Niche Switching Research Articles

A model-based hypothesis framework to define and estimate the diel niche via the 'Diel.Niche' R package.

How animals use the diel period (24-h light-dark cycle) is of fundamental importance to understand their niche. While ecological and evolutionary literature abound with discussion of diel phenotypes (e.g. diurnal, nocturnal, crepuscular, cathemeral), they lack clear and explicit quantitative definitions. As such, inference can be confounded when evaluating hypotheses of animal diel niche switching or plasticity across studies because researchers may be operating under different definitions of diel phenotypes. We propose quantitative definitions of diel phenotypes using four alternative hypothesis sets (maximizing, traditional, general and selection) aimed at achieving different objectives. Each hypothesis set is composed of mutually exclusive hypotheses defined based on the activity probabilities in the three fundamental periods of light availability (twilight, daytime and night-time). We develop a Bayesian modelling framework that compares diel phenotype hypotheses using Bayes factors and estimates model parameters using a multinomial model with linear inequality constraints. Model comparison, parameter estimation and visualizing results can be done in the Diel.Niche R package. A simplified R Shiny web application is also available. We provide extensive simulation results to guide researchers on the power to discriminate among hypotheses for a range of sample sizes (10-1280). We also work through several examples of using data to make inferences on diel activity, and include online vignettes on how to use the Diel.Niche package. We demonstrate how our modelling framework complements other analyses, such as circular kernel density estimators and animal movement modelling. Our aim is to encourage standardization of the language of diel activity and bridge conceptual frameworks and hypotheses in diel research with data and models. Lastly, we hope more research focuses on the ecological and conservation importance of understanding how animals use diel time.

Clustering and classification of vertical movement profiles for ecological inference of behavior

AbstractVertical movements can expose individuals to rapid changes in physical and trophic environments—for aquatic fauna, dive profiles from biotelemetry data can be used to quantify and categorize vertical movements. Inferences on classes of vertical movement profiles typically rely on subjective summaries of parameters or statistical clustering techniques that utilize Euclidean matching of vertical movement profiles with vertical observation points. These approaches are prone to subjectivity, error, and bias. We used machine learning approaches on a large dataset of vertical time series (N = 28,217 dives) for 31 post‐nesting leatherback turtles (Dermochelys coriacea). We applied dynamic time warp (DTW) clustering to group vertical movement (dive) time series by their metrics (depth and duration) into an optimal number of clusters. We then identified environmental covariates associated with each cluster using a generalized additive mixed‐effects model (GAMM). A convolutional neural network (CNN) model, trained on standard dive shape types from the literature, was used to classify dives within each DTW cluster by their shape. Two clusters were identified with the DTW approach—these varied in their spatial and temporal distributions, with dependence on environmental covariates, sea surface temperature, bathymetry, sea surface height anomaly, and time‐lagged surface chlorophyll a concentrations. CNN classification accuracy of the five standard dive profiles was 95%. Subsequent analyses revealed that the two clusters differed in their composition of standard dive shapes, with each cluster dominated by shapes indicative of distinct behaviors (pelagic foraging and exploration, respectively). The use of these two machine learning approaches allowed for discrete behaviors to be identified from vertical time series data, first by clustering vertical movements by their movement metrics (DTW) and second by classifying dive profiles within each cluster by their shapes (CNN). Statistical inference for the identified clusters found distinct relationships with environmental covariates, supporting hypotheses of vertical niche switching and vertically structured foraging behavior. This approach could be similarly applied to the time series of other animals utilizing the vertical dimension in their movements, including aerial, arboreal, and other aquatic species, to efficiently identify different movement behaviors and inform habitat models.

