MS09 - ECOP-11

How environmental changes can impact spatial growth and spread: From the small to large scale

Friday, July 18 at 4:00pm

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Diana White (Clarkson University)

Description:

Many factors contribute to environmental shifts that alter species location and abundance. On the flip side, changes in species location and abundance can influence how a surrounding environment changes. In this minisymposium, we will explore the dynamics of populations (at both small and large scale) and explore how such species grow and move in spatially structured environments, as well as explore how changes in an environment can affect species growth and movement. At the microbial level, we study how spatial structure can alter bacteria growth and movement in a lab, and explore how microbial communities living within small brine pockets within sea ice impact the biological productivity of these polar regions. At the large scale, we look at how certain invasive aquatic and terrestrial plants grow, and how their growth and spatial spread can be altered by changes in their environment. This session emphasizes data collection from field work and lab experiments in combination with model analysis and simulation.

Jody Reimer

University of Utah

"Population and community dynamics of sea ice ecosystems"

Despite its barren appearance, sea ice hosts rich microbial communities adapted to the extreme conditions within a network of liquid brine inclusions. Among these extremophiles, ice algae thrive in part by excreting extracellular polymeric substances (EPS), which serve multiple ecological functions: EPS helps anchor microbes to ice surfaces, buffers against harsh physicochemical conditions, and alters the microstructure of sea ice by clogging pores. This clogging is hypothesized to reduce brine connectivity, potentially inhibiting nutrient transport and, in turn, limiting algal growth. To investigate this biophysical feedback, we develop and analyze a mathematical model of EPS-modulated ice algal bloom dynamics. Using fast-slow decomposition techniques, we explore how the timescale of EPS production and decay influences system behavior. Our results suggest that EPS-mediated pore clogging can impose a negative feedback that self-limits bloom intensity under a range of realistic conditions. Interestingly, we observe that oscillatory bloom dynamics emerge only when EPS is explicitly modeled; simplified EPS-implicit models fail to reproduce this behavior, indicating a loss of essential dynamics. These findings underscore the ecological significance of microbial modification of their environment and raise new questions about the coupled biological and physical processes governing life in polar sea ice.

Christopher Heggerud

University of California, Davis

"Shining light on phytoplankton dynamics: How light availability and niche differentiation can promote coexistence in the water column"

The paradox of the plankton highlights the apparent contradiction between Gause’s law of competitive exclusion and the observed diversity of phytoplankton. It is well known that phytoplankton dynamics depend heavily on light availability. Here we treat light as a continuum of resources rather than a single resource by considering the visible light spectrum. We propose a spatially explicit reaction–diffusion–advection model to explore under what circumstance coexistence is possible from mathematical and biological perspectives. Furthermore, we provide biological context as to when coexistence is expected based on the degree of niche differentiation within the light spectrum and overall turbidity and quality of the water.

Diana White

Clarkson University

"Modeling growth of invasive Eurasian watermilfoil under varying lake conditions"

The invasive species Myriophyllum spicatum, more commonly known as Eurasian Watermilfoil (EWM), has recently been identified as a major problem species in North America, originally discovered in the 1940s (originating from Europe, Asia, and North Africa). Like other invasive plants, EWM has the ability to grow and spread quickly, forming dense mono-cultures, due to its ability to out-compete many native aquatic plants. A recent ordinary differential equation (ODE) was developed to study local biomass changes of EWM in a single patch within a lake over a single growing season, and depends on lake characteristics such as temperature, water clarity, irradiance, depth, while also including plant properties such a respiration and leaf structure. The original analyses primarily concerned describing total biomass dynamics across a column of water over that patch, given by integrating biomass distribution over lake depth. We reformulate the original model to more accurately describe the dynamics of the biomass distribution (plants with differing heights) across a water column. As EWM grows in long, non-branching strands, we model the lengths of the EWM plants in the column, represented by the depths of the plants’ tips, which can later be used to obtain the integral biomass by integration. Similar to previous methods, our model takes into account the photosynthetic and respiratory properties of the plant, where in addition to this we assume that plant growth is governed by an advective process, where irradiance at each depth is connected to the “velocity” of the plant tips at that depth. Variations in parameters (like those related to water clarity) show how EWM can form dense patches where plants canopy at the surface of the water.

Susan Bailey

Clarkson University

"Impacts of spatial structure on population growth in bacteria: Connecting experiments with models"

Microbes grow almost everywhere on earth, from soil ecosystems to the human lungs, and their diverse habitats are often spatially heterogeneous and structured. A range of theoretical models suggest that spatial structure can both increase and decrease population growth compared to an equivalent well-mixed environment, depending on the specifics of cell interactions and movement. However, in lab experiments, it is often accepted that well-mixed environments (i.e. shaken liquid media) are the typically best for growing dense cultures of bacteria. In contrast to these wide-spread assumptions, we were surprised to observe increased population growth of the bacteria Pseudomonas fluorescens (Pf) when cultured in spatially-structured lab conditions (semi-solid agar media), compared to in the equivalent well-mixed conditions (shaken liquid media). Further tests showed that this increase in Pf population growth in structured environments only occurs when nutrient concentration is low (i.e. food resources are scarce). We hypothesized that these patterns may be driven by how effective directed movement towards food resources (i.e. chemotaxis) can be in structured versus well-mixed environments, and then developed an agent-based model (ABM) to explore this potential mechanism. Results from our ABM qualitatively match our experimental observations of Pf populations, supporting our hypothesis that effective chemotactic movement drives increased access to food resources, and so may be important in driving population growth in spatially structured environments, particularly when food resources are scarce.

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Annual Meeting for the Society for Mathematical Biology, 2025.