Realized Population Growth Rate Research Articles

Exploring the population dynamics of waterfowl hunters using a mark‐recapture approach

AbstractThe number of waterfowl hunters in the United States has declined since the 1980s despite relatively abundant waterfowl populations and liberal hunting regulations. Programs focused on recruiting, retaining, and reactivating (R3) waterfowl hunters have become important to avoid further losses in traditional revenue for habitat management and protection and political support for waterfowl conservation and management. We focus on 4 waterfowl hunter population vital rates (i.e., recruitment rate, retention probability, license purchase probability, realized population growth rate), which can be used to improve the effectiveness of waterfowl hunter R3 activities and initiatives by providing a deeper understanding of waterfowl hunter population dynamics to determine who programs should target, where programs should be targeted, and finally the evaluation of programs. To do so, we analyzed Nebraska state electronic license data from 2012–2019 using Pradel survival and recruitment models in a mark‐recapture framework. Female waterfowl hunter recruitment was higher than males; however, retention and license purchase probabilities were lower. Recruitment was highest in younger generations and retention highest in older generations. License purchase probabilities were highest among those in the oldest and youngest generations. The availability of hunting opportunity increased license purchase probabilities but had a minimal influence on retention and no association with recruitment. There were weak relationships between rurality and recruitment, and retention and license purchase probabilities. Finally, belonging to Ducks Unlimited was positively associated with higher license purchase and retention probabilities. Targeting an increase in license purchase probability by promoting social support for hunters through conservation organization membership should be a focus of waterfowl hunter R3 efforts to have the greatest influence on increasing waterfowl hunter participation.

Immigration as the main driver of population dynamics in a cryptic cetacean.

Empirical evidence about the role and interaction of immigration with local demographic processes in shaping population dynamics is still scarce. This knowledge gap limits our capability to derive a conceptual framework that can be used to inform conservation actions. Populations exposed to nonstationary environment do not converge to a stable stage distribution, implying the need for evaluating the demographic role of both vital rates and stage distribution using appropriate tools. This is particularly important for species with larger generation times like cetaceans. We explored the relative demographic role of vital rates and population structure of a poorly known cetacean, the Mediterranean Cuvier's beaked whale, while accounting for the exposure to nonstationary environments. We performed a retrospective analysis through transient life table response experiments (tLTRE) using demographic rates and population structure of both sexes obtained from an integrated population model. The contribution of immigration to variation in realized population growth rates was 4.2, 7.6, and 12.7 times larger than that of female apparent survival, proportional abundance of breeding females with a 2-year-old calf, and proportional abundance of breeding females with a 3-year-old calf, respectively. Immigration rate and proportional abundance of breeding females with a 2- or 3-year-old calf explained, respectively, 65% and 20% of total temporal variability in realized population growth rates. Changes in realized population growth rate between successive years were mainly driven by changes in immigration and population structure, specifically the proportional abundance of breeding females with a 2-year-old calf. Our study provides insight into the demographic processes that affect population dynamics and in a cryptic cetacean. We presented an analytical approach for maximizing the use of available data through the integration of multiple sources of information for individuals of different distinctiveness levels.

Multiple coping strategies maintain stability of a small mammal population in a resource-restricted environment.

In semi‐arid environments, aperiodic rainfall pulses determine plant production and resource availability for higher trophic levels, creating strong bottom‐up regulation. The influence of climatic factors on population vital rates often shapes the dynamics of small mammal populations in such resource‐restricted environments. Using a 21‐year biannual capture–recapture dataset (1993 to 2014), we examined the impacts of climatic factors on the population dynamics of the brush mouse (Peromyscus boylii) in semi‐arid oak woodland of coastal‐central California. We applied Pradel's temporal symmetry model to estimate capture probability (p), apparent survival (φ), recruitment (f), and realized population growth rate (λ) of the brush mouse and examined the effects of temperature, rainfall, and El Niño on these demographic parameters. The population was stable during the study period with a monthly realized population growth rate of 0.993 ± SE 0.032, but growth varied over time from 0.680 ± 0.054 to 1.450 ± 0.083. Monthly survival estimates averaged 0.789 ± 0.005 and monthly recruitment estimates averaged 0.175 ± 0.038. Survival probability and realized population growth rate were positively correlated with rainfall and negatively correlated with temperature. In contrast, recruitment was negatively correlated with rainfall and positively correlated with temperature. Brush mice maintained their population through multiple coping strategies, with high recruitment during warmer and drier periods and higher survival during cooler and wetter conditions. Although climatic change in coastal‐central California will likely favor recruitment over survival, varying strategies may serve as a mechanism by which brush mice maintain resilience in the face of climate change. Our results indicate that rainfall and temperature are both important drivers of brush mouse population dynamics and will play a significant role in predicting the future viability of brush mice under a changing climate.

