Journal of Zoology最新文献

For animals exhibiting range residency, the home range is a useful framework to quantify space use. Some reptiles can live decades in the wild and experience extreme environmental variation that influences patterns of habitat use. Individuals may modify their use of space over time, reducing the utility of single-year home range estimates. Very high frequency (VHF) telemetry data were collected for Gila monsters (Heloderma suspectum) at three Mojave Desert sites in Clark County, Nevada, and home range utilization distributions were calculated using an autocorrelated kernel density estimator. Home range size was consistent within individuals and populations, and home range size did not vary across years at any site. To measure home range fidelity (year-to-year reuse), we calculated Bhattacharyya's coefficient (BC) for each combination of years in which an individual was tracked and averaged estimates across individuals and populations. The average BC score was 0.86 (scale from 0 to 1; 0 = no overlap and 1 = complete overlap) and did not vary among populations. We modeled home range area accumulation to estimate the minimum sample size needed for asymptotic stability and found home range accumulation to be dynamic and variable within and across years and individuals. Analysis of the frequency of movement by individuals, average distance traveled per movement, and cumulative distance traveled per active season revealed that movement patterns vary considerably by year. Heterogeneity of space use among populations and individuals suggests that individual and local environmental variation, rather than annual variation in resource availability, may drive home range size and movement patterns of Gila monsters in southern Nevada. Annual variability in movement patterns did not translate to variability in home range size or location, and the species exhibits extremely high philopatry, using the same areas for periods of at least 3–5 years.

Although the spotted hyaena (Crocuta crocuta) has been widely considered to be resilient to human disturbance, the species is now thought to be undergoing widespread population declines. Nevertheless, only a handful of population density estimates are available for the species, despite the importance of this information for informing conservation management. This is a consequence of both a lack of surveys and logistical challenges associated with processing spotted hyaena data. In this study, we collaborated with a cohort of students to process camera trap data from the Ruaha-Rungwa landscape initially collected to estimate lion (Panthera leo) and leopard (Panthera pardus) population density. By doing so, we provide the first spatially explicit population density estimates for spotted hyaena in Tanzania, via spatially explicit capture-recapture (SECR) modelling. We also examine the relationship between population densities of spotted hyaena, lion and leopard at each site. Spotted hyaena densities varied from 3.55 ± 0.72 adults and sub-adults per 100 km² in a miombo (Brachystegia-Julbernardia) woodland area of Ruaha National Park, to 10.80 ± 1.08 per 100 km² in a prey-rich open woodland savannah habitat in Ruaha National Park, with intermediate densities recorded in Rungwa Game Reserve and MBOMIPA Wildlife Management Area. Our results suggest that spotted hyaena density is influenced by prey availability and protection, and the species may be less resilient to human pressures than widely thought. Spotted hyaena densities were generally positively correlated with densities of lion and leopard, suggesting that prey availability and anthropogenic disturbance had a greater impact than interspecific effects in shaping large carnivore densities in this system. Overall, our study provides some of the first insights into an under-studied species in an under-researched part of its range, while shedding light into the impact of anthropogenic versus interspecific effects in shaping population status of spotted hyaena in human-impacted African systems.

Species assemblages are influenced by trophic and intraguild interactions, which may be competitive, facilitative, or neutral. These interactions vary in relative importance depending on resource availability. We assessed the nature of interactions among six carnivore species (Ursus arctos, Panthera uncia, Vulpes vulpes, Mustela altaica, and Martes foina) and their prey (Capra sibirica, Pseudois nayaur, Hemitragus jemlahicus, Moschus leucogaster, Ochotona sp., and Rodentia sp.) by examining their spatial–temporal overlaps using camera-trap data gathered between 2016 and 2019 from the resource-limited landscapes of the high Himalayas. We examined fine scale pairwise spatial interaction using multi-species occupancy method and temporal overlap using time activity kernel densities function. Carnivore species showed relatively high spatio-temporal overlap. We found spatial avoidance between two pairs and temporal avoidance between four out of 15 pairs. Contrary to our expectation that carnivore species would segregate due to competition in a resource-poor environment, our results showed that they generally showed significant co-occurrence and appeared to track their prey's activity. Our findings highlight the potentially overriding role of prey availability in influencing carnivore species occurrence in resource-poor landscapes.

