Variation In Demographic Rates Research Articles

Approaching a population‐level assessment of body size in pinnipeds using drones, an early warning of environmental degradation

AbstractBody mass is a fundamental indicator of animal health closely linked to survival and reproductive success. Systematic assessment of body mass for a large proportion of a population can allow early detection of changes likely to impact population growth, facilitating responsive management and a mechanistic understanding of ecological trends. One challenge with integrating body mass assessment into monitoring is sampling enough animals to detect trends and account for individual variation. Harbour seals (Phoca vitulina) are philopatric marine mammals responsive to regional environmental changes, resulting in their use as an indicator species. We present a novel method for the non‐invasive and semi‐automatic assessment of harbour seal body condition, using unoccupied aerial vehicles (UAVs/drones). Morphological parameters are automatically measured in georeferenced images and used to estimate volume, which is then translated to estimated mass. Remote observations of known individuals are utilized to calibrate the method. We achieve a high level of accuracy (mean absolute error of 4.5 kg or 10.5% for all seals and 3.2 kg or 12.7% for pups‐of‐the‐year). We systematically apply the method to wild seals during the Spring pupping season and Autumn over 2 years, achieving a near‐population‐level assessment for pups on land (82.5% measured). With reference to previous mark‐recapture work linking Autumn pup weights to survival, we estimate mean expected probability of over‐winter survival (mean = 0.89, standard deviation = 0.08). This work marks a significant step forward for the non‐invasive assessment of body condition in pinnipeds and could provide daily estimates of body mass for thousands of individuals. It can act as an early warning for deteriorating environmental conditions and be utilized as an integrative tool for wildlife monitoring. It also enables estimation of yearly variation in demographic rates which can be utilized in parameterizing models of population growth with relevance for conservation and evolutionary biology.

Survival of red knots in the northern Gulf of Mexico

Highly migratory shorebirds are among the fastest declining avian guilds, so determining causes of mortality is critically important for their conservation. Most of these species depend on a specific geographic arrangement of suitable sites that reliably provide resources needed to fuel physiologically demanding life histories. Long-term mark-resight projects allow researchers to investigate specific potential sources of variation in demographic rates between populations. Red Knots (Calidris canutus) occur in three relatively distinct regions across the northern Gulf of Mexico, and two of these areas have been experiencing episodic harmful algal blooms (red tide) with increased frequency in recent decades. Since knots are mostly molluscivorous during the nonbreeding season in the Gulf, they are potentially exposed to red tide toxins at high concentrations via their filter-feeding prey. We used long-term mark-resight data from Texas, Louisiana, and Florida (USA) to estimate apparent survival, and to assess the effects of red tides on survival of Red Knots. We also assessed effects of tracking devices deployed in conjunction with the projects over the years. While overall apparent annual survival rates were similar across the three locations (0.768 – 0.819), several red tide events were associated with catastrophically low seasonal (fall) survival in Florida (as low as 0.492) and Texas (as low as 0.510). Leg-mounted geolocators, but not temporary glued-on VHF tags, were associated with a reduction in apparent survival (~8%/year). Movement of knots between the three areas was rare and site fidelity is known to be high. Harmful algal blooms are predicted to increase in frequency and severity with climate change and increased anthropogenic degradation of coastal habitats, which may further endanger these as well as other shorebird populations around the world.

Understanding the demography of a reinforced population: Long-term survival of captive-bred and wild-born houbara bustards in Morocco

Translocation of captive-bred animals to reinforce threatened populations is widely used as a conservation strategy for small and declining wildlife populations. A fundamental goal of these interventions is that translocated animals will survive and improve the future viability of populations. To evaluate this goal, we need to estimate the long-term survival of both captive-bred and wild-born animals in reinforced populations in order to best assess the relative contribution of translocated individuals to population growth. Here, we used tracking data from a large-scale, long-term translocation program in Morocco to estimate long-term survival in a reinforced population of houbara bustards (Chlamydotis undulata undulata). We estimated annual survival rates of captive-bred and wild-born houbara, and considered sources of individual and temporal variation in survival, including how age-specific rates vary between captive-bred and wild-born birds. Our results reveal key differences in how survival varied with age between captive-bred and wild-born houbara. Survival of wild-born houbara was relatively high and constant beyond the first year of life, while survival of captive-bred birds increased more gradually in early years, approaching that of wild-born individuals in older ages. These results suggest that captive-bred houbara have high potential to contribute to the growth and persistence of houbara populations. Our estimates also highlight the importance of considering sources of individual variation in demographic rates when assessing the contribution of reinforcements to population growth. Finally, these analyses emphasise the need to estimate long-term survival when predicting the future viability of reinforced populations.

