Capita Recruitment Research Articles

Strawberry guava invasion of a Hawaiian rainforest: Changing population patterns

AbstractStrawberry guava (waiawī, Psidium cattleyanum Sabine, Myrtaceae) is a small tree invasive on oceanic islands where it may alter forest ecosystem processes and community structure. To better understand the dynamics of its invasion in Hawaiian rainforests in anticipation of the release of a biocontrol agent, we measured growth and abundance of vertical stems ≥0.5 cm DBH for 16 years (2005–2020) in Metrosideros‐Cibotium rainforest on windward Hawai'i Island. Specifically, we compared the growth and abundance of both shoots (originating from seed or from the root mat) and sprouts (originating above ground from established stems) in four replicate study sites. Mean stem density increased from 9562 stems/ha in 2005 to 26,595 stems/ha in 2020, the majority of which were stems <2 cm DBH. Early in the invasion, both density and per capita recruitment of shoots was greater than that of sprouts, but as overall stem density increased, sprout abundance and recruitment came to surpass that of shoots. Relative growth rates among small stems <2 cm DBH declined over time for both shoots and sprouts, but relative growth rates of sprouts were consistently greater than that of shoots after the first 3 years. The capacity of strawberry guava to recruit from both shoots and sprouts facilitates its invasion of rainforest, its persistence in the forest understory, and its response to canopy opening. Strawberry guava thus poses a considerable risk of stand replacement for Hawaiian rainforests. Stand management will require perpetual efforts to control both seed production and sprouting.

No long‐term effect of black bear removal on elk calf recruitment in the southern Appalachians

AbstractIn 2001 and 2002, 52 elk (Cervus canadensis; 21 males, 31 females), originally obtained from Elk Island National Park, Alberta, Canada, were transported and released into Cataloochee Valley in the northeastern portion of Great Smoky Mountains National Park (GRSM, Park), North Carolina, USA. The annual population growth rate (λ) was negative (0.996, 95% CI = 0.945–1.047) and predation by black bears (Ursus americanus) on elk calves was identified as an important determinant of population growth. From 2006 to 2008, 49 bears from the primary elk calving area (i.e., Cataloochee Valley) were trapped and translocated about 70 km to the southwestern portion of the Park just prior to elk calving. Per capita recruitment (i.e., the number of calves produced per adult female that survive to 1 year of age) increased from 0.306 prior to bear translocation (2001–2005) to 0.544 during years when bears were translocated (2006–2008) and λ increased to 1.118 (95% CI = 1.096–1.140). Our objective was to determine whether per capita calf recruitment rates after bear removal (2009–2019) at Cataloochee were similar to the higher rates estimated during bear removal (i.e., long‐term response) or if they returned to rates before bear removal (i.e., short‐term response), and how those rates compared with recruitment from portions of our study area where bears were not relocated. We documented 419 potential elk calving events and monitored 129 yearling and adult elk from 2001 to 2019. Known‐fate models based on radio‐telemetry and observational data supported calf recruitment returning to pre‐2006 levels at Cataloochee (short‐term response); recruitment of Cataloochee elk before and after bear relocation was lower (0.184) than during bear relocation (0.492). Recruitment rates of elk outside the removal area during the bear relocation period (0.478) were similar to before and after rates (0.420). In the Cataloochee Valley, cause‐specific annual calf mortality rates due to predation by bears were 0.319 before, 0.120 during, and 0.306 after bear relocation. In contrast, the cause‐specific annual mortality rate of calves in areas where bears were not relocated was 0.033 after the bear relocation period, with no bear predation on calves before or during bear relocation. The mean annual population growth rate for all monitored elk was 1.062 (95% CI = 0.979–1.140) after bear relocation based on the recruitment and survival data. Even though the effects of bear removal were temporary, the relocations were effective in achieving a short‐term increase in elk recruitment, which was important for the reintroduction program given that the elk population was small and vulnerable to extirpation.

