Correcting for missing and irregular data in home-range estimation.

Home-range estimation is an important application of animal tracking data that is frequently complicated by autocorrelation, sampling irregularity, and small effective sample sizes. We introduce a novel, optimal weighting method that accounts for temporal sampling bias in autocorrelated tracking data. This method corrects for irregular and missing data, such that oversampled times are downweighted and undersampled times are upweighted to minimize error in the home-range estimate. We also introduce computationally efficient algorithms that make this method feasible with large data sets. Generally speaking, there are three situations where weight optimization improves the accuracy of home-range estimates: with marine data, where the sampling schedule is highly irregular, with duty cycled data, where the sampling schedule changes during the observation period, and when a small number of home-range crossings are observed, making the beginning and end times more independent and informative than the intermediate times. Using both simulated data and empirical examples including reef manta ray, Mongolian gazelle, and African buffalo, optimal weighting is shown to reduce the error and increase the spatial resolution of home-range estimates. With a conveniently packaged and computationally efficient software implementation, this method broadens the array of data sets with which accurate space-use assessments can be made.

Estimating where and how animals travel: an optimal framework for path reconstruction from autocorrelated tracking data.

An animal's trajectory is a fundamental object of interest in movement ecology, as it directly informs a range of topics from resource selection to energy expenditure and behavioral states. Optimally inferring the mostly unobserved movement path and its dynamics from a limited sample of telemetry observations is a key unsolved problem, however. The field of geostatistics has focused significant attention on a mathematically analogous problem that has a statistically optimal solution coined after its inventor, Krige. Kriging revolutionized geostatistics and is now the gold standard for interpolating between a limited number of autocorrelated spatial point observations. Here we translate Kriging for use with animal movement data. Our Kriging formalism encompasses previous methods to estimate animal's trajectories--the Brownian bridge and continuous-time correlated random walk library--as special cases, informs users as to when these previous methods are appropriate, and provides a more general method when they are not. We demonstrate the capabilities of Kriging on a case study with Mongolian gazelles where, compared to the Brownian bridge, Kriging with a more optimal model was 10% more precise in interpolating locations and 500% more precise in estimating occurrence areas.

Rigorous home range estimation with movement data: a new autocorrelated kernel density estimator.

Quantifying animals' home ranges is a key problem in ecology and has important conservation and wildlife management applications. Kernel density estimation (KDE) is a workhorse technique for range delineation problems that is both statistically efficient and nonparametric. KDE assumes that the data are independent and identically distributed (IID). However, animal tracking data, which are routinely used as inputs to KDEs, are inherently autocorrelated and violate this key assumption. As we demonstrate, using realistically autocorrelated data in conventional KDEs results in grossly underestimated home ranges. We further show that the performance of conventional KDEs actually degrades as data quality improves, because autocorrelation strength increases as movement paths become more finely resolved. To remedy these flaws with the traditional KDE method, we derive an autocorrelated KDE (AKDE) from first principles to use autocorrelated data, making it perfectly suited for movement data sets. We illustrate the vastly improved performance of AKDE using analytical arguments, relocation data from Mongolian gazelles, and simulations based upon the gazelle's observed movement process. By yielding better minimum area estimates for threatened wildlife populations, we believe that future widespread use of AKDE will have significant impact on ecology and conservation biology.

Movement ecology of vulnerable lowland tapirs between areas of varying human disturbance.

