Net Population Growth Rates Research Articles

Successful establishment, spread, and impact of the introduced parasitoid Spathius galinae (Hymenoptera: Braconidae) on emerald ash borer (Coleoptera: Buprestidae) populations in postinvasion forests in Michigan.

Spathius galinae is a larval parasitoid native to the Russian Far East that was approved for release in the United States in 2015 for biological control of the emerald ash borer (EAB), Agrilus planipennis, an invasive beetle from Asia responsible for widespread mortality of ash trees (Fraxinus spp.) in North America. From 2015 to 2017, 1,340-1,445 females of S. galinae along with males were released into each release plot, paired with a nonrelease control plot (1-12.5 km apart), at 6 postinvasion forested sites containing abundant pole-sized ash trees in Michigan. By 2018, S. galinae had spread to all but one control plot. Based on the first year that S. galinae was found in trees in each control plot and the distances of those trees to the parasitoid release point within each site, we estimated that S. galinae spread at 3.7 (±1.9) km per year after its initial releases in 2015. The proportion of sampled trees with S. galinae broods, brood densities within sampled trees, and parasitism of EAB larvae increased sharply in both control and release plots after the last field releases in 2017, with the highest parasitism rates (42.8-60.3%) in 2020. Life table analysis showed that S. galinae alone reduced EAB's net population growth rate by 35-55% across sites from 2018 to 2020. These results demonstrate that S. galinae has established an increasing population in Michigan and now plays a significant role in reducing EAB populations in the area.

Non-consumptive effects of predation risk on prey population regulations: empirical evidence from the invasive spider mite Tetranychus ludeni

Tetranychus ludeni Zacher is an invasive pest from Europe. It infests more than 300 plant species, including many economically important crops such as bean Phaseolus vulgaris L. (Fabales: Fabaceae), eggplant Solanum melongena L. (Solanales: Solanaceae), and many other cucurbitaceous plants. Gotoh et al. (2015) predict that this species could replace T. urticae to become a major crop pest in the world. It is often assumed that the success of biological control using predators is achieved through direct predation. However, it is still largely unknown whether predation risk could contribute to the effectiveness of prey biological control. In the present study we investigated the effects of cues from the predatory mite Phytoseiulus persimilis and killed T. ludeni on life history traits and offspring fitness of T. ludeni, providing novel knowledge for evaluation of the non-consumptive contribution to the biological control of T. ludeni and for future development of new spider mite control methods using these cues. We demonstrated that the cues from the predators and killed prey shortened the longevity by more than 23% and oviposition period by more than 35% and reduced the number of eggs laid by more than 31% in T. ludeni females. These cues also significantly reduced the intrinsic rate of increase and net population growth rate and prolonged the time to double the population size. Furthermore, in response to predator cues females significantly delayed their lifetime production of daughters and laid significantly smaller eggs. Offspring from predator-exposed mothers developed significantly more slowly. Our findings strongly suggest that the non-consumptive mortality caused by cues from both predators and killed prey can significantly reduce prey fitness, suppressing their population and lowering their damage to crops. The earlier prey death caused by these cues could result from the energic costs of natural enemy avoidance (Luong et al. 2017), decrease of foraging rate or food intake (Hermann & Thaler 2014) and increase of oxidative damage (Janssens & Stoks 2013). The present study partially supports previous reports that non-consumptive impacts of predation risk on prey are transgenerational (Tariel et al. 2020). Our study provides critical information for evaluation of biological control effectiveness using predators and paves the way for identification of chemical odors from the predator and killed prey and development of new materials and methods for the control of spider mite pests.

