Finite Population Growth Rate Research Articles

Using state‐space models to estimate recreational angling effort and infer processes that regulate angler dynamics

AbstractObjectiveState‐space models are a flexible modeling approach and are often fit to ecological time series data exhibiting temporal autocorrelation. Traditionally, angler effort data collected using on‐site creel surveys are analyzed using design‐based methods. With some exceptions, state‐space models are rarely used to model creel survey data that are also generally a time series of temporally autocorrelated counts.MethodsIn this study, we demonstrated how to fit state‐space models to a time series of angler counts in 11 sections of three trout fisheries in Idaho. The basic model was extended to make inference about processes that may regulate angling dynamics, such as “population growth rate” of angling effort and recreational carrying capacity.ResultEstimated angling effort varied from 21,179 h in the lowermost section of the Henrys Fork Snake River to 199,457 h in the uppermost section of the South Fork Snake River. The finite population growth rate of angling effort was 1.82 when transitioning from a weekday to a weekend, suggesting that angling effort was 1.82 times greater, on average, on Saturdays than on Fridays, and the population growth rate was 0.38 (i.e., 0.38 times smaller) when transitioning from a Sunday to a Monday. Estimated carrying capacity among fishery sections varied from 129 daily hours of angling effort on the Big Lost River to 693 h on the middle section of the South Fork Snake River. Carrying capacity was 1.88 times higher on fishery sections that had ≥0.5 access points/km than on sections with <0.5 access points/km.ConclusionThe state‐space models used in this study can be modified or extended to fit a variety of data types or can be used to evaluate additional hypotheses regarding the angling process.

Hidden demographic impacts of fishing and environmental drivers of fecundity in a sea turtle population.

Fisheries bycatch is a critical threat to sea turtle populations worldwide, particularly as turtles are vulnerable to multiple gear types. The Canary Current is an intensely fished region, yet there has been no demographic assessment integrating bycatch and population management information of the globally significant Cabo Verde loggerhead turtle (Caretta caretta) population. Using Boa Vista island (Eastern Cabo Verde) subpopulation data from capture-recapture and nest monitoring (2013-2019), we evaluated population viability in combination with estimated regional bycatch rates (2016-2020) in longline, trawl, purse-seine and artisanal fisheries. We further evaluated current nesting trends in the context of bycatch estimates, existing hatchery conservation measures, and environmental (net primary productivity) variability in turtle foraging grounds. Current bycatch mortality rates present a risk of near extinction this century, when projecting the Boa Vista subpopulation with matrix population models. Bycatch reduction could increase finite population growth rate by 1.95%, and 1.76% for longline fisheries alone. Hatchery conservation increases hatchling production and reduces extinction risk, but cannot achieve population growth alone. Short-term increases in nest counts (2013-2021), putatively driven by temporary increases in net primary productivity, may be crucially masking ongoing long-term population declines. When fecundity was linked to net primary productivity, our hindcast models simultaneously predicted these opposing long-term and short-term trends. Consequently, our results show conservation management must diversify from land-based management. The masking effect we found has broad-reaching implications for monitoring sea turtle populations worldwide, demonstrating the importance of directly estimating adult survival and that nest counts might inadequately reflect underlying population trends. This article is protected by copyright. All rights reserved.

Demographic analyses reveal differential biological vulnerability in four Southwestern Atlantic skates

More than 33 skate species have been registered in the Southwestern Atlantic Ocean (SAO) 34°S, where hotspots of the endemic threatened marine chondrichthyans with high scientific and conservation priorities have been detected. The lack of species-specific landing data highlights the importance of biological data-based methods to determine the vulnerability and productivity of skate species. In this work, we estimated the demographic parameters for the skates Atlantoraja castelnaui, Rioraja agassizi, Sympterygia bonapartii, and Zearaja brevicaudata in SAO, by implementing Leslie matrix models. The finite rate of population growth ( ʎ) for the four skate's species ranged from 1.036 ( Z. brevicaudata) to 1.196 ( R. agassizi). Elasticity analyses and the performance of different harvest strategies show that reducing juvenile catches appears to be one of the most effective management actions for these species since they result in higher survivorship of age classes with more influence in λ. Differences in the biological productivity of the skates suggest that, to achieve sustainable exploitation of skates, the commitment of all stakeholders to improve species-level information is necessary.

