Habitat Utilization Research Articles

Home Range and Habitat Use of Breeding Black-Necked Cranes.

Simple SummaryThe Black-necked Crane is the only crane that breeds on the Qinghai–Tibetan Plateau, and it is currently classified as a vulnerable species. Habitat destruction and loss are the main threats for the Black-necked Crane. However, the breeding needs of Black-necked Cranes with regard to their preferred habitat remain unknown. To find the driving factors of their habitat selection, we studied the utilization rate of three habitats within the home range of Black-necked Cranes during four consecutive breeding stages. Black-necked Cranes mainly utilize meadows in the whole breeding season, followed by marsh meadows and marshes. Compared with other stages, the utilization of marsh habitat slightly increased in the postfledging stage. Since this stage is a very vulnerable period for young cranes, we suggest that grazing needs to be managed during this stage, that is, from late May to early September.To effectively protect a species, understanding its habitat needs and threats across its life-history stages is necessary. The Black-necked Crane (Grus nigricollis) is an endangered wetland bird species of the Qinghai–Tibetan Plateau, which is an important grazing area in China. To overcome the conflict between increasing grazing activities and the protection of wild cranes, we investigated the variation of habitat utilization within the home range of cranes at different stages (preincubation, incubation, postfledging, and fully fledged stages). We manually tracked 13 pairs of cranes in the Zoige international wetland, used the fixed-kernel-polygon (FKP) method to determine home-range size, and used satellite images to identify different habitat types. The average home-range size was 143.38 ± 34.46 ha. Cranes were most often located in meadow habitats followed by marsh meadows and marshes. During the postfledging stage, home-range size was significantly decreased, with the proportion of marsh habitat slightly increased. Since this stage is crucial for young-crane survival, research on the importance of marshes and effective protection measures should be further strengthened.

Disease Vector Relative Spatio-Temporal Abundances to Water Bodies and Thermal Fitness Across Malaria Endemic Semi-Arid Areas.

The biophysical environment plays an important role in the spatio-temporal abundance and distribution of mosquitoes. This has implications for the spread of vectors and diseases they cause across diverse landscapes. Here, we assessed vector mosquito abundances in relation to large water bodies, from three malaria districts in a semi-arid environment. Furthermore, we explored thermal limits to activity of the dominant and most medically important malaria vector across malaria-endemic areas. Mosquitoes were trapped near permanent water bodies across different districts. Critical thermal limits (critical thermal-maxima and -minima) to activity of wild adults and 4th instar larvae Anopheles arabiensis (Diptera: Culicidae) were assessed. Our results showed that Anopheles spp. dominate mosquito communities across all three districts, but that their numbers were far greater in Okavango than in other regions. At the Okavango sites, the numbers of Anopheles spp. decreased with distance from main water source. Anopheles spp. sampled in this region comprised Anopheles gambiae (Giles,1902) and Anopheles funestus (Giles, 1900) species complexes, with the former dominating in numbers. Thermal activity assays showed An. arabiensis females had wider thermal tolerance windows than males while larval thermal activity limits differed significantly across space. These results confirm that the Okavango district should be prioritized for vector control measures. Moreover, intervention strategies should consider recommendations for proximity effects to large water bodies, given the differential risk associated with distance from water. The wider thermal window on female vectors has implications for possible future malaria transmission and diverse habitat utilization under changing environments.

Habitat segregation and migration in tropical anguillid eels, Anguilla bengalensis bengalensis and A. bicolor bicolor

Anguillid eels of the genus Anguilla, which have a unique catadromous life history, are widely distributed across many parts of the world. However, little research has been conducted on the behavioural mechanisms of habitat segregation between sympatric species in tropical anguillid eels. To understand the ecological and behavioural mechanisms involved in the life history and migration of tropical anguillid eels, strontium (Sr):calcium (Ca) ratios were examined in otoliths of A. bengalensis bengalensis (41 specimens) and A. bicolor bicolor (130 specimens) collected from ten rivers in northwestern Peninsular Malaysia. The otolith Sr:Ca ratios revealed different habitat use between the two species. The broad range of otolith Sr:Ca ratios and habitat shift found in A. bicolor bicolor suggested that its habitat utilization was opportunistic in environments of varying salinity. A. bicolor bicolor prefers to live in the midstream to downstream areas with tidal influences. A. bengalensis bengalensis, however, was found to only reside in freshwater environments throughout their continental growth. A. bengalensis bengalensis tends to live in upstream area with no tidal influence. Their habitat use, migratory history, and habitat distribution indicate that habitat segregation occurs between the two species, leading to the different habitat preferences in tropical river systems.

