Biology subjects

Byrnes, J. E. K.

Publications and source records attributed to Byrnes, J. E. K..

7 recordsLinked to original sources

bioRxiv2026

Changes in species composition of sessile communities on subtidal rock walls in the southern Gulf of Maine during four decades of warming

Climate change is driving species range shifts and population change in density and location globally. Two theories behind these shifts, that species in the ocean are largely tracking climate velocities, and the concept of long-term temporal turnover, have garnered increased attention recently. However, research in marine ecosystems has largely focused on mobile species, namely commercially important fishes. Here we examine changes in sessile invertebrate and algal species on vertical surfaces, subtidal rock walls, in the southern Gulf of Maine (GOM), and to what extent these changes might have been driven by 42 years of warming. In part due to ocean circulation patterns in the GOM, the thermally-sensitive species in this community are unlikely to track climate velocities by moving laterally, and are therefore disappearing, moving into deeper water, or adapting to novel thermal conditions. We find that some species, including one of the previously competitive dominants, Alcyonium siderium, have become exceedingly rare at these sites. Two other competitive dominants, Metridium senile and Aplidiiuam glabrum, have also declined precipitously. Meanwhile, the blue mussel, Mytilus edulis, the non-native tunicate Didemnum vexillum, and a complex of erect bryozoans have become dominant space holders. Over the same period of time, average summer temperatures in the southern GOM increased by more than 3{degrees}C. Using occupancy derived thermal affinities, we find warm-affinity species increasing, while generally, cool and cold-affinity species are decreasing. All species which decreased in abundance normally occupy sites with temperatures below a mean of 17.4{degrees}C maximum summer temperatures. A few species did not change abundance despite the rapidly warming surface waters, indicating their broad tolerances and the importance of other biological processes in mediating community structure in the GOM. Overall, sessile rock wall communities in the southern GOM are transitioning to more thermally-tolerant species, most of which are not native to the Atlantic coast of North America.

ecology↗

bioRxiv2024

Causal inference with observational data and unobserved confounding variables

Experiments have long been the gold standard for causal inference in Ecology. Observational data has been primarily used to validate experimental results or to find patterns that inspire experiments - not for causal inference. As ecology tackles progressively larger problems, we are moving beyond the scales at which randomized controlled experiments are feasible. Using observational data for causal inference raises the problem of confounding variables, those affecting both a causal variable and response of interest. Unmeasured confounders lead to statistical bias, creating spurious correlations and masking true causal relationships. To combat this Omitted Variable Bias, other disciplines have developed rigorous approaches for causal inference from observational data addressing the problems of confounders. We show how Ecologists can harness some of these methods: identifying confounders via causal diagrams, using nested sampling designs, and statistical designs that address omitted variable bias for causal inference. Using a motivating example of warming effects on intertidal snails, we show how current methods in Ecology (e.g., mixed models) produce incorrect inferences, and how methods presented here outperform them, reducing bias and increasing statistical power. Our goal is to enable the widespread use of observational data as tool for causal inference for the next generation of Ecological studies.

ecology↗

bioRxiv2024

A range expanding ecosystem engineer influences historical and expanded habitats via the same causal pathways

Species are shifting their ranges in response to climate change. There remain many unknowns about relative impacts of range-expanding ecosystem engineers between historical and expanded habitats, however. The mud fiddler crab Minuca pugnax (=Uca pugnax) is shifting its range northward likely due to increased warming in the Gulf of Maine. A burrowing crab, M. pugnax affects ecosystem functioning in salt marshes south of Cape Cod, Massachusetts with unknown effects in expanded marsh habitats over 150km to the north. We therefore studied the M. pugnax range expansion to determine the extent that range expanding ecosystem engineers are influencing ecosystem functioning expanded ranges relative to historical habitats. We installed in 2017 and 2018 a series of crab-inclusion cages at both the UMass Boston Nantucket Field Station (historical range) and the Plum Island Estuary Long Term Ecological Research site (PIE-LTER, expanded range). For each site, year, and block, we measured in the beginning and end of the three-month experiment metrics of sediment strength, primary production, and decomposition. We developed and tested causal models using structural equation modeling (SEM) to determine direct and indirect effects of fiddler crabs on ecosystem functions. Despite site, year, and block variability, local environment influenced burrow density, which directly affected sediment strength and indirectly affected primary production in both ranges. Overall, understanding range-expanding ecosystem engineers in historical ranges was predictive for how they influence expanded habitats, despite inter-site heterogeneity. Therefore, it is critical to study relative impacts of range-expanding ecosystem engineers to understand total impacts of global range shifts.

ecology↗

bioRxiv2022

Understandable Multifunctionality Measures Using Hill Numbers

In ecology, multifunctionality measures the simultaneous performance of multiple ecosystem functions. If species diversity describes the variety of species that together build the ecosystem, multifunctionality attempts to describe the variety of functions these species perform. A range of methods have been proposed to quantify multifunctionality, successively attempting to alleviate problems that have been identified with the previous methods. This has led to a proliferation of more-or-less closely related metrics which, however, lack an overarching theoretical framework. Here we borrow from the comprehensive framework of species diversity to derive a new metric of multifunctionality. Analogously to the effective number of species used to quantify species diversity, the metric we propose is influenced both by the number of functions as well as, crucially, the evenness of performance levels across functions. In addition, the effective multifunctionality also considers the average level at which the functions are performed. The result is a measure of the cumulative performance of the system were all functions provided equally. The framework allows for the inclusion of the correlation structure among functions, thus allowing it to account for non-independence between functions. We show that the average metric is a special case of the newly proposed metric when all functions are uncorrelated and performed at equal levels. We hope that by providing a new metric of multifunctionality anchored in the rigorous framework of species diversity based on effective numbers, we will overcome the considerable skepticism that the larger community of ecologists has built against indices of multifunctionality. We thereby hope to help popularize this important concept which, as biological diversity, describes a fundamental property of ecosystems and thus lies at the heart of ecology.

