Variation between individuals fosters regional species coexistence

Abstract

Although individual-level variation (IV) is ubiquitous in nature, it is not clear how it influences species coexistence. Theory predicts that IV will hinder coexistence but empirical studies have shown that it can facilitate, inhibit, or have a neutral effect. We use a theoretical model to explore the consequences of IV on local and regional species coexistence in the context of spatial environmental structure. Our results show that individual variation can have a positive effect on species coexistence and that this effect will critically depend on the spatial structure of such variation. IV facilitates coexistence when a negative, concave-up relationship between individuals' competitive response and population growth rates propagates to a disproportionate advantage for the inferior competitor, provided that each species specialises in a habitat. While greater variation in the preferred habitat generally fosters coexistence, the opposite is true for non-preferred habitats. Our results reconcile theory with empirical findings.

Linking intra‐specific trait variation and plant function: seed size mediates performance tradeoffs within species

“…This work helps characterize the degree of empirical plant performance variation due to intra‐specific trait variation, which influences whether and how intraspecific trait variation impacts species coexistence (Hart et al , Turcotte and Levine , Uriarte and Menge ). We show that the degree of trait‐based performance variation ranges from no effect (for example, there was no effect of seed size on dispersal ability for P. serratifolia ) to several fold variation (for example, the largest Premna seeds produced seedlings three–four times larger than seedlings from the smallest seeds).…”

“…Intra‐specific trait variation accounts for roughly a quarter of trait variation in plant communities (Siefert et al ) and trait‐based community ecology research has recently emphasized the theoretical implications of intra‐specific variation for community assembly and coexistence (Barabás and D'Andrea , Hart et al , Turcotte and Levine , Crawford et al , Uriarte and Menge ). For example, incorporating intra‐specific variation can improve the predictive power of community assembly models (Jung et al , Laughlin et al ), and intra‐specific performance variation can reduce the likelihood of coexistence in theoretical population dynamics models by blurring niche differences among species (Barabás and D'Andrea , Hart et al ) or favour coexistence when variation is spatially structured (Uriarte and Menge ). These theoretical findings have inspired a call for more empirical work to determine whether observed intra‐specific trait variation operates in a similar manner as inter‐specific trait variation, causing functionally important impacts on components of plant performance (e.g.…”

“…Trait-based approaches in community ecology are complicated by recent research highlighting the existence of large trait variation within plant species (Albert et al 2011, Bolnick et al 2011, Siefert 2012, Violle et al 2012, Moran et al 2016. Intra-specific trait variation accounts for roughly a quarter of trait variation in plant communities (Siefert et al 2015) and trait-based community ecology research has recently emphasized the theoretical implications of intra-specific variation for community assembly and coexistence (Barabás and D'Andrea 2016, Hart et al 2016, Turcotte and Levine 2016, Crawford et al 2019, Uriarte and Menge 2018. For example, incorporating intra-specific variation can improve the predictive power of community assembly models (Jung et al 2010, Laughlin et al 2012, and intra-specific performance variation can reduce the likelihood of coexistence in theoretical population dynamics models by blurring niche differences among species (Barabás andD'Andrea 2016, Hart et al 2016) or favour coexistence when variation is spatially structured (Uriarte and Menge 2018).…”

An unbiased method to estimate individual specialisation from multi‐tissue isotopic data

“…However, it has become increasingly clear that trophic niches of many species cannot be assumed to be homogeneous, since individuals of a single population can substantially differ in their resource use (Bolnick et al, 2003(Bolnick et al, , 2010Ingram et al, 2018). This differentiation is commonly referred to as individual specialisation (IS), and studies conducted during recent years suggest that it can affect several ecological and evolutionary processes, at different spatial and temporal scales (Araujo, Layman, & Bolnick, 2011;Bolnick et al, 2003;Cloyed & Eason, 2016;Quevedo, Svanback, & Eklov, 2009;Start, 2018;Uriarte & Menge, 2018). From an operational perspective, IS for a given trait is usually measured as the ratio between the average variance within individuals (within-individual component of variance, WIC) and the overall variance observed for that trait (or total niche width, TNW).…”

Intra-Specific variability in fluctuating environments - mechanisms of impact on species diversity

“…In recent years, ITV is drawing increasing attention [12][13][14][15][16][17][18]. This interest was triggered by the observation of considerable ITV in multiple ecological communities [14,17], and motivated many studies of the mechanisms by which ITV influences ecological dynamics and biodiversity.…”