Wildlife Service. Licensed under Public Domain via Commons https://wccyusoueahdpdicsyrg.supabase.co/storage/v1/object/public/question-images/images/b9c32b2e-53b8-4722-a4a4-2c906ad6d8f4.jpg] The graph shows fork length frequency of juvenile O. nerka caught during their first months in marine waters in autumn 2008 and ocean age one O. nerka caught 15 months later during winter 2009 in the North Pacific Ocean. Key: □ autumn 2008 (juvenile O. nerka) □ winter 2009 (ocean age one O. nerka) [Source: Adapted from Edward V. Farley, Alexander Starovoytov, Svetlana Naydenko, Ron Heintz, Marc Trudel, Charles Guthrie, Lisa Eisner and Jeffrey R. Guyon (2011) 'Implications of a warming eastern Bering Sea for Bristol Bay sockeye salmon'. ICES Journal of Marine Science, 68 (6), pages 1138-1146, by permission of Oxford University Press.]

In a population of rabbits studied over a period of six months, it was found that natality was greater than mortality and emigration was greater than immigration. What can be concluded about the final population of rabbits?

What is the trophic level of the Leopard seal?

[Source: adapted from http://amurdoch.tripod.com/yr4/AntFoodWeb.JPG]

I. Secondary consumer II. Tertiary consumer III. Quaternary consumer

A researcher captures 100 sparrows (a small bird), tags them and then releases them. One week later, the researcher recaptures 50 sparrows, 20 of which have tags on them. What is the size of the sparrow population?

Phenologists are biologists who study the timing of seasonal activities in animals and plants, such as the opening of tree leaves and the laying of eggs by birds. Data such as these can provide evidence of climate changes, including global warming. The date in the spring when new leaves open on horse chestnut trees (Aesculus hippocastaneum) has been recorded in Germany every year since 1951. The graph below shows the difference between each year's date of leaf opening and the mean date of leaf opening between 1970 and 2000. Negative values indicate that the date of leaf opening was earlier than the mean. The graph also shows the difference between each year's mean temperature during March and April and the overall mean temperature for these two months. The data for temperature was obtained from the records of thirty-five German climate stations. [Source: Walther et al., Nature (2002), 416, pages 389-395] From 1973 onwards phenologists in the Netherlands have been studying a population of great tits (Parus major) in a forest on the Hoge Veluwe. Nest boxes are checked every week to find out when the great tits lay their eggs and how many eggs they lay. Young birds are ringed when they are seven days old, to allow the reproductive success of their parents to be monitored. Great tits feed on arthropods, especially caterpillars. The phenologists found that the date of maximum caterpillar biomass each year in the forest could be estimated accurately using temperature records. The graphs below show the mean date of egg laying and the estimated date of maximum caterpillar biomass for each year from 1973 to 1995. [Source: Visser, Noordwijk, Tinbergen and Lessells, Proceedings of the Royal Society of London, (1998), 265, pages 1867-1870] There was no statistically significant change in the date of egg laying between 1973 and 1995, but the phenologists found evidence that natural selection will eventually cause a change in the date of egg laying.