The Influence of Ecological Factors on Detecting Drumming Ruffed Grouse

Abstract: We surveyed drumming ruffed grouse (Bonasa umbellus) to estimate the probability of detecting an individual, and we used Bayesian model selection to assess the influence of factors that may affect detection probabilities of drumming grouse. We found the average probability of detecting a drumming ruffed grouse during a daily survey was 0.33. The probability of detecting a grouse was most strongly influenced by the temperature change during a survey (_{temp change} = 0.23, 95% probability interval [PI] = 0.13 ≤ ≤ 0.33) and its interaction with temperature at the start of the survey (_interaction = 0.01, 95% PI = 1.42 × 10⁻³ ≤ ≤ 0.03). Although the best model also included a main effect of temperature at the start of surveys, this variable did not strongly correlate with detection probabilities (_{start temp} = −0.03, 95% PI = −0.06 ≤ ≤ 9.80 × 10⁻⁵). Model assessment using data collected at other sites indicated that this best model performed adequately (i.e., positive correlation between observed and predicted values) but did not explain much of the variation in detection rates. Our results are useful for understanding the historical drumming index used to assess ruffed grouse populations and for designing auditory surveys for this important game bird.     

Using Statistical Population Reconstruction to Estimate Demographic Trends in Small Game Populations

ABSTRACT Statistical population reconstruction offers a robust approach to demographic assessment for harvested populations, but current methods are restricted to big-game species with multiple age classes. We extended this approach to small game and analyzed 14 years of age-at-harvest data for greater sage-grouse (Centrocercus urophasianus) in Oregon, USA, in conjunction with radiotelemetry data to reconstruct annual abundance levels, recruitment, and natural survival probabilities. Abundance estimates ranged from a low of 26,236 in 1995 to a high of 39,492 in 2004. Annual abundance estimates for adult males were correlated with a spring lek count index (r = 0.849, P < 0.029). We estimated the average annual harvest mortality for the population to be 0.028, ranging from 0.021 to 0.031 across years. We estimated the probability of natural survival of adult females to be 0.818 ( = 0.052), somewhat higher than that of adult males (Ŝ = 0.609, = 0.163). Our precision in reconstructing the population was hampered by low harvest rates and the few birds tagged in the radiotelemetry investigations. Despite these issues, our analysis illustrates how modern statistical reconstruction procedures offer a flexible framework for demographic assessment using commonly collected data. This approach offers a useful alternative to small-game indices and would be most appropriate for species with 5 or more years of age-at-harvest data and moderate-to-heavy harvest rates.     

Assessment of the Sustainability of Wolverine Harvest in British Columbia,Canada

ABSTRACT Wolverines (Gulo gulo) are distributed across much of northern and western Canada and Alaska, USA, and they extend south into the mountainous western United States. Wolverines occur in most regions of British Columbia, Canada, with the highest population densities occurring in the interior mountainous areas. Wolverine populations in British Columbia have been primarily managed to provide a sustainable harvest for trappers and hunters. We used spatially based population estimates, population vital rate data, and spatially based harvest data to evaluate the sustainability of wolverine harvest (trapping and hunting) from 1985 to 2004. The median annual provincial wolverine harvest from 1985 to 2004 was 172 wolverines per year ( = 174.8), which was less than the median simulated estimate of provincial recruitment (195.9 wolverines/yr; = 209.7). Harvests in individual population units ranged from 0 to 280 over the 20-year period. Spatially, wolverine harvest was likely to have been unsustainable in 15 of the 71 population units with wolverines, and it was likely to have been sustainable in the remaining population units. Harvest in 5 of the other 56 population units was marginally sustainable and thus of potential management concern. To improve harvest management of wolverines in British Columbia, wildlife managers should focus on improved data collection and monitoring at a provincial scale, and they should work with trappers and hunters at regional scales to address issues specific to individual population units. Further research is required to improve the reliability of wolverine vital rate and population data.     

