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1.
Understanding how reproductive tradeoffs act in concert with abiotic elements to affect survival is important for effective management and conservation of wildlife populations, particularly for at-risk or harvested species. Wild turkeys (Meleagris gallopavo) are a high-interest species for consumptive and non-consumptive uses, and female survival is a primary factor influencing turkey population dynamics. We radio-tracked and collected survival data on 140 female Merriam's wild turkeys (M. g. merriami) in the northern Black Hills, South Dakota, USA, 2016–2018. We developed and compared a set of candidate models to evaluate how nest incubation, brood rearing, and precipitation could be associated with female survival. Increased time spent incubating was associated with reduced female survival. Additionally, daily precipitation was associated with reduced survival of incubating females. Seasonal survival was lowest during spring and winter. A female that did not incubate a nest was predicted to have a higher rate of annual survival (0.53, 85% CI = 0.48–0.59) than a female that incubated a single nest (0.47, 85% CI = 0.42–0.53). Despite the relative proximity of population segments, we estimated that annual survival for nesting and non-nesting females was lower in the northern Black Hills compared to annual female survival in the southern Black Hills, underscoring the need for region-specific data when possible. © 2020 The Wildlife Society.  相似文献   

2.
Population growth is highly sensitive to changes in reproductive rates for many avian species. Understanding how reproductive rates are related to environmental conditions can give managers insight into factors contributing to population change. Harvest trends of eastern wild turkey in northeastern South Dakota suggest a decline in abundance. We investigated factors influencing reproductive success of this important game bird to identify potential factors contributing to the decline. We monitored nesting rate, nest survival, renesting rate, clutch size, hatchability, and poult survival of 116 eastern wild turkey hens using VHF radio transmitters during the springs and summers of 2017 and 2018. Heavier hens were more likely to attempt to nest than lighter hens, and adult hens were more likely to renest than yearling hens. Nest survival probability was lowest in agricultural fields relative to all other cover types and positively related to horizontal visual obstruction and distance to the nearest road. Daily nest survival probability demonstrated an interaction between temperature and precipitation, such that nest survival probability was lower on warm, wet days, but lowest on dry days. Egg predation was the leading cause of nest failure, followed by haying of the nest bowl and death of the incubating hen. Poults reared by adult hens had a greater probability of survival than poults reared by yearling hens. Our estimate of survival probability of poults raised by yearling hens was low relative to other studies, which may be contributing to the apparent regional population decline. However, there is little managers can do to influence poult survival in yearling hens. Alternatively, we found nest survival probability was lowest for nests initiated in agricultural fields. Wildlife‐friendly harvesting practices such as delayed haying or installation of flushing bars could help increase productivity of eastern wild turkey in northeastern South Dakota.  相似文献   

3.
Wild horses (Equus caballus) are a non‐native species occupying over 2800 km2 of the nationally significant Australian Alps National Parks. We estimated key demographic parameters (fecundity, adult and juvenile survival and annual finite population growth rate) over 3 years and related these to horse body condition and available food for three populations under natural conditions, and found a trend consistent with food limitation. The populations were independent, with different site characteristics and occupied areas, identified by land managers, as areas of concern about possible conservation impacts. Annual fecundity and juvenile survival varied across sites averaging between 0.21 and 0.31 female young per adult female, and 0.83 and 0.90 per annum, respectively, and annual adult survival was consistent across sites averaging 0.91 per annum. One population was increasing (λ = 1.09 year?1; 95% CI 1.04–1.14) and two populations were stable (λ ~ 1.0 year?1). Mean body condition of horses was positively correlated with mean pasture biomass rank. Across the three populations, fecundity, recruitment, body condition and annual finite population growth rate were lowest when mean pasture biomass rank was lowest and conversely highest when pasture rank was highest. We conclude that food limitation appears to be operating across these three sites. We used our results to assess the sensitivity of annual finite rate of increase (λ) to changes in key demographic parameters and found that λ was most sensitive to a change in adult survival, with the second most sensitive parameter being fecundity. Thus, if the aim of management is to reduce the size of the wild horse population then targeting adult survival is most important, followed by fecundity. Finally, we estimated the linear, negative, numerical response for wild horses between annual λ and horses per unit pasture biomass.  相似文献   

