Publications by authors named "Donald L DeAngelis"

57 Publications

Directed movement changes coexistence outcomes in heterogeneous environments.

Ecol Lett 2021 Nov 24. Epub 2021 Nov 24.

Department of Environmental Science and Policy, University of California, Davis, Davis, California, USA.

Understanding mechanisms of coexistence is a central topic in ecology. Mathematical analysis of models of competition between two identical species moving at different rates of symmetric diffusion in heterogeneous environments show that the slower mover excludes the faster one. The models have not been tested empirically and lack inclusions of a component of directed movement toward favourable areas. To address these gaps, we extended previous theory by explicitly including exploitable resource dynamics and directed movement. We tested the mathematical results experimentally using laboratory populations of the nematode worm, Caenorhabditis elegans. Our results not only support the previous theory that the species diffusing at a slower rate prevails in heterogeneous environments but also reveal that moderate levels of a directed movement component on top of the diffusive movement allow species to coexist. Our results broaden the theory of species coexistence in heterogeneous space and provide empirical confirmation of the mathematical predictions.
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http://dx.doi.org/10.1111/ele.13925DOI Listing
November 2021

Towards Building a Sustainable Future: Positioning Ecological Modelling for Impact in Ecosystems Management.

Bull Math Biol 2021 Sep 4;83(10):107. Epub 2021 Sep 4.

Mathematics and Statistics, Unit 5, Irving K. Barber, School of Arts and Sciences, University of British Columbia-Okanagan, Kelowna, British Columbia, V1V 1V7, Canada.

As many ecosystems worldwide are in peril, efforts to manage them sustainably require scientific advice. While numerous researchers around the world use a great variety of models to understand ecological dynamics and their responses to disturbances, only a small fraction of these models are ever used to inform ecosystem management. There seems to be a perception that ecological models are not useful for management, even though mathematical models are indispensable in many other fields. We were curious about this mismatch, its roots, and potential ways to overcome it. We searched the literature on recommendations and best practices for how to make ecological models useful to the management of ecosystems and we searched for 'success stories' from the past. We selected and examined several cases where models were instrumental in ecosystem management. We documented their success and asked whether and to what extent they followed recommended best practices. We found that there is not a unique way to conduct a research project that is useful in management decisions. While research is more likely to have impact when conducted with many stakeholders involved and specific to a situation for which data are available, there are great examples of small groups or individuals conducting highly influential research even in the absence of detailed data. We put the question of modelling for ecosystem management into a socio-economic and national context and give our perspectives on how the discipline could move forward.
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http://dx.doi.org/10.1007/s11538-021-00927-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8418459PMC
September 2021

Carrying Capacity of Spatially Distributed Metapopulations.

Trends Ecol Evol 2021 02 28;36(2):164-173. Epub 2020 Oct 28.

School of Mathematics, University of Minnesota, Minneapolis, MN, USA; Department of Mathematics, Chinese University of Hong Kong, Shenzhen, China.

Carrying capacity is a key concept in ecology. A body of theory, based on the logistic equation, has extended predictions of carrying capacity to spatially distributed, dispersing populations. However, this theory has only recently been tested empirically. The experimental results disagree with some theoretical predictions of when they are extended to a population dispersing randomly in a two-patch system. However, they are consistent with a mechanistic model of consumption on an exploitable resource (consumer-resource model). We argue that carrying capacity, defined as the total equilibrium population, is not a fundamental property of ecological systems, at least in the context of spatial heterogeneity. Instead, it is an emergent property that depends on the population's intrinsic growth and dispersal rates.
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http://dx.doi.org/10.1016/j.tree.2020.10.007DOI Listing
February 2021

Effect of Stressors on the Carrying Capacity of Spatially Distributed Metapopulations.

Am Nat 2020 08 10;196(2):E46-E60. Epub 2020 Jun 10.

Stressors such as antibiotics, herbicides, and pollutants are becoming increasingly common in the environment. The effects of stressors on populations are typically studied in homogeneous, nonspatial settings. However, most populations in nature are spatially distributed over environmentally heterogeneous landscapes with spatially restricted dispersal. Little is known about the effects of stressors in these more realistic settings. Here, we combine laboratory experiments with novel mathematical theory to rigorously investigate how a stressor's physiological effect and spatial distribution interact with dispersal to influence population dynamics. We prove mathematically that if a stressor increases the death rate and/or simultaneously decreases the population growth rate and yield, a homogeneous distribution of the stressor leads to a lower total population size than if the same amount of the stressor was heterogeneously distributed. We experimentally test this prediction on spatially distributed populations of budding yeast (). We find that the antibiotic cycloheximide increases the yeast death rate but reduces the growth rate and yield. Consistent with our mathematical predictions, we observe that a homogeneous spatial distribution of cycloheximide minimizes the total equilibrium size of experimental metapopulations, with the magnitude of the effect depending predictably on the dispersal rate and the geographic pattern of antibiotic heterogeneity. Our study has implications for assessing the population risk posed by pollutants, antibiotics, and global change and for the rational design of strategies for employing toxins to control pathogens and pests.
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http://dx.doi.org/10.1086/709293DOI Listing
August 2020

An overview of agent-based models in plant biology and ecology.