Demographic Analysis of Shortfin Mako Shark (Isurus oxyrinchus) in the South Pacific Ocean.

The shortfin mako shark (Isurus oxyrinchus) demonstrates low productivity and is thus relatively sensitive to fishing. Natural mortality (M) and fishing mortality (F) data are critical to determine their population dynamics. However, catch and fishing effort data are unavailable for this species in the South Pacific Ocean, making stock assessments difficult. Demographic quantitative methods aid in analyzing species with limited data availability. We used a two-sex stage-structured matrix population model to examine the demographic stock status of mako sharks. However, data-limited models to determine fishery management strategies have limitations. We performed Monte Carlo simulations to evaluate the effects of uncertainty on the estimated mako shark population growth rate. Under unfished conditions, the simulations demonstrated that the mako sharks showed a higher finite population growth rate in the 2-year reproductive cycle compared to the 3-year reproductive cycle. Protecting immature mako sharks led to a higher population growth rate than protecting mature mako sharks. According to the sex-specific data, protecting immature male and female sharks led to a higher population growth rate than protecting mature male and female sharks. In conclusion, sex-specific management measures can facilitate the sustainable mako shark conservation and management.

Intraspecific competition and persistence in Acanthoscelides macrophthalmus (Coleoptera: Chrysomelidae): an experimental analysis in a stage‐structured population

AbstractIntraspecific competition is an ecological process that can affect the structure of populations with important consequences for population persistence. In this study, we investigated (in the larval stage) the effect of intraspecific competition in the seed‐feeding beetle Acanthoscelides macrophthalmus on its population structure and persistence. By using Leslie matrices, which are useful to project future population sizes of structured populations, we conducted demographic analysis when competition was (more than one larva per seed) and was not (one larva per seed) present. The hypothesis that competition reduces the finite rate of population growth, the survival of the immatures and the fecundity of females, influencing population persistence, was tested. To understand whether intraspecific competition is a common process in this system, the oviposition pattern was also studied. We found that in the presence of competition, the larvae from the third instar were smaller than those in the absence of competition and, in the presence of competition, fewer larvae reached the adult stage. Larval survival was lower in the presence of competition, particularly from the third larval stage until the pupal stage, and the fecundity of females was also reduced in the presence of competition, which affected the population structure. Although we showed that populations may either grow geometrically or go extinct in absence and presence of competition, respectively, the finite rates of population increase did not differ from 1.0 when compared to the estimated confidence intervals. Therefore, although larval competition may affect the structure of this seed‐feeding beetle, there is no clear evidence that this ecological process can negatively affect its persistence. Furthermore, most seeds with eggs had just one egg per seed, which suggests that competition should occur with low frequency under natural conditions.

Some Population Aspects of Common Tern Sterna hirundo Breeding in Algeria at a Small Mediterranean Island (East Coast of Algeria)

Abstract We present the first detailed study of population dynamics, breeding biology and egg measurement of Common Terns. During six years (from 2004 to 2009) of monitoring, from mid-May to mid-August, 74 Common Terns individual were recorded at Laouinet small island, El Tarf, northeast of Algeria, witha finite population growth rate that indicated an alarming population decline(λ = -0.62: Lambda). Sterna hirundo build its nests (n = 37) in the northeast at a mean distance of 7.58 m from the closest edge of rocks. The nests were closed and ovoid, constituted mainly of mussel shells Sandpit, stems and leaves. Incubation was performed by pairs of common tern and lasted 25.5 ±3.4 days. We recorded a clutch size of 1 to 3 eggs with mean clutch size of 2.45±0.65 (41.24±0.83 × 30.46±0.62 mm). The egg parameters (volume, mass, shape index) varied between the six years of the study. The egg volume (19.24±0.87) depended more on egg width (30.46±0.62), however the egg shape (0.73±0.20) depended negatively on the egg length (41.24±0.83) but not on the egg width. Our results also showed a stabilized hatching success and a best estimation of breeding success. The hatching success did not vary between years: 70.5% in 2004, 68.75% in 2005, 71.42% in 2006, 71.42% in 2007, 69.23% in 2008 and 69.23% in 2009.

