[NatureNS] possible declines in under cover life

Date: Thu, 16 Sep 2010 11:54:12 -0300
From: "Frederick W. Schueler" <bckcdb@istar.ca>
Organization: Bishops Mills Natural History Centre
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On 9/16/2010 9:42 AM, David & Alison Webster wrote:

> I have been wondering for some decades if acid rain has impacted land
> snail populations and you may be able to shed some light on this.

* this is a fear that haunts everyone who studies shelled animals. 
There's certainly concern about this with aquatic Molluscs, but I'm not 
familiar with the literature on terrestrial Gastropods.

> An observation in the early 80's got me wondering; Common Garden snails
> were so abundant at the Marble Mountain limestone quarry that it was
> difficult to walk without stepping on some.
>
> In contrast, these snails were relatively abundant in roadside ditches
> in Cambridge Kings Co in the early 40's but I have seen almost none
> since about 1970.

* but another thing that may have happened is that you may have seen a 
pulse of abundance as the snails occupied a new habitat in the 1940s, 
and then they've subsided as they've used up the resources that made the 
abundance possible, or ecological succession may have changed the 
communities, so that their niche is gone. The snails portrayed from the 
road across from our house - http://pinicola.ca/cepaea.htm and 
http://pinicola.ca/cepaea1.htm - are now much less abundant than they 
were just a couple of years ago, though we can't distinguish between 
reduced numbers because they've used up the resources that made their 
initial abundance possible (they colonized that side of the road in 
2001), and changed conditions by a new owner who is mowing their 
roadside habitat as a lawn.

Since we've been in the Maritimes, however, we've seen only one 
individual of Cepaea hortensis, which has rather spooked me, since this 
big yellow snail is supposed to be generally distributed and common, 
though our travels haven't been directed towards limey habitats, and 
we're generally unfamiliar with the area. Where are they still abundant?

Maybe it's time to make a listing of all the museum collections of 
Cepaea in the Maritimes, and to go back and see what their status is at 
each site where they've been found in the past. Even if they're still 
abundant, the changes or stability of the genetics of shell banding 
would be a worthwhile study.

fred schueler
------------------------------------------------------------
          Frederick W. Schueler & Aleta Karstad
Bishops Mills Natural History Centre - http://pinicola.ca/bmnhc.htm
now in the field on the Thirty Years Later Expedition -
http://fragileinheritance.org/projects/thirty/thirtyintro.htm
Daily Paintings - http://karstaddailypaintings.blogspot.com/
     RR#2 Bishops Mills, Ontario, Canada K0G 1T0
   on the Smiths Falls Limestone Plain 44* 52'N 75* 42'W
    (613)258-3107 <bckcdb at istar.ca> http://pinicola.ca/
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