Biogeography

There are many factors that detemine where a particular plant or animal species is found on planet earth. The study of where plants and animals live, and why and how they came to live there, is called "biogeography".

Each plant or animal species is found in a defined geographic area called it's "range". This is where it can find the habitat it needs, where it can tolerate the climate, and where it has been able to spread to. Some geographical features, like mountains, large lakes or rivers, or expanses with no suitable habitat, such as a desert, can stop the spread of a species.

Range of the Northern Prairie Skink

In North America prairie skinks have a range that covers a large area in the eastern part of the Great Plains (Map 1). In the United States they are found in the western edge of the tall grass prairie region. The tall grass prairie is the eastern part of the Great Plains region. Precipitation amounts decrease from east to west in the Great Plains. Throughout their range in the United States prairie skinks are found in areas where soils are very soft or sandy.

(Maps 1-4 on this page are large images: 1428 x 980 pixels, 350 Kb.)

Manitoba’s skink populations are separated from the rest of North America’s northern prairie skinks by about 150 km. Skinks occur in northern North Dakota and Minnesota, in fact very close to the Manitoba border on both sides of the Red River Valley. Skinks are found in Lake Bronson State Park in Minnesota, only 30 Km south of the Manitoba border, about 40 km south of Stuartburn. The northern prairie skink range extends southward to central Kansas. The southern prairie skink (E. s. obtusirostris) has a range that extends from southern Kansas down to the Gulf Coast in Texas.

Skinks have only been found in two regions of southwestern Manitoba. One is a small pocket in the Lauder Sandhills southwest of Brandon (Map 2). This isolated population is found in a small location, only about 1 ha. The main skink population (Map 3) occurs within the Assiniboine Delta region, east of Brandon.

The areas of sandy soils in southern Manitoba are shown in Map 4. The large deposits of sand east of Brandon represent the Assiniboine Delta region, where the Old Assiniboine River emptied into Glacial Lake Agassiz (see below). Wherever native prairies occur on areas of sandy soils in southern Manitoba there is a chance skinks might be found.

Skinks and Google Earth. If you have Google Earth Plus, you can download the KMZ file that will let you view these images in greater detail in Google Earth. Here's a chance for those of you into GPS or Geocaching to try and figure out some spots to go looking for new skink populations!

Download the Save Our Skinks.kmz file by right-clicking on it and use "Save Target As" in Internet Explorer or "Save Link As" in Firefox. In Explorer it is best to rename the file extension to ".kmz", IE treats it as a zip file if you don't.

Save Our Skinks.kmz

This is a large file (6 Mb as a KMZ file, 18 Mb as a KML) because it includes 4000 polygons. Using it in Google Earth requires a PC with ample memory and a high speed internet connection. If anyone out there knows how to combine these polygons into one smaller file, please drop us an email at: Contact NatureNorth.com about SOS!

The Assiniboine Delta and origins of the Carberry Sandhills

For the last 2 million years, the Pleistocene Epoch, the climate of Earth has varied widely resulting in as many as 12 different periods of glaciation. A cooling period that resulted in the most recent glacial period, the Wisconsinan, began about 75,000 years ago. About 23,000 years ago the last advance of Wisconsinan glaciers began and Manitoba was covered by glaciers more than 2 km thick. Earth's climate began to warm again around 16,000 years ago. About 11,500 years ago the glaciers began to recede from southern Manitoba. The southwest corner of the province was the first region to be ice-free. It would be another 4000 years before all the province would be relieved of its burden of ice. As the glaciers receded much of the lands east of the Manitoba escarpment became filled with water from the melting ice to form Lake Agassiz. Until 8,200 years ago Lake Agassiz still covered much of southern Manitoba stretching all the way to the US border in the Red River Valley. By 8000 years ago Lake Agassiz was retreating, rapidly exposing most of southern Manitoba, leaving the landscapes we see today.

During the period of peak glacial melting the Old Assiniboine River, carrying meltwater from Saskatchewan and Alberta, was much larger than it is today. The Assiniboine River Valley was carved by this ancient, giant river. Today's Assiniboine River is a mere trickle by comparison. The Old Assiniboine River carried huge amounts of sand and gravel along its course and deposited these in its delta with Lake Agassiz, east of present day Brandon (see Map 4). Deposits of sand and gravel, intermixed with silts and clays, are as much as 150 metres thick in places. The western edge of the delta tends to contain larger deposits of sand and gravel, while more easterly deposits are more silty, though areas of sand deposits can be found even at the eastern edge of the delta. The Portage Sandhills are near the eastern edge of the old delta. Large areas of exposed sand in this region were worked by winds to form large dunes which remain today as sand hills, such as the Carberry and Portage Sandhills, in various locations. Most of these hills are now stabilized by vegetation covering the sand. The Spirit Sands or Bald Head Hills are the only remaining open sand dunes in this area.

The Lauder Sandhills, to the southwest of Brandon, which harbour a small skink population, owe their origins to similar processes surrounding glacial Lake Hind. Download the University of Calgary thesis: Late quaternary geoarchaeology of the Lauder sandhills, southwestern Manitoba, Canada by Matthew James Boyd (13 Mb PDF) for insight into the Lauder Sandhills.

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Biology	Conservation
Biodiversity	Biogeography

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