Recent Boston Globe "monarchs are threatened" article

[Patrick Foley]

Paul,

    I claimed that the Eastern NA migration is more fragile than the 
species' viability. You are arguing that it is not fragile at all. I 
doubt that. If it were not fragile at all, why is it that so few 
butterfly species show any similar migration?
    You make an interesting point that migrations reappear in farflung 
populations of the Monarch. That is well worth studying. Do you think it 
is due to built-in genetically controlled tendencies? Do you think it is 
a matter of immediate good decisionmaking by the butterflies? Is it a 
vestige or an easily selectively reinforced set of traits? All good 
questions. But if the eastern NA Monarchs do not achieve sufficient 
Darwinian fitness by their migration, the migration will sputter out. As 
it may have in untold other species. And it will sputter out either 
because the wintering sites or the feeding sites become compromised.

    If the wintering site for the Eastern NA monarchs has no special 
features, could you explain why the Monarchs don't overwinter in all the 
closer (to the NA milkweeds) habitats on their routes? I gather that the 
cool, but not frigid winter (similar to CA coast) helps to both lower 
their metabolism, increasing their lifespans, and thaqt there are fewer 
predators in these conditions. The fact that the eastern NA Monarchs 
make such substantial migrations, despite their costs, suggests that the 
payoff is pretty good, and that they cannot get it cheaper. In 
California, such long migrations do not occur, probably because the 
overwintering conditions are met along the coast.

    Paul, how are milkweed populations doing in the Midwestern US? You 
are pretty sanguine concerning them? Does anyone have any data about them?

Patrick
patfoley at csus.edu

Paul Cherubini wrote:

>Pat Foley wrote:
>
>  
>
>>But as we have cleared up several times on this list, the Monarch's
>>Eastern NA migration behavior is a much more fragile thing. Why?
>>1) This kind of migration is not common in butterflies. It
>>apparently requires just the right conditions.
>>    
>>
>
>Fragile?  I'd say quite the opposite.  During the 19th century
>monarchs were inadvertently introduced to several other temperate
>latitude islands and continents around the world and
>in each case seasonal migrations with overwintering clusters
>developed that mirror those in North America.
>Examples: southwestern Europe, Australia, New Zealand.
>And within Australia itself, seasonal migrations with
>overwintering clusters developed in three widely
>geographically disjunct regions; Sydney, Adelaide and some
>islands between Tasmania and Australia -- in just a matter of
>decades.
> 
>  
>
>>2) These conditions include the availability of a wintering site with
>>special features.
>>    
>>
>
>Special features?  I'd say quite the opposite.  In California and
>around the world we have seen that practically any kind of
>evergreen tree, either native or exotic, will provide adequate
>overwintering cluster habitat.  And we have also seen monarchs
>overwintering successfully in a rather wide range of climates.
>Santa Barbara, California for example, has a considerably warmer,
>less cloudy and less rainy fall / winter climate than the San
>Francisco Bay Area yet monarchs overwinter by he tens of
>thousands in both regions.  And we also see monarchs
>overwintering successfully in highly developed and disturbed habitats
>such as clumps of trees surrounded by residential subdivisions,
>industrial buildings, factories, shopping centers and in cemeteries,
>golf courses and city parks.
>
>  
>
>>3)  Chip Taylor is certainly correct that the elimination of
>>the host plant will end the migration. Surely you are not
>>arguing with that statement.
>>Presumably you are claiming that milkweed populations will remain
>>sufficient in the future even with increased intensity of "weed"
>>control. How do you know this?
>>    
>>
>
>Well since 1996, the upper Midwest has been the region of the
>USA with the most extensive plantings of herbicide resistant crops
>and yet this also continues to be the same region with the most
>intensive abundance of monarchs.  And last summer there was a
>spectacular outbreak of Painted Ladies that occurred in Iowa and
>surrounding States http://www.saber.net/~monarch/suv.jpg
>In other words, a spectacular outbreak of Painted Ladies occurred
>on the very same croplands where herbicide resistant crops are most
>intensively grown.
>
>None of this surprises me because herbicide resistant crops provide
>only an incremental improvement in weed control rather than a
>revolutionary improvement.  Therefore I think monarchs scientists and
>conservationists who tell newspaper reporters that herbicide resistant
>crops could "threaten" or "could wipe out" milkweeds and could "threaten"
>or "end the monarch migration" are being wildly unreasonable and dramatic.
>Just like some of them were behaving 15 years ago:
>http://www.saber.net/~monarch/extinction2.jpg
>
>Paul Cherubini
>
> 
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