Population Growth Rates of Aedes atropalpus (Diptera: Culicidae) Are Depressed at Lower Temperatures Where Aedes japonicus japonicus (Diptera: Culicidae) Are Naturally Abundant in Rock Pools

Recent studies report extensive reductions in the abundance of the North American rock pool mosquito, Aedes atropalpus (Diptera: Culicidae), following the invasion of Ae. japonicus japonicus in the United States. Although developmental temperature is recognized as an important component of the invasion biology of Ae. j. japonicus, its impacts on the population growth and fitness of Ae. atropalpus remain largely undefined. In this study we reared Ae. atropalpus larvae at three temperature ranges reflecting ecologically important temperatures in natural rock pools: a low temperature range (mean: 19°C) where Ae. j. japonicus is common and Ae. atropalpus is often rare, a middle temperature range (mean: 25°C) where both species are naturally found in similar relative abundances, and a higher temperature range (mean: 31°C) where Ae. atropalpus is the dominant species. We measured survival, development time, wing length, and fecundity to calculate a finite population growth rate at each temperature. Our results indicate that Ae. atropalpus population growth suffers in colder rock pools, which informs the perceived displacement of the species in temperate habitats. The population growth rate was highest in the middle temperature range, but not significantly higher than in the highest temperature range used in this study. The developmental success of Ae. atropalpus at the intermediate temperature range suggests that competition with Ae. j. japonicus in rock pools within that range may significantly impact natural Ae. atropalpus populations.

Erratum

The Journal of Wildlife ManagementVolume 82, Issue 8 p. 1808-1808 ErratumFree Access Erratum This article corrects the following: Greater sage-grouse population trends across Wyoming David R. Edmunds, Cameron L. Aldridge, Michael S. O'Donnell, Adrian P. Monroe, Volume 82Issue 2The Journal of Wildlife Management pages: 397-412 First Published online: October 27, 2017 First published: 10 September 2018 https://doi.org/10.1002/jwmg.21560Citations: 3AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Edmunds, D. R., C. L. Aldridge, M. S. O'Donnell, and A. P. Monroe. 2018. Greater sage-grouse population trends across Wyoming. Journal of Wildlife Management 82:397–412. In this article, we calculated the intrinsic per capita rate of growth (r; Dennis et al. 1991, Morris and Doak 2002), which we then transformed to the finite rate of population growth (λ) based on the conversion λ = er (Case 2000, Mills 2013). However, we made an error in the reporting of λ for several models, including reporting the density-dependent effect for the Ricker (Ricker 1954, Dennis and Taper 1994) and Gompertz (Jacobson et al. 2004) models rather than the overall λ estimate. We also reported the difference in λ between trend and numbered intervals for the period effects models rather than the average of the λ estimates across intervals. These errors resulted from reporting the incorrect model coefficients from the generalized linear model (glm) output and resulted in values that were less than the λ estimates in most cases but did not alter our primary conclusion that fine-scale population trends may differ from large-scale trends. The authors regret these errors. These 2 errors resulted in incorrect λ estimates reported in tables 1–4, S1, and S3–S7, and shown in figures 3–6. The errors were embedded within the output reporting of our program R code provided in table S2. We have corrected all of the affected text, tables, and figures (see Supporting Information A, available online), including correcting the R code to create the proper output and all other material that was in the original Supporting Information (see Supporting Information B, available online). When we fixed the reporting error for the density-dependent models, including the Gompertz and Ricker models with and without period effects terms, we realized it was not appropriate to report a single λ estimate because λ varied by density. We have chosen to report the 25th, 50th (or median), and 75th percentile estimates in all tables and the median estimates in the figures. Supporting Information Additional supporting information may be found in the online version of this article at the publisher's website. Filename Description jwmg21560-sup-0001-SuppData-S1.docx1.8 MB Supporting Data S1. jwmg21560-sup-0002-SuppData-S2.docx343.6 KB Supporting Data S2. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. LITERATURE CITED Case, T. J. 2000. An illustrated guide to theoretical ecology. Oxford University Press, New York, New York, USA. Dennis, B., P. L. Munholland, and J. M. Scott. 1991. Estimation of growth and extinction parameters for endangered species. Ecological Monographs 61: 115– 143. Dennis, B., and M. L. Taper. 1994. Density dependence in time series observations of natural populations: estimation and testing. Ecological Monographs 64: 205– 224. Jacobson, A. R., A. Provenzale, A. von Hardenberg, B. Bassano, and M. Festa-Bianchet. 2004. Climate forcing and density dependence in a mountain ungulate population. Ecology 85: 1598– 1610. Mills, L. S. 2013. Conservation of wildlife populations: demography, genetics, and management. Second edition. John Wiley & Sons, Chichester, West Sussex, United Kingdom. Morris, W. F., D. F. Doak. 2002. Quantitative conservation biology: theory, practice of population viability analysis. Sinauer, Sunderland, Massachusetts, USA. Ricker, W. E. 1954. Stock and recruitment. Journal of the Fisheries Board of Canada 11: 559– 623. Citing Literature Volume82, Issue8November 2018Pages 1808-1808 ReferencesRelatedInformation

