Population Viability Assessment Research Articles

Assumptions about survival estimates and dispersal processes can have severe impacts on population viability assessments

Population viability analysis (PVA) is a central tool for conservation decision-making. To ensure the reliability of PVA projections, it is important to identify factors that can introduce biases. This study addresses two general but overlooked related issues in PVAs that can significantly affect the reliability of their projections. First, we examined the effects of using apparent versus true survival estimates on PVA outcomes. Second, we incorporated emigration and immigration into the models to assess their influence on the accuracy of projections based on each type of survival estimate. To evaluate these concerns, we implemented PVAs structured by age, sex, and breeding status using as a study system a threatened raptor population (Bonelli's eagle, Aquila fasciata) from which apparent and true survival were available (2008–2020). The performances of PVA projections based on each survival type and dispersal process were assessed by evaluating their fit to census data. Our findings revealed that using apparent survival underestimated census data, while true survival showed a considerably better fit. However, models including dispersal processes showed that each survival type may only deliver precise projections at very specific levels of emigration and immigration. Given the potentially large differences found when using true and apparent survival, we suggest that the relevance of this issue should be elevated to that of other widely reported PVA limitations. Recently developed, accessible analytical methods may permit an easier estimation of true survival and dispersal processes. Otherwise, calibrating projections against observed data may be fundamental to test the adequacy of survival estimates.

Body size constrains the annual apparent survival of lekking Great Snipe Gallinago media males of eastern, lowland population

Survival of adult individuals is a key demographic parameter, that is critical for conservation programs of species and evolutionary research focused on life-history traits. Here, we present the estimates of the apparent annual survival of lekking male Great Snipes of the lowland population, breeding in wet meadow habitats in the valley of the Pripyat River. We also investigate individual traits such as body size and body condition, that may influence birds’ survival. The annual apparent survival in the studied population was low (Φ (.) = 0.43), but no change in this parameter was found over the period of 22 years. The chances for survival increased with the body size of an individual. We hypothesize that smaller individuals with shorter bills might face limited foraging options compared to larger birds, which may result in insufficient nutrition during challenging life cycle events such as moulting of primaries combined with preparation for long-distance migration conducted in one non-stop flight. Additionally, the presented results indicate that the wet meadow in the Pripyat River Valley provides suitable breeding habitat for this species with sufficient conservation practices held there, and the low annual apparent survival is probably a life-history trait of this species resulting from a “high pace of life” and elevated metabolic rate. To our knowledge, this study provides the first estimates of the long-term population characteristic for the eastern, lowland population of this species, which could prove helpful in the assessment of population viability for this globally declining species.

Population viability assessment of an endangered raptor using detection/non-detection data reveals susceptibility to anthropogenic impacts.

As the demand for carbon-neutral energy sources increases, so does the need to understand the impacts that these technologies have on the environment. Here, we assess the potential consequences of additional mortality on an Endangered raptor recently exposed to wind farms for the first time, the Black Harrier Circus maurus, one of the world’s rarest harriers. We conduct a population viability assessment using a Bayesian model integrating life-history information and annual reporting rates from detection/non-detection surveys from the South African Bird Atlas Project. Our model estimates a global population of approximately 1300 birds currently declining at 2.3% per year, and one that could collapse in under 100 years, if an average of three to five adult birds are killed annually. This level of mortality may soon exist, given the current rate of fatalities and the number of wind farms planned within the species’ distribution. In addition, we find that the population is sensitive to changes in climate. Our results highlight the critical need for appropriate placement, and adaptive management of wind farms and other infrastructure causing harrier mortality. We also show how detection/non-detection data may be used to infer population dynamics and viability, when population counts are unavailable.

