Beyond population regulation and limitation

Abstract

Abstract. The study of population dynamics addresses three questions that are not always separated in discussions with empirical data. Two questions address population regulation. What stabilises population density is the first question, and, in spite of much theory, little progress has been made in answering this question empirically. The assumption of an equilibrium density is impossible to test and direct experimental tests to answer this question are rare. What prevents population growth is a second question, and is the classic question of population regulation. To answer this question requires an increasing population, and, with adequate experimental manipulations, the densitydependent factors preventing increase can be identified. Surprisingly, answering this question has provided little assistance in solving practical problems in population dynamics, possibly because most populations are rarely in the state of growth and show a limited range of densities. What limits population density in good and poor habitats is a third question, which addresses population limitation rather than regulation, and has been the most useful question for empirical ecologists to ask. Population limitation admits of little theory and no elegant models, and highlights the gap between theory and practice in much of ecology. Defining the question clearly and adopting an experimental approach with clear alternative hypotheses will be essential to avoiding the controversies of the past while building useful generalisations for the practical problems of population management.

Density dependence: an ecological Tower of Babel

“…Behind such a simple definition lies a long history of debates that has ramified into a colourful body of jargon. Inconsistencies in the lexicon used to denote statistical and semantic properties of density dependence, and associated population phenomena and mechanisms Cooper 2001;Murray 1982;Sale and Tolimieri 2000), have nourished an old debate through ecology's infancy (Andrewartha 1958(Andrewartha , 1959Nicholson 1958Nicholson , 1959Varley 1959), maturation (den Boer 1968;Hanski et al 1993;Krebs 1995;Reddingius 1971;Slobodkin et al 1967;Strong 1986;Wolda 1995) and modern sophistication (Berryman 2004;Bjørnstad and Grenfell 2001;Krebs 2002a;Murray 2001;White 2008). This debate has contrasted (in simple terms) the demographic roles of biotic interactions (as inferred from density dependence) and stochastic and abiotic factors, and has focussed on how to provide quantitative evidence for those roles in the single-most important theme Communicated by Ola Olsson.…”

Population dynamics of red-backed voles (Myodes) in North America

“…Unlike the study of the North American Microtus voles and lemmings, the study of red-backed voles on this continent has made little contribution here as they do not seem to cycle nor show latitudinal gradients, with densities generally being low and often fluctuating in irregular ways (note that previous papers have referred to this genus as Clethrionomys, but it has now been revised to Myodes; Carleton et al 2003). However, the study of their dynamics has been directly related to a second major problem in population ecology-what are the factors that limit numbers, setting equilibrium density, and thus affecting population growth (Krebs 2002)?…”

Revisiting reproduction and population structure and dynamics ofProcambarus clarkiieight years after its introduction into Lake Trasimeno (Central Italy)

“…At early stages of invasion, the removal of the alien taxa may be effective with little knowledge of the introduced species' ecology (Simberloff, 2003), but once the opportunity for early eradication has been lost, biological details are useful to develop procedures for an effective management strategy (see Scalici et al, 2009b). Mechanisms of population dynamics and regulation have attracted interest from ecologists (e.g., Murray, 1979;Huffaker et al, 1984;Turchin, 1999;Krebs, 2002) since this issue is fundamental for predicting the invasiveness of alien taxa (Capinha et al, 2011) and for elaborating control strategies (Takimoto, 2009;Burlakova et al, 2010). Alien taxa often show an explosive increase in abundance soon after establishment, reaching high levels of biomass and density.…”