Diel Activity Patterns Research Articles

Shrub encroachment, landscape restoration, and intraguild predation

Shrub encroachment into arid grasslands occurs globally with the potential to affect vertebrates and their interactions. In the Chihuahuan Desert of southern New Mexico, shrub encroachment has prompted intensive efforts by land management agencies to remove shrubs and restore historical grassland habitats. We asked if restoration actions involving shrub removal affected dynamics of intraguild predation (IGP) including an IGP predator (coyote, Canis latrans), an IGP prey (kit fox, Vulpes macrotis), plus their shared lagomorph prey. We used camera traps on 14 sites with paired treated and untreated areas to examine spatial and temporal niche partitioning of coyotes and kit foxes. Shrub removal did not produce straightforward effects on abundances of coyotes, kit foxes, or their prey resources. Instead, abundances of kit foxes were constrained when coyote abundance reached a threshold. Below this threshold, kit foxes were more common on areas with low shrub cover, possibly due to lack of hiding cover for lagomorph prey that increased their predation risk. Our system included two alternative states: IGP predator dominated and coexistence of IGP predator and prey. Coexistence may have been facilitated by temporal niche partitioning as diel activity patterns differed for coyotes and kit foxes. Future research on intraguild predation should integrate spatial and temporal niches to understand species coexistence including on dynamic landscapes undergoing restoration.

Diel activity patterns of two syntopic range-restricted geckos suggest idiosyncratic responses to climate change

Measures of activity patterns in relation to environmental conditions provide insights into ecologically driven requirements and climate preferences of species, particularly for ectotherms, due to the strong relationship between body temperature (Tb) and environmental temperatures. Lygodactylus incognitus (cryptic dwarf gecko) and Lygodactylus soutpansbergensis (Soutpansberg dwarf gecko) are range-restricted endemics to the Soutpansberg Mountains, South Africa, and have recently been shown to be potentially vulnerable to the effects of climate change. This prompted us to study the relationship between the thermoregulatory characteristics and environmental temperatures for these syntopic species. Active geckos (i.e. those outside of a refuge) and environmental variables were recorded during scan surveys across two seasons. Binomial logistic regressions were used to predict and explain activity based on presence/absence measures and environmental variables for each species. Of the variables measured, air temperature (Ta) was the main predictor of activity for both species. Cryptic dwarf geckos were active in cooler Ta than warmer temperatures in comparison to Soutpansberg dwarf geckos. Cryptic dwarf geckos are thus well adapted to temperate conditions. Soutpansberg dwarf geckos appear well adapted for warmer conditions, as they were more likely to be active at higher Ta. Our findings suggest that both species will alter their daily activity times in response to changing climate, but that the cryptic dwarf gecko is likely to be more negatively impacted than the Soutpansberg dwarf gecko, due to their affinity for cooler temperatures and avoidance of the hottest temperatures exhibited during the study period. Therefore, although these broadly sympatric, syntopic, range-restricted species are closely related and have similar life histories, they occupy different thermal niches and are likely to respond to climate change idiosyncratically. Our findings caution against the overuse of proxy species in predicting species geographic distribution changes in response to climate change.

Diel and seasonal activity pattern of alien sika deer with sympatric mammalian species from Muljangori-oreum wetland of Hallasan National Park, South Korea

BackgroundSika deer, Cervus nippon, were originally introduced to South Korea from Japan and Taiwan for commercial farming purposes. Unfortunately, they were released into the wild during religious events and have since begun to impact the native ecosystem and species endemic to South Korea. The study of activity patterns can improve our understanding of the environmental impact of non-native species and their association with sympatric species. Using camera traps, we studied the diel and seasonal activity patterns of non-native sika deer and quantified the temporal overlap with sympatric mammalian species in the Muljangori-oreum wetlands of Hallasan National Park, South Korea.ResultsA total of 970 trap events were recorded for five mammalian species from nine locations during the camera-trap survey. Siberian roe deer (Capreoluspygargus tianschanicus) had the highest number of recorded events (72.0%), followed by sika deer (Cervus nippon) (16.2%), wild boar (Sus scrofa) (5.0%), Asian badger (Meles leucurus) (4.5%), and the Jeju weasel (Mustela sibirica quelpartis) (2.0%). Sika deer had bimodal activity patterns throughout the year, with peaks throughout the spring-autumn twilight, and day and night time throughout the winter. Relating the daily activity of sika deer with other mammalian species, roe deer expressed the highest degree of overlap (∆4 = 0.80) while the Asian badger demonstrated the lowest overlap (∆4 = 0.37).ConclusionsOur data show that sika deer are a crepuscular species with seasonal variations in daily activity patterns. Additionally, we identified the temporal differences in activity peaks between different mammals in the Muljangori-oreum wetlands and found higher degree of overlap between sika deer and roe deer during twilight hours.