Reproductive success of the wood warbler Phylloscopus sibilatrix varies across Europe

Differences in population trends across a species' breeding range are ultimately linked to variation in demographic rates. In small songbirds, demographic rates related to fecundity typically have strong effects on population trends. Populations of a forest songbird, the wood warbler Phylloscopus sibilatrix, have been declining in many but not all regions of the European breeding range. We investigated if clutch size, hatching rate, nest survival and number of fledglings vary across Europe, and if nest survival is related to differences in the regionally dominant nest predator class (birds versus mammals). From 2009 to 2020, we monitored 1896 nests and used cameras at a subsample of 645 nests in six study regions: the United Kingdom (mid‐Wales, Dartmoor, the New Forest), Germany (Hessen), Switzerland (Jura mountains) and Poland (Białowieża National Park). Number of fledglings was lowest in the New Forest (1.43 ± CI 0.23), intermediate in Jura (2.41 ± 0.31) and Białowieża (2.26 ± 0.24) and highest in mid‐Wales (3.02 ± 0.48) and Dartmoor (2.92 ± 0.32). The reason for low reproductive success in the New Forest, Jura and Białowieża was low nest survival, and large clutch sizes in Białowieża did not compensate for high nest losses. High reproductive success in mid‐Wales and Dartmoor was due to high nest survival and large clutch sizes. Overall predation rates were similar everywhere despite variation between the regions in the dominant nest predator class. Unsuccessful nests in mid‐Wales were mainly predated by birds; in Dartmoor, the New Forest, Hessen and Jura similarly by birds and mammals; and in Białowieża exclusively by mammals. Regional reproductive success does not match the population trends recently reported for the wood warbler in the six study regions (i.e. high reproduction ≠ positive trend). Annual survival may be a decisive factor, but it is difficult to quantify for a nomadic species such as the wood warbler that rarely returns to the same breeding locations.

Demographic variation in space and time: implications for conservation targeting.

The dynamics of wild populations are governed by demographic rates which vary spatially and/or temporally in response to environmental conditions. Conservation actions for widespread but declining populations could potentially exploit this variation to target locations (or years) in which rates are low, but only if consistent spatial or temporal variation in demographic rates occurs. Using long-term demographic data for wild birds across Europe, we show that productivity tends to vary between sites (consistently across years), while survival rates tend to vary between years (consistently across sites), and that spatial synchrony is more common in survival than productivity. Identifying the conditions associated with low demographic rates could therefore facilitate spatially targeted actions to improve productivity or (less feasibly) forecasting and temporally targeting actions to boost survival. Decomposing spatio-temporal variation in demography can thus be a powerful tool for informing conservation policy and for revealing appropriate scales for actions to influence demographic rates.

Opposing trends in survival and recruitment slow the recovery of a historically overexploited fishery

Quantifying temporal variation in demographic rates is a central goal of population ecology. In this study, we analyzed a multidecadal age-structured time series of Arctic char (Salvelinus alpinus) abundance in Lake Mývatn, Iceland, to infer the time-varying demographic response of the population to reduced harvest in the wake of the fishery’s collapse. Our analysis shows that while survival probability of adults increased following the alleviation of harvesting pressure, per capita recruitment consistently declined over most of the study period, until the final three years when it began to increase. The countervailing demographic trends resulted in only limited directional change in the total population size and population growth rate. Rather, the population dynamics were dominated by large interannual variability and a shift towards an older age distribution. Our results are indicative of a slow recovery of the population after its collapse, despite the rising number of adults following relaxed harvest. This underscores the potential for heterogeneous demographic responses to management efforts due to the complex ecological context in which such efforts take place.

