Parasites and Monarchs

[Paul Cherubini]

Stanley A. Gorodenski wrote:

> I am in the process of reading this paper now. At this time 
> I do not see it as political propaganda in the least. What I 
> see is good science that draws upon results of research on 
> other taxa and puts the interpretation of their results in that 
> context.

Stan, here is another write up of the same study
http://news.emory.edu/Releases/monarch1109713157.html

I would tend to agree with Ron Gatrelle this write up contains 
inappropriate alarmist type propaganda rather than just science. 

Using tethered monarchs in a lab, the authors measured the flight 
endurance of lab reared monarchs that were infected with variable
levels of a protozoan parasite. They found highly infected 
monarchs flew somewhat slower, for shorter periods, etc. This 
is fairly interesting (though not real interesting since they 
apparently didn't flight test wild caught monarchs) and fairly good 
science as far as it went. But then the authors decided to launch 
into unjustified, alarmist monarch migration extinction propaganda 
with these statements:

"monarch migration in eastern North America is threatened by
several environment factors such as habitat loss at wintering sites,
climate warming trends and an increase of tropical milkweed 
species in milder climates."

"The results of our study add one more reason to protect monarch
migration east of the Rockies. If this migration collapses due to
climate warming, habitat loss, pesticide use or other reasons, we
probably won't lose monarchs as a species, but we'd be left with
remnant, nonmigratory populations that are heavily infected with
parasites, which could have several negative effects, from higher
mortality rates, smaller body sizes and deformities, to more virulent
strains of the parasite," Altizer says."

Why, in my opinion, is this propaganda? Several reasons:

1. As Ron Gatrelle pointed out "climate change is neutral,
its functions work just as much against a disease  / parasite / plant /
animal etc. as it can for it." Ditto in regards to the authors' claim
of an "increase of tropical milkweed species in milder climates."
An increase in the abundance of tropical milkweed could have
neutral, positive or negative impacts on the abundance of migrant
monarchs.  In fact, back in 1961, Dr. Lincoln Brower hypothesized
winter monarchs in Florida bred on tropical milkweed then
migrated north in the spring and repopulated the entire eastern USA 
with monarchs.

2. The authors state "habitat loss at wintering sites" as if the loss
was an established fact when to the contrary we know every
mountain in Mexico that contained overwintering sites
30 years ago still has them today and in similar quantities.

3. The authors state "If this migration collapses due to climate
warming, habitat loss, pesticide use or other reasons" as if 
there was a solid body of evidence to support the notion that 
small, incremental changes in climate, habitat loss or pesticide 
use could cause a catastrophic collapse of the migration 
phenomenon.

To the contrary, we know the monarch migration has been
robust for the past 125 years despite massive human caused
changes in the vegetation of the upper Midwest, Great Lakes 
States and New England (where monarchs breed in the summer)
during that time period.

4. The authors state "if this migration collapses we'd be left with
remnant, nonmigratory populations that are heavily infected with
parasites, which could have several negative effects, from higher
mortality rates, smaller body sizes and deformities, to more virulent
strains of the parasite,"  as if there was a solid body of evidence 
to support the notion that non-migratory monarch populations
are uniformly small, unhealthy and riddled with deformities, etc.

To the contrary, there are dozens and dozens of  island populations 
of monarchs in the tropics that have survived since the mid-late 
1800's with no reports of extinctions that I am aware of.

Paul Cherubini

 
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