Theoretical Population Models Research Articles

Application of a catch multiple survey analysis for Atlantic horseshoe crab Limulus polyphemus in the Delaware Bay

AbstractObjectiveThis paper applies a catch multiple survey analysis (CMSA) to Atlantic horseshoe crabs Limulus polyphemus in the Delaware Bay to generate robust population estimates for harvest management. Currently, horseshoe crabs along the U.S. Atlantic coast are harvested as bait for other fisheries and collected for their blood, which is used in a biomedical industry. The Delaware Bay is home to the largest population of horseshoe crabs and is a significant stopover for shorebirds to rebuild energy by consuming horseshoe crab eggs prior to completing their northward migration. To address this interrelationship, the Adaptive Resource Management (ARM) Framework has been used since 2013 to ensure that horseshoe crab harvest within the region takes into account the forage needs of migratory birds. Since its inception, the ARM Framework has used a single trawl survey's swept area‐based population estimates of horseshoe crab relative abundance and a theoretical population model developed primarily from literature‐derived values. With more data collected in the region in recent years and other sources of mortality that can now be quantified, a catch survey model can provide horseshoe crab population estimates going forward.MethodsA CMSA was used to estimate male and female horseshoe crab population size for 2003–2021 using all quantifiable sources of mortality and three fishery‐independent indices of abundance.ResultThe CMSA results indicated that adult abundance of male and female horseshoe crabs was stable from 2003 to 2013 and then began to increase through 2017, a result that is consistent with stock rebuilding following a period of harvest restrictions as recommended by the ARM Framework. Population estimates were lower in recent years but remained above the levels estimated before implementation of the ARM Framework. In 2021, the CMSA estimated that there were over 6 million mature females and nearly 16 million mature male horseshoe crabs in the region.ConclusionThe CMSA provides the best and most comprehensive population estimates of horseshoe crabs in Delaware Bay and will improve modeling efforts within the ARM Framework going forward.

THE EFFECT OF ALLEE FACTOR ON A NONLINEAR DELAYED POPULATION MODEL WITH HARVESTING

The Allee effect may have a stabilizing or destabilizing effect on population dynamics, or reaching stability may be delayed. Also this effect can push populations to extinction, especially under sharp harvesting effect. Compensatory or overcompensatory population maps are situations that change the effect of the Allee factor on population dynamics. The harvesting factor has also the effect of changing the equilibrium levels differently in theoretical population models. This study includes the local stability of the equilibrium point of the delayed discrete-time population model exposed to the harvest effect with and without Allee effect. We also review the effect of Allee factor on the local stability of equilibrium point of the discrete-time population model involving delay [1]. The dynamics of this population models are given together with the enriched dynamics.

What goes up must come down – why high fecundity orchids challenge conservation beliefs

The life history of orchids is relatively well understood qualitatively, but quantifying this model and extracting a conservation message remains challenging. Orchid conservation requires the means to assess a species' vulnerability, and to restore populations that have lost numbers or range. In this study, we examine orchid population dynamics and, by extension, a large number of similar organisms with Type-III survival strategy: high fecundity and high mortality at early stages of life. By assuming a balance between fecundity and mortality, we establish a theoretical dynamic population model for orchid species, which also runs under scenarios of high environmental variability for various levels of fecundity. Our findings show that population variability increases mainly through survival variability. High fecundity acts as an amplifier of environmental variability and can cause populations to reach levels where extinction is a threat. Thus, extinction probability can paradoxically rise with increasing fecundity. In addition, at high fecundities, the extinction probability of orchids and other organisms characterized by very high fecundity and high pre-reproductive mortality may be relatively insensitive to initial population size, compared with organisms with low fecundity and mortality. The high fecundities of orchids do not shield them from extinction but may cause them to be more vulnerable to extinction. Changes in the environment have even greater impact than low initial population sizes.

P.005 Traumatic-like fear memory recall causes persistent morphine seeking behaviour in mice

The life history of orchids is relatively well understood qualitatively, but quantifying this model and extracting a conservation message remains challenging. Orchid conservation requires the means to assess a species' vulnerability, and to restore populations that have lost numbers or range. In this study, we examine orchid population dynamics and, by extension, a large number of similar organisms with Type-III survival strategy: high fecundity and high mortality at early stages of life. By assuming a balance between fecundity and mortality, we establish a theoretical dynamic population model for orchid species, which also runs under scenarios of high environmental variability for various levels of fecundity. Our findings show that population variability increases mainly through survival variability. High fecundity acts as an amplifier of environmental variability and can cause populations to reach levels where extinction is a threat. Thus, extinction probability can paradoxically rise with increasing fecundity. In addition, at high fecundities, the extinction probability of orchids and other organisms characterized by very high fecundity and high pre-reproductive mortality may be relatively insensitive to initial population size, compared with organisms with low fecundity and mortality. The high fecundities of orchids do not shield them from extinction but may cause them to be more vulnerable to extinction. Changes in the environment have even greater impact than low initial population sizes.