Demographic Rate Variability of Bighead and Silver Carps Along an Invasion Gradient

Abstract Invasive Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix have infested and caused largescale ecological and economic damage to the Illinois, Mississippi, and Ohio rivers. We compiled demographic data from 42,995 fish from 23 pools in the Illinois, Mississippi, and Ohio rivers, which universities and management agencies previously collected as part of management, monitoring, and research activities. We used this data set to test whether demographic rates (length–weight relations including body condition, mortality, growth curves, and female maturity curves) varied among subpopulations across a gradient of invasion status. We found that length–weight relations and growth curves varied among subpopulations, whereas maturity curves did not. Our findings demonstrated spatial variability in demographic rates for Bighead and Silver carp across a broad geographic area in relation to invasion status and river conditions. Herein, we provide general subpopulation management options and present different hypotheses to explain the observed spatial variability in demographic rates.

Closing the life cycle of forest trees: The difficult dynamics of seedling‐to‐sapling transitions in a subtropical rainforest

Abstract Experimental and observational studies on seedling dynamics posit mechanisms that can influence forest diversity, structure and function. However, high mortality and slow growth of seedlings make it difficult to evaluate the importance of this life‐history filter to total tree life history. Quantifying the duration and transition of the seedling phase would help us understand this ‘black box’ in tree population biology. We used a 16‐year dataset of comprehensive seedling‐to‐sapling demography from a subtropical rainforest to construct population models that capture temporal demographic fluctuations for eight major tree species. We used data‐driven demographic models and simulations to estimate the transition ratios from newly recruited seedlings to saplings of 2‐m height and the time taken to attain 2‐m height for a newly recruited seedling conditional on its survival. Projections among species estimated that as few as 57 to more than 40,000 seedlings (with a median of 2,087) were required to make a single 2‐m high sapling. Furthermore, it would take 22–200 years (with a median of 47) for a newly recruited seedling to become a 2‐m high sapling. We found that temporal variation in demographic rates could greatly reduce the number of seedlings per established sapling, but not passage times (PTs). We also identified the importance of consistently fast growth rates for seedlings to escape the high mortality of early stages. Synthesis. Our findings demonstrate that high mortality in the very early seedling stage severely limits the probability that a newly recruited seedling will transition to the sapling stage. Although the PTs vary, we found this to be true across species with a range of life‐history strategies. Only seedlings with consistently fast growth rates are expected to pass through this life‐history filter. Findings from seedling studies should consider how short‐term studies of seedling demography might capture the rare exceptional individuals and exceptional conditions that might define the dynamics of this seedling bottleneck.

Evidence of demographic buffering in an endangered great ape: Social buffering on immature survival and the role of refined sex‐age classes on population growth rate

Theoretical and empirical research has shown that increased variability in demographic rates often results in a decline in the population growth rate. In order to reduce the adverse effects of increased variability, life-history theory predicts that demographic rates that contribute disproportionately to population growth should be buffered against environmental variation. To date, evidence of demographic buffering is still equivocal and limited to analyses on a reduced number of age classes (e.g. juveniles and adults), and on single sex models. Here we used Bayesian inference models for age-specific survival and fecundity on a long-term dataset of wild mountain gorillas. We used these estimates to parameterize two-sex, age-specific stochastic population projection models that accounted for the yearly covariation between demographic rates. We estimated the sensitivity of the long-run stochastic population growth rate to reductions in survival and fecundity on ages belonging to nine sex-age classes for survival and three age classes for female fecundity. We found a statistically significant negative linear relationship between the sensitivities and variances of demographic rates, with strong demographic buffering on young adult female survival and low buffering on older female and silverback survival and female fecundity. We found moderate buffering on all immature stages and on prime-age females. Previous research on long-lived slow species has found high buffering of prime-age female survival and low buffering on immature survival and fecundity. Our results suggest that the moderate buffering of the immature stages can be partially due to the mountain gorilla social system and the relative stability of their environment. Our results provide clear support for the demographic buffering hypothesis and its predicted effects on species at the slow end of the slow-fast life-history continuum, but with the surprising outcome of moderate social buffering on the survival of immature stages. We also demonstrate how increasing the number of sex-age classes can greatly improve the detection of demographic buffering in wild populations.

