Biology subjects

Neubert, M. G.

Publications and source records attributed to Neubert, M. G..

6 recordsLinked to original sources

bioRxiv2025

Small phytoplankton community composition cycles annually with a coastal bloom

Small photosynthetic eukaryotes are a productive and dynamic component of marine planktonic communities. Here, we investigate how seasonal changes in abundance of these primary producers relate to changes in their community composition at a coastal site on the Northeast U.S. Shelf. We present a 9-yr time series of 18S rRNA sequencing data and identify gradual transitions within the pico- and nanoplankton community that occur repeatedly over the annual cycle. We compare these compositional changes to concurrent high-resolution in situ flow cytometry measurements of eukaryotic phytoplank-ton abundance and division rate. We find that the Chlorophyta contribute a large proportion of the sequences in our samples and drive much of the seasonal variability within the small phytoplankton community. Across the time series, Bathycoccus, Micromonas, and Picochlorum are the dominant genera, with the first being present year round, while Micromonas bravo and Picochlorum are representative of the summer community. We also find a strong winter Phaeocystis signal which might be leading to flow cytometry measurements of relatively large cells in the early spring. Our results provide fundamental knowledge of the taxonomic composition of the phytoplankton community on the Northeast U.S. Shelf, improving our understanding of the regions diversity and compositional variability over time.

ecology↗

bioRxiv2025

A nonequilibrium framework for community responses to pulse perturbations

Understanding responses of ecological communities to shocks that displace species abundances is of paramount importance given the increasing frequency of extreme climatic events. However, current theory on responses to such pulse perturbations focuses on equilibrium points and we lack a unified framework that accommodates other common, but more complicated, types of population fluctuations such as transients and cycles. Here we introduce this frame-work by deriving metrics that quantify the minimum, typical, and maximum amplification of perturbed abundances under nonequilibrium population dynamics. By simulating models under several nonequilibrium scenarios, we demonstrate that these metrics accurately characterize the full range of amplification of perturbed abundances in the short and long terms. Notably, we show that perturbation amplification depends strongly on community state in the short term, but this state dependency vanishes in the long term. Overall, our framework enables stability analysis for model and natural communities that do not exhibit equilibrium dynamics.

ecology↗

bioRxiv2025

Timing the initiation of sex: Delay mechanisms alter fitness outcomes in a rotifer population model

Species that inhabit variable environments have complex mechanisms to precisely time their life-history transitions as conditions change. One such mechanism in rotifers is a block on sexual reproduction that extends across multiple asexual generations after emergence from diapause. It has been hypothesized that this delay is advantageous in competitive and stochastic environments. Here, we develop a model of cyclically parthenogenic rotifer populations with a novel formulation of a "mictic block" that prevents sexual reproduction by females that are not sufficiently distant, generationally, from a stem ancestor that was produced sexually. We find that mictic blocks are indeed adaptive but that the most successful phenotypes have shorter blocks than previously reported and that the success of different delay phenotypes is highly dependent on the duration of the growing season. For a fixed environmental regime, a stable polymorphism is possible, wherein a phenotype with a longer block performs better in years with an average-length growing season, and a phenotype with a shorter block and lower mixis ratio performs better in years with an "extreme" growing season, whether short or long. Our model provides an eco-evolutionary framework for the study of Brachionus rotifers, a model system for non-genetic maternal effects and the evolution of sex.

evolutionary biology↗

bioRxiv2023

The curse of zombie dispersal in discrete-time models of spatial population dynamics

In many metapopulation and metacommunity models, individuals disperse between discrete habitat patches. When those models treat time as a discrete variable, the formulation of the dispersal term must be handled with care. A commonly made mistake is to model dispersal with terms identical to those found in continuous-time models. Such terms can inadvertently resurrect dead individuals, effectively creating "zombie dispersers." Zombie dispersal, in turn, can have dramatic, but spurious, effects on model dynamics. In this manuscript, we illustrate the misleading effects generated by zombie dispersal in a published model used to investigate how dispersal mediates synchrony in population dynamics.

ecology↗

bioRxiv2019

Maternal Effect Senescence and Fitness: A Demographic Analysis of a Novel Model Organism

Maternal effect senescence--a decline in offspring fitness with maternal age--has been demonstrated in a range of taxa, including humans. Despite decades of phenotypic studies, it remains unclear how maternal effect senescence impacts population structure or evolutionary fitness. To understand the impact of maternal effect senescence on population dynamics, fitness, and selection, we used data from individual-based culture experiments on the microscopic aquatic invertebrate, Brachionus manjavacas (Rotifera), to develop a series of matrix population models in which individuals are classified jointly by age and maternal age. By comparing the results derived from models with and without maternal effects, we found that the fitness difference due to maternal effect senescence arises primarily through decreased fertility, particularly at maternal ages corresponding to the peak reproductive output. In all models, selection gradients decrease with increasing age. They also decrease with maternal age for large maternal ages, implying that maternal effect senescence can evolve through the same process as in Hamiltons theory of the evolution of demographic senescence. We find that maternal effect senescence significantly alters population structure and fitness for B. manjavacas, a species with high maternal investment and maximum reproduction in early-to mid-life. The models developed here were built with data from an emerging model organism, and are widely applicable to evaluate the fitness consequences of maternal effect senescence across species with diverse aging and fertility schedule phenotypes.

evolutionary biology↗

bioRxiv2019

Preference and switching in the Kill-the-Winner functional response: Diversity, size structure, and synergistic grazing in plankton models

Grazing by zooplankton can maintain diversity in phytoplankton communities by allowing coexistence between competitors in situations that would otherwise lead to competitive exclusion. In mathematical models, grazing is represented by a functional response that describes the consumption rate by an individual zooplankter as a function of phytoplankton concentration. Since its initial description, the Kill-the-Winner functional response has been increasingly adopted for large-scale biogeochemical modeling. Here, we analyze how two properties of the Kill-the-Winner functional response--preference and switching--interact to promote coexistence and increase diversity in two simple models: a diamond-shaped nutrient-phytoplankton-zooplankton model and a size-structured phytoplankton community model. We found that, compared to preference, switching leads to coexistence and increased diversity over a much wider range of environmental conditions (nutrient supply and mixing rate). In the absence of switching, preference only allows for coexistence within the narrow range of environmental conditions where the preference is precisely balanced against the competitive difference between phytoplankton types. We also explored a counterintuitive aspect of the Kill-the-Winner functional response that we have termed "synergistic grazing". Synergistic grazing occurs when the grazing rate on one phytoplankton type increases as the biomass of an alternative phytoplankton type increases. This unrealistic effect is most evident when switching is strong and when zooplankton have a preference for the weaker competitor.

ecology↗