Spoor density as a measure of true density of a known population of free-ranging wild cheetah in Botswana

Knowledge of the abundance of animal populations is essential for their management and conservation. Determining reliable measures of abundance is, however, difficult, especially with wide-ranging species such as cheetah Acinonyx jubatus . This study generated a correction factor to calculate true cheetah density from spoor survey data and subsequently tested its accuracy using the following season's data. Data were collected from October 2005 to December 2006 on a known population of wild, free-ranging cheetah in the Jwana Game Reserve, Botswana. The cheetahs in the area were captured, tagged and photographed. The reserve was divided into twelve 9 km transects covering all vegetation types and prey densities. The total sampling distance was 8226 km, with a spoor density of 2.32 individual cheetah spoor per 100 km². To determine a precise and accurate spoor density, it was necessary to sample for a longer period during the dry season (April–September) than during the wet season (October–March). This difference may be due to cheetah behavioural changes with seasonal variations in habitat and prey. The true density was 5.23 cheetahs  per 100 km² ranging from 3.33 to 7.78 at the low and high points of the population, respectively. A positive linear correlation between spoor and true density was observed. This relationship differed in the wet and dry season and required refinement with the following season's data. Correction factors may be viable, but require further testing taking the behavioural responses to seasonal, habitat and prey variations into consideration.     

Lion density and population structure in the Selous Game Reserve: evaluation of hunting quotas and offtake

In 1992, tourist hunting in the Selous Game Reserve generated 1.28 million dollars for the Tanzanian government, of which 0·96 million dollars were returned to wildlife conservation. Lions ( Panthera leo ) are one of three critical species for tourist hunting, consistently generating 12%–13% of hunting revenue from 1988 to 1992. Because of their ecological and economic importance (and intrinsic value), it is important that lion quotas be set so that offtake is sustainable. The population density of lions in Selous ranges from 0·08 to 0·13 adults km⁻², comparable to unhunted ecosystems. The adult sex ratio (36–41% male) and the ratio of cubs to adults (29% cubs) are similar to those of unhunted populations. The ratio of lions to hyaenas is lower in heavily hunted areas (0·17 lions/hyena) than in unhunted areas (0·43 lions/hyena). Hunting levels between 1989 and 1994 took 2·7–4·3% of adult males annually, which is sustainable. The current quota is 10–16% of the adult male population, which exceeds natural mortality rates for male lions. To remain stable if the quota was filled, the population would have to compensate via increased fecundity, increased juvenile survival, or an altered sex‐ratio. Compensation occurs in Selous by producing (or raising) more male than female cubs (66–81% of juveniles are male). Only 28% of the Selous quota was filled in 1992. The percentage of quota filled (both in Selous and nationwide) has dropped since 1988 as quotas have increased. The current intensity of lion hunting in Selous is sustainable, but the quota cannot be filled sustainably.     

The relationship between percentage of singletons and sampling effort: A new approach to reduce the bias of richness estimates

Estimate the richness of a community with accuracy despite differences in sampling effort is a key aspect to monitoring high diverse ecosystems. We compiled a worldwide multitaxa database, comprising 185 communities, in order to study the relationship between the percentage of species represented by one individual (singletons) and the intensity of sampling (number of individuals divided by the number of species sampled). The database was used to empirically adjust a correction factor to improve the performance of non-parametrical estimators under conditions of low sampling effort. The correction factor was tested on seven estimators (Chao1, Chao2, Jack1, Jack2, ACE, ICE and Bootstrap). The correction factor was able to reduce the bias of all estimators tested under conditions of undersampling, while converging to the original uncorrected values at higher intensities. Our findings led us to recommend the threshold of 20 individuals/species, or less than 21% of singletons, as a minimum sampling effort to produce reliable richness estimates of high diverse ecosystems using corrected non-parametric estimators. This threshold rise for 50 individuals/species if non-corrected estimators are used which implies in an economy of 60% of sampling effort if the correction factor is used.     

