arXiv subjects

Urvashi Verma

Publications and source records attributed to Urvashi Verma.

7 recordsLinked to original sources

arXiv2026

Additional Food Enhances the Bifurcation Structure of Predator Competition Models

Additional food sources and predator competition are both known to impact the dynamics of predator-prey models. The Bazykin model of predator competition, with Holling type II functional response, possesses a rich bifurcation structure consisting of a focus-type degenerate Bogdanov-Takens bifurcation of codimension 3, and a degenerate Hopf bifurcation of codimension at most 2. Additional food models on the other hand are able to drive pest populations lower, with vast applicability in biological control. Despite these models being studied rigorously in the literature, the global bifurcation structure, of their possible complex dynamics, in a unified model, is unknown. In this work, we study an additional food model with generalized predator competition and Holling type-II functional response. Depending on the parameter values, the system can have up to three interior equilibria. Further, we show that this system exhibits a cusp-type (or focus-type) Bogdanov-Takens bifurcation of codimension at least 4 (or 3), a global Hopf bifurcation of codimension 3, and a homoclinic bifurcation of codimension 3. This shows there could exist three limit cycles around the BT point. These results demonstrate that additional food in Bazykin type models, can enhance their bifurcation structure. We discuss the applicability of these results to integrated pest management programs for the soybean aphid, wherein long term field data in the North-Central United States, shows two distinct limit cycles in aphid populations and their predators. Our results suggest biological control with additional food, is an effective management tactic for invasive pests.

q-bio.PE↗

arXiv2026

An Investigation of Additional Food Models with Generalised Functional Response

Additional food sources are often used to improve the effectiveness of predators in controlling pest populations. However, the non-symmetric structure of additional food predator-prey models can cause certain aspects of their dynamics challenging to analyze. In this work, we study a general class of additional food models and establish conditions under which the coexistence equilibrium is globally stable. We then focus on a Holling type IV functional response with AF and show the existence of a Bogdanov-Takens bifurcation of codimension 3. We also study these models through the lens of deterministic chemical reaction network theory. Our analysis shows that the introduction of additional food increases the deficiency of the underlying reaction network and suggests a possible link between higher deficiency and complex bifurcations.

q-bio.PE↗

arXiv2025

Synthesis and optical characterization of Mn-doped ZnS nanocrystalline thin films prepared via chemical bath deposition

Manganese-doped zinc sulfide nanocrystalline thin films were synthesized using a low-temperature chemical bath deposition and deposited on glass substrates for controlled durations using triethanolamine (TEA) as a complexing and capping agent. After deposition, the films were annealed at 200 degrees Celsius and characterized by X-ray diffraction (XRD), SEM, and UV-Vis spectroscopy. XRD patterns confirmed the formation of nanocrystalline cubic zinc blende ZnS with an average crystallite size of approximately 37 nm. Optical measurements revealed strong transparency in the visible region, blue-shifted absorption edges due to quantum confinement, and a band gap value of approximately 3.70 eV. Mn incorporation resulted in a slight red shift of the absorption edge, attributed to particle growth and sp-d exchange interactions. These results demonstrate that Mn doping modifies the optical response of ZnS while preserving its crystalline structure, suggesting its suitability for optoelectronic and photovoltaic applications.

cond-mat.mtrl-sci↗

arXiv2025

An "adaptive" approach to control explosive aphid populations

Classical models of aphid population dynamics are unable to explain multi-peak patterns in field populations. We consider the variable carrying capacity model (VCM), which can generate such complex multi-peak dynamics, but is also demonstrated to show finite-time blow-up behavior via a sign switching structural instability. We build an adaptive behavioral model with a density-dependent switch to stabilize growth, effectively eliminating blow-up, and also capable of generating multiple peaks. Furthermore, guided by empirical work on environment drivers for pests, we devise a non-autonomous model with time-dependent host plant fitness, successfully connecting transient population dynamics with abiotic drivers such as flooding. Finally, we discuss the practical significance of the results through the Economic Threshold (ET) and Economic Injury Level (EIL) calculation for all models. Our simulations all clearly show that aphid abundances exceed these threshold levels, and control is required. Our work provides a stable and biologically relevant prediction scheme for pest outbreaks and their management strategy.

q-bio.PE↗

arXiv2025

An additional food driven biological control patch model, incorporating generalized competition

Additional food sources for an introduced predator are known to increase its efficiency on a target pest. In this context, inhibiting factors such as interference, predator competition, and the introduction of temporally dependent quantity and quality of additional food are all known to enable pest extinction. As climate change and habitat degradation have increasing effects in enhancing patchiness in ecological systems, the effect of additional food in patch models has also been recently considered. However, the question of complete pest extinction in such patchy systems remains open. In the current manuscript, we consider a biological control model where additional food drives competition among predators in one patch, and they subsequently disperse to a neighboring patch via drift or dispersal. We show that complete pest extinction in both patches is possible. Further, this state is proved to be globally asymptotically stable under certain parametric restrictions. We also prove a codimension-2 Bogdanov-Takens bifurcation. We discuss our results in the context of designing pest management strategies under enhanced climate change and habitat fragmentation. Such strategies are particularly relevant to control invasive pests such as the Soybean aphid (\emph{Aphis glycines}), in the North Central United States.

q-bio.PE↗

arXiv2025

Towards improved pest management of the soybean aphid

The soybean aphid (\emph{Aphis glycines}) is an invasive insect pest that continues to cause large-scale damage to soybean crops in the North Central United States. The current manuscript proposes several mathematical models for the top-down bio-control of the aphid, as well as control via pesticides and neonicotinoids. The models are motivated empirically, and constructed based on laboratory experiments conducted to test control of aphids by Lacewing larvae, as well as by a parasitic wasp (\emph{Aphidius colemani}). The effectiveness of these models is compared by taking into account factors such as economic injury levels for soybeans, life history traits such as cannibalism amongst the predator, and intraguild predation between competing bio-control agents such as predators and parasitoids. The models predict multiple population peaks and transient chaotic dynamics when a predator and/or insecticides are used. It is observed that parasitoids, in conjunction with predators, are more efficient at stabilizing the population dynamics than insecticide use. They also suggest a combination of predators, parasitoids, and insecticides would be more efficient at suppressing aphid populations than using only predators or parasitoids. The models also qualitatively capture the features seen in long-time field data from 2000-2013. We discuss applications of our results to pest management strategies for soybean aphids in the context of a changing climate, as well as regime shifts.

q-bio.PE↗

arXiv2024

T(w)o patch or not t(w)o patch: A novel additional food model

A number of top down bio-control models have been proposed where the introduced predators' efficacy is enhanced via the provision of additional food (AF). However, if the predator has a pest dependent monotone functional response, pest extinction is unattainable. In the current manuscript, we propose a model where a predator with pest dependent monotone functional response is introduced into a ``patch" such as a prairie strip with AF, and then disperses or drifts into a neighboring ``patch" such as a crop field, to target a pest. We show the pest extinction state is attainable in the crop field and can be globally attracting. The AF model with patch structure can eliminate predator explosion present therein and can keep pest densities lower than the classical top-down bio-control model. We provide the first proof of the global stability of the interior equilibrium for the classical AF model. We also observe ``patch-specific chaos" - the pest occupying the crop field can oscillate chaotically, while the pest in the prairie strip oscillates periodically. We discuss these results in light of bio-control strategies that utilize state-of-the-art farming practices such as prairie strips and drift and dispersal pressures driven by climate change.

q-bio.PE↗