Habitat Utilization by Indian Peafowl, Pavo cristatus (<i>Phasianidae</i>), in Indroda Nature Park, Gandhinagar, Gujarat, India

The behavioural activities of the Indian Peafowl (Pavo cristatus) from the various environments oflndroda Nature Park (INP), Gandhinagar, Gujarat was evaluated based on the Activity Budget method. It was inferred that Indian Peafowl utilize the INP for all m ajorbehavioural activities. However, maximum time was spent for foraging activity followed by resting activity. The study has also brought out that Botanical Garden and Campsite of lNP were utilized for all requisites. These areas were observed to be suitable forresting as they are covered with tall trees.

Factors influencing riverine utilization patterns in two sympatric macaques

Many species of terrestrial animals, including primates, live in varied association with the aquatic (e.g., riverine or coastal) environment. However, the benefits that each species receive from the aquatic environment are thought to vary depending on their social and ecological characteristics, and thus, elucidating those benefits to each species is important for understanding the principles of wild animal behaviour. In the present study, to gain a more complete picture of aquatic environment use, including social and ecological factors in primates, factors affecting riverine habitat utilization of two macaque species (Macaca nemestrina and M. fascicularis) were identified and qualitative comparisons were made with sympatric proboscis monkeys (Nasalis larvatus), which have different social and ecological characteristics. Temporal variation in sighting frequency of macaques at the riverbanks was positively related to the fruit availability of a dominant riparian plant species and negatively related to the river water level which affects the extent of predation pressure. Riverine utilization of macaques was greatly influenced by distribution and abundance of food (especially fruit) resources, possibly in association with predation pressure. Additionally, qualitative ecological comparisons with sympatric proboscis monkeys suggest that the drivers of riverine utilization depend on the feeding niches of the species, and different anti-predator strategies resulting from their differing social structures.

Habitat utilization and feeding ecology of small round goby in a shallow brackish lagoon

We examined small-scale distribution and feeding ecology of a non-native fish species, round goby (Neogobius melanostomus (Pallas, 1814)), in different habitats of a coastal lagoon situated in the south-western Baltic Sea. First observations of round goby in this lagoon were reported in 2011, 3 years before the current study was conducted, and information on this species’ basic ecology in different habitats is limited. We found that mainly juvenile round gobies are non-randomly distributed between habitats and that abundances potentially correlate positively with vegetation density and thus structural complexity of the environment. Abundances were highest in shallower, more densely vegetated habitats indicating that these areas might act as a refuge for small round gobies by possibly offering decreased predation risk and better feeding resources. Round goby diet composition was distinct for several length classes suggesting an ontogenetic diet shift concerning crustacean prey taxa between small (≤ 50 mm total length, feeding mainly on zooplankton) and medium individuals (51–100 mm, feeding mainly on benthic crustaceans) and another diet shift of increasing molluscivory with increasing body size across all length classes. Differences in round goby diet between habitats within the smallest length class might potentially be related to prey availability in the environment, which would point to an opportunistic feeding strategy. Here, we offer new insights into the basic ecology of round goby in littoral habitats, providing a better understanding of the ecological role of this invasive species in its non-native range, which might help to assess potential consequences for native fauna and ecosystems.

The Sawshark Redemption: Current knowledge and future directions for sawsharks (Pristiophoridae)

AbstractSawsharks (Order: Pristiophoriformes, Family: Pristiophoridae) are a highly distinctive group of sharks, characterized by a tapering saw‐like rostrum with a pair of elongate barbels on the ventral surface. Their unusual characteristics should attract attention; however, very few studies have been dedicated to sawsharks. As a result, our understanding of their biology and ecology is limited. However, information on aspects of their biology and ecology can be found in studies not directly focussing on sawsharks. This review provides a synthesis of information pertaining to the 10 recognized sawshark species following a comprehensive search of the scientific literature. We cover their distributions, habitat utilization, life histories, reproduction, trophic dynamics and sensory biology. Current knowledge on their unique rostral structures, the evolutionary history of pristiophorids, taxonomy, behaviour and threats to sawshark populations are also reviewed. This compilation serves as a foundation for sawshark researchers and highlights key knowledge gaps in this unique group of elasmobranchs, thereby beginning the sawshark redemption.