Males die young, which may cause an Allee effect during a population collapse of the Vendace Coregonus albula

AbstractObjectiveWe estimated the difference in mortality between mature male and female Vendace Coregonus albula based on a large data set of catch samples from 25 locations in Finland. We then used this estimate and age distribution data from Lake Etelä‐Konnevesi to illustrate how the sex ratio (females per one male) might decrease as the average age of spawners increases during a several‐year‐long period of recruitment failure.MethodsWe estimated mortalities first from sex‐specific age–ln(catch) curves and second from the average age‐specific proportions of different sexes.ResultThe estimate of the additional mortality of males was around 0.2–0.4, depending on the method of estimation, and assumed true proportions in the population at age 1 (two growing seasons), when Vendace reaches sexual maturity. When using the additional mortality estimate and age distribution data from Lake Etelä‐Konnevesi, the hypothetical sex ratio in the most extreme year was even as skewed as four females per one male.ConclusionIf the lack of males per female spawner during a population decline reduces the per capita recruitment success of females, this is a depensatory density‐dependent effect, the Allee effect. This phenomenon may partly explain the rapid population collapses and contribute to 2‐year cyclicity typical of the dynamics of Vendace populations.

Multi‐scale effects of land cover, weather, and fire on Columbian sharp‐tailed grouse

AbstractColumbian sharp‐tailed grouse (Tympanuchus phasianellus columbianus) are endemic to grassland and shrub‐steppe ecosystems of western North America, yet their distribution has contracted to <10% of their historical range. Primary threats to Columbian sharp‐tailed grouse include loss of native habitat and conversion to agriculture, reductions in habitat once provided by the Conservation Reserve Program (CRP), wildfire, and drought conditions, yet population‐level consequences of these threats and their spatio‐temporal scales of effect are poorly understood. We evaluated multi‐scale effects of land cover, weather, and fire histories on patterns of abundance and productivity for Columbian sharp‐tailed grouse populations during 1995–2020 in Idaho, USA, using mixed‐effects generalized regression and remotely sensed data. We demonstrated negative effects of fire, tree encroachment, and bare ground, positive effects of spring and summer precipitation and cover of shrubs and perennial forbs and grasses, and positive effects of CRP on grouse abundance that changed in magnitude with cover of perennials and shrubs near leks (i.e., strongest effects when average cover of shrubs and perennial forbs and grasses were less abundant). We also demonstrated per capita recruitment of Columbian sharp‐tailed grouse is positively associated with late‐summer greenness. Our results show that several suspected threats have measurable, population‐level impacts to Columbian sharp‐tailed grouse within Idaho. Moreover, our results suggest ongoing changes occurring within the core range of Columbian sharp‐tailed grouse, including loss of CRP cover to tilled agriculture and changes to wildfire and precipitation dynamics are likely to have negative effects on populations.

Analysis of per capita contributions from a spatial model provides strategies for controlling spread of invasive carp

AbstractMetapopulation models may be applied to inform natural resource management to guide actions targeted at location‐specific subpopulations. Model insights frequently help to understand which subpopulations to target and highlight the importance of connections among subpopulations. For example, managers often treat aquatic invasive species populations as discrete populations due to hydrological (e.g., lakes, pools formed by dams) or jurisdictional boundaries (e.g., river segments by country or jurisdictional units such as states or provinces). However, aquatic invasive species often have high rates of dispersion and migration among heterogenous locations, which complicates traditional metapopulation models and may not conform to management boundaries. Controlling invasive species requires consideration of spatial dynamics because local management activities (e.g., harvest, movement deterrents) may have important impacts on connected subpopulations. We expand upon previous work to create a spatial linear matrix model for an aquatic invasive species, Bighead Carp, in the Illinois River, USA, to examine the per capita contributions of specific subpopulations and impacts of different management scenarios on these subpopulations. Managers currently seek to prevent Bighead Carp from invading the Great Lakes via a connection between the Illinois Waterway and Lake Michigan by allocating management actions across a series of river pools. We applied the model to highlight how spatial variation in movement rates and recruitment can affect decisions about where management activities might occur. We found that where the model suggested management actions should occur depend crucially on the specific management goal (i.e., limiting the growth rate of the metapopulation vs. limiting the growth rate of the invasion front) and the per capita recruitment rate in downstream pools. Our findings illustrate the importance of linking metapopulation dynamics to management goals for invasive species control.