ecology↗

bioRxiv2021

Automated satellite remote sensing of giant kelp at the Falkland Islands (Islas Malvinas)

Giant kelp populations support productive and diverse coastal ecosystems in both hemispheres at temperate and subpolar latitudes but are vulnerable to changing climate conditions as well as direct human impacts. Observations of giant kelp forests are spatially and temporally patchy, with disproportionate coverage in the northern hemisphere, despite the size and comparable density of southern hemisphere kelp forests. Satellite imagery enables the mapping of existing and historical giant kelp populations in understudied regions, but automating the detection of giant kelp in large satellite datasets requires approaches that are robust to the optical complexity of the shallow, nearshore environment. We present and compare two approaches for automating the detection of giant kelp in satellite datasets: one based on crowd sourcing of satellite imagery classifications and another based on a decision tree paired with a spectral unmixing algorithm (automated using Google Earth Engine). Both approaches are applied to satellite imagery (Landsat) of the Falkland Islands or Islas Malvinas (FLK), an archipelago in the southern Atlantic Ocean that supports expansive giant kelp ecosystems. The performance of each method is evaluated by comparing the automated classifications with a subset of expert-annotated imagery cumulatively spanning over 2,700km of coastline. Using the remote sensing approaches evaluated herein, we present the first continuous timeseries of giant kelp observations in the FLK region using Landsat imagery spanning over three decades. We do not detect evidence of long-term change in the FLK region, although we observe a recent decline in total canopy area from 2017-2021. Using a nitrate model based on nearby ocean state measurements obtained from ships and incorporating satellite sea surface temperature products, we find that the area of giant kelp forests in the FLK region is positively correlated with the nitrate content observed during the prior year. Our results indicate that giant kelp classifications using citizen science are approximately consistent with classifications based on a state-of-the-art automated spectral approach. Despite differences in accuracy and sensitivity, both approaches find high interannual variability that impedes the detection of potential long-term changes in giant kelp canopy area, although recent canopy area declines are notable and should continue to be monitored carefully.

ecology↗

bioRxiv2020

Sediment Selection: Range Expanding Fiddler Crab are Better Burrowers Than Their Natal Counterparts

Species ranges are shifting in response to climate change. In New England saltmarshes, the mud fiddler crab, Minuca pugnax, is expanding north of Cape Cod, MA into the Gulf of Maine (GoM) due to warming waters. The burrowing lifestyle of M. pugnax means sediment compaction in saltmarshes may influence the ability for crabs to dig, with more compact soils being resilient to burrowing. Previous studies indicate that saltmarshes along the GoM have higher soil strength (i.e., compaction) relative to marshes south of Cape Cod. Together, physical characteristics and temperature of this habitat may be influencing the burrowing performance of M. pugnax, and therefore the continuation of their northward range expansion into the GoM. To determine if compaction affects burrowing activity of M. pugnax in historical and range expanded populations, we conducted a controlled laboratory experiment. We manipulated soil compaction in standardized lab assays and measured crab burrowing performance with individuals collected from Nantucket (i.e., historical range) and the Plum Island Estuary (PIE, i.e., expanded range). We determined compaction negatively affected burrowing ability in crabs from both sites; however, crabs from PIE burrowed in higher soil compactions than Nantucket crabs. In addition, PIE crabs were more likely to burrow overall. We conclude that site level differences in compaction are likely altering burrowing behavior in the crabs expanded range territory by way of phenotypic plasticity or rapid evolution. Our study demonstrates that non-temperature physical habitat traits can be as important as temperature in influencing climate driven range expansions.

ecology↗

bioRxiv2017

Human activities influence the direction and magnitude of local biodiversity change over time

In recent decades, environmental drivers of community change have been associated with changes in biodiversity from local to global scales. Here we evaluate the role of anthropogenic drivers in marine ecosystems as drivers of change in local species richness with a meta-analysis of a novel dataset of temporal change in species richness. We paired biodiversity data from 144 sites with large-scale drivers derived from geospatial databases: human cumulative impact scores, sea surface temperature change, nutrient loading, and invasion potential. Three specific drivers (nutrient inputs, rate of linear temperature change, and non-native species invasion potential) explained patterns in local marine species richness change. We show that these drivers have opposing effects on biodiversity trends. In some cases, variability in drivers can create contrasting directions of change yielding observations of no net change when localities are pooled in an attempt to find a global average. Further, long-term studies reveal different effects of drivers that are not observed in short-term studies. These findings begin to explain high variability observed in species diversity trends at local scales. Formally attributing local species diversity change to human drivers is essential to understanding global patterns of local species diversity change and their consequences.

ecology↗