QUANTIFYING HOME-RANGE OVERLAP: THE IMPORTANCE OF THE UTILIZATION DISTRIBUTION

Factors affecting home range size and overlap in Calomys venustus (Muridae: Sigmodontinae) in Argentine agroecosystems

Simple SummaryIntraspecific and interspecific interactions regulate the extent and spatial patterns of animal home ranges. If we are able to estimate the home range overlap for a large number of individuals, populations and/or species, then we can readily identify important ecological properties, such as social network structure, competition during the breeding season, contact rates with implications for disease transmission, change in space use over time, interactions among different age classes and site fidelity for a particular individual, population or species. We can also evaluate the robustness of probabilistic home range assessment through the degree of overlap of several estimators. Accordingly, in this study, we first solve the issue of measuring the degree of overlap/segregation among a large number of probabilistic animal home ranges and provide a demonstrative case study.Home range overlap/segregation has several important applications to wildlife conservation and management. In this work, we first address the issue of measuring the degree of overlap/segregation among an arbitrarily large number (i.e., n ≥ 2) of probabilistic animal home ranges (i.e., utilization distributions). This subject matter has recently been solved for home ranges measured as polygons (e.g., percent minimum convex polygons and multinuclear cores) but not yet for probabilistic ones. Accordingly, we introduce a novel index named the PGOI (probabilistic general overlap index), and its complement, the PGSI (probabilistic general segregation index), an index for computation of probabilistic home range overlap/segregation at individual, population and species levels. Whatever the number of probabilistic home ranges, the PGOI returns a single score ranging in the [0, 100] interval. We applied the PGOI to five lesser kestrels (Falco naumanni) at Santeramo in Colle (Apulia region; Southern Italy) as a case study. Our new index can be applied to any animal species and to home ranges derived from any type of probabilistic home range estimator.

Giraffes reside in a fission–fusion social system, with sex, age proximity, kinship and home range overlap accounting for some of the variance in herd composition, while season, sex, age and time of day influence diet, home range size and distance travelled. To increase our knowledge of habitat use and fission–fusion herd dynamics, we placed GPS devices on eight adult female South African giraffes (Giraffa camelopardalis giraffa) living in the Khamab Kalahari Nature Reserve (South Africa). We tested four predictions about how season, kinship, home range and travel patterns influence habitat use and herd dynamics. Our two key findings were that females with a greater degree of home range overlap were more likely to form herds, but the degree of overlap was independent of the amount of time that they spent together in a herd, and that on the day prior to herd formation, females travelled about twice as far as their daily average and tended to move directly towards their future herd mate. We conclude that habitat use and movement patterns regulating fission–fusion dynamics reflect an interaction of ecological, social and reproductive factors operating in tandem, not independently.

Red foxVulpes vulpes (Linnaeus, 1758) are generally regarded as strictly territorial animals, inhabiting distinct and well-separated ranges. The home ranges of these predators can vary in size from a few dozen hectares to as much as 20–30 km2. Because it seemed impossible that foxes could defend areas so different in size with the same intensity, the published data were analysed in order to see how changes in home range size could affect the following parameters: home range overlap, the area visited daily and the distance travelled by animals during 24 h. It was found that the overlap between fox families (groups) occupying large ranges was much greater than between foxes living in small ranges. The ratio of the area visited daily to the seasonal home range size was greater in small ranges than in large ones. No significant correlation was found between the mean distance moved daily and home range size (r = −0.118,p = 0.75). These results suggest different patterns of the use of space and differences in territorial defence by red foxes inhabiting large and small ranges. The implications of home range overlap and intensity of contacts between foxes occupying neighbouring ranges for the spread of disease are discussed. The significant overlap between large ranges found in this paper is discussed in the light of Andrzejewski’s (2002) home range concept.

Effect of high density on the short term Calomys musculinus spacing behaviour: A fencing experiment

Quantifying animal movements is necessary for answering a wide array of research questions in ecology and conservation biology. Consequently, ecologists have made considerable efforts to identify the best way to estimate an animal's home range, and many methods of estimating home ranges have arisen over the past half a century. Most of these methods fall into two distinct categories of estimators that have only recently been described in statistical detail: those that measure range distributions (methods such as kernel density estimation that quantify the long-run behavior of a movement process that features restricted space use) and those that measure occurrence distributions (methods such as Brownian bridge movement models and the Correlated Random Walk Library that quantify uncertainty in an animal movement path during a specific period of observation). In this paper, we use theory, simulations, and empirical analysis to demonstrate the importance of appropriately using these two categories of distributions and their estimators. Conflating range and occurrence distributions can have serious consequences for ecological inference and conservation practice. For example, in most situations, home ranges estimated using estimators of occurrence distributions are too small, and this problem is exacerbated by ongoing improvements in tracking technology that enable more frequent and more accurate data on animal movements. We encourage researchers to use estimators of range distributions to quantify home ranges and estimators of occurrence distributions to answer other questions in movement ecology, such as when and where an animal crossed a linear feature, visited a location of interest, or interacted with other animals.

