Biology subjects

Wisnoski, N. I.

Publications and source records attributed to Wisnoski, N. I..

8 recordsLinked to original sources

bioRxiv2025

Dispersal kernels influence the magnitude of environmental, biotic, and stochastic effects on the maintenance of metacommunity diversity

Dispersal plays a central role in shaping patterns of diversity in metacommunities. However, a primary focus on emigration rates may mischaracterize dispersal effects that actually arise from dispersal kernels. Kernels describe probabilistic movements between donor and recipient patches, but the influence of kernel shape on metacommunity diversity remains unclear. We used simulations to measure how kernels affect diversity across metacommunity scales and ecological contexts. We disentangled causes of these patterns using a novel approach quantifying the effects of environmental filtering, competition, stochasticity, and dispersal on fitness. Although metacommunities with shallow kernels followed expectations where emigration increased alpha-but decreased beta- and gamma-diversity, metacommunities with steeper kernels did not. Steeper kernels maintained regional diversity by reducing interspecific competition and stochastic extinctions, with dispersal conferring weaker benefits but less homogenization. Our work suggests dispersal kernels and emigration rates jointly regulate exposure to environmental variation and the balance of assembly mechanisms in metacommunities.

ecology↗

bioRxiv2022

Diversity-stability relationships become decoupled across spatial scales: a synthesis of organism and ecosystem types

The relationship between biodiversity and stability, or its inverse, temporal variability, is multidimensional and complex. Temporal variability in aggregate properties, like total biomass or abundance, is typically lower in communities with higher species diversity (i.e., the diversity-stability relationship or DSR). Recent work has shown that, at broader spatial extents, regional-scale aggregate variability is also lower with higher regional diversity (in plant systems) and with lower spatial synchrony. However, it is not yet clear whether regional DSRs hold across a broad range of organisms and ecosystem types. Furthermore, focusing exclusively on aggregate properties of communities may overlook potentially destabilizing compositional shifts. To test these questions, we compiled a large collection of long-term spatial metacommunity data spanning a wide range of taxonomic groups (e.g., birds, fish, plants, invertebrates) and ecosystem types (e.g., deserts, forests, oceans). We applied a newly developed quantitative framework for jointly analyzing aggregate and compositional variability across scales. We quantified DSRs for composition and total abundance in local communities and metacommunities. At the local scale, compositional DSRs suggested that higher local () diversity was associated with lower variability in animal populations but higher variability in plant populations, while aggregate DSRs supported the classic stabilizing effects of diversity. Spatial synchrony differed among taxa (birds had the lowest, plants the highest), suggesting differences in stabilization by spatial processes. Spatial synchrony declined with higher diversity among sites ({beta}) for both compositional and aggregate properties. However, at the regional ({gamma}) scale, we found no aggregate DSR, but a positive compositional DSR. Across a broader range of taxa, our results suggest that high {gamma}-diversity does not consistently stabilize aggregate properties at regional scales without sufficient spatial {beta}-diversity to reduce spatial synchrony. Open research statementAll data sets are accessible via the Environmental Data Initiative, and a specific data package of the data sets used in this analysis will be made publicly available (doi: pending). Citations to original sources are included in Appendix S1. Code to reproduce the analyses is found in a Zenodo archive (doi: pending) of the GitHub repository for this project (https://github.com/sokole/ltermetacommunities/tree/master/Manuscripts/MS3).

ecology↗

bioRxiv2021

Seed banks alter metacommunity diversity: the interactive effects of competition, germination, and survival

Dispersal and dormancy are two common strategies allowing for species persistence and the maintenance of ecological diversity in variable environments. However, theory and empirical tests of spatial diversity patterns tend to examine either mechanism in isolation. Here, we developed a stochastic, spatially explicit metacommunity model incorporating seed banks with varying germination and survival rates. We found that dormancy and dispersal had interactive, nonlinear effects on the maintenance and distribution of metacommunity diversity, where scale-dependent effects of seed banks were modified by local competitive interactions and dispersal. The interplay between seed germination and survival regulated the benefits of seed banks for diversity. Our study shows that the role of seed banks depends critically on spatial processes, and that classic predictions for how dispersal affects metacommunity diversity can be strongly influenced by dormancy. Together, these results highlight the need to consider both temporal and spatial storage when predicting multi-scale patterns of diversity.

ecology↗

bioRxiv2021

The dual nature of metacommunity variability

There is increasing interest in measuring ecological stability to understand how communities and ecosystems respond to broad-scale global changes. One of the most common approaches is to quantify the variation through time in community or ecosystem aggregate attributes (e.g., total biomass), referred to as aggregate variability. It is now widely recognized that aggregate variability represents only one aspect of communities and ecosystems, and compositional variability, the changes in the relative frequency of species in an assemblage, is equally important. Recent contributions have also begun to explore ecological stability at regional spatial scales, where interconnected local communities form metacommunities, a key concept in managing complex landscapes. However, the conceptual frameworks and measures of ecological stability in space have only focused on aggregate variability, leaving a conceptual gap. Here, we address this gap with a novel framework for quantifying the aggregate and compositional variability of communities and ecosystems through space and time. We demonstrate that the compositional variability of a metacommunity depends on the degree of spatial synchrony in compositional trajectories among local communities. We then provide a conceptual framework in which compositional variability of (i) the metacommunity through time and (ii) among local communities combine into four archetype scenarios: spatial stasis (low/low); spatial synchrony (high/low); spatial asynchrony (high/high) and spatial compensation (low/high). We illustrate this framework based on numerical examples and a case study of a macroalgal metacommunity in which low spatial synchrony reduced variability in aggregate biomass at the metacommunity scale, while masking high spatial synchrony in compositional trajectories among local communities. Finally, we discuss the role of dispersal, environmental heterogeneity, species interactions and suggest future avenues. We believe this framework will be helpful for considering both aspects of variability simultaneously which is important to better understand ecological stability in natural and complex landscapes in response to environmental changes.