Socially Defined Subpopulations Reveal Demographic Variation in a Giraffe Metapopulation

ABSTRACTPopulations are typically defined as spatially contiguous sets of individuals, but large populations of social species can be composed of discrete social communities that often overlap in space. Masai giraffes (Giraffa camelopardalis tippelskirchi) of Tanzania live in distinct social subpopulations that overlap spatially, enabling us to simultaneously explore environmental and social factors correlated with demographic variation in a metapopulation of >1,400 adult females and calves. We considered statistically distinct communities in the social network as subpopulations and tested for variation among the 10 subpopulations in adult female survival, calf survival, and reproductive rate (calf‐to‐adult female ratio). We then related variation in demographic rates among subpopulations to differences in vegetation, soil type, proximity to 2 types of human settlements, local giraffe population density, and social metrics of relationship strength and exclusivity among adult females. We did not find any among‐subpopulation effects on adult female survival, suggesting adult female survival is buffered against environmental heterogeneity among subpopulations. Variation in calf demographic rates among subpopulations were correlated with vegetation, soils, anthropogenic factors, and giraffe population density but not with adult female relationship metrics, despite substantial spatial overlap. Subpopulations with more dense bushlands in their ranges had lower calf survival probabilities, and those closer to human settlements had higher reproductive rates, possibly because of spatial gradients in natural predation. Reproductive rates were higher in subpopulations with more volcanic soils, and calf survival probabilities were greater in subpopulations with higher local adult female densities, possibly related to higher‐quality habitat associated with fertile soils or lower predation risk, or to greater competitive ability. The variation in fitness among subpopulations suggests that giraffes do not move unhindered among resource patches to equalize reproductive success, as expected according to an ideal free distribution. The differences in calf survival and reproductive rates could rather indicate intercommunity differences in competitive ability, perception, learning, or experience. Our approach of comparing demography among spatially overlapping yet distinct socially defined subpopulations provides a biologically meaningful way to quantify environmental and social factors influencing fine‐scale demographic variation for social species. © 2021 The Wildlife Society.

Partial and complete dependency among data sets has minimal consequence on estimates from integrated population models

Integrated population models (IPMs) are widely used to combine disparate data sets in joint analysis to better understand population dynamics and provide guidance for conservation activities. An often-cited assumption of IPMs is independence among component data sets within the combined likelihood. Dependency among data sets should lead to underestimation of variance and bias because individuals contribute data to>1 data set. In practice, studied individuals often occur in multiple data sets in IPMs (i.e., overlap), which is one way for the independence assumption to be violated. Such cases have the potential to dissuade practitioners and limit application of IPMs to solve emerging ecological problems. We assessed precision and bias of demographic rates estimated from IPMs using a complete gradient (0-100%) of overlap among data sets, wide ranges in demographic rates (e.g., survival 0.1-0.8) and sample sizes (100-1200 individuals) and variable data sources. We compared results from our simulations with those from IPMs constructed using empirical data on tree swallows (Tachycineta bicolor) where data sets either had complete overlap or included different individuals. Contrary to previous investigators, we found no substantive bias or uncertainty in any demographic rate from IPMs derived from data sets with complete overlap. While variability in demographic rates was greater at low sample sizes (i.e., low capture, recapture and survey probabilities), there were negligible differences in the posterior mean or root mean square error of demographic rates among IPMs with strong dependence versus complete independence among data sets. Our simulations suggest IPMs can be designed using only capture-recapture data or harvest and capture-recovery data where population estimates are obtained from the same data as survival and productivity data. While we encourage researchers to carefully consider the modeling approach best-suited for their data sets, our results suggest that dependence among data sets does not generally compromise IPM estimates. Thus, violation of the independence assumption should not dissuade researchers from the application of IPMs in ecological research.

Tensor decomposition for infectious disease incidence data.

