Assessing the relative strength of the effects of food resources and predators on a population: A review of methods

Abstract

An understanding of the mechanisms that underlie species distribution and abundance is one of the key problems in population ecology. In order to tackle this problem, it is important to assess the relative strength of the effects of food and predators (consumers) on a focal population. In this study we analysed the advantages and disadvantages of the basic methods that are used to quantify the relative strength of the two types of effects. These methods can be divided into two groups. In the first group, we included the search for examples that are consistent with a proposed hypothesis, the assessment of correlations of abundance at adjacent trophic levels and biomanipulations. What is common for these methods is that they assume the existence of only one type of effect—either bottom-up or top-down. The methods of the second group assume the simultaneous presence of both types of effects and are aimed at quantifying their relative strength. This group includes factorial design experiments and the population-dynamics approach (analysis of population growth, death and birth rates). Here, we have shown that, due to the constraints of each of the methods of the second group, none of them can be considered universal. However, their combined application can be a promising approach to the assessment of the mechanisms that drive population abundance variability, both in experimental and field studies.