Ann Bot 2020 09;126(4):539-557

U. S. Geological Survey, Wetland and Aquatic Research Center, Davie, FL, USA.

Agent-based modelling (ABM) has become an established methodology in many areas of biology, ranging from the cellular to the ecological population and community levels. In plant science, two different scales have predominated in their use of ABM. One is the scale of populations and communities, through the modelling of collections of agents representing individual plants, interacting with each other and with the environment. The other is the scale of the individual plant, through the modelling, by functional-structural plant models (FSPMs), of agents representing plant building blocks, or metamers, to describe the development of plant architecture and functions within individual plants. The purpose of this review is to show key results and parallels in ABM for growth, mortality, carbon allocation, competition and reproduction across the scales from the plant organ to populations and communities on a range of spatial scales to the whole landscape. Several areas of application of ABMs are reviewed, showing that some issues are addressed by both population-level ABMs and FSPMs. Continued increase in the relevance of ABM to environmental science and management will be helped by greater integration of ABMs across these two scales.
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http://dx.doi.org/10.1093/aob/mcaa043DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7489105PMC
September 2020

Mathematical ecologists describe apparently long-stable dynamics that undergo sudden change to a different regime: Comment on "Long transients in ecology: theory and applications by Andrew Morozov et al."

Phys Life Rev 2020 03 28;32:44-45. Epub 2019 Nov 28.

U. S. Geological Survey, Wetland and Aquatic Research Center, Davie, FL 33314, USA. Electronic address:

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http://dx.doi.org/10.1016/j.plrev.2019.11.010DOI Listing
March 2020

Dispersal asymmetry in a two-patch system with source-sink populations.

Theor Popul Biol 2020 02 25;131:54-65. Epub 2019 Nov 25.

U.S. Geological Survey, Wetland and Aquatic Research Center, Gainesville, FL 32653, USA.

This paper analyzes source-sink systems with asymmetric dispersal between two patches. Complete analysis on the models demonstrates a mechanism by which the dispersal asymmetry can lead to either an increased total size of the species population in two patches, a decreased total size with persistence in the patches, or even extinction in both patches. For a large growth rate of the species in the source and a fixed dispersal intensity, (i) if the asymmetry is small, the population would persist in both patches and reach a density higher than that without dispersal, in which the population approaches its maximal density at an appropriate asymmetry; (ii) if the asymmetry is intermediate, the population persists in both patches but reaches a density less than that without dispersal; (iii) if the asymmetry is large, the population goes to extinction in both patches; (iv) asymmetric dispersal is more favorable than symmetric dispersal under certain conditions. For a fixed asymmetry, similar phenomena occur when the dispersal intensity varies, while a thorough analysis is given for the low growth rate of the species in the source. Implications for populations in heterogeneous landscapes are discussed, and numerical simulations confirm and extend our results.
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http://dx.doi.org/10.1016/j.tpb.2019.11.004DOI Listing
February 2020

A Generically Parameterized model of Lake eutrophication (GPLake) that links field-, lab- and model-based knowledge.

Sci Total Environ 2019 Dec 13;695:133887. Epub 2019 Aug 13.

Water Systems and Global Change Group, Wageningen University & Research, PO Box 47, 6700 AA Wageningen, the Netherlands.

Worldwide, eutrophication is threatening lake ecosystems. To support lake management numerous eutrophication models have been developed. Diverse research questions in a wide range of lake ecosystems are addressed by these models. The established models are based on three key approaches: the empirical approach that employs field surveys, the theoretical approach in which models based on first principles are tested against lab experiments, and the process-based approach that uses parameters and functions representing detailed biogeochemical processes. These approaches have led to an accumulation of field-, lab- and model-based knowledge, respectively. Linking these sources of knowledge would benefit lake management by exploiting complementary information; however, the development of a simple tool that links these approaches was hampered by their large differences in scale and complexity. Here we propose a Generically Parameterized Lake eutrophication model (GPLake) that links field-, lab- and model-based knowledge and can be used to make a first diagnosis of lake water quality. We derived GPLake from consumer-resource theory by the principle that lacustrine phytoplankton is typically limited by two resources: nutrients and light. These limitations are captured in two generic parameters that shape the nutrient to chlorophyll-a relations. Next, we parameterized GPLake, using knowledge from empirical, theoretical, and process-based approaches. GPLake generic parameters were found to scale in a comparable manner across data sources. Finally, we show that GPLake can be applied as a simple tool that provides lake managers with a first diagnosis of the limiting factor and lake water quality, using only the parameters for lake depth, residence time and current nutrient loading. With this first-order assessment, lake managers can easily assess measures such as reducing nutrient load, decreasing residence time or changing depth before spending money on field-, lab- or model- experiments to support lake management.
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http://dx.doi.org/10.1016/j.scitotenv.2019.133887DOI Listing
December 2019

Success of lake restoration depends on spatial aspects of nutrient loading and hydrology.

Sci Total Environ 2019 Aug 1;679:248-259. Epub 2019 May 1.