Seasonal variation and tracking of climate niche of a migratory bird

Migratory birds inhabit different areas during breeding and non-breeding seasons. Depending on the time of the year, they may utilize different resources available in seasonal habitats, but also are subjected to changing climate regimes during their annual life cycle. Migratory birds may adopt ecological niche tracking to cope with different environmental conditions between breeding and non-breeding grounds. The American White Pelican ( Pelecanus erythrorhynchos , hereafter ‘AWPE’) is a short-distance migrant between the Gulf of Mexico coastal regions (non-breeding grounds) and the Northern Great Plains (breeding grounds) of Canada and the US. The American White Pelican is a piscivore, feeding on fish, crayfish, and salamanders in inland freshwater wetlands. Cold, icy winter weather conditions substantially reduce and limit food resource availability at the breeding grounds during winters. Thus, we hypothesize that AWPEs would migrate between the breeding and non-breeding grounds to track climatic conditions that allow easier availability of resources. However, the niche tracking strategies have not been tested in AWPEs mainly due to the lack of reliable tracking data. Our objectives were to test whether the niche tracking or niche switching hypothesis would better explain seasonal variations in ecological niche overlap of AWPEs using the GPS locations of 19 tracked migrating birds, which had GPS locations at both breeding and non-breeding grounds. We estimated overlap of climate niche to test for seasonal niche tracking behaviors at both individual and population levels. Our results indicate that six out of 13 GPS-tracked AWPE individuals tracked climatic niche during the annual migration cycle. The analysis of the combined data of all 19 tracked AWPEs demonstrated that AWPEs tracked seasonal climate niche at the population level. Cold winter temperatures below zero (℃) may freeze the water surface of wetlands and shallow waterbodies, preventing AWPEs from acquiring sufficient food. The coupling of winter food resources with winter climatic conditions may result in climate niche tracking. Variation in climate niche tracking among individuals may offer ecological plasticity for AWPEs to cope with climatic changes. • Migratory birds may either track or switch ecological niche during the annual cycle. • American white pelicans are short-distance migratory birds. • American white pelicans tracked climate niche at individual and population levels. • Climate niche tracking may make American white pelicans vulnerable to warming.

Seasonal climatic niche and migration movements of Double-crested Cormorants.

Avian migrants are challenged by seasonal adverse climatic conditions and energetic costs of long‐distance flying. Migratory birds may track or switch seasonal climatic niche between the breeding and non‐breeding grounds. Satellite tracking enables avian ecologists to investigate seasonal climatic niche and circannual movement patterns of migratory birds. The Double‐crested Cormorant (Nannopterum auritum, hereafter cormorant) wintering in the Gulf of Mexico (GOM) migrates to the Northern Great Plains and Great Lakes and is of economic importance because of its impacts on aquaculture. We tested the climatic niche switching hypothesis that cormorants would switch climatic niche between summer and winter because of substantial differences in climate between the non‐breeding grounds in the subtropical region and breeding grounds in the northern temperate region. The ordination analysis of climatic niche overlap indicated that cormorants had separate seasonal climatic niche consisting of seasonal mean monthly minimum and maximum temperature, seasonal mean monthly precipitation, and seasonal mean wind speed. Despite non‐overlapping summer and winter climatic niches, cormorants appeared to be subjected to similar wind speed between winter and summer habitats and were consistent with similar hourly flying speed between winter and summer. Therefore, substantial differences in temperature and precipitation may lead to the climatic niche switching of fish‐eating cormorants, a dietary specialist, between the breeding and non‐breeding grounds.

Interspecific Asymmetries in Behavioral Plasticity Drive Seasonal Patterns of Temporal Niche Partitioning in an Island Carnivore Community.

Animals vary considerably in the amount of behavioral plasticity they exhibit in daily activity timing and temporal niche switching. It is not well understood how environmental factors drive changes in temporal activity or how interspecific differences in the plasticity of activity timing ultimately manifest in free-living animals. Here, we investigated the temporal structure and organization of activity patterns of two insular mammalian carnivores living in sympatry, the island fox (Urocyon littoralis) and island spotted skunk (Spilogale gracilis amphiala). Using collar-mounted accelerometers, we assessed the plasticity of behavioral activity rhythms in foxes and skunks by investigating how environmental factors drive the distribution of locomotor activity across the day and year, and subsequently examined the dynamics of temporal niche overlap between the two species. We documented that foxes express phenotypic plasticity in daily activity timing across the year, ranging from nocturnal to diurnal to crepuscular rhythms depending on the individual and time of year. Most notably, foxes increased the proportion of daytime activity as seasonal temperatures decreased. Overall, activity patterns of foxes were consistent with the circadian thermoenergetics hypothesis, which posits that animals that switch their patterns of activity do so to coincide with the most energetically favorable time of day. In contrast to foxes, skunks exhibited little behavioral plasticity, appearing strictly nocturnal across the year. While the duration of skunk activity bouts increased with the duration of night, timing of activity onset and offset extended into daytime hours during summer when the duration of darkness was shortest. Analysis of temporal niche overlap between foxes and skunks suggested that niche overlap was highest during summer and lowest during winter and was dictated primarily by temporal niche switching in foxes, rather than skunks. Collectively, our results highlight how interspecific asymmetries in behavioral plasticity drive dynamic patterns of temporal niche overlap within an island carnivore community.

