Habitat fragmentation srm
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Habitat fragmentation involves reducing the area of habitats and dividing remaining habitat into smaller, isolated patches. This disrupts connectivity and species may struggle to adjust. Fragmentation begins with gap formation and increases over time as gaps expand and connectivity is lost. Biological consequences include initial exclusion of species, crowding in fragments, insularization effects, isolation, edge effects, and matrix effects. Roads pose additional threats through mortality, barriers to movement, and enabling invasive species. Species vulnerable to fragmentation are endemics, interior specialists, those requiring mixed habitats, and those with low mobility or reproduction.
Habitat fragmentation srm
- 1. S. R. Maharjan Asst. Professor Tribhuvan University
- 2. Habitat fragmentation is the conversion of landscape to small fraction of its former area Habitat fragmentation has two components: ◦ A reduction in the area covered by a habitat type ◦ A change in habitat, with remaining habitat divided into smaller and isolated patches 2
- 3. Fragmentation and heterogeneity The fragmentation process Biological consequences of fragmentation Species vulnerable to fragmentation 3
- 4. 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. 4
- 5. 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. 5
- 6. In terrestrial ecosystems, fragmentation typically begins with gap formation. As the gaps get bigger or more numerous, they eventually become the matrix.The connectivity of original vegetation is broken. At this point, in the fragmentation process, it ceases to support some species 6
- 7. Initial exclusion Crowding effect Insularization and area effects Isolation Edge effects Matrix effects The special problem of roads ◦ Species invasions 7
- 8. One of the rapid effect of fragmentation is elimination of species that are endemics with narrow distribution. ◦ Eg. 90 species of plants were lost when small patch of forest destroyed by logging 8
- 9. When habitat is isolated by fragmentation, population density of animals increase in fragments. Population of large habitats will be displaced in small fragments, known as crowding effect. ◦ Eg In Amazonian forest of Brazil, capture rate of understorey birds in a 10 ha fragment increased more than double after its isolation ◦ Density of ovenbirds increased in forest fragments due to logging. 9
- 10. The number of species decrease with decline of insular(like an island) habitat ◦ A small island or nature reserve may be smaller than the territory or home range of organism ◦ A cougar is unlikely to ramain in 100 ha park which requires average of 400 km2. ◦ Grizzly bears reuire 900 km2 ◦ in N america, parks smaller than 9500 km2 didn’t sustained wolves population ◦ Animals are vulnerable to mortality while attempts to travel through fragments 10
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- 12. Species with specific habitat requirements depend on many habitat patches in close proximity Many animals require a mix of different habitat with distinct resources- roosting sites, breeding sites, food patches etc. Human created barriers- roads, urban areas, agricultural lands, clearcuts inhibit movement and affect population viability 12
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- 14. Reduction in genetic diversity Inbreeding depression (reduced biological fitness due to inbreeding) increase extinction risks Human created barriers such as dams also fragment freshwater habitats, block migration and recolonization of freshwater fishes 14
- 15. Best documented impacts Outer boundary influenced by light and wind Shade intolerate species dominate due to edge effect. Accelerated growth of trees and shrubs Animals attracted to edge, ecological trap Birds- Brood parasitism/ nest predation Extinction od interior birds/ no core areas 15
- 17. Matrix- landscape surrounding habitat fragments Alteration of matriz increase isolation When contrast of matrix increase, edge effect also increase Diversity of birds is lower in patches surrounded by urban areas 17
- 18. Habitat fragmentation supplemented by road construction Effects of roads documented- ◦ Mortality from road construction ◦ Mortality from collision with vehicles ◦ Modification of animal behaviour ◦ Alteration of physical environment ◦ Alteration of chemical environment ◦ Spread of invasive species ◦ Increase of edge effects ◦ Barriers for animals 18
- 19. 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. 19
- 20. Top-down regulation (Cascading effects) Microclimate changes decrease invertibrate communities Allee effect(below some threshold population size, no pollinators visit) 20
- 21. Wide-ranging species Nonvagile species (with poor dispersal abilities) Species with specialized requirements Large-patch or interior species Species with low fecundity or recruitment Species vulnerable to human exploitation 21