The interplay among intraspecific leaf trait variation, niche breadth and species abundance along light and soil nutrient gradients

Abstract

It is assumed that widespread, generalist species have high phenotypic variation, but we know little about how intraspecific trait variation (ITV) relates to species abundance and niche breadth. In the temperate rainforest of southern Chile, we hypothesized that species with wide niche breadth would exhibit 1) high among‐plot ITV, 2) a strong relationship between trait values and the environment, and 3) a close fit between traits and local environment trait optima. We measured leaf functional traits (leaf area, LMA, leaf N and P concentrations) of saplings in woody species, and compared the relative abundance of each species with its niche breadth, measured as the range of light, soil N and P availability. We used the slope of the linear regression of species’ trait–environment relationships to assess the strength and direction of these relationships, and measured the degree to which species’ trait values track the environmental optimum across plots. In some cases, species having wide niche breadth had high ITV in leaf N and also matched traits (LMA and leaf P) to local optima along the light gradient; they also had high ITV in general and matched leaf P to local optima along the soil P gradient. The relationship between species with wide niche breadth and the strength of intraspecific trait–environment relationships was generally weak and varied depending on the niche dimension and trait in question. Species varied considerably in the strength of trait–environment relationships and total magnitude of ITV, and this variation was not generally strongly related to species abundances or niche breadth patterns. In conclusion, trait variation at the community level is not driven by a few abundant, widely distributed species, but depends on the aggregate trait responses of both abundant and rare species. This makes it difficult to scale individual species trait responses up to the community level.

Functional traits explain the Hutchinsonian niches of plant species

“…Trait-based approaches of species niches that span entire geographical ranges should promote an understanding of how traits determine range limits. Given that we found that greater intraspecific trait variation in wood density, leaf longevity and seed N:P extends niche widths, an important next step is to determine whether range-wide variation in these traits arises from genetic differentiation or phenotypically plastic responses to environmental gradients (Fajardo & Siefert, 2019;Sides et al, 2014;Violle et al, 2012;Yang et al, 2018). Given that we found that greater intraspecific trait variation in wood density, leaf longevity and seed N:P extends niche widths, an important next step is to determine whether range-wide variation in these traits arises from genetic differentiation or phenotypically plastic responses to environmental gradients (Fajardo & Siefert, 2019;Sides et al, 2014;Violle et al, 2012;Yang et al, 2018).…”

“…Although species-mean trait values (which reflect the general phenotype across a species' geographical range) should relate to species niches, greater intraspecific trait variation also allows populations to grow in a broader range of environments, thereby extending niche widths (Fajardo & Siefert, 2019;Violle et al, 2012;Violle & Jiang, 2009). Positive relationships between intraspecific trait variation and niche widths result from phenotypic plasticity or adaptive trait differentiation between populations, both of which can increase the range of environmental conditions where population growth is positive (see Violle et al, 2012 and references therein).…”

Does trait variation within broadly distributed species mirror patterns across species? A case study in Puerto Rico

“…However, these interpretations should be considered carefully since changes in δ 15 N could be influenced by additional factors and our mechanistic understanding of the drivers of δ 15 N variation is still underdeveloped (Evans ). Furthermore, this result indicates that local‐scale (i.e., within population) environmental gradients, that frequently go unmeasured, are very important for determining trait distributions (Fajardo and Siefert , ).…”

“…A further consequence of the observed idiosyncratic trait covariance patterns across species is that species would respond differentially to potential climatic changes. Those species with trait covariance patterns that track the environmental changes would have better chances to succeed, given that their trait variation will allow them to tolerate broader range of conditions, while species with a trait covariance that does not follow the climatic changes will exhibit a more restricted capacity to tolerate climatic changes (see Fajardo and Siefert ). Similar ideas have been discussed previously by Laughlin and Messier () as dynamic adaptive landscapes and these could be readily applied in future studies in combination with demographic data.…”

“…). In particular, for broadly distributed species, trait variance across populations or ecotypes (conspecific organisms located at different portions of environmental gradients) could be comparable in magnitude to the trait variance across species if differences in biotic and abiotic conditions result in a great phenotypic variation to cope the local demands (Fajardo and Siefert ). Alternatively, if strong constraints operate at the species level maintaining species identities over their entire range, trait variation within species should not exceed the variance across species.…”