Seasonality, niche management and vertical migration in landscapes of relief

Landscapes of vertical relief, such as mountains and continental slopes, intensify ecological and climatological variation within narrow spatial windows. Seasonal vertical migrants exploit this variation during their residence in, and movements between, vertically stratified seasonal ranges. Animals in terrestrial, marine and even human‐ecological systems undergo similar patterns of seasonal vertical movements. The diversity of arenas in which vertical migration evolved lends insight to the factors promoting seasonal use of landscapes of relief. Because animals must contend with both endogenous circannual rhythms and exogenous environmental seasonality, vertical migrants may be sensitive to inconsistent change across stratified seasonal ranges under climate change. To better understand how ongoing and future climatic and environmental changes are likely to impact vertical migrants, we examine vertical migration in the context of niche tracking and niche switching. Whereas niche trackers minimize variation in realized environmental conditions throughout their seasonal movements, niche switchers undergo seasonal transitions in realized niche space. These strategies mediate the relationship between migrants and their changing environment, and can be used to forecast impacts of future change and effectively conserve systems of vertical migration. Niche tracking may be hindered by inconsistent or unpredictable environmental change along a single niche axis across strata, while niche switching may be sensitive to incongruous spatiotemporal change across factors. We suggest that climate change will affect seasonal patterns in vertical environments discontinuously across time, space and strata, and that vertical migrants are likely to face additional anthropogenic threats that interact with environmental seasonality. Conservation of vertical migrants should prioritize the availability of, and facilitate movement between, stratified seasonal ranges.

Niche switching and leapfrog foraging: movement ecology of sympatric petrels during the early breeding season

BackgroundThe timing of events in the early part of the breeding season is crucially important for successful reproduction. Long-lived animals that migrate large distances independently of each other meet at the breeding sites to re-establish their pair bonds and coordinate their breeding duties with their partners.MethodsUsing miniature light-geolocation and immersion data together with blood stable isotopes, we studied the early breeding season in Thin-billed prions Pachyptila belcheri, Antarctic prions P. desolata and Blue petrels Halobaena caerulea breeding at Kerguelen Islands in the Indian Ocean. These three species exhibit differences in their winter habitat and timing of migration, moult and breeding. We hypothesised that these differences would influence their behaviour during the early breeding season.ResultsIn line with our hypothesis, we found clear differences not only in the timing of colony attendance, but also in the time budgets while at sea and in habitat use. Both early breeding Blue petrels and late breeding Antarctic prions spent about 8 h per day in flight and 15 h foraging. In comparison, Thin-billed prions, which breed in mid-summer, spent less time (5 h daily) in flight and more time (18 h daily) foraging, thus maximizing the time spent foraging during the longest daylight days of the year. While the ecological habitat parameters (sea temperature, wind, productivity) of Thin-billed prions and Blue petrels were relatively stable throughout the year, Antarctic prions showed clear niche switching, caused by leapfrogging between the northernmost winter distribution to the southernmost distribution during the early breeding season. Blood stable isotopes confirmed the habitat switch between the inter-breeding and early breeding periods and highlighted trophic segregation with Blue petrels feeding more on fish and Antarctic petrels more on crustaceans during the early breeding period.ConclusionWe found that the three sympatric petrel species segregated in time and space, both in the winter and the early breeding season. The interplay of timing and distribution meant that the three species show the full range of migratory strategies, from niche-tracking Blue petrels to niche-switching Antarctic prions. The latitudinal distribution resembled the leapfrogging of terrestrial avian migrant species or populations.

Maximising survival by shifting the daily timing of activity.

