Size asymmetry of resource competition and the structure of plant communities

Abstract

Summary Plant communities show two general responses to gradients of soil resources: a decrease in species richness at high levels of resource availability and an associated shift in species composition from small and slow‐growing species to large and fast‐growing species. Models attempting to explain these responses have usually focused on a single pattern and provided contradicting predictions concerning the underlying mechanisms. We use an extension of Tilman's resource competition model to investigate the hypothesis that both patterns may originate from the size‐asymmetric nature of light exploitation by competing plants. The only mechanism producing changes in species richness and species composition in our model is mortality due to competition. Under the framework of the model, asymmetric light exploitation is a necessary and sufficient condition to obtain the empirically observed responses of species richness and species composition to soil resource gradients. This theoretical result is robust to relaxing the simplifying assumptions of the model. Our model shows that the traits enhancing competitive superiority depend on the mode of resource exploitation: under symmetric exploitation, competitive superiority is achieved by tolerance of low resource levels, while under asymmetric exploitation, it is achieved by the ability to grow fast and attain a large size. This result indicates that a long‐standing debate concerning the traits that enhance competitive superiority in plant communities (the ‘Grime–Tilman debate’) can be reduced into a single parameter of our model – the degree of asymmetry in resource competition. The model also explains the observed shift from below‐ground to above‐ground competition with increasing productivity, the associated increase in the asymmetry of competitive interactions and the increasing likelihood of competitive exclusion under high levels of productivity. None of these patterns could be obtained under symmetric competition in our model. Synthesis. The ability of the model to explain a wide range of observed patterns and the robustness of these predictions to its simplifying assumptions suggest that the size asymmetry of competition for light is a fundamental factor in determining the structure and diversity of plant communities.

100 yr of primary succession highlights stochasticity and competition driving community establishment and stability

“…This unification of stochastic processes with the more nichebased concept of resource exploitation strategies was proposed with stochastic niche theory (e.g., Tilman 2004) and formalized via the asymmetric exploitation of resources model (DeMalach et al 2016), which suggests that competitive dominance in plant communities can be explained by the degree to which larger individuals disproportionately utilize available resources. Under this framework, stochastic events such as early vs. late arrival thus confer an advantage in early successional environments that can "weight" competition even among symmetrically competitive species, for example, by giving a certain species an early height advantage (and thus access to light) by virtue of establishment timing, even if all species are generally the same height in isolation (DeMalach et al 2016). Under this framework, stochastic events such as early vs. late arrival thus confer an advantage in early successional environments that can "weight" competition even among symmetrically competitive species, for example, by giving a certain species an early height advantage (and thus access to light) by virtue of establishment timing, even if all species are generally the same height in isolation (DeMalach et al 2016).…”

New Allometric Equations to Support Sustainable Plantation Management of Rosewood (Aniba rosaeodora Ducke) in the Central Amazon

“…DeMalach et al [47] describe the Tilman-Grime debate in which the effects of competition can be separated into two groups: (1) where competitive capability causes competitors to overcome suppression by neighbors and grow faster [48]; and (2) when individuals survive longer with low levels of resources [49]. As a result of competition for spaces, water, light, and nutrients a higher or lower density of plants can generate dierent productive behavior responses [39].…”

“…This can be explained by the size and shape of the crown characteristic of the species and the relation of the trees to the water and fertility conditions of the environments [11]. In addition, regular spacing of trees within plantations both favors growth and is a cause tree shapes that differ from those in the wild [33,[37][38][39]47,48] For AGFM, the equation legally suggested by the normative instruction, gave an estimate that was only 23.5% of the total AGFM, an underestimation of 76.5%, tending to higher under-estimates for larger trees (Figure 6-Left). The application of equation generated in this study did not result in bias or systematic errors, while the equation suggested by law systematically underestimates all trees (Figure 6-Right).…”

Vertical size structure is associated with productivity and species diversity in a short‐stature grassland: Evidence for the importance of height variability within herbaceous communities

“…However, even small height differences between plants can impact a plant's responses to neighbours (Mullen, Weinig, & Hangarter, ; Purves & Law, ) due to the prevalence of size‐dependent processes, suggesting vertical size structure in a variety of herbaceous communities could play a functional role in determining community assembly. For example, when plants experience size‐asymmetric competition for light, taller individuals gain the competitive advantage as they are able to pre‐empt sunlight (Harper, ; Weiner, ), leading to their increased growth, and the possible reduction and removal of the shorter individuals (DeMalach, Zaady, Weiner, & Kadmon, ). Further, the height distributions among species may also dictate the long‐term performance of a species by impacting an individual's fitness (Aarssen & Taylor, ; de Jong & Klinkhamer, ; Weiner & Solbrig, ) possibly through controlling its visibility to herbivores or pollinators (Klinkhamer, de Jong, & de Bruyn, but see Klinkhamer & de Jong, ).…”