Seasonal Environments Research Articles

Routes matter: the effect of seasonality on bamboo lemur navigational strategies

Seasonal environments challenge animals, increasing the complexity of locating resources. Navigation may rely on ‘habitual routes’ or ‘Euclidean’ maps: following established routes or computing novel paths, respectively. Folivores are presumed to rely on evenly distributed resources and thus have a reduced reliance on navigation. We tested whether the navigation strategy of southern bamboo lemurs, Hapalemur meridionalis , a primarily folivorous strepsirrhine that periodically consumes fruit, varies across seasons. We recorded behaviour and location of three social groups during full-day, focal follows during January–December 2013. We analysed the macronutrient components of food items. Bamboo lemurs travelled through habitual routes during periods of food scarcity but relied on nodes (i.e. intersections where directional decisions are made) to navigate throughout the year. Likely, habitual route navigation promoted an energy-saving strategy during lean periods by easing lemur locomotion across the forest. In contrast, lemurs relied on Euclidean navigation during food abundant periods. The continuous use of nodes suggest that nodes may act as cognitive anchors to support efficient directional decisions across seasons. Linearity increased during periods of resource abundance when feeding on energy-rich items and during periods of scarcity to reach latrines. By travelling increasingly linearly towards energy-rich items, lemurs maximized energy intake during periods of food abundance. Overall, bamboo lemurs' combination of both Euclidean and route-based navigational strategies demonstrates a cognitive adaptation for coping with seasonal resource variability in a way that challenges previous research postulating constrained spatial skills in folivorous strepsirrhines. • Route navigation and Euclidean skills are not necessarily exclusive. • Seasonal landscapes likely favour the combination of both navigation strategies. • Bamboo lemurs relied on habitual routes during food scarcity periods. • Bamboo lemurs travelled more linearly off-route during food abundant periods. • Cognitive evidence from lemur navigation supports the energy frugality hypothesis.

Small mammal dynamics in snow-covered forests

AbstractIn seasonal environments, the winter months can drive the structure and dynamics of vertebrate communities. Most ecological studies have focused on species above the snow, overlooking those within the subnivium (below-snow environment). The Great Lakes region of North America is characterized by seasonal snow cover and a diverse assemblage of small mammals, both of which are changing rapidly in response to a changing climate. To study the seasonal dynamics of small mammals, we sampled communities in three forest types (hardwood, hemlock-cedar, and spruce bog) in summer and winter over 2 years. We hypothesized that seasonal differences in communities would be moderated by forest structure in summer and snow in winter. We assessed community dominance via species diversity and the abundances of deer mice (Peromyscus maniculatus), white-footed mice (P. leucopus), and southern red-backed voles (Myodes gapperi). We estimated a Community Temperature Index (CTI; a metric of the balance between warm- and cold-adapted species in a community) and tested seasonal drivers of CTI. Species diversity was highest in spruce bogs in winter due to increased species evenness, but diversity was consistent year-round in hardwood and hemlock-cedar forests due to unchanging species dominance. Spruce bogs supported the coldest CTI in summer, but CTIs converged across forest types in winter. In summer, forest structure drove CTI; in winter, colder CTIs were associated with deeper snow and a warmer subnivium. Our work reveals that snow is a critical habitat and filter for cold-adapted species that ultimately structures small mammal communities. Given rapid changes in snow conditions due to climate change, we predict continued range contractions for subnivium-adapted species.

Host phenology regulates parasite-host demographic cycles and eco-evolutionary feedbacks.

Parasite–host interactions can drive periodic population dynamics when parasites overexploit host populations. The timing of host seasonal activity, or host phenology, determines the frequency and demographic impact of parasite–host interactions, which may govern whether parasites sufficiently overexploit hosts to drive population cycles. We describe a mathematical model of a monocyclic, obligate‐killer parasite system with seasonal host activity to investigate the consequences of host phenology on host–parasite dynamics. The results suggest that parasites can reach the densities necessary to destabilize host dynamics and drive cycling as they adapt, but only in some phenological scenarios such as environments with short seasons and synchronous host emergence. Furthermore, only parasite lineages that are sufficiently adapted to phenological scenarios with short seasons and synchronous host emergence can achieve the densities necessary to overexploit hosts and produce population cycles. Host‐parasite cycles also generate an eco‐evolutionary feedback that slows parasite adaptation to the phenological environment as rare advantageous phenotypes can be driven extinct due to a population bottleneck depending on when they are introduced in the cycle. The results demonstrate that seasonal environments can drive population cycling in a restricted set of phenological patterns and provide further evidence that the rate of adaptive evolution depends on underlying ecological dynamics.

