Asymptotic Population Growth Rate Research Articles

Antecedent Effect Models as an Exploratory Tool to Link Climate Drivers to Herbaceous Perennial Population Dynamics Data

ABSTRACTUnderstanding mechanisms and predicting natural population responses to climate is a key goal of Ecology. However, studies explicitly linking climate to population dynamics remain limited. Antecedent effect models are a set of statistical tools that capitalize on the evidence provided by climate and population data to select time windows correlated with a response (e.g., survival, reproduction). Thus, these models can serve as both a predictive and exploratory tool. We compare the predictive performance of antecedent effect models against simpler models and showcase their exploratory analysis potential by selecting a case study with high predictive power. We fit three antecedent effect models: (1) weighted mean models (WMM), which weigh the importance of monthly anomalies based on a Gaussian curve, (2) stochastic antecedent models (SAM), which weigh the importance of monthly anomalies using a Dirichlet process, and (3) regularized regressions using the Finnish horseshoe model (FHM), which estimate a separate effect size for each monthly anomaly. We compare these approaches to a linear model using a yearly climatic predictor and a null model with no predictors. We use demographic data from 77 natural populations of 34 plant species ranging between seven and 36 years in length. We then fit models to the asymptotic population growth rate (λ) and its underlying vital rates: survival, development, and reproduction. We find that models including climate do not consistently outperform null models. We hypothesize that the effect of yearly climate is too complex, weak, and confounded by other factors to be easily predicted using monthly precipitation and temperature data. On the other hand, in our case study, antecedent effect models show biologically sensible correlations between two precipitation anomalies and multiple vital rates. We conclude that, in temporal datasets with limited sample sizes, antecedent effect models are better suited as exploratory tools for hypothesis generation.

Threats to the persistence of sugar pine (Pinus lambertiana) in the western USA

This study assesses how numerous stressors shape the vital rates (survival, growth, and fecundity) of sugar pine across the vast majority of its range. Sugar pine (Pinus lambertiana Dougl.) is the largest Pinus species, an important timber species, and a component of several dry conifer forest types of western North America, in particular the extensive Sierra Nevada mixed conifer forest. The species faces several challenges in the Anthropocene, including a disrupted fire regime, an invasive pathogen, forest structure changes, and drought with ensuing bark beetle epidemics. Managers are concerned about the conservation outlook for sugar pine, but it is unclear where and how to best invest conservation resources. Using data from the US Forest Service’s Forest Inventory and Analysis program, we estimate the parameters for the vital rate functions and use these to construct an integral projection model which predicts the effects of various stressors on the asymptotic population growth rate. The asymptotic population growth rate is near or slightly below one even under reference conditions, and the actual abundance (in terms of both stem density and basal area) slightly declined over the duration of the study (2001–2019). The analysis reveals that wildfire, white pine blister rust, and forest density are key drivers of the demographic rates of sugar pine across its range. Drought and site dryness had lesser, but still meaningful, effects. Fire has strong negative effects on survival, resulting in a strongly negative population trajectory on burned sites. Conversely, lower than average forest density (plot-level basal area) results in a positive population growth rate via beneficial effects on individual growth. These results highlight the value of fire hazard mitigation, particularly where it also reduces forest density, in the conservation of this important species.

High-resolution data are necessary to understand the effects of climate on plant population dynamics of a forest herb.

Climate is assumed to strongly influence species distribution and abundance. Although the performance of many organisms is influenced by the climate in their immediate proximity, the climate data used to model their distributions often have a coarse spatial resolution. This is problematic because the local climate experienced by individuals might deviate substantially from the regional average. This problem is likely to be particularly important for sessile organisms like plants and in environments where small-scale variation in climate is large. To quantify the effect of local temperature on vital rates and population growth rates, we used temperature values measured at the local scale (in situ logger measures) and integral projection models with demographic data from 37 populations of the forest herb Lathyrus vernus across a wide latitudinal gradient in Sweden. To assess how the spatial resolution of temperature data influences assessments of climate effects, we compared effects from models using local data with models using regionally aggregated temperature data at several spatial resolutions (≥1 km). Using local temperature data, we found that spring frost reduced the asymptotic population growth rate in the first of two annual transitions and influenced survival in both transitions. Only one of the four regional estimates showed a similar negative effect of spring frost on population growth rate. Our results for a perennial forest herb show that analyses using regionally aggregated data often fail to identify the effects of climate on population dynamics. This emphasizes the importance of using organism-relevant estimates of climate when examining effects on individual performance and population dynamics, as well as when modeling species distributions. For sessile organisms that experience the environment over small spatial scales, this will require climate data at high spatial resolutions.

