Contents: What is it? Why is it so important ? What causes habitat loss and fragmentation ? What are its effect? So what we can do ? Conclusion
What is it? Many times, natural habitats show a “patchy” distribution. This affects the organisms that live there.
However, in today’sworld the effect ofanthropogenic habitatfragmentation isprobably much moresignificant.Equally significant isthe fact that many ofthe organisms in thesehabitats are not“adapted” for suchfragmentation.
Activities such as “clear-cutting” havecreated a mosaic of forested andunforested areas in many regions that wereonce completely covered with forests.
• A simplistic view of fragmentation is larger patches being broken into smaller ones
Why is it so important ? Habitat loss reduces the amount of habitat and habitat type available Thought to be the most important threat to biodiversity at the moment Fragmentation results in the pieces of habitat increasing in insularity with larger edges as well as a loss of total habitat
What causes habitat loss and fragmentation ? -dams in rivers -roads in parks -canals -power lines -fences -fire lands -other ???
Roads as barriers
Roads as avenues for invasion by humansand exotic species Initial road 20 yrs later
What are its effect?A. initial exclusionB. isolationC. Island biogeographyD. edge effects
Initial exclusion, isolation and consequentloss of biota
Island biogeography MacArthur and Wilson(1960)• Since the remaining habitat begins to resemble an island, the ideas of island biogeography theory are applied to them.• On small islands, the number of species results primarily from the interaction of two processes: Colonization and Extinction rate.• The point at which these two rates are in equilibrium will determine the number of species found on the island.
Colonization rate Close islandColonization rate is aFunction of distance Distant islandFrom mainland Number of species Ex tinction rat e Extinction rate is a Function of island Small island size Large island Number of species
Colonization rate (Distance) Close, large island EquilibriumNumber of species Extinction rate (Size)
Colonization rate (Distance)Number of species Equilibrium Distant, Small island Extinction rate (Size)
• So, what happens if we form an “island” from an area that was once part of a larger habitat.• It will, initially, probably contain more species than the equilibrium of colonization and extinction can support.• This, in theory, would lead to biotic relaxation.• Biotic relaxation is simply a decline in the number of species when a formerly “connected” region becomes isolated as it approaches a new equilibrium.
National Parks arehabitat islands, andoften show bioticrelaxation. This isoften most pronouncedin the smaller parks.Mount Rainier NationalPark in Washington hasseen a reduction in thenumber of mammalsfound there from 68 to37 species.
D. edge effects• One of the best documented effects of fragmentation are ‘edge effects’• Brings change in species composition with invasion of exotic species• For e.g. Cowbird parasitism (fragmented forests of Illinois) may be significant for 100’s of m into a forest
i) Cowbird removing eggs of host songbirdii) woodthrush nest parasitized by cowbirdiii) Mother blue-winged warbler feeds cowbird chickiv) Endangered Kirtland’s warbler - highly parasitized by cowbirds
• Predation can also be significantly higher near the edges as densities and movements of raccoons, opossums, crows, foxes, jays, skunks, are all higher.
Edge effects: Greater vulnerability to invasion by exotics
• The degree to which fragmentation affects ecosystems depends on the relative responses of many different organisms which may respond differently.• Habitat loss and fragmentation Increasingly leading to ex situ breeding and conservation efforts.
So what we can do ?• The first strategy for minimizing habitat fragmentation is to avoid sensitive habitats.• Another important concept is to have corridors between fragments to allow the movement of species.
• Combination of techniques to improve connectivity of isolated habitat areas. Spanaway Creek, Washington Roadside Vegetation Fences and Walls
Wildlife Underpass High Bridges to preserveWildlife Overpass riparian ecosystems Box Culverts Small Culverts
• cowbirds - put trapped birds into bags hooked up to car exhaust for killing• Solutions - reforestation of deforested lands to create larger core areas for songbird breeding
Conclusion• Anthropogenic activities are accelerating the rate of habitat loss and fragmentation.• Due to which rate of species extinction is increasing and much are being endangered giving threat to biodiversity.• Therefore, our motto should be to understand this process and develop various strategy to mitigate this problem as soon as possible.