Models of poisoning effects on vulture populations show that small but frequent episodes have a larger effect than large but rare ones

Vultures are among the most threatened avian taxa in the world. When vultures aggregate in large numbers to feed, poisoned carcasses can extirpate entire populations at once. In the light of shrinking numbers worldwide, restocking and reintroduction projects, where wild or captive-bred vultures are released back into nature, constitute a crucial management tool, successfully implemented in many countries. However, reestablishment of sustainable vulture populations to their historical ranges remains a serious challenge, especially if the threat of poisoning persists, which is usually the case. In this study, we model the outcome of a restocking project where an initial colony is subject to repeated poisoning events. We use as an example the isolated population of the griffon vulture (Gyps fulvus) in Cyprus. Mathematical considerations and model simulations show that the probability of colony persistence depends on the initial population size and the intensity and frequency of the poisoning incidents. This type of scenario creates an Allee effect that requires a colony to exceed a minimum size in order to survive. Also in this scenario, a sequence of small but frequent poisoning episodes is worse on average than a few large and rare ones of the same cumulative mortality. Future population reinforcement efforts for vultures should focus on the release of adult birds in adequate numbers for the successful establishment of sustainable colonies and should involve a reduction in small but persistent sources of mortality such as the poison baiting of small canids that until now has been neglected by conservation scientists.

Local extinction of an isolated dugong population near Okinawa Island, Japan

A small animal population becomes extinct owing to demographic and environmental stochasticity after declining below the minimum viable population (MVP). However, the actual process of extinction derived by stochastic factors after crossing MVP has not been recorded for long-lived marine mammals. Here, we reconstructed the extinction history of a small, isolated population of dugongs in Okinawa over 125 years. The initial population size of 300 in the 19th century declined to 50 in 1916 (because of overfishing), 20 in 1979, 10 in 1999, 3 after 2006, and finally extinct in 2019. After 1979, a decline in the natural growth rate for only 20 individuals led to extinction. Long-lived animals fall below the MVP; thus, active conservation measures should have been taken much sooner than when the actual extinction happened.

Blanding’s Turtle Demography and Population Viability

In anticipation of US federal status classification (warranted, warranted but precluded, not warranted), scheduled for 2023, we provide population viability analysis of the Blanding’s turtle Emydoidea blandingii , a long-lived, late-maturing, semi-aquatic species of conservation concern throughout its range. We present demographic data from long-term study of a population in northeastern Illinois and use these data as the basis for viability and sensitivity analyses focused on parameter uncertainty and geographic parameter variation. We use population viability analysis to identify population sizes necessary to provide population resiliency to stochastic disturbance events and catastrophes and demonstrate how alternative definitions of ‘foreseeable future’ might affect status decisions. Demographic parameters within our focal population resulted in optimistic population projections (probability of extinction = 0% over 100 years) but results were less optimistic when catastrophes or uncertainty in parameter estimates were incorporated (probability of extinction = 3% and 16%, respectively). Uncertainty in estimates of age-specific mortality had the biggest impact on population viability analysis outcomes but uncertainty in other parameters (age of first reproduction, environmental variation in age-specific mortality, % females reproducing, clutch size) also contributed. Blanding’s turtle demography varies geographically and incorporating this variation resulted in both mortality- and fecundity-related parameters affecting population viability analysis outcomes. Possibly, compensatory variation among demographic parameters allows for persistence across a wide range of parameter values. We found that extinction risk decreased and retention of genetic diversity increased rapidly with increasing initial population size. In the absence of catastrophes, demographic conservation goals could be met with a smaller initial population size than could genetic conservation goals; ≥20-50 adults were necessary for extinction risk <5% whereas ≥50-110 adults were necessary to retain >95% of existing genetic diversity over 100 yrs. These thresholds shifted upward when catastrophes were included; ≥50-200 adults were necessary for extinction risk <5% and ≥110 to more than 200 adults were necessary to retain >95% of existing genetic diversity over 100 yrs. Impediments to Blanding’s turtle conservation include an incomplete understanding of geographic covariation among demographic parameters, the large amount of effort necessary to estimate and monitor abundance, and uncertainty regarding the impacts of increasingly frequent extreme weather events.

Bistable Bacterial Growth Dynamics in the Presence of Antimicrobial Agents

The outcome of an antibiotic treatment on the growth capacity of bacteria is largely dependent on the initial population size (Inoculum Effect). We characterized and built a model of this effect in E. coli cultures using a large variety of antimicrobials, including conventional antibiotics, and for the first time, cationic antimicrobial peptides (CAMPs). Our results show that all classes of antimicrobial drugs induce an inoculum effect, which, as we explain, implies that the dynamic is bistable: For a range of anti-microbial densities, a very small inoculum decays whereas a larger inoculum grows, and the threshold inoculum depends on the drug concentration. We characterized three distinct classes of drug-induced bistable growth dynamics and demonstrate that in rich medium, CAMPs correspond to the simplest class, bacteriostatic antibiotics to the second class, and all other traditional antibiotics to the third, more complex class. These findings provide a unifying universal framework for describing the dynamics of the inoculum effect induced by antimicrobials with inherently different killing mechanisms.