Review of range-wide vital rates quantifies eastern wild Turkey population trajectory.

Recent declines in eastern wild turkeys (Meleagris gallopavo silvestris) have prompted increased interest in management and research of this important game species. However, the mechanisms underlying these declines are unclear, leaving uncertainty in how best to manage this species. Foundational to effective management of wildlife species is understanding the biotic and abiotic factors that influence demographic parameters and the contribution of vital rates to population growth. Our objectives for this study were to (1) conduct a literature review to collect all published vital rates for eastern wild turkey over the last 50 years, (2) perform a scoping review of the biotic and abiotic factors that have been studied relative to wild turkey vital rates and highlight areas that require additional research, and (3) use the published vital rates to populate a life-stage simulation analysis (LSA) and identify the vital rates that make the greatest contribution to population growth. Based on published vital rates for eastern wild turkey, we estimated a mean asymptotic population growth rate (λ) of 0.91 (95% CI=0.71, 1.12). Vital rates associated with after-second-year (ASY) females were most influential in determining population growth. Survival of ASY females had the greatest elasticity (0.53), while reproduction of ASY females had lower elasticity (0.21), but high process variance, causing it to explain a greater proportion of variance in λ. Our scoping review found that most research has focused on the effects of habitat characteristics at nest sites and the direct effects of harvest on adult survival, while research on topics such as disease, weather, predators, or anthropogenic activity on vital rates has received less attention. We recommend that future research take a more mechanistic approach to understanding variation in wild turkey vital rates as this will assist managers in determining the most appropriate management approach.

Demography_Lab, an educational application to evaluate population growth: Unstructured and matrix models.

Training in Population Ecology asks for scalable applications capable of embarking students on a trip from basic concepts to the projection of populations under the various effects of density dependence and stochasticity. Demography_Lab is an educational tool for teaching Population Ecology aspiring to cover such a wide range of objectives. The application uses stochastic models to evaluate the future of populations. Demography_Lab may accommodate a wide range of life cycles and can construct models for populations with and without an age or stage structure. Difference equations are used for unstructured populations and matrix models for structured populations. Both types of models operate in discrete time. Models can be very simple, constructed with very limited demographic information or parameter‐rich, with a complex density‐dependence structure and detailed effects of the different sources of stochasticity. Demography_Lab allows for deterministic projections, asymptotic analysis, the extraction of confidence intervals for demographic parameters, and stochastic projections. Stochastic population growth is evaluated using up to three sources of stochasticity: environmental and demographic stochasticity and sampling error in obtaining the projection matrix. The user has full control on the effect of stochasticity on vital rates. The effect of the three sources of stochasticity may be evaluated independently for each vital rate. The user has also full control on density dependence. It may be included as a ceiling population size controlling the number of individuals in the population or it may be evaluated independently for each vital rate. Sensitivity analysis can be done for the asymptotic population growth rate or for the probability of extinction. Elasticity of the probability of extinction may be evaluated in response to changes in vital rates, and in response to changes in the intensity of density dependence and environmental stochasticity.

Comparison of asymptotic population growth rates with heterogeneous variances

AbstractThis report explores how the heterogeneity of variances affects randomization tests used to evaluate differences in the asymptotic population growth rate, λ. The probability of Type I error was calculated in four scenarios for populations with identical λ but different variance of λ: (1) Populations have different projection matrices: the same λ may be obtained from different sets of vital rates, which gives room for different variances of λ. (2) Populations have identical projection matrices but reproductive schemes differ and fecundity in one of the populations has a larger associated variance. The two other scenarios evaluate a sampling artifact as responsible for heterogeneity of variances. The same population is sampled twice, (3) with the same sampling design, or (4) with different sampling effort for different stages. Randomization tests were done with increasing differences in sample size between the two populations. This implies additional differences in the variance of λ. The probability of Type I error keeps at the nominal significance level (α = .05) in Scenario 3 and with identical sample sizes in the others. Tests were too liberal, or conservative, under a combination of variance heterogeneity and different sample sizes. Increased differences in sample size exacerbated the difference between observed Type I error and the nominal significance level. Type I error increases or decreases depending on which population has a larger sample size, the population with the smallest or the largest variance. However, by their own, sample size is not responsible for changes in Type I errors.