An assessment of the medium-term reproductive success of an extralimital white rhinoceros population

The white rhinoceros (Ceratotherium simum) is threatened primarily due to continued poaching for its horns. In South Africa, partly to promote the conservation of the species, white rhinos have been introduced into areas where they did not occur historically (i.e. where they are considered extralimital). Few studies have investigated the conservation contribution of extralimital white rhinos to the overall national herd. We aimed to determine whether the white rhinos introduced to a private game reserve in the Eastern Cape province have been successful from a reproductive perspective. We calculated inter-calving intervals, age at first calving, sex ratios of calves, and recruitment rates for white rhinos at a single site between 1992 and 2019. The average net annual population growth rate for the population was 10%, which is higher than the recommended 5% by the Biodiversity Management Plan for white rhinos. Trends in density-dependent parameters such as age at first calving and inter-calving intervals also indicated that the study population is still well below the density at which ecological constraints may manifest. We demonstrate that an extralimital white rhino population in the Eastern Cape can be successful from a reproductive perspective.

Predator- and killed prey-induced fears bear significant cost to an invasive spider mite: Implications in pest management.

The success of biological control using predators is normally assumed to be achieved through direct predation. Yet it is largely unknown how the predator- and killed prey-induced stress to prey may contribute to biological control effectiveness. Here, we investigate variations in life-history traits and offspring fitness of the spider mite Tetranychus ludeni in response to cues from the predatory mite Phytoseiulus persimilis and killed T. ludeni, providing knowledge for evaluation of the nonconsumptive contribution to the biological control of T. ludeni and for future development of novel spider mite control measures using these cues. Cues from predators and killed prey shortened longevity by 23-25% and oviposition period by 35-40%, and reduced fecundity by 31-37% in T. ludeni females. These cues significantly reduced the intrinsic rate of increase (rm ) and net population growth rate (R0 ), and extended time to double the population size (Dt ). Predator cues significantly delayed lifetime production of daughters. Mothers exposed to predator cues laid significantly smaller eggs and their offspring developed significantly more slowly but these eggs had significantly higher hatch rate. Predator- and killed prey-induced fears significantly lower the fitness of T. ludeni, suggesting that these nonconsumptive effects can contribute to the effectiveness of biological control to a great extent. Our study provides critical information for evaluation of biological control effectiveness using predators and paves the way for identification of chemical odors from the predator and killed prey, and development of new materials and methods for the control of spider mite pests. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Modeling total predation to avoid perverse outcomes from cat control in a data-poor island ecosystem.

Data hungry, complex ecosystem models are often used to predict the consequences of threatened species management, including perverse outcomes. Unfortunately, this approach is impractical in many systems, which have insufficient data to parameterize ecosystem interactions or reliably calibrate or validate such models. Here we demonstrate a different approach, using a minimum realistic model to guide decisions in data- and resource-scarce systems. We illustrate our approach with a case-study in an invaded ecosystem from Christmas Island, Australia, where there are concerns that cat eradication to protect native species, including the red-tailed tropicbird, could release meso-predation by invasive rats. We use biophysical constraints (metabolic demand) and observable parameters (e.g. prey preferences) to assess the combined cat and rat abundances which would threaten the tropicbird population. We find that the population of tropicbirds cannot be sustained if predated by 1607 rats (95% credible interval (CI) [103, 5910]) in the absence of cats, or 21 cats (95% CI [2, 82]) in the absence of rats. For every cat removed from the island, the bird's net population growth rate improves, provided that the rats do not increase by more than 77 individuals (95% CI [30, 174]). Thus, in this context, one cat is equivalent to 30-174 rats. Our methods are especially useful for on-the-ground predator control in the absence of knowledge of predator-predator interactions, to assess whether 1) the current abundance of predators threatens the prey population of interest, 2) managing one predator species alone is sufficient to protect the prey species given potential release of another predator, and 3) control of multiple predator species is needed to meet the conservation goal. Our approach demonstrates how to use limited information for maximum value in data-poor systems, by shifting the focus from predicting future trajectories, to identifying conditions which threaten the conservation goal. This article is protected by copyright. All rights reserved.

