Answers to the exploration questions: local threats to biodiversity

If you are wondering where the suggested answers came from, you can review the videos and articles in this tutorial.

1.     After watching the video on introduced species and biodiversity, your friend is confused about exotic, introduced, and invasive species and asks you to explain how they are the same or different. In your own words, write a few sentences to explain the meaning of these terms:

Answer: A complete explanation would mention that the terms exotic species and introduced species are synonymous and mean that the species is not native to a particular area. The terms exotic and introduced refer to any species that is knowingly or accidently transferred by humans from its native habitat to a new environment. Sometimes the introduction is intentional, such as humans bringing cattle as livestock to new areas, or planting trees from another country in their yards. Sometimes the introductions are accidental, such as when the organism stows away on a type of transport and then gets carried onto new land or into new waters. The brown tree snake, for example, originally native to northern Australia and Papua New Guinea, was accidently introduced on the island of Guam by cargo planes during World War II. Invasive species, on the other hand, are a special type of introduced species. Invasive species are introduced species that are very successful in their new habitat, reach large population sizes, and outcompete or harm native species. The financial and ecological burden of invasive species is huge (see the selected references for some specifics, such as the U.S. spending $8 million annually trying to manage the brown snakes on Guam and protect the native birds). So, bottom line, all invasive species are introduced (or exotic), but not all introduced (exotic) species become invasive.

2.     Your friend tells you that a good way to increase biodiversity is by intentionally introducing a species to a new environment because the introduced species increases the species richness of that area by one species. Do you agree or disagree with your friend’s statement? Hint: Use the example of the comb jellies that were introduced to the Black Sea to explain how introduced species can cause a decrease in species richness in an area.

Answer: A complete explanation would mention that your friend is right that the species richness would go up by one after the introduction, at least temporarily, but your answer should also mention that this would NOT be a good thing to do. Introduced species can become invasive and cause a chain of events that decreases the species richness and ecosystem function of an environment. For example, in the 1980s a species of comb jelly (Mnemiopsis leidyi), native to the coastal waters of the Atlantic off the eastern shore of North America, was accidentally introduced into the Black Sea, most likely through the ballast water of a ship. The comb jellies thrived in the environmental conditions of the Black Sea, with few predators, and an abundant food supply of anchovies. The comb jelly population boomed, but within months, the jellies had caused the collapse of the anchovy fisheries in the Black Sea by eating the anchovy eggs and larvae. The loss of anchovies from the food web also negatively impacted other organisms, disrupting the stability of the ecosystem network and its functions. So after temporarily increasing species diversity in the Black Sea, the invasive comb jelly ultimately decreased biodiversity and ecosystem function. If you’d like to review the concept of biodiversity and ecosystem function, watch the Ecosystems and Ecological Networks video.

Answer: A complete answer would mention that the more humans there are on Earth, the greater the pressure and threats this creates for other species. The 2003 paper by McKee et al. measured a number of factors that threatened biodiversity and determined that human population growth and species richness were tightly linked. If you think about it in the simplest terms, no two things can occupy the same place at the same time. If humans are living in a given area, then there can be fewer native plants and animals living there. But it is not just the total number of people on Earth and where they are occupying space, but also how much they change the landscape, consume natural resources, and create pollution. To support their needs and life styles, humans convert natural habitat to housing, roadways, stores, factories, farmland, and entertainment centers, for example. If we’re looking at just the threats posed by humans, they cut down forests, strip mine the land, dump chemicals into waterways, and burn fossil fuels, all of which threaten biodiversity.