Agglomeration economies, congestion diseconomies, and fertility dynamics in a two-region economy

Using a small, open, two-region economy model populated by two-period-lived overlapping generations, we analyze long-term agglomeration economy and congestion diseconomy effects of young worker concentration on migration and the overall fertility rate. When the migration-stability condition is satisfied, the distribution of young workers between regions is obtainable in each period for a predetermined population size. Results show that migration stability does not guarantee dynamic stability of the economy. The stationary population size stability depends on the model parameters and the initial population size. On a stable trajectory converging to the stationary equilibrium, the overall fertility rate might change non-monotonically with the population size of the economy because of interregional migration. In each period, interregional migration mitigates regional population changes caused by fertility differences on the stable path. Results show that the inter-regional migration-stability condition does not guarantee stability of the population dynamics of the economy.

The impact of management on the behavior of an isolated logistics population

The article considers the isolated population described by the logistic equation and studies the influence of management on the change of its number. Depending on the value of the control parameter, there are three different cases of behavior of an isolated population. In the first case, when the quota is equal to the corresponding value, depending on the initial value, the population either goes to a stationary value, or dies out. In the second case, when the quota does not exceed the established value, depending on the initial population size, the population either goes to the largest stationary point, or dies out. And in the third case, when the quota exceeds the established value, regardless of the initial population size, the population dies out. Stationary points for stability in all three cases are studied and graphs of population behavior depending on different initial conditions are presented.

One out of ten: low sampling efficiency of cloth dragging challenges abundance estimates of questing ticks

Hard ticks (Acari: Ixodidae) act as important vectors of zoonotic pathogens. For instance, Borrelia burgdorferi s.l. spirochetes pose a severe health risk as aetiological agents of Lyme borreliosis. Commonly, to study the abundance of questing (host-seeking) ticks, a 1 m2 piece of cloth is dragged over vegetation for a determined distance. Here, we designed a tick-sampling study to estimate the sampling efficiency of this standard method. We established 10 m dragging transects in a hemiboreal mixed forest patch in SW Finland for a 5-day monitoring period. Five of the transects were cloth-dragged 3× a day, whereas another five transects were dragged 6× a day in a manner that after each morning, midday and afternoon dragging, a second dragging was conducted on the same transect immediately. Captured Ixodes ricinus ticks were subsequently analysed for tick-borne pathogens. The initial population size of nymphal ticks on a transect was approximated by the accumulated nymph catch from the dragging sessions. The sampling efficiency of the cloth dragging was low, as a single dragging in a previously untouched vegetation strip always caught less than 12% (mean 6%) of the estimated population of active nymphs that were assumed to be questing during the study. Clear results were not found for daily activity rhythm, as ticks were caught in all daily dragging sessions. Approximately every third nymph and every second adult carried a pathogen, but nothing indicated that the occurrence of a pathogen affected the likelihood of the tick being caught by cloth dragging. Our results suggest that only a minority of active ticks can be caught by a single cloth dragging. The abundance estimates in many tick investigations might thus be downward biased.

Monitoring vertebrate abundance in Austria: developments over 30 years

SummaryLoss of biodiversity is one of the major challenges of the anthropocene. Various indices are used to quantify biodiversity. For vertebrates, the World Wide Fund for Nature (WWF) uses the Living Planet Index (LPI). It is calculated globally as well as separately for the species occurring in terrestrial, freshwater, and marine biomes. Action to prevent biodiversity loss can be taken by countries or provinces, so it is important to understand the changes in biodiversity at local scales. We present LPIs for vertebrates in Austria, both unweighted and weighted, according to species richness. Vertebrate populations seem to have declined strongly in Austria, and their abundance was stabilized at about 60% of the initial population size in the base year 1990—the LPI declined from 1 in 1990 to ~0.6 (unweighted) or ~0.7 (weighted) in 2015. This is almost double the global decline for the same period. LPIs were calculated separately for the terrestrial biome (~0.6), the freshwater biome (~0.9), birds (~0.7), and native species (~0.6). These indices give evidence that conservation measure to halt biodiversity loss in Austria is necessary and show where more data are needed. In Austria, more research is needed especially on populations of reptile species.

Mutualistic cross-feeding in microbial systems generates bistability via an Allee effect

ABSTRACTMutualistic interactions are characterized by the positive influence that two species exert on each other. Such mutualism can lead to bistability. Depending on the initial population size species will either survive or go extinct. Various phenomenological models have been suggested to describe bistability in mutualistic systems. However, these models do not account for interaction mediators such as nutrients. In contrast, nutrient-explicit models do not provide an intuitive understanding of what causes bistability. Here, we reduce a theoretical nutrient-explicit model of two mutualistic cross-feeders in a chemostat, uncovering an explicit relation to a growth model with an Allee effect. We show that the dilution rate in the chemostat leads to bistability by turning a weak Allee effect into a strong Allee effect. This happens as long as there is more production than consumption of cross-fed nutrients. Thanks to the explicit relationship of the reduced model with the underlying experimental parameters, these results allow to predict the biological conditions that sustain or prevent the survival of mutualistic species.

The Effects of CMA-ES Style Selection and Restart Criteria on DE

Over the years, a lot of research has gone into the creation of different mutation operators and adaptive parameters for differential evolution (DE). However, the literature is fairly quiet about automatically setting population size and completely silent about varying the selection operator used within DE. In this paper, we steal a page from CMA-ES/IPOP: using ES-style µ+λ selection, which selects across the entire population, in place of more individualistic DE selection with its use of local selection on the target and its child. We find that the most effective choice of selection can depend on the function being optimized, although for most of the functions we tested, the original DE selection was preferable. When adding IPOP style restarting, EqualFunValHist is the most applicable of the stagnation criteria, and it is used to trigger the doubling of the population size upon restart. The initial population size is set to the same as CMA-ES. Here we find, that the restartable DE behave as well and better as regular DE with population size set as lower than the default settings used.