A cost-benefit analysis of leaf carbon economy with consideration of seasonal changes in leaf traits for sympatric deciduous and evergreen congeners: implications for their coexistence.

Deciduous and evergreen species, which have evolved repeatedly across different clades, can coexist in a given environment despite substantial differences in their leaf traits. It remains unclear how these two groups differ in the development of leaf traits over their lifespans or how their carbon economy - the balance between lifetime carbon gain and leaf construction cost - is determined. We determined the photosynthetic rate (Aarea ), leaf mass per area (LMA), leaf mechanical strength and leaf water potentials and estimated the lifetime carbon gain and leaf construction cost of five closely related pairs of evergreen and deciduous species co-occurring in a temperate forest. Aarea of evergreen species was lower during their first spring, similar in summer and higher than the autumn until the following spring than their deciduous counterparts. Leaf mechanical strength, osmotic pressures and LMA increased continuously towards winter in evergreen species while remaining largely constant in deciduous species. The ratio of lifetime carbon gain to leaf construction cost was similar between the two groups. The additional cost associated with enduring winter is paid back by a longer revenue of photosynthesis in evergreen species, allowing evergreen and deciduous leaf habits to coexist in the seasonal environment.

Palaeoecological significance of the “wolf event” as revealed by skull ecometrics of the canid guilds

Members of the mammalian order Carnivora are rarely considered as proxies for palaeoecological reconstructions due to their broad phenotypic plasticity and high climatic tolerance. However, palaeontologists have traditionally interpreted the appearance of some particular carnivoran species in relation to major climatic events. The ‘wolf event’ characterised the inset of climatic deterioration for continental Eurasian fauna, ca 2.0 million years ago. It was defined as the dispersal of cursorial wild canids from East Asia to Europe consequently to the spread of the steppe environment. Anecdotal interpretations were never supported by rigorous testing about the palaeoecological significance of these canid taxa. Here, we employ two dimensional geometric morphometrics of canid skulls to characterise and interpret the structure of extant guilds and its relationship with climate and provide inferences on the early Pleistocene Valdarno community. Averaged skull size and shape of canid guilds are currently associated with climatic parameters that reflect annual mean temperature, seasonality and precipitation. The canid guild from Valdarno showed a clustered phylogenetic structure and its average shape resembles those of communities characterised by relatively high seasonal environments. This study supports the use of canid community structure for palaeoclimatic reconstructions and validate the early Pleistocene as a period of climatic deterioration for Eurasian large mammal fauna.

Adaptive significance of flowering time variation across natural seasonal environments in Arabidopsis thaliana.

The relevance of flowering time variation and plasticity to climate adaptation requires a comprehensive empirical assessment. We investigated natural selection and the genetic architecture of flowering time in Arabidopsis through field experiments in Europe across multiple sites and seasons. We estimated selection for flowering time, plasticity and canalization. Loci associated with flowering time, plasticity and canalization by genome-wide association studies were tested for a geographic signature of climate adaptation. Selection favored early flowering and increased canalization, except at the northernmost site, but was rarely detected for plasticity. Genome-wide association studies revealed significant associations with flowering traits and supported a substantial polygenic inheritance. Alleles associated with late flowering, including functional FRIGIDA variants, were more common in regions experiencing high annual temperature variation. Flowering time plasticity to fall vs spring and summer environments was associated with GIGANTEA SUPPRESSOR 5, which promotes early flowering under decreasing day length and temperature. The finding that late flowering genotypes and alleles are associated with climate is evidence for past adaptation. Real-time phenotypic selection analysis, however, reveals pervasive contemporary selection for rapid flowering in agricultural settings across most of the species range. The response to this selection may involve genetic shifts in environmental cuing compared to the ancestral state.

