Part 2: Why are some counties more diverse than others and why do the species occur where they do?
Here we ask why we see the patterns that we do in terms of diversity in the state. Why do some
counties have more diversity than others? This is not a simple question -- part of it has to do with the
migrations of organisms. If organisms were pushed south by glaciers (and a large part of Ohio was in
fact covered by glaciers) and then moved northward again, it might make sense to expect more species
in the southern part of the state, since they would have arrived there first. But species get to be where
they are in various ways -- seeds are carried by birds or blown in storms, for example. When they arrive,
whether they will be able to survive or not depends on whether there is proper habitat for them.
We will focus on habitat here. We can look at the patterns of soils in Ohio and see where we find
the most different conditions occurring near to each other -- we can then see whether diversity of soil
types is related to diversity of species by comparing the soils map with our species diversity map.
We can also ask why particular species occur where they do. Some species grow in a wide variety of habitats, while others are very limted. We chose species here that are fairly limited in where they will grow -- they can be good indicators of quality habitats.
Comparing Ohio's plant diversity with geological history
The map on the right shows the different ages of exposed rocks and soils in Ohio -- the oldest are toward the west and the younger are toward the east. In Ohio, the older soils tend to be more limestone-derived, while the more eastern younger soils are sandstone types that are more acidic. Each type tends to support a different set of species (although some will occur in both). Do you see a pattern when you compare the species map with the geological map? Where are the counties with the largest numbers of species in relation to the colors (and numbers of colors) on the geological map? Why do you think that this might be?
Next, let's look at a few species in particular. Click on Blue Ash, Spotted Pipsissewa and Huckleberry and look at their distributions -- in what part of the state do you find these plants? Which of these species might you find growing together? Given the habitat information provided with each species and compared to the geological map above, why do you think that they have the distributions that they do?
The distributions of some species do not match geological patterns. Look at Bog Buckbean and the prairie species that were included -- Prairie Dock, Prairie Loosestrife, and Prairie Milkweed. Why do you think that they have the distributions that they do?
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