The best defence is not being there: avoidance of larger carnivores is not driven by risk intensity

AbstractSpecies interactions are key factors determining the distribution and structure of species assemblages. Owing to their central positions, mid‐ranking mammalian carnivores are involved in interactions with numerous species, including competition for resources and instances of killing by higher ranking predators. Lethal interactions can directly influence species’ demography. However, the fear of lethal interactions, competition or both may also affect when and where individuals are active (i.e. non‐lethal interactions). Although differences in body–size and trophic overlap are known predictors of the frequency of lethal interactions, their influence on non‐lethal interactions is uncertain. Through camera trapping, we studied non‐lethal interactions between a small mesocarnivore (pine marten), a potential killer and intense competitor (red fox) and a moderate competitor and unlikely killer (Eurasian badger). We determined overlap and differences in their diel activity patterns and the degree of spatial overlap in two seasons with contrasting resource availability. Additionally, we estimated the effect of larger carnivore detection rates on pine marten detection rates. We also compared time intervals between pine marten visits to baited stations in the absence and presence of either or both larger carnivores. Our results are consistent with pine martens distributing their daily activity to maximize overlap with prey and to minimize competition and risk of aggression over the spatial scale. Pine martens also responded to the immediate threat of larger carnivores irrespective of the threat they pose by taking 4–7 days longer to re‐visit a station. Small‐scale non‐lethal interactions such as these may enable pine martens to coexist closely with two larger carnivores, yet it remains uncertain whether their population incurs a demographic cost through restricted access to resources. Carnivore's risk‐avoidance strategies could be harnessed to protect prey species of interest. However, our results suggest avoidance is short‐lived and recurrent stimuli would be necessary.

Diel patterns of foraging and microhabitat use by sympatric rainbow trout and bull trout: implications for adaptive differentiation and instream flow assessment

Salmonids make flexible and adaptive trade-offs between foraging efficiency and predation risk that result in variable patterns of diel activity and habitat use. However, the following remains unclear: (1) how patterns differ among salmonid species; and (2) how this affects the interpretation of habitat suitability models that inform instream flow management. We combined snorkel observations with experimental additions of cover to investigate how predation risk, cover, and bioenergetics affect diel activity and habitat use patterns by sympatric rainbow trout (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus) in the Skagit River, British Columbia, Canada. Both species foraged primarily at dusk, supporting the well-described trade-off between foraging efficiency and predation risk. However, only rainbow trout responded to cover additions, suggesting that risk tolerance and the nature of foraging-predation risk trade-offs differ between species. Diel shifts in activity and habitat use also substantially altered predictions of habitat suitability models, with potentially large consequences for flow management.

Sensing underground activity: diel digging activity pattern during nest escape by sea turtle hatchlings

Synchronous digging activity and emergence from underground nests is important for sea turtle hatchlings, as it reduces predation risk and decreases energy consumption. However, patterns of underground hatching and diel digging activity prior to emergence are invisible and remain largely unknown. In this study, we acoustically monitored the activity of green turtle, Chelonia mydas , hatchlings from hatching to emergence in the field and laboratory. During the hatching period, we did not observe characteristic acoustic events corresponding to pipping and hatching. Hatchlings started digging even though there were still unhatched eggs above them, indicating that green turtles did not hatch as one synchronous group. This observation did not support our hypothesis that synchronized hatching facilitates synchronous emergence. Digging activity tended to increase at night as the hatchlings approached the sand surface and nest emergence became imminent. It is not surprising that there was diel variation in digging activity as the hatchlings approached the surface because diel fluctuations in sand temperature can provide a diel cue. Surprisingly, a diel change in digging activity was also observed when hatchlings were still at a sand depth where temperature remained relatively constant throughout the day (that is, a few days before emergence) and in the laboratory at a constant temperature. This study suggests that the diel activity pattern of hatchling green turtles may occur even in the absence of a diel temperature fluctuation cue. • Green turtle hatchlings did not hatch synchronously. • Digging activity occurred even when some eggs of the nest were unhatched. • Synchronous digging increased at night as the emergence became imminent. • Diel change in activity occurred even under constant conditions. • Acoustic monitoring is useful for investigating underground animal behaviour.