Susceptible-infectious-susceptible (SIS) model with virus mutation in a variable population size

The complex dynamics of a contagious disease in which populations experience horizontal and vertical transmissions, size variation, and virus mutations are of considerable practical and theoretical interest. We model such a system by dividing a population into three distinct groups: susceptibles (S), C-infected (C) and F-infected (F), based on the Susceptible-Infectious-Susceptible (SIS) model. Once the individuals in the C-infected group recover from the disease, they gain no permanent immunity. The virus can mutate in the group C. When it does, the individuals become members of the F-infected group. The mutated virus causes a lethal and incurable disease with a high mortality rate. We discuss the model for two cases. For the first case, all the newborns from infected mothers develop the disease shortly after their birth. For the second case, there exist equal transmission rates and the C-infected population is lifelong infectious. Our analysis shows that both systems have positive solutions, and the first model possesses four equilibrium points, the trivial one (extinction of the species), C-free equilibrium (extinction of the ancestor virus) and two endemic equilibria of different properties. We identify the net population growth rates of the susceptible and C-infected groups for the existence of the equilibria of the first model. We define the conditions of parameters for which species extinction and endemic equilibria are locally asymptotically stable. We observe that bifurcation occurs at the C-free equilibrium. For the second model, we find that there is only one endemic equilibrium and it is always locally asymptotically stable. We also determine the region for the net population growth rates of the susceptible and F-infected groups for the existence of the endemic equilibrium.

Modeling the persistence of plant populations in fragmented ecosystems

Ecosystem fragmentation is one of the main threats to species persistence via habitat reduction and isolation which often lead to species extinctions. A question that has long been of interest is the minimum habitat size that can sustain viable populations in fragmented landscape. Despite numerous empirical and theoretical efforts on this topic, most studies fail to address this central question, and our mechanistic understanding of and capacity to predict the effects and outcomes associated with fragmentation stressor is still illusive. We develop an ordinary differential equation (ODE) based framework that incorporates the effect of the patch area on the net population growth rate for a plant species in fragmented ecosystem via a general net growth function. We investigate the minimum patch area needed to sustain a given plant species. We use data from the Amazonian herb Heliconia acuminata to test our model. Furthermore, we compare the performance ODE model and a linear matrix model to predict the observed data. We provide a general formula for a threshold value for the fragment area, below which a plant population is not viable. For Heliconia acuminata, our ODE-based model predicts a value for the minimum fragment area of ≈0.7ha, which reflects the observed data and is smaller than the value obtained using the matrix projection model. Our findings suggest that the Heliconia’s mortality rate responds more negatively to fragmentation. Furthermore, we found that the ODE-based model can serve as an alternative to the linear demographic model.

Phytoplankton mortality in a changing thermal seascape.

Predicting spatiotemporal distributions of phytoplankton biomass and community composition heavily relies on experimental studies that document how environmental conditions influence population growth rates. In unicellular phytoplankton, the net population growth rate is the difference between the cell division rate and the death rate. Along with predation and disease, phytoplankton mortality arises from abiotic stress. Although the effect of temperature on the net population growth rate is well understood, studies examining thermally induced death rates in phytoplankton are scarce. We investigated how cell division and death rates of the diatom Phaeodactylum tricornutum varied within its thermal tolerance limits (thermal niche), and at temperatures just above its upper thermal tolerance limit. We show that death rates were largely independent of temperature when P. tricornutum was grown within its thermal niche, but increased significantly at temperatures that approached or exceeded its upper thermal tolerance limit. Furthermore, the sensitivity of mortality increased with the duration of exposure to heat stress and was affected by the pre-acclimation temperature. Heat waves can be expected to significantly affect phytoplankton mortality episodically. The increasing frequency of heat waves accompanying global warming can be expected to drive changes in phytoplankton community structure due to interspecific variability of thermal niches with potential implications for food web dynamics and biogeochemical cycles.