Giraffe diurnal recumbent behavior and habitat utilization in Katavi National Park, Tanzania

AbstractResting behaviors play an important role in animals’ daily activities by minimizing energy consumption. Although this may be equally important to other behavioral states for sustaining life, it has not been well studied in the giraffe (Giraffa camelopardalis). This study characterized the bout duration, frequency, and age–sex class differences in diurnal recumbent behavior of free‐ranging giraffe. Additionally, it is currently unknown whether giraffe utilize shady or safe areas for diurnal recumbency, as many other animals do. Therefore, we also investigated this in the present study. Data were collected in Katavi National Park, Tanzania, during four time periods. The duration of recumbency bouts was calculated from 170 episodes, and the frequency of recumbency was determined by following 24 individuals for more than 10 h each. Habitat type was categorized into wooded grassland or miombo woodland, and habitat preference was analyzed based on 173.6 h of observations. We found no significant difference in the duration of recumbency bouts among the four age‐classes and between sexes in adults. On the other hand, calves (n = 2) rested more frequently than did other age‐groups, possibly due to differences in predation risk or activity budgets. Adult males had a higher frequency of recumbency compared to adult females, possibly because pregnant/nursing females were hindered in adopting this posture. We also found that giraffe primarily utilized the miombo woodland for daytime recumbency, likely because the high tree density reduces heat stress, and its seclusion from the river reduces predation risk.

A dynamic approach to estimate the probability of exposure of marine predators to oil exploration seismic surveys over continental shelf waters

The ever-increasing human demand for fossil fuels has resulted in the expansion of oil exploration efforts to waters over the continental shelf. These waters are largely utilized by a complex biological community. Large baleen whales, in particular, utilize continental shelf waters as breeding and calving grounds, foraging grounds, and also as migration corridors. We developed a dynamic approach to estimate the likelihood that individuals from different populations of blue whales Balaenoptera musculus and humpback whales Megaptera novaeangliae could be exposed to idealized, simulated seismic surveys as they move over the continental shelf. Animal tracking data for the different populations were filtered, and behaviors (transit and foraging) were inferred from the tracks using hidden Markov models. We simulated a range of conditions of exposure by having the source of noise affecting a circular area of different radii (5, 25, 50 and 100 km), moving along a gridded transect of 270 and 2500 km2 at a constant speed of 9 km h-1, and starting the simulated surveys every week of the year. Our approach allowed us to identify the temporal variability in the susceptibility of the different populations under study, as we ran the simulations for an entire year, allowing us to identify periods when the surveys would have an intensified effect on whales. Our results highlight the importance of understanding the behavior and ecology of individuals in a site-specific context when considering the likelihood of exposure to anthropogenic disturbances, as the habitat utilization patterns of each population are highly variable.

Dolphinfish movements in the Eastern Pacific Ocean of Mexico using conventional and electronic tags

