Monitoring Population Trends Research Articles

Population Status of Nile Crocodiles in Ndumo Game Reserve, Kwazulu-Natal, South Africa (1971–2012)

Establishing and monitoring population trends is essential for implementing informed and timely management decisions and also for the conservation of threatened species. We examined changes in Nile Crocodile (Crocodylus niloticus) population size and changes in the size–class distribution within the population using aerial and ground survey data from 1971–2009 in the Ndumo Game Reserve (NGR), South Africa. In addition, crocodiles were caught opportunistically for aging, sexing, and tagging. Precision and accuracy of population estimates were affected by water level, season, and the use of different observers. Future surveys should occur in austral winter and at low water levels. The NGR population increased from an absolute abundance of 348 (±3.4; an estimate of precision based on 1 SE) in the early 1970s to maximum absolute abundance of 992 (±58.7) in 1994 as a result of a restocking program initiated in the late 1960s and early 1970s. The population structure is currently skewed towards subadults and adults and the current population is in decline. This is a result of low recruitment levels in NGR, which are unable to sustain the artificially high population size created by the restocking program. Also contributing to this decline is the poaching of crocodiles and destruction of suitable and historical nest sites. Sex ratios were skewed toward females in juveniles and subadults and toward males in adults, while the overall sex ratio in the population was even. The current NGR Nile Crocodile population is estimated at an absolute abundance of 846 (±263). We predict that the NGR Nile Crocodile population will continue to decline in the future as part of the natural process, but the decline will be accelerated on account of poaching, uncontrolled harvesting, and destruction of nesting habitat.

Temporal and spatial patterns of defecation in wild boar

ABSTRACTWorldwide, wild boar (Sus scrofa) and feral pigs are involved in environmental damage and disease transmission. These impacts are often associated with relatively high local densities of pigs, so the monitoring of population trends is important. Dung counts can be used to estimate population trends, but knowledge of daily defecation rates (DDRs) is needed to estimate absolute numbers. To address this issue, we calculated the DDRs of 18 captive, adult wild boar in July 2005 and November 2007. The mean DDR was 3.8–4.3 dung/boar/day, depending on the trial. We discuss the results by comparing the DDR of wild boar to that of other ungulates and omnivores, and we consider the implications of these results for estimating feral pig and wild boar density through dung counts. © 2014 The Wildlife Society.

Patterns in lung cancer incidence rates and trends by histologic type in the United States, 2004–2009

ObjectiveThe examination of lung cancer by histology type is important for monitoring population trends that have implications for etiology and prevention, screening and clinical diagnosis, prognosis and treatment. We provide a comprehensive description of recent histologic lung cancer incidence rates and trends in the USA using combined population-based registry data for the entire nation. Materials and methodsHistologic lung cancer incidence data was analyzed from CDC's National Program of Cancer Registries (NPCR) and the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program. Standardized rates and trends were calculated for men and women by age, race/ethnicity, and U.S. Census region. Rate ratios were examined for differences in rates between men and women, and annual percent change was calculated to quantify changes in incidence rates over time. ResultsTrend analysis demonstrate that overall rates have decreased, but incidence has remained stable for women aged 50 or older. Adenocarcinoma and squamous cell carcinoma were the two most common histologic subtypes. Adenocarcinoma rates continued to increase in men and women, and squamous cell rates increased in women only. All histologic subtype rates for white women exceeded rates for black women. Histologic rates for black men exceeded those for white men, except for small cell carcinoma. The incidence rate for Hispanics was nearly half the rate for blacks and whites. ConclusionThe continuing rise in incidence of lung adenocarcinoma, the rise of squamous cell cancer in women, and differences by age, race, ethnicity and region points to the need to better understand factors acting in addition to, or in synergy with, cigarette smoking that may be contributing to observed differences in lung cancer histology.

