Habitat change and Island Biogeography


Millenium Ecosystem Assessment (2005): Take stock of the state of the climatic zones on the planet and the threats facing the biodiversity in each habitat. 

Climate change has not yet had a major impact- but it is starting to. Pollution is increasing in every single habitat. Habitat change seems to be having the largest impact currently.

Habitat change: Loss, fragmentation, degradation

Terrestrial: Land conversion e.g. for urban or agricultural use, resource extraction e.g. forestry, mining, pollution e.g. waste, air pollution, pesticides, fertilizers. 

Marine: Fisheries e.g. towed fishing gear, sedimentation/pollution

Future: climate change-coral reefs, forests, marine algae. 

Most species do better and have higher populations in the most protected areas with low land use intensity. Although for some species e.g. birds may actually see increases in populations as land use becomes more artificial due to the new habitats made e.g. urban rooftops.  

Habitat Fragmentation- Where large continous areas of habitat are reduced in area and divided into fragments. Fragments are often isolated from each other by highly modified or degraded landscapes. Edges experience altered conditions or "edge effects". 

Example: only 7% of the Brazilian Atlantic forests are left compared to 500 years ago- this is in a highly fragmented state. 

Consequences- Limits dispersal + colonisation (moving between areas). Populations are divided into smaller groups- increased risk of inbreeding. Restricts access to resources. Increased vulnerability to invasion by species or disease- no way to escape. 

Only a few areas left in the world with forest that is more than 1000m to the edge from the centre. 65% of all the forest in the world is less than a km in fragment size

Reduced area, increased isolation, increased edge

Habitat degradation- Reduction in the quality of habitats for suporting life. Can be physical or chemical e.g. pollution, 

Islands at risk- These plant and animal communities have so far been the worst affected by humans. Nearly half of the species that have gone exitinct since 1500 have been island species even though islands…


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