Factors driving California pocket mice (Chaetodipus californicus) population dynamics

AbstractUnderstanding how demographic parameters respond to climatic variables is essential for predicting species’ response to changing environmental conditions. The California pocket mouse (Chaetodipus californicus) is an inhabitant of coastal-central California oak (Quercus spp.) woodland that is undergoing a rapid anthropogenic transformation while also facing effects of global climate change. We analyzed the population dynamics of the California pocket mouse by applying Pradel’s temporal symmetry model to a 10-year (2004 – 2013) capture–mark–recapture data set to estimate survival and recruitment rates and realized population growth rate. The overall monthly apparent survival probability (ϕ) was 0.76 ± 0.01 SE and was slightly higher in the dry season (0.79 ± 0.02 SE) than the wet season (0.74 ± 0.01 SE). Coefficients of variation (CV) of temperature and rainfall (with and without a one-season lag), average seasonal temperature, and regional climatic variation (El Niño index) positively influenced ϕ. Overall monthly recruitment rate (f) was 0.17 ± 0.01 SE but varied seasonally; f was substantially higher during the dry season (0.39 ± 0.04 SE) than the wet season (0.09 ± 0.02 SE). Average seasonal temperature, CV of temperature and rainfall (without a one-season lag), and total seasonal rainfall (with a one-season lag) positively influenced recruitment, whereas regional climatic variation (El Niño index), total seasonal rainfall (without a one-season lag), and CV of rainfall (with a one-season lag) had a negative effect on f. Monthly realized population growth rate (λ) was 1.00 ± 0.02 SE for the entire study period, but it varied temporally. Our study provides the first estimates of demographic parameters for the California pocket mouse and tests for the influence of climatic variables on these parameters. Although the California pocket mouse population remained relatively stable during our study (as indicated by λ = 1.00), changing climate and anthropogenic influences on California oak woodland could adversely influence demographic parameters and population dynamics and might also indicate effects of climate change on its ecologically sensitive habitat.

Decomposing fecundity and evaluating demographic influence of multiple broods in a migratory bird

Relevance of breeding season fecundity as a driver of population dynamics has been highlighted by many studies. Despite that, knowledge about how brood type specific (i.e. first, second or replacement) fecundity affects demography of multiple-brooded species is limited. In fact, estimation of brood type specific fecundity is often challenging due to imperfect detection of nesting attempts. We examined the demographic contribution and the feedback on population density of different components of fecundity, along with other vital rates, in a facultative multiple-brooded migratory bird. We used a novel formulation of a fecundity model that allows incorporating reproductive data for which information on the type of brood was unknown in some cases, and embedded it into an integrated population model (IPM) to obtain consensual estimates of all demographic rates, including brood type specific fecundities, reproductive success probabilities and proportion of breeding pairs that performed a second or replacement brood. We then conducted transient life table response experiments on IPM estimates to account for non-stationary environments. We applied the model to two 20-year datasets collected in a Swiss and a German local population of wrynecks Jynx torquilla. Brood type specific fecundities and temporal patterns of brood type specific probabilities of success, number of successful and unsuccessful first broods, probability of starting a second or a replacement brood and proportion of pairs that performed a second or a replacement brood differed between the two populations. However, changes in immigration rate and apparent survival were the dominant contributors to temporal variation and large sequential changes in realized population growth rates in both populations. In the Swiss population we also found that second brood fecundity declined when population size increased. Our study provides insight into the reproductive processes that affect population dynamics and mediate density-dependent fecundity in a migratory bird. In addition, the analytical approach proposed can be used in other studies of multiple-brooded species to maximize the use of available fecundity data through the estimation of unknown brood types, thus favouring a better understanding of the demographic contribution of brood type specific fecundity.