BackgroundThe dolphinfish, Coryphaena hippurus, is a fast-swimming, predatory fish exhibiting relatively fast growth and early maturation among marine teleosts. It is an important, potentially renewable resource throughout its global subtropical-to-tropical range. Understanding the ecology of this wide-ranging fish is critical to proper fisheries management, but studies have historically depended heavily upon aggregated catch data reported by fisheries. This study uses tagging data to explore finer scale dolphinfish movements in two subregions of the Eastern Pacific Ocean (EPO)—the west coasts of Baja California Peninsula (WBC) and Oaxaca (OAX), Mexico.ResultsAdult dolphinfish (fork length 66–129 cm) were tagged with conventional (n = 132 tags) and electronic tags (n = 30 tags, miniPAT) between 2010 and 2014. Recapture rate of conventional tags was 4.5% with a maximum days of liberty of 141 days (mean = 56 d); 20 electronic tags reported but all did so prior to programmed release dates, with days at liberty ranging from 4 to 62 (mean = 24 d). Fish remained within the region they were tagged except for six fish tagged in WBC and one in OAX. Latitudinal (WBC) and longitudinal (OAX) extensions of observed fish movements (determined via a novel analytical approach) increased with days at liberty. Despite occasional deep dives (max 262 m), fish remained surface oriented with short excursions below the isothermal layer but larger OAX fish (fork length [103 cm, 120 cm]) inhabiting warmer waters (sea surface temperatures (SST) > ~ 26 °C) spent more time below the isothermal layer than smaller fish (fork length [90 cm, 112 cm]) inhabiting colder WBC surface waters (SST > ~ 22 °C).ConclusionsThis study reveals movements of dolphinfish that infer regional differences in thermal habitat utilization and displacement over time. This inference evokes questions important to fisheries management regarding the three-dimensional extent of the dolphinfish’s realized thermal niche, its population structure, and the spatiotemporal connectivity of its habitats within the multinational EPO. With improved tag retention, longer deployments should capture increasing displacements along observed axes (N/S vs. E/W); the orientation of seasonal displacement axes suggest longer-distance movements would provide opportunities for reproductive mixing via trans-national migrations.

Ensemble Modelling of Skipjack Tuna (Katsuwonus pelamis) Habitats in the Western North Pacific Using Satellite Remotely Sensed Data; a Comparative Analysis Using Machine-Learning Models

To examine skipjack tuna’s habitat utilization in the western North Pacific (WNP) we used an ensemble modelling approach, which applied a fisher- derived presence-only dataset and three satellite remote-sensing predictor variables. The skipjack tuna data were compiled from daily point fishing data into monthly composites and re-gridded into a quarter degree resolution to match the environmental predictor variables, the sea surface temperature (SST), sea surface chlorophyll-a (SSC) and sea surface height anomalies (SSHA), which were also processed at quarter degree spatial resolution. Using the sdm package operated in RStudio software, we constructed habitat models over a 9-month period, from March to November 2004, using 17 algorithms, with a 70:30 split of training and test data, with bootstrapping and 10 runs as parameter settings for our models. Model performance evaluation was conducted using the area under the curve (AUC) of the receiver operating characteristic (ROC), the point biserial correlation coefficient (COR), the true skill statistic (TSS) and Cohen’s kappa (k) metrics. We analyzed the response curves for each predictor variable per algorithm, the variable importance information and the ROC plots. Ensemble predictions of habitats were weighted with the TSS metric. Model performance varied across various algorithms, with the Support Vector Machines (SVM), Boosted Regression Trees (BRT), Random Forests (RF), Multivariate Adaptive Regression Splines (MARS), Generalized Additive Models (GAM), Classification and Regression Trees (CART), Multi-Layer Perceptron (MLP), Recursive Partitioning and Regression Trees (RPART), and Maximum Entropy (MAXENT), showing consistently high performance than other algorithms, while the Flexible Discriminant Analysis (FDA), Mixture Discriminant Analysis (MDA), Bioclim (BIOC), Domain (DOM), Maxlike (MAXL), Mahalanobis Distance (MAHA) and Radial Basis Function (RBF) had lower performance. We found inter-algorithm variations in predictor variable responses. We conclude that the multi-algorithm modelling approach enabled us to assess the variability in algorithm performance, hence a data driven basis for building the ensemble model. Given the inter-algorithm variations observed, the ensemble prediction maps indicated a better habitat utilization map of skipjack tuna than would have been achieved by a single algorithm.

Niche partitioning between river shark species is driven by seasonal fluctuations in environmental salinity

