Which of the following can be estimated from a sample of invertebrates collected from a pond?

Step 3: Evaluate each option based on biological principles. For example, the age of the pond cannot be determined directly from invertebrates, as this requires geological or historical data. Similarly, the pH of the pond water and the amount of sunlight are environmental factors that require direct measurement using instruments, not invertebrate sampling.

Step 4: Focus on the population density of invertebrates. This can be estimated by counting the number of invertebrates in the sample and dividing it by the area or volume of the pond sampled. This is a direct biological measurement derived from the sample.