Introduction
Ecologist traditionally relied on the deterministic process, such as environmental niche, and the coexistence of species was explained by a stationary state of ecologically different species (Gause, 1934; Hutchinson, 1957). Recently ecologist recognized also the role of stochastic process. The neutral dynamics were derived from the primary assumption of per capita equivalence among individuals and community saturation, such as ecological drift, random speciation and migration, and the coexistence of species was explained by a dynamical equilibrium of ecologically equivalent species in a set of local communities (Durrett & Levin, 1996; Hubbell, 2001; Rosindell, Hubbell, & Etienne 2011). In contemporary ecology, the reconciling of these divergent ecological-evolutionary mechanisms is a promising perspective to explain the origin and maintenance of biodiversity (Hubbell, 2001; Leibold & Mcpeek, 2006; Munoz & Huneman, 2016; Rosindell et al., 2011).
Neutral dynamics were based on individual-based model. The models were implemented mostly in the spatially-implicit and hierarchical conjecture, in that the extinction was balanced by the speciation under panmixis; while, the local extinction was balanced by the immigrats from a metacommunity. The regional dynamics were predicted by population size and speciation rate of metacommunity, and the local dynamics were predicted by further two parameters of population size and dispersal rate of local community (Hubbell, 2001; Etienne, 2005; Etienne, 2007; Etienne & Oiff, 2004; Hankin, 2007; Munoz, Couteron, Ramesh, & Etienne 2007). However, the spatially-implicit conjecture seems inconsistent in that the neutral dynamics assume panmixis in a metacommunity; whereas, dispersal-limitation to each local community embedded in it (Etienne, 2007). The spatially-explicit conjecture was one step approach allowing the speciation and dispersal-limitation across spatio-temporal scales. A metacommunity was usually a portion of an infinite system, and the models were implemented in a grid of local communities specifying neighbourhood or more general dispersal kernel (Durrett & Levin, 1996; Hubbell, 2001; Chave & Leigh, 2002; Chave, Muller-Landau, & Levin 2002; Pigolotti & Cencini, 2009).
Reconciling niche-based process and neutral dynamics in spatially-implicit conjecture, ecologist tried to explain the community assembly in successional patchy habitats, in that the vacant local community created by perturbation was initially colonized by the immigrants from a metacommunity under the ecological equivalence among species; then, the competitive exclutions were followed in each local community (Mouquet, Munguia, Kneitel, & Miller 2003). In stable environment, the immigrants from a metacommunity was filtered along environmental gradients, and the coexistence of species in each local community was achieved under the per capita equivalence among individuals in homogeneous environment (Jabot, Etienne, & Chave 2007; Janzen, Haegeman, & Etienne 2015; Munoz, Ramesh, & Couteron 2014; Munoz et al., 2018). In spatially-implicit conjecture; however, the regional dynamics were not predicted but usually specified by a fixed metacommunity. Strikingly, if the per capita ecological difference among species contributed to the competitions in each local community or the dispersals from a metacommunity; in general, the spatio-temporal scales on which the per capita ecological difference and equivalence among species contributed to metacommunity dynamics were credible assumpsions.
Reconciling niche-based process and neutral dynamics in spatially-explicit conjecture, a metacommunity may be a portion of an infinite system. The regional species pool may be already not free parameter, and the divergent ecological-evolutionary mechanisms may operate consistently at different spatio-temporal-environmental scales. For instance, exploring the neutral model with nearest neighboring communities, an approximate scale on which individuals were expected to diffuse before speciation was predicted by a pair of speciation and dispersal rates (Cencini, Pigolotti, & Muñoz 2012). In other words, the area of model communities must exceed an approximate scale predicted by these parameters to encompass at least one independent biogeographic unit. In the synthetic model with periodic boundary condition, where the environmental gradient repeats continuously across opposite sides of system, the relative role of neutral dynamics may increase in an area encompassing independent biogeographic units because the species richness but the number of functional groups (i.e. guilds) may increase through speciation.
In the present study, the individual-based model was implemented in the two-dimensional grid with periodic boundary condition. In simulations, the model parameters and the species properties in simulation outcomes were known by researcher, and the focus was to detecting the spatio-temporal-environmental scales on which the per capita ecological difference and equivalence among species were emerged through divergent ecological-evolutionary mechanisms. Exploring the model across a range of parameters, I proved specifically three hypotheses. First, the competitive exclusion may be advanced by the per capita ecological difference among species so the number of guilds may achieve first to a stationary state; while, the competitive exclusion may be retarded by the per capita ecological equivalence among species so the species richness may converge eventually to a dynamical equilibrium through extinction-speciation balance (Leibold & Mcpeek, 2006). Second, the relative role of neutral dynamics may increase in an area encompassing independent biogeographic units. Third, the neutral dynamics may operate among the species of each guild in patchy habitats (Leibold & Mcpeek, 2006; Economo & Keitt, 2008). The trajectory and contrast between alternative processes establish the false premises that the niche-based process is only important in each local community; while, the neutral dynamics are only important in a set of local communities. I discuss finally the implication of false premises and consistent patterns observed in the present study for the performance of heuristic methods, the manner of their applications, and the interpretation of their results in field observations.