<span>It may be difficult for ecologists to determine the size of a bird population if that population migrates to different locations throughout the year. During migration, some birds may split off from the group and not return, others may die, and still others may join. Therefore, the bird population will be in constant flux. It is hard to know, when the birds return to their prior location, if the population consists of the same group of birds (in addition to deaths and births) or whether it has grown or shrank through other means. However, to estimate the size, an ecologist can track a migratory flock through several years, counting each year to get a general sense of the population size. Additionally, given one measurement, an ecologist could consider the average lifespan and birth rates of the population to extrapolate the size of the population in subsequent years.</span>
The chemicals, neurotransmitters are released to carry a nerve impulse which is an electric signal transmitted by the nervous system. This impulse transmitted from one neuron to another. Examples of neurotransmitters are serotonin in which scientists thinks that a low level of this is one of the causes of depression.
Metals, non metals, and metalloids
Answer:
All the choices are correct