Microplastics reduce net population growth and fecal pellet sinking rates for the marine copepod, Acartia tonsa

Microplastics (<5 mm) are ubiquitous in the global environment and are increasingly recognized as a biological hazard, particularly in the oceans. Zooplankton, at the base of the marine food web, have been known to consume microplastics. However, we know little about the impacts of microplastics across life history stages and on carbon settling. Here, we investigated the effects of ingestion of neutrally buoyant polystyrene beads (6.68 μm) by the copepod Acartia tonsa on (1) growth and survival across life history stages, (2) fecundity and egg quality, (3) and fecal characteristics. We found that microplastic exposure reduced body length and survival for nauplii and resulted in smaller eggs when copepods were exposed during oogenesis. Combining these life history impacts, our models estimate a 15% decrease in population growth leading to a projected 30-fold decrease in abundance over 1 year or 20 generations with microplastic exposure. In addition, microplastic-contaminated fecal pellets were 2.29-fold smaller and sinking rates were calculated to be 1.76-fold slower, resulting in an estimated 4.03-fold reduction in fecal volume settling to the benthos per day. Taken together, declines in population sizes and fecal sinking rates suggest that microplastic consumption by zooplankton could have cascading ecosystem impacts via reduced trophic energy transfer and slower carbon settling.

&lt;p&gt;&lt;strong&gt;Response to thermal environment in &lt;em&gt;Tetranychus ludeni&lt;/em&gt; (Acari: Tetranychidae)&lt;/strong&gt;&lt;/p&gt;

Tetranychus ludeni Zacher is a spider mite that has invaded all continents except Antarctica and become an economically important pest around the world. Understanding the plasticity of its life history traits as a response to temperatures provides critical information for its risk analysis and management. Here we tested its response to temperatures ranging from 15 to 30ºC over two generations. We found that there was no difference in the egg hatch rate and immature survival rate across temperatures in the first generation. However, the egg hatch rate was lower and immature survival rate was higher at 30ºC in the second generation. The sex ratio (proportion of females) of resultant adults was consistent under all test temperatures in both generations except for 30ºC in the second generation which was lower. Higher temperature accelerated development in both generations but the development at the lower temperatures was faster in the second generation. Adult body size in both generations generally decreased with the increase of temperature, with females being more likely than males to adjust body size in response to temperature changes they first experienced. Temperature-dependent body size was not translated into fecundity, but larger adults lived longer. The thermal threshold was lower and degree days (DD) were greater in the second generation than in the first generation. Our findings indicate that life history traits of T. ludeni are highly flexible and adaptive to dynamic thermal environment in successive generations. Furthermore, increasing temperature elevated the intrinsic rate of increase (rm) but shortened the generation time (T) and the time to double the population size (Dt). The net population growth rate (R0) was higher at 20 and 25ºC as compared to lower and higher temperatures.

The Simulated Biological Response to Southern Ocean Eddies via Biological Rate Modification and Physical Transport

We examine the structure and drivers of anomalous phytoplankton biomass in Southern Ocean eddies tracked in a global, multiyear, eddy‐resolving, 3‐D ocean simulation of the Community Earth System Model. We examine how simulated anticyclones and cyclones differentially modify phytoplankton biomass concentrations, growth rates, and physical transport. On average, cyclones induce negative division rate anomalies that drive negative net population growth rate anomalies, reduce dilution across shallower mixed layers, and advect biomass anomalously downward via eddy‐induced Ekman pumping. The opposite is true in anticyclones. Lateral transport is dominated by eddy stirring rather than eddy trapping. The net effect on anomalous biomass can exceed 10–20% of background levels at the regional scale, consistent with observations. Moreover, we find a strong seasonality in the sign and magnitude of regional anomalies and the processes that drive them. The most dramatic seasonal cycle is found in the South Pacific Antarctic Circumpolar Current, where physical and biological processes dominate at different times, modifying biomass in different directions throughout the year. Here, in cyclones, during winter, anomalously shallow mixed layer depths first drive positive surface biomass anomalies via reduced dilution, and later drive positive depth‐integrated biomass anomalies via reduced light limitation. During spring, reduced iron availability and elevated grazing rates suppress net population growth rates and drive the largest annual negative surface and depth‐integrated biomass anomalies. During summer and fall, lateral stirring and eddy‐induced Ekman pumping create small negative surface anomalies but positive depth‐integrated anomalies. The same mechanisms drive biomass anomalies in the opposite direction in anticyclones.