The effects of age on the demography of a perennial plant depend on interactions with size and environment

Abstract Age‐dependence of the demographic rates survival, fecundity and individual growth is a fundamental aspect of population biological theory. Knowledge about plant ageing can also be important for conservation and agriculture as it will improve the accuracy of population viability assessments and long‐term performance assessments in perennial crops. Recent studies show age effects on demographic rates for several plant species, yet much remains to be learned about the patterns and mechanisms of plant ageing, particularly about how age effects interact with the environment and with plant size. We collected age‐and‐size‐based demographic data, as well as individual‐based environmental data, for the perennial herb Plantago lanceolata in Denmark over three annual transitions (4 years). We combined frequent field monitoring of carefully mapped individuals with the underused technique of root histology to determine age of herbaceous plants. We used generalized linear mixed effects models to assess how age, soil properties and year influenced survival, growth and reproduction. Our results show no strong evidence of consistent age declines, rather, we found mostly positive effects of age on vital rates. For all vital rates, i.e. survival, growth, flowering and reproductive output, age effects also differed significantly among years. Additionally, we detected an interactive effect of age and size in the growth model. Size, and temporal and spatial environmental variation also affected vital rates independently of age. Synthesis. Our study shows that age‐dependence of demographic rates can depend both on individual size and environmental variation. These results suggest that a consideration of potential age‐interactions may improve the accuracy of comparative studies of ageing and population projections. Moreover, this study shows that much is still unknown about how plant ageing can be affected by the environment.

Post-emergence survival and dispersal of juvenile Jefferson salamander (Ambystoma jeffersonianum) and their unisexual dependents

Abstract Understanding population demography and dispersal of species at risk is integral for evaluating population viability, identifying causes of decline, and assessing the effectiveness of recovery actions. In pond-breeding amphibians, juvenile survival and dispersal are key components linked to population and metapopulation stability but little is known about this life stage. We use mark-recapture methods to estimate juvenile daily apparent survival, dispersal distance, and initial dispersal orientation during summer and fall dispersal of endangered Ambystoma jeffersonianum and their unisexual dependents (Ambystoma laterale – jeffersonianum). Over four years (2015-2018), 1018 juveniles (612 bisexual, 406 unisexual) were marked and 192 (19%) were recaptured at least once. Total captures varied widely between years, with the highest number of captures (88% of all individuals) occurring in 2017. Cormack-Jolly-Seber estimates of daily apparent survival were low in all years (0.76-0.95) but was higher for unisexuals than bisexuals. The majority of juveniles (71%) did not disperse further than 10-40 m after which movement appeared to cease. While most juveniles remained close to their natal pond, at least 2% of juveniles in 2017 travelled further than 100 m. Dispersal orientation varied by year and there was no difference in either dispersal orientation or distance between bisexual and unisexual individuals. This work is the first to estimate and compare juvenile survival and dispersal of sympatric A. jeffersonianum and A. laterale – jeffersonianum individuals, the results of which help inform population viability assessment and increase our understanding of juvenile dispersal dynamics and habitat use.

Puberty and oestral cycle length in captive female jaguars Panthera onca.

Habitat loss and fragmentation have been leading jaguars to constant conflicts with humans, and as a result, jaguar populations have been declining over the last decades. Captive breeding is often a tool for species conservation, and it is not different for jaguars. However, success is far from optimal due to the lack of basic knowledge about species’ reproductive biology. In the present study, we assessed gonadal hormonal profiles of natural oestral cycles and puberty and compared our data to those of other wild felids. We collected faecal samples from two to seven times per week for 18 months from two adults and three pre-pubertal females. We defined baseline levels for progestins and oestrogens in order to estimate oestrous cycle length and age at puberty. We compared our data with 16 other species through generalized linear model, using weight and genus as two explanatory variables. Cycle length was 38.28 ± 2.52 days, ranging from 25 to 44 days, while sexual maturity was attained within 22 months. Due to our analysis of both hormonal and behavioural data, there is a variation between this research from other studies that employed only behavioural observations. Such difference may be caused by the absence of behavioural oestrous at the peri-pubertal period. When compared to wild felids of similar size, puberty and oestral cycle durations of the jaguar females fell within the same range. Our modelling showed that age at maturity was influenced mostly by size and only Leopardus partially explained the observed variation. Conversely, oestral cycle length did not differ among genera or size categories. Our study adds to the body literature in the reproductive endocrinology of wild felids, and because female gametes are more challenging to collect and preserve, a strong understanding on the female reproductive physiology is essential to assisted reproduction and wild population viability assessment.

