Abstract
Coexistence in fire-prone Mediterranean-type shrublands has been explored in the past using both neutral and niche-based models. However, distinct differences between plant functional types (PFTs), such as fire-killed vs resprouting responses to fire, and the relative similarity of species within a PFT, suggest that coexistence models might benefit from combining both neutral and niche-based (stabilizing) approaches. We developed a multispecies metacommunity model where species are grouped into two PFTs (fire-killed vs resprouting) to investigate the roles of neutral and stabilizing processes on species richness and rank-abundance distributions. Our results show that species richness can be maintained in two ways: i) strictly neutral species within each PFT, or ii) species within PFTs differing in key demographic properties, provided that additional stabilizing processes, such as negative density regulation, also operate. However, only simulations including stabilizing processes resulted in structurally realistic rank-abundance distributions over plausible time scales. This result underscores the importance of including both key species traits and stabilizing (niche) processes in explaining species coexistence and community structure.
Highlights
Neutral models have been used to describe coexistence and some aspects of community structure in species-rich plant communities, such as tropical rainforests and fire-prone Mediterranean-type shrublands [1,2,3]
We systematically varied two key demographic parameters, maximum fire survival probability psurv,max and the number of seedlings produced by non-sprouters - by varying the number of non-sprouter seedlings at age 9 bi (Fig. 2a,d,g) for the three specific scenarios: 1. If all species within one Plant Functional Types (PFTs) have the same demographic parameters and there is no density regulation species can coexist across a wide range of parameter combinations given a positive correlation between bi and psurv,max (Fig. 2a, for 21% of all 441-parameter combinations, all 16 species persist)
If intraspecific density regulation is in place and species differ within each PFT species coexist across a wide range of parameter combinations (Fig. 2g)
Summary
Neutral models have been used to describe coexistence and some aspects of community structure in species-rich plant communities, such as tropical rainforests and fire-prone Mediterranean-type shrublands [1,2,3]. In Mediterranean-type ecosystems two distinct adaptations to recurrent disturbance by fire can be identified [5]: some species are killed by fire (non-sprouters) and rely on post-fire recruitment from seeds, while others recover vegetatively (resprouters). These two Plant Functional Types (PFTs) defined by their response to disturbance differ in their longevities by at least an order of magnitude [5,6]; and the outcomes of neutral theory are sensitive to such differences [7]. The assumptions of perfect equalizing processes are, rarely met [8,13]
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