Quick questions on Population Dynamics and Sampling - TCE Biology (Tasmania)

Two idealised growth patterns are commonly described:

Density-dependent factors have a stronger effect as the population becomes more crowded. They include:

Density-independent factors affect a population regardless of how crowded it is. They are usually abiotic events such as:

It is rarely possible to count every individual, so ecologists sample and estimate. For organisms that do not move much (plants, slow invertebrates), quadrats are placed, ideally at random, and counts are scaled up to the whole area. For mobile animals, the capture-mark-recapture method is used:

Estimates are only as good as the sampling. Reliability improves with larger sample sizes, random placement of quadrats to avoid bias, and meeting the assumptions of the method used. Repeating the sampling and reporting a range rather than a single figure gives a more honest picture of the true population size.