by
Susan Evarts, Department of Biology, University of St. Thomas
Alison Krufka, Department of Biological Sciences, Rowan University
Chester Wilson, Department of Biology, University of St. Thomas
By the end of this case, you will:
White clover (Trifolium repens), a small perennial plant, is found throughout the world, and has two forms. One variant has entirely green leaves (plain) and the other has green leaves with a prominent white stripe (striped).
Both variants of white clover (plain and striped) are found along the coast of Long Island, New York. Most of Long Island is only a few feet above sea level. A series of low grass-covered hills separated by shallow depressions covers the area behind the oceanfront dunes. The shallow depressions reach to the water table, so they tend to be permanently moist year round and do not freeze in winter. Water drains away quickly from the low hills, which tend to dry out many times over the year and freeze in the winter. The habitat in the shallow depressions is more hospitable to molluscs (snails and slugs) that feed on clover. One type of clover is more common in shallow depressions while the other type is more likely to be found on low hills.
At the end of the case, we will come back to New York and ask you to predict which type of white clover is most abundant in each microhabitat. But first, let’s consider the abundance of these two types of clover on a larger scale.
Figure 1, below, shows the relative frequency of white clover variants in Minnesota and North Carolina.
Figure 1
Table 1 provides additional information on Minnesota and North Carolina.
| Minnesota | North Carolina | |
|---|---|---|
| Latitude | 43–49° N | 34–36° N |
| Mean elevation | 0.365 km | 0.213 km |
| Ave. monthly temp. range | −19.4° to 28.6° C | −2.6° to 31.3° C |
| High temperature | 45.6° C | 43.3° C |
| Low temperature | −51° C | −37° C |
| Mean # days with high above 32° C* | 14 | 38 |
| Mean # of days with low below 0° C* | 154 | 75 |
| Ave. yearly precipitation | 66–76 cm | 107–117 cm |
| Presence of herbivores (molluscs such as snails, slugs) | smaller population, not present in winter | larger, more active population, present all year |
| Data from Netstate.com and National Oceanic and Atmospheric Administration. *Data for capitol cities (St. Paul , MN, and Raleigh, NC). | ||
A habitat is defined as the place and conditions under which an organism lives. This includes physical factors such as temperature, soil type, availability of nutrients, and availability of moisture as well as biological factors such as presence of herbivores, competitors for nutrients, and pathogens. Using the information in Table 1, briefly summarize the habitat features for white clover in each state.
Date Posted: 11/28/06 nas
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