Sighting frequency and food habits of the leopard tortoise, Geochelone pardalis, in northern Tanzania

Sighting frequency and food habits of the leopard tortoise (Geochelone pardalis) were studied in northern Tanzania from October 1993 to June 1996. Sighting frequency varied significantly between protected (0.22 mhr^?1) and unprotected sites (0.59 mhr^?1), and between Arusha (0.27 mhr^?1) and Serengeti sites (0.56 mhr^?1). The tortoise diet comprised mostly plants (97.8%) and rarely inorganic matter (2.2%). A total of 47 plant species from 21 families was eaten. Forbs made up 74.5% of the plant items and monocots the remainder. Succulents contributed 51.0% of the plant items eaten while grasses and legumes accounted for 16.8% and 13.5%, respectively. Some plant items were eaten more frequently than their occurrence in the habitats.     

Evolution of reproductive effort in viscous populations: the importance of population dynamics

I present two ecological models for the evolution of reproductive effort in viscous populations with empty sites. In contrast with previous studies, I show that limited dispersal needs not have a positive effect on the evolutionarily stable allocation of resources to fecundity versus survival. Rather, depending on the feedback between the trait and the population dynamics, population viscosity may have no effect or even lead to a decrease in the evolutionarily stable reproductive effort when individuals can degrade their environment during their lifetime. I show that the different evolutionary outcomes can be explained by the asymmetry in the level of kin competition resulting from investing into juveniles or into adults.     

Estimating population density from indirect sign: track counts and the Formozov–Malyshev–Pereleshin formula

For many purposes it is often desirable to estimate animal population densities over large areas. Where total counts are not possible and sightings are relatively rare, a range of methods exists to estimate densities from indirect sign. Such methods are frequently unreliable and usually require independent calibration or confirmation. We present an analytical method for estimating population density from track counts. The method, widely known in the Russian Federation but not in the English language scientific literature, requires counts of tracks of known age, together with estimates of animal daily travel distances. We use simulations to verify the theoretical basis of the approach and to indicate potential precision that may be achieved. We illustrate application of the approach using a large data set on ungulate track counts in the Russian Far East. We suggest that under most circumstances, nonparametric bootstrapping will be the most appropriate method for deriving estimates of confidence intervals about density estimates. As with other approaches to estimating density from indirect sign, the method that we discuss is vulnerable to violations of an array of underlying assumptions. However, it is easily applied and could represent an important method by which the relationship between indices of abundance and absolute density can be understood.     

Distribution-abundance relationship for passerines breeding in Tunisian oases: test of the sampling hypothesis

The positive relationship between local abundance and distribution of species is a widely recognized pattern in community ecology. However, it has been suggested that this relationship can simply be an artefact of sampling because locally rare species are less detectable then locally abundant ones, and hence their distribution can easily be underestimated. Here, we use count data to investigate the relationship between distribution and abundance of passerines breeding in a sample of oases from southern Tunisia, and we provide a test of the sampling artefact hypothesis. In particular, we checked for a difference in detection probability between localized and widespread species, and we tested if increasing the sampling effort affects the significance of the relationship. A significant positive relationship between the average local abundance of passerine species and the proportion of occupied oases was found. The use of a capture-recapture approach allowed us to estimate and to compare the detection probabilities of localized and widespread species subsets. We found that localized species were locally less detectable than widespread species, which is consistent with the main assumption of the sampling artefact hypothesis. However, increasing the detection probability of species by conducting more counts did not affect the significance of the relationship, which did not give support to the sampling artefact hypothesis. Our work implies that sampling contributed to the distribution-abundance relationship we found, but that it is unlikely that such a relationship could entirely be explained by an artefact of sampling. It also underlines the insight that can be gained by using probabilistic approaches of estimating species number and detection probability when attempting to disentangle sampling from ecological effects in community ecology studies.     