Maximising survival requires animals to balance the competing demands of maintaining energy balance and avoiding predation. Here, quantitative modelling shows that optimising the daily timing of activity and rest based on the encountered environmental conditions enables small mammals to maximise survival. Our model shows that nocturnality is typically beneficial when predation risk is higher during the day than during the night, but this is reversed by the energetic benefit of diurnality when food becomes scarce. Empirical testing under semi‐natural conditions revealed that the daily timing of activity and rest in mice exposed to manipulations in energy availability and perceived predation risk is in line with the model’s predictions. Low food availability and decreased perceived daytime predation risk promote diurnal activity patterns. Overall, our results identify temporal niche switching in small mammals as a strategy to maximise survival in response to environmental changes in food availability and perceived predation risk.

Cryptic niche switching in a chemosymbiotic gastropod.

Life stages of some animals, including amphibians and insects, are so different that they have historically been seen as different species. 'Metamorphosis' broadly encompasses major changes in organism bodies and, importantly, concomitant shifts in trophic strategies. Many marine animals have a biphasic lifestyle, with small pelagic larvae undergoing one or more metamorphic transformations before settling into a permanent, adult morphology on the benthos. Post-settlement, the hydrothermal vent gastropod Gigantopelta chessoia experiences a further, cryptic metamorphosis at body sizes around 5-7 mm. The terminal adult stage is entirely dependent on chemoautotrophic symbionts; smaller individuals do not house symbionts and presumably depend on grazing. Using high-resolution X-ray microtomography to reconstruct the internal organs in a growth series, we show that this sudden transition in small but sexually mature individuals dramatically reconfigures the organs, but is in no way apparent from external morphology. We introduce the term 'cryptometamorphosis' to identify this novel phenomenon of a major body change and trophic shift, not related to sexual maturity, transforming only the internal anatomy. Understanding energy flow in ecosystems depends on the feeding ecology of species; the present study highlights the possibility for adult animals to make profound shifts in biology that influence energy dynamics.

Seasonal variations in sleep of free-ranging Arabian oryx (Oryx leucoryx) under natural hyperarid conditions

The Arabian oryx lives under hyperarid conditions in the Arabian Desert and exhibits temporal niche switching of activity patterns at a seasonal level. The objective of the current study was to provide a polysomnographic-based study of sleep in free-roaming Arabian oryx in their natural habitat to determine whether extreme seasonal climate variations resulted in changes in sleep patterns and physiology associated with the seasonal switching of temporal niches. Electroencephalography, nuchal electromyography, actigraphy, and subcutaneous temperature were recorded in free-roaming Arabian oryx in the Mahazat as-Sayd Protected Area, Kingdom of Saudi Arabia during winter and summer. Total daily sleep time in winter was 6.69 and 3.77 hr in summer. In winter, oryx exhibited nocturnal sleep typical of artiodactyls of around 60 kg body mass. In summer, oryx slept mostly during the day and subcutaneous temperature was seen to rise during sleep, but not as rapidly as the rises observed in ambient air temperature. Rapid eye movement sleep formed a very small percentage of total sleep time, especially so in the summer. The unusual sleep patterns and physiology during summer appear to be related to high ambient air temperatures that affect both intrinsic and extrinsic factors necessary for survival. The Arabian oryx appears to use sleep physiology as an adaptive thermoregulatory mechanism in the hot summer months.

Temporal niche switching in Arabian oryx (Oryx leucoryx): Seasonal plasticity of 24 h activity patterns in a large desert mammal

The Arabian oryx, a moderately large mammal that inhabits a harsh desert environment, has been shown to exhibit seasonal variations in activity and inactivity patterns. Here we analyzed the continuous year-round activity patterns of twelve free-roaming Arabian oryx under natural conditions from two varying desert environments in Saudi Arabia using abdominally implanted activity meters. We simultaneously recorded weather parameters at both sites to determine whether environmental factors are responsible for temporal niche switching as well as the seasonal structuring and timing of this behavioural plasticity. Our results demonstrate that Arabian oryx undergo temporal niche switching of 24h activity patterns at a seasonal level and exhibit distinct nocturnal/crepuscular activity during summer, diurnal activity during winter and intermittent patterns of behaviour during the transitional seasons of autumn and spring. In addition, the oryx exhibited inter- and intra-seasonal variations in the temporal budgeting of 24h activity patterns. Strong relationships with both photoperiod and ambient temperatures were found and in some instances suggested that increasing ambient temperatures are a primary driving force behind seasonal shifts in activity patterns. These adaptive patterns may be dictated by the availability of food and water, which in turn are strongly influenced by seasonal climate variations. Overall, the adaptive responses of free-roaming Arabian oryx in such harsh and non-laboratorial conditions provide a framework for comparing wild populations as well as aiding conservation efforts.