Obituary

Obituary

Population dynamics and spatial ecology of a declining desert rodent,Pseudomys australis: the importance of refuges for persistence

Desert rodents exhibit irruptive (boom–bust) population dynamics in response to pulses of primary productivity. Such unpredictable population dynamics are a challenge for monitoring population trends and managing populations, particularly for species in decline. We studied the population dynamics and occurrence of populations of the vulnerable plains mouse, Pseudomys australis (42-g body mass), during the low (bust) phase of the cycle in the Simpson Desert, Australia, to examine the use of refuges by the species and the predation pressure experienced from native and introduced predators. Specifically we investigated landscape-scale occurrence; body mass, reproduction, and population size; and presence of native and introduced predators. Our results demonstrate that P. australis contracted to discrete areas of the landscape (refuges) during the low phase and that these areas occupied a small proportion (~17%) of the range occupied during population peaks. Animals in refuge populations had comparable body mass, occurred at similar densities to populations during the boom phase, and continued to reproduce during dry conditions. Such refuges represented a significant concentration of biomass to predators in a resource-poor environment. Native predators were rare during the low phase, suggesting that refuges naturally experienced low predation levels. Two introduced predators, feral house cats and red foxes, persisted during the low phase and exploited refuge populations of P. australis, thus representing a significant threat to population persistence. We advocate a novel approach to management of rodents in arid systems that involves identifying the discrete parts of the landscape that function as drought refuges and then focusing threat management there. The relatively small size of these refuges increases the likelihood of cost-effective management.

Summer distribution and abundance of the giant devil ray (<em>Mobula mobular</em>) in the Adriatic Sea: Baseline data for an iterative management framework

The giant devil ray ( Mobula mobular ) is a poorly understood protected endemic species of the eastern Atlantic-Mediterranean region. However, to date there are no range-wide management actions in place. This paper provides the first overview of the summer distribution and abundance of this species and other Myliobatiformes within the Adriatic Sea based on an aerial survey. Although the survey´s primary targets were cetaceans and sea turtles, the study showed that it was possible to use the survey to monitor other species. Abundance estimates are derived using conventional distance sampling analysis. Giant devil rays were observed mainly in the central-southern Adriatic (88% of total sightings). A total of 1595 giant devil rays were estimated in the central-southern Adriatic Sea [coefficient of variation(CV)=25%, uncorrected estimate for perception and availability bias]. When corrected for availability bias the number of specimens was estimated at 3255 (CV=56%). Population growth rate was estimated using life history traits and a sensitivity analysis was conducted to evaluate the benefit of improving biological knowledge on this data-poor species. A power analysis showed that a long-term commitment to an aerial survey would be necessary to monitor population trends. Conservation implications and future work, including how the study could be used to conduct an ecological risk assessment are discussed.

Initial population trends from a 5-year butterfly monitoring scheme

The Irish Butterfly Monitoring Scheme started in 2007. The main objective of this study was to examine initial population trends from data gathered over 5 years (2008–2012) by approximately 150 volunteers across the Republic of Ireland. Nine of the 15 species analysed showed changes in population over the 5-year period; three species showed steep or moderate increases while six species showed moderate or steep declines in population. Some of these population changes are due to the highly variable weather conditions over the five years of monitoring, particularly the unusually cool, wet summer of 2012. However, factors affecting butterfly population trends are many and varied, so longer-term data are required to assess trends more reliably. A further six species had indeterminate trends over the 5-year period however, as the scheme develops, longer-term trends will have greater statistical reliability and give a clearer insight into Irish butterfly populations. The Irish Butterfly Monitoring Scheme is important in the national context, as there is little other countrywide systematic monitoring of insect populations. Furthermore, with a growing number of such standardised monitoring schemes internationally and development of bioindicators, it is now possible to monitor and track butterfly populations at larger spatial scales. We recommend that the Irish Butterfly Monitoring Scheme is continued over the long term and expanded to ensure that more Irish butterfly species are sufficiently monitored. However, in addition to monitoring population trends, basic research is still needed into the ecology and population dynamics of common butterfly species.

