factors:- the greater diversity of the urban landscape, combining extreme ecological conditions;
- the human introduction of non-native species, directly by domestication of plants and animals, and indirectly by transportation of seeds and insects by cargo and cars.
The number of native and alien species is related to the size of human settlements (Table 10.10). Birds, occupying a special position in urban ecological food-chains, require detailed and differentiated habitat conditions. The vegetation structure is undoubtedly the major factor affecting birds in towns, but pollutants such as heavy metals and PCBs also influence bird life. The danger is greater around industrial areas and high traffic lanes. Birds are exposed to direct and indirect effects of air and aquatic pollution through the food-chain. In this way therefore, the number of bird species living in towns and cities can act as an indicator of urban environmental quality.Source: Falinski, 1971
Table 10.10 - Proportion of native and alien species in villages and cities in PolandType of settlement | Native (%) | Alien (%) |
---|
Forest settlements | 7080 | 2030 |
Villages | 70 | 30 |
Small towns | 6065 | 3540 |
Medium towns | 5060 | 4050 |
Cities | 3050 | 5070 |