Population estimates of photo-identified individuals using a modified POPAN model reveal that Raja Ampat’s reef manta rays are thriving

The 6.7-million-hectare Raja Ampat archipelago is home to Indonesia’s largest reef manta ray (Mobula alfredi) population and a representative network of nine marine protected areas (MPAs). However, the population dynamics ofM. alfrediin the region are still largely unknown. Using our photo-identification database, we fitted modified POPAN mark-recapture models with transience and per capita recruitment parameters to estimate key demographic characteristics ofM. alfredifrom two of Raja Ampat’s largest MPAs: Dampier Strait and South East (SE) Misool. A total of 1,041 unique individuals were photo-identified over an 11-year period (2009–2019) from Dampier Strait (n = 515) and SE Misool (n = 536). In our models, apparent survival probabilities and per capita recruitment rates were strongly linked with El Niño–Southern Oscillation (ENSO) events. Our models also estimated high apparent survival probabilities and significant increases in (sub)population sizes in both MPAs over a decade. In Dampier Strait, the estimated population size increased significantly (p = 0.018) from 226 (95% CI: 161, 283) to 317 (280, 355) individuals. Likewise, the estimated population size in SE Misool increased significantly (p = 0.008) from 210 (137, 308) to 511 (393, 618) individuals. Regardless of variation in the percentage change in population size between years throughout the study, the estimated overall population change shows a compound growth of 3.9% (0.7, 8.6) per annum in Dampier Strait and 10.7% (4.3, 16.1) per annum in SE Misool. Despite the global decline in oceanic sharks and rays due to fishing pressure in the last five decades, our study demonstrates the positive impact of a suite of long-term conservation efforts, coupled with the influence of ENSO events, on increasingM. alfrediabundance in Raja Ampat MPAs. Our study also underscores the importance of long-term monitoring to evaluate the effectiveness of conservation management measures on manta ray populations. Our modification of the standard POPAN model by incorporating per capita recruitment and transience parameters represents an important advance in mark-recapture modelling that should prove useful when examining other manta ray populations and other highly migratory species that are likely to have a substantial percentage of transient individuals.

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.

Pasteurellosis transmission dynamics in free range chicken and wild birds: A deterministic and stochastic modeling approach

Pasteurellosis remains a major problem for poultry worldwide. The disease causes high mortality in chicken, affecting the livelihood of rural poultry farmers. In this paper, both deterministic and continuous time Markov chain (CTMC) models are formulated and analyzed to study the dynamics of pasteurellosis in chicken and wild birds. The next generation matrix method is adopted to determine the basic reproduction number for the deterministic model whereas the multitype branching process is used to compute stochastic threshold for the CTMC model. The normalized forward sensitivity index method is implemented to derive sensitivity indices of model parameters. The results show that the per capita recruitment rate of susceptible chicken and its infection rate due to direct contact are the most positive sensitive parameters, whereas the consumption rate of susceptible chicken by humans and the disease induced death rate are the most negative sensitive parameter. This suggests that infectious chicken drive the disease. Thus efforts on vaccinating and treating susceptible and infectious chicken respectively, will reduce the number of pasteurellosis cases in both chicken and wild bird populations. Numerical simulations for the CTMC stochastic model indicate that the solutions of CTMC stochastic model are relatively close to the solutions of the deterministic model. The probability of pasteurellosis extinction is high when it emerges from infectious birds unlike if it emerges from infectious chicken or P. multocida bacteria. Thus, any intervention that focuses on reducing the number of infectious chicken at the beginning of pasteurellosis outbreak is essential for reducing the transmission of pasteurellosis in chicken and wild birds.

Episodes of high recruitment buffer against climate-driven mass mortality events in a North Pacific seabird population.