Tropical seagrass Halophila stipulacea shifts thermal tolerance during Mediterranean invasion.

Exotic species often face new environmental conditions that are different from those that they are adapted to. The tropical seagrass Halophila stipulacea is a Lessepsian migrant that colonized the Mediterranean Sea around 100 years ago, where at present the minimum seawater temperature is cooler than in its native range in the Red Sea. Here, we tested if the temperature range in which H. stipulacea can exist is conserved within the species or if the exotic populations have shifted their thermal breadth and optimum due to the cooler conditions in the Mediterranean. We did so by comparing the thermal niche (e.g. optimal temperatures, and upper and lower thermal limits) of native (Saudi Arabia in the Red Sea) and exotic (Greece and Cyprus in the Mediterranean Sea) populations of H. stipulacea. We exposed plants to 12 temperature treatments ranging from 8 to 40°C for 7 days. At the end of the incubation period, we measured survival, rhizome elongation, shoot recruitment, net population growth and metabolic rates. Upper and lower lethal thermal thresholds (indicated by 50% plant mortality) were conserved across populations, but minimum and optimal temperatures for growth and oxygen production were lower for Mediterranean populations than for the Red Sea one. The displacement of the thermal niche of exotic populations towards the colder Mediterranean Sea regime could have occurred within 175 clonal generations.

Seagrass Posidonia oceanica diel pH fluctuations reduce the mortality of epiphytic forams under experimental ocean acidification

It is hypothesized that pH fluctuations produced by seagrasses metabolism may confer marine calcifiers resistance to ocean acidification. Here, we tested this thesis by comparing the net population growth rate (NPGR) of a foraminifer species (Rosalina sp.) epiphytic of Mediterranean seagrass (Posidonia oceanica) to average current and projected pH scenarios under either stable conditions or diel fluctuations in pH of 0.3 units; variations similar to that experienced in their habitat. No significant differences were found in NPGRs between the fluctuating and stable pH treatments at current pH levels. NPGRs in treatments where pH fluctuated did not present significant differences to the treatment with high and stable pH conditions. In contrast, foraminifers exposed to stable low pH regimes experienced a steep decline in NPGR. These results suggest that diel pH fluctuations generated by P. oceanica photosynthetic activity could confer resistance to ocean acidification to Rosalina sp.

Effects of Temperature on Life History Strategy of the Rotifer Euchlanis dilatata.

The cosmopolitan littoral rotifer Euchlanis dilatata is a potential model species in eco-toxicological and ecological studies, owing to its unique characteristics, such as periphytic benthic living, sensitivity to toxicity, and laying eggs on substrates instead of carrying them on the mother's body. However, studies about the life history strategy of this species, in contrast to the intensely studied planktonic Brachionus species, are relatively scarce. Temperature is an important factor that affects the rotifer's life history traits, and is well known to induce phenotypic plasticity in planktonic rotifers. The present study measured life table parameters of the rotifer E. dilatata originating from one clonal population local to Beijing under three temperature treatments: 14°C, 20°C and 26°C (10 females/replicate × 4 replicates for each treatment). We also examined trade-offs between egg size and egg number, as well as current reproduction and future survival to evaluate the life history strategy of the rotifer. In contrast to cold conditions, in which mothers produced a few large eggs with similar egg sizes, in warm environments, mothers produced many smaller eggs and a few larger eggs, thus resulting in a clear variation in egg sizes. With increasing temperature, the pre-mature period, reproductive period, life span and generation time shortened, while the net reproductive rate and population growth rate increased. Temperature also affected the trade-off between current reproduction and future survival. This work provides basic data for the potential model species E. dilatata.