Are protected populations of two globular cactus species facing a demographic explosion or just a “bonanza” year?

Despite decades of research, controversy has emerged as to whether positive and negative interactions predictably shift with increasing environmental stress. We used projection matrices, to determine growth rate and elasticity and a LTR experiment to quantify the contribution of each matrix elements to the differences in λ observed between sympatric and syntopic sub-populations of globular cactus species in Brazil (Discocactus placentiformis and D. pseudoinsignis). We addressed the following questions: What is the growth rate of the two species when in sympatry and syntopy? What are the relative contributions of survival, growth, and fecundity to population growth? Which life cycle stages have the highest mortality? Do demographic differences between the two species account for observed differences in sub-population sizes? Both species exhibited higher densities when in syntopy than in sympatry. Seedling establishment and survival were high, and fecundity increased as plant diameter increased. Asymptotic population growth rates were significantly greater than one. The highest elasticity values were for stasis for the later ontogenetic stage and for the growths. It seems that the protection provided by the conservation area is efficient, and that the data were collected during a “bonanza” year, with high rainfall, when all or most reproduction and/or recruitment occur.

Relative Importance of Vital Rates to Population Dynamics of Wood Ducks

ABSTRACTThe wood duck (Aix sponsa) is a common and important cavity‐nesting duck in North America; however, we know very little about how changes in vital rates influence population growth rate (λ). We used estimates of fertility and survival of female wood ducks from our nest‐box studies in South Carolina, Alabama, and Georgia, USA, to create a stage‐based matrix population model. We conducted perturbation analyses and ranked elasticity values to examine the relative importance of 17 component vital rates to λ. Female survival is influenced by nest success, so we recognized this female heterogeneity in our analyses. Four vital rates showed the greatest importance to λ. Analytic elasticities were greatest for breeding season and nonbreeding season survival of females that nested successfully, followed by nest success and female recruitment to the breeding population. Differences in female quality were important to λ. Next, we used process variation of vital rates and conducted life‐stage simulation analyses (LSA) followed by variance decomposition to determine the amount of variation in λ explained by each vital rate. Female recruitment to the breeding population explained 57.7% of the variation in λ followed by nest success (11.4%), and breeding and nonbreeding season survival of females that nested successfully (9.3% and 9.4%, respectively). Together these 4 vital rates explained 88% of the variation in λ. Mean asymptotic population growth rate (λ = 0.80 ± 0.08 [SD]) from LSA revealed a declining population. Recruitment of females hatched from nest boxes was insufficient to sustain the nest‐box population. However, including yearling (SY) females that were produced outside of nest boxes (i.e., immigrants) increased recruitment rates 1.5 to 2 times more than when only SY females recruited from nest boxes were included. Future research that examines how emigration and immigration interact with survival and reproduction to influence local population dynamics of wood ducks will be important for identifying the value of nest‐box programs to wood duck conservation and management. © 2019 The Wildlife Society.

Persistent problems in the construction of matrix population models

Matrix population models (MPMs) are powerful tools for translating demographic and life history information into a form that can be used to address a wide range of research topics, such as projecting population dynamics, evaluating stressor impacts on populations, and studying life history evolution. However, the reliability of such studies depends on the MPM being constructed in a way that accurately reflects the species’ life history. We highlight three errors commonly encountered in published MPMs: (1) failing to include survival in the fertility coefficient; (2) introducing a one-year delay in age at first reproduction; and (3) incorrectly calculating the growth rate out of a stage class. We review the sources of such errors and provide new analyses revealing the impact of such errors on model predictions, using lionfish and American alligator models as examples. To quantify the prevalence of such errors we examined and scored the original publications underlying the models in the COMADRE Animal Matrix Database. The first two errors were found in 34% and 62%, respectively, of the published studies; nearly all were in models that used a “postbreeding census” representation of the life cycle (in which newborns—eggs, neonates, fledglings, etc.—are explicitly included). Of the studies where stages may last longer than one time step, 53% constructed the growth rate using inappropriate formulas for estimating the asymptotic population growth rate or its sensitivity to demographic parameters. These results suggest that further efforts may be required to educate biologists on the construction of MPMs, perhaps in concert with the development of new software tools. Furthermore, the conclusions of many studies that are based on MPMs may need to be re-examined, and synthetic studies using the COMADRE Database need to be accompanied by careful examination of the underlying studies.