The diel activity pattern of mountain hare (Lepus timidus) on managed heather moorland in Scotland.

The research presented in this paper provides an insight into the behavioral ecology of mountain hares on heather moorland in the Lammermuir Hills of southeast Scotland. We examine the seasonal and diel activity patterns using camera traps over a period of 12 months. The rate of camera detections was calculated for the different divisions of the 24‐hr cycle (daylight, dusk, night, and dawn). During autumn and winter (October–February), the activity pattern was crepuscular with greater activity at dusk than at dawn. Daylight activity was relatively low, and there was a regular pattern of small peaks of activity during the night. In spring and summer (March–September), peaks of crepuscular activity remained evident but daylight activity was much more prevalent than during autumn and winter, and night activity was lower. We discuss the problematic definition of twilight and present an explanation for seasonal changes in the pattern of diel activity that is linked to the reproductive cycle of the mountain hare.

An apex carnivore's life history mediates a predator cascade.

Apex predators can shape communities via cascading top-down effects, but the degree to which such effects depend on predator life history traits is largely unknown. Within carnivore guilds, complex hierarchies of dominance facilitate coexistence, whereby subordinate species avoid dominant counterparts by partitioning space, time, or both. We investigated whether a major life history trait (hibernation) in an apex carnivore (black bears Ursus americanus) mediated its top-down effects on the spatio-temporal dynamics of three sympatric mesocarnivore species (coyotes Canis latrans, bobcats Lynx rufus, and gray foxes Urocyon cinereoargenteus) across a 15,000km2 landscape in the western USA. We compared top-down, bottom-up, and environmental effects on these mesocarnivores using an integrated modeling approach. Black bears exerted top-down effects that varied as a function of hibernation and were stronger than bottom-up or environmental impacts. High black bear activity in summer and fall appeared to buffer the most subordinate mesocarnivore (gray foxes) from competition with dominant mesocarnivores (coyotes and bobcats), which were in turn released by black bear hibernation in winter and early spring. The mesocarnivore responses occurred in space (i.e., altered occupancy and site visitation intensity) rather than time (i.e., diel activity patterns unaffected). These results suggest that the spatio-temporal dynamics of mesocarnivores in this system were principally shaped by a spatial predator cascade of interference competition mediated by black bear hibernation. Thus, certain life history traits of apex predators might facilitate coexistence among competing species over broad time scales, with complex implications for lower trophic levels.

Diel activity patterns of urban Woodchucks (<i>Marmota monax</i>) revealed by camera traps at burrows in southwestern Ontario, Canada

Animals display a range of diurnal and nocturnal activity patterns and, among mammals, a high proportion of species are crepuscular or nocturnal. Daily activities are often endogenous and oscillate on a light:dark regime. Such cycles are referred to as ‘circadian’ and are generally influenced by biotic and abiotic factors. I investigated the daily activity of urban Woodchucks (Marmota monax) by using 24-hour camera traps at backyard burrows in London, Ontario, Canada, in June. Cameras enabled the collection of data that would otherwise have been labour intensive by direct observation. Statistical modelling showed that Woodchucks exhibited a strictly diurnal activity pattern. The unimodal activity pattern started at sunrise and ended before sunset. The general daily activity trend was similar to the pattern described by others who used direct observations and telemetry to monitor Woodchucks in more rural settings. Temperature and wind were not included in the best-fit model. Camera trapping is a non-invasive method that could give insight to diel activity as it can easily monitor extended periods and reduce the effort required by direct observation.

Night of the hunter: using cameras to quantify nocturnal activity in desert spiders.