An Island-Wide Monitoring Program Demonstrates Decline in Reporting Rate for the Christmas Island Flying-FoxPteropus melanotus natalis

Flying-foxes (Pteropodidae) show a high rate of island endemism, but island-endemic taxa have shown a high rate of decline and extinction, mostly because their small population sizes are susceptible to hunting pressure and habitat loss. The Christmas Island flying-fox is restricted to the 135 Km2 Christmas Island (Indian Ocean), as either an endemic species Pteropus natalis or a markedly distinct subspecies of Pteropus melanotus. Given recent declines and extinctions of other native vertebrate species on this Island, this study sought to monitor population trends for this taxon. Monitoring flying-foxes at roost sites is difficult because they are highly vagile, not all roost sites may be known to observers, and dense vegetation at some sites may make counts inaccurate. These constraints are particularly evident on Christmas Island. In this study, we sought to establish a monitoring program complementary to roost counts, and to assess changes in reporting rate from a baseline sampling of 107 sites spaced a...

Multidisciplinary population monitoring when demographic data are sparse: a case study of remote trout populations

The potential of genetic, genomic, and phenotypic metrics for monitoring population trends may be especially high in isolated regions, where traditional demographic monitoring is logistically difficult and only sporadic sampling is possible. This potential, however, is relatively underexplored empirically. Over eleven years, we assessed several such metrics along with traditional ecological knowledge and catch data in a socioeconomically important trout species occupying a large, remote lake. The data revealed largely stable characteristics in two populations over 2–3 generations, but possible contemporary changes in a third population. These potential shifts were suggested by reduced catch rates, reduced body size, and changes in selection implied at one gene-associated single nucleotide polymorphism. A demographic decline in this population, however, was ambiguously supported, based on the apparent lack of temporal change in effective population size, and corresponding traditional knowledge suggesting little change in catch. We illustrate how the pluralistic approach employed has practicality for setting future monitoring efforts of these populations, by guiding monitoring priorities according to the relative merits of different metrics and availability of resources. Our study also considers some advantages and disadvantages to adopting a pluralistic approach to population monitoring where demographic data are not easily obtained.

Estimating crop pollinator population using mark–recapture method

Xylocopa species are large solitary bees, which are effective pollinators of yellow passion fruit, a self-incompatible crop dependent on pollination for fruit production and economic viability. We tested the mark–recapture method to estimate these bees' population size in a passion fruit commercial orchard in Central Brazil. We collected data during 3 years and population was estimated as 118, 339, and 1,032 individuals. Population size and abundance of Xylocopa bees were higher in the last studied year. These bees maintained 32.5 % of natural fruit set, above economic viability levels, and higher than other commercial orchards, although population size showed no direct correlation with natural fruit set. Improvement of nesting site may explain population increase, reinforcing the importance of management. Our results showed that the mark–recapture technique can provide reliable estimates of Xylocopa bees population size and, thus, be useful in monitoring population trends.

World Health Organization infant and young child feeding indicators and their associations with child anthropometry: a synthesis of recent findings

As the World Health Organization (WHO) infant and young child feeding (IYCF) indicators are increasingly adopted, a comparison of country-specific analyses of the indicators' associations with child growth is needed to examine the consistency of these relationships across contexts and to assess the strengths and potential limitations of the indicators. This study aims to determine cross-country patterns of associations of each of these indicators with child stunting, wasting, height-for-age z-score (HAZ) and weight-for-height z-score (WHZ). Eight studies using recent Demographic and Health Surveys data from a total of nine countries in sub-Saharan Africa (nine), Asia (three) and the Caribbean (one) were identified. The WHO indicators showed mixed associations with child anthropometric indicators across countries. Breastfeeding indicators demonstrated negative associations with HAZ, while indicators of diet diversity and overall diet quality were positively associated with HAZ in Bangladesh, Ethiopia, India and Zambia (P < 0.05). These same complementary feeding indicators did not show consistent relationships with child stunting. Exclusive breastfeeding under 6 months of age was associated with greater WHZ in Bangladesh and Zambia (P < 0.05), although CF indicators did not show strong associations with WHZ or wasting. The lack of sensitivity and specificity of many of the IYCF indicators may contribute to the inconsistent associations observed. The WHO indicators are clearly valuable tools for broadly assessing the quality of child diets and for monitoring population trends in IYCF practices over time. However, additional measures of dietary quality and quantity may be necessary to understand how specific IYCF behaviours relate to child growth faltering.