Understanding the limits to species‐wide demographic generalizations: the ecology and management of Parkinsonia aculeata

AbstractThe search for generalizations in the face of complex species–environment interactions is particularly important for minimizing the cost of managing populations of species. We tested whether we could generalize, at various nested scales, the species‐level demography of the widely invasive plant species Parkinsonia aculeata (Fabaceae) and whether these generalizations were representative of the demography observed locally. Full demographic surveys at all life stages of the species were conducted in 23 Australian sites during seven years (from 2000 to 2007), across a 1000‐km climatic gradient. Sites were nested across four climate regions (arid, semi‐arid, semi‐wet/dry tropics, wet/dry tropics) and three habitat types (upland, wetland, and riparian). We estimated the vital rates (growth/retrogression, survival, fecundity) at all life stages and size classes and combined them to create 99 site–year demographic matrix population models. With these models, we then estimated site–year‐specific asymptotic population growth rates and their corresponding prospective elasticity values to perturbation of the vital rates. We then developed a nested retrospective elasticity analysis (nested LTRE) to test whether and how upscaling the results (i.e., from site to habitat, to climate region, and to the invaded range) produced averaging bias, which could lead to spurious interpretations of the relationships between the retrospective elasticity values. The prospective analysis highlighted that site–year variation in the matrix population models, population growth rates, and corresponding elasticities could not be well summarized by a single species‐level analysis and that the spread was as diverse as found in previously reported multispecies‐level demographic analyses. The nested LTRE analysis showed that upscaling demographic models introduced for most sites new sources of errors in the estimation (in terms of magnitude and sign of retrospective elasticities), which increased drastically as we progressively aggregate the demographic information between nested scales of observation. Our findings suggest that regardless of the scale, demographic generalizations at the species scale are not always useful for managing P. aculeata across sites in its invaded range, given its plasticity in demography.

Demographic processes underlying fitness restoration in bdelloid rotifers emerging from dehydration

Abstract Bdelloid rotifers are able to survive habitat desiccation in a dehydrated state termed anhydrobiosis. They suffer from decreasing fitness when they are exposed to permanent hydration, yet they restore fitness when they go through anhydrobiosis. The demographic processes underlying this rejuvenation, however, are still largely unknown. To investigate these processes in detail, we analysed life tables of permanently hydrated and repeatedly desiccated lines of two species of bdelloid rotifers, Macrotrachela quadricornifera and Adineta ricciae. Experimental lineages of these two species originated from habitats with contrasting desiccation frequencies. First, we built a three‐stage life cycle including juveniles as well as prime and senescent adults. Next, we estimated stage‐specific vital rates (survival, development, and reproduction) and used the estimates to project the asymptotic population growth rates λ (= er). Finally, we applied life‐table response experiment methods and performed elasticity analysis to assess the contributions of each vital rate to differences in λ and to estimate effects of proportional changes in vital rates on λ, respectively. We demonstrated that repeatedly desiccated lines grew faster than permanently hydrated lines. In addition, we confirmed that offspring of post‐anhydrobiotic individuals had higher fecundities and matured faster than individuals of the permanently hydrated lines. Survival rates usually did not differ between the two lines, but λ was most elastic to survival rates of prime adults and juveniles. These general life‐history patterns were observed in both species. The analyses performed here provide a detailed investigation of the demographic processes underlying fitness restoration in anhydrobiotic bdelloid rotifers. They reveal that habitat desiccation has profound and consistent effects on the life histories of the two study species. Because laboratory lineages of these species originated from habitats characterised by different wet/dry regimes, we suggest that the desiccation responses identified here may be representative for the entire taxon. As such, our study offers a starting point for comparative analyses beyond bdelloid rotifers.

