Monday, November 28, 2011

Predator Control: Does it work or doesn't it?

A recent study on predator-prey interaction led Kim Murrey Berger to investigate the problem. In a study made by Berger, "Carnivore-Livestock Conflicts: Effects of Subsidized Predator Control and Economic Correlates on the Sheep Industry" , the problem of predator control was examined. Predator control which is one of the oldest form of wildlife control and conservation was measured using data from 1990 to 1998 using the change in sheep population as a way to determine the efficiency of the control. Unique to this study is how the discussion of what predators are killed as a necessity to ensure sheep survive. Among the animal killed are Bobcat, Mountain Lions, Black Bears, etc. This also makes things complicated as the problem seems to go in the direction of having to kill some or a lot of endangered predators out there to ensure the survival of an industry that makes millions if not billions yearly in profit. Another funny and interesting way this study went through with was the purchasing wool and sheep product as a measurement of variability in the sheep industry and correlating that with efficiency of predator control made by the government. The results even though it was explained in a serious manner seems very funny.

Despite the importance of carnivores in terrestrial ecosystems, many nations have implemented well-coordinated, state-funded initiatives to remove predators, largely because of conflicts with humans over livestock. Although these control efforts have been successful in terms of the number of carnivores removed, their effects on the viability of the industries they seek to protect are less understood. I assessed the efficacy of long-term efforts by the U.S. government to improve the viability of the sheep industry by reducing predation losses. I used regression analysis and hierarchical partitioning of a 60-year data set to explore associations among changes in sheep numbers and factors such as predator control effort, market prices, and production costs. In addition, I compared trends in the sheep industry in the western United States, where predator control is subsidized and coyotes (Canis latrans) are abundant, with trends in eastern states that lack federally subsidized predator control and that were (1) colonized by coyotes before 1950 or (2) colonized by coyotes between 1950 and 1990. Although control efforts were positively correlated with fluctuations in sheep numbers, production costs and market prices explained most of the model variation, with a combined independent contribution of 77%. Trends in sheep numbers in eastern and western states were highly correlated (r ≥0.942) independent of the period during which they were colonized by coyotes, indicating either that control has been ineffective at reducing predation losses or that factors other than predation account for the declines in both regions. These results suggest that government-subsidized predator control has failed to prevent the decline in the sheep industry and alternative support mechanisms need to be developed if the goal is to increase sheep production and not simply to kill carnivores.

Work Cited: BERGER, K. M. (2006), Carnivore-Livestock Conflicts: Effects of Subsidized Predator Control and Economic Correlates on the Sheep Industry. Conservation Biology, 20: 751–761. doi: 10.1111/j.1523-1739.2006.00336.x

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