Demographic consequences of conservation reserve program grasslands for lesser prairie‐chickens

ABSTRACTKnowledge of landscape and regional circumstances where conservation programs are successful on working lands in agricultural production are needed. Converting marginal croplands to grasslands using conservation programs such as the United States Department of Agriculture Conservation Reserve Program (CRP) should be beneficial for many grassland‐obligate wildlife species; however, addition of CRP grasslands may result in different population effects based on regional climate, characteristics of the surrounding landscape, or species planted or established. Within landscapes occupied by lesser prairie‐chickens (Tympanuchus pallidicinctus), CRP may provide habitat only for specific life stages and habitat selection for CRP may vary between wet and dry years. Among all study sites, we captured and fitted 280 female lesser prairie‐chickens with very high frequency (VHF)‐ and global positioning system (GPS) transmitters during the spring lekking seasons of 2013–2015 to monitor habitat selection for CRP in regions of varying climate. We also estimated vital rates and habitat selection for 148 individuals, using sites in northwest Kansas, USA. The greatest ecological services of CRP became apparent when examining habitat selection and densities. Nest densities were approximately 3 times greater in CRP grasslands than native working grasslands (i.e., grazed), demonstrating a population‐level benefit (CRP = 6.0 nests/10 km2 ± 1.29 [SE], native working grassland = 1.7 nests/10 km2 ± 0.62). However, CRP supporting high nest density did not provide brood habitat; 85% of females with broods surviving to 7 days moved their young to other cover types. Regression analyses indicated lesser prairie‐chickens were approximately 8 times more likely to use CRP when 5,000‐ha landscapes were 70% rather than 20% grassland, indicating variation in the level of ecological services provided by CRP was dependent upon composition of the larger landscape. Further, CRP grasslands were 1.7 times more likely to be used by lesser prairie‐chickens in regions receiving 40 cm compared to 70 cm of average annual precipitation and during years of greater drought intensity. Demographic and resource selection analyses revealed that establishing CRP grasslands in northwest Kansas can increase the amount nesting habitat in a region where it may have previously been limited, thereby providing refugia to sustain populations through periods of extreme drought. Nest survival, adult survival during breeding, and nonbreeding season survival did not vary between lesser prairie‐chickens that used and did not use CRP grasslands. The finite rate of population growth was also similar for birds using CRP and using only native working grasslands, suggesting that CRP provides habitat similar to that of native working grassland in this region. Overall, lesser prairie‐chickens may thrive in landscapes that are a mosaic of native working grassland, CRP grassland, with a minimal amount of cropland, particularly when nesting and brood habitat are in close proximity. © 2018 The Wildlife Society.