Department of Aquatic Ecology, Netherlands Institute of Ecology (NIOO-KNAW), PO Box 50, 6700, AB, Wageningen, the Netherlands; Aquatic Ecology and Water Quality Management, Wageningen University & Research, PO Box 47, 6700, AA, Wageningen, the Netherlands.

Many aquatic ecosystems have deteriorated due to human activities and their restoration is often troublesome. It is proposed here that the restoration success of deteriorated lakes critically depends on hitherto largely neglected spatial heterogeneity in nutrient loading and hydrology. A modelling approach is used to study this hypothesis by considering four lake types with contrasting nutrient loading (point versus diffuse) and hydrology (seepage versus drainage). By comparing the longterm effect of common restoration measures (nutrient load reduction, lake flushing or biomanipulation) in these four lake types, we found that restoration through reduction of nutrient loading is effective in all cases. In contrast, biomanipulation only works in seepage lakes with diffuse nutrient inputs, while lake flushing will even be counterproductive in lakes with nutrient point sources. The main conclusion of the presented analysis is that a priori assessment of spatial heterogeneity caused by nutrient loading and hydrology is essential for successful restoration of lake ecosystems.
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http://dx.doi.org/10.1016/j.scitotenv.2019.04.443DOI Listing
August 2019

Energetic constraints and the paradox of a diffusing population in a heterogeneous environment.

Theor Popul Biol 2019 02 5;125:30-37. Epub 2018 Dec 5.

U.S. Geological Survey, Wetland and Aquatic Research Center, Gainesville, FL 32653, USA. Electronic address:

Previous mathematical analyses have shown that, for certain parameter ranges, a population, described by logistic equations on a set of connected patches, and diffusing among them, can reach a higher equilibrium total population when the local carrying capacities are heterogeneously distributed across patches, than when carrying capacities having the same total sum are homogeneously distributed across the patches. It is shown here that this apparently paradoxical result is explained when the resultant differences in energy inputs to the whole multi-patch system are taken into account. We examine both Pearl-Verhulst and Original Verhulst logistic models and show that, when total input of energy or limiting resource, is constrained to be the same in the homogeneous and heterogeneous cases, the total population in the heterogeneous patches can never reach an asymptotic equilibrium that is greater than the sum of the carrying capacities over the homogeneous patches. We further show that, when the dynamics of the limiting resources are explicitly modeled, as in a chemostat model, the paradoxical result of the logistic models does not occur. These results have implications concerning the use of some ubiquitous equations of population ecology in modeling populations in space.
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http://dx.doi.org/10.1016/j.tpb.2018.11.003DOI Listing
February 2019

Global dynamics of a mutualism-competition model with one resource and multiple consumers.

J Math Biol 2019 02 4;78(3):683-710. Epub 2018 Sep 4.

U.S. Geological Survey, Wetland and Aquatic Research Center, Gainesville, FL, 32653, USA.

Recent simulation modeling has shown that species can coevolve toward clusters of coexisting consumers exploiting the same limiting resource or resources, with nearly identical ratios of coefficients related to growth and mortality. This paper provides a mathematical basis for such as situation; a full analysis of the global dynamics of a new model for such a class of n-dimensional consumer-resource system, in which a set of consumers with identical growth to mortality ratios compete for the same resource and in which each consumer is mutualistic with the resource. First, we study the system of one resource and two consumers. By theoretical analysis, we demonstrate the expected result that competitive exclusion of one of the consumers can occur when the growth to mortality ratios differ. However, when these ratios are identical, the outcomes are complex. Either equilibrium coexistence or mutual extinction can occur, depending on initial conditions. When there is coexistence, interaction outcomes between the consumers can transition between effective mutualism, parasitism, competition, amensalism and neutralism. We generalize to the global dynamics of a system of one resource and multiple consumers. Changes in one factor, either a parameter or initial density, can determine whether all of the consumers either coexist or go to extinction together. New results are presented showing that multiple competing consumers can coexist on a single resource when they have coevolved toward identical growth to mortality ratios. This coexistence can occur because of feedbacks created by all of the consumers providing a mutualistic service to the resource. This is biologically relevant to the persistence of pollination-mutualisms.
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http://dx.doi.org/10.1007/s00285-018-1288-9DOI Listing
February 2019

A parasitism-mutualism-predation model consisting of crows, cuckoos and cats with stage-structure and maturation delays on crows and cuckoos.

J Theor Biol 2018 06 27;446:212-228. Epub 2018 Feb 27.

U.S. Geological Survey, Department of Biology, University of Miami, Coral Gables, Florida 33124, USA.