Radar observability of near-Earth objects using EISCAT 3D

Abstract. Radar observations can be used to obtain accurate orbital elements for near-Earth objects (NEOs) as a result of the very accurate range and range rate measureables. These observations allow the prediction of NEO orbits further into the future and also provide more information about the properties of the NEO population. This study evaluates the observability of NEOs with the EISCAT 3D 233 MHz 5 MW high-power, large-aperture radar, which is currently under construction. Three different populations are considered, namely NEOs passing by the Earth with a size distribution extrapolated from fireball statistics, catalogued NEOs detected with ground-based optical telescopes and temporarily captured NEOs, i.e. mini-moons. Two types of observation schemes are evaluated, namely the serendipitous discovery of unknown NEOs passing the radar beam and the post-discovery tracking of NEOs using a priori orbital elements. The results indicate that 60–1200 objects per year, with diameters D>0.01 m, can be discovered. Assuming the current NEO discovery rate, approximately 20 objects per year can be tracked post-discovery near the closest approach to Earth. Only a marginally smaller number of tracking opportunities are also possible for the existing EISCAT ultra-high frequency (UHF) system. The mini-moon study, which used a theoretical population model, orbital propagation, and a model for radar scanning, indicates that approximately seven objects per year can be discovered using 8 %–16 % of the total radar time. If all mini-moons had known orbits, approximately 80–160 objects per year could be tracked using a priori orbital elements. The results of this study indicate that it is feasible to perform routine NEO post-discovery tracking observations using both the existing EISCAT UHF radar and the upcoming EISCAT 3D radar. Most detectable objects are within 1 lunar distance (LD) of the radar. Such observations would complement the capabilities of the more powerful planetary radars that typically observe objects further away from Earth. It is also plausible that EISCAT 3D could be used as a novel type of an instrument for NEO discovery, assuming that a sufficiently large amount of radar time can be used. This could be achieved, for example by time-sharing with ionospheric and space-debris-observing modes.

Population estimate and rate of increase of southern right whales Eubalaena australis in southeastern Australia

In Australian waters, southern right whales Eubalaena australis form 2 genetically distinct populations that have shown contrasting patterns of recovery since whaling ceased: a western population in South Australia and Western Australia and an eastern population in southeastern Australia (Tasmania, Victoria and New South Wales). Here, we provide an abundance estimate derived from a breeding female superpopulation mark-recapture model for the southeastern southern right whale population. The population comprises 268 individuals (68 breeding females) and has increased at a rate of 4.7% per annum between 1996 and 2017. There has been no significant change in the annual abundance of mother-calf pairs sighted at the only calving ground (Logans Beach in Victoria) over the last 3 decades. The total number of southern right whales (i.e. all adults and calves) using the southeastern Australian coastline has increased by 7% since 1985. Unlike the population estimate (which was restricted to breeding females sighted prior to the post-breeding southward migration), this estimate is likely to include transiting whales from the southwestern population. The theoretical population model predicts 19 breeding females at Logans Beach in 2018 and 28 in 2028; the actual number of breeding females, as of 2018, is 14. This study provides the first complete estimate of population size and rate of increase of southern right whales along the southeastern Australian coastline. This knowledge is critical for assessing population status and recovery of southern right whales in Australia. It provides a basis for monitoring persistence and responses of the population to environmental stressors.

The interplay between fishery yield and top predator culling in a multispecies fishery context.

In food webs, fishery can play the role of top predator, competing thus with other top predators for valuable food resources. In this view, it has been claimed in fisheries management that culling of top predators can be a means to improve fishery yield. To investigate this hypothesis, we use theoretical population models to assess in a multispecies context how fishery yield from target species harvest responds to top predator cull. Defying crisp summary, the four analysed food web models show that this response may be either positive or negative or both, indicating that in terms of multispecies fishery management the harvest yield may not accrue as a consequence of predator removal. In addition, this multitude of behaviours points also to the fact that the response of fishery yield to top predator cull may be difficult to assess.