Invertebrates dominate the animal world in terms of abundance, diversity and biomass, and play critical roles in maintaining ecosystem function. Despite their obvious importance, disproportionate research attention remains focused on vertebrates, with knowledge and understanding of invertebrate ecology still lacking. Due to their inherent advantages, usage of camera traps in ecology has risen dramatically over the last three decades, especially for research on mammals. However, few studies have used cameras to reliably detect fauna such as invertebrates or used cameras to examine specific aspects of invertebrate ecology. Previous research investigating the interaction between wolf spiders (Lycosidae: Lycosa spp.) and the lesser hairy-footed dunnart (Sminthopsis youngsoni) found that camera traps provide a viable method for examining temporal activity patterns and interactions between these species. Here, we re-examine lycosid activity to determine whether these patterns vary with different environmental conditions, specifically between burned and unburned habitats and the crests and bases of sand dunes, and whether cameras are able to detect other invertebrate fauna. Twenty-four cameras were deployed over a 3-month period in an arid region in central Australia, capturing 2,356 confirmed images of seven invertebrate taxa, including 155 time-lapse images of lycosids. Overall, there was no clear difference in temporal activity with respect to dune position or fire history, but twice as many lycosids were detected in unburned compared to burned areas. Despite some limitations, camera traps appear to have considerable utility as a tool for determining the diel activity patterns and habitat use of larger arthropods such as wolf spiders, and we recommend greater uptake in their usage in future.

Fine-scale activity patterns of large- and medium-sized mammals in a deciduous broadleaf forest in the Qinling Mountains, China

The composition of animal species and interactions among them are widely known to shape ecological communities and fine-scale (e.g., < 1 km) monitoring of animal communities is essential for understanding the relationships among animals and plants. Although the co-existence of large- and medium-sized species has been studied across different scales, research on fine-scale interactions of herbivores in deciduous broadleaf forests is limited. Camera trapping of large- and medium-sized mammals was carried out over a 1 year period within a 25 ha deciduous broadleaf forest dynamics plot in the Qinling Mountains, China. Fourteen species of large- and medium-sized mammals, including six carnivores, six ungulates, one primate and one rodent species were found. Kernel density estimations were used to analyse the diel or 24 h activity patterns of all species with more than 40 independent detections and general linear models were developed to explore the spatial relationships among the species. The combination of overlapping diel activity patterns and spatial associations showed obvious niche separation among six species: giant panda (Ailuropoda melanoleuca David), takin (Budorcas taxicolor Hodgson), Reeves’s muntjac (Muntiacus reevesi Ogilby), tufted deer (Elaphodus cephalophus Milne-Edwards), Chinese serow (Capricornis milneedwardsii David) and wild boar (Sus scrofa Linnaeus). Long-term fine-scale monitoring is useful for providing information about the co-existence of species and their interactions. The results demonstrate the importance for fine-scale monitoring of animals and plants for improving understanding of species interactions and community dynamics.

Diel Activity Patterns of Three Sympatric Medium-Sized Carnivores during Winter and Spring in a Heavy Snowfall Area in Northeastern Japan

In a heavy snowfall area in northeastern Japan, we clarified the diel activity patterns of and seasonal differences in three sympatric carnivores (red foxes, raccoon dogs, and Japanese martens) during winter and spring, and the interspecific differences among the activity patterns in each season. The activity time of the target species was obtained by camera-trap surveys at seven sites around the Experimental Forest of Yamagata University from January to June 2019. The diel activity patterns of each species, and seasonal and interspecific differences in the activity patterns were evaluated using the kernel density method. Red foxes showed a unimodal nocturnal pattern in spring, whereas they were also observed during the daytime in winter. Raccoon dogs showed a unimodal nocturnal pattern, and peak activity after sunset in both seasons. Japanese martens were clearly nocturnal during both seasons. Because there were a few interspecific differences in diel activity patterns among three species, species interactions had little effect on diel activity patterns. Our findings indicate that the diel activity of medium-sized carnivores responding to winter conditions may vary depending on species.

