Final answer:
The mark and recapture method is used by ecologists to estimate both the size and density of a population by marking a sample of the population, releasing them, and then recapturing some to calculate total population numbers.
Step-by-step explanation:
The method that will provide information to an ecologist about both the size and density of a population is mark and recapture. This technique is used primarily for mobile organisms, such as mammals, birds, or fish. It involves capturing a sample of the animals, marking them in some identifiable way, and then releasing them back into their environment. Once they have had time to mix with the rest of the population, a second sample is captured, containing both marked (recaptured) and unmarked individuals. The proportion of marked to unmarked animals in the second sample is used to estimate the total population size. To determine density, the estimated population size is divided by the area in which the population is spread.
There are, however, some limitations to this method. For instance, some animals might learn to avoid capture after being marked or may actually become more likely to be recaptured if a reward was used initially. Furthermore, marking techniques might reduce the survival rates of certain species. Despite these limitations, mark and recapture remains a valuable tool for ecologists studying population dynamics.