Abstract Tropical rivers and estuaries are highly dynamic environments, where environmental conditions change dramatically over spatial and temporal scales. This creates both physiological and ecological challenges for euryhaline elasmobranchs, where fluctuations in salinity can impact not only osmoregulatory function but also the ability to find and acquire prey. We investigated how spatial and temporal variation in environmental salinity influences physiological homoeostasis, habitat utilization and migration timing in two euryhaline carcharhinid sharks within a tropical river in northern Australia. Neonate and juvenile bull sharks Carcharhinus leucas and speartooth sharks Glyphis glyphis were tracked over a 4‐year period using implanted acoustic tags and an array of hydrophone receivers. Tissue samples were also collected from captured sharks and analysed for interspecific differences in plasma osmolarity, urea and electrolyte (Na+ and K+) concentrations and the stable isotopes δ13C and δ15N. We discovered that immature C. leucas and G. glyphis segregate spatially along a salinity gradient between September and December, where the mean volume of intersection between species dropped as low as 0.01. While G. glyphis used higher salinity environments (mean salinity = 19.22) located between 30 and 70 km from the mouth of the estuary, C. leucas occupied freshwater reaches (mean salinity = 1.98) between 60 and 110 km upstream. Plasma osmolarities of both species were always hyperosmotic to the environment, with electrolyte concentrations maintained within a narrow range independent of environmental osmolarities. At the onset of the wet season, both C. leucas and G. glyphis undertook a coordinated downstream migration towards the lower estuary before returning upstream. Carcharhinus leucas blood tissues were more enriched in δ15N and δ13C than samples collected from similar size G. glyphis, suggesting that these species not only spatially segregate within low salinity habitats but also prey on different dietary resources. Furthermore, a loss of enriched isotopic values in fin tissue with increasing body length provides further support for marine use by adult sharks in conjunction with dependence on rivers as important nursery habitat. Our results illustrate the importance of long‐term integrative studies into resource competition and the significance of discrete brackish habitats for threatened euryhaline elasmobranchs. A free Plain Language Summary can be found within the Supporting Information of this article.

Ecomorphological diversification of some barbs and carps (Cyprininae, Cyprinidae) in the Lower Mekong Basin of Thailand

Morphological variation is fundamentally related to various aspects of fish ecology, including foraging, locomotion, and habitat utilisation. Twenty-six species of closely related cyprinid fish (n = 502) were analysed for patterns of morphological variations by using geometric morphometric methods. Ecological data of feeding and habitat preferences were determined by the observations in fields and laboratory together with the gathering of bibliographic information. The findings of major variation displayed in all parts of the fish body and correlated with ecological parameters. Variations of head shape especially form and position of mouthpart involved with feeding behaviours, whereas the variations of body depth and length which affected swimming patterns reflected responsiveness of water currents and habitat uses. Adaptation of head shape and body elongation was remarkably related to the feeding regime, swimming manoeuvrability and habitat utilisation of the species. Some convergent variation was observed between the tribes Smiliogastrini and Poropuntiini. Therefore, we propose that the morphological diversity of cyprinine fish is mainly affected by ecological gradients, while phylogenetic effects on morphology are minor.

Variation of body temperature of active amphibians along elevation gradients in eastern Nepal Himalaya.

Understanding the thermal ecology of active amphibians, as well as its relationship with habitat and environmental features, is a central theme in ecology. However, this topic has been poorly studied in eastern Himalaya, which is a global biodiversity hotspot. To bridge this gap, we investigated how the body temperatures of active amphibians varied along an elevation gradient in the Arun and Tamor River catchments in eastern Nepal Himalaya in the present study. Amphibian assemblages were sampled from May to July in both 2014 and 2015 using nocturnal time-constrained visual encounter surveys, and the body temperature of each individual was directly measured using a digital infrared thermometer in the field. A combination of linear regression and hierarchical partitioning analyses was used to determine the effects of elevation and environmental variables on the body temperatures of active amphibians. In total, the body temperatures of 599 amphibian individuals belonging to 28 species from six families were recorded. Our results indicated that amphibian body temperature exhibited monotonically declining trends with increasing elevations in eastern Nepal Himalaya. Interestingly, this tread was much more pronounced in subtropical (lowland) areas than in warm and cool temperate regions. Inter- and intraspecies variations in body temperature were large, which can be attributed to distinct habitat utilization among species and the change in vegetation cover in different bioclimatic zones. Among all environmental variables, substrate temperature and water temperature were the best predictors of the amphibian body temperature. Overall, this study revealed amphibian body temperature patterns along an elevation gradient in eastern Nepal Himalaya, which were principally driven by temperature-related environmental factors. We believe our results can provide important information on amphibian physiological traits, which may help ecologists predict their responses to future climate change and formulate protection strategies.