A Theoretical Population and Harvest Model for American Alligators (Alligator mississippiensis)

Abstract The American Alligator (Alligator mississippiensis) is a crocodilian species that was once listed as endangered in the United States but is now harvested both recreationally and commercially throughout its range in the southeastern United States. Harvest of alligators typically includes egg collecting and hunting. However, review of scientific literature reveals that the effects of harvest on alligator populations have received little scientific scrutiny. We built a theoretical simulation model to evaluate the impact of several harvest strategies on long-term (i.e., 100 yr) alligator population trends. We used system dynamics software to develop the model and acquired data for the model from literature and field studies on alligator ecology. Although widely applicable across the species range and for other crocodilians, we used the Texas alligator management program as an example for model use. Results of model simulations showed that current harvest (50% egg harvest, 2% subadult harvest, 2% adul...

A comparative study of highly-ionized Al plasma based on dual pulse laser-induced breakdown spectroscopy

We built a collinear dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) system to study the aluminum (Al) plasma emission by installing a pair of Nd: YAG lasers operating at 266 and 1064 nm. The spectral intensities of selected aluminum doubly-ionized lines were employed to evaluate the optical emission spectra. The influences of the energy ratio of two pulsed lasers on the LIBS intensity for different Al doubly-ionized spectral lines were investigated. The de-excitation rate parameters of the excited ion and the electron impact excitation were computed using the analytical formulas proposed by Smeets and Vriens. The transition probabilities and energy states were computed using Hibbert’s configuration interaction, computer package (CIV3). By solving the coupled rate equations including 1s22s22p6ns (2S), 1s22s22p6np (2P), 1s22s22p6nd (2D) (n = 3–5) and 1s22s22p6nf (2F) (n = 4, 5) states, the level population densities were computed. We also proposed a theoretical population model in order to investigate the effectiveness of the various processes that might affect the population of the upper levels in Al plasma by using the rate coefficients. In addition, the population densities for the 19 upper levels were also computed. Good compatibility between the experimental and the theoretical model data had been observed. Our results might be significant as reference data for the optimization of the DP-LIBS spectrometry and diagnostics of laser produced plasmas.

Conservation of passively dispersed organisms in the context of habitat degradation and destruction

Summary Passively dispersed species, such as many plant species, rely on abiotic forces to achieve movement. Despite the fact that such species form the base of many terrestrial and oceanic food webs, these species are often overlooked by conservation management plans because it is assumed that they are dispersed easily and widely, and therefore are relatively unthreatened by anthropogenic influences in comparison with poorly dispersing species. To quantify the threat presented by habitat degradation and destruction to passively dispersed species, we present a theoretical population model of passively dispersed organisms that incorporates the effects of increased dispersal‐associated mortality. We examine how the effects of habitat degradation and destruction depend on species’ dispersal tactics, specifically: highly dispersive, highly retentive or spatially biased. Contrary to prevailing intuition, highly dispersive species may suffer the strongest absolute negative demographic effects in the face of changes in human‐modified landscapes. These results suggest that passively dispersed organisms may be more threatened by landscape modification than previously thought, and should be more carefully considered in plans for conservation and management. Synthesis and applications. Since passively dispersed species cannot choose their ultimate settling location, they are therefore less likely to arrive at suitable habitat in landscapes that are degraded or destroyed. If we do not understand the implications for population dynamics of demographic costs of dispersal in fragmented landscapes, we may fail to predict declines of apparently widespread species, including many wind‐dispersed plants and insects, benthic invertebrates and airborne microbes. Conservation and management plans should consider loss of propagules to unsuitable habitat for highly dispersive as well as poorly dispersive species, to avoid potential errors.

The RoboPol optical polarization survey of gamma-ray-loud blazars

We present first results from RoboPol, a novel-design optical polarimeter operating at the Skinakas Observatory in Crete. The data, taken during the 2013 May–June commissioning of the instrument, constitute a single-epoch linear polarization survey of a sample of gamma-ray-loud blazars, defined according to unbiased and objective selection criteria, easily reproducible in simulations, as well as a comparison sample of, otherwise similar, gamma-ray-quiet blazars. As such, the results of this survey are appropriate for both phenomenological population studies and for tests of theoretical population models. We have measured polarization fractions as low as 0.015 down to R-mag of 17 and as low as 0.035 down to 18 mag. The hypothesis that the polarization fractions of gamma-ray-loud and gamma-ray-quiet blazars are drawn from the same distribution is rejected at the 3σ level. We therefore conclude that gamma-ray-loud and gamma-ray-quiet sources have different optical polarization properties. This is the first time this statistical difference is demonstrated in optical wavelengths. The polarization fraction distributions of both samples are well described by exponential distributions with averages of |$\langle p \rangle =6.4 ^{+0.9}_{-0.8}\times 10^{-2}$| for gamma-ray-loud blazars, and |$\langle p \rangle =3.2 ^{+2.0}_{-1.1}\times 10^{-2}$| for gamma-ray-quiet blazars. The most probable value for the difference of the means is |$3.4^{+1.5}_{-2.0}\times 10^{-2}$|⁠. The distribution of polarization angles is statistically consistent with being uniform.