Applying science to pressing conservation needs for penguins.

More than half of the world's 18 penguin species are declining. We, the Steering Committee of the International Union for Conservation of Nature Species Survival Commission Penguin Specialist Group, determined that the penguin species in most critical need of conservation action are African penguin (Spheniscus demersus), Galápagos penguin (Spheniscus mendiculus), and Yellow‐eyed penguin (Megadyptes antipodes). Due to small or rapidly declining populations, these species require immediate scientific collaboration and policy intervention. We also used a pairwise‐ranking approach to prioritize research and conservation needs for all penguins. Among the 12 cross‐taxa research areas we identified, we ranked quantifying population trends, estimating demographic rates, forecasting environmental patterns of change, and improving the knowledge of fisheries interactions as the highest priorities. The highest ranked conservation needs were to enhance marine spatial planning, improve stakeholder engagement, and develop disaster‐management and species‐specific action plans. We concurred that, to improve the translation of science into effective conservation for penguins, the scientific community and funding bodies must recognize the importance of and support long‐term research; research on and conservation of penguins must expand its focus to include the nonbreeding season and juvenile stage; marine reserves must be designed at ecologically appropriate spatial and temporal scales; and communication between scientists and decision makers must be improved with the help of individual scientists and interdisciplinary working groups.

Variations in age- and sex-specific survival rates help explain population trend in a discrete marine mammal population.

Understanding the drivers underlying fluctuations in the size of animal populations is central to ecology, conservation biology, and wildlife management. Reliable estimates of survival probabilities are key to population viability assessments, and patterns of variation in survival can help inferring the causal factors behind detected changes in population size. We investigated whether variation in age‐ and sex‐specific survival probabilities could help explain the increasing trend in population size detected in a small, discrete population of bottlenose dolphins Tursiops truncatus off the east coast of Scotland. To estimate annual survival probabilities, we applied capture–recapture models to photoidentification data collected from 1989 to 2015. We used robust design models accounting for temporary emigration to estimate juvenile and adult survival, multistate models to estimate sex‐specific survival, and age models to estimate calf survival. We found strong support for an increase in juvenile/adult annual survival from 93.1% to 96.0% over the study period, most likely caused by a change in juvenile survival. Examination of sex‐specific variation showed weaker support for this trend being a result of increasing female survival, which was overall higher than for males and animals of unknown sex. Calf survival was lower in the first than second year; a bias in estimating third‐year survival will likely exist in similar studies. There was some support first‐born calf survival being lower than for calves born subsequently. Coastal marine mammal populations are subject to the impacts of environmental change, increasing anthropogenic disturbance and the effects of management measures. Survival estimates are essential to improve our understanding of population dynamics and help predict how future pressures may impact populations, but obtaining robust information on the life history of long‐lived species is challenging. Our study illustrates how knowledge of survival can be increased by applying a robust analytical framework to photoidentification data.

Population Viability of Endangered Lost River Sucker and Shortnose Sucker and the Effects of Assisted Rearing

Abstract The Lost River Sucker Deltistes luxatus and Shortnose Sucker Chasmistes brevirostris are two narrowly endemic fish species in the upper Klamath Basin of southern Oregon and northern California. Both species have been federally listed as endangered pursuant to the U.S. Endangered Species Act since 1988 because of dramatic declines in abundance and distribution. In Upper Klamath Lake, Oregon, both species have only recruited a single cohort to the adult populations since that time. Most individuals in this population are at or older than the expected life span of the species. Consequently, the U.S. Fish and Wildlife Service and the Klamath Tribes have initiated assisted rearing efforts to stabilize the population. However, it is unclear how quickly these populations might become extirpated and how assisted rearing might alter population trajectories. We modeled the potential for extinction and recovery of the populations of endangered Lost River Sucker and Shortnose Sucker in Upper Klamath Lake. We simulated population trajectories over the next 50 y with a stochastic population viability assessment approach. Projections indicate that if population trajectories do not change, the Shortnose Sucker population may decline by 78% to number < 5,000 in 10 y and become completely extirpated within the next 30 (18.6% probability) to 40 y (99% probability). The two Lost River Sucker populations have a greater likelihood to remain extant after 50 y, with only 1% probability of extinction given our scenarios and assumptions, but the populations are likely to number fewer than 1,000 individuals. Our results also suggest that rearing of Klamath Lake sucker species in a controlled environment for augmenting the natural population will be effective in reducing extirpation probabilities over the next 50 y if survival to recruitment can be achieved, but a long-term effort of at least 40 y will be required. The necessity of long-term augmentation to ensure population persistence in the absence of natural recruitment underscores the urgent need to determine and address the causes of recruitment failure in the wild.