In this paper, a parasitism-mutualism-predation model is proposed to investigate the dynamics of multi-interactions among cuckoos, crows and cats with stage-structure and maturation time delays on cuckoos and crows. The crows permit the cuckoos to parasitize their nestlings (eggs) on the crow chicks (eggs). In return, the cuckoo nestlings produce a malodorous cloacal secretion to protect the crow chicks from predation by the cats, which is apparently beneficial to both the crow and cuckoo population. The multi-interactions, i.e., parasitism and mutualism between the cuckoos (nestlings) and crows (chicks), predation between the cats and crow chicks are modeled both by Holling-type II and Beddington-DeAngelis-type functional responses. The existence of positive equilibria of three subsystems of the model are discussed. The criteria for the global stability of the trivial equilibrium are established by the Krein-Rutman theorem and other analysis methods. Moreover, the threshold dynamics for the coexistence and weak persistence of the model are obtained, and we show, both analytically and numerically, that the stabilities of the interior equilibria may change with the increasing maturation time delays. We find there exists an evident difference in the dynamical properties of the parasitism-mutualism-predation model based on whether or not we consider the effects of stage-structure and maturation time delays on cuckoos and crows. Inclusion of stage structure results in many varied dynamical complexities which are difficult to encompass without this inclusion.
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http://dx.doi.org/10.1016/j.jtbi.2018.02.028DOI Listing
June 2018

Carrying capacity in a heterogeneous environment with habitat connectivity.

Ecol Lett 2017 09 16;20(9):1118-1128. Epub 2017 Jul 16.

Department of Biology, University of Miami, Coral Gables, FL, USA.

A large body of theory predicts that populations diffusing in heterogeneous environments reach higher total size than if non-diffusing, and, paradoxically, higher size than in a corresponding homogeneous environment. However, this theory and its assumptions have not been rigorously tested. Here, we extended previous theory to include exploitable resources, proving qualitatively novel results, which we tested experimentally using spatially diffusing laboratory populations of yeast. Consistent with previous theory, we predicted and experimentally observed that spatial diffusion increased total equilibrium population abundance in heterogeneous environments, with the effect size depending on the relationship between r and K. Refuting previous theory, however, we discovered that homogeneously distributed resources support higher total carrying capacity than heterogeneously distributed resources, even with species diffusion. Our results provide rigorous experimental tests of new and old theory, demonstrating how the traditional notion of carrying capacity is ambiguous for populations diffusing in spatially heterogeneous environments.
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http://dx.doi.org/10.1111/ele.12807DOI Listing
September 2017

A new mechanistic approach for the further development of a population with established size bimodality.

PLoS One 2017 26;12(6):e0179339. Epub 2017 Jun 26.

Institute for Zoology of the University of Cologne, Department of General Ecology, Cologne, Germany.

Usually, the origin of a within-cohort bimodal size distribution is assumed to be caused by initial size differences or by one discrete period of accelerated growth for one part of the population. The aim of this study was to determine if more continuous pathways exist allowing shifts from the small to the large fraction within a bimodal age-cohort. Therefore, a Eurasian perch population, which had already developed a bimodal size-distribution and had differential resource use of the two size-cohorts, was examined. Results revealed that formation of a bimodal size-distribution can be a continuous process. Perch from the small size-cohort were able to grow into the large size-cohort by feeding on macroinvertebrates not used by their conspecifics. The diet shifts were accompanied by morphological shape changes. Intra-specific competition seemed to trigger the development towards an increasing number of large individuals. A stage-structured matrix model confirmed these assumptions. The fact that bimodality can be a continuous process is important to consider for the understanding of ecological processes and links within ecosystems.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0179339PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5484486PMC
September 2017

Similarity of plant functional traits and aggregation pattern in a subtropical forest.

Ecol Evol 2017 06 26;7(12):4086-4098. Epub 2017 Apr 26.

Key Laboratory of Soil and Water Conservation and Ecological Restoration in Jiangsu Province Collaborative Innovation Center of Sustainable Forestry in Southern China Nanjing Forestry University Nanjing China.

The distribution of species and communities in relation to environmental heterogeneity is a central focus in ecology. Co-occurrence of species with similar functional traits is an indication that communities are determined in part by environmental filters. However, few studies have been designed to test how functional traits are selectively filtered by environmental conditions at local scales. Exploring the relationship between soil characteristics and plant traits is a step toward understanding the filtering hypothesis in determining plant distribution at local scale. Toward this end, we mapped all individual trees (diameter >1 cm) in a one-ha subtropical forest of China in 2007 and 2015. We measured topographic and detailed soil properties within the field site, as well as plant leaf functional traits and demographic rates of the seven most common tree species. A second one-ha study plot was established in 2015, to test and validate the general patterns that were drawn from first plot. We found that variation in species distribution at local scale can be explained by soil heterogeneity and plant functional traits. (From first plot). (1) Species dominant in habitats with high soil ammonium nitrogen and total phosphorus tended to have high specific leaf area (SLA) and relative growth rate (RGR). (2) Species dominant in low-fertility habitats tended to have high leaf dry matter content (LDMC), ratio of chlorophyll a and b (ratioab), and leaf thickness (LT). The hypothesis that functional traits are selected in part by environmental filters and determine plant distribution at local scale was confirmed by the data of the first plot and a second regional site showed similar species distribution patterns.
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http://dx.doi.org/10.1002/ece3.2973DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5478052PMC
June 2017

Moving forward in circles: challenges and opportunities in modelling population cycles.

Ecol Lett 2017 08 20;20(8):1074-1092. Epub 2017 Jun 20.

Department of Mathematics and Statistics, University of British Columbia Okanagan, Kelowna, BC, Canada.