Population dynamics of an endangered forest bird using mark–recapture models based on DNA-tagging

Populations of vertebrates are built of individuals of different sex, age class or stage, which often affect distinctly the population dynamics. Such intrapopulation partitioning of vital rates needs to be identified to develop efficient conservation actions. Using DNA extracted from feces and feathers we combined DNA-tagging and mark–recapture analyses to evaluate sex-specific population dynamics of an endangered population of capercaillie (Tetrao urogallus; Phasianidae). We built encounter histories for 120 individuals in the mating seasons of 2009–2011, in a study area of about 424 km2. Minimum number of individuals per mating season and estimates of population size ranged 56–67 and 76–115, respectively. Estimates of population size were consistently lower in multiple-season, open-population models than in single-season closed-population models. The super-population in the study area was 149 individuals for the whole study period. Sex-ratio was notably male-biased. Probability of recapture p ranged 0.62–0.70, and was similar for males and females. Female apparent survival φ was lower than expected, and much lower than male apparent survival. It includes however movements in and out of the sampled population, thus comparison with previously reported values based on conventional tagging should be cautious. Females showed higher turnover, indicated by higher probability β of entering the sampled population, and higher number of entries from the super-population, Bgross. Realized population growth rate ʎ was > 1 for both females and males. The combination of non-intrusive DNA-tagging and the analytical framework of mark–recapture models provided inferences on population dynamics that would have been hardly feasible with conventional methods. Male-biased sex ratios, higher female turnover and seemingly low female apparent survival were our key findings. While the whole population needs continuous monitoring, we believe that adult females deserve priority attention in evaluation and design of conservation actions.

Climatic drivers of pinyon mouse Peromyscus truei population dynamics in a resource‐restricted environment

AbstractHighly variable patterns in temperature and rainfall events can have pronounced consequences for small mammals in resource‐restricted environments. Climatic factors can therefore play a crucial role in determining the fates of small mammal populations. We applied Pradel's temporal symmetry model to a 21‐year capture–recapture dataset to study population dynamics of the pinyon mouse (Peromyscus truei) in a semi‐arid mixed oak woodland in California, USA. We examined time‐, season‐ and sex‐specific variation in realized population growth rate (λ) and its constituent vital rates, apparent survival and recruitment. We also tested the influence of climatic factors on these rates. Overall monthly apparent survival was 0.81 ± 0.004 (estimate ± SE). Survival was generally higher during wetter months (October–May) but varied over time. Monthly recruitment rate was 0.18 ± 0.01, ranging from 0.07 ± 0.01 to 0.63 ± 0.07. Although population growth rate (λ) was highly variable, overall monthly growth rate was close to 1.0, indicating a stable population during the study period (λ ± SE = 0.99 ± 0.01). Average temperature and its variability negatively affected survival, whereas rainfall positively influenced survival and recruitment rates, and thus the population growth rate. Our results suggest that seasonal rainfall and variation in temperature at the local scale, rather than regional climatic patterns, more strongly affected vital rates in this population. Discerning such linkages between species' population dynamics and environmental variability are critical for understanding local and regional impacts of global climate change, and for gauging viability and resilience of populations in resource‐restricted environments.

