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PubMed2003

Combining endogenous and exogenous spatial variability in analytical population models.

Analytically tractable models of dynamics in continuous space rarely incorporate both endogenous and exogenous spatial heterogeneity. We use spatial moment equations in combination with simulation models to analyze the combined effects of endogenous and exogenous variability on population viability in a simple single-population model where landscape heterogeneity and local population density both affect mortality rate. The equations partition the effects of heterogeneity into an effect of local crowding and an effect of habitat association caused by differential mortality. Exogenous heterogeneity in mortality rate increases population viability through habitat association and decreases it through increased crowding; the net effect of exogenous heterogeneity is generally to improve population viability. This result is contrary to some (but not all) conclusions in the literature, which usually focus on the effects of fragmentation rather than the benefits of refuges to short-dispersing individuals.

Algorithms↗
PubMed2003

Conservation and control strategies for the wolf (Canis lupus) in western Europe based on demographic models.

Securing the long-term acceptance of large carnivores such as the wolf (Canis lupus) in Europe and North America raises a difficult challenge to conservation biologists: planning removals to reduce depredations on livestock while ensuring population viability. We use stochastic-stage-structured population models to investigate wolf population dynamics and to assess alternative management strategies. Among the various management strategies advocated by agencies, zoning that involves eliminating wolves outside a restricted area should be designed with caution, because probabilities of extinction are extremely sensitive to the maximum number of packs that a zone can support and to slight changes in stage specific survival probabilities. In a zoned population, viability is enhanced more by decreasing mortality rates in all classes than by increasing wolf zone size. An alternative to zoning is adaptive management, where there is no limit on pack number but population control can be operated whenever some predefined demographic conditions are met. It turns out that an adaptive management strategy that removes a moderate percentage (10%) of the population following each year of more than 5% of total population growth would provide visible actions addressing public concerns while keeping extinction probability low.

Animals↗
PubMed2026

Sexual selection purges mutation load, but not overall genetic diversity, decreasing vulnerability to extinction.

Theory suggests sexual selection will enhance population viability by purging deleterious alleles. However, direct genomic evidence for this fundamental idea is scarce and contradictory. We combined long-term experimental evolution with whole-genome resequencing to directly test how sexual selection affects mutation load, genomic divergence, and extinction risk in small populations (maximum Ne = 40) of Tribolium castaneum. After 156 generations, populations evolving under strong sexual selection carried substantially fewer deleterious alleles than populations under weak sexual selection, based on both individual-level estimates of missense and nonsense variants and population-level Rxy analyses, indicating more efficient purging of deleterious alleles. In contrast, nucleotide diversity and runs of homozygosity were similar across treatments, indicating that purging acted most strongly on deleterious variation, and that reduced mutation load in these small populations under strong sexual selection was not explained by demographic effects. Importantly, population-level mutation load estimates best explained extinction risk under inbreeding, directly linking sexual selection to purging and population viability. Genome scans of high and low sexual selection populations revealed peaks of divergence, which included genes involved in courtship, sex discrimination, and seminal fluid proteins. Our results provide direct genomic evidence that sexual selection can reduce mutation load without eroding standing genetic diversity and thus adaptive potential, while driving adaptive divergence in reproductive traits. This beneficial purging may help explain the widespread prevalence of sexual reproduction in nature despite inherent costs and have important ramifications as to how we manage populations of conservation concern.

Animals↗
PubMed2002

Effects of agricultural runoff on native amphibians in the Lower Fraser River Valley, British Columbia, Canada.

Hatching success, deformity rates, and survivorship of northern red-legged frogs (Rana aurora) and northwestern salamanders (Ambystoma gracile) were assessed at three agricultural and three reference sites in the Sumas Prairie, British Columbia, Canada. In 1997 and 1998, eggs of both species and eggs of R. aurora, respectively, were placed in Nytex mesh cages (Irwindale, CA, USA) in roadside ditches at each site. Concurrently in 1997, eggs of R. aurora were reared in the laboratory but were exposed to water samples from each of the study sites. Hatching success was significantly lower at all agricultural sites compared to the reference sites for both species. However, no differences were observed in hatching success among sites for eggs of R. aurora reared in the laboratory. Water chemistry differed among all sites, but the largest differences were between reference and agricultural sites. Ammonia (maximum of 1.27 mg/L), total phosphate (maximum of 8.14 mg/L), and biological oxygen demand (maximum of 79.00 mg/L) were high at some of the agricultural sites during the development period. Results suggest that agricultural runoff may contribute to lower reproductive success and ultimately to reduced population viability of amphibian populations in the Lower Fraser Valley (BC, Canada).