Population cycling is a widespread phenomenon, observed across a multitude of taxa in both laboratory and natural conditions. Historically, the theory associated with population cycles was tightly linked to pairwise consumer-resource interactions and studied via deterministic models, but current empirical and theoretical research reveals a much richer basis for ecological cycles. Stochasticity and seasonality can modulate or create cyclic behaviour in non-intuitive ways, the high-dimensionality in ecological systems can profoundly influence cycling, and so can demographic structure and eco-evolutionary dynamics. An inclusive theory for population cycles, ranging from ecosystem-level to demographic modelling, grounded in observational or experimental data, is therefore necessary to better understand observed cyclical patterns. In turn, by gaining better insight into the drivers of population cycles, we can begin to understand the causes of cycle gain and loss, how biodiversity interacts with population cycling, and how to effectively manage wildly fluctuating populations, all of which are growing domains of ecological research.
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http://dx.doi.org/10.1111/ele.12789DOI Listing
August 2017

Dispersal and spatial heterogeneity: single species.

J Math Biol 2016 Jan 11;72(1-2):239-54. Epub 2015 Apr 11.

Department of Biology, University of Miami, Coral Gables, FL, 33124, USA.

A recent result for a reaction-diffusion equation is that a population diffusing at any rate in an environment in which resources vary spatially will reach a higher total equilibrium biomass than the population in an environment in which the same total resources are distributed homogeneously. This has so far been proven by Lou for the case in which the reaction term has only one parameter, m(x), varying with spatial location x, which serves as both the intrinsic growth rate coefficient and carrying capacity of the population. However, this striking result seems rather limited when applies to real populations. In order to make the model more relevant for ecologists, we consider a logistic reaction term, with two parameters, r (x) for intrinsic growth rate, and K(x) for carrying capacity. When r (x) and K(x) are proportional, the logistic equation takes a particularly simple form, and the earlier result still holds. In this paper we have established the result for the more general case of a positive correlation between r (x) and K(x) when dispersal rate is small. We review natural and laboratory systems to which these results are relevant and discuss the implications of the results to population theory and conservation ecology.
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http://dx.doi.org/10.1007/s00285-015-0879-yDOI Listing
January 2016

Equation-free modeling unravels the behavior of complex ecological systems.

Proc Natl Acad Sci U S A 2015 Mar 17;112(13):3856-7. Epub 2015 Mar 17.

Biology Department, University of Miami, Miami, FL 33124.

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http://dx.doi.org/10.1073/pnas.1503154112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4386356PMC
March 2015

A spatial individual-based model predicting a great impact of copious sugar sources and resting sites on survival of Anopheles gambiae and malaria parasite transmission.

Malar J 2015 Feb 5;14:59. Epub 2015 Feb 5.

Department of Public Health Sciences, Miller School of Medicine, University of Miami, Miami, Florida, USA.

Background: Agent-based modelling (ABM) has been used to simulate mosquito life cycles and to evaluate vector control applications. However, most models lack sugar-feeding and resting behaviours or are based on mathematical equations lacking individual level randomness and spatial components of mosquito life. Here, a spatial individual-based model (IBM) incorporating sugar-feeding and resting behaviours of the malaria vector Anopheles gambiae was developed to estimate the impact of environmental sugar sources and resting sites on survival and biting behaviour.

Methods: A spatial IBM containing An. gambiae mosquitoes and humans, as well as the village environment of houses, sugar sources, resting sites and larval habitat sites was developed. Anopheles gambiae behaviour rules were attributed at each step of the IBM: resting, host seeking, sugar feeding and breeding. Each step represented one second of time, and each simulation was set to run for 60 days and repeated 50 times. Scenarios of different densities and spatial distributions of sugar sources and outdoor resting sites were simulated and compared.

Results: When the number of natural sugar sources was increased from 0 to 100 while the number of resting sites was held constant, mean daily survival rate increased from 2.5% to 85.1% for males and from 2.5% to 94.5% for females, mean human biting rate increased from 0 to 0.94 bites per human per day, and mean daily abundance increased from 1 to 477 for males and from 1 to 1,428 for females. When the number of outdoor resting sites was increased from 0 to 50 while the number of sugar sources was held constant, mean daily survival rate increased from 77.3% to 84.3% for males and from 86.7% to 93.9% for females, mean human biting rate increased from 0 to 0.52 bites per human per day, and mean daily abundance increased from 62 to 349 for males and from 257 to 1120 for females. All increases were significant (P < 0.01). Survival was greater when sugar sources were randomly distributed in the whole village compared to clustering around outdoor resting sites or houses.

Conclusions: Increases in densities of sugar sources or outdoor resting sites significantly increase the survival and human biting rates of An. gambiae mosquitoes. Survival of An. gambiae is more supported by random distribution of sugar sources than clustering of sugar sources around resting sites or houses. Density and spatial distribution of natural sugar sources and outdoor resting sites modulate vector populations and human biting rates, and thus malaria parasite transmission.
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http://dx.doi.org/10.1186/s12936-015-0555-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4324791PMC
February 2015

Modelling the effects of seasonality and socioeconomic impact on the transmission of rift valley Fever virus.

PLoS Negl Trop Dis 2015 Jan 8;9(1):e3388. Epub 2015 Jan 8.

