Fwd: Re: Size of the overwintering monarch populations - published data.

Chip Taylor chip at ku.edu
Mon Oct 13 07:56:07 EDT 2003

>Stan, et. al.: I'm glad you raised a question. I looked at the data 
>again and realized there is a typo. The population size in hectares 
>for 2000/2001 should be 2.83 and not 12.83. 
>The largest population known was in 96 - almost 21 hectares and the 
>smallest 2.83. As insect populations go, this is a relatively small 
>difference being only a 7.4 ratio of high to low. Presumably, the 
>variation in population size is somewhat buffered by the continental 
>nature of the population. Which is another way of saying that it 
>unlikely to be universally bad or good for breeding over the entire 
>The mean appears to be roughly 9.6 hectares but this mean is 
>strongly influenced by the one big year. Frankly, I don't see any 
>trends in the data. The series is too short but the 2.83 was 
>alarmingly low. However, the monarchs' capacity to recover from such 
>low numbers was demonstrated each of the last two winters. So far, 
>we haven't seen a bad winter followed by poor breeding conditions 
>over a wide area. Should this happen, recovery would certainly be 
>The size of the wintering population may be related to the amount of 
>winter and spring rain in Texas, droughts in the breeding areas in 
>the north, and droughts during the fall migration. One cannot 
>predict one wintering population from another with accuracy. Natural 
>rather than anthropogenic factors appear to govern the population 
>for the moment but there are anthropogenic factors at work and the 
>question/argument is when, where and to what extent they will have 
>an impact on the population. It's not a matter of if but of when and 
>how much.  A lot of time has been wasted arguing about the eastern 
>monarch population when, in fact, we know very little about it.
>>What I was getting at is that if the counts at the beginning of the 
>>series were the results of undercounts (and it seems so from what 
>>you said), then the drop as shown in recent numbers may be 
>>something to be even more concerned about because the claim can be 
>>less easily made that it is a natural fluctuation - the first part 
>>of the series reflect undercounts and so one cannot claim it is a 
>>natural drop. In light of  this, is ths drop in the recent part of 
>>the series something to be more concerned about?

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