Population development of the predatory mite Amblydromalus limonicus is modulated by habitat dispersion, diet and density of conspecifics

Habitat dispersion, diet and density can influence the per capita population growth of predators, and dispersed habitat can provide a spatial refuge that reduces the possibility of cannibalism among predators, thereby increasing their realized population growth rate. We tested the influence of variable habitat dispersion (dispersed patches, general patches and aggregated patches), two diets (Typha orientalis pollen and Ephestia kuehniella eggs) and initial predator density-one or two Amblydromalus limonicus (Garman and McGregor) (Acari: Phytoseiidae) founder females-on the population growth of A. limonicus in 7days. Dispersed patches resulted in a higher total number of A. limonicus than the other two types of habitat dispersion from days 3-7 when fed on either of the diets, and started with either one or two A. limonicus females. Compared with E. kuehniella eggs, T. orientalis pollen resulted in more A. limonicus regardless of one or two founder females. Compared with two founder females, beginning with one founder female on pollen produced significantly more predatory mite females in dispersed and aggregated patches. A four-way ANOVA showed that the main effects indicated that habitat, diet, density, and time significantly influenced the number of immature and female A. limonicus. Significant interactions between habitat dispersion and diet were detected on immature and female A. limonicus. Our findings suggest that increasing the dispersion of artificial shelters on crop leaves may stimulate the control efficiency of predators in greenhouses. Furthermore, T. orientalis pollen provides a high nutritional quality supplemental diet that could enhance the ability of A. limonicus to control pests.

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.

Survival, recruitment, and population growth rate of an important mesopredator: the northern raccoon.

Populations of mesopredators (mid-sized mammalian carnivores) are expanding in size and range amid declining apex predator populations and ever-growing human presence, leading to significant ecological impacts. Despite their obvious importance, population dynamics have scarcely been studied for most mesopredator species. Information on basic population parameters and processes under a range of conditions is necessary for managing these species. Here we investigate survival, recruitment, and population growth rate of a widely distributed and abundant mesopredator, the northern raccoon (Procyon lotor), using Pradel’s temporal symmetry models and >6 years of monthly capture-mark-recapture data collected in a protected area. Monthly apparent survival probability was higher for females (0.949, 95% CI = 0.936–0.960) than for males (0.908, 95% CI = 0.893–0.920), while monthly recruitment rate was higher for males (0.091, 95% CI = 0.078–0.106) than for females (0.054, 95% CI = 0.042–0.067). Finally, monthly realized population growth rate was 1.000 (95% CI = 0.996–1.004), indicating that our study population has reached a stable equilibrium in this relatively undisturbed habitat. There was little evidence for substantial temporal variation in population growth rate or its components. Our study is one of the first to quantify survival, recruitment, and realized population growth rate of raccoons using long-term data and rigorous statistical models.

Density dependence or climatic variation? Factors influencing survival, recruitment, and population growth rate of Virginia opossums

Abstract Mesopredators play an increasingly important role in ecosystems where apex predators have been eliminated, but population ecology of these midsized mammalian carnivores remains poorly understood. We applied Pradel's temporal symmetry models to > 6 years of monthly capture–mark–recapture data and investigated factors influencing apparent survival, recruitment, and realized population growth rate of the Virginia opossum (Didelphis virginiana), an important mesopredator with unique life-history characteristics. Apparent survival did not vary temporally; monthly survival probabilities were 0.86 ± 0.01 (SE) for females and 0.76 ± 0.02 for males. Recruitment rate varied monthly, with the highest recruitment in December (0.32 ± 0.12 for females and 0.57 ± 0.22 for males). Realized population growth rate varied monthly and was also highest in December (1.30 ± 0.17). Both recruitment and population growth rate were positively influenced by the monthly coefficient of variation of precipitation. There was n...

Environmental context influences both the intensity of seed predation and plant demographic sensitivity to attack

Variation in mutualistic and antagonistic interactions are important sources of variation in population dynamics and natural selection. Environmental heterogeneity can influence the outcome of interactions by affecting the intensity of interactions, but also by affecting the demography of the populations involved. However, little is known about the relative importance of environmental effects on interaction intensities and demographic sensitivity for variation in population growth rates. We investigated how soil depth, soil moisture, soil nutrient composition, and vegetation height influenced the intensity of seed predation as well as host plant demography and sensitivity to seed predation in the perennial herb Primula farinosa. Intensity of seed predation ranged from 0% to 80% of seeds damaged among the 24 study populations and was related to soil moisture in two of four years. The effect of seed predation on plant population growth rate (lambda) ranged from negligible to a reduction in lambda by 0.70. Sensitivity of population growth rate to predation explained as much of the variation in the reductions in population growth rate due to seed predation as did predation intensity. Plant population growth rate in the absence of seed predation and sensitivity to predation were negatively related to soil depth and soil moisture. Both intensity of predation and sensitivity to predation were positively correlated with potential population growth rate and, as a result, there was no significant relationship between predation intensity and realized population growth rate. We conclude that in our study system environmental context influences the effects of seed predation on plant fitness and population dynamics in two important ways: through variation in interaction intensity and through sensitivity to the effects of this interaction. Moreover, our results show that a given abiotic factor can influence population growth rate in different directions through effects on potential growth rate, intensity of biotic interactions, and the sensitivity of population growth rate to interactions.

