Question

The town council learned that you have recently conducted some research on the relationship between Lyme disease risk and forest fragmentation in Dutchess County, NY, the county with the highest incidence of Lyme disease in the United States (Orloski et al. 2000). They have asked that you give them a presentation on your research. In preparation for your presentation, you need to analyze a dataset you recently collected. You were interested in whether forest fragmentation reduction in forested areas-for example, through clear- cutting, development, or conversion to agriculture - resulting in smaller patches of forest surrounded by non- forested areas) would affect the risk of Lyme disease. You designed a study to test the hypothesis that Lyme disease risk is related to forest fragment size. You decided to measure Lyme disease risk as the density of Ixodes scapularis tick nymphs infected with Borrelia burgdorferi and followed the following methods to collect your data: 1. You selected 14 forest fragments of various sizes (measured as area in hectares) throughout Rutchess County. All sites were maple-dominated forests, to control for the effects of acorn abundance. You visited each site during peak tick activity. 2. At each site, you collected ticks using a standardized protocol which allowed you to record the number of ticks per area. You counted only tick nymphs, since that is the life stage most likely to infect humans (Barbour and Fish 1993). 3. You brought the collected tick nymphs back to your laboratory and tested each one for the presence of B. burgdorferi. You pulverized each tick and then added rabbit antibodies to B. burgdorferi which were labeled with a fluorescent marker. If the antibodies found and associated with B. burgdorferi in the tick, the sample appeared to glow under immunofluorescence microscopy. Using this method, you were able to determine which of the ticks you collected were infected with B. burgdorferi. 4. You recorded your data (below) for each site as density of infected nymphs / m2 (DIN). Area (ha) 0.57 DIN 0.107 0.034 0.89 1.16 0.027 1.20 1.21 0.081 0.054 0.017 0.019 2.93 3.05 3.65 0.027 3.71 4.00 4.04 0.006 0.005 0.019 0.021 0.008 0.004 4.61 7.09 7.43

Answer 1

Density pattern of nymphs with realtion to forest fragment size DIN (nymphs/m2) DIN (nymphs/m2) Expon. (DIN (nymphs/m2)) 6 8 Area (in hectares)

5.

1. Maple dominated forests were used as control for the effects of acorn. Acorn will affect the data since acorns are eaten by mice which are fed upon by ticks. Thus presence of more acorns will result in increased number of ticks. This makes it difficult to analyze the relation between forest fragment sizes and relative abundance of ticks.

2. The hypothesis was - Forest fragment size inversely affects the density of ticks. Yes the results supports the hypothesis.

3. Increased forest fragment size may also indicate the presence of a larger number of diverse predators of mice which harbor these ticks. In addition, the time of data collection is important.

Warm, dry spring or winter weather generally reduces the density of infected nymphs since they spend 95% of their life inside host in moisture filled environment and are prone to drying out. Thus the monitoring should expand to all the seasons of an annual year, to get a clear idea .