Chapter 18 - The Dominance of Different Regulating Factors for Rangeland Grasshoppers

Abstract

This chapter discusses the dominance of different regulating factors for rangeland grasshoppers. Developing a unified, conceptual framework that explains population fluctuations presents a fundamental and critical challenge to ecologists. Although, the standard notion is that grasshopper densities are related to annual weather, the population mechanisms associated with weather have not been established. Comparative results on intraspecific competition for food, predation, and abiotic factors that were obtained from common experiments with the most abundant grasshoppers at each site have been summarized in the chapter. The foregoing results indicate the importance of long-term experiments. To develop an integrated perspective, the chapter focuses on demographic responses most likely to exhibit significant density-dependent and -independent effects. An individual's probability of surviving should be a function of initial hatchling density. The density-independent production is set by a female's ability to process food and convert it into young, given food quality and the abiotic environment. Much of the 50-year debate over population limitation arises in part from weaknesses in the available data sets, but largely stems from the desire of ecologists to attribute limitation to a single mechanism studies to indicate that one of the key mechanisms that changes over time and between sites for herbivore populations is the influence of plant quality and quantity. Studies of population dynamics must consider food resources and how they vary over time and space, especially to resolve issues like population limitation and top-down versus bottom-up control.