Final answer:
A large lake may cause speciation in lizards, which cannot cross water easily, leading to isolation and genetic divergence. Birds, however, can fly over such barriers, maintaining gene flow and preventing speciation.
Step-by-step explanation:
A large lake can act as a geographic barrier that causes speciation in lizards but not birds due to the different capabilities these animals have in overcoming physical barriers. Lizards may be limited by geographical constraints, while birds can typically fly over obstacles, maintaining gene flow between populations.
Lizards, being terrestrial creatures, can be separated by geographic features such as lakes, leading to allopatric speciation. Isolation can prevent the transfer of genetic information, causing two groups from the same species to diverge into distinct species over time. In contrast, birds, due to their ability to fly, are less likely to be geographically isolated by features like lakes. They are capable of crossing these barriers, thereby continuing gene flow, which counters the process of speciation.
Thus, geographic barriers impact species differently, depending on the mobility and biology of the species involved, and these patterns are evident in the distribution of biological diversity around barriers like large lakes and mountain ranges.