Learning module developed by K Langin H Sofaer and S Sillett for Hubbard Brook

# Learning module developed by k langin h sofaer and s

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Learning module developed by K. Langin, H. Sofaer and S. Sillett for Hubbard Brook Research Foundation (2009). 5. Next, we’ll do another regression analysis to test if the relationship we graphed in question 4 is statistically significant. This time, you don’t need to save the residuals. a)Are your results statistically significant? What output did you use to make this determination? (3 pts.) 6. Summarize the biological interpretation of your results, and the effects of food and nest predator abundance on warbler fecundity. (6 pts.) Both food abundance and nest predator abundance affected average warbler reproductive success in each year. In our analyses, we showed that variation in food accounted for approximately 1/3 of the variation in fecundity between years. Fecundity was higher in years with more food. When we analyzed the residuals from that regression, we found that deviations from expected fecundity were explained by variation in nest predator abundance between years. Specifically, nest predator abundance explained half of the variation in reproductive success that was not explained by food abundance. As the abundance of nest predators increased, reproductive success declined. This can be seen on the second figure where high nest predator abundance is associated with negative values of residual fecundity. This means that in years with many predators, fecundity was lower than would be expected just based on the amount of food. 7. Based on the background information on the effects of density on warbler fecundity, look at the point for 1995 in both graphs, and predict whether the density in that year was above average, below average, or approximately average. Be clear about why you made the prediction you did. (5 pts.) In 1995, residual fecundity was approximately -1, so that year’s fecundity was lower than expected given the food abundance. The abundance of nest predators in that year was relatively high, but the point still falls below the expected relationship between nest predator abundance and residual fecundity. High densities are expected to reduce fecundity. I would therefore predict that density in that year was higher than average, since fecundity was lower than expected given both food and nest predator abundance. 8. Can we say that variation in food and predators causesvariation in warbler fecundity? If so, why? If not, what would need to be done to establish causation? (5 pts.)

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• Spring '16
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• Statistics, Regression Analysis, Errors and residuals in statistics, reproductive success, Hubbard Brook Research Foundation, K. Langin

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