Department of Mathematics, University of Miami, Coral Gables, Florida, United States of America.

Rift Valley fever (RVF) is an important mosquito-borne viral zoonosis in Africa and the Middle East that causes human deaths and significant economic losses due to huge incidences of death and abortion among infected livestock. Outbreaks of RVF are sporadic and associated with both seasonal and socioeconomic effects. Here we propose an almost periodic three-patch model to investigate the transmission dynamics of RVF virus (RVFV) among ruminants with spatial movements. Our findings indicate that, in Northeastern Africa, human activities, including those associated with the Eid al Adha feast, along with a combination of climatic factors such as rainfall level and hydrological variations, contribute to the transmission and dispersal of the disease pathogen. Moreover, sporadic outbreaks may occur when the two events occur together: 1) abundant livestock are recruited into areas at risk from RVF due to the demand for the religious festival and 2) abundant numbers of mosquitoes emerge. These two factors have been shown to have impacts on the severity of RVF outbreaks. Our numerical results present the transmission dynamics of the disease pathogen over both short and long periods of time, particularly during the festival time. Further, we investigate the impact on patterns of disease outbreaks in each patch brought by festival- and seasonal-driven factors, such as the number of livestock imported daily, the animal transportation speed from patch to patch, and the death rate induced by ceremonial sacrifices. In addition, our simulations show that when the time for festival preparation starts earlier than usual, the risk of massive disease outbreaks rises, particularly in patch 3 (the place where the religious ceremony will be held).
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http://dx.doi.org/10.1371/journal.pntd.0003388DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4287488PMC
January 2015

Individual-based models in ecology after four decades.

F1000Prime Rep 2014 2;6:39. Epub 2014 Jun 2.

Department of Ecological Modelling, Helmholtz Centre for Environmental Research-UFZ, Permoserstr. 15, 04318 Leipzig Germany ; Institute for Biochemistry and Biology, University of Potsdam, Maulbeerallee 214469 Potsdam Germany ; German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig Deutscher Platz 5e, 04103 Leipzig Germany.

Individual-based models simulate populations and communities by following individuals and their properties. They have been used in ecology for more than four decades, with their use and ubiquity in ecology growing rapidly in the last two decades. Individual-based models have been used for many applied or "pragmatic" issues, such as informing the protection and management of particular populations in specific locations, but their use in addressing theoretical questions has also grown rapidly, recently helping us to understand how the sets of traits of individual organisms influence the assembly of communities and food webs. Individual-based models will play an increasingly important role in questions posed by complex ecological systems.
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http://dx.doi.org/10.12703/P6-39DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4047944PMC
July 2014

Exposures to a selective serotonin reuptake inhibitor (SSRI), sertraline hydrochloride, over multiple generations: changes in life history traits in Ceriodaphnia dubia.

Ecotoxicol Environ Saf 2014 Mar 11;101:124-30. Epub 2014 Jan 11.

Institute of Applied Sciences, Department of Environmental Science, University of North Texas, Denton, TX 76201, USA. Electronic address:

Selective serotonin reuptake inhibitors (SSRIs) have been reported to range from low parts per trillion to parts per billion levels in surface waters, wastewater effluents, and sediments. These low levels have led to concern for their potential long-term risks to the survival, growth, and reproduction of aquatic organisms. We investigated the acute and chronic effects of sertraline on the life history traits of Ceriodaphnia dubia over the course of three generations under environmentally realistic concentrations. Acute toxicity of sertraline in C. dubia offspring resulted in a 48h median effective concentration of 126µgL(-1). Under chronic exposure, the lowest concentration to affect fecundity and growth was at 53.4µgL(-1) in the first two generations. These parameters become more sensitive during the third generation where the LOEC was 4.8µgL(-1). The median effective concentrations (EC50) for the number of offspring per female, offspring body size, and dry weight were 17.2, 21.2, and 26.2µgL(-1), respectively. Endpoints measured in this study demonstrate that chronic exposure of C. dubia to sertraline leads to effects that occur at concentrations only an order of magnitude higher than predicted environmental concentrations. However, this study also demonstrates that multigenerational effects should be considered in chronic exposure studies because standard toxicity tests do not account for increases in sensitivity in successive generations to toxicants.
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http://dx.doi.org/10.1016/j.ecoenv.2013.11.026DOI Listing
March 2014

Strong species-environment feedback shapes plant community assembly along environmental gradients.

Ecol Evol 2013 Oct 20;3(12):4119-28. Epub 2013 Sep 20.

National Institute for Mathematical and Biological Synthesis, University of Tennessee Knoxville, Tennessee, 37996.

