urbanisation Flashcards
what is the current extent of urban areas
1% of earths land area , up to 10 % in some regions
What is an example of an area with relatively constant urban extents
London has had a relatively constant level of urbanisation since the 1950’s
what is an example of how urbanisation is increasing in intensity
I.E. Garden types, has become much more common to have paved gardens now reducing green space
- urban areas are increasingly “covered” up/ Tarmacs cement etc.
Example of how urbanisation affects biodiversity
Example: Africa (1% urban cover)
- 245 globally threatened bird species in Africa, 29 of which (10%) are directly linked to urbanisation.
- 1 % urbanisation cover threatens 10% of bird species
What are some of the other main factors affecting African bird species
- Commerical + industrial areas
- Light pollution
- Roads and railroads
- Transport
- almost all have direct links to urbanisation
to what extent does urbanisation affect ecoregions and threaten species (1995)
- 29/867 ecoregions are >33% urban
- These regions contain 213 endemic vertebrates (threatened by urban sprawl)
- 8% of vertebrates on IUCN red list primarily threatened with urban sprawl ( only 1 % urban cover)
Example of a species significantly affected by urban sprawl
- I.E. Wimmer tree shrew , endemic to ivory coast
- has not been recorded since 1976
- originally found in “shrub” habitat on urban fringes , these spaces have now been covered by urban sprawl
Why does urbanisation have such strong conservation effects
- At broad spatial scales there is a strong correlation between number of species and human population
(explanation - humans are another species- just settled in most productive areas) - At small spatial scales urban development often is focused in areas of high wildlife importance
Balmford et al .(2001) + Gonzales- Abraham (2007) `
Effects of urbanization in the USA
urbanisation is the 2nd largest cause of threatened species in the UK `
What is the projected urban expansion by 2030
- 300% increase in urban cover
- 900% increase of urban cover in biodiveristy hotspots (areas with low current urbanisation)
E.g. eastern afromontane + guinean forests of west africa
Proximity to urban areas has the following effects on ecoregions
- fragmentation of green space
- urban heat island
- pollution
- disturbance
- biotic reactions
- these all affect species composition
(local scale) effects of urbanisation
Graph shows that for uk birds as housing density increases , species number first increases up to a point and then plummets
For example: Blackbird population grew with housing density (0-1555), then plummeted as housing increased further (1555-9799)
Why do we see this trend in species number vs housing density
Depends on the habitat type.
- i.e. agriculture vs woodland cover
- gardens more diverse then agriculture monoculture , facilitates higher species richness
- However when you move to high density housing , richhness goes down
What are the three types of species response to urbanisation
- Urban avoider (population decreases with urbanisation)
- Urban adapter (population increases initially and then returns to normal levels as urbanisation increases)
- Urban exploiter (population increases with urbanisation)
what does urbanisation promote
-urbanisation promotes biotic homogenisation
I.E. urban assemblages similair regardless of their location
How was the assembly structure of Adelaide changed with increasing urbanisation
Over time plant species have increased, natives have decreased and exotics have increased
- this is indicative of a characteristic of urbanisation (intro of exotics)
How dangerous is the introduction of new species to a habitat
Invasion of alien species is as large a driver of extinctions as urbanisation.
Genetic structure of urban populations
- On average genetic populations are less diverse and often genetically distinct from other populations
Species example of urban and rural trait divergence
Crepir sancta
- 55% of seeds land on cement (cant germinate)
- Shift -> Significant increase in proportion of non-dispersing seeds
- selection experiments suggest short term evolution over 5-12 generations
2nd example of urban vs rural trait divergence (communication)
- Birds are singing at higher frequencies in urban environments
- Most urban sounds are low freq
- Adaptive however unknown if females will begin to select for higher pitched voices
3rd example of urban vs. rural trait divergence in plant reproduction
- Rural pollinator (rich) - herkogamy spatially isolated male anthers and female stigma
- Urban pollinators (few) - no herkogamy , heritability index H2 = 0.62
Evolutionary response in urban populations due to reduced availability of pollinators
*Good example of adaption and reduced success of plants in urban areas
What are the effects of bird feeders
- there is mixed evidence that it increases population densities
- May promote aggressive or invasive species (grey squirrel)
Affects of domesticated cats on wildlife
- Direct mortality
- probably limits population size
- hard to estimate rates in some locations
- Sub lethal affects of predation
- another secondary affect can be drawing attention to nest sites through the birds mobbing the cat
What are the sub-lethal effects of predation
Fear of predators -> reduced provisioning -> smaller clutch size / reduced chick growth rates I.e.
Additive and compensatory mortality
Not all predation increases mortality
I.e. if a cat kills a bird that was going to starve anyway it does not matter