The optimal population size under pollution and migration externalities: a spatial control approach

We analyze the implications of pollution and migration externalities on the optimal population dynamics in a spatial setting. We focus on a framework in which pollution affects the mortality rate and decreases utility, while migration occurs within the spatial economy. Agents optimally determine their fertility rate which, along with pollution-induced mortality and spatial migration, determines the net population growth rate. This setting implies that human population follows an endogenous logistic-type dynamics where fertility choices determine what the optimal limit of human population will be. We compare the decentralized and the centralized outcomes showing that such fertility decisions generally differ, quantifying the extent to which pollution and migration induced externalities matter in determining the difference between the two outcomes. We show that, due to the effects of pollution on utility and mortality, both the optimal fertility rate and the population size are smallest in the centralized economy but migration effects change not only the size of these differences but also their direction, suggesting that the spatial channel is an important mechanism to account for in the process of policymaking.

Robustness of early warning signals for catastrophic and non‐catastrophic transitions

Early warning signals (EWS) are statistical indicators that a rapid regime shift may be forthcoming. Their development has given ecologists hope of predicting rapid regime shifts before they occur. Accurate predictions, however, rely on the signals being appropriate to the system in question. Most of the EWS commonly applied in ecology have been studied in the context of one specific type of regime shift (the type brought on by a saddle‐node bifurcation, at which one stable equilibrium point collides with an unstable equilibrium and disappears) under one particular perturbation scheme (temporally uncorrelated noise that perturbs the net population growth rate in a density independent way). Whether and when these EWS can be applied to other ecological situations remains relatively unknown, and certainly underappreciated. We study a range of models with different types of dynamical transitions (including rapid regime shifts) and several perturbation schemes (density‐dependent uncorrelated or temporally‐correlated noise) and test the ability of EWS to warn of an approaching transition. We also test the sensitivity of our results to the amount of available pre‐transition data and various decisions that must be made in the analysis (i.e. the rolling window size and smoothing bandwidth used to compute the EWS). We find that EWS generally work well to signal an impending saddle‐node bifurcation, regardless of the autocorrelation or intensity of the noise. However, EWS do not reliably appear as expected for other types of transition. EWS were often very sensitive to the length of the pre‐transition time series analyzed, and usually less sensitive to other decisions. We conclude that the EWS perform well for saddle‐node bifurcation in a range of noise environments, but different methods should be used to predict other types of regime shifts. As a consequence, knowledge of the mechanism behind a possible regime shift is needed before EWS can be used to predict it.

Correction to 'Dynamics of phytoplankton blooms in turbulent vortex cells'.