4.
Demographic studies of imperiled populations can aid managers in planning conservation actions. However, applicability of findings for a single population across a species’ range is sometimes questionable. We conducted long-term studies (8 and 9 years, respectively) of 2 populations of the lizard Phrynosoma cornutum separated by 1000 km within the historical distribution of the species. The sites were a 15-ha urban wildlife reserve on Tinker Air Force Base (TAFB) in central Oklahoma and a 6000-ha wildland site in southern Texas, the Chaparral Wildlife Management Area (CWMA). We predicted a trade-off between the effect of adult survival and fecundity on population growth rate (λ), leading to population-specific contributions of individual vital rates to λ and individualized strategies for conservation and management of this taxon. The CWMA population had lower adult survival and higher fecundity than TAFB. As predicted, there was a trade-off in the effects of adult survival and fecundity on λ between the two sites; fecundity affected λ more at CWMA than at TAFB. However, adult survival had the smallest effect on λ in both populations. We found that recruitment in P. cornutum most affected λ at both sites, with hatchling survival having the strongest influence on λ. Management strategies focusing on hatchling survival would strongly benefit both populations. As a consequence, within the constraint of the need to more accurately estimate hatchling survival, managers across the range of species such as P. cornutum could adopt similar management priorities with respect to stage classes, despite intra-population differences in population vital rates.  相似文献   

5.
We analyzed the population dynamics of a burrowing owl (Athene cunicularia) colony at Mineta San Jose International Airport in San Jose, California, USA from 1990–2007. This colony was managed by using artificial burrows to reduce the occurrence of nesting owls along runways and within major airport improvement projects during the study period. We estimated annual reproduction in natural and artificial burrows and age-specific survival rates with mark–recapture techniques, and we estimated the relative contribution of these vital rates to population dynamics using a life table response experiment. The breeding colony showed 2 distinct periods of change: high population growth from 7 nesting pairs in 1991 to 40 pairs in 2002 and population decline to 17 pairs in 2007. Reproduction was highly variable: annual nesting success (pairs that raised ≥1 young) averaged 79% and ranged from 36% to 100%, whereas fecundity averaged 3.36 juveniles/pair and ranged from 1.43 juveniles/pair to 4.54 juveniles/pair. We estimated annual adult survival at 0.710 during the period of colony increase from 1996 to 2001 and 0.465 during decline from 2002 to 2007, but there was no change in annual survival of juveniles between the 2 time periods. Long-term population growth rate (λ) estimated from average vital rates was λa = 1.072 with λi = 1.288 during colony increase and λd = 0.921 (Δλ = 0.368) during decline. A life table response experiment showed that change in adult survival rate during increasing and declining phases explained more than twice the variation in growth rate than other vital rates. Our findings suggest that management and conservation of declining burrowing owl populations should address factors that influence adult survival. © 2011 The Wildlife Society.  相似文献   

6.
Satu Ramula 《Oecologia》2014,174(4):1255-1264
Invaders generally show better individual performance than non-invaders and, therefore, vital rates (survival, growth, fecundity) could potentially be used to predict species invasiveness outside their native range. Comparative studies have usually correlated vital rates with the invasiveness status of species, while few studies have investigated them in relation to population growth rate. Here, I examined the influence of five vital rates (plant establishment, survival, growth, flowering probability, seed production) and their variability (across geographic regions, habitat types, population sizes and population densities) on population growth rate (λ) using data from 37 populations of an invasive, iteroparous herb (Lupinus polyphyllus) in a part of its invaded range in Finland. Variation in vital rates was often related to habitat type and population density. The performance of the populations varied from declining to rapidly increasing independently of habitat type, population size or population density, but differed between regions. The population growth rate increased linearly with plant establishment, and with the survival and growth of vegetative individuals, while the survival of flowering individuals and annual seed production were not related to λ. The vital rates responsible for rapid population growth varied among populations. These findings highlight the importance of both regional and local conditions to plant population dynamics, demonstrating that individual vital rates do not necessarily correlate with λ. Therefore, to understand the role of individual vital rates in a species ability to invade, it is necessary to quantify their effect on population growth rate.  相似文献   