Differences in the high-temperature tolerance of Aphis craccivora (Hemiptera: Aphididae) on cotton and soybean: implications for ecological niche switching among hosts

To forecast the effects of climate change and extreme temperature events on insect population dynamics, the high-temperature tolerance of insects must be taken into account. We compared the life-history characteristics of cowpea aphid (Aphis craccivora Koch) across different temperature regimes on two different host plants, soybean (a preferred host) and cotton (a non-preferred host). Most demographic parameters were superior for the aphid on soybean than on cotton. Temperatures affected aphid development more on cotton than on soybean. The intrinsic rate of increase, reproduction rate, number of progeny per adult, and longevity were significantly higher on soybean than on cotton for the same temperature regime. Temperatures that fluctuated to extreme levels caused a rapid decline in each of these parameters for aphids fed on cotton, but not for those fed on soybean. To our knowledge, this is the first report to note that the high-temperature tolerance of A. craccivora is host-specific (cotton vs. soybean). Our findings may partly explain the observed niche switching of the cowpea aphid (Aphis craccivora) from cotton to soybean at the beginning of summer when the temperature goes up in the Xinjiang cotton-growing zone (Northwest China). This host mediation of high-temperature tolerance in aphids should be taken into account when modeling population dynamics under the influence of global warming, host adaptation, and the risk analysis of alien pest invasions.

Metabolic modelling reveals the specialization of secondary replicons for niche adaptation in Sinorhizobium meliloti.

The genome of about 10% of bacterial species is divided among two or more large chromosome-sized replicons. The contribution of each replicon to the microbial life cycle (for example, environmental adaptations and/or niche switching) remains unclear. Here we report a genome-scale metabolic model of the legume symbiont Sinorhizobium meliloti that is integrated with carbon utilization data for 1,500 genes with 192 carbon substrates. Growth of S. meliloti is modelled in three ecological niches (bulk soil, rhizosphere and nodule) with a focus on the role of each of its three replicons. We observe clear metabolic differences during growth in the tested ecological niches and an overall reprogramming following niche switching. In silico examination of the inferred fitness of gene deletion mutants suggests that secondary replicons evolved to fulfil a specialized function, particularly host-associated niche adaptation. Thus, genes on secondary replicons might potentially be manipulated to promote or suppress host interactions for biotechnological purposes.

Reticulate evolution is favored in influenza niche switching.

Reticulate evolution is thought to accelerate the process of evolution beyond simple genetic drift and selection, helping to rapidly generate novel hybrids with combinations of adaptive traits. However, the long-standing dogma that reticulate evolutionary processes are likewise advantageous for switching ecological niches, as in microbial pathogen host switch events, has not been explicitly tested. We use data from the influenza genome sequencing project and a phylogenetic heuristic approach to show that reassortment, a reticulate evolutionary mechanism, predominates over mutational drift in transmission between different host species. Moreover, as host evolutionary distance increases, reassortment is increasingly favored. We conclude that the greater the quantitative difference between ecological niches, the greater the importance of reticulate evolutionary processes in overcoming niche barriers.

Diurnality as an energy-saving strategy: energetic consequences of temporal niche switching in small mammals.

Endogenous daily (circadian) rhythms allow organisms to anticipate daily changes in the environment. Most mammals are specialized to be active during the night (nocturnal) or day (diurnal). However, typically nocturnal mammals become diurnal when energetically challenged by cold or hunger. The circadian thermo-energetics (CTE) hypothesis predicts that diurnal activity patterns reduce daily energy expenditure (DEE) compared with nocturnal activity patterns. Here, we tested the CTE hypothesis by quantifying the energetic consequences of relevant environmental factors in mice. Under natural conditions, diurnality reduces DEE by 6-10% in energetically challenged mice. Combined with night-time torpor, as observed in mice under prolonged food scarcity, DEE can be reduced by ∼20%. The dominant factor determining the energetic benefit of diurnality is thermal buffering provided by a sheltered resting location. Compared with nocturnal animals, diurnal animals encounter higher ambient temperatures during both day and night, leading to reduced thermogenesis costs in temperate climates. Analysis of weather station data shows that diurnality is energetically beneficial on almost all days of the year in a temperate climate region. Furthermore, diurnality provides energetic benefits at all investigated geographical locations on European longitudinal and latitudinal transects. The reduction of DEE by diurnality provides an ultimate explanation for temporal niche switching observed in typically nocturnal small mammals under energetically challenging conditions. Diurnality allows mammals to compensate for reductions in food availability and temperature as it reduces energetic needs. The optimal circadian organization of an animal ultimately depends on the balance between energetic consequences and other fitness consequences of the selected temporal niche.