You have accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Lindemann Christian, Visser Andre and Mariani Patrizio 2018Correction to ‘Dynamics of phytoplankton blooms in turbulent vortex cells'J. R. Soc. Interface.152017095120170951http://doi.org/10.1098/rsif.2017.0951SectionYou have accessCorrectionCorrection to ‘Dynamics of phytoplankton blooms in turbulent vortex cells' Christian Lindemann Christian Lindemann http://orcid.org/0000-0003-3684-2480 Google Scholar Find this author on PubMed Search for more papers by this author , Andre Visser Andre Visser Google Scholar Find this author on PubMed Search for more papers by this author and Patrizio Mariani Patrizio Mariani Google Scholar Find this author on PubMed Search for more papers by this author Christian Lindemann Christian Lindemann http://orcid.org/0000-0003-3684-2480 Google Scholar Find this author on PubMed Search for more papers by this author , Andre Visser Andre Visser Google Scholar Find this author on PubMed Search for more papers by this author and Patrizio Mariani Patrizio Mariani Google Scholar Find this author on PubMed Search for more papers by this author Published:17 January 2018https://doi.org/10.1098/rsif.2017.0951This article corrects the followingResearch ArticleDynamics of phytoplankton blooms in turbulent vortex cellshttps://doi.org/10.1098/rsif.2017.0453 Christian Lindemann, Andre Visser and Patrizio Mariani volume 14issue 136Journal of The Royal Society Interface01 November 2017J. R. Soc. Interface14, 20170453 (2017; Published online 1 November 2017) (doi:10.1098/rsif.2017.0453)The values for the sinking rate (w), given in table 1, were reported incorrectly. The values used in the model simulation were 0.96 m d−1. Furthermore, the caption of table 1 should only refer to reference [1]. The corrected table is given below. Table 1.Parameter values used in the simulations. ‘Standard values’ are the same as the values used by Huisman et al. [1], while the ‘deep convective values' represent values adjusted to deep convective systems in the North Atlantic. The value of kT (0.055 m−1) for the deep convective set up gives a euphotic depth, defined as the depth of 1% surface light, of approximately 80 m. Collapse parameterdescriptionstandard valuesdeep convection valuesunitphysicalI0surface light350100µmol photons m−2 s−1kTbackground turbidity of water0.20.055m−1biologicalkilight half-saturation constant3045µmol photons m−2 s−1Lspecific loss rate0.240.01d−1gmaxmax. specific growth rate0.960.96d−1wsinking velocity0.960.96m d−1In figure 4, the label of the x-axes was presented incorrectly. They should have stated unit of m d−1. Furthermore, the equation given in the figure caption refers to the dashed lines in figure 4a, as now clarified in the new figure caption. The corrected figure is displayed below. Figure 4. Sensitivity of the growth rate as a function of sinking velocity for different mean flow velocities (a–h) at a mixed layer depth of 25 m (light grey line); 50 m (dark grey line) and 100 m (black line). The dashed lines in figure 4a represent the net population growth rate estimated from r = w(−0.0037hz − 0.167) + 0.63. All other parameters as in table 1.Download figureOpen in new tabDownload PowerPointFootnotes© 2018 The Author(s)Published by the Royal Society. All rights reserved.ReferencesReference1Huisman J, Arrayás M, Ebert U, Sommeijer B. 2002How do sinking phytoplankton species manage to persist?Am. Nat. 159, 245–254. (doi:10.1086/338511) Crossref, PubMed, ISI, Google Scholar Previous Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsRelated articlesDynamics of phytoplankton blooms in turbulent vortex cells01 November 2017Journal of The Royal Society Interface This IssueJanuary 2018Volume 15Issue 138 Article InformationDOI:https://doi.org/10.1098/rsif.2017.0951PubMed:29343632Published by:Royal SocietyOnline ISSN:1742-5662History: Published online17/01/2018Published in print31/01/2018 License:© 2018 The Author(s)Published by the Royal Society. All rights reserved. Citations and impact Subjectscomputational biologyenvironmental science

Potential effects of incorporating fertility control into typical culling regimes in wild pig populations.