7.
Using field data from previous studies we built matrix models for two populations of giant rosettes, Espeletia timotensis Cuatrec. and E. spicata Sch. Bip. Wedd., from the Andes Cordillera in Mérida, Venezuela. We analysed the models and calculated population growth rate (λ), sensitivities, elasticities and the sensitivity of the elasticities to changes in the vital rates. The analysis showed that the two species behave alike in general demographic terms. In both models, population growth rate is positive and sensitivities of λ to changes in vital rates decrease markedly in this order: plant establishment, progression of juvenile–adult, germination and survival. The relative contributions of vital rates to λ (elasticities) are very similar to those of other woody plant species: a higher contribution of survival and a very low contribution of fecundity. Transition from seedling to juvenile is most important and the younger established stages (juveniles and young adults) play a predominant demographic role in both populations. Seed banks and older adults are playing a relatively minor role in the dynamics of both populations. However, they may be important in relation to unpredictable, favourable or detrimental events. Perturbation analysis of elasticities showed that increasing the rate of plant establishment will decrease the relative importance of stasis. We conclude that both species are demographically very close, and similar to other long‐lived woody plant species. However, the two species differ in the role of the seed bank, which seems more important in the demography of E. spicata than in E. timotensis.  相似文献   

8.
Despite decades of field research on greater sage-grouse, range-wide demographic data have yet to be synthesized into a sensitivity analysis to guide management actions. We reviewed range-wide demographic rates for greater sage-grouse from 1938 to 2011 and used data from 50 studies to parameterize a 2-stage, female-based population matrix model. We conducted life-stage simulation analyses to determine the proportion of variation in population growth rate (λ) accounted for by each vital rate, and we calculated analytical sensitivity, elasticity, and variance-stabilized sensitivity to identify the contribution of each vital rate to λ. As expected for an upland game bird, greater sage-grouse showed marked annual and geographic variation in several vital rates. Three rates were demonstrably important for population growth: female survival, chick survival, and nest success. Female survival and chick survival, in that order, had the most influence on λ per unit change in vital rates. However, nest success explained more of the variation in λ than did the survival rates. In lieu of quantitative data on specific mortality factors driving local populations, we recommend that management efforts for greater sage-grouse first focus on increasing female survival by restoring large, intact sagebrush-steppe landscapes, reducing persistent sources of human-caused mortality, and eliminating anthropogenic habitat features that subsidize species that prey on juvenile, yearling, and adult females. Our analysis also supports efforts to increase chick survival and nest success by eliminating anthropogenic habitat features that subsidize chick and nest predators, and by managing shrub, forb, and grass cover, height, and composition to meet local brood-rearing and nesting habitat guidelines. We caution that habitat management to increase chick survival and nest success should not reduce the cover or height of sagebrush below that required for female survival in other seasons (e.g., fall, winter). The success or failure of management actions for sage-grouse should be assessed by measuring changes in vital rates over long time periods to avoid confounding with natural, annual variation. © 2011 The Wildlife Society.  相似文献   

9.
Abstract: Age ratios (e.g., calf:cow for elk and fawn:doe for deer) are used regularly to monitor ungulate populations. However, it remains unclear what inferences are appropriate from this index because multiple vital rate changes can influence the observed ratio. We used modeling based on elk (Cervus elaphus) life-history to evaluate both how age ratios are influenced by stage-specific fecundity and survival and how well age ratios track population dynamics. Although all vital rates have the potential to influence calf:adult female ratios (i.e., calf:cow ratios), calf survival explained the vast majority of variation in calf:adult female ratios due to its temporal variation compared to other vital rates. Calf:adult female ratios were positively correlated with population growth rate (Λ) and often successfully indicated population trajectories. However, calf:adult female ratios performed poorly at detecting imposed declines in calf survival, suggesting that only the most severe declines would be rapidly detected. Our analyses clarify that managers can use accurate, unbiased age ratios to monitor arguably the most important components contributing to sustainable ungulate populations, survival rate of young and Λ. However, age ratios are not useful for detecting gradual declines in survival of young or making inferences about fecundity or adult survival in ungulate populations. Therefore, age ratios coupled with independent estimates of population growth or population size are necessary to monitor ungulate population demography and dynamics closely through time.  相似文献   