Longitudinal studies of marked animals provide an opportunity to assess the relative contributions of survival and reproductive output to population dynamics and change. Cassin's auklets are a long-lived seabird that maximizes annual reproductive effort in resource-rich years through a behaviour called double brooding, the initiation of a second breeding attempt following the success of the first during the same season. Our objective was to explore whether double brooding influenced population change by contributing a greater number of future recruits. We fit temporal symmetry models to 32 years of mark-recapture data of Cassin's auklets to infer the mechanisms underlying the observed variability in per capita recruitment rates. We found that periodic peaks in recruitment were explained by an increase in available nest sites, the proportion of the population double brooding 4years prior, and spring upwelling conditions. Estimates of population change suggests a relatively stable population throughout the time series, attributable to a 'floating' demographic class of sexually mature individuals excluded from breeding by competition which quickly fill vacant sites following periods of low adult survival. Our results highlight the importance of recruitment in maintaining the population of a long-lived seabird periodically impacted by adverse environmental conditions.

Demography of a Eurasian lynx (Lynx lynx) population within a strictly protected area in Central Europe

Large carnivores promote crucial ecosystem processes but are increasingly threatened by human persecution and habitat destruction. Successful conservation of this guild requires information on long-term population dynamics obtained through demographic surveys. We used camera traps to monitor Eurasian lynx between 2009 and 2018 in a strictly protected area in the Bohemian Forest Ecosystem, located in the core of the distribution of the Bohemian–Bavarian–Austrian lynx population. Thereby, we estimated sex-specific demographic parameters using spatial capture–recapture (SCR) models. Over 48,677 trap nights, we detected 65 unique lynx individuals. Density increased from 0.69 to 1.33 and from 1.09 to 2.35 individuals/100 km2 for open and closed population SCR models, respectively, with corresponding positive population growth rates (mean = 1.06). Estimated yearly sex-specific survival probabilities for the entire monitoring period were high (females 82%, males 90%) and per capita recruitment rate was low (females 12%, males 9%), indicating a low yearly population turnover. We ascertained an average number of recruits of 1.97 and a generation time of 2.64 years when considering resident reproducing females. We confirmed that reproduction in the study area took place successfully every year. Despite the overall increase in local lynx densities, the number of detected family groups remained constant throughout the study period. These results indicated that the strictly protected study area acts as a source for the multi-use landscapes in its surroundings. In this first open population SCR study on lynx, we provide sex-specific demographic parameters that are fundamental information for lynx management in the study area as well as in similar contexts Europe-wide.

Assessing Population Viability of Black Bears using Spatial Capture‐Recapture Models

ABSTRACTThe Central Georgia Bear Population (CGP) is the least abundant and most isolated of Georgia's 3 American black bear (Ursus americanus) populations. Beginning in 2011, changes to regulations governing harvest of the CGP resulted in an increase in female bear harvest, creating concern that future harvest could be an important influence on population viability. Hence, our objective was to assess viability of the CGP under various levels of female mortality. During 2012–2016, we used barbed‐wire hair snares to collect bear hair samples from within the range of the CGP in Georgia, USA. We used microsatellite genotyping to identify individual bears and created robust‐design, spatial detection histories for all female bears detected. We fit open population spatial capture‐recapture (SCR) models to the detection histories in a Bayesian framework. We used the Widely Applicable Information Criterion (WAIC) to rank models that varied with respect to sources of variation in detection probability, survival, and per capita recruitment, and used the model with the lowest WAIC to forecast dynamics of the CGP 50 years into the future under various levels of female mortality. We assessed the 50‐year extinction probability under a continuation of mortality levels documented during 2012–2016, and under incremental increases in female mortality above this baseline. The top model included density‐dependent per capita recruitment, annual variation in detection probability, and a trap‐level behavioral response. Abundance increased from 106 (95% CI = 86–132) females in 2012 to 136 (95% CI = 113–161) females in 2013 and remained relatively stable thereafter. Annual female survival was 0.75 (95% CI = 0.69–0.82) and did not vary among years. The per capita recruitment rate decreased over time as density increased, and was 0.49 (95% CI = 0.33–0.66) during the first time interval and 0.29 (95% CI = 0.20–0.38) during the final time interval. Annual growth rate () was 1.28 (95% CI = 1.07–1.52) between 2012 and 2013 but decreased throughout the study, ending at 1.04 (95% CI = 0.93–1.17). Forecasts indicated continuation of the female mortality levels experienced from 2012–2016 were sustainable over 50 years, with the estimated extinction risk being <0.001%. Increasing annual harvest by 5 females introduced a negligible increase in the 50‐year probability of extinction, but harvesting an additional 10 females/year caused extinction risk to rise to 1.15%. We recommend that harvest regulations are structured such that mortality rates remain at current levels or do not increase by more than an annual average of 5 females above levels observed during our study. Furthermore, we recommend that managers continue to monitor the population so that harvest regulations and population models can be refined over time. © 2020 The Wildlife Society.