Accelerometry to study fine-scale activity of invasive Burmese pythons (Python bivittatus) in the wild

BackgroundThe establishment of Burmese pythons (Python bivittatus) in Everglades National Park, Florida, USA, has been connected to a > 90% decline in the mesomammal population in the park and is a major threat to native reptile and bird populations. Efforts to control this population are underway, but are hampered by a lack of information about fine-scale activity cycles and ecology of these cryptic animals in the wild. We aimed to establish a technique for monitoring the activity of Burmese pythons in the wild using acceleration data loggers (ADLs), while attempting to identify any behavioral patterns that could be used to help manage this invasive species in the Greater Everglades and South Florida.ResultsWe obtained continuous acceleration and temperature data from four wild snakes over periods of 19 to 95 days (mean 54 ± 33 days). Snakes spent 86% of their time at rest and 14% of their time active, including transiting between locations. All snakes showed at least one period of continuous transiting lasting 10 h or more, with one animal transiting continuously for a period of 58.5 h. Acceleration data logger-derived transiting bout duration was significantly correlated with the distance snakes traveled per hour for two snakes that also carried GPS loggers. Snakes were most active in midday or early-night depending on individual and time of year, but all snakes were least likely to be active in the early mornings (0400–0700 h local time). Very little movement took place at temperatures below 14 °C or above 24 °C, with most movement taking place between 15° and 20 °C. One animal showed a highly unusual rolling event that may be indicative of a predation attempt, but this could not be confirmed.ConclusionsFine-scale activity and some behaviors were apparent from ADL data, making ADLs a potentially valuable, unbiased tool for monitoring large-bodied snakes in the wild. Snakes spent the majority of their time resting, but also moved continuously for several hours at a time during bouts of transiting. Results suggest that individuals may shift their diel activity pattern based on season. Understanding seasonal differences in activity levels can improve the accuracy of population estimates, help detect range expansion, and improve managers’ ability to find and capture individuals.

Time keeping in female Myotis emarginatus during reproduction (Chiroptera: Vespertilionidae)

In the years 2012–2017, we studied the annual and diel temporal activity patterns exhibited by female Geoffroy’s bats (Myotis emarginatus) during reproduction by using an infrared light barrier system, videotaping with an infrared camera and sporadic direct counts of juveniles in the roost when the adult bats were not present. We determined the effect of weather on timing and duration of maternity roost occupancy, reproductive periods, return and emergence flights and amount of time spent outside the roost, and estimated the yearly reproductive output. Contrary to the considerable effects of weather conditions on the reproduction phenology in Myotis daubentonii and M. nattereri, timing and duration of reproductive activities of M. emarginatus were remarkably similar over the study period despite distinct inter-annual differences in the occurrence of inclement weather spells causing food shortages and use of torpor. Pregnancy, lactation and roost occupation by adult females were completed every year within 10 to 11 weeks. Adverse spring weather bouts caused considerable fluctuations in the duration of colony formation during early pregnancy, but did not influence the total duration of the pregnancy period. The mean durations of both the emergence and return flights were markedly similar over the study years. An exception was the distinct increase in duration of emergence flight during pregnancy in 2016 and 2017 which might be related to increased colony numbers. With the exception of the year 2015, the standard deviations of emergence flights were small, but in contrast to the quite scheduled return flights during lactation, the mean durations of return flights during pregnancy varied strongly. The return flights executed by juveniles during post-lactation were highly irregular. The mean time spent outside the roost was quite similar over the study years. The estimated yearly reproductive output was low (&lt;52%) and the proportion of non-reproductive females in the maternity colony high. Nevertheless, the colony numbers increased considerably over the study period. The relevance of keeping the annual and diel activity patterns rather inflexible and of an effective social thermoregulation in relation to a trade-off between survival and reproduction are discussed.

