The Nature Of Marginal Areas

1 Recognizing margins 3

1.1 Defining margins 5

1.2 Margins and climate change 5

1.3 Limits to distribution 8

1.3.1 Physiological boundaries 9

1.3.2 Resource availability 9

1.3.3 Resource access and conservation in marginal areas 15

1.4 Genetic boundaries 17

1.5 Demographic factors 17 1.5.1 Limits for reproduction 19

1.6 Relict species and climate change 19

1.6.1 Evolutionary relicts 20

1.6.2 Climatic relicts 20

1.7 Endangered species 23

1.8 Agricultural margins 24

1.9 Conclusions 26

2 Biodiversity in marginal areas 29

2.1 Biodiversity at the periphery 31

2.2 Assessing biodiversity 31

2.2.1 Definitions of biodiversity 31

2.2.2 Problems of scale and classification 34

2.2.3 Variations in assessing genetic variation 35

2.3 Variation in peripheral areas 36

2.4 Disturbance and biodiversity 36 2.4.1 Grazing 37

2.5 The geography of marginal plant biodiversity 43

2.5.1 The South African Cape flora 45

2.5.2 Mediterranean heathlands 48

2.5.3 Mediterranean-type vegetation worldwide 50

2.5.4 The Brazilian Cerrado 51

2.6 Plant diversity in drylands 52

2.7 Plant diversity in the Arctic 57

2.8 Conclusions 59

3.7.6 Phosphate 100

3.7.7 Phosphate availability at high latitudes 101

3.8 Mycorrhizal associations in nutrient-poor habitats 102

3.8.1 Mycorrhizal associations in the Arctic 102

3.8.2 Cluster roots 103

3.9 Nutrient retention in marginal areas 103

3.10 Changes in resource availability in the Arctic as a result of climatic warming 106

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