chapter 53 community ecology copyright © 2002 pearson education, inc., publishing as benjamin...
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CHAPTER 53COMMUNITY ECOLOGY
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Section D: Biogeographic Factors Affecting the Biodiversity of Communities
1. Community biodiversity measures the number of species and their relative
abundance
2. Species richness generally declines along an equatorial-polar gradient
3. Species richness is related to a community’s geographic size
4. Species richness on an island depends on island size and distance from the
mainland
• Two key factors correlated with a community’s biodiversity (species diversity) are its size and biogeography.
Introduction
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The variety of different kinds of organisms that make up a community has two components.
• Species richness, the total number of species in the community.
• Relative abundance of the different species.
• Imagine two small forest communities with 100 individuals distributed among four different tree species.
1. Community biodiversity measures the number of species and their relative abundance
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Species richnessmay be equal,but relativeabundance maybe different.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 53.21
• Counting species in a community to determine their abundance is difficult, especially for insects and smaller organisms
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 53.22
• Tropical habitats support much larger numbers of species of organisms than do temperate and polar regions.
2. Species richness generally declines along an equatorial-polar gradient
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 53.23
• What causes these gradients?
• The two key factors are probably evolutionary history and climate.
• Organisms have a history in an area where they are adapted to the climate.
• Energy and water may factor into this phenomenon.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 53.24
• The species-area curve quantifies what may seem obvious: the larger the geographic area, the greaterthe numberof species.
3. Species richness is related to a community’s geographic size
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 23.25
• Because of their size and isolation, islands provide great opportunities for studying some of the biogeographic factors that affect the species diversity of communities.
• Imagine a newly formed island some distance from the mainland.
• Robert MacArthur and E. O. Wilson developed a hypothesis of island biogeography to identify the determinants of species diversity on an island.
4. Species richness on islands depends on island size and distance from the mainland
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Two factors will determine the number of species that eventually inhabit the island.
• The rate at which new species immigrate to the island.
• The rate at which species become extinct.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 53.26
• Studies of plants on many island chains confirm their hypothesis.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 53.27