4b 2 Flashcards
Habitat fragmentation
Small patches can only withstand small populations which may not be viable
Global problem
Major problem for large species needing a large area
3 main effects
- Reduced habitat area
- Changes at the fragment edges
- Increased isolation between habitats and populations
Theory of Ireland biogeography
Balance between extinction and colonisation
Fragmentation is mainly a problem for
Large species
Species with large territories
Species with large migratory or dispersal ranges
Edge effects
Trap or sink (roadkill) Barriers Humidity decreases Temperature increase Wind damage along forest edge
Reason for fragmentation
70% European territory = poorly connected woodland
40% of European woodlands = intensively used (100m from non forest land)
15% strongly fragmented by mainly intensive land use
Invasive species
Human movement between continents leads to increase non-natural range expansion of species = invasive
Some introductions were intentional, accidental as escapes or unintentional
Introduced pathogens
3 phases of invasion
Introduction to a new range
Establishment
Spread
Squirrels
1876-1920s
Grey squirrel replacing red
Competition for good=main reason. Pathogens introduced with grey
Single Crayfish 1975
Native crayfish near extinction through spread of plague and lack of resources
Single crayfish grower bigger, more aggressive and more tolerant to conditions
Impact of invasive plants
Impact on diversity = less severe than invasion of pathogens, herbivores or predators
Not shown to lead to extinction of native plants but this may take more time
Changes in water availability
Damage to infrastructure and economic loss
Japanese knotweed 1886
Garden escape
Urban arrears - come up through gaps in floor in conservatories and patios
Nuisance to damage of infrastructure
