Page 704 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

668 part IV Soils, Ecosystems, and Biomes
For two plots labeled i and j, Jaccard index (SJ–ij) is calculated by: SJ-ij = c
where yki is the abundance of species k in plot i, and ykj is the abundance of species k in plot j.
Table AQS 20.2 shows the effect of accounting for abundance of trees of each species. Four species are found in plot A and three species are found in plot E, with two species found in both plots, so SJ-AE is 0.40. But black spruce dominates both plots
(56 of the total 77 individual trees), so SRAE is much higher, 0.93.
TABLE AQS 20.2 Results of Jaccard Index and Similarity Ratio Calculations for Plots A–F Jaccard index (accounts only for presence or absence of species)
where a and b are the number of species unique to plots i and j, respectively, and c is the number common to both plots.
To calculate similarity ratio (SR ) ij
SRij = kykiykj
( y2+ y2+ yy)
(a+b+c)
k ki k kj k ki kj
A
B
C
D
E
F
A n/a 0.13 0.33 0.00 C n/a 0.00 E
Similarity ratio (accounts for abundance of trees of each species) A n/a 0.01 0.90 0.00
C n/a 0.00
E
0.40 0.00 0.00 0.14 n/a 0.14
0.93 0.00 0.00 0.49 n/a 0.01
B
n/a
0.00
0.00
0.00
0.00
D
n/a
0.50
0.29
F
n/a
A
B
C
D
E
F
B
n/a
0.00
0.00
0.00
0.00
D
n/a
0.92
0.02
F
n/a
concepts review
kEy lEArNINg
■ Locate the world’s biogeographic realms, and discuss the basis for their delineation.
The interplay of evolutionary and abiotic factors within Earth’s ecosystems determines biodiversity and the distri- bution of plant and animal communities. A biogeographic realm is a geographic region in which a group of plant or animal species evolved. This recognition laid the ground- work for understanding communities of flora and fauna known as biomes.
biogeographic realm (p. 642)
1. What is a biogeographic realm? What are the zoologi- cal realms? What is Wallace’s line?
■ Explain the basis for grouping plant communities into biomes, and list the major aquatic and terrestrial bi- omes on Earth.
A biome is a large, stable, terrestrial or aquatic ecosys- tem classified according to the predominant vegetation type and the adaptations of particular organisms to that
environment. Biomes carry the name of the dominant vegetation because it is the most easily identified feature. The six main terrestrial vegetation classifications are forest, savanna, grassland, shrubland, desert, and tun- dra. Within these general groups, biome designations are based on more specific growth forms; for example, forests are subdivided into rain forests, seasonal forests, broad- leaf mixed forests, and needleleaf forests. Ideally, a biome represents a mature community of natural vegetation. A boundary transition zone between adjoining ecosystems is an ecotone.
biome (p. 643) ecotone (p. 644)
2. Define biome. What is the basis for the designation? 3. Give some examples of vegetation growth forms.
4. Describe a transition zone between two ecosystems.
How wide is an ecotone? Explain.
■ Explain the potential impact of non-native species on biotic communities, using several examples.
Communities, ecosystems, and biomes can be affected by species that are introduced from elsewhere by humans, either accidentally or intentionally. These non-native spe- cies are also called exotic species or aliens. After arriving