Agriculture↗
PubMed2006

Habitat change and demography of Primula veris: identification of management targets.

Although the effects of deterministic factors on population viability often are more important than stochasticity, few researchers have dealt with the effect of deterministic habitat changes on plant population demography. We assessed population viability for the perennial herb Primula veris L. and identified targets for management based on demographic data from five different habitat types representing different degrees of canopy closure. We conducted replicate studies at the border of the distribution area and in more central parts. Demographic patterns were similar between the two regions. Most study populations had a positive population growth, and only populations in late phases of forest succession showed consistently negative trends. The populations of open habitats had high seedling recruitment, and the populations of early and middle forest succession had high seed production. The importance of survival for population growth rate increased with increasing habitat closure, whereas the importance of growth and reproduction decreased. Results of the elasticity analysis suggested that the best method to manage decreasing late-successional populations is to increase survival of the largest individuals. The life-table response experiment (LTRE) analysis, however showed that survival of the largest individuals contributed little to differences in population growth rates of different habitats, whereas seed production and growth of small individuals were more important. Moreover direct perturbation of the performance of the largest stages showed that late-successional populations would not attain positive population growth even if the largest stages had no mortality at all. We conclude that restoration of recruitment is the only possibility for positive population growth in late-successional populations of P. veris, although the elasticities of recruitment transitions are low. Our results also suggest that retrospective demographic methods such as LTRE constitute an important and necessary complement to prospective methods such as elasticities in identifying management targets.

Conservation of Energy Resources↗
PubMed2001

Estimation and management of genetic diversity in small populations of plains zebra (Equus quagga) in KwaZulu-Natal, South Africa.

Plains zebras (Equus quagga antiquorum) occur in few large, but many small, isolated populations in KwaZulu-Natal. Problems identified in small populations include reduced striping patterns on hind quarters, smaller size, elevated mortality rates and high number of still-births. Inbreeding may be implicated. Population viability analysis (PVA) was conducted with a computer model (VORTEX), and DNA and allozyme analyses were conducted to test the findings of the model. Using standard methods, DNA (PCR-RAPD) and allozyme diversity was assessed in blood samples from 72 plains zebra from four KwaZulu-Natal Nature Conservation Services (KZN-NCS) protected areas: Umfolozi Game Reserve (UGR), Albert Falls (AFNR), Vernon Crookes (VCNR) and Harold Johnson (HJNR) Nature Reserves. Populations of the latter three, small-sized (9-110 individuals) populations were seeded from the same source population (UGR: current population of 2000) during the past 25 years. Information from PCR-RAPD and allozyme analyses were compared with each other as well as to that predicted by population genetic modelling (using VORTEX). Allozyme heterozygosities were consistently high in all populations (12.1-12.9%), with no observable losses associated with reduced population size. On the other hand, percentage loss of polymorphism (20-39%) calculated from the PCR-RAPD study appeared to be positively correlated with the loss of heterozygosity predicted by population viability analysis (PVA), and negatively correlated with population size. On the basis of the above results, a policy of translocation was advocated for small, intensely managed populations of zebras, whereby a harem should be translocated every five years for a population size of nine (HJNR), while for a population size of 110 (VCNR) translocations should take place every 15 years if heterozygosity is to be maintained at more than 90% within each population over 100 years.

Journal Article↗
PubMed2005

A hierarchical matrix model to assess the impact of habitat fragmentation on population dynamics: an elasticity analysis.

