Final answer:
Larger poultry birds without summer adaptation capacities may suffer from heat stress and reduced survival rates. The northward movement could lead to habitat and predation issues, and changes in beak size in bird populations indicate natural selection at work based on environmental conditions.
Step-by-step explanation:
If poultry birds are larger in size and do not have summer adaptation capacity, there would likely be several consequences for the birds and the ecosystems they inhabit. Larger poultry birds could be susceptible to increased thermal stress during hot weather if their bodies are not adapted to disperse heat effectively. Without summer adaptations, such as the ability to find shade, alter behavior to minimize heat exposure, or physiological adaptations to cope with higher temperatures, these larger birds might experience reduced survival rates and difficulties in reproduction.
The movement northward of North American bird species, as reflected in the data showing the correlation with increasing average winter temperatures, suggest that birds could encounter various problems when using farther north areas. These issues include habitat change, which may not suit their ecological needs, and predation pressure from local predators that are not adapted to their presence. The graph also suggests that climate change and changing ecological conditions can have significant impacts on the bird populations.
Specifically, birds with small, thin beaks may struggle in regions where only larger seeds with tough cases are available, leading to a natural selection process favoring birds with larger, broader beaks for cracking these seeds. This is an example of an evolutionary change driven by environmental factors. Additionally, there could be other consequences such as changes to food chain dynamics, where the presence of new or increased populations of birds may alter the abundance of prey or predator species and disturb the balance of local ecosystems.