When roads, farms and towns are built across a large continuous forest, the forest is broken into smaller patches separated from one another. This breaking ...

(a) Relationship between patch size and number of species [2]
The larger the patch, the greater the number of species it contains; equivalently, as fragment size decreases the number of species falls. This holds for both birds and mammals shown on the graph.

(b) Percentage decrease in bird species from 100 ha to 1 ha [2]
From the graph the 100 ha patch has about 45 bird species and the 1 ha patch about 9. The percentage decrease is:
\(\dfrac{45 - 9}{45} \times 100 = 80\%\)
1 mark for correct working, 1 mark for the answer of 80%.

(c) Why smaller patches support fewer species [3]
A smaller area offers less habitat, less food and fewer resources [1]; it can support only small populations, which are more likely to die out [1]; and species that need large territories or ranges cannot survive in a small patch at all [1].

(d) How building a road causes fragmentation [2]
The cleared strip of the road cuts the once-continuous forest into two or more separate parts [1]; animals cannot cross the open road safely, so the populations on either side become isolated from one another [1].

(e) How wildlife corridors could help conservation [2]
The strips of forest join the separate patches so that animals can move between them [1]; this allows feeding, breeding (gene flow) and recolonisation of empty patches, which lowers the risk of extinction [1].

(f) Two consequences of reduced biodiversity for an ecosystem [2, any 2]
Any two of: food webs are disrupted; the ecosystem becomes less stable and recovers less well from change; useful species or resources are lost; services such as pollination or nutrient recycling are reduced.