habitat fragmentation 鄭先祐 (ayo) 台南大學 環境與生態學院 院長 japalura@hotmail.com

Habitat Fragmentation

鄭先祐 (Ayo)台南大學 環境與生態學院 院長

Japalura@hotmail.com

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Introduction

Habitat fragmentation has two components: A reduction in the area covered by a habitat type A change in habitat configuration

Essay 7.1 habitat “shredding” ( 破碎化 )

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Contents

Fragmentation and heterogeneity The fragmentation process Biological consequences of fragmentation Species vulnerable to fragmentation Fragmentation versus habitat loss, and

regional differences The problem of climate change Conclusion and recommendations

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Supplements

Essay 7.1 habitat shredding Essay 7.2 mosaics and patch dynamics

Box 7.1 Quantifying landscape pattern and fragmentation Box 7.2 Species vulnerable to fragmentation

Case Study 7.1 Subdividing the west Case Study 7.2 The fragmentation of aquatic ecosys

tems and the alteration of hydrologic connectivity: neglected dimensions of conservation ecology

Case Study 7.3 Dissecting nature: the islands of Lago Guri

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Nature is patchy vs. shreded

Metapopulation models, landscape mosaic metaphors, and other “nature is patchy” concepts do not fit the shred configuration well.

Shredded landscapes may demand that ecologists develop new or modified models of population dynamics, demography, dispersal, and genetics, or that they apply the principles of landscape ecology.

Most importantly, the conservation consequences of shredded habitats may differ significantly from those of fragmented habitats.

Essay 7.1 habitat shredding

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Shredded habitats invite empirical study and modeling in their own right, as ecologically interesting and significant landscape features along agricultural frontiers in the Neotropics at least.

They should arouse conservation concern, as possible refuges for native species, as corridors for, or barriers to exotics, and as potential reservoirs of native species for future restoration of their surroundings.

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Patchiness is good?

If patchiness is good then why is fragmentation caused by humans perceived as bad?

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Naturally patchy vs. fragmented landscapes

1. Fragmentation has resulted in a reduction of the extent and connectivity of habitats, and species may or adjust to this change in habitat availability and configuration.

2. A naturally patchy landscape has rich internal patch structure, whereas a fragmented landscape typically has simplified patches and matrix, such as parking lots, corn fields, clear-cuts, and tree farms.

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3. A natural landscape often has less contrast between adjacent patches than does a fragmented landscape, and therefore potentially less-intense edge effects.

4. Certain features of fragmented landscapes, such as roads and various human activities, pose specific threats to population viability.

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切割棲息地後，所含的生物種類數反而增加，可能的原因：

1. Habitat diversity 2. Population dynamics.

Priority effects Multiple stable equilibria Edge effects Disturbance Species pool and dispersal ability. Colonization Evolutionary effects. Extinctions.

3. Historical effects.

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Fig. 13. 島嶼生物地理學 (修改自 Case & Code, 1987)

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The fragmentation process

In terrestrial ecosystems, fragmentation typically begins with gap formation.

As the gaps get bigger or more numerous, they eventually become the matrix.

Fig. 7.4 (p.220)

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Biological consequences of fragmentation

Initial exclusion Crowding effect Insularization and area effects Isolation Edge effects Matrix effects The special problem of roads

Species invasions

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Fig. 7.13 populations of the forest-dwelling carabid beetle Abax alter were almost completely divided by a road and even by parking loops. Lines represent movements of marked beetles between capture and recapture points.

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Species invasions

Roads may serve as conduits for the invasion of some species.

Roads favor species with good dispersal abilities in disturbed habitats at the expense of species with limited mobility.

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Effects on ecological processes

Top-down regulation (Cascading effects) Microclimate changes Allee effect Mutualisms Low predictable sequence

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Species not vulnerable to fragmentation

1. A species might survive or even thrive in the matrix of human land use.

These species are typically considered “weedy” and of little conservation concern.

2. a species might survive by maintaining viable populations within individual habitat fragments.

These species are with small home ranges.

3. Is to be highly mobile

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Box 7.2Species vulnerable to fragmentation

Wide-ranging species Nonvagile species (with poor dispersal abilitie

s) Species with specialized requirements Large-patch or interior species Species with low fecundity or recruitment Species vulnerable to human exploitation or p

ersecution

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The problem of climate change

Fragmentation is a threat to biodiversity even in a relatively stable world.

If we add the phenomenon of rapid climate change, then we have perhaps the most ominous of all potential threats to biodiversity.

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Conclusions and recommendations

1. Conduct a landscape or seascape analysis ( 區塊間，是否需要 connections)

2. Evaluate the landscape or seascape of interest within a larger context. What is the significance of this landscape to conservation goals at regional, national, and global scales?

3. Avoid any further fragmentation or isolation of natural areas. ( 生態廊道 )

4. Minimize edge effects around remnant natural areas (establishing buffer zones)

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5. While conserving large, unfragmented patches of habitat, don’t “write off” the small fragments. Such areas may be the last refuges for many species in highly fragmented regions and can maintain populations of many species for decades.

6. Do not write off the landscape matrix as non habitat. There will rarely be enough area in reserves to conserve all of a region’s biodiversity.

7. Identify traditional wildlife migration routes and protect them.

8. Maintain native vegetation along streams, fencerows, roadsides, powerline rights-of-way, and other remnant corridors in strips as wide as possible.

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9. Minimize the area and continuity of artificially disturbed habitats dominated by weedy or non-native species, such as roadsides, in order to reduce the potential for biological invasions of natural areas.

10. Small fragments often suffer from disruption of natural processes, such as fire regimes. (Active management will be needed)

11. Avoid dam construction, water diversions, and other activities that disrupt aquatic or hydrologic connectivity, and reverse these disruptions where possible.

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Supplements

Case Study 7.1 Subdividing the west Case Study 7.2 The fragmentation of aquatic

ecosystems and the alteration of hydrologic connectivity: neglected dimensions of conservation ecology

Case Study 7.3 Dissecting nature: the islands of Lago Guri

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