In an era of anthropogenically altered disturbance regimes and increased nutrient loads, understanding how communities respond to these perturbations is essential for successful habitat restoration. Disturbance and resource supply can affect community diversity by altering community assembly processes, such as recruitment, mortality or competitive inequalities. The mechanisms behind community responses to these drivers will differentially affect multiple facets of diversity. Here we examine how factorial manipulations of disturbance (raking to remove above‐ground vegetation) and nitrogen supply affect taxonomic and phylogenetic diversity of predominantly annual California grassland communities spanning a 500‐km latitudinal and twofold rainfall gradient. The disturbance caused density‐independent biomass removal and increased access to resources such as space and light, thus mimicking demographic effects of disturbance as considered in ecological models and broadly applicable to empirical systems. We used paired metrics of richness, evenness and community composition to compare evidence from taxonomy and phylogeny. Disturbance increased species and phylogenetic diversity (richness and evenness metrics). However, nitrogen addition interacted with disturbance to reduce species richness and phylogenetic diversity. Undisturbed communities were more strongly clustered phylogenetically, but disturbance eroded this clustering such that communities became more random (i.e. indistinguishable from a null model of assembly). Species composition differed between disturbed and undisturbed communities, and many species were observed in only one community type. Disturbance interacted with nitrogen supply to alter phylogenetic composition of communities, and recently disturbed communities were more spatially variable in phylogenetic composition than undisturbed communities. Phylogenetic composition of communities also differed among nitrogen treatments.
Anthropogenic environmental changes are known to affect the Earth's ecosystems. However, how these changes influence assembly trajectories of the impacted communities remains a largely open question. In this study, we investigated the effect of elevated nitrogen (N) deposition and increased precipitation on plant taxonomic and phylogenetic β‐diversity in a 9‐year field experiment in the temperate semi‐arid steppe of Inner Mongolia, China. We found that both N and water addition significantly increased taxonomic β‐diversity, whereas N, not water, addition significantly increased phylogenetic β‐diversity. After the differences in local species diversity were controlled using null models, the standard effect size of taxonomic β‐diversity still increased with both N and water addition, whereas water, not N, addition, significantly reduced the standard effect size of phylogenetic β‐diversity. The increased phylogenetic convergence observed in the water addition treatment was associated with colonizing species in each water addition plot being more closely related to species in other replicate plots of the same treatment. Species colonization in this treatment was found to be trait‐based, with leaf nitrogen concentration being the key functional trait.
- NSF-PAR ID:
- 10364038
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Ecology
- Volume:
- 107
- Issue:
- 5
- ISSN:
- 0022-0477
- Page Range / eLocation ID:
- p. 2121-2132
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Understanding how abiotic disturbance and biotic interactions determine pollinator and flowering‐plant diversity is critically important given global climate change and widespread pollinator declines. To predict responses of pollinators and flowering‐plant communities to changes in wildfire disturbance, a mechanistic understanding of how these two trophic levels respond to wildfire severity is needed.
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Summary Global environmental change is altering the Earth's ecosystems. However, much research has focused on ecosystem‐level responses, and we know substantially less about community‐level responses to global change stressors.
Here we conducted a 6‐yr field experiment in a high‐altitude (4600 m asl) alpine grassland on the Tibetan Plateau to explore the effects of nitrogen (N) addition and rising atmospheric CO2concentration on plant communities.
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Abstract Aim Mountains provide uniquely informative systems for examining how biodiversity is distributed and identifying the causes of those patterns. Elevational patterns of species richness are well‐documented for many taxa but comparatively few studies have investigated patterns in multiple dimensions of biodiversity along mountainsides, which can reveal the underlying processes at play. Here, we use trait‐based diversity patterns to determine the role of abiotic filters and competition in the assembly of communities of small mammals across elevation and evaluate the surrogacy of taxonomic, functional, and phylogenetic dimensions of diversity.
Location Great Basin ecoregion, western North America.
Taxon Rodents and shrews.
Methods The elevational distributions of 34 species were determined from comprehensive field surveys conducted in three arid, temperate mountain ranges. Elevation–diversity relationships and community assembly processes were inferred from phylogenetic (PD) and functional diversity (FD) patterns of mean pairwise and mean nearest‐neighbor distances while accounting for differences in species richness. FD indices were calculated separately for traits related to either abiotic filtering (β‐niche traits) or biotic interactions (α‐niche traits) to test explicit predictions of the role of each across elevation.
Results Trait‐based tests of processes indicated that abiotic filtering tied to a strong aridity gradient drives the assembly of both low‐ and high‐elevation communities. Support for competition was not consistent with theoretical expectations under the stress‐dominance hypothesis, species interactions‐abiotic stress hypothesis, or guild assembly rule. Mid‐elevation peaks in species richness contrasted with overall FD and PD, which generally increased with elevation. PD and total FD were correlated on two of three mountains.
Main conclusions The functional diversity of small mammal communities in these arid, temperate mountains is most consistent with abiotic filters, whereas support for competition is weak. Decomposing FD into traits related to separate assembly processes and examining ecoregional variation in diversity were critical for uncovering the generality of mechanisms. Divergent patterns among dimensions revealed species richness to be a poor surrogate for PD and FD across elevation and reflect the effect of biogeographic and evolutionary history. This first analysis of elevational multidimensional diversity gradients for temperate mammals provides a versatile framework for future comparative studies.