Dynamics of springtail and mite populations: the role of density dependence, predation, and weather

Abstract 1. Ecological theory suggests that density‐dependent regulation of organism abundance will vary from exogenous to endogenous factors depending on trophic structure. Changes in abundance of soil arthropods were investigated at three trophic levels, springtails (Collembola), predaceous mites (Acari), and macro‐arthropods (spider, adult and larval beetles, centipedes). Predictions were that springtails are predator regulated and mites are food limited according to the Hairston et al. (1960) model, which predicts alternating regulation by competition and predation from fungi to springtails to mites to macro‐arthropods. The alternate hypothesis was based on the bottom‐up model of trophic dynamics, which predicts that each trophic level is regulated by competition for resources. 2. The relative contributions to springtail and mite population dynamics of endogenous (i.e. density‐dependent population growth related to food availability) and exogenous (i.e. predation and weather) factors were tested using time‐series analysis and experimental manipulation of water conditions. Box patterns were distributed within an aspen forest habitat located in the Canadian prairies and surveyed weekly from May to September 1997–1999. Each box depressed the leaf litter, creating a microhabitat island for soil arthropods that provided counts of invertebrates located immediately beneath the boxes. 3. Strong evidence was found for endogenous control of springtail and mite numbers, indicated by a reduction in population growth related to density in the previous week. Contrary to predictions, no evidence was found for regulation of springtail numbers by mites, or for regulation of mite numbers by macro‐arthropods. Springtail population growth rate was related positively to current springtail density (8 and 23% variation explained) and related negatively to 1‐week lagged density (85 and 58%), and related negatively to temperature (5 and 5%) for time‐series data and for experimental addition of water respectively. Mite population growth rate was related positively to current mite density (54%) and temperature (4%), and negatively to 1‐week lagged mite density (20%) and precipitation (6%) for time‐series analysis. For experimental addition of water, mite growth rate was related positively to current mite density (44%) and temperature (5%), and negatively to 1‐week lagged density (11%). Results differed from the Hairston et al. (1960) model predictions but were consistent with a bottom‐up view that springtail and mite populations were regulated intrinsically by competition for food and secondarily by temperature as a function of reproduction.     

茴香薄翅野螟虫口密度与油菜产量损失关系及其防治指标的研究

在网室内人工接茴香薄翅野螟Evergestis extimalis Scopoli卵,研究结果表明,随着幼虫数量的增加,油菜产量损失增加;与对照相比,当接卵数为216、399、858、1665和3279粒时,产量损失分别达3.13%,2.08%,12.5%,25.10%和43.33%。各网室实际接虫数(x)与其相应的小区油菜产量(y)的关系为:y=-0.0007x+4.8129,表明虫口密度与油菜产量为负相关。在青海省油菜种植区内每平米幼虫或卵数超过10头或粒时,应即时防治。     

Circadian analysis of large human populations: Inferences from the power grid

Few, if any studies have focused on the daily rhythmic nature of modern industrialized populations. The present study utilized real-time load data from the U.S. Pacific Northwest electrical power grid as a reflection of human operative household activity. This approach involved actigraphic analyses of continuously streaming internet data (provided in 5?min bins) from a human subject pool of approximately 43 million primarily residential users. Rhythm analyses reveal striking seasonal and intra-week differences in human activity patterns, largely devoid of manufacturing and automated load interference. Length of the diurnal activity period (alpha) is longer during the spring than the summer (16.64?h versus 15.98?h, respectively; p?<?0.01). As expected, significantly more activity occurs in the solar dark phase during the winter than during the summer (6.29?h versus 2.03?h, respectively; p?<?0.01). Interestingly, throughout the year a “weekend effect” is evident, where morning activity onset occurs approximately 1?h later than during the work week (5:54 am versus 6:52 am, respectively; p?<?0.01). This indicates a general phase-delaying response to the absence of job-related or other weekday morning arousal cues, substantiating a preference or need to sleep longer on weekends. Finally, a shift in onset time can be seen during the transition to Day Light Saving Time, but not the transition back to Standard Time. The use of grid power load as a means for human actimetry assessment thus offers new insights into the collective diurnal activity patterns of large human populations.     