Linking indices for biodiversity monitoring to extinction risk theory.

Biodiversity indices often combine data from different species when used in monitoring programs. Heuristic properties can suggest preferred indices, but we lack objective ways to discriminate between indices with similar heuristics. Biodiversity indices can be evaluated by determining how well they reflect management objectives that a monitoring program aims to support. For example, the Convention on Biological Diversity requires reporting about extinction rates, so simple indices that reflect extinction risk would be valuable. We developed 3 biodiversity indices that are based on simple models of population viability that relate extinction risk to abundance. We based the first index on the geometric mean abundance of species and the second on a more general power mean. In a third index, we integrated the geometric mean abundance and trend. These indices require the same data as previous indices, but they also relate directly to extinction risk. Field data for butterflies and woodland plants and experimental studies of protozoan communities show that the indices correlate with local extinction rates. Applying the index based on the geometric mean to global data on changes in avian abundance suggested that the average extinction probability of birds has increased approximately 1% from 1970 to 2009.Conectando Índices para el Monitoreo de la Biodiversidad con la Teoría de Riesgo de ExtinciónResumenLos índices de biodiversidad combinan frecuentemente los datos de diferentes especies cuando se usan en los programas de monitoreo. Las propiedades heurísticas pueden sugerir índices preferidos, pero carecemos de medios objetivos para discriminar a los índices con propiedades heurísticas similares. Los índices de biodiversidad pueden evaluarse al determinar qué tan bien reflejan los objetivos de manejo que un programa de monitoreo busca apoyar. Por ejemplo, la Convención sobre la Diversidad Biológica requiere reportar las tasas de extinción, así que los índices que reflejan el riesgo de extinción serían valiosos. Desarrollamos 3 índices de biodiversidad que se basan en modelos sencillos de viabilidad de población y que relacionan el riesgo de extinción con la abundancia. Basamos el primer índice en la media geométrica de la abundancia de especies, y el segundo en una media de poder más general. En el tercer índice integramos la media geométrica y la tendencia. Estos índices requieren los mismos datos que índices previos, pero también se relacionan directamente con el riesgo de extinción. La información de campo sobre mariposas y plantas de bosque, y los estudios experimentales de comunidades protozoarias, muestran que los índices se correlacionan con las tasas locales de extinción. Al aplicar el índice basado en la media geométrica sobre los datos globales de los cambios en la abundancia de aves, sugirió que la probabilidad de extinción promedio de aves ha incrementado aproximadamente 1% desde 1970 hasta 2009.Palabras ClaveÍndice de biodiversidad, media geométrica, medida de la biodiversidad, riesgo de extinción

Rapid ongoing decline of Baird's tapir in Cusuco National Park, Honduras

During the International Tapir Symposium 16-21 Oct 2011, the conservation of Baird's tapir (Tapirus bairdii) in Honduras received a boost with the signing of a memorandum of understanding between the Minister Director of the Honduran Institute of Conservation and Forestry (ICF) and the Tapir Specialist Group (TSG). Despite this agreement, accelerating levels of hunting and habitat loss continue to pose a threat to Baird's tapir in Honduras. An ongoing study in Cusuco National Park in northwestern Honduras has been monitoring changes in population dynamics of Baird's tapir since 2006 through the collection of occupancy data. The study has identified an increase in hunting pressure, coinciding with a drastic decline in the encounter rate with Baird's tapir spoor. Here, we examine the significance of a range of demographic variables on Baird's tapir occupancy in Cusuco National Park using the software PRESENCE, and simulate the effects of different management strategies on the future dynamics of the population using the stochastic simulation software VORTEX. The predictions of the theoretical population models are compared to observed changes in occupancy levels. We found that non-intervention resulted in the local extinction of Baird's tapir within a very short time frame, but that various intervention models enabled the population to recover to near carrying capacity. Occupancy and extinction probability were shown to respond markedly to the increase in hunting pressure; and occupancy models supported the future population predictions generated by VORTEX. Our study suggests that immediate intervention is required to reduce hunting pressure to near historical levels to prevent the imminent local extinction of the species.