Demográfía de Oreomunnea mexicana (Standl.) J. F. Leroy en el bosque de niebla de Sierra Juárez, Oaxaca

Se estudió la demografía de Oreomunnea mexicana una especie amenazada y un relicto del Cenozoico. Esta especie es un elemento arbóreo dominante en el bosque de niebla de La Sierra Juárez, Oaxaca. Se obtuvo la estructura poblacional de cuatro sitios en 2011 y 2016 a través de parcelas de 400 m2 (20 m × 20 m). Por medio del uso de matrices de tipo Lefkovitch se obtuvo la tasa finita de crecimiento poblacional (l) para la población de San Bernardo, además de un análisis de elasticidad para dos periodos (2011 - 2015 y 2015 - 2016). En marzo de 2016, se registraron fuertes vientos de 100 km/h, lo que incrementó la mortalidad dentro de las poblaciones, sin modificar su estructura poblacional en forma de J invertida. No obstante, el estudio demográfico en, San Bernardo mostró una l en decremento para el segundo periodo de 0.44 ± 0.009, en comparación con una l en crecimiento de 1.101 ± 1.083 del primer periodo. Se encontró que la permanencia de los individuos es el parámetro demográfico más importante para mantener la estabilidad demográfica de las poblaciones. La especie mostró alta vulnerabilidad a cambios extremos en el ambiente, con un decremento en su número poblacional en un período corto (2015-2016). Por lo anterior, si se desea restaurar estas poblaciones locales, la conservación in situ debe enfocarse a lograr mantener y aumentar a futuro el número de individuos adultos en la zona.

Refining mortality estimates in shark demographic analyses: a Bayesian inverse matrix approach.

Leslie matrix models are an important analysis tool in conservation biology that are applied to a diversity of taxa. The standard approach estimates the finite rate of population growth (λ) from a set of vital rates. In some instances, an estimate of λ is available, but the vital rates are poorly understood and can be solved for using an inverse matrix approach. However, these approaches are rarely attempted due to prerequisites of information on the structure of age or stage classes. This study addressed this issue by using a combination of Monte Carlo simulations and the sample-importance-resampling (SIR) algorithm to solve the inverse matrix problem without data on population structure. This approach was applied to the grey reef shark (Carcharhinus amblyrhynchos) from the Great Barrier Reef (GBR) in Australia to determine the demography of this population. Additionally, these outputs were applied to another heavily fished population from Papua New Guinea (PNG) that requires estimates of λ for fisheries management. The SIR analysis determined that natural mortality (M) and total mortality (Z) based on indirect methods have previously been overestimated for C.amblyrhynchos, leading to an underestimated λ. Updated distributions of Z and λ were produced for the GBR population and corrected obvious error in the demographic parameters for the PNG population. This approach provides opportunity for the inverse matrix approach to be applied more broadly to situations where information on population structure is lacking.

Individual‐Based Modeling of Delta Smelt Population Dynamics in the Upper San Francisco Estuary III. Effects of Entrainment Mortality and Changes in Prey

AbstractWe used an individual‐based model, developed previously for the endangered, endemic Delta Smelt Hypomesus transpacificus, to investigate two factors widely believed to affect its abundance in the San Francisco Estuary: entrainment in large water diversion facilities and declines and species shifts in their zooplankton prey. Previous analyses suggested that these factors had substantial effects on the Delta Smelt population, although evidence is accumulating that other factors, such as contaminants and predation, are also having effects. Simulations were performed for 1995–2005 with either entrainment mortality set to zero or zooplankton biomasses replaced with values sampled from pre‐decline years. The detailed individual‐based and spatial model output was summarized as the annual finite population growth rate (λ). Eliminating entrainment mortality increased the geometric mean λ by 39% through increased survival of larvae and adults. Substituting historical food for present‐day food resulted in variable annual λ values with a geometric mean that was 41% greater than the baseline value (14–81% across 10 alternative food scenarios). Historical food caused higher juvenile consumption and growth rates, leading to larger recruits, earlier maturity, and higher individual fecundity. These results were robust to four sets of simulations using alternative formulations for density dependence, mortality, maturity, and larval growth.

