Variation In Trait Composition Research Articles

From forest to forestry: Reassembly of spider communities after native forest replacement by pine monocultures

Abstract Worldwide, natural ecosystems have been replaced by intensive productive systems. This has led to an extreme simplification of habitat structure and loss of ecosystem heterogeneity but also might reduce the opportunities for species co‐occurrence. Anthropogenic disturbances offer an opportunity to explore how the functional diversity of spiders within a highly diverse ecosystem such as a subtropical forest change under intensive productive systems such as monoculture tree plantations. It allows to study the mechanisms underlying the community re‐assemblage process. Using a set of morphological and ecological traits of 259 species, the habitat filtering hypothesis was tested on spider communities inhabiting pine monocultures at different ages, where the stabilisation of habitat conditions such as vegetation complexity, maximum temperature/relative humidity and prey availability along the plantation cycle growth will promote spider colonisation of these productive areas. The conversion of native forest to pine monocultures decreased species and trait richness of spiders. Moreover, spiders from both communities differed in their identity but exhibited similar functional traits (low trait replacement). Variation in trait composition of spiders was explained by changes in vertical stratification complexity, tree density and relative humidity, rather than prey availability. The mechanistic processes structuring the spider community were not clear. Spiders from pine plantations might experience frequent changes in composition due to high species replacement levels in space and time. Because pine plantations harbour only a few species and exhibit low functional richness, the pressure for stabilisation of community composition can be low.

Soil resources mediate the strength of species but not trait convergence across grassland restorations

Ecological restoration is notoriously unpredictable because similar actions can result in different outcomes. Outcomes can also differ for species and functional components of communities depending on how restoration actions and abiotic conditions alter community assembly trajectories. Quantifying variation in community trajectories across restorations for both species and traits is rare, but can help to resolve underlying assembly processes and refine strategies to maximize restoration success. We quantified the importance of soil resources, seed mix richness, and prescribed fire for variation in plant species and functional trait trajectories over 6 years across 20 restored tallgrass prairies in the mid-western United States. We predicted stronger convergence for traits than species, with species and trait compositions converging more across restorations on resource-poor soils and with frequent fires due to stronger abiotic filtering. In contrast, we predicted species and trait compositions would converge more slowly or diverge across restorations with resource-rich soils, with less frequent fires, and seeded with more species due to weaker filtering and more stochasticity. Communities generally converged over time; however, the rate of convergence was determined by soil resources, not restoration actions. Restorations converged more across resource-rich sites. In contrast to patterns of species convergence, variation in trait composition remained stable over time regardless of soil resources or restoration actions. The unexpected pattern of species, but not trait, convergence during community assembly appears to result from increasing dominance of a native C4 bunchgrass, Andropogon gerardii that coincides with proportional declines of other C4 grasses that share similar traits. Synthesis and applications. Restoration outcomes may be more predictable than typically considered. Trait compositions were stable and variation in species compositions decreased over time owing to site conditions, where resource-rich soils produced more consistent outcomes. Our study shows monitoring multiple facets of biodiversity across restorations can reveal why outcomes vary and inform broad-scale restoration planning.

On the importance of niche packing for local species richness in taxonomic bird groups of the Neotropical region

In passerines, high species richness is driven mainly by dense occupation of the trait space rather than by an increased volume of the trait space. This niche packing mechanism would be allowed by increased specialization. Here we studied the Tyranni to investigate how species from the parvorders Tyrannida and Furnariida share the trait space. Because Furnariida include more specialized species in diet and foraging, we expected niche packing to be a predominant mechanism driving species richness in this group and tested (1) whether differences exist in local functional structure and the spatial regularity of occupied functional space between the groups and, if so, (2) whether the differences in local functional structure are explained by species trait combinations, species abundances, or both. We calculated indexes of functional diversity (alpha diversity), variation in trait composition (beta diversity), and generalized linear mixed models (GLMMs). We recorded 32 and 30 species in each passerine group using point counts for 4 years in an undisturbed continuous forest of southern Brazil. Although both groups presented similar overall richness, our models indicated that Furnariida had more species per transect and higher diversity values than those of Tyrannida but lower dissimilarity and turnover of traits. Furthermore, linear models of species richness and functional richness had higher slopes for Tyrannida than for Furnariida. Our study suggests two different strategies in Tyranni: while species richness in Tyrannida is reached by higher dissimilarity among local assemblages, in Furnariida species packing is the dominant mechanism.

Assessing long‐term effects of multiple, potentially confounded drivers in ecosystems from species traits

Although species traits have the potential to disentangle long-term effects of multiple, potentially confounded drivers in ecosystems, this issue has received very little attention in the literature. We aimed at filling this gap by assessing the relative effects of hydroclimatic and water quality factors on the trait composition of invertebrate assemblages over 30years in the Middle Loire River (France). Using a priori predictions on the long-term variation of trait-based adaptations over the three decades, we evaluated the ability of invertebrate traits to indicate the effects of warming, discharge reduction and water quality improvement. Hydroclimatic and water quality factors contributed to up to 65% of the variation in trait composition. More than 70% of the initial trait response predictions made according to observed long-term hydroclimatic changes were confirmed. They supported a general climate-induced trend involving adapted resistance and resilience strategies. A partial confounding effect of water quality improvement acting on trophic processes was also highlighted, indicating that improved water quality management can significantly help to reduce some adverse effects of climate change. This trait-based approach can have wider implications for investigating long-term changes driven by multiple, potentially confounded factors, as frequently encountered in the context of global change.