Biology subjects

Vandermeer, J.

Publications and source records attributed to Vandermeer, J..

12 recordsLinked to original sources

bioRxiv2025

Human subsidies facilitate hyperpredation of Mediterranean island wildlife by outdoor cats

Domestic cats (Felis catus) are avid wildlife predators and one of the most harmful invasive species. The lethal impacts of an introduced predator such as cats on wildlife can be further exacerbated by the introduction of an additional abundant non-native prey species capable of supporting an exceptionally dense predator population, a phenomenon known as hyperpredation. A special case of hyperpredation involves human food subsidies, when an invasive predator impacting native wildlife is supported not by another invasive taxon, but by human-derived food sources. To test whether access to anthropogenic food subsidies by cats is causing hyperpredation, mark-recapture methodology was used to measure twelve cat populations experiencing a gradient of human subsidies on the Mediterranean island of Naxos, Greece. Line-transect surveys were conducted at each site to measure reptile population abundance across this gradient, and other factors including human density and distance of reptiles from villages were considered as well. Strong evidence was found that the population size of cats is a direct result of the density of anthropogenic food available to them, and a corresponding decline in the size of reptile populations as cat density increased was observed. It was also shown that as cat populations exceed the available supply of human food, the negative effects of cat density on reptile populations are exacerbated. These results demonstrate that access to anthropogenic subsidies has allowed cat populations to expand to exceptional levels, driving hyperpredation on island wildlife.

ecology↗

bioRxiv2024

Consistent and scalable monitoring of birds and habitats along a coffee production intensity gradient

Land use change associated with agricultural intensification is a leading driver of biodiversity loss in the tropics. To evaluate the habitat-biodiversity relationship in production systems of tropical agricultural commodities, which is critical for certifying and examining the success of biodiversity-friendly agricultural practices, birds are commonly used as indicators. However, consistently and reliably monitoring how bird communities are affected by land use change throughout the annual cycle in a way that can be scalable is challenging using traditional survey methods. In this study, we examined whether the automated analysis of audio data collected by passive acoustic monitoring, together with the analysis of remote sensing data, can be used to efficiently monitor avian biodiversity along the gradient of habitat degradation associated with the intensification of coffee production. Coffee is an important crop produced in tropical forested regions, whose production is expanding and intensifying, and coffee production systems form a gradient of ecological complexity ranging from forest-like shaded polyculture to dense sun-exposed monoculture. We used LiDAR technology to survey the habitat, in combination with autonomous recording units and a vocalisation classification algorithm to assess bird community composition in a coffee landscape comprising a shade-grown coffee farm, a sun coffee farm, and a forest remnant, located in southern Mexico. We found that combining LiDAR with the automated analysis of continuously collected bioacoustics data can capture the expected functional signatures of avian communities as a function of habitat quality in the coffee landscape. Thus, we show that this approach can be a robust way to monitor how biodiversity responds to land use intensification in the tropics. A major advantage of this approach is that it has the potential to be deployed cost-effectively at large scales to help design and certify biodiversity-friendly productive landscapes.

ecology↗

bioRxiv2024

Complex interspecific interactions influence the interactions between pest control and pollination in coffee agroecosystems.

Ecosystem services mediated by biodiversity are essential for the well-being of human beings. While there is ample research on individual ecosystem services (such as pollination, nutrient cycling), there is now growing recognition to examine the interactions between multiple ecosystem services and their contribution to productivity in order to manage agroecosystems sustainably. In this study, we examined the interactions between pollination and pest control in coffee agroecosystems in Chiapas, Mexico. We tested how management of shade trees, particularly of nitrogen-fixing shade trees, at the farm scale mediated the outcome of the interactions between two ES. We found that there was no trade-off between pest control and pollination services despite the deterrence of pollinators by the dominant and aggressive ant species, Azteca sericeasur, which also controls the coffee berry borer, a major pest of Coffea arabica. We found additive effects of pest-control and pollination on early fruit set and fruit weight of coffee plants. Proximity to nitrogen-fixing shade trees had indirect effects on pest-control via the reduction of Azteca sericeasur activity on the coffee bushes. These findings highlight that ecosystem services are a result of complex interspecific interactions and that biodiversity-friendly management practices can promote favorable outcomes of these interactions on coffee yield.