To better understand the role of habitat quality and boundaries on population dynamics at the landscape scale, we develop a model combining a spatially implicit approach, a spatial population Leslie-type model and an implicit model of habitat fragmentation. An original approach of elasticity permits to identify which types of element and boundary influence the most population viability according to the wood fragmentation degree. The studied species is a corridor forest insect sensitive to fragmentation (Abax parallelepipedus, Coleoptera, Carabidae). We show that a single large patch of wood is better than several small patches for the population viability.

Animals↗
PubMed2003

Population-level ecological risk assessment of planar polychlorinated aromatic hydrocarbons in great cormorant (Phalacrocorax carbo) around Tokyo Bay, Japan.

Assessment of population-level ecological risk posed by planar polychlorinated aromatic hydrocarbons (p-PCAHs; including polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and dioxintike polychlorinated biphenyls) in sediment of Tokyo Bay (Japan) and rivers via fish ingestion to the great cormorant (Phalacrocorax carbo) population was conducted by means of a probabilistic approach. Population decline risk was used as an indicator of population-level effects and compared with other indicators of effects. The increment of egg mortality risk posed by current p-PCAH levels was estimated to be 11.7%. This risk was interpreted in terms of both the increase of the risk of population decline in a 10-year period on a recently abundant cormorant population, and the reduction in population growth rate (r). Population decline risks of 20% and below were estimated to be 16% for the reference population and 32% for the exposed population, whereas the reduction in r was estimated to be 10%. The risk expressed in terms of population viability is a more susceptible measure and a more easily understandable indicator than both egg mortality risk as an individual-level risk and the reduction in r. Translating the effects due to pollutants into the risk on population viability will make ecological risk assessment more conductive to risk management.

Animals↗
PubMed1986

Comparative toxicity of the cardiovascular toxin allylamine to porcine aortic smooth muscle and endothelial cells.

This study supports a recent hypothesis that the cardiovascular toxin, allylamine, is toxic to smooth muscle cells of large elastic arteries (aorta). Cultures of the porcine aortic smooth muscle, endothelial, and fibroblastic cells were exposed to varying concentrations of allylamine ranging from 5 microM to 340 microM. Monitored cytotoxic and cytolytic activities demonstrated that final concentrations of 60 microM allylamine decreased cell population viability of smooth muscle cells as much as 50%. Viability decreased approximately linearly with increasing concentrations of allylamine including spontaneous lysing of smooth muscle cells at 90 microM. Endothelial cells were more resistant to lower concentrations of allylamine requiring 90 microM to decrease cell population viability by 50%. In contrast, fibroblastic cells were very resistant to lower concentrations of allylamine. The specific lytic response of these cells in culture, measured by release of [3H]thymidine, gave findings parallel to the viability studies, i.e. at 100 microM allylamine smooth muscle cells demonstrated 75% specific lysis while endothelial cells showed 29%. Growth studies of cells surviving an 8-h exposure to allylamine indicate that surviving endothelial cells have better growth characteristics than surviving smooth muscle cells; both cell lines are also apparently injured at concentrations of allylamine much lower than the CT50. These studies show that of the cellular components of the vascular wall, smooth muscle cells appear to be the most sensitive to the toxic effects of allylamine.

Allylamine↗
PubMed2006

Harvest reserves reduce extinction risk in an experimental microcosm.

Overharvesting by humans threatens a substantial fraction of endangered species. Reserves have recently received enormous attention as a means of better conserving harvested resources, despite limited empirical evidence of their efficacy. We used manipulated microcosms to test whether reserves reduce extinction risk in mobile populations of harvested Tetrahymena thermophila, a ciliate. Here we show that patterns of population distribution inside and outside reserves can be accurately predicted on the basis of simple models of diffusion coupled with logistic controls on local population growth. No extinctions occurred in eight experimental trials with reserves, whereas extinction occurred in seven of eight trials without reserves, as predicted by population viability models based on stochastic population processes. These results suggest that marine reserves may be an effective means of improving long-term viability in heavily harvested fish species.

Animals↗
PubMed2002

Bet-hedging applications for conservation.