ecology↗

bioRxiv2020

Stabilizing role of seed banks and the maintenance of bacterial diversity

Coexisting species often exhibit negative frequency dependence due to mechanisms that promote population growth and persistence when rare. These stabilizing mechanisms can maintain diversity through interspecific niche differences, but also through life-history strategies like dormancy that buffer populations in fluctuating environments. However, there are few tests demonstrating how seed banks contribute to long-term community dynamics and the maintenance of diversity. Using a multi-year, high-frequency time series of bacterial community data from a north temperate lake, we documented patterns consistent with stabilizing coexistence. Bacterial taxa exhibited differential responses to seasonal environmental conditions, while seed bank dynamics helped maintain diversity over winter. Strong negative frequency dependence in rare, but metabolically active, taxa suggested a role for biotic interactions in promoting coexistence. Together, our results provide field-based evidence that niche differences and seed banks contribute to recurring community dynamics and the long-term maintenance of diversity in nature.

ecology↗

bioRxiv2020

Microbial community composition is affected by press, but not pulse, seawater intrusion

Tidal freshwater marshes (TFMs) are threatened by seawater intrusion, which can affect microbial communities and alter biogeochemical processes. Here, we report on Seawater Addition Long Term Experiment (SALTEx), a manipulative field experiment that investigated continuous (press) and episodic (pulse, 2 months/yr) inputs of brackish water on microbial communities in a TFM. After 2.5 years, microbial diversity was lower in press treatments than in control (untreated) plots. Sulfate reducers increased in response to both press and pulse treatments whereas methanogens did not differ among treatments. Our results suggest that microbial communities in TFMs are resilient to episodic events, but that continuous seawater intrusion may alter bacterial diversity in ways that affect ecosystem functioning. Scientific Significance StatementSea level rise and seawater intrusion threaten tidal freshwater marshes (TFMs) and the important ecosystem services they provide. Intrusion of seawater in TFMs can occur across a range of timescales, such as episodic events, like storm surges or drought, or continuous intrusion as a result of rising sea level. The effects of these stressors on TFM microbial communities are not well understood. Our multi-year field manipulation of brackish water inputs revealed that microbial communities were resilient to short-term pulses of salinity whereas continuous seawater intrusion led to reduced microbial diversity along with changes in relative abundance of key functional groups. Such alterations may diminish the ability of TFMs to sequester carbon and cycle nutrients.

ecology↗

bioRxiv2020

Microbial community assembly in a multi-layer dendritic metacommunity

A major goal of metacommunity ecology is to infer the local- and regional-scale processes that underlie community assembly. In dendritic ecological networks (e.g., stream metacommunities), branching and directional dispersal connectivity can alter the balance between local and regional factors during assembly. However, the implications of vertical habitat structure (e.g., planktonic versus benthic sediments) in dendritic metacommunities remain unclear. In this study, we analyzed the bacterial metacommunity of a fifth-order mountain stream network to assess habitat differences in the (1) dominant community assembly processes, (2) spatial scaling of community assembly processes, and (3) longitudinal variation in community assembly. Using taxonomic and phylogenetic null modeling approaches, we found habitat-specific spatial patterns of community assembly across the dendritic network. Compositional differences between planktonic and benthic communities were maintained by divergent species sorting, but stochasticity influenced assembly at local scales. Planktonic communities showed scale-dependent assembly, transitioning from convergent sorting at local scales to divergent sorting at regional scales, while sediment community assembly was less scale dependent (convergent sorting remained important across all scales). While divergent sorting structured headwaters in both habitat types, sediment communities converged in structure downstream. Taken together, our results show that vertical habitat structure regulates the scale-dependent processes of community assembly across the dendritic metacommunity.

ecology↗

bioRxiv2019

Metabolic insight into bacterial community assembly across ecosystem boundaries

The movement of organisms across habitat boundaries has important consequences for populations, communities, and ecosystems. However, because most species are not well adapted to all habitat types, dispersal into suboptimal habitats could induce physiological changes associated with persistence strategies that influence community assembly. For example, high rates of cross-boundary dispersal are thought to maintain sink populations of terrestrial bacteria in aquatic habitats, but these bacteria may also persist by lowering their metabolic activity, introducing metabolic heterogeneity that buffers the population against niche selection. To differentiate between these assembly processes, we analyzed bacterial composition along a hydrological flow path from terrestrial soils through an aquatic reservoir by sequencing the active and total (active + inactive) portions of the community. When metabolic heterogeneity was ignored, our data were consistent with views that cross-boundary dispersal is important for structuring aquatic bacterial communities. In contrast, we found evidence for strong niche selection when metabolic heterogeneity was explicitly considered, suggesting that, relative to persistence strategies, dispersal may have a weaker effect on aquatic community assembly than previously thought. By accounting for metabolic heterogeneity in complex communities, our findings clarify the roles of local- and regional-scale assembly processes in terrestrial-aquatic meta-ecosystems.

ecology↗