Calibrating Statistical Population Reconstruction Models Using Catch-Effort and Index Data

Abstract: This paper illustrates how age-at-harvest data, when combined with hunter-effort information routinely collected by state game management agencies, can be used to estimate and monitor trends in big game abundance. Twenty-four years of age-at-harvest data for black-tailed deer (Odocoileus hemionus) were analyzed to produce abundance estimates ranging from 1,281 adult females to 3,232 adult females on a 22,079-ha tree farm in Pierce County, Washington, USA. The annual natural survival probability was estimated to be 0.7293 ( = 0.0097) for this female population. The estimated abundance was highly correlated with an independent browse damage index (r = 0.8131, P < 0.001). A population reconstruction incorporating the browse index did not substantially improve the model fit but did provide an auxiliary model for predicting deer abundance. This population reconstruction illustrates a cost-effective alternative to expensive big game survey methods.     

Modelling evolutionary processes in small populations: not as ideal as you think

Evolutionary processes are routinely modelled using ‘ideal’ Wright–Fisher populations of constant size N in which each individual has an equal expectation of reproductive success. In a hypothetical ideal population, variance in reproductive success (V_k) is binomial and effective population size (N_e) = N. However, in any actual implementation of the Wright–Fisher model (e.g., in a computer), V_k is a random variable and its realized value in any given replicate generation () only rarely equals the binomial variance. Realized effective size () thus also varies randomly in modelled ideal populations, and the consequences of this have not been adequately explored in the literature. Analytical and numerical results show that random variation in  and  can seriously distort analyses that evaluate precision or otherwise depend on the assumption that  is constant. We derive analytical expressions for Var(V_k) [4(2N – 1)(N – 1)/N³] and Var(N_e) [N(N – 1)/(2N – 1) ≈ N/2] in modelled ideal populations and show that, for a genetic metric G = f(N_e), Var(?) has two components: Var_Gene (due to variance across replicate samples of genes, given a specific ) and Var_Demo (due to variance in ). Var(?) is higher than it would be with constant N_e = N, as implicitly assumed by many standard models. We illustrate this with empirical examples based on F (standardized variance of allele frequency) and r² (a measure of linkage disequilibrium). Results demonstrate that in computer models that track multilocus genotypes, methods of replication and data analysis can strongly affect consequences of variation in . These effects are more important when sampling error is small (large numbers of individuals, loci and alleles) and with relatively small populations (frequently modelled by those interested in conservation).     

The effects of predator removal on mallard production and population change in northeastern North Dakota

In 1994, Delta Waterfowl Foundation began trapping mammalian meso-predators in North Dakota during the breeding season in an attempt to increase waterfowl nest success and enhance recruitment into the fall flight and subsequent breeding population. Multiple studies on these sites demonstrated that removing predators results in near doubling of nest success, which previous simulation modeling suggests is the most influential vital rate influencing the population growth rate of mid-continent mallards (Anas platyrhynchos). We present an assessment of the impact of predator removal on mallard production using population models. We conducted this study on 9 township-sized (93.2 km²) sites (4–8 sites annually per vital rate) in northeastern North Dakota from 2006–2008. Trappers removed mammalian meso-predators on 5 sites and the other 4 served as unmanaged reference sites. To estimate recruitment, we used derived estimates and process variance of pair numbers, hen success (nest survival corrected for renesting), initial brood size, pre-fledging survival, and post-fledging survival, along with previously published estimates of breeding propensity and adult female survival rates. Trapped sites had greater hen success (H = 0.69, = 0.03) than reference sites (H = 0.53, = 0.06), but similar indicated breeding pairs, initial brood size, and pre-fledging survival. We estimated that females on trapped sites added 140 more mallards of both sexes to the fall flight than females on reference sites, at an approximate cost of $74.29 per incremental mallard. Additionally, trapping predators provided a marginal increase (0.04) in finite population growth. We found that predator removal targeted at mammalian nest predators did not produce as many incremental mallards as previously thought and may not be a viable strategy for increasing mallard productivity under conditions similar to those observed during this study. We conducted a sensitivity analysis and determined that pre-fledging survival was the most influential factor regulating mallard population growth. Although hen success increased as a result of trapping, duckling survival became a limiting factor. We suggest that waterfowl managers assess multiple vital rates to determine the likelihood that management actions focused on a single parameter, such as nest success, will yield desired population level effects. © 2012 The Wildlife Society.     