Greater sage‐grouse population trends across Wyoming

ABSTRACTThe scale at which analyses are performed can have an effect on model results and often one scale does not accurately describe the ecological phenomena of interest (e.g., population trends) for wide‐ranging species: yet, most ecological studies are performed at a single, arbitrary scale. To best determine local and regional trends for greater sage‐grouse (Centrocercus urophasianus) in Wyoming, USA, we modeled density‐independent and ‐dependent population growth across multiple spatial scales relevant to management and conservation (Core Areas [habitat encompassing approximately 83% of the sage‐grouse population on ∼24% of surface area in Wyoming], local Working Groups [7 regional areas for which groups of local experts are tasked with implementing Wyoming's statewide sage‐grouse conservation plan at the local level], Core Area status (Core Area vs. Non‐Core Area) by Working Groups, and Core Areas by Working Groups). Our goal was to determine the influence of fine‐scale population trends (Core Areas) on larger‐scale populations (Working Group Areas). We modeled the natural log of change in population size ( peak M lek counts) by time to calculate the finite rate of population growth (λ) for each population of interest from 1993 to 2015. We found that in general when Core Area status (Core Area vs. Non‐Core Area) was investigated by Working Group Area, the 2 populations trended similarly and agreed with the overall trend of the Working Group Area. However, at the finer scale where Core Areas were analyzed separately, Core Areas within the same Working Group Area often trended differently and a few large Core Areas could influence the overall Working Group Area trend and mask trends occurring in smaller Core Areas. Relatively close fine‐scale populations of sage‐grouse can trend differently, indicating that large‐scale trends may not accurately depict what is occurring across the landscape (e.g., local effects of gas and oil fields may be masked by increasing larger populations). Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Constructing stage-structured matrix population models from life tables: comparison of methods.

A matrix population model is a convenient tool for summarizing per capita survival and reproduction rates (collectively vital rates) of a population and can be used for calculating an asymptotic finite population growth rate (λ) and generation time. These two pieces of information can be used for determining the status of a threatened species. The use of stage-structured population models has increased in recent years, and the vital rates in such models are often estimated using a life table analysis. However, potential bias introduced when converting age-structured vital rates estimated from a life table into parameters for a stage-structured population model has not been assessed comprehensively. The objective of this study was to investigate the performance of methods for such conversions using simulated life histories of organisms. The underlying models incorporate various types of life history and true population growth rates of varying levels. The performance was measured by comparing differences in λ and the generation time calculated using the Euler-Lotka equation, age-structured population matrices, and several stage-structured population matrices that were obtained by applying different conversion methods. The results show that the discretization of age introduces only small bias in λ or generation time. Similarly, assuming a fixed age of maturation at the mean age of maturation does not introduce much bias. However, aggregating age-specific survival rates into a stage-specific survival rate and estimating a stage-transition rate can introduce substantial bias depending on the organism’s life history type and the true values of λ. In order to aggregate survival rates, the use of the weighted arithmetic mean was the most robust method for estimating λ. Here, the weights are given by survivorship curve after discounting with λ. To estimate a stage-transition rate, matching the proportion of individuals transitioning, with λ used for discounting the rate, was the best approach. However, stage-structured models performed poorly in estimating generation time, regardless of the methods used for constructing the models. Based on the results, we recommend using an age-structured matrix population model or the Euler-Lotka equation for calculating λ and generation time when life table data are available. Then, these age-structured vital rates can be converted into a stage-structured model for further analyses.