Explaining vote switching to niche parties in the 2009 European Parliament elections

Assuming that the electoral success of niche parties in EP elections is largely due to the vote switching in EP elections, this study seeks to explore the motivations leading mainstream party supporters to switch to niche parties in EP elections ( niche switching voters). From the results of analyses, some important findings could be drawn. First, for niche switching voters, the ‘protest voting’ motivation is very important motive. In particular, they are strongly driven by their profound distrust in mainstream politics in switching to niche parties. Second, unlike the existing literature, European considerations matter in their voting behavior. Third, vote choice based on the niche issues also has important effect on their voting behavior. This demonstrates clearly that, niche switching voters are different from other switching voters.

Cold and hunger induce diurnality in a nocturnal mammal.

The mammalian circadian system synchronizes daily timing of activity and rest with the environmental light-dark cycle. Although the underlying molecular oscillatory mechanism is well studied, factors that influence phenotypic plasticity in daily activity patterns (temporal niche switching, chronotype) are presently unknown. Molecular evidence suggests that metabolism may influence the circadian molecular clock, but evidence at the level of the organism is lacking. Here we show that a metabolic challenge by cold and hunger induces diurnality in otherwise nocturnal mice. Lowering ambient temperature changes the phase of circadian light-dark entrainment in mice by increasing daytime and decreasing nighttime activity. This effect is further enhanced by simulated food shortage, which identifies metabolic balance as the underlying common factor influencing circadian organization. Clock gene expression analysis shows that the underlying neuronal mechanism is downstream from or parallel to the main circadian pacemaker (the hypothalamic suprachiasmatic nucleus) and that the behavioral phenotype is accompanied by phase adjustment of peripheral tissues. These findings indicate that nocturnal mammals can display considerable plasticity in circadian organization and may adopt a diurnal phenotype when energetically challenged. Our previously defined circadian thermoenergetics hypothesis proposes that such circadian plasticity, which naturally occurs in nocturnal mammals, reflects adaptive maintenance of energy balance. Quantification of energy expenditure shows that diurnality under natural conditions reduces thermoregulatory costs in small burrowing mammals like mice. Metabolic feedback on circadian organization thus provides functional benefits by reducing energy expenditure. Our findings may help to clarify relationships between sleep-wake patterns and metabolic phenotypes in humans.

Temporal niche switching and reduced nest attendance in response to heat dissipation limits in lactating common voles (Microtus arvalis)

According to the heat dissipation limit theory, maximum metabolic turnover is limited by the capacity of the body to dissipate excess heat. Small mammals, including common voles (Microtus arvalis), face a heat dissipation limitation during lactation. Pup growth and milk production are reduced under higher ambient temperatures. Heat dissipation problems might in part be alleviated by modifying behavior, such as reducing nest attendance and being active at energetically optimal times of day. According to the circadian thermo-energetics hypothesis, animals can make use of daily ambient temperature fluctuations to alter their energetic expenditure. In this study we test whether heat challenged (housing at 30°C compared to 21°C) lactating common voles allocate their time differently among behaviors and whether their ultradian and circadian behavioral rhythmicity are altered.Behavior was scored every 13min from automated picture recordings, while general locomotor activity was measured by passive infrared detectors to assess ultradian and circadian organization. The effects of ambient temperature on the ultradian organization of behavior were assessed by determining the ultradian period length and the distribution of activity within the ultradian bout. Changes in circadian organization were assessed by the distribution of activity over the light and dark phase. As a complementary measure nest temperature recordings were used to quantify nest attendance distribution between day and night.Lactating dams at 30°C reduced the fraction of time spent on the nest while increasing the fraction of time resting without pups away from the nest. The ultradian period of locomotor activity was longer in voles housed at 30°C during pregnancy and lactation, but not after weaning when the pups were removed. No differences in the distribution of activity within the ultradian bout could be detected. The circadian organization was also modulated by ambient temperature. Lactating voles housed at 30°C became more day active and a loss of day–night differences in nest temperature suggests a shift of nest attendance towards the night.Reducing the time attending the nest can reduce the risk of hyperthermia, and may be the behavioral component resulting in lower milk production and hence reproductive output. Becoming more day active allows feeding and nursing of the pups during the rest phase to occur during the night at which lower ambient temperatures are expected in the field. In natural situations this strategy will increase heat dissipation and lactation capacity. Whether there are similar benefits associated with a longer ultradian period is currently unknown, but these are likely to result from decreased energy turnover at 30°C. In conclusion, our study shows that lactating common voles facing heat dissipation problems re-organize their behavior in a way that can maximize heat dissipation capabilities and thereby optimize lactation capacity.