Passive Acoustic Monitoring of Chaco Chachalaca (Ortalis canicollis) Over a Year: Vocal Activity Pattern and Monitoring Recommendations

Chaco Chachalaca ( Ortalis canicollis) is a declining Neotropical bird, for which our current knowledge about its natural history is very limited. Here, we evaluated for first time the utility of passive acoustic monitoring, coupled with automated signal recognition software, to monitor the Chaco Chachalaca, described the vocal behavior of the species across the diel and seasonal cycle patterns, and proposed an acoustic monitoring protocol to minimize error in the estimation of the vocal activity rate. We recorded over a complete annual cycle at three sites in the Brazilian Pantanal. The species was detected on 99% of the monitoring days, proving that this technique is a reliable method for detecting the presence of the species. Chaco Chachalaca was vocally active throughout the day and night, but its diel activity pattern peaked between 0500 and 0900. The breeding season of Chaco Chachalaca in the Brazilian Pantanal, based on seasonal changes in vocal activity, seems to occur during the last months of the dry season, with a peak in vocal activity between August and October. Our results could guide future surveys aiming to detect the presence of the species, both using traditional or acoustic surveys, or to evaluate changes in population abundance using passive acoustic monitoring, for which recorders should be left in the field for a minimum period of nine days to obtain a low-error estimate of the vocal activity of the species. Our results suggest that passive acoustic monitoring might be useful, as a complementary tool to field studies, for monitoring other cracids, a family with several threatened species that are reluctant to human presence.

Population Estimate, Habitat-Use and Activity Patterns of the Honey Badger in a Dry-Deciduous Forest of Central India

Studies on carnivores are skewed toward larger species in India, limiting ecological information of the smaller ones. Basic ecological understanding like population density, distribution, habitat-use patterns of small carnivores is lacking. This inadequate knowledge has led to disagreement between conservation approaches in different landscapes. Honey badgers (Mellivora capensis) are cryptic carnivores distributed across large areas of Africa and Asia; however, fundamental ecological knowledge is scarce. The species is thought to exist at low population densities throughout its range. We used a large camera trap dataset from a tiger reserve in Maharashtra State, India to understand the population density, habitat preference, and diel activity pattern of the species. We applied an extension of the spatial count model for the estimation of population. Habitat preference analyses were carried out using generalized linear models and activity patterns were analyzed using kernel-density functions. The population density was estimated as 14.09 (95% CI 10–22.25) individuals per 100 km2. Habitat use revealed a positive association with forest cover and negative association with elevation. This may expose the species to other large carnivores in the habitat but honey badger activity pattern peaked at midnight retaining minimum temporal overlap with other large carnivores (e.g., tiger Panthera tigris, leopard Panthera pardus, and dhole Cuon alpinus) and moderate overlap with small carnivores (e.g., jungle cat Felis chaus, rusty-spotted cat Prionailurus rubiginosus). These behaviors, in turn, may facilitate the coexistence of species at such high density even with high carnivore density. We hope the findings of this study will fill the existing knowledge gap of this species and aid in guiding the conservation of the species in other landscapes and reserves.

Low light intensities increase avoidance behaviour of diurnal fish species: implications for use of road culverts by fish.

Inadequately designed culverts can be physical barriers to fish passage if they increase the velocity of water flow in the environment, alter natural turbulence patterns or fail to provide adequate water depth. They may also act as behavioural barriers to fish passage if they affect the willingness of fish species to enter or pass through the structure due to altered ambient light conditions. To understand how reduced light intensity might affect fish behaviour in culverts, the authors performed a behavioural choice experiment quantifying the amount of time individual fish spent in dark and illuminated areas of a controlled experimental channel. They found that behavioural responses were largely reflective of the species' diel activity patterns; the diurnal species Craterocephalus stercusmuscarum and Retropinna semoni preferred illuminated regions, whereas the nocturnal/crepuscular Macquaria novemaculeata preferred the darkened region of the channel. Bidyanus bidyanus were strongly rheotactic, and their behaviour was influenced more by water flow direction than ambient light level. The authors then determined that a threshold light intensity of only c. 100-200 lx (cf. midday sunlight c. 100,000 lx) was required to overcome the behavioural barrier in c. 70% of the diurnally active C. stercusmuscarum and R. semoni tested. When these values were placed into an environmental context, 15 road-crossing (3.4-7.0 m long) box (c. 1 m × 1 m, height × width) and pipe (c. 1 m diameter) culverts sampled in Brisbane, Australia, recorded light intensities in the centre of the structure that were below the threshold for C. stercusmuscarum and R. semoni movement and could potentially be a barrier to their passage through the structure. Attention is required to better understand the impacts of low light intensity in culverts on fish passage and to prioritize restoration.

