Final answer:
Parapatric speciation is an intermediate between sympatric and allopatric speciation because it involves limited gene flow due to a gradient or hybrid zone, allowing for some genetic exchange while driving divergence and the development of new species.
Step-by-step explanation:
Parapatric speciation is an intermediate between sympatric and allopatric speciation because it shares characteristics of both. Parapatric speciation occurs when populations are not completely isolated but have limited gene flow due to a gradient or a hybrid zone. This allows for some genetic exchange but also drives divergence and the development of new species. For example, if a population of birds occupies a range of habitats with different ecological conditions, adaptation to those conditions may lead to the formation of distinct species along the gradient.