Movements of female white-tailed deer ( Odocoileus virginianus) in relation to timber harvests in the central Appalachians

Movement-based analysis of interactions in African lions

Female orangutans exhibit natal philopatry, living in stable home ranges that overlap with those of their maternal relatives. Using data collected from 2003 to 2017 at Tuanan in Central Kalimantan, Indonesia, we take a longitudinal approach to better understand the mechanisms of female philopatry and the factors that influence the home range establishment process of young female orangutans (Pongo pygmaeus wurmbii). Data on movement and sociality were collected during nest-to-nest focal follows of individual orangutans; four young nulli/primiparous females, their three multiparous mothers, and seven other unrelated adult females living in the same area. Our results show that a young female goes through an ‘exploration phase’, beginning when she is an independent immature and lasting through her adolescence, characterized by an increase in home range size and distance travelled each day. This exploration is facilitated by high resource availability and association with adult males. A young female maintains a high degree of overlap with her natal range but gradually decrease the degree of overlap with her mother’s concurrent range. By the time she is a sexually active adolescent, a young female and her mother share as much overlap as a young female does with other related adult females, although she continues to associate more with her mother than with them, even after the birth of her first offspring. Our findings indicate that the high habitat productivity and high orangutan population density of Tuanan lead to a high degree of life-time site fidelity and overlap among maternal kin. The mechanisms of philopatry and the process of home range establishment among solitary animals with slow life histories are difficult to study and poorly understood for most species. We investigated this process among female Bornean orangutans, using a unique long-term data set comprising 15 years of social and spatial data. We analysed changes in the ranging and association patterns of young female orangutans as they developed, matured and became mothers. We found that females went through a post-dependence phase of exploration characterized by an increase in range size and day journey length, and then settled into home ranges that overlapped highly with their mothers and other female kin, though they associated preferentially with their mothers. Our results illuminate the extreme long-term site fidelity of these female orangutans and emphasize the ecological and social importance of female philopatry among orangutans.

Secondary exposure of wildlife to pesticides has been well documented, yet exposure is typically associated with agricultural or wildland‐urban interface areas. Wildlife in undeveloped areas is generally presumed free from risk. In 2009, a male fisher was found dead in the Sierra National Forest and subsequent necropsy revealed that the animal died of acute rodenticide poisoning. Follow‐up testing revealed that 85% of fisher carcasses recovered by two research projects in the previous three years tested positive for rodenticides. Concern arose that exposure could predispose an animal to mortality from other causes, and that the underlying role of toxicants would escape notice. Further investigation indicated that the most likely source was the numerous illegal marijuana cultivation sites currently found on public lands throughout the western United States. To determine whether the presence of cultivation sites predisposed fishers to mortality from other sources, we related survival rates to the presence and number of cultivation sites found within that animal's home range over the past 10 years. Likelihood of exposure was related to the presence of cultivation sites, and female fisher survival was influenced by the number of cultivation sites within its home range. We discuss the conservation implications of this unexpected relationship.

The small Indian mongoose (Urva auropunctata) is the primary terrestrial wildlife rabies reservoir on at least four Caribbean islands, including Puerto Rico. In Puerto Rico, mongooses represent a risk to public health, based on direct human exposure and indirectly through the transmission of rabies virus to domestic animals. To date, the fundamental ecological relationships of space use among mongooses and between mongooses and domestic animals remain poorly understood. This study is the first to report mongoose home range estimates based on GPS telemetry, as well as concurrent space use among mongooses and free roaming domestic dogs (FRDD; Canis lupus familiaris). Mean (± SE) home range estimates from 19 mongooses in this study (145 ± 21 ha and 60 ± 14 ha for males and females, respectively) were greater than those reported in prior radiotelemetry studies in Puerto Rico. At the scale of their home range, mongooses preferentially used dry forest and shrubland areas, but tended to avoid brackish water vegetation, salt marshes, barren lands and developed areas. Home ranges from five FRDDs were highly variable in size (range 13–285 ha) and may be influenced by availability of reliable anthropogenic resources. Mongooses displayed high home range overlap (general overlap index, GOI = 82%). Home range overlap among mongooses and FRDDs was intermediate (GOI = 50%) and greater than home range overlap by FRDDs (GOI = 10%). Our results provide evidence that space use by both species presents opportunities for interspecific interaction and contact and suggests that human provisioning of dogs may play a role in limiting interactions between stray dogs and mongooses.