Acoustic communication occurs in all major groups of terrestrial vertebrates, having evolved independently in early clades of mammals, birds, geckos, crocodilians and frogs, about 100–200 MYA. There is little doubt that acoustic communication was used by ancestral therian mammals, but it is ambiguous whether the reconstruction of the root of the mammalian acoustic evolutionary tree includes basal prototherian monotremes. We present here five first-hand accounts of dove-like cooing sounds and analyse the acoustics of three vocalization recordings for two observations of wild short-beaked echidnas (Tachyglossus aculeatus) to quantitatively confirm acoustic communication by this species. The ‘cooing’ tones were quite distinctive from exhalations, wheezes and grunts, being ~0.044 s down-sweeps from ~320 to 190 Hz, peaking at ~260 Hz, with at least one harmonic overtone. Tones occurred singly or as doublets, triplets (most common), quadruplets and quintuplets, with the leading tone typically the strongest and most broadband. We conclude that echidnas do produce vocalizations, but they are infrequent and acoustic communication is not their primary mode of communication. This unequivocal evidence for vocalization by short-beaked echidnas resolves a long-standing debate concerning the occurrence of acoustic communication by echidnas, which together with well-documented vocalizations by platypus, support a very early evolution of acoustic communication amongst mammals, pre-dating at least the common ancestor of monotremes and therian mammals.

An animal with a large body can have larger sense organs than a smaller one, collecting more sensory information. However, many structures scale with body size to be relatively smaller in larger animals. This occurs with eyes, however the situation for mechanosensory organs is less clear. I investigated scaling of particular mechanosensory organs unique to dipteran flies, halteres, which replace hind wings and are important for the aerobatic ability underlying the success and diversity of dipterans. Halteres are shaped like drumsticks and beat up and down in time with the wings, acting as gyroscopes because yawing, pitching or rolling generate twisting forces in them. These forces are detected by campaniform sensilla (CS), dome-shaped sensory cells in the cuticle that are mainly clustered into three fields. Unusually for a sense organ, individual CS are visible on the cuticle surface. I compared how haltere size, shape and CS number scale with body size in four clades representing different branches of dipteran phylogeny: tipulids (craneflies); tabanids (horseflies); syrphids (hoverflies) and calyptrates (e.g. houseflies, blowflies). In all clades, haltere length scaled with body mass raised to the power 0.23, similar to that for eyes of insects and other animals. It was directly proportional to wing length, probably enabling halteres to beat in time with wings. In relation to body size or wing length, tipulids had longer halteres than other clades. In contrast to haltere length, the number of CS was not related to body size within each clade but did vary between clades, suggesting a basic pattern for each clade was laid down early in its evolution. Tipulids had the smallest number, associated with relatively ponderous flight. Tabanids had more CS than calyptrates or syrphids, reasons for which require further investigation.

Female density and distribution are dependent on resource phenology and female availability strongly influences male mating behaviour and success. When a male adopts a ‘resource defence’ tactic, his reproductive success depends on the location and attractiveness of his territory. Environmental factors associated with territory quality are expected to influence mating success, for example, through territory features or male–male competition. In a protected population of a mountain-dwelling polygynous herbivore, the Alpine chamois Rupicapra r. rupicapra, we investigated the relationships among mating opportunities, some environmental variables (snow depth, topographic features and size of territories) and male intra-sexual competition for mating. We recorded the mating behaviour and territory size of 15 GPS-GSM radio-tagged territorial males, during five rutting seasons (early November to early December: N = 8 individuals in 2011, N = 9 in 2012, N = 8 in 2015, N = 11 in 2016, N = 7 in 2017; 80% of them were observed for more than one mating season) and related them to snow depth and topography of territories. In ruts with deep snow cover, territorial males had smaller territories and higher number of mating opportunities than in ruts with lower snow cover. Smaller territories showed the highest values of terrain roughness, in turn with little or no snow cover in the mating season, and were visited by a greater number of females, than larger territories. Number of wins was positively influenced by snow depth and negatively related to the frequency of aggressions. The frequency of male–male aggressive interactions was greater during ruts with deep snow cover and for males with territories at higher elevations; additionally, it was negatively related to interactions won. Thus, snow depth, which influences resource distribution and female movements, is confirmed as a strong determinant of male mating opportunities and mating behaviour.

Populations inhabiting several biomes may experience different abiotic and biotic conditions, exerting local selection pressures. Temperature and water regimes are interconnected variables, that may differ between biomes, and greatly influence ecophysiological traits, such as metabolic and evaporative water loss rates. We hypothesized that Ptyodactylus guttatus (Sinai Fan-fingered Gecko) individuals, which occupy the Mediterranean and desert biomes across Israel, would follow the “metabolic cold adaptation” hypothesis and be adapted to the microclimate in the biome they inhabit. We thus predicted that desert individuals would prefer lower temperatures, and have lower resting metabolic rates and evaporative water loss rates at higher ambient temperatures than Mediterranean individuals. We also predicted that Mediterranean individuals would have a better body condition than individuals from the desert, because of higher primary productivity in the Mediterranean biome, and would therefore have higher mite loads. We further predicted that geckos from the desert would have longer limbs, enabling them to lose more heat to the environment, according to Allen's rule. To test these hypotheses, we measured the temperature preferences, field body temperatures, resting metabolic rates, evaporative water loss rates, body conditions, mite loads, and limb lengths of 82 P. guttatus individuals collected from four localities two from the desert biome and two from the Mediterranean biome. There were no significant differences in any of the tested traits when comparing between biomes. However, we found some differences in the evaporative water loss rates, body temperatures, body condition, and forelimb lengths between the northernmost and southernmost, and driest and wettest localities, supporting some of our predictions. Our results highlight the importance of the resolution of the analysis. Although some ecophysiological traits of P. guttatus seem to be conserved across localities and biomes, thermal plasticity in these traits may have helped this species reach its current distribution and occupy two biomes.