Temporal niche switching by grizzly bears but not American black bears in Yellowstone National Park

Grizzly bears (Ursus arctos) have been reported as either nocturnal or diurnal in various studies, but have not been known to switch between the 2 times unless disturbed by humans. Black bears (Ursus americanus) are almost solely diurnal in studies unless human influences occur. Because human disturbance is often difficult to control, the relative temporal niche of both species remains ill-defined. Thus, the present study examined bears in Yellowstone National Park (Wyoming) where hunting does not occur, human activities are relatively benign, and bear species are sympatric to determine if niche occupancy was a stable feature of the species. Onset of activity was anticipatory of both sunrise or morning civil twilight (illumination sufficient for human vision) for individuals of either species. The peak hour of activity in black bears was consistently midday, but fluctuated in grizzly bears from midday during early spring, late summer, and fall to evening during late spring and early summer. Black bears did not temporally avoid the times when the more dominant grizzly bears were active. Mean activity levels were higher for male black bears than for both male and female grizzly bears. Together, results suggest that the foraging needs of black bears necessitate ingestion of less-digestible, lower-quality foods requiring longer foraging time during daytime hours, whereas grizzly bears adapt their diet to seasonally available food sources, necessitating greater temporal flexibility.

Light Intensity Determines Temporal Niche Switching of Behavioral Activity in Deep-Water Nephrops norvegicus (Crustacea: Decapoda)

The temporal distribution of behavioral programs throughout the 24-h day, known as temporal niche of a species, is determined by ecological factors that directly affect the adaptive value of the timing of specific behaviors. Temporal niche switching has been described in several species and is likely adaptive in habitats where the daily timing of those factors changes. Benthic species whose habitats span a wide range of water depths are exposed to considerable depth-dependent environmental changes. Temporally scheduled trawl surveys of the Norway lobster, Nephrops norvegicus, reveal that animals emerge from burrows at night on the shallow shelf (10-50 m deep), at crepuscular hours on the lower shelf (50-200 m), and at daytime on the slope (200-400 m). The mechanisms underlying nocturnality/diurnality switches are chiefly unknown, and Nephrops offers a unique model for their study. The depth-dependent decrease in luminance is a likely candidate determining the temporal distribution of behavior. The authors explored this possibility in the laboratory by exposing Nephrops to light:dark (LD) cycles of 470-nm monochromatic lighting that mimic conditions at the 100-m-deep shelf (10 lux) or the 300-m slope (0.1 lux). Two groups of animals were respectively exposed to each light intensity according to the following protocol: an initial 12:12 LD stage followed by constant darkness (DD), followed in turn by a second 12:12 LD stage. Activity at the burrow opening (door-keeping = DK), as well as full emergence (E), was continuously monitored. Under 10-lux LD cycles, most animals showed nocturnal DK activity-with some being crepuscular or diurnal-and all animals showed nocturnal E activity. In contrast, both behaviors were clearly diurnal in animals under 0.1-lux LD cycles. The phase of the nocturnal and diurnal DK rhythms detected respectively at 10 and 0.1 lux upon release into DD revealed that these rhythms are entrained circadian rhythms. The present data indicate that nocturnality/diurnality switches in Nephrops in its natural habitat, evidenced by captures at different depths, are likely determined by light intensity. This temporal niche switching involves different patterns of photic entrainment, leading to bona fide circadian diurnal or nocturnal phenotypes, as well as exogenous masking of behavioral outputs.