Demographic processes limit upward altitudinal range expansion in a threatened tropical palm.

Understanding the factors that determine species’ range limits is a key issue in ecology, and is fundamental for biodiversity conservation under widespread global environmental change. Elucidating how altitudinal variation affects demographic processes may provide important clues for understanding the factors limiting current and future species distributions, yet population dynamics at range limits are still poorly understood. Here, we tested the hypothesis that lower abundance at a species’ upper altitudinal range limit is related to lower vital rates. We compared the dynamics of two populations of the tropical palm Euterpe edulis, located near and at the edge of its altitudinal limit of distribution in the Brazilian Atlantic Forest. Data from four annual censuses, from 2012 to 2015, were used. We used matrix population models to estimate asymptotic population growth rates and the elasticity values for the vital rates of the two populations of E. edulis. Life table response experiments were used to compare population performance by measuring the contribution of each vital rate to population growth rates. Population growth rates were not significantly different from one in either population, indicating that both populations were stable during the study period. However, the abundance of all ontogenetic stages was lower at the altitudinal range limit, which was related to decreases in some vital rates, especially fecundity. Additionally, there were higher elasticity values for the survival of immatures and reproductive individuals, compared to all other vital rates, in both populations. Synthesis. Our results show that even a small‐scale environmental variation near range limits is sufficient to drive changes in the demography of this threatened palm. A minor increase in elevation approaching the limit of altitudinal distribution may reduce environmental suitability and affect population vital rates, thus contributing to setting upper altitudinal range limits for plants.

Phenotypic selection and covariation in the life‐history traits of elephant seals: heavier offspring gain a double selective advantage

Early developmental conditions contribute to individual heterogeneity of both phenotypic traits and fitness components, ultimately affecting population dynamics. Although the demographic consequences of ontogenic growth are best quantified using an integrated measure of fitness, most analyses to date have instead studied individual fitness components in isolation. Here, we estimated phenotypic selection on weaning mass in female southern elephant seals Mirounga leonina by analyzing individual‐based data collected between 1986 and 2016 with capture–recapture and matrix projection models. In support of a hypothesis predicting a gradual decrease of weaning mass effects with time since weaning (the replacement hypothesis), we found that the estimated effects of weaning mass on future survival and recruitment probability was of intermediate duration (rather than transient or permanent). Heavier female offspring had improved odds of survival in early life and a higher probability to recruit at an early age. The positive link between weaning mass and recruitment age is noteworthy, considering that pre‐recruitment mortality already imposed a strong selective filter on the population, leaving only the most ‘robust’ individuals to reproduce. The selection gradient on asymptotic population growth rate, a measure of mean absolute fitness, was weaker than selection on first‐year survival and recruitment probabilities. Weaker selection on mean fitness occurs because weaning mass has little impact on adult survival, the fitness component to which the population growth of long‐lived species is most sensitive. These results highlight the need to interpret individual variation in phenotypic traits in a context that considers the demographic pathways between the trait and an inclusive proxy of individual fitness. Although variation in weaning mass do not translate to permanent survival differences among individuals in adulthood, it explains heterogeneity and positive covariation between survival and breeding in early life, which contribute to between‐individual variation in fitness.

Demographic projections of the Apennine brown bear population Ursus arctos marsicanus (Mammalia: Ursidae) under alternative management scenarios

Apennine brown bears are a very small, isolated population of central Italy, consisting of about 50 individuals and under a severe risk of extinction. We performed a population viability analysis (PVA) for this population, contrasting a deterministic model and an individual-based stochastic model, using a set of demographic parameters estimated for the same population during the last decade. We also built a set of simulated management scenarios, in which we compared the effectiveness of alternative conservation measures and assessed the susceptibility of the population to catastrophic mortality events. The deterministic model produced an estimate of the asymptotic population growth rate r = 0.001, corresponding to an asymptotically stable population. The stochastic model produced an estimate of r = − 0.013 (standard deviation = 0.103), corresponding to an annual population decrease of 1.3%, a 17% extinction risk in 100 years, an average population of 27 bears for non-extinct populations, and an average time to extinction of 81 years for those gone extinct. Extinction probability increased to more alarming levels (> 0.4) when at least one catastrophic event occurred during a 100-year period. Current vital rates of the population are not compatible with a more than negligible numerical increase, and this bear population is likely to remain small and exposed to a relatively high risk of extinction, if the average survival or reproductive rates do not increase. Management efforts aimed to increase food availability generated minimal to moderate variations in population growth rate and in the associated risk of extinction, whereas interventions meant to reduce adult female mortality were highly effective in increasing persistence probability. We propose that the general objectives of the action plan for the conservation of the Apennine brown bear for the incoming decade should explicitly contemplate quantitative demographic goals, focusing in particular on adult female and cub mortality.