The use of periodic matrices to model the population dynamics of the long‐lived semelparous Furcraea parmentieri (Asparagaceae) in a temperate forest in central Mexico

AbstractFurcraea parmentieri (Roezl ex Ortgies) García‐Mend. is a long‐lived, semelparous threatened species with a restricted geographic distribution. We studied the demography of this species in southwest of Mexico City using periodic matrices. We followed the fate of 404 individuals (in 2006–2007) and performed seed germination and seedling establishment experiments in the field (in 2007–2008) to estimate survival, growth and reproduction probabilities of individuals in eight size categories, according to plant height. Population structure was characterized by a high number of saplings, as well as medium and large plants. We built three annual matrices that described the demography in different phases of the population cycle: regular years (RG) characterized by low fecundity and low adult mortality; mast‐seeding years (MS) with low seedling emergence and high adult mortality (related to semelparity); and post mast‐seeding years (PS) with a high emergence of seedlings and bulbils. Periodic matrices were built simulating three scenarios, which consisted of mast‐seeding events occurring every 5, 10, or 15 years. Finite population growth rates (λ) were 1.03 (RG year), 0.99 (MS year), and 1.25 (PS year). The long term population growth rate values projected over a 90 year period (estimated on an annual basis) were higher as the frequency of mast‐seeding events increased. We estimated that individuals reproduce at an age of 60–90 years and that most new recruits originate via sexual reproduction. Although the population has a potential for growth, its persistence may be threatened due to land use change.

Chronic Wasting Disease Drives Population Decline of White-Tailed Deer.

Chronic wasting disease (CWD) is an invariably fatal transmissible spongiform encephalopathy of white-tailed deer, mule deer, elk, and moose. Despite a 100% fatality rate, areas of high prevalence, and increasingly expanding geographic endemic areas, little is known about the population-level effects of CWD in deer. To investigate these effects, we tested the null hypothesis that high prevalence CWD did not negatively impact white-tailed deer population sustainability. The specific objectives of the study were to monitor CWD-positive and CWD-negative white-tailed deer in a high-prevalence CWD area longitudinally via radio-telemetry and global positioning system (GPS) collars. For the two populations, we determined the following: a) demographic and disease indices, b) annual survival, and c) finite rate of population growth (λ). The CWD prevalence was higher in females (42%) than males (28.8%) and hunter harvest and clinical CWD were the most frequent causes of mortality, with CWD-positive deer over-represented in harvest and total mortalities. Survival was significantly lower for CWD-positive deer and separately by sex; CWD-positive deer were 4.5 times more likely to die annually than CWD-negative deer while bucks were 1.7 times more likely to die than does. Population λ was 0.896 (0.859–0.980), which indicated a 10.4% annual decline. We show that a chronic disease that becomes endemic in wildlife populations has the potential to be population-limiting and the strong population-level effects of CWD suggest affected populations are not sustainable at high disease prevalence under current harvest levels.

Evaluating vital rate contributions to greater sage‐grouse population dynamics to inform conservation

AbstractSpecies conservation efforts often use short‐term studies that fail to identify the vital rates that contribute most to population growth. Although the greater sage‐grouse (Centrocercus urophasianus; sage‐grouse) is a candidate for protection under the U.S. Endangered Species Act, and is sometimes referred to as an umbrella species in the sagebrush (Artemisia spp.) biome of western North America, the failure of proposed management strategies to focus on key vital rates that may contribute most to achieving population stability remains problematic for sustainable conservation. To address this dilemma, we performed both prospective and retrospective perturbation analyses of a life cycle model based on a 12‐yr study that encompassed nearly all sage‐grouse vital rates. To validate our population models, we compared estimates of annual finite population growth rates (λ) from our female‐based life cycle models to those attained from male‐based lek counts. Post‐fledging (i.e., after second year, second year, and juvenile) female survival parameters contributed most to past variation in λ during our study and had the greatest potential to change λ in the future, indicating these vital rates as important determinants of sage‐grouse population dynamics. In addition, annual estimates of λ from female‐based life cycle models and male‐based lek data were similar, providing the most rigorous evidence to date that lek counts of males can serve as a valid index of sage‐grouse population change. Our comparison of fixed and mixed statistical models for evaluating temporal variation in nest survival and initiation suggest that conservation planners use caution when evaluating short‐term nesting studies and using associated fixed‐effect results to develop conservation objectives. In addition, our findings indicated that greater attention should be paid to those factors affecting sage‐grouse post‐fledging females. Our approach demonstrates the need for more long‐term studies of species vital rates across the life cycle. Such studies should address the decoupling of sampling variation from underlying process (co)variation in vital rates, identification of how such variation drives population dynamics, and how decision makers can use this information to re‐direct conservation efforts to address the most limiting points in the life cycle for a given population.