One of the early tenets of conservation biology is that population viability is enhanced by maintaining multiple populations of a species. The strength of this tenet is justified by principles of bet-hedging. Management strategies that reduce variance in population size will also reduce risk of extinction. Asynchrony in population fluctuations in independent populations reduces variance in the aggregate of populations whereas environmental correlation among areas increases the risk that all populations will go extinct. We review the theoretical rationale of bet-hedging and suggest applications for conservation management of least terns in Nebraska and grizzly bears in the northern Rocky Mountains of the United States. The risk of extinction for least terns will be reduced if we can sustain the small central Platte River population in addition to the larger population on the lower Platte. Similarly, by restoring grizzly bears to the Bitterroot wilderness of Idaho and Montana can reduce the probability of extinction for grizzly bears in the Rocky Mountains of the United States by as much as 69-93%.

Altitude↗
PubMed2005

Autotoxicity in Lolium rigidum: analyzing the role of chemically mediated interactions in annual plant populations.

Autotoxicity is the chemical influence of one plant on the development of individuals of the same species. Autotoxicity in perennial plants can be a useful mechanism to avoid future conspecific competitors, however, the ecological role of autotoxicity in annuals, if any, remains uncertain. In this paper, we analyse the autotoxic phenomenon in Lolium rigidum, an annual, self-incompatible grass from semi-arid environments suspected to be autotoxic, and we dissert on the mechanisms of intraspecific interference, carrying out density-dependent experiments with additions of conspecific competitors and plant residues. Our experiments show that chemical interference and resource competition are density-dependent processes that act in opposite directions. Inhibitory chemical interference increases at low population densities whereas competition for resources intensifies at high densities. Based on these results, the manuscript theorizes on the ecological role of the autotoxic phenomenon in short-lived plants. We hypothesize that autotoxicity enhances population viability by restraining the development of populations with few individuals, which should decrease the chances of outcross and experience inbreeding depression. If this hypothesis proves true, it could contribute to explain the unusually high within-population diversity encountered in this species, which contrasts with reported values from other similar wind-pollinated, self-incompatible grasses.

Lolium↗
PubMed1998

[The population-demographic structure and the prevalence of multifactorial diseases affecting the viability of the population of Kursk region].

A significant effect of the population structure on the incidence of multifactorial diseases affecting the viability of the adult population was found in rural districts of Kursk oblast. The diseases studied were chronic bronchitis, pulmonary emphysema, pneumosclerosis, and atherosclerosis. The incidence of multifactorial pathology increased with an increase in the homozygosity level of district populations. On average, the population structure affected the incidence of multifactorial diseases by 30-50%.

Adult↗
PubMed2006

The impact of increased environmental stochasticity due to climate change on the dynamics of asiatic wild ass.

Theory proposes that increased environmental stochasticity negatively impacts population viability. Thus, in addition to the directional changes predicted for weather parameters under global climate change (GCC), the increase in variance of these parameters may also have a negative effect on biodiversity. As a case study, we assessed the impact of interannual variance in precipitation on the viability of an Asiatic wild ass (Equus hemionus) population reintroduced in Makhtesh Ramon Nature Reserve, Israel. We monitored the population from 1985 to 1999 to determine what environmental factors affect reproductive success. Annual precipitation during the year before conception, drought conditions during gestation, and population size determined reproductive success. We used the parameters derived from this model to assess population performance under various scenarios in a Leslie matrix type model with demographic and environmental stochasticity. Specifically, we used a change in the precipitation regime in our study area to formulate a GCC scenario and compared the simulated dynamics of the population with a no-change scenario. The coefficient of variation in population size under the global change scenario was 30% higher than under the no-change scenario. Minor die-offs (> or = 15%) following droughts increased extinction probability nearly 10-fold. Our results support the idea that an increase in environmental stochasticity due to GCC may, in itself, pose a significant threat to biodiversity.

Animals↗
PubMed2026

Ambrosia beetle invasions are structured by inbreeding, intraspecific hybridisation, and bridgeheads.