Historical abundance and spatial distributions of spawners determine juvenile habitat accessibility in salmon: implications for population dynamics and management targets

Spatial distribution of spawning may have important ramifications for population dynamics in species where early life stages suffer from low mobility and high density-dependent mortality. Here, we use time series of spatial spawning distribution in Atlantic salmon (Salmo salar) to test for density-dependent behavioural effects on the spatial utilization of spawning sites and resulting juvenile habitat availability. The probability of utilizing spawning sites in a given year increased both with increasing spawner abundance and proximity to sites used the previous year. The accessible area for juveniles increased asymptotically with both current and time-lagged spawner abundance. Several nonexclusive mechanisms may be responsible for the observed direct and lagged density dependence of spawner distributions, including social aggregation, asymmetric competition for space, local homing, and habitat modification by the previous year’s spawners. Time-lagged density-dependent spawner distributions can be predicted to reduce the realized population growth rate. If such effects are not accounted for, this may lead to a downward bias in estimates of spawning targets or other associated conservation or management measures derived from population abundance time series.

Are declines of an endangered mammal predation‐driven, and can a captive‐breeding and release program aid their recovery?

AbstractDeclines of imperiled small mammals are often attributed to predation without investigating the relative influence of survival and reproductive parameters on population growth. Accordingly, declines in the endangered Key Largo woodrat Neotoma floridana smalli (KLWR) population have been attributed to predation by feral cats Felis catus, Burmese pythons Python molurus bivittatus and raccoons Procyon lotor. We estimated survival, recruitment and realized population growth rates from four capture–mark–recapture studies to determine if the pattern of demographic variation was consistent with predation as the primary cause of KLWR declines. Additionally, we evaluated the KLWR captive‐breeding and release program by comparing survival of captive‐born and released KLWRs to wild‐born KLWRs. The realized population growth rate of wild‐born KLWRs had a strong pattern of covariation with recruitment; covariation between the realized population growth rate and apparent survival was negligible. Consistent with demographic theory, our results suggest that KLWR population dynamics were driven primarily by variation in recruitment, and that periodic reductions in recruitment led to population declines. We found that the survival curve and the first month (S1) and first 3‐month (S1–3) survival estimates for the wild‐born KLWRs [S1 = 0.929 (0.890–0.968); S1–3 = 0.942 (0.919–0.965)] were considerably higher (χ2 = 33.9, 1 d.f., P < 0.001) than released KLWRs [S1 = 0.521 (0.442–0.600); S1–3 = 0.561 (0.493–0.629)]. Low survival rates from predation limited the success of the captive‐breeding and release program. This study illustrates the importance of pre‐release conditioning of captive‐bred animals and the importance of considering reproductive parameters in conjunction with survival estimates to understand the drivers of population decline.

Long‐term demographic consequences of habitat fragmentation to a tropical understory bird community

