Final answer:
The population of small ground finches likely remains unaffected by the increasing number of small tree finches due to resource partitioning and niche differentiation where each finch species exploits different food sources based on their beak adaptations.
Step-by-step explanation:
One reason why the population of small ground finches has not been affected by the increasing number of small tree finches could be due to resource partitioning. The different beak sizes and shapes among the finches indicate specialization for different types of food sources, which reduces direct competition for resources.
For instance, small tree finches might be exploiting resources in the trees, whereas small ground finches could be feeding more on the ground. This distinct niche differentiation allows for the coexistence of both populations without significant competition affecting the ground finches' numbers.