Evidence of reproductive senescence of released individuals in a reinforced bird population

In free-ranging populations, age-dependent variation in fitness related parameters, in particular the pattern of senescence, has major eco-evolutionary implications and potential influence on population dynamics. Despite the recent surge of studies of senescence in the wild, senescence patterns in species for which population dynamics assessments are crucial, such as translocated populations, remain virtually unexplored. Based on a 15-year nest survey of a North-African Houbara bustard population in Morocco, we investigated age variation in the breeding performance of captive-bred females released in the wild. We identified 781 females, from 1 to 10years of age, on 1094 nests. We examined how age influenced nest initiation date, clutch size, egg volume, daily nest survival and daily brood survival, as well as whether age-dependent patterns varied according to environmental conditions. Most breeding parameters exhibited variation, suggesting an increase in breeding performance with age in young females (those from 1 to 3years old). In older females (>7–8years old), the egg volume and clutch size decreased with age, in concordance with expectations from senescence theories and previous empirical results obtained from captive Houbara bustards. Finally, our analysis uncovered a significant interaction between age and the amount of precipitation prior to the breeding season on clutch size, suggesting differential abilities of females of different ages to increase their breeding investment. Our study suggests that life histories in translocated individuals are not affected by translocation protocols and provides insights for implementing age dependencies in population viability assessments.

Importance of demographic surveys and public lands for the conservation of eastern hellbenders Cryptobranchus alleganiensis alleganiensis in southeast USA.

Comparisons of recent and historic population demographic studies of eastern hellbenders Cryptobranchus alleganiensis alleganiensis have identified significant population declines and extirpations associated with habitat degradation, poor water quality and disease, leading to nomination as a candidate for listing under the Endangered Species Act. However, populations in the southern Appalachian region of the range have received less attention despite relatively high levels of watershed protection due to the establishment of federally protected National Forest and National Park public lands. These watersheds likely represent some of the best remaining available habitat, yet the lack of published studies make assessment of population stability and viability very difficult. Our objectives were to (1) conduct a capture-mark-recapture (CMR) demographic study and a point transect survey on the Hiwassee River in Tennessee which is designated a National Scenic River, and is largely contained within the Cherokee National Forest, (2) quantify the size structure of the population, (3) compare abundance, survival and recruitment with historic and contemporary hellbender populations across the range, (4) assess the importance of this population and the significance of National Forest and National Park lands in the context of hellbender population conservation in the southeastern United States. We detected all age classes present, with larval hellbenders comprising 21.5% of captures. Using a combination of static life table and CMR methods, we determined that survival rates during the first year were low (~10%), but were high (68–94%) for taggable sized hellbenders. Density of hellbenders at the study site was very high (84 taggable sized hellbenders per 100m of river) compared to recent demographic studies conducted in other regions of the range. We detected hellbenders over ~28 km of river, with a mean density of 23 taggable sized hellbenders per 100m of river, and a total population estimate of 6440 taggable hellbenders. National Forest and National Park lands are likely to continue to play a particularly important role in providing suitable habitat for hellbenders in the southern Appalachians. In fact, only six of 21 known hellbender locations in Tennessee appear to show consistent larval recruitment, all of which are located within or adjacent to National Forest or National Park land.

Andean Condor (Vultur gryphus) in Ecuador: Geographic Distribution, Population Size and Extinction Risk.