Seasonal patterns in stable isotope and fatty acid profiles of southern stingrays (Hypanus americana) at Stingray City Sandbar, Grand Cayman

Ecotourism opportunities in the marine environment often rely heavily on provisioning to ensure the viewing of cryptic species by the public. However, intentional feeding of wildlife can impact numerous aspects of an animals’ behavior and ecology. Southern stingrays (Hypanus americana) provisioned at Stingray City Sandbar (SCS) in Grand Cayman have altered diel activity patterns and decreased measures of health. This study looked at seasonal changes in stable isotope (SI) and fatty acid (FA) profiles of provisioned stingrays at SCS. Plasma δ15N was higher in male stingrays (11.86 ± 1.71‰) compared to females (10.70 ± 1.71‰). Lower values for δ15N in males and females were measured in October during low tourist season, suggesting stingrays may be forced to rely on native prey items to supplement the decreased amount of provisioned squid available during this time. Plasma FA profiles were significantly different between sexes and across sampling time points, with FAs 22:6n3, 16:0, 20:5n3, 18:1n3C, 18:0 and 18:1n9T contributing to dissimilarity scores between groups. Dietary FAs primarily contributed to differences between males and females lending further evidence to differences in foraging patterns at SCS, likely due to intraspecific competition. Further, canonical analysis of principal coordinates (CAP) analysis of FA profiles suggest similar diets during peak tourist season and differences in diet between males and females during the low season. This study demonstrates alterations in feeding ecology in stingrays at SCS which is of critical importance for effective management of the SCS aggregation.

Predation risk increases intraspecific heterogeneity in white-tailed deer diel activity patterns

Abstract Prey species often mitigate predation risk through alteration of spatiotemporal diel activity patterns whereby prey access high-quality resources in risky areas during predator downtimes. However, dominance hierarchies exist in some prey species, and temporal partitioning is a mechanism thought to reduce aggressive intraspecific interactions. How demographic-specific responses to predation risk influence intraspecific temporal partitioning in prey are largely unknown and could be key to understanding the effects of predators on intraspecific interactions in prey. To assess the effects of predation risk on intraspecific interactions in white-tailed deer (Odocoileus virginianus), we monitored deer diel activity during the fawning season in four pairs of predator exclusion and control plots (~40 ha) from 2015 to 2018 using 16 camera traps. We examined the effect of predation risk on diel activity of males, females, and nursery groups by comparing the within-group coefficient of activity overlap (d̂) across predator exclusion and control plots. We then examined within-treatment activity overlap between groups in the predator exclosure and control plots. All groups maintained different diel activity patterns in safe and risky areas. Unconstrained by predation risk, all groups behaved more similarly, and interspecific group overlap was greater in the predator exclusion plots than control plots. Male-nursery group overlap exhibited the strongest treatment effect, increasing 24% in predator exclusion plots (d̂ = 0.91, confidence interval [CI]: 0.87–0.95) relative to control plots (d̂ = 0.67, CI: 0.57–0.76). Our results suggest predators increase heterogeneity in prey behavior and may be important drivers of behavioral processes, such as temporal partitioning, that minimize antagonistic intraspecific interactions of prey.

Non-lethal effects of the predator Meganyctiphanes norvegica and influence of seasonal photoperiod and food availability on the diel feeding behaviour of the copepod Centropages typicus.

Predators can induce changes in the diel activity patterns of marine copepods. Besides vertical migration, diel feeding rhythms have been suggested as an antipredator phenotypic response. We conducted experiments to assess the non-lethal direct effects of the predator Meganyctiphanes norvegica (northern krill) on the diel feeding patterns of the calanoid copepod Centropages typicus. We also analysed the influence of seasonal photoperiod and prey availability on the intensity of copepod feeding rhythms. We did not detect any large effect of krill presence on the diel feeding behaviour of copepods, either in day-night differences or total daily ingestions. Seasonal photoperiod and prey availability, however, significantly affected the magnitude of copepod feeding cycles, with larger diel differences in shorter days and at lower prey concentrations. Therefore, the role of non-lethal direct effects of predators on the diel feeding activity of marine copepods remain debatable and might not be as relevant as in freshwater zooplankton.