Monitoring Strategy for Eight Amphibian Species in French Guiana, South America

Although dramatic amphibian declines have been documented worldwide, only few of such events have been quantitatively documented for the tropical forests of South America. This is due partly to the fact that tropical amphibians are patchily distributed and difficult to detect. We tested three methods often used to monitor population trends in amphibian species in a remote lowland tropical forest of French Guiana. These methods are capture-mark-recapture (CMR), estimation of the number of calling males with repeated counts data and distance sampling, and rates of occupancy inferred by presence/absence data. We monitored eight diurnal, terrestrial amphibian species including five Dendrobatidae and three Bufonidae. We found that CMR, the most precise way of estimating population size, can be used only with two species in high density patches where the recapture rate is high enough. Only for one of the species (Dendrobates tinctorius), a low coefficient of variation (CV = 0.19) can be achieved with 15 to 20 capture events. For dendrobatid species with day-calling males, audio surveys yield a better probability of detection with only 8 audio surveys needed; quantitative estimates can be achieved by computing the number of calling males inferred from audio counts or distance sampling analysis. We therefore suggest that an efficient monitoring protocol for Neotropical amphibian species should include a combination of sighting and audio techniques, and we discuss the need of implementing a large-scale monitoring in order to provide a baseline for comparison with future changes.

Monitoring Trends in Violence

Reliable and valid indicators of assault are required to effectively monitor population trends and ensure that resources are targeted effectively. Trends in assault, reported by the media, based on crime statistics, or on victim surveys, are substantively affected by extraneous factors. In 2006, Estrada offered up solutions to the difficulties posed by crime statistics and victim surveys, by proposing the development of indicators based on hospital discharge data, albeit with identified limitations. This article is a response to Estrada's proposition, and works through each of Estrada's identified limitations of hospital discharge data. Potential problems with Estrada's suggestions are highlighted in our article and solutions, based on the current evidence, are proposed.

Relation between Occupancy and Abundance for a Territorial Species, the California Spotted Owl

Land and resource managers often use detection-nondetection surveys to monitor the populations of species that may be affected by factors such as habitat alteration, climate change, and biological invasions. Relative to mark-recapture studies, using detection-nondetection surveys is more cost-effective, and recent advances in statistical analyses allow the incorporation of detection probability, covariates, and multiple seasons. We examined the efficacy of using detection-nondetection data (relative to mark-recapture data) for monitoring population trends of a territorial species, the California Spotted Owl (Strix occidentalis occidentalis). We estimated and compared the finite annual rates of population change (λt ) and the resulting realized population change (Δt ) from both occupancy and mark-recapture data collected over 18 years (1993-2010). We used multiseason, robust-design occupancy models to estimate that territory occupancy declined during our study (Δt = 0.702, 95% CI 0.552-0.852) due to increasing territory extinction rates (ε(1993) = 0.019 [SE 0.012]; ε(2009) = 0.134 [SE 0.043]) and decreasing colonization rates (γ(1993) = 0.323 [SE 0.124]; γ(2009) = 0.242 [SE 0.058]). We used Pradel's temporal-symmetry model for mark-recapture data to estimate that the population trajectory closely matched the trends in territory occupancy (Δt = 0.725, 95% CI 0.445-1.004). Individual survival was constant during our study (φ(1993) = 0.816 [SE 0.020]; φ(2009) = 0.815 [SE 0.019]), whereas recruitment declined slightly (f(1993) = 0.195 [SE 0.032]; f(2009) = 0.160 [SE 0.023]). Thus, we concluded that detection-nondetection data can provide reliable inferences on population trends, especially when funds preclude more intensive mark-recapture studies.

Do singing-ground surveys reflect American woodcock abundance in the western Great Lakes region?