Prior adaptation,diversity, and introduction frequency mediate the positive relationship between propagule pressure and the initial success of founding populations

Propagule pressure is often considered the most consistent predictor of the success of founding populations. This relationship could be mediated by the composition of the founding group (e.g. level of prior adaptation to the recipient environment or its diversity) as well as the introduction scenario (i.e. the frequency, size and timing of discrete introduction events). We introduced groups of Tribolium castaneum (red flour beetle) eggs across three levels of propagule pressure (n?=?15, 30, 60), of three possible compositions (single, adapted lineage; single, unadapted lineage; mixed lineages) to a novel environment using six unique introduction scenarios, in a fully factorial design to evaluate the importance of composition and introduction scenario in influencing the relationship between propagule pressure and establishment. In our system, prior adaptation to the environment, including having some adapted individuals in mixed groups, rivaled the importance of propagule pressure in determining the establishment success and size of founding populations. More frequent introduction events resulted in fewer individuals that initially survived founding, but introduction scenario did not significantly influence establishment success or population size. This experimental evidence demonstrates the importance of context, both of the founding group and the recipient environment, in understanding how propagule pressure influences the success of founding populations.     

Interaction between hatchery and wild Pacific salmon in the Far East of Russia: A review

We review studies of interactions between hatchery and wild Pacific salmon in the Russian Far East. This includes the role of hatchery practices that result in premature migration to the sea and increased mortality, and data on feeding and territorial competition between juveniles of hatchery and wild origin. In the course of downstream migration many juvenile hatchery salmon are eliminated by wild salmon predation. During the marine period, Japanese hatchery chum salmon (Oncorhynchus keta) distribution overlaps the distribution of Russian wild salmon. Consequently, replacement of wild populations by hatchery fishes, as a result of abundant juvenile hatchery releases combined with extensive poaching in spawning grounds, is apparent in some Russian rivers. Interactions between the populations occur in all habitats. The importance of conservation of wild salmon populations requires a more detailed study of the consequences of interactions between natural and artificially reared fishes.     

Fur snagging as a method of evaluating the presence and abundance of a small carnivore, the pine marten (Martes martes)

The pine marten Martes martes was once considered one of Ireland's rarest carnivores, but is now recolonizing many of the areas where it was once extirpated. It is important to monitor its population expansion so that conservation management decisions can be made regarding the status of this species. In this study, we investigate the use of fur snagging devices as a method of estimating pine marten presence and abundance in lowland and upland broadleaf woodland. We investigated whether these devices reliably detected presence, and how quickly. It was found that hair traps functioned very well in detecting pine martens on all survey transects and was essential in their detection in the most isolated site. A survey length of 6 days was sufficient to detect pine marten in all survey sites, with most detections occurring within the first 4 days. The hair traps functioned equally well as scat location for detecting pine marten and had the added advantage of there being no confusion as to the origin of the sample. Live trapping was used to verify the estimates of relative abundance from hair traps. There was a trend for the number of hair samples per site and the number of times animals were trapped per site to be positively correlated, although this was not significant. Hair traps do provide a real alternative for the monitoring of pine martens in both lowland and upland broadleaf woodlands, overcoming many of the disadvantages associated with scat location.     

