Biology subjects

Sullivan, L. L.

Publications and source records attributed to Sullivan, L. L..

4 recordsLinked to original sources

bioRxiv2025

Nutrient enrichment intensifies plant competitive effects, favouring monocultures: a global meta-analysis

Excess nutrient deposition is a major driver of plant diversity loss, but the mechanisms of this loss remain unclear. Diversity loss has been interpreted through the niche dimension hypothesis, yet the mechanistic link via competitive effects remains unresolved. Establishing this link demands a global synthesis of how nutrients alter competitive effects, defined as a species ability to perform better or worse with heterospecific competitors than with conspecifics. Strong competitive effects from heterospecifics relative to conspecifics can lead to decline or exclusion of the focal species, whereas weaker competitive effects indicate niche differentiation that promotes coexistence. We conducted a global meta-analysis of 71 plant competition experiments to quantify how nutrient addition alters competitive effects, using biomass as the performance metric. Nutrient addition intensified competitive effects with heterospecifics by 1.5-fold, as focal species biomass was higher with conspecifics. Responses depended on the initial competitive effect under low nutrients: when effects were weak, nutrient addition increased biomass with conspecifics; when effects were strong, nutrient addition increased biomass with heterospecifics, alleviating competition and potentially countering species loss. Competitive effects were amplified most when higher temperatures occurred in dry quarters, suggesting nutrient additions may exacerbate competition under extreme climate conditions. Understanding these interactive effects of nutrient addition, changing climate, and competition is critical for predicting plant responses to global change in both managed and natural ecosystems. Significance StatementNutrient enrichment from agricultural runoff is a driver of plant diversity loss. While patterns of diversity loss from nutrient additions are clear, the processes driving competitive effects that lead to diversity loss remain uncertain. Our global meta-analysis reveals that multiple nutrient addition intensifies competitive effects favouring monocultures i.e, species accumulating more biomass with conspecifics than heterospecifics. Depending on the initial strength of competitive effects, nutrient addition amplified or alleviated them. Temperature and water availability interact with nutrient addition to amplify competitive asymmetries, likely further shaping species dominance under changing climate. These insights provide the first global-scale evidence of nutrient enrichment effects on plant communities and highlight the need to mitigate compounding impacts of fertilization and climate change on diversity.

ecology↗

bioRxiv2024

Quantifying seed rain patterns in a remnant and a chronosequence of restored tallgrass prairies in north central Missouri

O_LISeed rain is an influential process related to plant community diversity, composition, and regeneration. However, knowledge of seed rain patterns is limited to those observed in forests and late-assembling grasslands, which might not reflect early-assembling communities such as newly restored grasslands. Resolving this gap in our understanding provides further insight into the role of seed dispersal. C_LIO_LIHere, we measured seed rain in a remnant tallgrass prairie, which was the site of the foundational grassland seed rain study in 1978, and a nearby chronosequence of tallgrass prairie restorations. We sought to determine how the quantity, seed mass traits, timing, diversity, and composition of seed rain changed (1) long-term and (2) during community assembly. To do so, we deployed artificial turf grass seed traps into 2-year-old, 5-6-year-old, and 15-year-old restored prairies and the remnant prairie, replacing traps every two weeks from May to December 2019. C_LIO_LIWe captured over twice the density and richness of seed rain in the remnant prairie in 2019 compared to 1978. We also found that seed rain patterns changed as prairies aged, with each prairie possessing a distinct community of dispersing species. Significantly more seeds, seed biomass, and species were captured in the youngest restored prairie. However, seed mass traits were similar in all prairies. Except for composition, all other seed rain metrics in the oldest restoration were eventually comparable to the remnant prairie. C_LIO_LISynthesis and Applications: Our results revealed that grasslands, notably young prairies, produce larger quantities of seed rain than previously known (124,806 seeds m-2 year -1, 97.24 g m-2 year -1), and seed input in all sampled prairies far exceeded restoration broadcast seeding densities. We further found that decreases in seed rain quantity across the chronosequence did not correspond with increases in seed mass, suggesting a lack of tradeoffs between these metrics. Furthermore, tallgrass prairie restorations have not replicated the composition of seed rain seen in remnant systems. Increasing restoration seeding rates of desirable species may be needed to meet composition goals since current rates may not compete with the propagule pressure of undesirable species found in newly restored prairies. C_LI

ecology↗

bioRxiv2021

EcoEvoApps: Interactive Apps for Teaching Theoretical Models in Ecology and Evolutionary Biology

O_LIThe integration of theory and data drives progress in science, but a persistent barrier to such integration in ecology and evolutionary biology (EEB) is that theory is often developed and expressed in the form of mathematical models that can feel daunting and inaccessible for students and empiricists with variable quantitative training and attitudes towards math. C_LIO_LIA promising way to make mathematical models more approachable is to embed them into interactive tools with which one can visually evaluate model structures and directly explore model outcomes through simulation. C_LIO_LITo promote such interactive learning of quantitative models, we developed EcoEvoApps, a collection of free, open-source (R/Shiny) apps that include model overviews, interactive model simulations, and code to implement these models directly in R. The package currently focuses on canonical models of population dynamics, species interaction, and landscape ecology. We also outline a vision and approach for growing the collection to include more models from across EEB. C_LIO_LIThese apps help illustrate fundamental results from theoretical ecology and can serve as valuable teaching tools in classroom settings. We present data from student surveys which show that students rate these apps as useful learning tools, and that using interactive apps leads to substantial gains in students interest and confidence in mathematical models. This points to the potential for interactive activities to make theoretical models more accessible to a wider audience, and thus facilitate the feedback between theory and data across ecology and evolutionary biology. C_LI

scientific communication and education↗

bioRxiv2020

Local climate and habitat continuity interact to alter contemporary dispersal potential

Understanding the evolution of dispersal under changing global environments is essential to predicting a species ability to track shifting ecological niches. Two important, but anthropogenically altered, sources of selection on dispersal are climate and habitat continuity. Despite the likelihood these global drivers of selection act simultaneously on plant populations, their combined effects on dispersal are rarely examined. To understand the interactive effect of climate and habitat continuity on dispersal potential, we study Geum triflorum - a perennial grassland species that spans a wide range of environments, including both continuous prairie and isolated alvar habitats. We explore how the local climate of the growing season and habitat continuity (continuous vs isolated) interact to alter dispersal potential. We find a consistent interactive effect of local climate and habitat continuity on dispersal potential. Across continuous prairie populations, an increased number of growing degree days favors traits that increase dispersal potential. However, for isolated alvar populations, dispersal potential tends to decrease as the number of growing degree days increase. Our findings suggest that under continued warming, populations in continuous habitats will benefit from increased gene flow, while isolated populations will become increasingly segregated, with reduced potential to track shifting fitness optima.

evolutionary biology↗