Dehorning is a conservation measure used to protect rhinoceroses (‘rhinos’) from being poached by removing most of the visible horn and thus reducing the monetary reward for the risk that a poacher takes. Rhinos use their horns in comfort and aggressive social behaviours. The loss of the horn might result in a decrease in aggressive and affiliative behaviours and an increase in avoidance behaviours after dehorning due to a reduced effectiveness and potential discomfort when using the nasal body part. The dehorning procedure, which includes chasing and immobilization, can lead to the separation of groups and might therefore result in fewer social interactions. To estimate whether the stress of the dehorning procedure and the loss of the horn affect the activity budget of the rhino, we compared general activities and horn-related behaviours before and after dehorning. We observed nine (six females and three males) wild white rhinos (Ceratotherium simum simum) in Botswana for 1 month before and 1 month after dehorning. The proportions of feeding, resting, comfort, aggressive, avoidance and affiliative behaviours did not change significantly within 1 month after dehorning. We observed sex-specific changes in proportions of locomotion and in vocalization rates, which we linked to the chasing during the procedure and to the social events of two births in the study population. Effects of the dehorning itself seemed to be weak and short-lived. Our results suggest that dehorning has no major impact on rhino behaviour. However, there is a key need to investigate the effectiveness of dehorning in reducing poaching events.

As human development continues to expand, wildlife must relocate or adapt to survive. Many mammalian mesopredators, such as the Virginia opossum (Didelphis virginiana), have adapted to living alongside human development. Furthermore, top-down predation pressure may be altered in nuanced ways within the human environment. Species such as opossums may be shielded from predation by human development or behavioral changes in predators. Understanding how dominant and subordinate mesopredators co-exist across natural and developed areas will provide insight into how wildlife communities are structured. Our objective was to evaluate how opossum occupancy, abundance, and activity were associated with human development and the relative abundance of their predators. We used data from a nationwide camera trapping study, Snapshot USA, to estimate opossum occupancy, abundance, and activity. We related these measures to the surrounding landscape and urbanization variables. We found that opossum occupancy was positively associated with anthropogenic sound (a surrogate for human activity). Furthermore, opossums in heavily forested areas were more likely to be detected in locations with higher predicted anthropogenic sounds. In areas with a high density of human housing, opossum relative abundance increased when predator abundance increased. We also found opossums were strictly nocturnal and shifted their activity to earlier in the evening in the presence of high predator abundance. Our results suggest that humans and their urban development can have multidimensional impacts on opossum behavior and occurrence, and could facilitate changes in predator–prey dynamics. Future research should evaluate if the association of opossums with urban areas is due to human-subsidized resources or caused by reduced mortality from altered predator–prey dynamics.

Comparative studies, especially of related species that span across ecoregions, have the potential to increase our understanding of different ecological or evolutionary pressures that may drive host–pathogen dynamics. We quantified differences in immune investment, via differential leukocyte counts and bacteria-killing assays, across four closely related species of Gopherus tortoises, found across a gradient from the desert southwest to the subtropical southeast of the United States. We further quantified differences in a commensal nasal microbe (Pasteurella testudinis) and tested for associations among immune measures, P. testudinis, and previously quantified levels of the pathogen Mycoplasma agassizii and upper respiratory tract disease (URTD). We also evaluated the potential influence of environmental variables on immune investment, P. testudinis, and disease. We found that tortoise species in more arid environments had a reduced investment in inflammatory leukocytes, possibly as a strategy to reduce water loss, and invested more heavily in innate anti-inflammatory leukocytes. Conversely, we found that species in moister, resource-rich environments may face greater pathogen pressure, likely due to increased population densities and transmission rates among host tortoises. These tortoises had increased investment in inflammatory cells and appeared to reduce their nasal microbes (including P. testudinis) when they exhibited URTD. Thus, we quantified two negative correlational patterns: (1) between inflammatory responses and water conservation and (2) between resource quality and transmission rates. We hypothesize that these relationships across species may reflect variable development or evolution of innate immune functions.