The Andean Condor (Vultur gryphus) in Ecuador is classified as Critically Endangered. Before 2015, standardized and systematic estimates of geographic distribution, population size and structure were not available for this species, hampering the assessment of its current status and hindering the design and implementation of effective conservation actions. In this study, we performed the first quantitative assessment of geographic distribution, population size and population viability of Andean Condor in Ecuador. We used a methodological approach that included an ecological niche model to study geographic distribution, a simultaneous survey of 70 roosting sites to estimate population size and a population viability analysis (PVA) for the next 100 years. Geographic distribution in the form of extent of occurrence was 49 725 km2. During a two-day census, 93 Andean Condors were recorded and a population of 94 to 102 individuals was estimated. In this population, adult-to-immature ratio was 1:0.5. In the modeled PVA scenarios, the probability of extinction, mean time to extinction and minimum population size varied from zero to 100%, 63 years and 193 individuals, respectively. Habitat loss is the greatest threat to the conservation of Andean Condor populations in Ecuador. Population size reduction in scenarios that included habitat loss began within the first 15 years of this threat. Population reinforcement had no effects on the recovery of Andean Condor populations given the current status of the species in Ecuador. The population size estimate presented in this study is the lower than those reported previously in other countries where the species occur. The inferences derived from the population viability analysis have implications for Condor management in Ecuador. This study highlights the need to redirect efforts from captive breeding and population reinforcement to habitat conservation.

Effects of a range expansion on adaptive and neutral genetic diversity in dispersal limited Hazel grouse (Bonasa bonasia) in the French Alps

Biogeographic range expansions, when related to dispersal limitation, may have counter intuitive effects on genetic diversity. At range margins the relative roles of demographic changes, connectivity and genetic diversity need to be integrated for a successful assessment of population viability. Historically the Hazel grouse (Bonasa bonasia) in France was found in the north of the French Alps and also in a disjunct population in the nearby Jura Mountains. The species has recently undergone a range expansion in a north to south axis in the Alps. Local population size estimates and migration patterns during expansion have previously been studied. In this study, we performed genotyping at neutral (microsatellite) and adaptive (MHC) genetic markers in Hazel grouse. We compared diversity and differentiation (FST and DEST) at three sampling localities along the expansion axis in the French Alps and Jura, as well as at two sampling localities in Sweden, where the population has had a long-term continuous and stable distribution. Strong serial founder effects were found between the French localities, resulting in stronger isolation further south, with a relatively high neutral differentiation (pair-wise FST = 0.117). However, the loss of adaptive diversity MHC was slight. No adaptive differentiation (MHC DEST = −0.015) was observed, thus, the French localities can be considered uniform units with regard to MHC diversity, a criterion to treat populations in these localities as a management unit.

Current conservation status of the Blue Swallow Hirundo atrocaerulea Sundevall 1850 in Africa

The global Blue Swallow Hirundo atrocaerulea was classified as Vulnerable in 2010 on account of its small and rapidly declining population estimated at less than 1 500 pairs. We undertook this study to gain a better understanding of the current status and threats facing this migratory species. Three previously unknown areas that might be part of the species' non-breeding range were identified in Kenya and northern Tanzania. Within its breeding range we identified three previously unknown areas of potentially suitable habitat, one in Tanzania and two in Malawi, which require further exploration. Population viability assessment predicted that the Blue Swallow population will decline by 8% in 10 years. The overall probability of extinction of the species in the wild is 3%. Minimum viable population size analysis suggests that a goal for the long-term conservation of the Blue Swallow should be to mitigate current threats that are driving declines such that the population increases to a minimum of 3 600 individuals. This should consist of at least 900 individuals in each of the four clusters identified, along with a minimum of 500 individuals in at least one of the meta-populations per cluster. The four clusters are located in (1) the southeasten Democratic Republic of the Congo, (2) highlands of southern Tanzania and northern Malawi, (3) eastern highlands of Zimbabwe and (4) South Africa and Swaziland. The current proportions of the Blue Swallow population in strictly protected and unprotected areas on their breeding grounds are 53% and 47%, respectively, whereas on their non-breeding grounds the corresponding percentages are 25% and 75%, respectively. Our reassessment of the Blue Swallow's risk of extinction indicates that it continues to qualify as Vulnerable according to the IUCN/SSC criteria C2a(i).