An aim of community ecology is to understand the patterns of competing species assembly along environmental gradients. All species interact with their environments. However, theories of community assembly have seldom taken into account the effects of species that are able to engineer the environment. In this modeling study, we integrate the species' engineering trait together with processes of immigration and local dispersal into a theory of community assembly. We quantify the species' engineering trait as the degree to which it can move the local environment away from its baseline state towards the optimum state of the species (species-environment feedback). We find that, in the presence of immigration from a regional pool, strong feedback can increase local species richness; however, in the absence of continual immigration, species richness is a declining function of the strength of species-environment feedback. This shift from a negative effect of engineering strength on species richness to a positive effect, as immigration rate increases, is clearer when there is spatial heterogeneity in the form of a gradient in environmental conditions than when the environment is homogeneous or it is randomly heterogeneous. Increasing the scale over which local dispersal occurs can facilitate species richness when there is no species-environment feedback or when the feedback is weak. However, increases in the spatial scale of dispersal can reduce species richness when the species-environment feedback is strong. These results expand the theoretical basis for understanding the effects of the strength of species-environment feedback on community assembly.
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http://dx.doi.org/10.1002/ece3.784DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3853557PMC
October 2013

Spatially heterogeneous invasion of toxic plant mediated by herbivory.

Math Biosci Eng 2013 Oct-Dec;10(5-6):1519-38

Department of Mathematics, Nanjing University of Information Science and Technology, Nanjing 210044, China.

Spatially homogeneous (ODE) and reaction-diffusion models for plant-herbivore interactions with toxin-determined functional response are analyzed. The models include two plant species that have different levels of toxicity. The plant species with a higher level of toxicity is assumed to be less preferred by the herbivore and to have a relatively lower intrinsic growth rate than the less toxic plant species. Two of the equilibrium points of the system representing significant ecological interests are E1, in which only the less toxic plant is present, and E2, in which the more toxic plant and herbivore coexist while the less toxic plant has gone to extinction. Under certain conditions it is shown that, for the spatially homogeneous system all solutions will converge to the equilibrium E2, whereas for the reaction-diffusion model there exist traveling wave solutions connecting E1 and E2.
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http://dx.doi.org/10.3934/mbe.2013.10.1519DOI Listing
July 2014

Simulating the spread of an invasive termite in an urban environment using a stochastic individual-based model.

Environ Entomol 2013 Jun;42(3):412-23

University of Florida, Fort Lauderdale Research and Education Center, Davie, FL 33314, USA.

Invasive termites are destructive insect pests that cause billions of dollars in property damage every year. Termite species can be transported overseas by maritime vessels. However, only if the climatic conditions are suitable will the introduced species flourish. Models predicting the areas of infestation following initial introduction of an invasive species could help regulatory agencies develop successful early detection, quarantine, or eradication efforts. At present, no model has been developed to estimate the geographic spread of a termite infestation from a set of surveyed locations. In the current study, we used actual field data as a starting point, and relevant information on termite species to develop a spatially-explicit stochastic individual-based simulation to predict areas potentially infested by an invasive termite, Nasutitermes corniger (Motschulsky), in Dania Beach, FL. The Monte Carlo technique is used to assess outcome uncertainty. A set of model realizations describing potential areas of infestation were considered in a sensitivity analysis, which showed that the model results had greatest sensitivity to number of alates released from nest, alate survival, maximum pheromone attraction distance between heterosexual pairs, and mean flight distance. Results showed that the areas predicted as infested in all simulation runs of a baseline model cover the spatial extent of all locations recently discovered. The model presented in this study could be applied to any invasive termite species after proper calibration of parameters. The simulation herein can be used by regulatory authorities to define most probable quarantine and survey zones.
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http://dx.doi.org/10.1603/EN12325DOI Listing
June 2013

Intraspecific trait variation and its effects on food chains.

Math Biosci 2013 Aug 7;244(2):91-7. Epub 2013 May 7.

US Geological Survey and Department of Biology, University of Miami, 1301 Memorial Drive, Coral Gables, FL 33143, USA.

Traits such as skill at foraging and investment in anti-predator defense may vary among individuals within a species population. This intraspecific variation has implications for community dynamics. The implications of intraspecific variation of a consumer in the intermediate level of a tritrophic food chain are explored for the case in which two different phenotypes exist within the consumer population having tradeoffs in traits with respect to foraging for resources and resisting predation. The topology of such a web is similar to that of the diamond-shaped food web. An important result of prior studies on diamond-shaped webs is that conditions for equilibrium coexistence of two competing consumer species can be found, but the transient oscillations would make it likely for one competing species to become extinct. In the case of two phenotype subpopulations within a single consumer species, however, switching between the two subpopulations can occur, which is stabilizing. As a result, it is feasible for two distinct phenotype subpopulations of the consumer to exist between resources and predators in a tritrophic chain. The occurrence of two stably coexisting phenotype populations changes the nature of the bottom-up and top-down effects in the chain. The predator exerts a top-down effect on the resource, not the consumer subpopulations, and changes in the resource carrying capacity causes changes in the consumer subpopulations, but not the populations of the predators or the resources themselves.
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http://dx.doi.org/10.1016/j.mbs.2013.04.008DOI Listing
August 2013

Chronic effects of carbamazepine on life-history strategies of Ceriodaphnia dubia in three successive generations.

Arch Environ Contam Toxicol 2013 Apr 11;64(3):427-38. Epub 2012 Dec 11.

Institute of Applied Sciences, University of North Texas, Denton, TX 76201, USA.