Changes in nesting success and breeding abundance of Spectacled Eiders Somateria fischeri in the Chaun Delta, Chukotka, Russia, 2003–2016

The Spectacled Eider Somateria fischeri is a rare sea duck confined to breeding in the Yukon–Kuskokwim Delta and Arctic coasts of Alaska and Russia. Almost nothing is known about its status and breeding biology in the Russian Arctic. Stratified systematic nest searches were conducted annually of Spectacled Eider nests on Ayopechan Island in the Chaun Delta, Arctic Russia during 2003–2016. Mean nest densities were stable during 2003–2009 but declined by 8.0% per annum during 2009–2016. Mean clutch size and annual female survival did not change over the same period, during which time annual nest survival and hatching success declined significantly. A simple three age-class matrix model estimated annual asymptotic population growth rate (λ) using observed fecundity from the beginning (1.1 hatched chick per female, λ = 0.864) and end (0.45 hatched chick per female, λ = 0.828) of the study period. This confirmed that to stabilize this population required three immigrant recruits for every local recruit at the beginning of the study and nine towards the end. Declines in annual nest survival appear correlated with (i) declines in nesting Sabine’s Gulls Xema sabini and Arctic Terns Sterna paradisaea with which nesting Spectacled Eiders associated and may have gained protection from predators, and (ii) marginally significant increases in large gull and mammalian predators at the site. Should current trends in nest density and fecundity continue, the survival of this breeding Spectacled Eider population is in jeopardy.

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.

Perturbation approaches for integral projection models

Perturbation analysis of population models is fundamental to elucidating mechanisms of population dynamics and examining scenarios of change. The use of integral projection models (IPMs) has increased in the last decade, and while many of the tools and approaches developed for matrix models remain relevant, the nature of IPMs expands the framework of perturbation analysis, with different approaches often requiring important considerations. This article provides a review of – and practical guide to – different perturbation approaches for IPMs, formalizes methodologies for perturbing IPM size transition probabilities, and highlights areas where researchers should be particularly careful and critical when conducting and interpreting perturbation analysis. I use a simulated dataset to compare five hierarchical perturbation approaches for IPMs found within 63 published studies, and apply a combination of approaches to the example of an invasive perennial plant. Other perturbation approaches for IPMs are also highlighted.Most perturbation analyses for IPMs to date have focused on the response of the asymptotic population growth rate (λ) to changes in elements of the discretized projection kernel and/or the growth– survival and reproduction– recruitment sub‐kernels. Perturbations to vital rate functions and regression predictions underlying these kernels provide mechanistic insight, but are less common and can require important considerations regarding the perturbation of size transitions separate from survival and the nature of the state variable (used to represent size). The second most common approach is more specific to IPMs and examines the influence of vital rate regression parameters, each of which can have broad influence on the population growth rate. Researchers using IPMs have many perturbation options available and should carefully consider which approach or combination of approaches is most applicable and interpretable for their specific questions.

Are Brazil nut populations threatened by fruit harvest?

AbstractHarvest of Brazil nuts from the large, iconic tree Bertholletia excelsa generates substantial income for smallholders, providing a strong incentive to conserve the mature forests where it grows. Although much previous work has focused on the impact of nut harvest on new seedling recruits into B. excelsa populations, the connection between harvest rates and long‐term population stability is still unclear. Moreover, there is additional uncertainty for Brazil nut management in terms of population response to climate change and other anthropogenic influences. We drew on 14 years of research in two sites in Acre, Brazil with different B. excelsa nut harvest intensities (39% and 81%), to produce stochastic and deterministic matrix population models which incorporated parameter uncertainty in vital rates. Adult abundance was projected to remain close to the current observed abundance or higher through the next 50 years. Elasticity analyses revealed that the asymptotic population growth rate (λ) was most sensitive to stasis vital rates in sapling, juvenile, and adult stages. Deterministic transition matrices calculated using diameter growth rates dependent on rainfall yielded average λ values around 1.0 under extreme high, extreme low, and average annual rainfall. While sustained high rates of Brazil nut harvest and climate change could potentially negatively impact B. excelsa populations, changes in human use of the forested landscape are more immediate concern. To reduce the risk of population decline, smallholders and managers of B. excelsa rich forests should focus on conservation of pre‐mature and mature individuals.

