General Relationships between Species Diversity and Stability in Competitive Systems

Abstract

Investigating the effect of biodiversity on the stability of ecological communities is complicated by the numerous ways in which models of community interactions can be formulated. This has led to differences in conclusions and interpretations of how the number of species in a community affects its stability. Here, we derive a simple, general relationship between the coefficient of variation (CV) of combined species densities and the environmentally driven variability in species' per capita population growth rates. For a given level of environmentally driven variability in per capita population growth rates, increasing the number of species in a community decreases the CV of combined species densities, provided that species do not respond to environmental fluctuations in a perfectly correlated way. Thus, a community with more species of competitors will be more stable (have lower CV in combined species densities for a given level of environmental variability) than a species-poor community, provided that the species in both communities show equal variability in per capita population growth rates and provided that species within each community do not show strongly correlated responses to environmental fluctuations. This conclusion also applies to "noninteractive" models in which there is no competition between species.

Predation Alters Relationships between Biodiversity and Temporal Stability

“…Although theory and most experimental studies support a positive effect of diversity on temporal stability of competitive communities (e.g., Ives and Hughes 2002;Tilman et al 2006), diversity did not influence community stability in the controls. While uncommon, this lack of diversity effect on community stability has previously been reported (Petchey et al 2002;Zhang and Zhang 2006).…”

“…Current evidence suggests possibly different diversity-temporal stability patterns at different levels of ecological organization. At the community or ecosystem level, theory (Yachi and Loreau 1999;Ives and Hughes 2002;Thebault and Loreau 2005) and most empirical studies (McNaughton 1977;Dodd et al 1994;Tilman 1996;McGrady-Steed and Morin 2000;Valone and Hoffman 2003a;Caldeira et al 2005;Steiner et al 2005;Romanuk et al 2006;Tilman et al 2006;Vogt et al 2006;Zhang and Zhang 2006;van Ruijven and Berendse 2007; but see Petchey et al 2002;Gonzalez and Descamps-Julien 2004;Morin and McGrady-Steed 2004;France and Duffy 2006;Zhang and Zhang 2006) indicate a positive diversity effect on temporal stability, often attributed to several community-level stabilizing mechanisms (sensu Cottingham et al 2001). On the other hand, accompanying inconsistent theoretical predictions on the relationship between diversity and temporal stability at the population level (May 1973;De Angelis 1975;Lehman and Tilman 2000;Li and Charnov 2001;Brose et al 2006), empirical studies have documented various relationships between the two: positive (Kolasa and Li 2003;Valone and Hoffman 2003b;Romanuk and Kolasa 2004;Romanuk et al 2006;Vogt et al 2006), neutral (McGrady-Steed andMorin 2000;Romanuk and Kolasa 2002;Steiner et al 2005), and negative (Tilman 1996;...…”

Shrub Invasion Decreases Diversity and Alters Community Stability in Northern Chihuahuan Desert Plant Communities

“…Furthermore, theoretical work indicates that in competitive communities (e.g., primary producers) the structure of interspecific interactions is the most relevant factor determining community stability [12]. In particular, community models reveal that the mean and variance of interspecific interactions are decisive parameters that dictate community stability [7]. Specifically, these models show that competitive communities are destabilized when an invading species has a large effect on the mean and variance of interspecific interactions within a community [14], [17].…”

“…Both theory and manipulative experiments have demonstrated a positive relationship between community stability and species diversity in ecological communities [1]–[3]. Critical evidence for this relationship occurs primarily in competitive communities (e.g., producers) where species diversity and the structure of species interactions affect species composition and turnover [4], [5], population stability (e.g., rates of variation in population densities) [6], [7], and community stability (e.g., temporal variation in net primary production) [2], [8]. However, empirical research exploring how specific changes in the structure of species interactions alters multiple aspects of community stability, including species diversity and the temporal rates of population and community change, are still needed.…”

Community stability under different correlation structures of species’ environmental responses

“…However, this prediction rests upon extremely simplified assumptions about the structuring of competitive communities. Three common assumptions in theoretical community ecology are: (1) that competition is diffuse (i.e., all pair-wise interactions are equal in strength; Ives and Hughes, 2002;Ripa and Ives, 2003;Ruokolainen and Fowler, 2008) or random between species (Ranta et al, 2008;Ruokolainen et al, 2007), (2) there is equivalency in species demographic traits (e.g., growth rates and carrying capacities; Ives et al, 1999;Ives and Hughes, 2002;Ripa and Ives, 2003;Ruokolainen and Fowler, 2008; but see Fowler, 2009), and (3) there is uniform covariance in species-specific responses to environmental variation across the whole community (e.g., Ives et al, 1999;Ripa and Ives, 2003;Ruokolainen and Fowler, 2008). Here we will relax these simplifications by considering a hierarchical niche-gradient model where species differ in their demographic traits and where interspecific competition and the similarity in species-specific responses to stochasticity both reflect the similarity in species niche use.…”