An improved understanding of ungulate population dynamics using count data: Insights from western Montana.

Understanding the dynamics of ungulate populations is critical given their ecological and economic importance. In particular, the ability to evaluate the evidence for potential drivers of variation in population trajectories is important for informed management. However, the use of age ratio data (e.g., juveniles:adult females) as an index of variation in population dynamics is hindered by a lack of statistical power and difficult interpretation. Here, we show that the use of a population model based on count, classification and harvest data can dramatically improve the understanding of ungulate population dynamics by: 1) providing estimates of vital rates (e.g., per capita recruitment and population growth) that are easier to interpret and more useful to managers than age ratios and 2) increasing the power to assess potential sources of variation in key vital rates. We used a time series of elk (Cervus canadensis) spring count and classification data (2004 to 2016) and fall harvest data from hunting districts in western Montana to construct a population model to estimate vital rates and assess evidence for an association between a series of environmental covariates and indices of predator abundance on per capita recruitment rates of elk calves. Our results suggest that per capita recruitment rates were negatively associated with cold and wet springs, and severe winters, and positively associated with summer precipitation. In contrast, an analysis of the raw age ratio data failed to detect these relationships. Our approach based on a population model provided estimates of the region-wide mean per capita recruitment rate (mean = 0.25, 90% CI = 0.21, 0.29), temporal variation in hunting-district-specific recruitment rates (minimum = 0.09; 90% CI = [0.07, 0.11], maximum = 0.43; 90% CI = [0.38, 0.48]), and annual population growth rates (minimum = 0.83; 90% CI = [0.78, 0.87], maximum = 1.20; 90% CI = [1.11, 1.29]). We recommend using routinely collected population count and classification data and a population modeling approach rather than interpreting estimated age ratios as a substantial improvement in understanding population dynamics.

Sex‐specific population dynamics of ocelots in Belize using open population spatial capture–recapture

AbstractWe used open population, spatial capture–recapture (SCR) models to estimate sex‐specific density, survival, per capita recruitment, and population growth rate of ocelots (Leopardus pardalis) at five sites in Belize with up to 12 yr of data per site. Open population SCR models enabled us to separate survival and recruitment from migration using an ecologically realistic, spatially explicit movement model. Yearly survival probability across 4 broadleaf forest sites was estimated at 0.73–0.84 for males and 0.81–0.87 for females, with no clear indication of sex differences. Yearly per capita recruitment was estimated across four broadleaf forest sites at 0.06–0.08 recruits/N for males and 0.09–0.12 recruits/N for females, again with no clear indication of sex differences. At a pine forest site with a population comprised largely of males, survival and recruitment estimates were similar to the broadleaf sites. Population densities in the broadleaf forest sites ranged from 6.5 to 14.7 ocelots/100 km2, and 0.9–2.5 ocelots/100 km2 in the pine forest site, with strong evidence of a female‐biased sex ratio in the broadleaf sites and a male‐biased sex ratio in the pine forest site. We also found strong evidence that female within‐year space use at the broadleaf sites was smaller than that of males, and that within‐year space use at the pine forest site was larger than that at broadleaf sites. Between‐year home‐range relocation at broadleaf sites was of a similar spatial scale as within‐year space use, consistent with philopatry. We found evidence of a small population decline (posterior probability > 0.9) at two of four broadleaf sites; however, given the level of uncertainty about decline magnitudes, we suggest continued monitoring of these sites to increase site‐years and gain further precision on population growth rate estimates. Estimating demographic parameters at large spatial and temporal scales is important for establishing reliable baseline estimates for future comparison and for understanding changes in population dynamics. Long‐term data sets like those we collected are of particular importance for long‐lived species living at low densities and large spatial scales, where not many individuals are exposed to capture in any one year.