The relationship between biodiversity and population centres: the high Andes region as an example

Several coarse-scale studies have demonstrated a positive correlation between biodiversity and human population density. In this paper this relationship is studied for part of the Andean highland, on a finer spatial scale than in earlier studies, and comparing bird distribution data with pre-Columbian as well as contemporary population centres. A particularly close correspondence was found between ancient population centres and high numbers of species with small distributions. This suggests that the growth of resident human cultures was related, in some way, to local factors which—over a much longer time-scale—stimulated the process of evolution of new species. This correspondence may be a consequence of climate moderation in the mountain areas leading to local persistence, of wild species as well as human communities. However, the result also suggests that we need to study to what extent high biodiversity as such, under certain conditions, yields environmental services which were important for people. It also suggests that traditional efforts to preserve biodiversity in wilderness areas with few people should be supplemented with efforts to promote a more sustainable development in the populated areas, allowing cloud forest and other biologically rich habitats to persist in suitable places near population centres.     

Corridors for migration between large subdivided populations, and the structured coalescent

We study the ancestral genetic process for samples from two large, subdivided populations that are connected by migration to, from, and within a small set of subpopulations, or demes. We consider convergence to an ancestral limit process as the numbers of demes in the two large, subdivided populations tend to infinity. We show that the ancestral limit process for a sample includes a recent instantaneous adjustment to the sample size and structure followed by a more ancient process that is identical to the usual structured coalescent, but with different scaled parameters. This justifies the application of a modified structured coalescent to some hierarchically structured populations.     

Genetic structure in large, continuous mammal populations: the example of brown bears in northwestern Eurasia

Knowledge of population structure and genetic diversity and the spatio-temporal demographic processes affecting populations is crucial for effective wildlife preservation, yet these factors are still poorly understood for organisms with large continuous ranges. Available population genetic data reveal that widespread mammals have for the most part only been carefully studied at the local population scale, which is insufficient for understanding population processes at larger scales. Here, we provide data on population structure, genetic diversity and gene flow in a brown bear population inhabiting the large territory of northwestern Eurasia. Analysis of 17 microsatellite loci indicated significant population substructure, consisting of four genetic groups. While three genetic clusters were confined to small geographical areas-located in Estonia, southern Finland and Leningrad oblast, Russia-the fourth cluster spanned a very large area broadly falling between northern Finland and the Arkhangelsk and Kirov oblasts of Russia. Thus, the data indicate a complex pattern where a fraction of the population exhibits large-scale gene flow that is unparalleled by other wild mammals studied to date, while the remainder of the population appears to have been structured by a combination of demographic history and landscape barriers. These results based on nuclear data are generally in good agreement with evidence previously derived using mitochondrial markers, and taken together, these markers provide complementary information about female-specific and population-level processes. Moreover, this study conveys information about spatial processes occurring over multiple generations that cannot be readily gained using other approaches, e.g. telemetry.     

Predicting fluctuations of reintroduced ibex populations: the importance of density dependence, environmental stochasticity and uncertain population estimates

1. Development of population projections requires estimates of observation error, parameters characterizing expected dynamics such as the specific population growth rate and the form of density regulation, the influence of stochastic factors on population dynamics, and quantification of the uncertainty in the parameter estimates. 2. Here we construct a Population Prediction Interval (PPI) based on Bayesian state space modelling of future population growth of 28 reintroduced ibex populations in Switzerland that have been censused for up to 68 years. Our aim is to examine whether the interpopulation variation in the precision of the population projections is related to differences in the parameters characterizing the expected dynamics, in the effects of environmental stochasticity, in the magnitude of uncertainty in the population parameters, or in the observation error. 3. The error in the population censuses was small. The median coefficient of variation in the estimates across populations was 5.1%. 4. Significant density regulation was present in 53.6% of the populations, but was in general weak. 5. The width of the PPI calculated for a period of 5 years showed large variation among populations, and was explained by differences in the impact of environmental stochasticity on population dynamics. 6. In spite of the high accuracy in population estimates, the uncertainty in the parameter estimates was still large. This uncertainty affected the precision in the population predictions, but it decreased with increasing length of study period, mainly due to higher precision in the estimates of the environmental variance in the longer time-series. 7. These analyses reveal that predictions of future population fluctuations of weakly density-regulated populations such as the ibex often become uncertain. Credible population predictions require that this uncertainty is properly quantified.