Effective management of widespread invasive species such as wild pigs (Sus scrofa) is limited by resources available to devote to the effort. Better insight of the effectiveness of different management strategies on population dynamics is important for guiding decisions of resource allocation over space and time. Using a dynamic population model, we quantified effects of culling intensities and time between culling events on population dynamics of wild pigs in the USA using empirical culling patterns and data-based demographic parameters. In simulated populations closed to immigration, substantial population declines (50–100%) occurred within 4 years when 20–60% of the population was culled annually, but when immigration from surrounding areas occurred, there was a maximum of 50% reduction, even with the maximum culling intensity of 60%. Incorporating hypothetical levels of fertility control with realistic culling intensities was most effective in reducing populations when they were closed to immigration and when intrinsic population growth rate was too high (> = 1.78) to be controlled by culling alone. However, substantial benefits from fertility control used in conjunction with culling may only occur over a narrow range of net population growth rates (i.e., where net is the result of intrinsic growth rates and culling) that varies depending on intrinsic population growth rate. The management implications are that the decision to use fertility control in conjunction with culling should rely on concurrent consideration of achievable culling intensity, underlying demographic parameters, and costs of culling and fertility control. The addition of fertility control reduced abundance substantially more than culling alone, however the effects of fertility control were weaker than in populations without immigration. Because these populations were not being reduced substantially by culling alone, fertility control could be an especially helpful enhancement to culling for reducing abundance to target levels in areas where immigration can’t be prevented.

Emerald ash borer biocontrol in ash saplings: The potential for early stage recovery of North American ash trees

In many parts of North America, ash (Fraxinus) stands have been reduced by the emerald ash borer (Agrilus planipennis) invasion to a few surviving mature trees, saplings, basal sprouts, and seedlings. Without a soil seed bank for Fraxinus spp., tree recovery will require survival and maturation of these younger cohorts to reproductive age. Here we report and analyze the population dynamics of emerald ash borer and its associated natural enemies in ash saplings (2.5–5.8cmDBH) in six deciduous forest stands in southern Michigan. At these sites, the outbreak population of the pest collapsed during the study, and a biocontrol agent introduced from China, the larval parasitoid Tetrastichus planipennisi, became widely established and increased in rates of parasitism. To assess the potential for ash recovery in these stands, we also quantified the abundance and crown condition of the ash saplings and surviving ash trees at the study sites. We found that T. planipennisi was the dominant biotic mortality factor in saplings, killing 36–85% of the late instar borer larvae. Neither woodpecker predation nor native parasitoids caused more than minor levels (<20%) of borer mortality in saplings. Life table analyses of these data further showed that the net population growth rate of the pest in saplings was near or under replacement levels, and that the introduced biocontrol agent reduced the pest’s net population growth rate in saplings at our study sites by over 50%. In addition, stand inventories found that healthy ash saplings (4–16 per 100m2) and smaller (pole size) trees (2–9 per 100m2) remained in the six study sites, despite an early high density population of the pest at the sites. These findings indicate that the introduced biocontrol agent T. planipennisi is providing significant biocontrol services, enhancing ash survival and promoting recovery of the ash in southern Michigan.

Effective Biological Control Depends on Life History Strategies of Both Parasitoid and Its Host: Evidence from Aphidius colemani-Myzus persicae System.

Mechanisms behind the success and failure of aphid biological control using parasitoids are largely unknown, probably because of the lack of knowledge of life history strategies of the insects involved. Here, we measured and compared life history strategies of Myzus persicae (Sulzer) (Hemiptera: Aphididae) and its parasitoid Aphidius colemani (Viereck) (Hymenoptera: Aphidiidae), providing essential information for evaluation of the potential of A. colemani to control M. persicae. Our results show that one A. colemani female parasitized ≈220 aphids within 1 wk regardless of the aphid age. Almost all aphids parasitized at <4th instar died before reaching adulthood, and those parasitized at ≥4th instar produced very few offspring, contributing little to population growth. Although having 21% lower intrinsic rate of increase and 33% longer life cycle than the aphid, the parasitoid possessed reproductive output and net population growth rate twice as high as the aphid, and reached maximum lifetime reproductive potential 1 wk earlier than the aphid. The life history strategies reported here imply that A. colemani is potentially a good biological control agent of M. persicae. On the basis of this study, we hypothesize that immediately after the onset of M. persicae, a release rate of ≈1:220 (female parasitoid:aphids) at a weekly interval during the first 3 wk could effectively control the pest. We suggest that the success of biological control of aphids using parasitoids largely depends on life history strategies of both insects involved and time of the season when they meet.