Effects of power lines on habitat use and demography of greater sage‐grouse (Centrocercus urophasianus)

ABSTRACTEnergy development and its associated infrastructure, including power lines, may influence wildlife population dynamics through effects on survival, reproduction, and movements of individuals. These infrastructure impacts may be direct or indirect, the former occurring when development acts directly as an agent of mortality (e.g., collision) and the latter when impacts occur as a by‐product of other processes that are altered by infrastructure presence. Functional or numerical responses by predators to power‐line corridors are indirect impacts that may suppress demographic rates for certain species, and perceived predation risk may affect animal behaviors such as habitat selection. Greater sage‐grouse (Centrocercus urophasianus) are a species of conservation concern across western North America that may be affected by power lines. Previous studies, however, have not provided evidence for causal mechanisms influencing demographic rates. Our primary objective was to assess the influence of power lines on multiple sage‐grouse vital rates, greater sage‐grouse habitat selection, and ultimately greater sage‐grouse population dynamics. We used demographic and behavioral data for greater sage‐grouse collected from 2003 to 2012 in central Nevada, USA, accounting for sources of underlying environmental heterogeneity. We also concurrently monitored populations of common ravens (Corvus corax), a primary predator of sage‐grouse nests and young. We focused primarily on a single 345 kV transmission line that was constructed at the beginning of our study; however, we also determined if similar patterns were associated with other nearby, preexisting power lines. We found that numerous behaviors (e.g., nest‐site selection, brood‐site selection) and demographic rates (e.g., nest survival, recruitment, and population growth) were affected by power lines, and that these negative effects were predominantly explained by temporal variation in the relative abundance of common ravens. Specifically, in years of high common raven abundance, avoidance of the transmission line was extended farther from the line, re‐nesting propensity was reduced, and nest survival was lower near the transmission line relative to areas more distant from the transmission line. Additionally, we found that before and immediately after construction of the transmission line, habitats near the footprint of the transmission line were generally more productive (e.g., greater reproductive success and population growth) than areas farther from the transmission line. However, multiple demographic rates (i.e., pre‐fledging chick survival, annual male survival, per capita recruitment, and population growth) for groups of individuals that used habitats near the transmission line declined to a greater extent than for individuals using habitats more distant in the years following construction of the transmission line. These decreases were correlated with an increase in common raven abundance. The geographical extent to which power lines negatively influence greater sage‐grouse demographic processes was thus contingent on local raven abundance and behavior. In this system, we found that effects of power lines, depending on the behavior or demographic rate, extended 2.5–12.5 km, which exceeds current recommendations for the placement of structures in areas around sage‐grouse leks. Nests located 12.5 km from the transmission line had 0.06 to 0.14 higher probabilities of hatching in years of average to high levels of raven abundance, relative to nests located within 1 km of the transmission line. Similarly, leks located 5 km from the transmission line had 0.02 to 0.16 higher rates of population growth (λ) in years of average to high levels of raven abundance, relative to leks located within 1 km of the transmission line. Our finding that negative impacts of the transmission line were associated with common raven abundance suggest that management actions that decouple this association between common raven abundance and power lines may reduce the negative indirect impacts of power lines on greater sage‐grouse population dynamics. However, because the removal of common ravens or the use of perch deterrents on power lines has not been demonstrated to be consistently effective in reducing common raven predation rates on greater sage‐grouse nests, we recommend preferential treatment to mitigation strategies that reduce the number of elevated structures placed within 10 km of critical greater sage‐grouse habitat. © 2018 The Wildlife Society.

Factors influencing Northern Bobwhite recruitment, with implications for population growth

