Recent Boston Globe "monarchs are threatened" article

[Patrick Foley]

Stan,

Monarchs of Eastern North America have a collection of traits (color, 
behavior, lifespan etc) which are, of course, maintained by a genetic 
system interacting with an ecological system. There is surely some 
genetic diversity for the migratory behavior. And the environments 
change all the time. So the migratory behavior is not set in stone, but 
neither is it a ghostly apparition. If the Monarchs have more young by 
making the Migration than by some other lifehistory choice, then the 
Migration will continue. If milkweeds in some area decline to some 
critical density, a path through that area will become increasingly 
selected against. If an overwintering site has high enough mortality, 
the behavior of choosing that site will be selected against.

Humans may cause the changes to the migratory path, as do other 
ecological influences. Climate, weed eradication, logging are all 
human-influenced, but of course climate and vegetation change occurs 
"naturally".  It is not necessary to lay blame on humans, in order to 
find ways to avoid disrupting the Migration. Encourage the milkweeds and 
the oyamel fir. But keep in mind that we really don't know most of what 
there is to know about the evolution of this complex migratory behavior. 
Maybe the perfect timing of nectar plants along the path is a key 
feature. Or the avoidance of predators. Or fungi!

Patrick
patfoley at csus.edu

Stanley A. Gorodenski wrote:

> Patrick,
> About a year ago, I don't remember how long, I was part of a 
> discussion on the Monarch. I don't keep all my messages and so I am 
> going on memory. It seems I recall that from a population genetics 
> point of view you, or someone else of a similar research background, 
> made a statement in response to something I said that, essentially, it 
> is likely only a matter of time when genetic changes occur in the 
> migratory populations resulting in a non-migratory status, as has 
> already occurred in some Monarch populations. My impression of the 
> context of the statement was that it would not be in response to 
> habitat destruction by Man-Woman, but as part of a response to the 
> natural evolutionary forces of "Nature". Could you clarify this or set 
> my memory straight because it seems, if this is the outlook by 
> population geneticists, that the importance (and significance) being 
> placed on the Monarch migrations is misplaced.
> Stan
>
> Patrick Foley wrote:
>
>> 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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>>>  
>>>
>>
>
>



 
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