When invasive populations establish in regions far from their origin, they may accumulate deleterious mutations that limit population viability and later expansion. Invasions stemming from such bridgehead populations may experience further sequential bottlenecks. However, deleterious mutations can be masked or eliminated when populations outbreed with other lineages. Here, we analyse global invasions of a species complex of persistently inbreeding ambrosia beetles, using genomic data (N=247) from invasive populations in Africa, North America and Australia, and from native populations in Asia. We mostly focus on one species of this complex (Euwallacea fornicatus) which poses a severe threat to tree species worldwide and is rapidly expanding its global range. We uncover a single lineage of this species across California, South Africa, and Western Australia, involving an invasive bridgehead and containing almost no nuclear genetic variation. In South Africa we identify a second lineage that has repeatedly hybridised with the first lineage. Genetic patterns in the native range indicate that such opportunistic outbreeding may be common. Despite lacking nuclear variation, the first lineage contained two CO1 haplotypes that were also observed in every hybrid lineage, pointing to heteroplasmy and possible hybrid origins of this lineage. Native populations had fewer missense mutations than invasive populations, indicating that opportunistic outbreeding may help purge fixed deleterious mutations when local lineage diversity is high. These findings highlight the importance of outbreeding even when inbreeding is common, and they demonstrate the biosecurity threat posed by subsequent gene flow into invasive populations.

Journal Article↗
PubMed2002

Evaluating the ecological significance of laboratory response data to predict population-level effects for the estruarine amphipod Ampelisca abdita.

Ten-day acute mortality of the benthic amphipod Ampelisca abdita is used in a number of regulatory, research, and monitoring programs to evaluate chemical contamination of marine sediments. Although this endpoint has proven to be valuable for characterizing the relative toxicities of sediments, the significance of acute mortality with respect to population viability has not yet been established. In this study, population modeling along with empirical extrapolation were used to describe a relationship between acute mortality and population-level response of A. abdita. The research involved the performance of a standard 10-d sediment toxicity bioassay and a 70-d full life-cycle chronic population (including reproduction) bioassay exposing A. abdita to sediments spiked with concentrations of the divalent metal cadmium (normalized to acid volatile sulfide) expected to produce a range of biological effects. These data provided age-specific schedules of survival and fecundity that were used to parameterize an age-classified projection matrix model for A. abdita. Measured exposure data and population growth rate estimates, obtained using the demographic information collected during the 70-d assay, were used to develop exposure-response models. These data were also used to develop an empirical relationship between population growth rate (lambda) and acute mortality. This relationship describes how acute data may be used to predict concentrations that produce population-level effects. Model manipulations permit extrapolation of early life-stage mortality (the acute endpoint) to changes in population growth rate. These relationships were used to evaluate a range of ecologically acceptable acute mortality for A. abdita.

Animals↗
PubMed2005

Settling behavior of unpurified Cryptosporidium oocysts in laboratory settling columns.

The settling behavior of fresh and aged unpurified oocysts was examined in settling column suspensions with varied ionic strengths and concentrations of calcium and magnesium. Independent measurements of the size and density of unpurified oocysts were performed to determine a theoretical settling velocity for the test populations. Viability of the oocysts was assessed using a dye permeability assay. Latex microspheres were included to provide a standard by which to assess the settling conditions in the columns. Mean settling velocities for viable oocysts measured in this work were faster than predicted and faster than measured for purified oocysts in other work: 1.31 (+/-0.21) microm/s for viable oocysts from populations having a low percentage of viable oocysts and 1.05 (+/-0.20) microm/s for viable oocysts from populations with a high percentage of viable oocysts. Results were attributed to the higher than previously reported densities measured for oocysts in this study and the presence of fecal material, which allowed opportunity for particle agglomeration. Settling velocity of oocysts was significantly related to the viability of the population, particle concentration, ionic strength, and presence of calcium and magnesium in the suspending medium. Behavior of the latex microspheres was not entirely predictive of the behavior of the oocysts under the test conditions. Viable oocysts may have a greater probability of settling than previously assumed; however, nonviable, and especially nonintact, oocysts have the potential to be significantly transported in water. This work underscores the importance of assessing the viability of oocysts to predict their response to environmental and experimental conditions.

Animals↗