10.
Abstract: Nest success is an important parameter affecting population fluctuations of wild turkeys (Meleagris gallopavo). Factors influencing mammalian predation on turkey nests are complicated and not well understood. Therefore, we assessed nest hazard risk by testing competing hypotheses of Merriam's turkey (M. g. merriami) nest survival in a ponderosa pine (Pinus ponderosa) ecosystem during 2001–2003. We collected nesting information on 83 female Merriam's turkeys; annual nest success averaged 50% for adult females (range = 45–59%) and 83% for yearling females (range = 75–100%). Proportional hazard modeling indicated that precipitation increased the hazard of nest mortality. However, estimated hazard of nest predation was lowered when incubating females had greater shrub cover and visual obstruction around nests. Coyotes (Canis latrans) were the primary predator on turkey nests. We hypothesize that precipitation is the best predictor of nest survival for first nests because coyotes use olfaction effectively to find nesting females during wet periods. Temporally, as the nesting season progressed, precipitation declined and vegetation cover increased and coyotes may have more difficulty detecting nests under these conditions later in the nesting period. The interaction of concealment cover with precipitation indicated that nest hazard risk from daily precipitation was reduced with greater shrub cover. Management activities that promote greater shrub cover may partially offset the negative effects of greater precipitation events.  相似文献   

11.
We estimated grizzly bear (Ursus arctos) population vital rates and trend for the Northern Continental Divide Ecosystem (NCDE), Montana, between 2004 and 2009 by following radio-collared females and observing their fate and reproductive performance. Our estimates of dependent cub and yearling survival were 0.612 (95% CI = 0.300–0.818) and 0.682 (95% CI = 0.258–0.898). Our estimates of subadult and adult female survival were 0.852 (95% CI = 0.628–0.951) and 0.952 (95% CI = 0.892–0.980). From visual observations, we estimated a mean litter size of 2.00 cubs/litter. Accounting for cub mortality prior to the first observations of litters in spring, our adjusted mean litter size was 2.27 cubs/litter. We estimated the probabilities of females transitioning from one reproductive state to another between years. Using the stable state probability of 0.322 (95% CI = 0.262–0.382) for females with cub litters, our adjusted fecundity estimate (mx) was 0.367 (95% CI = 0.273–0.461). Using our derived rates, we estimated that the population grew at a mean annual rate of approximately 3% (λ = 1.0306, 95% CI = 0.928–1.102), and 71.5% of 10,000 Monte Carlo simulations produced estimates of λ > 1.0. Our results indicate an increasing population trend of grizzly bears in the NCDE. Coupled with concurrent studies of population size, we estimate that over 1,000 grizzly bears reside in and adjacent to this recovery area. We suggest that monitoring of population trend and other vital rates using radioed females be continued. © 2011 The Wildlife Society.  相似文献   

12.
Abstract Many current wild turkey (Meleagris gallopavo) harvest models assume density-independent population dynamics. We developed an alternative model incorporating both nonlinear density-dependence and stochastic density-independent effects on wild turkey populations. We examined model sensitivity to parameter changes in 5% increments and determined mean spring and fall harvests and their variability in the short term (3 yr) and long term (10 yr) from proportional harvesting under these conditions. In the long term, population growth rates were most sensitive to poult:female ratios and the form of density dependence. The nonlinear density-dependent effect produced a population that maximized yield at 40% carrying capacity. The model indicated that a spring or fall proportional harvest could be maximized for fall harvest rates between 0% and 13% of the population, assuming a 15% spring male harvest and 5% spring illegal female kill. Combined spring and fall harvests could be maximized at a 9% fall harvest, under the same assumptions. Variability in population growth and harvest rates increased uncertainty in spring and fall harvests and the probability of overharvesting annual yield, with growth rate variation having the strongest effect. Model simulations suggested fall harvest rates should be conservative (≤9%) for most management strategies.  相似文献   

13.
The 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.  相似文献   

14.
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16.
Population viability analyses are useful tools to predict abundance and extinction risk for imperiled species. In southeastern North America, the federally threatened gopher tortoise (Gopherus polyphemus) is a keystone species in the diverse and imperiled longleaf pine (Pinus palustris) ecosystem, and researchers have suggested that tortoise populations are declining and characterized by high extinction risk. We report results from a 30-year demographic study of gopher tortoises in southern Alabama (1991–2020), where 3 populations have been stable and 3 others have declined. To better understand the demographic vital rates associated with stable and declining tortoise populations, we used a multi-state hierarchical mark-recapture model to estimate sex- and stage-specific patterns of demographic vital rates at each population. We then built a predictive population model to project population dynamics and evaluate extinction risk in a population viability context. Population structure did not change significantly in stable populations, but juveniles became less abundant in declining populations over 30 years. Apparent survival varied by age, sex, and site; adults had higher survival than juveniles, but female survival was substantially lower in declining populations than in stable ones. Using simulations, we predicted that stable populations with high female survival would persist over the next 100 years but sites with lower female survival would decline, become male-biased, and be at high risk of extirpation. Stable populations were most sensitive to changes in apparent survival of adult females. Because local populations varied greatly in vital rates, our analysis improves upon previous demographic models for northern populations of gopher tortoises by accounting for population-level variation in demographic patterns and, counter to previous model predictions, suggests that small tortoise populations can persist when habitat is managed effectively. © 2021 The Wildlife Society.  相似文献   