The Singing-ground Survey (SGS) is the primary monitoring tool used to assess population status and trends of American woodcock (Scolopax minor). Like most broad-scale surveys, the SGS cannot be directly validated because there are no independent estimates of abundance of displaying male American woodcock at an appropriate spatial scale. Furthermore, because locations of individual SGS routes have generally remained stationary since the SGS was standardized in 1968, it is not known whether routes adequately represent the landscapes they were intended to represent. To indirectly validate the SGS, we evaluated whether 1) counts of displaying male American woodcock on SGS routes related to land-cover types known to be related to American woodcock abundance, 2) changes in counts of displaying male American woodcock through time were related to changes in land cover along SGS routes, and 3) land-cover type composition along SGS routes was similar to land-cover type composition of the surrounding landscape. In Wisconsin and Minnesota, USA, counts along SGS routes reflected known American woodcock-habitat relations. Increases in the number of woodcock heard along SGS routes over a 13-year period in Wisconsin were related to increasing amounts of early successional forest, decreasing amounts of mature forest, and increasing dispersion and interspersion of cover types. Finally, the cover types most strongly associated with American woodcock abundance were represented along SGS routes in proportion to their composition of the broader landscape. Taken together, these results suggest that in the western Great Lakes region, the SGS likely provides a reliable tool for monitoring relative abundance and population trends of breeding, male American woodcock. © 2013 The Wildlife Society.

Movements by Adfluvial Bull Trout during the Spawning Season between Lake and River Habitats

AbstractMovements of adfluvial Bull Trout Salvelinus confluentus were evaluated with acoustic telemetry during spawning seasons 2006–2011 in Chester Morse Lake,Washington. Ninety‐six percent of the individuals made multiple trips between the lake and river habitat during the spawning season,which lasted from less than 1 day to more than a month. Male Bull Trout took an average 13.2 (± 8.7 SD) trips,while females averaged 18.0 (± 14.0 SD) trips. Directional movement between the lake and a river occurred throughout the day; however,the distribution of movement activity was bimodal,peaking from 0600 to 0900 hours (downstream movement) and from 1700 to 2000 hours (upstream movement). The majority of time spent in the river per trip occurred during nighttime hours for female (mean = 74%) and male Bull Trout (mean = 72%). While spawning activity was not confirmed for each trip,this study illustrates an as‐yet unreported movement pattern of adfluvial Bull Trout during the spawning season. These results are relevant to managers considering monitoring population trends by way of redd count surveys because multiple redd sites per spawning season are possible,a situation that could lead to overestimating population numbers. Additional research to determine whether spawning occurs on individual trips would help assess whether population numbers could be overestimated by simply using redd counts in systems similar to the one studied.

Habitat suitability model for red deer (Cervus elaphus Linnaeus, 1758): spatial multi-criteria analysis with GIS application

Monitoring population trends is essential in wildlife management. In fact, to identify those environmental conditions linked to habitat use and selection is a key task in any conservation plan. Our aim in this work was predict red deer (Cervus elaphus Linnaeus, 1758) colonization in the Lombada National Hunting Area (LNHA), one of the largest wild populations in Portugal. The sharply increase in density and range of red deer over the last decades justify the careful monitoring of this population. A multi-criteria model using the Analytical Hierarchic Process (AHP) and GIS weighted spatial analysis with matrix algebra techniques were applied in this approach. This method was developed in three distinct phases: i) setting the objectives, ii) analysing pairs of factors through the application of a comparison matrix and iii) its synthesis with the weight assignment that followed a predetermined numeric range according to the ecological requirements of the study species. The variables used in the red deer habitat suitability model included the hydrographic network, asphalted roads, relief aspects and land use. From October 2010 to March 2011, a total of 129 observations along line transects were recorded and used to validate the final model. By using the AUC method it was obtained a success rate of 72%. Our results suggest that this method would be applied on a larger scale being suitable to predict red deer expansion. To our knowledge, this is the first study performed in Portugal using this methodological approach to assess the red deer-habitat relationships.