Життєвість (віталітет) як інтегральний показник стану популяції у рослин

To further unification of approaches to the terminology and methodology of research in the demographic ecology, it is important to seek consensus on a number of issues, including the concept of “population vitality”. There is a need to develop a consolidated approach to the assessment of a population-based set of characteristics – individual and group. Based on current views, we can assume that the vitality of population is an integral characteristic that reflects the current state of a population on the basis of major individual and group parameters of structure, growth, development and reproduction. Vitality represents the actual position of population in the realized ecological niche and corresponds to the norm of reaction that reflects actual habitat conditions at a particular time. The main parameters to establish the vitality of a population are its size, age, vital and sex structure, population density, the intensity of generative and vegetative propagation, phytomass and others. Evaluation of the vitality does not provide long-term prognosis instead of population viability, which means the establishment of perspectives. Monitoring of population vitality should form the basis for population viability assessment. Keywords: plant population, vitality, viability.

Network modularity reveals critical scales for connectivity in ecology and evolution

For nearly a century, biologists have emphasized the profound importance of spatial scale for ecology, evolution and conservation. Nonetheless, objectively identifying critical scales has proven incredibly challenging. Here we extend new techniques from physics and social sciences that estimate modularity on networks to identify critical scales for movement and gene flow in animals. Using four species that vary widely in dispersal ability and include both mark-recapture and population genetic data, we identify significant modularity in three species, two of which cannot be explained by geographic distance alone. Importantly, the inclusion of modularity in connectivity and population viability assessments alters conclusions regarding patch importance to connectivity and suggests higher metapopulation viability than when ignoring this hidden spatial scale. We argue that network modularity reveals critical meso-scales that are probably common in populations, providing a powerful means of identifying fundamental scales for biology and for conservation strategies aimed at recovering imperilled species.

A ‘fragile cell’ sub-population revealed during cytometric assessment ofSaccharomyces cerevisiaeviability in lipid-limited alcoholic fermentation

To show that in anaerobic fermentation with limiting lipid nutrients, cell preparation impacts the viability assessment of yeast cells, and to identify the factors involved. Saccharomyces cerevisiae viability was determined using propidium iodide staining and the flow cytometry. Analyses identified intact cells, dead cells and, under certain conditions, the presence of a third subpopulation of apparently damaged cells. This intermediate population could account for up to 40% of the entire cell population. We describe, analyse and discuss the effects of different solutions for cell resuspension on the respective proportion of these three populations, in particular that of the intermediate population. We show that this intermediate cell population forms in the absence of Ca(2+)/Mg(2+). Cell preparation significantly impacts population viability assessment by FCM. The intermediate population, revealed under certain conditions, could be renamed as 'fragile cells'. For these cells, Ca(2+) and Mg(2+) reduce cell membrane permeability to PI. This is the first study that analyses and discusses the factors influencing the formation of an intermediate population when studying viability in yeast alcoholic fermentation. With a wider application in biological research, this study provides important support to the relatively new questioning of propidium iodide staining as a universal cell death indicator.

Minimum prey and area requirements of the Vulnerable cheetahAcinonyx jubatus: implications for reintroduction and management of the species in South Africa

AbstractIn South Africa there are efforts to manage reintroduced subpopulations of the Vulnerable cheetahAcinonyx jubatusin small reserves (10–1,000 km2) as a managed metapopulation. We estimated areas required to support cheetahs given varying prey densities, prey profiles and presence/absence of competing predators. A recent population and habitat viability assessment indicated that 20 subpopulations of 10 cheetahs or 10 subpopulations of 15 cheetahs are required to retain 90% of the heterozygosity of free-ranging cheetahs and to overcome stochastic events in the absence or presence of lionsPanthera leo, respectively. We estimate that 203 ± SE 42 km2(range 48–466 km2) is required to support 10 cheetahs in the absence of lions, whereas 703 ± SE 311 km2(166–2,806 km2) is required to support 15 cheetahs given equal numbers of lions, and 2,424 ± SE 890 km2(727–3,739 km2) given equal numbers of leopardsPanthera pardus, spotted hyaenasCrocuta crocuta, wild dogsLycaon pictusand lions. Existing subpopulations of cheetahs generally occur at densities higher than our mean predicted densities but usually within the range of predicted densities. The large area requirements of cheetahs have implications for the development of the managed metapopulation. Sourcing reintroduction sites of the sizes required to support recommended subpopulation sizes will be difficult. Consequently, innovative measures to increase the carrying capacity of reserves for cheetahs and/or to enlarge reserves will be required. Managers may be forced to stock cheetahs close to or beyond the carrying capacity of their reserves. Consequently, careful management of reintroduced subpopulations will be required to prevent declines in prey populations.

