Final answer:
Species are shifting their ranges due to climate change, which alters their habitats and the availability of food resources, as well as forces them to adapt to new competitive environments, such as the interbreeding of polar bears and grizzly bears.
Step-by-step explanation:
Hundreds of species have shifted their ranges primarily due to climate change, which is altering habitats and forcing species to move to new areas to find suitable conditions for survival. For instance, European bird species' ranges have moved northward to adapt to warmer temperatures. This range shift is not fast enough, as observed with the birds moving 91 km northward when the optimal shift based on warming trends is double that. This phenomenon also affects other species, including plants, butterflies, other insects, freshwater fishes, reptiles, and mammals. As species move, they encounter habitat gaps and new competitive pressures from species that were not present in their historical range. An example of this is the previously separate species of polar bears and grizzly bears now overlapping in range and interbreeding, suggesting a significant ecological impact of climate change.
Moreover, the rate of warming is more accelerated in the Arctic, posing a serious threat to species like the polar bear that depend on sea ice for hunting. Climate change also disrupts species' timed adaptations to seasonal food resources and breeding cycles, leading to mismatches in resource availability and adverse effects on their survival.