Understanding and quantifying demographic parameters that influence population growth is necessary to effectively maintain population persistence in the presence of recent changes in climate and land use. We used a combination of capture–recapture and harvest information from a 42 yr dataset to create an integrated population model that estimates population abundance, annual survival, and per capita recruitment in Northern Bobwhite (Colinus virginianus). We evaluated the associations of commonly reported population metrics (age ratios from harvests, annual survival, and recruitment) to population growth rate using correlation analysis. We also modeled the effects of population abundance, breeding-season temperature, breeding-season precipitation, fall minimum temperature, and fall precipitation on recruitment. Recruitment averaged 1.55 (range: 0.82–2.21) and was most strongly correlated with population growth (r = 0.78, 95% confidence interval [CI]: 0.63–0.88), followed by annual survival (r = 0.38, 95% CI: 0.09–0.61). We found a weak correlation between fall age ratios and population growth rate (r = 0.11, 95% CI: −0.19 to 0.40). Recruitment exhibited weak, nonlinear, negative density dependence (β1 = −0.13, 95% credible intervals [CRI]: −0.17 to −0.08 and β2 = −0.03, 95% CRI: −0.07 to 0.004). Breeding-season maximum temperature and breeding-season precipitation had a significant, positive effect on recruitment (β3 = 0.15, 95% CRI: 0.11–0.19 and β4 = 0.10, 95% CRI: 0.05–0.16, respectively). Fall minimum temperature and fall precipitation both had negative but uncertain effects on recruitment (β5 = −0.03, 95% CRI: −0.08 to 0.01 and β6 = −0.02, 95% CRI: −0.07 to 0.01, respectively) but less so compared to weather in the breeding season. Our results illustrate that recruitment (1) can be estimated without data on fecundity and chick survival by using integrated population models and (2) is highly correlated with population growth in Northern Bobwhites. We encourage natural resource managers to focus on actions that increase Northern Bobwhite recruitment.

No flood effect on recruitment in a Louisiana black bear population

ABSTRACTA flood event in 2011 had minor impacts on apparent survival and movement probabilities of a small, isolated population of Louisiana black bears (Ursus americanus luteolus) in the Upper Atchafalaya River Basin, Louisiana, USA. However, the potential effects of the flood on recruitment of juveniles into the population, then listed as threatened under the United States Endangered Species Act, were not evaluated. We used hair trapping data collected from 2007 to 2015 and Pradel temporal symmetry models in a robust‐design framework to investigate changes in per capita recruitment that could have resulted from the flood. We detected 91 bears (37 M:54 F) within the flooded area during our study period, ranging from 21 to 44 individuals/year. Models that tested for reduced recruitment resulting from the flood were not supported more than models with constant recruitment, and the population growth rate did not decline. Although we documented marginally lower recruitment following the 2011 flood, lag effects and detectability biases complicated our analysis. We suggest that wildlife managers continue monitoring recruitment and survival in this recently delisted black bear population given the potential for heightened flood frequency and severity in the future. © 2017 The Wildlife Society.

Integrated population modelling reveals a perceived source to be a cryptic sink

Summary Demographic links among fragmented populations are commonly studied as source‐sink dynamics, whereby source populations exhibit net recruitment and net emigration, while sinks suffer net mortality but enjoy net immigration. It is commonly assumed that large, persistent aggregations of individuals must be sources, but this ignores the possibility that they are sinks instead, buoyed demographically by immigration.We tested this assumption using Bayesian integrated population modelling of Greenland white‐fronted geese (Anser albifrons flavirostris) at their largest wintering site (Wexford, Ireland), combining capture–mark–recapture, census and recruitment data collected from 1982 to 2010. Management for this subspecies occurs largely on wintering areas; thus, study of source‐sink dynamics of discrete regular wintering units provides unprecedented insights into population regulation and enables identification of likely processes influencing population dynamics at Wexford and among 70 other Greenland white‐fronted goose wintering subpopulations.Using results from integrated population modelling, we parameterized an age‐structured population projection matrix to determine the contribution of movement rates (emigration and immigration), recruitment and mortality to the dynamics of the Wexford subpopulation.Survival estimates for juvenile and adult birds at Wexford and adult birds elsewhere fluctuated over the 29‐year study period, but were not identifiably different. However, per capita recruitment rates at Wexford in later years (post‐1995) were identifiably lower than in earlier years (pre‐1995). The observed persistence of the Wexford subpopulation was only possible with high rates of immigration, which exceeded emigration in each year. Thus, despite its apparent stability, Wexford has functioned as a sink over the entire study period.These results demonstrate that even large subpopulations can potentially be sinks, and that movement dynamics (e.g. immigration) among winters can dramatically obscure key processes driving subpopulation size. Further, novel population models which integrate capture–mark–recapture, census and recruitment data are essential to correctly ascribing source‐sink status and accurately informing development of site‐safeguard networks.