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↗

bioRxiv2023

Above- and below-ground links mediated by arboreal ants and host tree modify soil aggregation scaling, infiltration, and chemistry

Soils are increasingly recognized as complex systems, emphasizing a need to study unique properties such as long-tailed scaling laws and the role of indirect interactions among arboreal above- and below-ground soil invertebrates. However, few studies consider the above-below-ground connections mediated by invertebrates activity and behavior compared to mediated by tree physiology. Given previous work showing that arboreal ants can compete and affect ground foragers as well as alter foraging behavior on different host trees, it is plausible that persistent above-ground ant nesting could extend to affect soil properties including structure and chemistry, mediated by ground ant exclusion. This study analyzes soil aggregation, water infiltration, and macro-chemical data associated with longer-term (5+ year) ant nesting in a rustic tropical agroforest. Results show that, 1) ant nesting maintained scaling law exponents or fractal dimensions of soil aggregate size distributions, and was significantly associated with relatively larger micro-aggregate diameters and log-normal variance in macro-aggregate size distributions, suggesting more consistent (less variable) underlying aggregation processes similar to host tree species effects; 2) areas in the vicinity of trees with no dominant ant nests had three-times faster water infiltration than in the vicinity of trees with dominant ant nests; and 3) a tendency toward changes in soil carbon and nitrogen stocks by one-quarter depending on host tree. These patterns are consistent with expected effects of ground ant suppression by an aggressive keystone arboreal ant, and are supported by previous studies reporting positive ground ant nest effects on soil chemistry and documenting ground ant foraging as a source of soil aggregate fragmentation. This study presents new ecological processes affecting ecosystem-scale functions, and suggests that future research on indirect interaction cascades would be beneficial to advance fundamental understanding of whole-ecosystem processes.

ecology↗

bioRxiv2023

Keystone competitor creates spatial patterns of biodiversity

Conventional ecological theory on competition and competitive exclusion states that competition should limit diversity. However, diversity of all species is more common than competitive exclusion would suggest, especially in the tropics. Here, we use theoretical and field approaches to examine the relationship between a keystone ant competitor (Azteca sericeasur) and the richness of a ground-foraging ant community in a spatially explicit context. Theoretically, we demonstrate that a fixed keystone competitor can increase species diversity. In addition, we sampled the ground-foraging ant community in three differentially managed coffee habitats and found - with the exception of plots in the most intensified coffee habitat - a consistently higher species richness near to the keystone competitor and lower richness with increasing distance. These patterns show that keystone competitors may contribute to the maintenance of local species richness.

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↗

bioRxiv2021

High-order interactions maintain or enhance structural robustness of a coffee agroecosystem network

The capacity of highly diverse systems to prevail has proven difficult to explain. In addition to methodological issues, the inherent complexity of ecosystems and issues like multicausality, non-linearity and context-specificity make it hard to establish general and unidirectional explanations. Nevertheless, in recent years, high order interactions have been increasingly discussed as a mechanism that benefits the functioning of highly diverse ecosystems and may add to the mechanisms that explain their persistence. Until now, this idea has been explored by means of hypothetical simulated networks. Here, we test this idea using an updated and empirically documented network for a coffee agroecosystem. We identify potentially key nodes and measure network robustness in the face of node removal with and without incorporation of high order interactions. We find that the systems robustness is either increased or unaffected by the addition of high order interactions, in contrast with randomized counterparts with similar structural characteristics. We also propose a method for representing networks with high order interactions as ordinary graphs and a method for measuring their robustness. HighlightsO_LIThe robustness of a coffee-associated ecological network is either increased or unaffected by the incorporation of high order interactions. C_LIO_LIA method is proposed for representing high order interactions in ordinary networks. C_LIO_LIA method is proposed to measure the robustness of networks with high order interactions. C_LIO_LIHigh order interactions may promote the persistence of diverse ecosystems. C_LI

ecology↗

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↗

bioRxiv2017

Competitive release from native range does not predict invasive success of a globally dominant exotic ant species

A major goal of invasion biology is to understand under what conditions exotic species thrive in the introduced range. High competitive abilities are thought to be an important characteristic of exotic species. Most invasion studies focus on the competitive ability of exotic species in the introduced range and attribute their ecological success to competitive release, but fewer studies have compared the relative competitive differences within the native range. These comparative studies are important in order to determine if competitive abilities of exotic species are strong predictors of invasion success. The little fire ant Wasmmnia auropunctata is a highly invasive species that has spread from its original range (Central and South America) to becoming a globally distributed exotic species in recent decades. It is generally accepted that island ecosystems offer weak biotic resistance to exotic species as compared to their native range. Here, we examined this empirically by comparing the relative competitive difference of W. auropunctata and locally dominant ants, between its native range of Mexico and introduced range of Puerto Rico. Resource competition was assessed between W. auropunctata and native ants under field conditions and in the laboratory. Furthermore, we compared resource competition at different temporal intervals ranging from short-term (< 2 hours) to long-term (14-days) dynamics. Our results are in contrast to common invasion predictions on island communities because we show that native species were resistant to W. auropunctata in its introduced range of Puerto Rico. We observed that the ground-foraging ant Solenopsis invicta competitive displaced W. auropunctata in Puerto Rico during short-term experiments. Meanwhile, the native arboreal ant Linepithema iniquum withstood competitive pressure from W. auropunctata. In the native range of Mexico, W. auropunctata was superior against Solenopsis Picea and Pheidole protensa species, but was outcompeted by dominant ants Solenopsis geminata and Pheidole synanthropica. This study challenges the relative importance of competitive ability in predicting invasion success. This is one of the few detailed comparative studies that examines exotic species performance between native and introduced habitats.

ecology↗