Analysis of the impact of trap-neuter-return programs on populations of feral cats

To evaluate 2 county trap-neuter-return (TNR) programs for feral cat population management via mathematical modeling. Theoretical population model. Feral cats assessed from 1992 to 2003 in San Diego County, California (n = 14,452), and from 1998 to 2004 in Alachua County, Florida (11,822). Data were analyzed with a mathematical Ricker model to describe population dynamics of the feral cats and modifications to the dynamics that occurred as a result of the TNR programs. In both counties, results of analyses did not indicate a consistent reduction in per capita growth, the population multiplier, or the proportion of female cats that were pregnant. Success of feral cat management programs that use TNR can be monitored with an easily collected set of data and statistical analyses facilitated by population modeling techniques. Results may be used to suggest possible future monitoring and modification of TNR programs, which could result in greater success controlling and reducing feral cat populations.

Perspective of practical biological control and population theories

AbstractWe have not yet had sufficient theoretical explanation for successful biological control in which a key pest is controlled after an introduction of natural enemies. I compare here real features of successful biological control and theoretical host–parasitoid population models to reduce the gap between theory and practice. I first review the historical interaction between classical biological control projects and theoretical population models. Second, I consider the importance of host refuges in host–parasitoid population dynamics as concerns the mechanisms of low and stable host density. The importance of density–dependent parasitism through parasitoid reproduction in multivoltine host–parasitoid systems and supplemental generalist natural enemies are also discussed. Finally, I consider the difference in tactics for classical biological control and for augmentation of natural enemies in annual crop systems.

Effects of Individual Variation in Size on Growth and Development of Larval Salamanders

Theoretical population models suggest that variation among individuals can affect population—level properties like stability and equilibrial density. Few studies, however, have tested the importance of individual variation to factors affecting population dynamics (e.g., average individual growth rates, developmental rates, survivorship, etc.) using natural populations. We conducted a field experiment designed to test effects of larval density and individual variability in body size on growth and development of larval tiger salamanders (Ambystoma tigrinum nebulosum). We performed our experiment in a natural sinkhole lake in central Arizona; experimental populations differing in density and initial variability in body size were held in nylon mesh enclosures. Effects of individual variability in size were examined independently of any effects due to mean body size of the population or total population biomass. Density affected growth rates and development to metamorphosis of experimental larvae in a manner consistent with other studies. Initial variability in body size did not affect larval growth rates or diets but did interact with density to affect survivorship and development: experimental larvae held with similarly sized individuals experienced lower survivorship and were metamorphosing earlier than experimental larvae held with variably sized individuals. These effects did not appear to be mediated by size—specific competitive abilities but may have been mediated by individual behavioral responses to size structure. This study underscores the importance of incorporating information about interindividual variability into our understanding of processes affecting population dynamics.

Experimental electron-impact excitation rate coefficients for beryllium-like Si XI

Absolute excitation rate coefficients for a large number of levels (up to n = 4) of the singlet and triplet system of Si XI have been experimentally determined in a well-diagnosed theta-pinch plasma with the plasma spectroscopic method. The population of the metastable triplet ground state has been derived from the intensity of the intercombination line. A theoretical population model has been developed to investigate whether collisional coupling of the levels and cascading affected the measurements. The model has also been used to calculate line intensity ratios of strongly density or temperature dependent line pairs which can be used for plasma diagnostic purposes. The measured effective excitation rate coefficients are accurate to about ±50%. All of them, apart from the value for the 2s4s 3S1 level, agreed within the error margins with existing theoretical data.

DUST AND IONIZED GAS IN ELLIPTICAL GALAXIES

DUST AND IONIZED GAS IN ELLIPTICAL GALAXIES

Minimum variance stratification

The equations for the solution of minimum variance stratification under Neyman allocation are not easily tractable and hence approximate solutions have been suggested by various workers. These approximate solutions are in general not satisfactory as they do not achieve global minimum variance. An iterative procedure which results in global minimum variance solution to the stratification problem under Neyman allocation, is suggested herein with illustrations using six theoretical population models.

Analytical Population Dynamics

Despite considerable effort, ecologists still have an incomplete understanding of the processes that cause changes in insect population densities. Although there have been significant advancements in the development of theoretical population models, considerable debate still exists on how to deduce the underlying processes that drive the dynamics of natural populations.