Many demographic and ecological processes generate seasonal and other periodicities. Seasonality in infectious disease transmission can result from climatic forces such as temperature and humidity; variation in contact rates as a result of migration or school calendar; or temporary surges in birth rates. Seasonal drivers of acute immunizing infections can also drive longer‐term fluctuations.Tensor decomposition has been used in many disciplines to uncover dominant trends in multi‐dimensional data. We introduce tensors as a novel method for decomposing oscillatory infectious disease time series.We illustrate the reliability of the method by applying it to simulated data. We then present decompositions of measles data from England and Wales. This paper leverages simulations as well as much‐studied data to illustrate the power of tensor decomposition to uncover dominant epidemic signals as well as variation in space and time. We then use tensor decomposition to uncover new findings and demonstrate the potential power of the method for disease incidence data. In particular, we are able to distinguish between annual and biennial signals across locations and shifts in these signals over time.Tensor decomposition is able to isolate variation in disease seasonality as a result of variation in demographic rates. The method allows us to discern variation in the strength of such signals by space and population size. Tensors provide an opportunity for a concise approach to uncovering heterogeneity in disease transmission across space and time in large datasets.

Integrating evolutionary, demographic and ecophysiological processes to predict the adaptive dynamics of forest tree populations under global change

Three types of process-based models (PBMs) are traditionally used to predict the response of forest tree populations to global change (GC): (i) ecophysiological models, which simulate carbon and water fluxes in forest ecosystems by explicitly integrating the effects of climate and CO2; (ii) forest dynamics models which simulate forest successions by explicitly linking mortality, growth and regeneration processes; and (iii) evolutionary dynamics models, which simulate the variation and evolution of adaptive traits by explicitly accounting for selection, mutation, gene flow and inheritance rules. The ongoing context of rapid GC, however, questions the boundaries between these types of models. Here, we review different strategies of model integration: (i) physio-demographic PBMs, integrating physiological and demographic processes; (ii) demo-genetic PBMs, integrating demographic and evolutionary processes; and (iii) physio-demo-genetic PBMs, which attempt to integrate these three types of processes. We show that these integrative models allow a better understanding of how different functional traits influence demographic rates (the phenotype-demography map), how the variation in demographic rates influences fitness (the demography-fitness map) and how individual variations of fitness may in turn influence the genetic composition of a population. Our review highlights that accounting for inter-individual variation in ecological processes is increasingly recognized as crucial for modelling the ecosystem response to environmental change. We argue that the effort of integrating these different processes is valuable, both for a basic understanding of their interactive effects on the responses of forests to GC and for applied horizon scanning to support adaptive strategies.

Assessing Accuracy and Bias of Protocols to Estimate Age of Pacific Salmon Using Scales

AbstractAccurate estimates of age composition are essential for fisheries management, but evaluation of protocols to estimate age data are rarely conducted. Herein, known‐age Pacific salmon Oncorhynchus spp. from six hatchery stocks were used to examine accuracy of multiple scale‐aging protocols and to assess how errors in age assignment may affect age composition estimated from scale data. Accuracy reached 1.0 for one stock of Coho Salmon Oncorhynchus kisutch, over 0.9 for three stocks of spring Chinook Salmon Oncorhynchus tshawytscha, and was no higher than 0.8 for two stocks of fall Chinook Salmon. For all hatchery stocks, accuracy increased and bias decreased when readers had auxiliary information about a fish's fork length and sex. Results suggest that a protocol that collects scales from above the lateral line, provides auxiliary information on fork length and sex, allows readers to exclude individuals for which age appears unclear, and uses an arbitrator to assign age when two initial readers disagree may produce the most accurate and unbiased age data from scales. This study highlights the importance of assessing patterns in age errors both qualitatively and quantitatively. A general pattern of overestimating age for younger age‐classes and underestimating age for older age‐classes was evident. This pattern in age errors could affect age composition estimates for adult Pacific salmon and other species with few (e.g., two to six) age‐classes. In addition, individual variation in demographic rates may affect individual patterns identified on scales; thus, for stocks with more extensive individual demographic variability, like fall Chinook Salmon stocks, accuracy may be lower and bias higher, resulting in less accurate estimates of age composition.

