Thus, stable numerical harvests and stable recruitment do not 

 necessarily mean stable populations. 



The main point of these examples is to show the pitfalls 

 in the path of anyone making decisions based on data reported 

 only as ratios or percentages. Estimates of population 

 numbers or trend are almost essential for confidence in the 

 meaning of ratios and percentages . 



Interpreting Population Trend 



Trends are one of the most widely used and abused tools 

 of all aspects of life. If correctly used, trend information 

 can be valuable, especially if data are sufficient to provide 

 long-term perspective. When quick answers or decisions are 

 required, we all usually rely on the trend ( "Go with the 

 trend" - "The trend is your friend"). However, trend data are 

 also subject to misuse and overuse, and we often place too 

 much confidence in its reliability. 



At minimum, only 2 data points are required to establish 

 a trend. Although most people are justifiably reluctant to 

 place confidence in a 2 data-point trend, many decisions are 

 based on no more than that. A longer-term data set is 

 necessary to place annual changes in perspective. However, 

 the particular data set or its specific length can greatly 

 influence that perspective and the conclusions drawn. 



Examples of both the value and the pitfalls inherent in 

 trend data are illustrated by changes in numbers for the 

 Missouri River Breaks mule deer population over time (Fig. 

 13.1). Five years of trend information, starting in 1960 

 (Fig. 13. 1A), indicated that both short- and long-term trend 

 for the population were up. However, addition of only 1 more 

 year of data (Fig. 13. IB) indicated just the opposite 

 conclusion; both short- and long-term trend were down. 

 Expansion of the study to a "long-term" 10-year data set (Fig. 

 13. 1C) indicated that, given a "longer-term" perspective, the 

 "real" long-term trend was up. Again, however, once this 

 uptrend was clearly established, the population immediately 

 turned downward, and by 1975 after 16 years (Fig. 13. ID), the 

 obvious trend was toward increased fluctuation, with higher 

 highs and lower lows. After the lower low was established 

 (1975), the population almost immediately began an uptrend 

 (Fig. 13. IE). After 23 years, it appeared the trend for 

 higher highs was coming to an end, but once again, one year of 

 additional data (Fig. 13. IF) falsified trend projections by 

 re-establishing the trend of higher highs. Finally, after 28 

 years (Fig. 13. 1G), the trend of lower lows and higher highs 

 appears to have been halted. Can we trust this interpretation 

 of the trend? Is the population now fluctuating around a 

 higher "equilibrium" level than that of the 1960s? A higher 



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