BACKGROUND: Animal movement is a key ecological process that is tightly coupled to local environmental conditions. While agriculture, urbanisation, and transportation infrastructure are critical to human socio-economic improvement, these have spurred substantial changes in animal movement across the globe with potential impacts on fitness and survival. Notably, however, human disturbance can have differential effects across species, and responses to human activities are thus largely taxa and context specific. As human disturbance is only expected to worsen over the next decade it is critical to better understand how species respond to human disturbance in order to develop effective, case-specific conservation strategies. METHODS: Here, we use an extensive telemetry dataset collected over 22 years to fill a critical knowledge gap in the movement ecology of lowland tapirs (Tapirus terrestris) across areas of varying human disturbance within three biomes in southern Brazil: the Pantanal, Cerrado, and Atlantic Forest. RESULTS: From these data we found that the mean home range size across all monitored tapirs was 8.31 km2 (95% CI 6.53-10.42), with no evidence that home range sizes differed between sexes nor age groups. Interestingly, although the Atlantic Forest, Cerrado, and Pantanal vary substantially in habitat composition, levels of human disturbance, and tapir population densities, we found that lowland tapir movement behaviour and space use were consistent across all three biomes. Human disturbance also had no detectable effect on lowland tapir movement. Lowland tapirs living in the most altered habitats we monitored exhibited movement behaviour that was comparable to that of tapirs living in a near pristine environment. CONCLUSIONS: Contrary to our expectations, although we observed individual variability in lowland tapir space use and movement, human impacts on the landscape also had no measurable effect on their movement. Lowland tapir movement behaviour thus appears to exhibit very little phenotypic plasticity in response to human disturbance. Crucially, the lack of any detectable response to anthropogenic disturbance suggests that human modified habitats risk being ecological traps for tapirs and this information should be factored into conservation actions and species management aimed towards protecting lowland tapir populations.

Using the GOHAI to assess oral health status of frail homebound elders: reliability, sensitivity, and specificity.

A pilot study assessed the clinically determined and self-reported oral health status of 50 randomly selected homebound patients served by Boston's Home Medical Service. The sample was largely female, low-income, and edentulous. The median age of the patients was 81 years (range, 64-101). While 76% deemed themselves to be in good to excellent oral health, 80% of the patients had not seen a dentist within the last two years, and 80% were found to be in need of routine dental care. To assess whether the Geriatric Oral Health Assessment Index (Atchison and Dolan, 1990) could be used by non-dental health professionals to determine the need for requesting dental consultation, the study physician repeated the administration of the GOHAI for 23 of the 50 subjects within eight weeks of the initial examination. For the 23 subjects having both dentist- and physician-administered GOHAI scores, the intraclass correlation coefficient was r = 0.61 (p = 0.002), indicating good agreement between the dentist's and physician's administrations of the GOHAI. However, given the high prevalence of need for care, the GOHAI appears to be of less value than an examination for identifying persons who need dental care in this population. Future research is needed to examine the GOHAI's sensitivity and specificity in populations with low to moderate prevalence of treatment need.

Effects of a parent-child communications intervention on young adolescents' risk for early onset of sexual intercourse.

CONTEXT: The quality of parent-child communications about sex and sexuality appears to be a strong determinant of adolescents' sexual behavior. Evaluations of interventions aimed at improving such communications can help identify strategies for preventing early onset of sexual behavior. METHODS: A school-based abstinence-only curriculum was implemented among 351 middle school students, who were randomly assigned to receive either the classroom instruction alone or the classroom instruction enhanced by five homework assignments designed to be completed by the students and their parents. An experimental design involving pretest and posttest surveys was used to assess the relative efficacy of the curriculum delivered with and without the parent-child homework assignments. RESULTS: In analyses of covariance controlling for baseline scores, immediately after the intervention, adolescents who received the enhanced curriculum reported greater self-efficacy for refusing high-risk behaviors than did those who received the classroom instruction only (mean scores, 16.8 vs. 15.8). They also reported less intention to have sex before finishing high school (0.4 vs. 0.5), and more frequent parent-child communications about prevention (1.6 vs. 1.0) and sexual consequences (1.6 vs. 1.1). In all significant comparisons, the direction of the findings favored adolescents who received the enhanced curriculum. Dose-response relationships supported the findings. CONCLUSIONS: Parent-child homework assignments designed to reinforce and support school-based prevention curricula can have an immediate impact on several key determinants of sexual behavior among middle school adolescents.