Introduction

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Nekola, J.C. 2002. Distribution and ecology of terrestrial gastropods in Northwestern Minnesota. Final report submitted to the Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resources. 178+ pp.

Introduction:

Minnesota has one of the most poorly known land snail faunas in the eastern U.S. (Hubricht 1985). Prior to 1999, 60 terrestrial gastropod taxa had been reported from the state (Dawley 1955, Hubricht 1985, Ostlie 1991). Of these, only 23 had been recorded from northwestern Minnesota (Hubricht 1985).

Fully 22% of Minnesota's land snail species are rare throughout the eastern U.S. A number of these are restricted to algific slope and carbonate cliff habitats in the southeast (e.g., Hendersonia occulta, Vertigo hubrichti, Vertigo 'iowaensis', Vertigo mermacensis; Frest 1991). Mafic igneous outcrops and conifer wetlands in northeastern Minnesota also support a number of rarities (Planogyra asteriscus, Vertigo cristata, Vertigo modesta modesta, Vertigo modesta parietalis, Vertigo paradoxa, Zoogenetes harpa; Nekola et al 1999).

During the summer of 1999, a preliminary survey for land snails was conducted in northwestern Minnesota by myself and Dr. Brian Coles. We encountered 41 taxa at 12 sites scattered across Beltrami, Clearwater, Itasca, Kittson, Polk, and Roseau Counties. 20 of these were previously unreported from the region and 5 were new to the state. Some of the taxa encountered are very rare, including Vertigo arthuri (previously known from ca. 2 dozen sites in the Black Hills), V. cristata (not known to occur in the U.S. until 1996), and V. nylanderi (previously known from only 18 sites, and last seen in Minnesota in 1949). Not only were rare taxa encountered during this brief foray, but the diversities per site were the highest encountered at this latitude in central North America (over 20 taxa/site in some cases). The discovery of these globally rare taxa and diverse communities suggested that a more thorough inventory of the land snail fauna in this region was warranted.

Two habitats, in particular, harbored important faunas. The first was calcareous wooded peatlands dominated by tamarack, white cedar, and/or black ash. These sites harbored Vertigo nylanderi, which had been lost to science for almost 50 years. All previous known; recent sites were limited to northeastern Wisconsin and the Upper Peninsula of Michigan. The Minnesota populations include the largest yet discovered. More individuals were . observed at Iron Springs Bog than had previously been seen at all other extant sites. Additionally, these sites were found to harbor over 20 associated species, making them among the richest wooded peatland faunas yet encountered. Associates included the rare Vertigo arthuri, V. cristata, V. elatior (new to the state), V. paradoxa, and Zoogenetes harpa.

The second important habitat was aspen parkland. Vertigo arthuri was located at both inventoried sites, with the colony at Two Rivers SNA being perhaps the largest yet known globally. This site also supported Vertigo elatior, as well as 19 other taxa (21 total). The number of sympatic species at Two Rivers SNA was the most encountered at that time an upland woods in central North America. This richness is likely due to the highly calcareous nature of the Lake Agassiz plain.

Our cursory survey of the region in 1999 did not permit analysis of other habitats which are also likely reservoirs of land snail biodiversity. Among the more important of these are fens, which support diverse land snail communities and very large populations in Iowa (Frest 1990), Michigan (Nekola 1998), and Wisconsin (Nekola et al 1996). These sites have been found to harbor the European disjunct Euconulus alderi, the presumed glacial relicts Catinella exile, Vertigo elatior, and Vertigo morsei, plus at least two undescribed endemic taxa (Hawaiia n.sp. and Punctum n.sp.; Frest 1990). It is very likely that other important habitats and species exist in the region. Only by investigating representative examples of all major habitat types habitats throughout the region the true extent of this fauna can be documented. The documentation of this fauna is particularly important as land snail communities are among the most sensitive known to anthropogenic and other disturbances (Frest and Johannes 1995). Because of this, such unique communities can be lost from development and agricultural pressures (Frest 1991, Nekola et al. 1996) before the full extent of their biodiversity can be assessed.

The following report summarizes findings from a land snail survey of all important natural communities found within the 14 most northwestern Minnesota counties. The large spatial and ecological extent of this analysis permits not only documentation of the distribution and abundance of individual species, in the regional fauna, but also the potential ecological patterns and processes that influence their distribution and abundance. This study represents the most extensive such survey of its kind made in North America.

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