[Leps-l] [leps-talk] Monarch Armageddon

[Paul Cherubini]

On Feb 15, 2013, at 11:25 AM, Foley, Patrick wrote:

> Paul, Of course there are short-distance migrating
> Monarchs. Many California monarchs migrate
> short distances

Yes many California monarchs migrate short distances
in the fall, but they are physiologically capable of
migrating the same very long 2,000 miles from 
Canada to central Mexico as the eastern monarchs are. 
And that's because eastern and western fall
migrant monarchs are the same physiologically; i.e. 
the dates of onset of diapause and migration and the 
length of time (2-3 months) that the migratory instinct 
is active are the same (at similar latitudes).

> Monarch migration strategies do not depend on latitude.
> Latitude simply correlates with climate features. 

No, latitude has a major influence on monarch physiology;
e.g. at high latitudes (e.g. 49 degrees N)  summer 
monarchs to enter diapause and start migrating in 
early August vs early September at 35 degrees N 
latitude.

> Migration strategies depend on overall energy balance,
> dangers of migration, corridors that are phenologically
> appropriate etc. 

As I have already explained, even though western 
and eastern monarchs breed in hugely varied
landscapes (deserts to high mountains) they
are physiologically the same (at similar latitudes), 
hence their migration behaviors are the same. 

> Natural selection on migration strategies will change
> with climate change and Mexican and US land use
> policy changes. The rate of these changes is arguable,
> and so is the danger to the Eastern migration. 

It is indisputable that millions of milkweed plants
and therefore monarchs will continue to exist for
many, many decades to come in the same regions 
of the USA and Canada as they do now despite
minor climate changes and moderate land use changes.  

Therefore it is highly questionable whether or not
Dr. Chip Taylor has a legitimate scientific basis for 
telling the public and reporters that just because there 
will be less - but still millions - of wild milkweed plants 
growing in the decades to come the monarch migration 
could be on the "brink of collapse": 
http://monarchwatch.org/blog/2008/04/butterfly-on-the-brink/
http://www.youtube.com/watch?v=MdtDcKg-x8w

> I am arguing that the Eastern migration strategy is not
> so secure as you claim, especially in the light of so
> many butterfly species and many Monarchs choosing
> a different migration strategy. 

You and Chip Taylor have not provided evidence that 
millions of milkweeds and thousands of forest trees in 
Mexico will NOT still be available to support a population of 
millions of migratory eastern monarchs 50 - 100 years 
from now.

> Do you think ongoing climate changes will not change
> the Appalachians or Mexican highlands?

The climate changes since 1895 have been minor (a 1-2
degree rise in temperature) so they are likely to be minor 
for the next 100 years as well given that the rate of temperature
rise between 1895-2012 has been relatively linear (and flat
worldwide since 1999)

So these changes should have only minor impacts, both 
positive and negative.  Example: Despite some global 
warming since 1977-78, the years the Mexican overwintering 
sites were first mapped, the altitude where the monarchs 
cluster has not changed, nor have California overwintering
clusters moved northward up the coast since they were first 
mapped in the 1930's - 1950's.

Paul Cherubini
El Dorado, Calif.