Biology subjects

Kortessis, N.

Publications and source records attributed to Kortessis, N..

4 recordsLinked to original sources

bioRxiv2023

Neglected consequences of spatio-temporal heterogeneity and dispersal: Metapopulations, the inflationary effect, and real-world consequences for public health

The metapopulation perspective is an important conceptual framework in ecology and evolutionary ecology. Metapopulations are spatially distributed populations linked by dispersal. Both metapopulation models and their community and ecosystem level analogues, metacommunity and meta-ecosystem models, tend to be more stable regionally than locally and display enhanced abundance because of the interplay of spatiotemporal heterogeneity and dispersal (an effect that has been called the "inflationary effect"). We highlight the essential role of spatiotemporal heterogeneity in metapopulation biology, sketch empirical demonstrations of the inflationary effect, and provide a mechanistic interpretation of how the inflationary effect arises and impacts population growth and abundance. We illustrate the effect with examples from the spread of infectious disease. Namely, failure to recognize the full possible effects of spatiotemporal heterogeneity likely enhanced the spread of COVID-19, a failure based on lack of understanding of emergent population processes at large scales which may hamper control and eradication of other infectious diseases. We finish by noting how the effects of spatiotemporal heterogeneity have implicitly played roles in the history of ecology, ranging across subdisciplines as diverse as natural enemy-victim dynamics, species coexistence, and conservation biology. Seriously confronting the complexity of spatiotemporal heterogeneity could push many of these subdisciplines forward.

ecology↗

bioRxiv2023

Increasing environmental fluctuations can dampen variability of endogenously cycling populations

Understanding how populations respond to increasingly variable conditions is a major objective for natural resource managers attempting to forecast extinction risk. The lesson from current modeling is clear: Increasing environmental variability increases population abundance variability. We show that this paradigm fails to describe a broad class of empirically observed dynamics, namely endogenously-driven population cycles. In contrast to the dominant paradigm, these populations can exhibit reduced long-run population variance under increasing environmental variability. We hypothesize that this paradox arises from interactions between environmental stochasticity and nonlinear density dependence. Such interactions violate the oft-assumed additivity of stochastic and deterministic drivers of population fluctuations present in many models that forecast population size. We show evidence for the interaction in two canonical cyclical populations: flour beetles and Canadian Lynx. To help identify the interaction, we develop new theory to quantify the strength of these interactions by partitioning the effects of nonlinear dynamics and stochastic variation on dynamical systems. In both empirical examples, the partitioning shows that the interaction between deterministic and stochastic dynamics reduces the overall variance in population size. Our results highlight that previous predictions about extinction under environmental variability may prove inadequate to understand the effects of climate change in many populations.

ecology↗

bioRxiv2023

Dynamics of mixed-ploidy populations under demographic and environmental stochasticities

The theoretical population dynamics of autopolyploids - organisms with more than two genome copies of a single ancestral species - and their diploid progenitors have been extensively studied. The acquisition of multiple genome copies, being in essence a stochastic process, strongly suggests a probabilistic approach to examine the long-term dynamics of a population with multiple cytotypes. Yet, our current understanding of empirical evidence on the dynamics of autopolyploid populations has not incorporated stochastic population dynamics. To investigate the factors contributing to the probability and stability of coexisting cytotypes, we designed a new population dynamics model with demographic and environmental stochasticities to simulate the formation, establishment, and persistence of diploids, triploids, and autotetraploids over time when gene flow is allowed among cytotypes. Contrary to previous research, increased selfing rates and pronounced reproductive isolation stabilized the long-run coexistence of multiple cyto-types. In stressful environments, these dynamics become much more complex, and our stochastic modeling approach helped reveal the resulting intricacies that give tetraploids competitive advantage over their diploid progenitors. Our work is fundamental to a better understanding of the dynamics of coexistence of multiple cytotypes and is a necessary step for further work modeling the dynamics between an autopolyploid and its diploid progenitor.

evolutionary biology↗

bioRxiv2022

Effects of disease emergence on invasive grass impacts

Invasive species impact ecosystems through their large abundances and strong per capita effects. Enemies can regulate abundances and per capita effects, but are notably absent for many new invaders. However, invaders acquire enemies over time and as they spread; processes hypothesized to mitigate negative invader impacts by reducing abundance or per capita effects. Alternatively, properties of invaders or acquired enemies, such as an enemys ability to attack multiple species, may hinder enemy mitigation of invader impacts. We used field experiments to evaluate disease mitigation of invader impacts using the invasive grass Microstegium vimineum, which hosts an emerging fungal disease, and a native grass competitor, Elymus virginicus. We manipulated competition through density gradients of each plant species, and we reduced ambient foliar diseases with fungicide and autoclaving. We then modeled long-term population dynamics with field-estimated parameters. In the field, disease did not reduce invader abundance or per capita effects. The invader amplified disease on itself and the competitor, and disease reduced invader and competitor fitness components (e.g., germination). The dynamical model predicted that disease impacts on the competitor are greater than on the invader, such that disease will reduce invader abundance by 18%, and competitor abundance by 88%, over time. Our study suggests that enemies acquired by invaders will not necessarily mitigate invader impacts if the invader amplifies the enemy and the enemy attacks and suppresses competitor species.

ecology↗