Biology subjects

Hajian-Forooshani, Z.

Publications and source records attributed to Hajian-Forooshani, Z..

6 recordsLinked to original sources

bioRxiv2025

Disturbance interacts with dispersal and niche breadth to shape scale-dependent diversity change in metacommunities

Disturbances influence the maintenance of diversity in important, but complex, ways across spatial and temporal scales. Although disturbance effects on diversity are known to be scale-dependent and taxon-specific, there is little mechanistic understanding of the processes that influence the observed context-dependency. Here, we take a theoretical approach based on metacommunity theory to examine the interaction between metacommunity processes and disturbance in shaping diversity patterns across spatial scales. We find that disturbance shapes diversity at local and regional scales in ways which can lead to either homogenization (decreases in {beta}-diversity) or differentiation (increases in {beta}-diversity). How it does so depend on the spatial extent of the disturbance in the landscape, the dispersal rates and niche breadth of species in the metacommunity, and whether diversity is measured immediately following disturbance or during recovery.We show that high dispersal jointly promotes the rapid recovery of local diversity and the loss of regional diversity, resulting in decreases in {beta}-diversity. Niche breath buffers against diversity loss at both scales during disturbance, but interacts with dispersal to drive transient diversity loss at the regional scale after disturbance. Our results suggest that particular processes in metacommunities interact with disturbance and leave behind distinct signatures of diversity change across scales that can be used to better parse observed patterns of diversity change in empirical systems.

ecology↗

bioRxiv2023

Interplay between harvesting, planting density and ripening time affects coffee leaf rust dispersal and infection

The relationship between the spatial structure of hosts and the individual movement of vectors is central to developing a comprehensive representation of pathogen dynamics. Here we focus on the dynamics of coffee leaf rust (CLR; Hemileia vastatrix), which is one of the principal coffee diseases around the globe. This fungus disperses between plants or regions through direct contact, water splash, or local turbulent wind conditions. Some studies have proposed that coffee harvesters can also bear CLR during harvesting. However, it is not clear how relevant these movements are for CLR dispersal and plot-level infection in plots with different planting densities. Besides, there are bidirectional interactions between the plantation characteristics (e.g. planting density and ripening synchronicity) and the movement of harvesters that might modify their dispersal potential. Overall, there is a lack of mechanistic models to represent these interactions. Here we present a computational model to explore the role of coffee ripening synchronicity in reproducing the different movement trajectories observed in the field. We then evaluate how these harvesting trajectories modify rust dispersal and change CLR infection in plots with increasing planting densities and a constant contact-mediated rust dispersal mechanism. For both synchronization scenarios, the distribution of step lengths is positively skewed. Interplant asynchronous ripening and scarcity of trees with berries generate trajectories with medium to long steps contrary to scenarios with synchronous ripening and without scarcity. The harvest dispersal significantly increases coffee plot infection (up to 15%) compared to scenarios where only local mechanisms for CLR dispersal are present. This effect is maximal for trajectories with medium to long steps from the asynchronous scenario and in plantations with medium planting densities. In particular, medium-sized steps are more likely to create new foci and networks of contact-mediated infected plants. The interaction between the proportion and the size of infected networks results in a nonlinear behavior of rust increase due to harvest. Our results aim to spur discussion on practices that could reduce the impact of harvesting and specific trajectories, in scenarios where one can benefit from asynchronous maturation of berries and shaded plantations. Some examples of practices include reducing the medium to long-distance movements during the same day, for instance, by avoiding harvesting at the end of the harvest season when trees ripening asynchronicity and CLR levels are higher.

ecology↗

bioRxiv2022

Dispersion and Plant Arrangement Condition the Timing and Magnitude of Coffee Rust Infection

One central issue in coffee-leaf rust (Hemileia vastatrix) epidemiology is to understand what determines the intensity and the timing of yearly infections in coffee plantations. However, most experimental and theoretical studies report infection as an average at the plot level, obscuring the role of potentially key factors like rust dispersal or the planting pattern. Here, we first review the rust epidemic patterns of different sites, which reveal large variability in the duration and magnitude of the different epidemiologic phases. We then present a spatially explicit and parametrised model, where the host population is subdivided into discrete patches linked through spore dispersal, modelled as simple diffusion. With this model, we study the role of the planting arrangement, the dispersal intensity and plant-level variables on the maximum average tree infection (MATI) and its timing. Our results suggest that the epidemic timeline can be divided into two phases: a time lag and a growth phase per se. The model shows that the combination of the dispersal magnitude and plant aggregation modifies the MATI and the time to MATI, mainly by preventing some plants from reaching their maximum peak during the epidemic. It also affects the epidemic curves, which can have a stepped, or a rather smooth pattern in plots with otherwise similar conditions. The initial rust infection modulates the time lag before the epidemic and the infected leaf-fall rate drastically changes the MATI. These findings highlight the importance of explicitly considering the spatial aspects of coffee agroecosystems when measuring and managing rust infection, and help us to further understand the spatio-temporal dynamics of ecological systems in general.

