These lines (there is four of them) are residuals of the fusion of the five sacrum vertebrae that are fused. These "vertebrae" or segments present a characteristics, being the first of them very similar to a lumbar vertebra, large, and the other vertebrae are<span> progressively smaller and flattened. They also present a curved shape being anteriorly concave.</span>
Well, depending on how long the migration is, many of the animals (mainly birds) could get sick and die, lowering the population. They could be shot by hunters, lowering the population. The children of the population could get left behind and lose their way, lowering the population. I'm not entirely sure how the population could grow other than them finding and staying with another group of their own kind. hope I was helpful! :)
The leaf has 2 types of venation the parallel venation and reticulate venation.
All of the veins, the petiole, and the midrib help position the blade so that it is facing the light source.