Habitat suitability model for red deer (Cervus elaphus Linnaeus, 1758): spatial multi-criteria analysis with GIS application

Monitoring population trends is essential in wildlife management. In fact, to identify those environmental conditions linked to habitat use and selection is a key task in any conservation plan. Our aim in this work was predict red deer (Cervus elaphus Linnaeus, 1758) colonization in the Lombada National Hunting Area (LNHA), one of the largest wild populations in Portugal. The sharply increase in density and range of red deer over the last decades justify the careful monitoring of this population. A multi-criteria model using the Analytical Hierarchic Process (AHP) and GIS weighted spatial analysis with matrix algebra techniques were applied in this approach. This method was developed in three distinct phases: i) setting the objectives, ii) analysing pairs of factors through the application of a comparison matrix and iii) its synthesis with the weight assignment that followed a predetermined numeric range according to the ecological requirements of the study species. The variables used in the red deer habitat suitability model included the hydrographic network, asphalted roads, relief aspects and land use. From October 2010 to March 2011, a total of 129 observations along line transects were recorded and used to validate the final model. By using the AUC method it was obtained a success rate of 72%. Our results suggest that this method would be applied on a larger scale being suitable to predict red deer expansion. To our knowledge, this is the first study performed in Portugal using this methodological approach to assess the red deer-habitat relationships.

Incorporating harvest rates into the sex‐age‐kill model for white‐tailed deer

AbstractAlthough monitoring population trends is an essential component of game species management, wildlife managers rarely have complete counts of abundance. Often, they rely on population models to monitor population trends. As imperfect representations of real‐world populations, models must be rigorously evaluated to be applied appropriately. Previous research has evaluated population models for white‐tailed deer (Odocoileus virginianus); however, the precision and reliability of these models when tested against empirical measures of variability and bias largely is untested. We were able to statistically evaluate the Pennsylvania sex‐age‐kill (PASAK) population model using realistic error measured using data from 1,131 radiocollared white‐tailed deer in Pennsylvania from 2002 to 2008. We used these data and harvest data (number killed, age‐sex structure, etc.) to estimate precision of abundance estimates, identify the most efficient harvest data collection with respect to precision of parameter estimates, and evaluate PASAK model robustness to violation of assumptions. Median coefficient of variation (CV) estimates by Wildlife Management Unit, 13.2% in the most recent year, were slightly above benchmarks recommended for managing game species populations. Doubling reporting rates by hunters or doubling the number of deer checked by personnel in the field reduced median CVs to recommended levels. The PASAK model was robust to errors in estimates for adult male harvest rates but was sensitive to errors in subadult male harvest rates, especially in populations with lower harvest rates. In particular, an error in subadult (1.5‐yr‐old) male harvest rates resulted in the opposite error in subadult male, adult female, and juvenile population estimates. Also, evidence of a greater harvest probability for subadult female deer when compared with adult (≥2.5‐yr‐old) female deer resulted in a 9.5% underestimate of the population using the PASAK model. Because obtaining appropriate sample sizes, by management unit, to estimate harvest rate parameters each year may be too expensive, assumptions of constant annual harvest rates may be necessary. However, if changes in harvest regulations or hunter behavior influence subadult male harvest rates, the PASAK model could provide an unreliable index to population changes. © 2012 The Wildlife Society.

First estimation of Eurasian lynx (Lynx lynx) abundance and density using digital cameras and capture–recapture techniques in a German national park

Eurasian lynx are individually identifiable by their unique coat markings, making them ideal candidates for capture–recapture (CMR) surveys. We evaluated the use of digital photography to estimate Eurasian lynx population abundance and density within the Bavarian Forest National Park. From November 2008 to January 2009 we placed 24 camera trap sites, each with two cameras facing each other on well–used walking tracks). The units were placed based on a systematic grid of 2.7 km. We captured five independent and three juvenile lynx and calculated abundance estimates using Program Mark. We also compared density estimates based on the MMDM method (Mean Maximum Distance Moved) from telemetry data (½MMDMGPS) and from camera trapping data (½MMDMCAM). We estimated that in an effectively sampled area of 664 km2 the Eurasian lynx density was 0.9 individuals/100 km2 with ½MMDMCAM. The Eurasian lynx density calculated with ½MMDMGPS was 0.4 individuals/100 km2 in an effectively sampled area of 1,381 km2. Our results suggest that long–term photographic CMR sampling on a large scale may be a useful tool to monitor population trends of Eurasian lynx in accordance with the Fauna–Flora–Habitat Directive of the European Union.