A population of the rock-inhabiting lizard, Sceloporus undulatus erythrocheilus, was studied over two activity seasons in the eastern Colorado foothills. The convex polygon method was used to determine home range and figures were adjusted to eliminate sample size bias. Ninety-seven lizards (53 8 and 44 9) were captured. On the basis of ten or more observations, resident adults (= 50 mm snout-vent length) had an average home-range size of 826 m2 for 12 males and 363 m2 for 9 females. Male home-range size decreased significantly after the breeding season. The large degree of male home-range overlap (52%) suggests that home range is not equal to territory in this population. A promiscuous mating system is implied from the overlap of male and female home ranges and from behavioral notes.

ABSTRACTSeveral habitats may be required for an animal’s persistence, and movements within and among these habitats characterise an animal’s home range. For species of lizards, variation in home range size is typically best explained by either sit-and-wait or active foraging styles. In this study, we explore movements, home range size, and territoriality of Reticulate Collared Lizards (Crotaphytus reticulatus) from the typically sit-and-wait foraging subfamily Crotaphytinae. Over three years, we tracked 10 adult males and four adult females using GPS telemetry and found male C. reticulatus moved significantly longer distances and maintained significantly larger home ranges and core areas than females. We observed no home range overlap in females and one case of overlap in males, although all females maintained home ranges overlapped by a single male home range. The one-to-one pattern of a male home range overlapping just a single female home range is consistent with male mate guarding observed in active foragers. Moreover, compared to classic sit-and-wait foraging Common Collared Lizards (C. collaris), C. reticulatus moves more frequently, maintains a larger home range, is less territorial, and exhibits less sexual dimorphism; all traits of active foraging lizards. Indeed, C. reticulatus was observed actively stalking prey throughout its larger home range similar to G. wislizenii, which supports previous predictions regarding convergence in active foraging predatory behaviours between the species.

To estimate the home range (HR) and investigate the potential predictors for roaming of 58 dogs in four Aboriginal communities in the Northern Territory. Prospective study. Global positioning system (GPS) collars were attached to the dogs for 1-4 days, recording location fixes every 1-3 min. Utilisation distributions (UDs) and extended (95% isopleth) and core (50% isopleth) HRs of dogs were determined. Potential predictors of roaming were assessed. Estimated core (median, 0.27 ha) and extended (median, 3.1 ha) HRs differed significantly (P = 0.0225 and 0.0345, respectively) between the four communities; dogs in the coastal community travelled significantly (P < 0.0001) more per day than dogs in the three inland communities studied. Significant associations were found between extended HR size and sex (P = 0.0050) and sex + neuter (P = 0.0218), and between core HR size and sex (P = 0.0010), neuter status (P = 0.0255) and sex + neuter (P = 0.0025). Entire males roamed more than neutered females. The core HR of dogs with poor/fair body condition scores (BCSs) was larger than dogs with ideal/obese BCSs (P = 0.0394). Neutered male dogs also travelled more per day than entire female dogs (P = 0.0475). Roaming information can be used to inform the management of dogs in remote communities and to design disease control programs. Widespread data collection across the Northern Territory should be undertaken to further investigate the associations found in this study, considering that data were collected during relatively short periods of time in one season.

Home ranges provide a conceptual and quantitative representation of animal-habitat associations over time. Methods to estimate home ranges have swiftly progressed by dynamically accounting for various sources of bias. Across that period of growth, one potentially influential source of bias has yet to be robustly scrutinized. Animals inhabiting the terrestrial spatial domain make movement decisions in environments with variable landscape complexity. Despite that reality, home range estimation methods tend to be informed by two-dimensional (2D) data (i.e., x and y coordinates), which analytically presume that these landscapes are flat. This analytical tendency potentially misrepresents the configuration and size of animal home range estimates. To examine the prevalence of this bias, we reviewed literature of terrestrial animal home range estimation published between 2000 and 2019. We recorded the proportion of studies that (1) recognized and (2) incorporated landscape complexity. Over 22.0% (n = 271) of the 1,203 studies recognized the importance of landscape complexity for animal movement. Interestingly, just 0.7% (n = 8) incorporated landscape complexity into the home range estimation. We infer then that landscape complexity represents an important source of bias resulting in the underestimation of terrestrial animal home range size. Given the influence of landscape complexity on terrestrial animal decision making, energetics, and fitness, our analysis highlights an important gap in current home range methodologies. We discuss the implications of our analysis for biased understandings of terrestrial animal spatial ecology with subsequent impacts on management and conservation practices built upon these estimates.