Understanding the demographic drivers of realized population growth rates.

Identifying the demographic parameters (e.g., reproduction, survival, dispersal) that most influence population dynamics can increase conservation effectiveness and enhance ecological understanding. Life table response experiments (LTRE) aim to decompose the effects of change in parameters on past demographic outcomes (e.g., population growth rates). But the vast majority of LTREs and other retrospective population analyses have focused on decomposing asymptotic population growth rates, which do not account for the dynamic interplay between population structure and vital rates that shape realized population growth rates (λt=Nt+1/Nt) in time-varying environments. We provide an empirical means to overcome these shortcomings by merging recently developed "transient life-table response experiments" with integrated population models (IPMs). IPMs allow for the estimation of latent population structure and other demographic parameters that are required for transient LTRE analysis, and Bayesian versions additionally allow for complete error propagation from the estimation of demographic parameters to derivations of realized population growth rates and perturbation analyses of growth rates. By integrating available monitoring data for Lesser Scaup over 60yr, and conducting transient LTREs on IPM estimates, we found that the contribution of juvenile female survival to long-term variation in realized population growth rates was 1.6 and 3.7 times larger than that of adult female survival and fecundity, respectively. But a persistent long-term decline in fecundity explained 92% of the decline in abundance between 1983 and 2006. In contrast, an improvement in adult female survival drove the modest recovery in Lesser Scaup abundance since 2006, indicating that the most important demographic drivers of Lesser Scaup population dynamics are temporally dynamic. In addition to resolving uncertainty about Lesser Scaup population dynamics, the merger of IPMs with transient LTREs will strengthen our understanding of demography for many species as we aim to conserve biodiversity during an era of non-stationary global change.

Sooty FalconFalco concolorreproduction and population dynamics on the islands in the Sea of Oman

Knowledge of demographic parameters affecting population dynamics is critical to the formulation of effective conservation strategies. Sooty FalconFalco concoloris a little‐studied, Near‐threatened species; estimates of global population size and trend for this species are uncertain. They lay eggs during mid‐summer and sometimes nest in colonies. This unusual breeding ecology suggests that demographic parameters driving their population growth rate may differ from those of most other falcons. We studied Sooty Falcon reproduction at breeding aggregations on Fahal Island and the Daymaniyat islands in the Sea of Oman during 2007–2014, modelled population growth and identified important life history parameters using elasticity analysis. The mean (± se) clutch and brood size was 2.83 ± 0.06 and 2.11 ± 0.07, respectively. Overall, 11.7% of nests failed between the egg and nestling stages, and the failure rate differed significantly between Fahal and the Daymaniyats, and across years. The mean proportion of eggs that hatched annually was 0.66 ± 0.02, and broods were significantly smaller on the Daymaniyats than on Fahal. Falcons on Fahal Island had a higher rate of hatching, a higher rate of nests that produced at least one chick, and produced more chicks per nest than on the Daymaniyats. We suggest that Fahal's proximity to the mainland gives breeding Sooty Falcons access to a more plentiful and stable source of food, especially during the period between arrival from the wintering grounds and the onset of the autumn migration of prey birds, resulting in the better reproductive rates for falcons on Fahal Island, relative to those on the Daymaniyat Islands. The annual asymptotic population growth rate (λ) was 0.87 (95% confidence interval (CI) 0.75–0.99), suggesting a declining population, although Sooty Falcons enjoyed a slightly higher population growth rate on Fahal than on the Daymaniyats. Because our study population is on the edge of the breeding range and is isolated from other breeding areas, measures to improve reproductive success of Sooty Falcons breeding on the islands in the Sea of Oman could be important for conservation of Sooty Falcons in Oman.