Life History Traits and Demographic Parameters of Triatoma infestans (Hemiptera: Reduviidae) Fed on Human Blood.

Triatoma infestans (Klug, 1834) (Hemiptera: Reduviidae), the main vector of Chagas disease in South America, feeds primarily on humans, but ethical reasons preclude carrying out demographical studies using people. Thus, most laboratory studies of T. infestans are conducted using bird or mammal live hosts that may result in different demographic parameters from those obtained on human blood. Therefore, it is of interest to determine whether the use of an artificial feeder with human blood would be operational to rear triatomines and estimate population growth rates. We estimated life history traits and demographic parameters using an artificial feeder with human blood and compared them with those obtained on live hens. Both groups of T. infestans were kept under constant conditions [28 ± 1°C, 40 ± 5% relative humidity, a photoperiod of 12:12 (L:D) h] and fed weekly. On the basis of age-specific survival and age-specific fecundity, we calculated the intrinsic rate of natural increase (r), the finite rate of population growth (λ), the net reproductive rate (Ro), and the mean generation time (Tg). Our results show differences in life history traits between blood sources, resulting in smaller population growth rates on human blood than on live hens. Although demographic growth rate was smaller on human blood than on hens, it still remains positive, so the benefit/cost ratio of this feeding method seems relatively attractive. We discuss possibility of using the artificial feeder with human blood for both ecological and behavioral studies.

Vital Statistics of Triatominae (Hemiptera: Reduviidae) Under Laboratory Conditions: IV.Panstrongylus geniculatus

A cohort of 100 eggs of Panstrongylus geniculatus (Latreille) was reared in the laboratory under constant conditions (temperature 26 ± 1°C, 60 ± 10% RH), with mortality and fecundity data recorded weekly. We calculated stage-specific development times, age-specific mortality and fecundity (18.4 eggs/♀/wk), and stage-specific and total preadult mortality (31.6%), and the weekly intrinsic rate of natural increase (r(o) = 0.096), the finite population growth rate (λ = 1.109), the net reproductive rate (R(0) = 60.45), and the generation time (T = 46.34 wk). Elasticity analysis showed that the dominant life-history trait determining λ was survival (particularly the adult female's survival). Adult females dominated the stage-specific reproductive value, and the egg stage dominated the stable stage distribution (SSD). The damping ratio (ρ = 1.096) suggests a relatively rapid period of recovery to a disturbed SSD. Results were compared with one previous study and conform relatively well, considering that environmental conditions were not the same. We estimated the colonizing ability of P. geniculatus, using as a criterion the ro/b index, and obtained the value of 0.74, an indicator of a good colonizer, and similar to well-known invasive species such as Rhodnius prolixus and Triatoma infestans. The life history traits and demographic parameters here presented for P. geniculatus are discussed in terms of their usefulness for evolutionary studies and vector control activities.

Density but not climate affects the population growth rate of guanacos ( Lama guanicoe) (Artiodactyla, Camelidae).

We analyzed the effects of population density and climatic variables on the rate of population growth in the guanaco ( Lama guanicoe), a wild camelid species in South America. We used a time series of 36 years (1977-2012) of population sampling in Tierra del Fuego, Chile. Individuals were grouped in three age-classes: newborns, juveniles, and adults; for each year a female population transition matrix was constructed, and the population growth rate (λ) was estimated for each year as the matrix highest positive eigenvalue. We applied a regression analysis with finite population growth rate (λ) as dependent variable, and total guanaco population, sheep population, annual mean precipitation, and winter mean temperature as independent variables, with and without time lags. The effect of guanaco population size was statistically significant, but the effects of the sheep population and the climatic variables on guanaco population growth rate were not statistically significant.