systems biology↗

bioRxiv2020

Spatial structure and pathogen epidemics: the influence of management and stochasticity in agroecosystems

O_LIOrganisms susceptible to disease, from humans to crops, inevitably have spatial geometry that influence disease dynamics. Understanding how spatial structure emerges through time in ecological systems and how that structure influences disease dynamics is of practical importance for natural and human management systems. Here we use the annual crop, coffee, Coffea arabica, along with its pathogen, the coffee leaf rust, Haemelia vastatrix, as a model system to understand how spatial structure is created in agroecosystems and its subsequent influence on the dynamics of the system. C_LIO_LIHere, we create a simple null model of the socio-ecological process of death and stochastic replanting of coffee plants on a plot. We then use spatial networks to quantify the spatial structures and make comparisons of our stochastic null model to empirically observed spatial distributions of coffee. We then present a simple model of pathogen spread on spatial networks across a range of spatial geometries emerging from our null model and show how both local and regional management of agroecosystems interact with space and time to alter disease dynamics. C_LIO_LIOur results suggest that our null model of evolving spatial structure can capture many critical features of how the spatial arrangement of plants changes through time in coffee agroecosystems. Additionally, we find that small changes in management practices that influence the scale of pathogen transmission, such as shade tree removal, can result in a rapid transition to epidemics with lattice-like spatial arrangements but not irregular planting geometries. C_LIO_LIThe results presented here may have practical implications for farmers in Latin America who are in the process of replanting and overhauling management of their coffee farms in response to a coffee leaf rust epidemic in 2013. We suggest that shade reduction in conjunction with more lattice-like planting schemes may result in coffee being more prone to epidemic-like dynamics of the coffee leaf rust in the future. C_LI

ecology↗

bioRxiv2020

Viewing communities as coupled oscillators: elementary forms from Lotka and Volterra to Kuramoto

Ecosystems and their embedded ecological communities are almost always by definition collections of oscillating populations. This is apparent given the qualitative reality that oscillations emerge from consumer-resource interactions, which are the simple building blocks for ecological communities. It is also likely always the case that oscillatory consumer-resource pairs will be connected to one another via trophic cross-feeding with shared resources or via competitive interactions among resources. Thus, one approach to understanding the dynamics of communities conceptualizes them as collections of oscillators coupled in various arrangements. Here we look to the pioneering work of Kuramoto on coupled oscillators and ask to what extent can his insights and approaches be translated to ecological systems. We explore all possible coupling arrangements of the simple case of three oscillator systems with both the Kuramoto model and with the classical Lotka-Volterra equations that are foundational to ecology. Our results show that the six-dimensional analogous Lotka-Volterra systems behave strikingly similarly to that of the corresponding Kuramoto systems across all possible coupling combinations. This qualitative similarity in the results between these two approaches suggests that a vast literature on coupled oscillators that has largely been ignored by ecologists may in fact be relevant in furthering our understanding of ecosystem and community organization.

ecology↗

bioRxiv2018

From Metapopulation to Metacommunity and the Complications of Community Structure

The metacommunity, as it evolved from Levins metapopulation, provides a framework to consider the spatial organization of species interactions. Arguably the most fundamental feature of metapopu-lations and metacommunities are that demes are connected via migration. An important result from Levins metapopulation work--that increasing migration lowers regional extinction probability--is often incorporated into conceptions of metacommunities. We first use a toy model to show how this result from Levins metapopulation does not necessarily hold when considering community interactions in a metacommunity context. We also report results from a metacommunity field experiment conducted with a tropical terrestrial leaf litter community and show that migration induces the extinction of predators in the metacommunity. Our result corroborates the findings of a prior metacommunity experiment in a temperate terrestrial leaf litter community. The concordance between these experiments even with vastly different communities highlights the importance of considering trophic and non-trophic community structure to understand metacommunity dynamics.

ecology↗