Turgor and osmotic relations of the desert shrub Larrea tridentata

Abstract Leaf water relations characteristics of creosote bush, Larrea tridentata, were studied in view of previous reports that its leaves commonly experience zero or negative turgor under dry conditions. Leaf turgor loss point () was determined by a pressure-volume method for samples subjected to a hydration procedure and for untreated samples. Hydration caused to increase by as much as 3 M Pa. Hydration of samples also caused changes in other leaf water relations characteristics such as symplastic solute content, tissue elasticity and symplasmic water fraction, but total leaf solute content was unchanged. Comparison of our field plant water potential data with values of obtained by the two methods resulted in predictions of turgor loss during part or all of a diurnal cycle based on hydrated samples, and turgor maintenance (at least 0.3 MPa) based on untreated samples. Pooled data for obtained from both partially hydrated and untreated samples showed that L. tridentata maintains fairly constant levels of turgor over a wide range of leaf water potential. Dilution of cell contents by apoplastic water introduced significant errors in psychrometric determinations of osmotic potential in both frozen and thawed leaf tissue and expressed cell sap. Use of these values of osmotic potential resulted in predictions of zero turgor at all plant water potentials measured in the field.     

Seasonal changes of osmotic pressure, symplasmic water content and tissue elasticity in the blades of dune grasses growing in situ along the coast of Oregon

Abstract Midday water potentials of blades of the dune grasses Ammophila arenaria (L.) Link and Elymus mollis Trin. ex Spreng. growing in situ declined over the summer growing period, indicating a trend of increasing water stress. An analysis of the water relations characteristics of these blades using pressure-volume techniques demonstrated that both species increased bulk osmotic pressure at full hydration () and, therefore, bulk turgor as an acclimation response. In A. arenaria, however, the increase of osmotic pressure (+ 0.35 MPa) was entirely the result of decreasing symplasmic water content. The increase of osmotic pressure (+ 0.54 MPa) observed in E. mollis blades was due to solute accumulation (72% of Δ) and to a lesser degree, decreased symplasmic water content (28% of Δ). Osmotic adjustment in E. mollis blades was accompanied by a significant decrease in tissue elasticity (_max went from 12 to 19 MPa). The elastic properties of A. arenaria blades remained constant over the same period and had a maximum modulus (10 MPa) that was always less than that of E. mollis, As estimated from Höfler plots, these seasonal adjustments of osmotic pressure and differences in tissue elasticity enabled plants in situ to maintain turgor pressure in the range of 0.5–0.6 MPa at the lowest water potentials of mid-August. Laboratorygrown plants exhibited the species-specific differences in osmotic pressure, turgor pressure, and tissue elasticity observed in field plants. Although certain alterations of leaf structure were expected to coincide with the observed changes and species-specific differences in symplasmic water content and tissue elasticity, these could not be detected by measurements of specific leaf weight or the ratio of dry matter to saturated water content.     