Parsing the effects of demography, climate and management on recurrent brucellosis outbreaks in elk

Abstract Zoonotic pathogens can harm human health and well‐being directly or by impacting livestock. Pathogens that spillover from wildlife can also impair conservation efforts if humans perceive wildlife as pests. Brucellosis, caused by the bacterium Brucella abortus, circulates in elk and bison herds of the Greater Yellowstone Ecosystem and poses a risk to cattle and humans. Our goal was to understand the relative effects of climatic drivers, host demography and management control programmes on disease dynamics. Using >20 years of serologic, demographic and environmental data on brucellosis in elk, we built stochastic compartmental models to assess the influences of climate forcing, herd immunity, population turnover and management interventions on pathogen transmission. Data were collected at feedgrounds visited in winter by free‐ranging elk in Wyoming, USA. Snowpack, hypothesized as a driver of elk aggregation and thus brucellosis transmission, was strongly correlated across feedgrounds. We expected this variable to drive synchronized disease dynamics across herds. Instead, we demonstrate asynchronous epizootics driven by variation in demographic rates. We evaluated the effectiveness of test‐and‐slaughter of seropositive female elk at two feedgrounds. Test‐and‐slaughter temporarily reduced herd‐level seroprevalence but likely reduced herd immunity while removing few infectious individuals, resulting in subsequent outbreaks once the intervention ceased. We simulated an alternative strategy of removing seronegative female elk and found it would increase herd immunity, yielding fewer infections. We evaluated a second experimental treatment wherein feeding density was reduced at one feedground, but we found no evidence for an effect despite a decade of implementation. Synthesis and applications. Positive serostatus is often weakly correlated with infectiousness but is nevertheless used to make management decisions including lethal removal in wildlife disease systems. We show how this can have adverse consequences whereas efforts that maintain herd immunity can have longer‐term protective effects. Climatic drivers may not result in synchronous disease dynamics across populations unless vital rates are also similar because demographic factors have a large influence on disease patterns.

Species-habitat association affects demographic variation across different life stages in an old-growth temperate forest

The sustainability of tree populations in old-growth temperate forests has motivated many ecologists to investigate the mechanisms by which species coexistence is maintained in a local-scale habitat. Species-habitat association could indicate assembly rules that support demographic processes in a particular habitat due to the effect of spatial distribution. In this study, we hypothesized that plant performance with a positive association is better than that for species with a negative association or with no association. We used demographic census data from 2010 and 2015 from the 9-ha Liangshui forest dynamic plot in northeastern China. A one-way ANOVA was used to examine the variation in the relative growth rate (RGR) and mortality rate (MR) in three life stages (saplings, juveniles, and adults) in different habitat types and to analyse the variations in the recruitment rate (RR) in different habitat types. The habitat types were determined by multivariate regression trees (MRT). The three habitat types are Hab I (very high soil organic carbon with a moderate slope), Hab II (low soil organic carbon with a gentle slope), and Hab III (low soil organic carbon with a strong slope). A t-test comparison was performed to compare the differences in RGR and MR between the positive associations group and the non-positive associations (negative and no association) group. The species habitat association statuses were determined by a torus translation test. We used a generalized linear mixed-effects model to analyse the effect of habitat types, diameter and habitat association status on the demographic rate in three different life stages. The RGR of the saplings was significantly higher than that of the juveniles and adults in the three habitat types (P < 0.001). The variation in the MR in the saplings and juveniles in habitats with high soil organic carbon was significantly higher than that in the adults (P < 0.001). However, the variation in the RR showed no significant difference among the three habitat types. The RGR in the saplings and juveniles with positive habitat associations was significantly lower than in those with negative and no habitat associations (P < 0.001). Moreover, the MR in the saplings with positive habitat associations was significantly higher than in those with negative and no habitat associations (P < 0.05). The species-habitat association status significantly affected tree survival, growth, and recruitment. These results demonstrate both positive and negative effects on forest dynamic processes across different life stages. Our study indicated that habitat association status has a significant influence on variation in demographic rates. We suggest that including different life stages in different habitat types is the key to obtaining ecological insight about forest dynamic processes, mechanisms of species coexistence, and maintenance of sustainable forest ecosystems.