Movements and Habitat Use of Dolphinfish (Coryphaena hippurus) in the East China Sea

To refine the regional and global stock and ecological assessments of dolphinfish in fisheries, it is necessary to have information on the species habitat use, fisheries interaction, migration corridors, and on changes in spatial-temporal patterns over their ontogeny. In order to inform management, pop-up satellite archival tags (PSATs) were deployed on dolphinfish (Coryphaena hippurus) in the Northern East China Sea to get data on the movement patterns and habitat utilization of this species in this location. During October–November 2018, four dolphinfish (94–102 cm fork length) were captured by set-nets and PSAT tagged. Tagged dolphinfish retained PSATs for 5–31 days-at-liberty (total 69 days) and linear dispersion from deployment to pop-up locations ranged from 63 to 204 km. According to most probable tracks, tagged fish made primarily northward movements. Tagged fish reached depths of ~94 m and experienced ambient temperatures from 17.8 to 23 °C. Movements appeared to be limited by a 3 °C change relative to sea surface temperature (SST) and were confined to the mixed-layer. Diel diving patterns indicated dolphinfish spent >80% of daytime activity and 40% of nighttime activity near the surface, where variability in diving patterns was more pronounced. The vertical diving patterns showed pronounced changes during dawn and dusk, where dolphinfish mirrored the movements of diel migrating prey organisms. Our preliminary results provide vertical distribution patterns of dolphinfish in a location that supports important fisheries. This information will be useful for management to develop stock assessments which support the sustainable use of this species.

Movements, habitat utilization, and post-release survival of cobia (Rachycentron canadum) that summer in Virginia waters assessed using pop-up satellite archival tags

BackgroundCobia (Rachycentron canadum) is a cosmopolitan marine fish that inhabits tropical, sub-tropical, and temperate marine and estuarine waters and supports a major recreational fishery along the U.S. Atlantic and Gulf of Mexico coasts. Recent changes in U.S. cobia management have sparked controversy and highlighted limitations in our understanding of the species’ biology. This study utilized pop-up satellite archival tags (PSATs) to assess the movements, habitat utilization, and post-release survival of cobia that summer in Virginia waters.ResultsPSATs were deployed on 36 cobia caught in Virginia state waters using standard recreational techniques in August 2016 and August–September 2017. All fish larger than 37-in total length were tagged, and several of these were hooked deeply. No mortalities were inferred for the 20 cobia whose PSATs reported and remained attached for at least 10 days. Premature release of tags was an issue, and only five PSATs remained attached for the full 180-day deployment period. Some fish undertook long seasonal movements, with one individual entering Florida waters well beyond the current stock demarcation boundary. Several fish overwintered in waters offshore of North Carolina near the continental shelf break. Cobia demonstrated a strong affinity for waters ≥ 20 °C, even in the coldest months. They displayed distinct seasonal differences in habitat utilization, spending high proportions of their time near the surface during the summer months and extended periods at depths ≥ 20 m in the winter months.ConclusionsCobia are hardy fish with low post-release mortality when handled respectfully. Their migratory patterns are clearly temperature driven, and seasonal changes in habitat utilization means varied vulnerability to fishing gears. Further understanding of cobia migratory patterns, particularly in conjunction with spawning activity, is needed to best manage this species.

Seasonal habitat utilisation and morphological characteristics of Chamaeleo dilepis on Telperion Nature Reserve, Mpumalanga, South Africa

ABSTRACT Limited information on the habitat utilisation and seasonal activity of flap-necked chameleons (Chamaeleo dilepis) is available. We investigated habitat utilisation, seasonal distribution, and sexual dimorphism of C. dilepis on Telperion Nature Reserve (a privately protected natural area) in South Africa. Seven broad plant habitat units were surveyed for one year, which included a wet and a dry season. Plant species richness and species diversity, woody plant densities and canopy cover were recorded and analysed in each of the habitat units. Location, sex, age class and morphological measurements were recorded for located chameleons. Gravid adult females were found to be significantly heavier and larger than adult males, but no differences were found in size or mass for subadults. The occurrence of hatchlings was significantly influenced by rainfall, whereas minimum temperature had a significant influence on the occurrence of adults and subadults. Hatchlings occurred from mid-December to March in habitats associated with high shrub and grass canopy cover and low plant species diversity. Subadults were located from mid-March to the end of May in woody habitats and adults were located from the end of October until the end of May. Subadult and adult chameleons preferred dense woodland with high tree canopy cover and rockiness with high plant species diversity. The results of this study suggest that C. dilepis on Telperion have seasonal habits influenced by rainfall, minimum temperature and habitat structure.