Abundance trends of American martens in Michigan based on statistical population reconstruction

Estimating the dynamics of furbearer populations is challenging because their elusive behavior and low densities make observations difficult. Statistical population reconstruction is a flexible approach to demographic assessment for harvested populations, but the technique has not been applied to furbearers. We extended this approach to furbearers and analyzed 8 yr of age-at-harvest data for American marten (Martes americana) in the Upper Peninsula of Michigan. Marten abundance estimates showed a general downward trend from an estimate of = 1,733.3 animals in 2000 to = 1,163.9 in 2007. The harvest probability of martens increased nearly 5-fold from 0.0542 in 2000 to 0.2637 in 2007, which corresponded to a 5-fold increase in trap-nights. Continued monitoring of martens in the Upper Peninsula, Michigan, and a reassessment of current harvest regulations are necessary given the estimated decreases. Moreover, we do not encourage the use of harvest indices as the sole technique to assess the status and trends of marten and fisher populations. Auxiliary studies in the Upper Peninsula, Michigan, will allow for continued use and improvement in the application of these models. © 2011 The Wildlife Society.     

RISK OF POPULATION EXTINCTION FROM FIXATION OF NEW DELETERIOUS MUTATIONS

The fixation of new deleterious mutations is analyzed for a randomly mating population of constant size with no environmental or demographic stochasticity. Mildly deleterious mutations are far more important in causing loss of fitness and eventual extinction than are lethal and semilethal mutations in populations with effective sizes, N_e, larger than a few individuals. If all mildly deleterious mutations have the same selection coefficient, s against heterozygotes and 2s against homozygotes, the mean time to extinction, , is asymptotically proportional to for 4N_es > 1. Nearly neutral mutations pose the greatest risk of extinction for stable populations, because the magnitude of selection coefficient that minimizes is about ? = 0.4/N_e. The influence of variance in selection coefficients among mutations is analyzed assuming a gamma distribution of s, with mean and variance . The mean time to extinction increases with variance in selection coefficients if is near ?, but can decrease greatly if is much larger than ?. For a given coefficient of variation of , the mean time to extinction is asymptotically proportional to for . When s is exponentially distributed, (c = 1) is asymptotically proportional to . These results in conjunction with data on the rate and magnitude of mildly deleterious mutations in Drosophila melanogaster indicate that even moderately large populations, with effective sizes on the order of N_e = 10³, may incur a substantial risk of extinction from the fixation of new mutations.     

THE MAINTENANCE OF POLYGENIC VARIATION IN FINITE POPULATIONS

Models of the maintenance of genetic variance in a polygenic trait have usually assumed that population size is infinite and that selection is weak. Consequently, they will overestimate the amount of variation maintained in finite populations. I derive approximations for the equilibrium genetic variance, in finite populations under weak stabilizing selection for triallelic loci and for an infinite “rare alleles” model. These are compared to results for neutral characters, to the “Gaussian allelic” model, and to Wright's approximation for a biallelic locus under arbitrary selection pressures. For a variety of parameter values, the three-allele, Gaussian, and Wrightian approximations all converge on the neutral model when population size is small. As expected, far less equilibrium genetic variance can be maintained if effective population size, N, is on the order of a few hundred than if N is infinite. All of the models predict that comparisons among populations with N less than about 10⁴ should show substantial differences in . While it is easier to maintain absolute when alleles interact to yield dominance or overdominance for fitness, less additivity also makes more susceptible to differences in N. I argue that experimental data do not seem to reflect the predicted degree of relationship between N and . This calls into question the ability of mutation-selection balance or simple balancing selection to explain observed . The dependence of on N could be used to test the adequacy of mutation-selection balance models.     

Demographics of an Experimentally Released Population of Elk in Great Smoky Mountains National Park

ABSTRACT We assessed the potential for reestablishing elk (Cervus elaphus) in Great Smoky Mountains National Park (GSMNP), USA, by estimating vital rates of experimentally released animals from 2001 to 2006. Annual survival rates for calves ranged from 0.333 to 1.0 and averaged 0.592. Annual survival for subadult and adult elk (i.e., ≥ 1 yr of age) ranged from 0.690 to 0.933, depending on age and sex. We used those and other vital rates to model projected population growth and viability using a stochastic individual-based model. The annual growth rate (λ) of the modeled population over a 25-year period averaged 0.996 and declined from 1.059 the first year to 0.990 at year 25. The modeled population failed to attain a positive 25-year mean growth rate in 46.0% of the projections. Poor calf recruitment was an important determinant of low population growth. Predation by black bears (Ursus americanus) was the dominant calf mortality factor. Most of the variance of growth projections was due to demographic variation resulting from the small population size (n = 61). Management actions such as predator control may help increase calf recruitment, but our projections suggest that the GSMNP elk population may be at risk for some time because of high demographic variation.     