17.
Understanding variation in plant vital rates (survival, growth, and reproduction) and population demographic parameters for rare plant taxa facilitates effective management for long-term persistence. We evaluated demographics of the rare plant Astragalus peckii (Fabaceae), a state-listed Threatened plant in Oregon, USA, with particular emphasis on how a microlepidopteran herbivore, Sparganothis tunicana, impacted vital rates and population growth. Stage-based transition matrix models were used to compute population growth rate (λ) and elasticity from 2006 to 2009 at two populations: Bull Flat, which was located in the main population center; and Chiloquin, a naturally isolated population. Population growth at Bull Flat was stable to slightly declining (λ = 0.96, 95 % CI 0.91–1.00) whereas at Chiloquin, the isolated population, population growth was increasing (λ = 1.20, 95 % CI 1.15–1.24). Microlepidopteran herbivory was associated with different plant responses in each population. At Bull Flat, plant survival was lower with greater herbivore presence. At Chiloquin, reproduction was reduced in plants when herbivores were active earlier in the growing season. Despite these effects on plant vital rates, we found lower population growth only during one transition period at Bull Flat when we compared matrices with and without herbivory. In addition to herbivory, we also address the potential role precipitation plays as a contributor to site differences and temporal variation within sites. Overall, we illustrate how two populations can have different responses to the same disturbance factor and highlight implications for management of different populations across the landscape.  相似文献   

18.
Highly 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.  相似文献   

19.
American Dippers (Cinclus mexicanus) were once known to occur in streams throughout the Black Hills of South Dakota and Wyoming, but now dippers number about 50–75 individuals and reside almost exclusively in a single stream. The recent decline of the American Dipper in the Black Hills of South Dakota is thought to be due to local stream degradation. As a result of the decline of C. mexicanus in the Black Hills of South Dakota and Wyoming, the Black Hills population of American Dippers is a candidate for designation as a distinct population segement (DPS) and might warrant protection and special management. One criterion for DPS designation is genetic uniqueness. Here we present the results of a genetic assessment of the Black Hills population of C. mexicanus. Data presented here indicate that the dipper population in the Black Hills is genetically distinct from other sampled populations. Further population sampling will be needed to understand the genetic population structure of C. mexicanus throughout its range. Furthermore, the recent decline in the Black Hills dipper population should be a warning that other populations (and other species) may be experiencing similar declines and that such montane habitats are worthy of special management.  相似文献   

20.
Wildfire and mountain pine beetle infestations are naturally occurring disturbances in western North American forests. Black-backed woodpeckers (Picoides arcticus) are emblematic of the role these disturbances play in creating wildlife habitat, since they are strongly associated with recently-killed forests. However, management practices aimed at reducing the economic impact of natural disturbances can result in habitat loss for this species. Although black-backed woodpeckers occupy habitats created by wildfire, prescribed fire, and mountain pine beetle infestations, the relative value of these habitats remains unknown. We studied habitat-specific adult and juvenile survival probabilities and reproductive rates between April 2008 and August 2012 in the Black Hills, South Dakota. We estimated habitat-specific adult and juvenile survival probability with Bayesian multi-state models and habitat-specific reproductive success with Bayesian nest survival models. We calculated asymptotic population growth rates from estimated demographic rates with matrix projection models. Adult and juvenile survival and nest success were highest in habitat created by summer wildfire, intermediate in MPB infestations, and lowest in habitat created by fall prescribed fire. Mean posterior distributions of population growth rates indicated growing populations in habitat created by summer wildfire and declining populations in fall prescribed fire and mountain pine beetle infestations. Our finding that population growth rates were positive only in habitat created by summer wildfire underscores the need to maintain early post-wildfire habitat across the landscape. The lower growth rates in fall prescribed fire and MPB infestations may be attributed to differences in predator communities and food resources relative to summer wildfire.  相似文献   

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