Can intense predation by bears exert a depensatory effect on recruitment in a Pacific salmon population?

It has long been recognized that, as populations increase in density, ecological processes affecting growth and survival reduce per capita recruitment in the next generation. In contrast to the evidence for such "compensatory" density dependence, the alternative "depensatory" process (reduced per capita recruitment at low density) has proven more difficult to demonstrate in the field. To test for such depensation, we measured the spawner-recruit relationship over five decades for a sockeye salmon (Oncorhynchus nerka) population in Alaska breeding in high-quality, unaltered habitat. Twenty-five years of detailed estimates of predation by brown bears, Ursus arctos, revealed strong density dependence in predation rate; the bears killed ca. 80% of the salmon in years of low salmon spawning abundance. Nevertheless, the reconstructed spawner-recruit relationship, adjusted to include salmon intercepted in the commercial fishery, provided no evidence of demographic depensation. That is, in years when few salmon returned and the great majority were killed by bears, the few that spawned were successful enough that the population remained highly productive, even when those killed by bears were included as potential spawners. We conclude that the high quality of breeding habitat at this site and the productive nature of semelparous Pacific salmon allowed this population to avoid the hypothesized depressed recruitment from depensatory processes expected at low density. The observed lack of demographic depensation is encouraging from a conservation standpoint because it implies that depleted populations may have the potential to rebound successfully given suitable spawning and rearing habitat, even in the presence of strong predation pressure.

Spatial variation in life-history trade-offs results in an ideal free distribution in Black Brant Geese.

Ideal free distribution theory predicts that individuals distribute themselves so fitness is equal among patches. In this paper we evaluate all components of adult fitness to assess the hypothesis that individuals distribute themselves among seven brood-rearing areas so that trade-offs among different life history traits result in equal mean fitness among individuals using different areas. We used estimates of vital rates (clutch size, nest survival, pre-fledging survival, post-fledging survival, juvenile survival, and breeding probability) to estimate brood-rearing-area-specific per capita recruitment rates and survival for adult females. We summed brood-rearing-area-specific per capita recruitment and adult survival to calculate brood-rearing-area-specific estimates of lambda. We found little variation in lambda among brood-rearing areas and lifetime fitness implications of changing brood-rearing area were negligible (< 1% brood-rearing area mean fitness). We conclude that adult female Black Brant distribute themselves in an ideal free manner, resulting in equal fitness among females using these areas.

Inferences about population dynamics from count data using multistate models: a comparison to capture–recapture approaches

Wildlife populations consist of individuals that contribute disproportionately to growth and viability. Understanding a population's spatial and temporal dynamics requires estimates of abundance and demographic rates that account for this heterogeneity. Estimating these quantities can be difficult, requiring years of intensive data collection. Often, this is accomplished through the capture and recapture of individual animals, which is generally only feasible at a limited number of locations. In contrast, N-mixture models allow for the estimation of abundance, and spatial variation in abundance, from count data alone. We extend recently developed multistate, open population N-mixture models, which can additionally estimate demographic rates based on an organism's life history characteristics. In our extension, we develop an approach to account for the case where not all individuals can be assigned to a state during sampling. Using only state-specific count data, we show how our model can be used to estimate local population abundance, as well as density-dependent recruitment rates and state-specific survival. We apply our model to a population of black-throated blue warblers (Setophaga caerulescens) that have been surveyed for 25 years on their breeding grounds at the Hubbard Brook Experimental Forest in New Hampshire, USA. The intensive data collection efforts allow us to compare our estimates to estimates derived from capture–recapture data. Our model performed well in estimating population abundance and density-dependent rates of annual recruitment/immigration. Estimates of local carrying capacity and per capita recruitment of yearlings were consistent with those published in other studies. However, our model moderately underestimated annual survival probability of yearling and adult females and severely underestimates survival probabilities for both of these male stages. The most accurate and precise estimates will necessarily require some amount of intensive data collection efforts (such as capture–recapture). Integrated population models that combine data from both intensive and extensive sources are likely to be the most efficient approach for estimating demographic rates at large spatial and temporal scales.