Ch. 52 - Community Ecology

Problem 14

Chapter 51, Problem 14

Lyme disease is caused by infections of the bacterium Borrelia burgdorferi (stained blue in inset, among red blood cells) which is transferred to humans via blood-sucking bites from the tick, Ixodes scapularis. Lyme disease can cause flu-like symptoms in the short term and more serious illnesses in the long term, if not treated. Why is Lyme disease on the rise in eastern North America? Researchers have measured a positive correlation between forest fragmentation and incidence of Lyme disease. According to the theory of island biogeography, how do you predict fragmentation will affect species richness?

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Step 1: Understand the problem. The question is asking why Lyme disease is on the rise in eastern North America and how forest fragmentation, according to the theory of island biogeography, might affect species richness.

Step 2: Recall what you know about Lyme disease. It's caused by the bacterium Borrelia burgdorferi, which is transferred to humans through tick bites. The ticks that carry this bacterium are often found in forested areas.

Step 3: Consider the theory of island biogeography. This theory suggests that larger habitats, or 'islands', have more species because they can support larger populations and a greater range of habitats. When a large habitat is fragmented into smaller 'islands', the number of species each can support decreases.

Step 4: Apply this theory to the problem. Forest fragmentation could lead to an increase in the population of ticks, as they may have fewer predators or competition in the smaller, fragmented habitats. This could lead to an increase in the incidence of Lyme disease.

Step 5: Formulate your answer. According to the theory of island biogeography, forest fragmentation would likely decrease overall species richness due to smaller habitat size and isolation. However, it could potentially increase the population of certain species, like ticks, leading to a rise in Lyme disease.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lyme Disease and Its Transmission

Lyme disease is an infectious disease caused by the bacterium Borrelia burgdorferi, primarily transmitted to humans through the bites of infected ticks, particularly Ixodes scapularis. The disease can lead to various symptoms, including flu-like signs initially, and if untreated, can result in more severe health issues. Understanding the transmission dynamics is crucial for addressing the rise of Lyme disease in certain regions.

Forest Fragmentation

Forest fragmentation refers to the process where large, continuous forests are divided into smaller, isolated patches due to human activities such as urban development and agriculture. This alteration of habitats can significantly impact wildlife populations, including ticks and their hosts, potentially increasing the incidence of diseases like Lyme disease. The relationship between fragmentation and disease spread is an important area of ecological research.

Island Biogeography Theory

The theory of island biogeography, developed by Robert MacArthur and Edward O. Wilson, explains how the size and distance of islands (or habitat patches) affect species richness and biodiversity. According to this theory, smaller and more isolated habitats tend to support fewer species due to limited resources and increased extinction rates. In the context of forest fragmentation, this theory suggests that smaller forest patches may lead to reduced species richness, impacting the dynamics of Lyme disease transmission.

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Textbook Question

The carnivorous plant Nepenthes bicalcarata ('fanged pitcher plant') has a unique relationship with a species of ant—Camponotus schmitzi ('diving ant'). The diving ants are not digested by the pitcher plants, but instead live on the plants and consume nectar. Diving ants also dive into the digestive juices in the pitcher, swim to the bottom, and capture and consume trapped insects, leaving uneaten body parts and ant feces behind. What nutritional impact do the ants have on fanged pitcher plants? Do the pitcher plants derive any nutritional benefit from this relationship? Based on the background information presented here, does the relationship between diving ants and pitcher plants appear to be mutualistic? Explain.

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Textbook Question

Lyme disease is caused by infections of the bacterium Borrelia burgdorferi (stained blue in inset, among red blood cells) which is transferred to humans via blood-sucking bites from the tick, Ixodes scapularis. Lyme disease can cause flu-like symptoms in the short term and more serious illnesses in the long term, if not treated. Why is Lyme disease on the rise in eastern North America? Deer are hosts of ticks but are not reservoirs of B. burgdorferi—their immune systems detect and kill the bacterium. But a tick with a prior bacterial infection can consume a blood meal from a deer and then bite and infect a human. The fitness effects of a deer on B. burgdorferi can be summarized as: a. + because the deer supplies the bacterium with food. b. − because the deer kills the bacteria in its blood. c. + because the deer feeds and disperses the tick that can then infect a human with the bacterium. d. − or + depending on whether the deer is the tick's last host.

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Textbook Question

The carnivorous plant Nepenthes bicalcarata ('fanged pitcher plant') has a unique relationship with a species of ant—Camponotus schmitzi ('diving ant'). The diving ants are not digested by the pitcher plants, but instead live on the plants and consume nectar. Diving ants also dive into the digestive juices in the pitcher, swim to the bottom, and capture and consume trapped insects, leaving uneaten body parts and ant feces behind. What nutritional impact do the ants have on fanged pitcher plants? Do the pitcher plants derive any nutritional benefit from this relationship? Explain why carnivorous and parasitic plants are most common in nutrient-poor habitats.

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Textbook Question

A team of 102 scientists spent a year surveying a small area of the San Lorenzo rain forest in Panama to count the number of species of arthropods living there. After collecting 129,494 specimens—using nets, traps, shovels, tree-climbing harnesses, helium balloons, and other creative gear—it took the team eight years to sort and identify the arthropods.A team of 102 scientists spent a year surveying a small area of the San Lorenzo rain forest in Panama to count the number of species of arthropods living there. After collecting 129,494 specimens—using nets, traps, shovels, tree-climbing harnesses, helium balloons, and other creative gear—it took the team eight years to sort and identify the arthropods. Use the data in the graph to analyze the following statements. Select True or False for each statement, then correct any false statements to make them true. T/F All taxa shown in the graph are insects. T/F All taxa shown in the graph have segmented bodies and limbs. T/F All taxa shown in the graph are terrestrial. T/F If the researchers had sampled for mollusks, they probably would have found almost as many species as they did for arthropods.

Lyme disease is caused by infections of the bacterium Borrelia burgdorferi (stained blue in inset, among red blood cells) which is transferred to humans via blood-sucking bites from the tick, Ixodes scapularis. Lyme disease can cause flu-like symptoms in the short term and more serious illnesses in the long term, if not treated. Why is Lyme disease on the rise in eastern North America? White-footed mice occupy a broad ecological niche—they occur in most communities regardless of habitat quality. Many other species, like the opossum, are absent from low-quality forest fragments. Based on this information and the data in Question 12, propose a hypothesis to explain the observed relationship between increased forest fragmentation and increased incidence of Lyme disease.

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