Wolf Use of Summer Territory in Northeastern Minnesota

ABSTRACT Movements of wolves (Canis lupus) during summer 2003 and 2004 in the Superior National Forest were based around homesites but included extensive use of territories. Away from homesites, wolves used different areas daily, exhibiting rotational use. Mean daily range overlap was 22% (SE = 0.02) and that of breeding wolves was significantly greater than for nonbreeders ( = 25% and 16%, respectively). Rotational use may improve hunting success. Managers seeking to remove entire packs must maintain control long enough to ensure that all pack members are targeted.     

Variation in spring harvest rates of male wild turkeys in New York,Ohio, and Pennsylvania

Spring harvest rates of male wild turkeys (Meleagris gallapavo) influence the number and proportion of adult males in the population and turkey population models have treated harvest as additive to other sources of mortality. Therefore, hunting regulations and their effect on spring harvest rates have direct implications for hunter satisfaction. We used tag recovery models to estimate survival rates, investigate spatial, temporal, and demographic variability in harvest rates, and assess how harvest rates may be related to management strategies and landscape characteristics. We banded 3,266 male wild turkeys throughout New York, Ohio, and Pennsylvania during 2006–2009. We found little evidence that harvest rates varied by year or management zone. The proportion of the landscape that was forested within 6.5 km of the capture location was negatively related to harvest rates; however, even though the proportion forested ranged from 0.008 to 0.96 across our study area, this corresponded to differences in harvest rates of only 2–5%. Annual survival was approximately twice as high for juveniles as adults . In turn, spring harvest rates for adult turkeys were greater for adults than juveniles . We estimated the population of male turkeys in New York and Pennsylvania ranged from 104,000 to 132,000 in all years and ranged from 63,000 to 75,000 in Ohio. Because of greater harvest rates for adult males, the proportion of adult males in the population was less than in the harvest and ranged from 0.40 to 0.81 among all states and years. The high harvest rates observed for adults may be offset by greater recruitment of juveniles into the adult age class the following year such that these states can sustain high harvest rates yet still maintain a relative high proportion of adult males in the harvest and population. © 2011 The Wildlife Society.     

Sensitivity analysis of equilibrium in density-dependent matrix population models

We consider the effects of parameter perturbations on a density‐dependent population at equilibrium. Such perturbations change the dominant eigenvalue λ of the projection matrix evaluated at the equilibrium as well as the equilibrium itself. We show that, regardless of the functional form of density dependence, the sensitivity of λ is equal to the sensitivity of an effective equilibrium density , which is a weighted combination of the equilibrium stage densities. The weights measure the contributions of each stage to density dependence and their effects on demography. Thus, is in general more relevant than total density, which simply adds all stages regardless of their ecological properties. As log λ is the invasion exponent, our results show that successful invasion will increase , and that an evolutionary stable strategy will maximize . Our results imply that eigenvalue sensitivity analysis of a population projection matrix that is evaluated near equilibrium can give useful information about the sensitivity of the equilibrium population, even if no data on density dependence are available.     

