Concepts of Large Herbivore Population Dynamics

This paper considers the conceptual basis of large herbivore population dynamics. Carrying capacity is discussed in its many meanings, and K-carrying capacity, the maximum number of animals an area will support based on resources, is suggested as the basic meaning of the term. I-carrying capacity is defined as the population yielding the maximum sustainable yield (MSY). Density-dependent functions and how they are detected are considered. There is a growing appreciation of the non-linear density functions of large mammals, with more K-selected ones having a “plateau” of nearly constant population growth rate, followed by a “ramp” of density dependent decline in growth rate. This complicates the detection of density dependence, and shifts I-carrying capacity to much nearer K-carrying capacity than the K/2 of the linear model. Constraints on the range of reproductive parameter values are severe, and population limits are strongly conditioned by the limitations on life expectance. Age at first reproduction is the most important parameter influencing population growth rate in most K-selected large herbivores. As population growth rate declines near K-carrying capacity the necessary adjustment in life expectancy to maintain population equilibrium increases rapidly. Yield can be taken periodically rather than annually without loss of yield if the species has a long, constant growth rate plateau, I-carrying capacity occurs at, and MSY is obtained from the point of conjunction of the plateau and ramp. Consequently, the more K- selected the species, the nearer I-carrying capacity will be to K-carrying capacity. Assuming a linear density-dependent function (as with the logistic model where I-carrying capacity is K/2) is a formula for overexploitation of large herbivores.