Trace quantities of pharmaceuticals are continuously being discharged into the environment through domestic and industrial wastewater effluents, causing concern among scientists and regulators regarding potential long-term impacts on aquatic ecosystems. These compounds and their metabolites are constantly interacting with organisms at various life-cycle stages and may differentially influence the development of embryonic, larval, juvenile, and adult stages. To understand the possible cumulative effects of exposure to carbamazepine (CBZ), a multigenerational approach was taken in which survival, reproduction, respiration, growth, brood size, and biomass of Ceriodaphnia dubia were assessed at sublethal concentrations over the course of three successive generations. CBZ exposure significantly decreased fecundity at 196.7 μg/L in the F0 and F1 generations over 2 weeks and acclimatized at 264.6 μg/L in the F2 generation. Similarly, a significant decrease of neonate dry weight was observed at the 196.7 μg/L CBZ treatment in the F1 generation, and it acclimatized at 264.6 μg/L treatment level in the F2 generation. Median time to first brood release was significantly delayed at 264.6 μg/L in the F2 generation, indicating slower maturation. Results over three successive generations are not different than what one would obtain by testing simply the F0 generation. Furthermore, the effects measured were observed at concentrations two orders of magnitude higher than are environmentally relevant, and it is unlikely that CBZ poses a substantial risk to the environment regarding the end points measured in this study. However, additional research through laboratory and field multigenerational studies may be required to understand the overall risk of CBZ to other nontarget organisms.
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http://dx.doi.org/10.1007/s00244-012-9845-5DOI Listing
April 2013

Single species models with logistic growth and dissymmetric impulse dispersal.

Math Biosci 2013 Feb 5;241(2):188-97. Epub 2012 Dec 5.

College of Mathematics and Systems Science, Xinjiang University, Urumchi 830046, PR China.

In this paper, two classes of single-species models with logistic growth and impulse dispersal (or migration) are studied: one model class describes dissymmetric impulsive bi-directional dispersal between two heterogeneous patches; and the other presents a new way of characterizing the aggregate migration of a natural population between two heterogeneous habitat patches, which alternates in direction periodically. In this theoretical study, some very general, weak conditions for the permanence, extinction of these systems, existence, uniqueness and global stability of positive periodic solutions are established by using analysis based on the theory of discrete dynamical systems. From this study, we observe that the dynamical behavior of populations with impulsive dispersal differs greatly from the behavior of models with continuous dispersal. Unlike models where the dispersal is continuous in time, in which the travel losses associated with dispersal make it difficult for such dispersal to evolve e.g., [25,26,28], in the present study it was relatively easy for impulsive dispersal to positively affect populations when realistic parameter values were used, and a rich variety of behaviors were possible. From our results, we found impulsive dispersal seems to more nicely model natural dispersal behavior of populations and may be more relevant to the investigation of such behavior in real ecological systems.
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http://dx.doi.org/10.1016/j.mbs.2012.11.005DOI Listing
February 2013

A mutualism-parasitism system modeling host and parasite with mutualism at low density.

Math Biosci Eng 2012 Apr;9(2):431-44

School of Mathematics and Computational Science, Sun Yat-sen University, Guangzhou, China.

A mutualism-parasitism system of two species is considered, where mutualism is the dominant interaction when the predators (parasites) are at low density while parasitism is dominant when the predators are at high density. Our aim is to show that mutualism at low density promotes coexistence of the species and leads to high production of the prey (host). The mutualism-parasitism system presented here is a combination of the Lotka-Volterra cooperative model and Lotka-Volterra predator-prey model. By comparing dynamics of this system with those of the Lotka-Volterra predator-prey model, we present the mechanisms by which the mutualism improves the coexistence of the species and production of the prey. Then the parameter space is divided into six regions, which correspond to the four outcomes of mutualism, commensalism, predation/parasitism and neutralism, respectively. When the parameters are varied continuously among the six regions, it is shown that the interaction outcomes of the system transition smoothly among the four outcomes. By comparing the dynamics of the specific system with those of the Lotka-Volterra cooperative model, we show that the parasitism at high density promotes stability of the system. A novel aspect of this paper is the simplicity of the model, which allows rigorous and thorough analysis and transparency of the results.
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http://dx.doi.org/10.3934/mbe.2012.9.431DOI Listing
April 2012

Uni-directional interaction and plant-pollinator-robber coexistence.

Bull Math Biol 2012 Sep 18;74(9):2142-64. Epub 2012 Jul 18.

School of Mathematics and Computational Science, Sun Yat-sen University, Guangzhou, 510275, P.R. China.

A mathematical model for the plant-pollinator-robber interaction is studied to understand the factors leading to the widespread occurrence and stability of such interactions. In the interaction, a flowering plant provides resource for its pollinator and the pollinator has both positive and negative effects on the plant. A nectar robber acts as a plant predator, consuming a common resource with the pollinator, but with a different functional response. Using dynamical systems theory, mechanisms of species coexistence are investigated to show how a robber could invade the plant-pollinator system and persist stably with the pollinator. In addition, circumstances are demonstrated in which the pollinator's positive and negative effects on the plant could determine the robber's invasibility and the three-species coexistence.
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http://dx.doi.org/10.1007/s11538-012-9750-0DOI Listing
September 2012
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