Effects of rubble zones from oyster cultivation on habitat utilization and foraging behaviour of the endangered tri-spine horseshoe crab: An implication for intertidal oyster cultivation practices

Estuarine structured habitats, including benthic cultivation structure, are widely cited as substantial nursery and feeding grounds for fish and macroinvertebrates. Activities such as locomotion and foraging behaviour of sediment-dwelling species, however, may be hindered in the presence of the obstacles. In this study, collected field evidence demonstrated that habitat utilization of the juvenile tri-spine horseshoe crab Tachypleus tridentatus, an iconic and endangered macroinvertebrate, was adversely affected by high-density intertidal oyster rubble zones. Despite the fact that the utilization area of individual juvenile horseshoe crabs was independent of the presence of these obstacles, the abundance and number of positional fixes of tagged juveniles in these areas were lower. The effects of these obstacles and their associated topographic changes on the movement of the juvenile horseshoe crabs was investigated in a simulated laboratory experiment. Both the simulated oyster cultches and hummocks formed between the cultches reduced the total distance and displacement of the feeding trail, and less juveniles preferred to forage on elevated, dry hummocks (dry at low tide) formed between the cultches. Our findings suggested that oyster cultches and rubbles reduced the habitat quality for juvenile horseshoe crabs. On-bottom oyster cultivation activities seeking to conserve horseshoe cabs by avoiding nursery habitats should instead consider off-bottom or offshore cultivation methods.

Skull-shape variation and modularity in two Japanese field mice, Apodemus speciosus and Apodemus argenteus (Rodentia: Muridae)

Two congeneric species of Japanese field mice, Apodemus speciosus and Apodemus argenteus, differ considerably in their feeding strategies and habitat utilizations. Although both species are omnivorous, previous studies demonstrated that A. argenteus typically eats a wide variety of food items than A. speciosus. Moreover, A. speciosus is a ground dweller, while A. argenteus commonly shows arboreal movements. These dietary and lifestyle differences suggest potential disparity in morphological structure. In this study, we used geometric morphometrics to examine the skull shape differences are related to their feeding strategies and habitat preferences. We found that A. argenteus showed wider zygomatic arches and a broader mandibular ramus. These traits are linked to enlargement of the attachment sites for the masticatory muscles. We also found a relatively short mandibular diastema in A. argenteus, which may increase the mechanical advantage of the lower jaw by reducing the out-lever arm. These results suggest that A. argenteus has a greater relative bite force that is suitable for diversified diets as a more generalist feeder. Interspecific differences in the upper incisor, inter-orbital width, and auditory bullae might be associated with the lifestyles of these two species. Additionally, the presence of two distinct modules in the cranium (rostrum and braincase) and mandible (ascending ramus and alveolar region) may reflect similar patterns of intraspecific variation within both species. In conclusion, skull shape enables distinction between these two species and may favor adaptation to their ecology and lifestyle, despite the similarities in craniomandibular modules associated with common developmental factors.

Food Habits and Habitat Utilization of the Japanese Badger (Meles anakuma) in a Grassland/Forest Mosaic

Like European badgers, Japanese badgers are known to use earthworms as a staple food. However, while European badgers mainly eat the family Lumbricidae, Japanese badgers are thought to primarily take the family Megascolecidae in forest areas. In this study, we investigated the feeding habits and habitat utilization of Japanese badgers inhabiting a mountainous dairy farm, where a previously less-investigated mosaic of forest and open areas occurred. Invertebrates, particularly earthworms and beetles, formed the bulk of badger diet throughout the study period, while the frequency of occurrence of fruit and larvae partially depended on their seasonal availabilities. Soil sampling showed that both Megascolecidae and Lumbricidae were present in the study area, with the former being more abundant in natural forests and the latter being more abundant in pastures. Furthermore, their seasonal availability showed opposite patterns, with biomasses being the highest in summer for Megascolecidae and in spring and fall for Lumbricidae, resulting in the total biomass of earthworms in the whole study area remaining relatively consistent between seasons. Habitat use by Japanese badgers did not mirror food availability, pastures and natural forests being preferred throughout the year.