Survival of white-tailed deer fawns in the grasslands of the northern Great Plains

Environmental factors, such as forest characteristics, have been linked to fawn survival in eastern and southern white-tailed deer (Odocoileus virginianus) populations. In the Great Plains, less is known about how intrinsic and habitat factors influence fawn survival. During 2007–2009, we captured and radiocollared 81 fawns in north-central South Dakota and recorded 23 mortalities, of which 18 died before 1 September. Predation accounted for 52.2% of mortality; remaining mortality included human (hunting, vehicle, and farm accident; 26.1%) and hypothermia (21.7%). Coyotes (Canis latrans) accounted for 83.3% of predation on fawns. We used known-fate analysis in Program MARK to estimate summer (15 May–31 Aug) survival rates and investigated the influence of intrinsic and habitat variables on survival. We developed 2 a priori model sets, including intrinsic variables and a test of annual variation in survival (model set 1) and habitat variables (model set 2). Model set 1 indicated that summer survival varied among years (2007–2009); annual survival rates were 0.94 (SE = 0.06, n = 22), 0.78 (SE = 0.09, n = 27), and 0.54 (SE = 0.10, n = 32), respectively. Model set 2 indicated that survival was further influenced by patch density of cover habitats (Conservation Reserve Program [CRP]-grasslands, forested cover, and wetlands). Mean CRP-grassland and wetland patch density (no. patches/100 ha) were greater (P < 0.001) in home-range areas of surviving fawns ( = 1.81, SE = 0.10, n = 63; = 1.75, SE = 0.14, n = 63, respectively) than in home-range areas of fawns that died ( = 0.16, SE = 0.04, n = 18; = 1.28, SE = 0.10, n = 18, respectively). Mean forested cover patch density was less (P < 0.001) in home-range areas of surviving fawns ( = 0.77, SE = 0.10, n = 63) than in home-range areas of fawns that died ( = 1.49, SE = 0.21, n = 18). Our results indicate that management activities should focus on CRP-grassland and wetland habitats in order to maintain or improve fawn survival in the northern Great Plains, rather than forested cover composed primarily of tree plantings and shelterbelts. © 2012 The Wildlife Society.     

The role of predator removal,density-dependence,and environmental factors on mallard duckling survival in North Dakota

Duckling survival is an important component of mallard (Anas platyrhynchos) recruitment and population growth, yet many factors regulating duckling survival are poorly understood. We investigated factors affecting mallard duckling survival in the drift prairie of northeastern North Dakota, 2006–2007. Mammalian meso-predators were removed by trapping on 4 92.3 km² study sites and another 4 study sites served as controls. We monitored 169 broods using telemetry and periodic resighting, and we modeled cumulative survival to 30 days of age using the nest survival module in Program MARK. Duckling survival was not affected by predator removal ( , 85% CI: 0.182–0.234; , 85% CI: 0.155–0.211) and was only weakly negatively correlated with duckling density. Duckling survival was higher in 2007 ( , 85% CI: 0.193–0.355) than 2006 ( , 85% CI: 0.084–0.252) and increased with total seasonal and semipermanent wetland area and declined with perennial cover in the surrounding landscape. Broods that hatched earlier in the season (especially in 2006) and ducklings that were heavier at hatch also had higher survival. Our estimates of duckling survival are among the lowest reported for mallards and contradict previous research in Saskatchewan that found predator removal increased duckling survival. However, our results are consistent with other studies suggesting that earlier hatch date, increased wetland availability, and better duckling condition lead to increased survival. Management actions that increase wetland density, improve nest success early in the season, and potentially target brood-specific predators such as mink (Neovison vison) would likely lead to higher duckling survival. © 2011 The Wildlife Society.     

Assessing the Semelparity Hypothesis: Egg-guarding and Fecundity in the Malaysian Treehopper Pyrgauchenia tristaniopsis