Tropical deforestation continues to cause population declines and local extinctions in centers of avian diversity and endemism. Although local species extinctions stem from reductions in demographic rates, little is known about how habitat fragmentation influences survival of tropical bird populations or the relative importance of survival and fecundity in ultimately shaping communities. We analyzed 22 years of mark-recapture data to assess how fragmentation influenced apparent survival, recruitment, and realized population growth rate within 22 forest understory bird species in the Usambara Mountains, Tanzania. This represents the first such effort, in either tropical or temperate systems, to characterize the effect of deforestation on avian survival across such a broad suite of species. Long-term demographic analysis of this suite of species experiencing the same fragmented environment revealed considerable variability in species' responses to fragmentation, in addition to general patterns that emerged from comparison among species. Across the understory bird community as a whole, we found significantly lower apparent survival and realized population growth rate in small fragments relative to large, demonstrating fragmentation effects to demographic rates long after habitat loss, Demographic rates were depressed across five feeding guilds, suggesting that fragmentation sensitivity was not limited to insectivores. Seniority analyses, together with a positive effect of fragmentation on recruitment, indicated that depressed apparent survival was the primary driver of population declines and observed extinctions. We also found a landscape effect, with lower vital rates in one mountain range relative to another, suggesting that fragmentation effects may add to other large-scale drivers of population decline. Overall, realized population growth rate (lambda) estimates were < 1 for most species, suggesting that future population persistence, even within large forest fragments, is uncertain in this biodiversity hotspot.

Estimating grizzly and black bear population abundance and trend in Banff National Park using noninvasive genetic sampling.

We evaluated the potential of two noninvasive genetic sampling methods, hair traps and bear rub surveys, to estimate population abundance and trend of grizzly (Ursus arctos) and black bear (U. americanus) populations in Banff National Park, Alberta, Canada. Using Huggins closed population mark-recapture models, we obtained the first precise abundance estimates for grizzly bears ( = 73.5, 95% CI = 64–94 in 2006; = 50.4, 95% CI = 49–59 in 2008) and black bears ( = 62.6, 95% CI = 51–89 in 2006; = 81.8, 95% CI = 72–102 in 2008) in the Bow Valley. Hair traps had high detection rates for female grizzlies, and male and female black bears, but extremely low detection rates for male grizzlies. Conversely, bear rubs had high detection rates for male and female grizzlies, but low rates for black bears. We estimated realized population growth rates, lambda, for grizzly bear males ( = 0.93, 95% CI = 0.74–1.17) and females ( = 0.90, 95% CI = 0.67–1.20) using Pradel open population models with three years of bear rub data. Lambda estimates are supported by abundance estimates from combined hair trap/bear rub closed population models and are consistent with a system that is likely driven by high levels of human-caused mortality. Our results suggest that bear rub surveys would provide an efficient and powerful means to inventory and monitor grizzly bear populations in the Central Canadian Rocky Mountains.

Synergistic influences of phase, density, and climatic variation on the dynamics of fluctuating populations

Although ecologists have long recognized that certain mammalian species exhibit high-amplitude, often multiannual, fluctuations in abundance, their causes have remained poorly understood and the subject of intense debate. A key contention has been the relative role of density-dependent and density-independent processes in governing population dynamics. We applied capture-mark-recapture analysis to 25 years of monthly trapping data from a fluctuating prairie vole Microtus ochrogaster population in Illinois, USA, to estimate realized population growth rates and associated vital rates (survival and recruitment) and modeled them as a function of vole density and density-independent climatic variation. We also tested for phase dependence and seasonality in the effects of the above processes. Variation in the realized population growth rate was best explained by phase-specific changes in vole density lagged by one month and mean monthly temperatures with no time lags. The underlying vital rates, survival and recruitment, were influenced by the additive and interactive effects of phase, vole density, and mean monthly temperatures. Our results are consistent with the observation that large-scale population fluctuations are characterized by phase-specific changes in demographic and physiological characteristics. Our findings also support the growing realization that the interaction between climatic variables and density-dependent factors may be a widespread phenomenon, and they suggest that the direction and magnitude of such interactive effects may be phase specific. We conclude that density-dependent and density-independent climatic variables work in tandem during each phase of density fluctuations to drive the dynamics of fluctuating populations.