Geographic variation in demography of black perch (Embiotoca jacksoni): Effects of density, food availability, predation, and fishing

It is well known that demographic rates such as growth and mortality may vary among populations, but the degree of variation in demography is often unknown, especially when considering multiple populations at large spatial scales (e.g., across hundreds of kilometers). Likewise, of the many factors that may affect demography, it is often unknown which are the major factors responsible for spatial variation in demographic rates. In this study, we estimated rates of growth and examined age distributions within nine populations of black perch (Embiotoca jacksoni) distributed across ~350 km of coastline. We tested whether spatial variation in demography was associated with several explanatory variables including population density, predator density, food availability, and fishing activity. Our study revealed a substantial amount of spatial variation in demographic rates. Among-population variation in growth accounted for 55% of the total variation, and the coefficient of variation for mean age within a population was 27%, suggesting substantial variation in mortality. Spatial variation in growth was most sensitive to variation in food availability and mean age was lowest at locations with high levels of spearfishing activity. Although the fishery for black perch is not a major one, fishing mortality rates may be very high in some areas. Overall, our results shed light on the ecological forces that shape demographic variation of this species, and suggest that fishing mortality may have a major influence on the dynamics of perch populations.

Increasing trends in fecundity and calf survival of bottlenose dolphins in a marine protected area

Estimates of temporal variation in demographic rates are critical for identifying drivers of population change and supporting conservation. However, for inconspicuous wide-ranging species, births may be missed and fecundity rates underestimated. We address this issue using photo-identification data and a novel robust design multistate model to investigate changes in bottlenose dolphin fecundity and calf survival. The model allows for uncertainty in breeding status, and seasonal effects. The best model estimated an increase in the proportion of females with newborn calves from 0.16 (95% CI = 0.11–0.24) in 2001 to 0.28 (95% CI = 0.22–0.36) in 2016. First year calf survival also increased over this period from 0.78 (95% CI = 0.53–0.92) to 0.93 (95% CI = 0.82–0.98). Second year calf survival remained lower, but also showed an increase from 0.32 (95% CI = 0.19–0.48) to 0.55 (95% CI = 0.44–0.65). Females with newborn calves had a slightly higher mortality than those with older calves, but further work is required to evaluate potential costs of reproduction. This study presents a rare example of empirical evidence of a positive trend in reproduction and survival for a cetacean population using a Marine Protected Area.

Assessing the effect of density on population growth when modeling individual encounter data.

The relative role of density-dependent and density-independent variation in vital rates and population size remains largely unsolved. Despite its importance to the theory and application of population ecology, and to conservation biology, quantifying the role and strength of density dependence is particularly challenging. We present a hierarchical formulation of the temporal symmetry approach, also known as the Pradel model, that permits estimation of the strength of density dependence from capture-mark-reencounter data. A measure of relative population size is built in the model and serves to detect density dependence directly on population growth rate. The model is also extended to account for temporal random variability in demographic rates, allowing estimation of the temporal variance of population growth rate unexplained by density dependence. We thus present a model-based approach that enable to test and quantify the effect of density-dependent and density-independent factors affecting population fluctuations in a single modeling framework. More generally, we use this modeling framework along with simulated and empirical data to show the value of including density dependence when modeling individual encounter data without the need for auxiliary data.

Temporal and environmental variation in growth and maturity and effects on management reference points of Georges Bank Atlantic cod

Temporal variation in demographic rates has been observed in various fish populations and environmental influences are likely to be a key factor. Here we show how it can be important to combine state-space models for environmental covariates and demographic rates when evaluating effects of the former on the latter. In an application to Georges Bank Atlantic cod (Gadus morhua), we show how estimates of the environmental covariate can be aliased with unknown temporal variation in growth rates and that stronger and opposite effects of the environment can incorrectly be found when the autocorrelation in the growth rate is not separately modeled. The perception of effects on maturity also depends on whether an appropriate distribution is considered for the maturity observations. Bottom temperature did not improve prediction of maturity parameters, but temporal variation driven by other sources did. Both bottom temperature and temporal variation improved performance of growth models. Finally, we found growth and maturity estimation to be important contributors to uncertainty of spawning biomass and biological reference points when incorporated into a state-space assessment model.