Patterns of gastro‐intestinal parasites and commensals as an index of population and ecosystem health: the case of sympatric western chimpanzees (Pan troglodytes verus) and guinea baboons (Papio hamadryas papio) at Fongoli, Senegal

The exponential decline of great apes over the past 50 years has resulted in an urgent need for data to inform population viability assessment and conservation strategies. Health monitoring of remaining ape populations is an important component of this process. In support of this effort, we examined endoparasitic and commensal prevalence and richness as proxies of population health for western chimpanzees (Pan troglodytes verus) and sympatric guinea baboons (Papio hamadryas papio) at Fongoli, Senegal, a site dominated by woodland-savanna at the northwestern extent of chimpanzees' geographic range. The small population size and extreme environmental pressures experienced by Fongoli chimpanzees make them particularly sensitive to the potential impact of pathogens. One hundred thirty-two chimpanzee and seventeen baboon fecal samples were processed using sodium nitrate floatation and fecal sedimentation to isolate helminth eggs, larvae, and protozoal cysts. Six nematodes (Physaloptera sp., Ascaris sp., Stronglyloides fuelleborni, Trichuris sp., an unidentified hookworm, and an unidentified larvated nematode), one cestode (Bertiella sp.), and five protozoans (Iodamoeba buetschlii, Entamoeba coli, Troglodytella abrassarti, Troglocorys cava, and an unidentified ciliate) were detected in chimpanzee fecal samples. Four nematodes (Necator sp., S. fuelleborni, Trichuris sp., and an unidentified hookworm sp.), two trematodes (Shistosoma mansoni and an unidentified fluke), and six protozoans (Entamoeba histolytica/dispar, E. coli, Chilomastix mesnili, Balantidium coli, T. abrassarti, and T. cava) were detected in baboon fecal samples. The low prevalence of pathogenic parasite species and high prevalence of symbiotic protozoa in Fongoli chimpanzees are indicative of good overall population health. However, the high prevalence of pathogenic parasites in baboons, who may serve as transport hosts, highlight the need for ongoing pathogen surveillance of the Fongoli chimpanzee population and point to the need for further research into the epidemiology and cross-species transmission ecology of zoonotic pathogens at this site.

Joint effects of inverse density-dependence and extreme environmental variation on the viability of a social bird species

Environmental stochasticity and density-dependence can have critical synergetic effects on population dynamics, especially when dealing with threatened species. In this study, we examine the effects of these interactions on the dynamics of a vulnerable bird species, the Dalmatian pelican (Pelicanus crispus). We conducted demographic analysis and population dynamics modelling of the Amvrakikos pelican population (western Greece) based on a 20-y dataset. Results indicated that annual juvenile survival probability is low (mean = 0.65) and varies according to both negative (regulation) and positive (Allee effect) density-dependent processes. In contrast, adult survival is relatively high (mean = 0.95) and less variable. Deterministic and stochastic population dynamics models based on means, inter-annual variances, and covariances between vital rates revealed that the population is increasing deterministically. Simulations of the extinction risk for the study population and also for various population sizes revealed that short-term extinction risk remains extremely low, even for very small populations of the species. However, when we considered the possibility of rare catastrophic events and their interactions with density-dependence patterns, the projected extinction risk increased dramatically, especially for small populations. Given that many European Dalmatian pelican populations are small, most of them could be at risk for local extinction. Our results illustrate the critical and general importance of considering interactions between all potential factors of extinction in population viability assessments.