RECOLONIZING WOLVES AND MESOPREDATOR SUPPRESSION OF COYOTES: IMPACTS ON PRONGHORN POPULATION DYNAMICS

Food web theory predicts that the loss of large carnivores may contribute to elevated predation rates and, hence, declining prey populations, through the process of mesopredator release. However, opportunities to test predictions of the mesopredator release hypothesis are rare, and the extent to which changes in predation rates influence prey population dynamics may not be clear due to a lack of demographic information on the prey population of interest. We utilized spatial and seasonal heterogeneity in wolf distribution and abundance to evaluate whether mesopredator release of coyotes (Canis latrans), resulting from the extirpation of wolves (Canis lupus) throughout much of the United States, contributes to high rates of neonatal mortality in ungulates. To test this hypothesis, we contrasted causes of mortality and survival rates of pronghorn (Antilocapra americana) neonates captured at wolf-free and wolf-abundant sites in western Wyoming, USA, between 2002 and 2004. We then used these data to parameterize stochastic population models to heuristically assess the impact of wolves on pronghorn population dynamics due to changes in neonatal survival. Coyote predation was the primary cause of mortality at all sites, but mortality due to coyotes was 34% lower in areas utilized by wolves (P < 0.001). Based on simulation modeling, the realized population growth rate was 0.92 based on fawn survival in the absence of wolves, and 1.06 at sites utilized by wolves. Thus, wolf restoration is predicted to shift the trajectory of the pronghorn population from a declining to an increasing trend. Our results suggest that reintroductions of large carnivores may influence biodiversity through effects on prey populations mediated by mesopredator suppression. In addition, our approach, which combines empirical data on the population of interest with information from other data sources, demonstrates the utility of using simulation modeling to more fully evaluate ecological theories by moving beyond estimating changes in vital rates to analyses of population-level impacts.

Spatiotemporal variation in reproductive parameters of yellow-bellied marmots

Spatiotemporal variation in reproductive rates is a common phenomenon in many wildlife populations, but the population dynamic consequences of spatial and temporal variability in different components of reproduction remain poorly understood. We used 43 years (1962-2004) of data from 17 locations and a capture-mark-recapture (CMR) modeling framework to investigate the spatiotemporal variation in reproductive parameters of yellow-bellied marmots (Marmota flaviventris), and its influence on the realized population growth rate. Specifically, we estimated and modeled breeding probabilities of two-year-old females (earliest age of first reproduction), >2-year-old females that have not reproduced before (subadults), and >2-year-old females that have reproduced before (adults), as well as the litter sizes of two-year old and >2-year-old females. Most reproductive parameters exhibited spatial and/or temporal variation. However, reproductive parameters differed with respect to their relative influence on the realized population growth rate (lambda). Litter size had a stronger influence than did breeding probabilities on both spatial and temporal variations in lambda. Our analysis indicated that lambda was proportionately more sensitive to survival than recruitment. However, the annual fluctuation in litter size, abetted by the breeding probabilities, accounted for most of the temporal variation in lambda.

SPATIOTEMPORAL VARIATION IN SURVIVAL RATES: IMPLICATIONS FOR POPULATION DYNAMICS OF YELLOW-BELLIED MARMOTS

Spatiotemporal variation in age-specific survival rates can profoundly influence population dynamics, but few studies of vertebrates have thoroughly investigated both spatial and temporal variability in age-specific survival rates. We used 28 years (1976-2003) of capture-mark-recapture (CMR) data from 17 locations to parameterize an age-structured Cormack-Jolly-Seber model, and investigated spatial and temporal variation in age-specific annual survival rates of yellow-bellied marmots (Marmota flaviventris). Survival rates varied both spatially and temporally, with survival of younger animals exhibiting the highest degree of variation. Juvenile survival rates varied from 0.52 +/- 0.05 to 0.78 +/- 0.10 among sites and from 0.15 +/- 0.14 to 0.89 +/- 0.06 over time. Adult survival rates varied from 0.62 +/- 0.09 to 0.80 +/- 0.03 among sites, but did not vary significantly over time. We used reverse-time CMR models to estimate the realized population growth rate (lamda), and to investigate the influence of the observed variation in age-specific survival rates on lamda. The realized growth rate of the population closely covaried with, and was significantly influenced by, spatiotemporal variation in juvenile survival rate. High variability in juvenile survival rates over space and time clearly influenced the dynamics of our study population and is also likely to be an important determinant of the spatiotemporal variation in the population dynamics of other mammals with similar life history characteristics.