Читать книгу Ecology - Michael Begon - Страница 143

We have seen throughout this chapter that intraspecific competition can influence the number of deaths, the number of births and the amount of growth within a population. We have illustrated this largely by looking at the end results of competition. But in practice the effects are often progressive. As a cohort ages, the individuals grow in size, their requirements increase, and they therefore compete at a greater and greater intensity. This in turn tends to increase their risk of dying. But if some individuals die, then the density is decreased as is the intensity of competition – which affects growth, which affects competition, which affects survival, which affects density, and so on.

In trying to understand these interconnected processes it is important to distinguish three types of study: (i) those in which the ‘final’ performance of competitors is monitored over a range of densities and hence over a range of intensities of competition; (ii) those in which density and performance are monitored together over time as groups of competitors grow and undergo density‐dependent mortality; and (iii) those which seek relationships between density and performance in sets of populations, each observed just once (Weiner & Freckleton, 2010). Each type of study involves density and the performance of either individual competitors or the whole population, but the three tend to be aimed at addressing rather different questions. We examined the first in Section 5.2.2 when we discussed constant final yield. We turn here to the second and third.