According to the semelparity hypothesis, iteroparous insects should provide either no maternal care or less care than related semelparous species. We present field data on reproductive output and maternal care in the Southeast Asian treehopper Pyrgauchenia tristaniopsis (Mt. Kinabalu, Borneo) relevant to a preliminary assessment of the hypothesis. In a mark‐recapture experiment, more females than expected under semelparity were found to have oviposited a second clutch (37%). Female longevity was a of 75 d. Both these estimates were highly conservative. Oviposition was successive resulting in a of 46 eggs per clutch. Females provided care for eggs only, occasionally scraping their legs along the sides of the clutch apparently attempting to deter Brachygrammatella sp. egg parasitoids (Trichogrammatidae). Females straddled their clutch for a of 27 d, i.e. until 8 d after the beginning of first instar hatching. First instars hatched successively over a period of 11 d. When a female deserted her clutch, it contained about 37% yet unhatched eggs. Egg‐guarding effectively reduced egg mortality: the earlier a female was experimentally removed from her clutch the higher the egg mortality. Displacement experiments demonstrated that egg‐guarding is a behaviour actively maintained despite disturbances and specifically directed towards the egg clutch but not to the feeding site. We interpret our findings as being in accordance with the weaker claim of the semelparity hypothesis, i.e. the iteroparous P. tristaniopsis provided less maternal care than semelparous membracid species. Continued female feeding is discussed as a mechanism to display some level of care despite iteroparity.     

SMALL POPULATION GENETIC VARIABILITY AT LOCI UNDER STABILIZING SELECTION

Genetic variability at a locus under stabilizing selection in a finite population is investigated using analytic methods and computer simulations. Three measures are examined: the number of alleles k, heterozygosity H, and additive genetic variance Vg. A nearly-neutral theory results. The composite parameter S = NV_M/V_s (where N is the population size, V_M the variance of new mutant allelic effects and V_s the weakness of stabilizing selection) figures prominently in the results. The equilibrium heterozygosity is similar to that of strictly neutral theory, H = 4N_μc/ (1 + 4N_μc), except that μ_c = where c is about 0.5. Simulations corroborate except for very low N. Genetic variability attains similar equilibrium values at both a “lone” locus and at an “embedded” locus. This agrees with my earlier work concerning molecular clock rates. These results modify the neutralist interpretation of data concerning genetic variability and genetic distances between populations. Low H values are proportional not to N but to . This may explain the narrow observed range of H among species. Heterozygosities need not be highly correlated to genetic variances. Genetic variances are not highly dependent on population size except in very small populations which are difficult to sample without bias because the smallest populations go extinct the fastest. Nearly neutral evolution will not be easily distinguished from strictly neutral theory under the Hudson-Kreitman-Aguade inter-/intraspecific variation ratio test, since a similar effective mutation rate holds for genetic distances and D = 2μ_ct, where . As with strictly neutral theory, comparisons across loci should show D and H to be positively correlated because of the shared μ_c. But unlike neutral theory, for a given locus, comparisons across species should show D and H to be negatively correlated. There is no obvious threshold of population size below which genetic variability inevitably declines. Extinction depends on both genetic variation and natural selection. Neither theory nor observation presently indicates the measure of genetic variability (k, H, V_G or other) that best indicates vulnerability of a small population to extinction.     

Sensitivity analysis of effective population size to demographic parameters in house sparrow populations

The ratio between the effective and the census population size, , is an important measure of the long‐term viability and sustainability of a population. Understanding which demographic processes that affect most will improve our understanding of how genetic drift and the probability of fixation of alleles is affected by demography. This knowledge may also be of vital importance in management of endangered populations and species. Here, we use data from 13 natural populations of house sparrow (Passer domesticus) in Norway to calculate the demographic parameters that determine . Using the global variance‐based Sobol’ method for the sensitivity analyses, we found that was most sensitive to demographic variance, especially among older individuals. Furthermore, the individual reproductive values (that determine the demographic variance) were most sensitive to variation in fecundity. Our results draw attention to the applicability of sensitivity analyses in population management and conservation. For population management aiming to reduce the loss of genetic variation, a sensitivity analysis may indicate the demographic parameters towards which resources should be focused. The result of such an analysis may depend on the life history and mating system of the population or species under consideration, because the vital rates and sex–age classes that is most sensitive to may change accordingly.