Photovoice exploration of physical activity norms and values among rural and remote pulmonary rehabilitation participants in British Columbia, Canada

Purpose Individuals with chronic obstructive pulmonary disease (COPD) engage in less physical activity compared to the general population, which can lead to worsened symptoms. In pulmonary rehabilitation (PR) programs, participants learn strategies to complete activities more easily. For such strategies to be effective, however, PR clinicians must understand their clients’ activity values and practices within their geocultural contexts. In this qualitative study, our aim was to explore physical activity norms and values among people with COPD living in remote and rural locations, using Photovoice methodology. Materials and methods We recruited 12 participants from rural PR sites in British Columbia, Canada. During two distinct seasons (winter and summer), participants photographed meaningful activities then completed semi-structured interviews. We analyzed transcripts using a three-step hermeneutic method, which revealed three themes. Results Participants discussed feeling conflicted regarding their COPD symptoms and physical activity, as difficulties in activity engagement cause stress, but remaining active also fosters a sense of purpose and well-being. Meanwhile, participants’ activities are inextricably linked to their rural, remote, and seasonal environment. Conclusions Our study provides insight into how people with COPD resiliently engage in activities in a rural environment with distinct weather variations. Findings highlight the importance of considering individual factors when recommending activities in PR programs. Implications for rehabilitation Although people with chronic lung disease often encounter difficulty and stress in completing their daily activities, they both recognize the importance of and derive great personal meaning from remaining active. The unique social, geographical, physical, and climatic environments of rural and remote dwelling people with chronic lung disease can both enable and challenge their activity engagement. Pulmonary rehabilitation (PR) programs and clinicians must situate their activity recommendations within the geographic contexts of their clients – which can vary across the seasons. Support for participants’ mental health is a vital aspect of PR.

Effects of primary seed dormancy on lifetime fitness of Arabidopsis thaliana in the field

Background and AimsSeed dormancy determines the environmental niche of plants in seasonal environments, and has consequences for plant performance that potentially go far beyond the seed and seedling stages. In this study, we examined the cascading effects of seed dormancy on the expression of subsequent life-history traits and fitness in the annual herb Arabidopsis thaliana.MethodsWe planted seeds of >200 recombinant inbred lines (RILs) derived from a cross between two locally adapted populations (Italy and Sweden), and both parental genotypes at the native site of the Swedish population in three consecutive years. We quantified the relationship between primary seed dormancy and the expression of subsequent life-history traits and fitness in the RIL population with path analysis. To examine the effects of differences in dormancy on the relative fitness of the two parental genotypes, we planted dormant seeds during the seed dispersal period and non-dormant seeds during the germination period of the local population.Key ResultsIn the RIL population, strong primary dormancy was associated with high seedling survival, but with low adult survival and fecundity, and path analysis indicated that this could be explained by effects on germination timing, rosette size and flowering start. The relationship between primary seed dormancy and germination proportion varied among years, and this was associated with differences in seasonal changes in soil moisture. The planting of dormant and non-dormant seeds indicated that the lower primary dormancy of the local Swedish genotype contributed to its higher germination proportion in two years and to its higher fecundity in one year.ConclusionsOur results show that seed dormancy affects trait expression and fitness components across the life cycle, and suggest that among-year variation in the incidence of drought during the germination period should be considered when predicting the consequences of climatic change for population growth and evolution.

Dietary shifts and social interactions drive temporal fluctuations of the gut microbiome from wild redfronted lemurs

Animals living in highly seasonal environments adapt their diets accordingly to changes in food availability. The gut microbiome as an active participant in the metabolization of the host’s diet should adapt and change with temporal diet fluctuations, but dietary shifts can be short-term and, hence, difficult to detect in cross-sectional studies. Therefore, we performed a longitudinal study combining repeated sampling of fecal samples with observations of feeding behavior in wild redfronted lemurs. We amplified taxonomical marker genes for assessing the bacteria, archaea, protozoa, helminths, and fungi, as well as the active bacterial community inhabiting their gut. We found that the most abundant protozoans were Trichostomatia and Trichomonadida, and the most abundant helminths were Chromadorea. We detected known members of the gut mycobiome from humans but in low abundances. The archaeal community is composed only of members of Methanomethylophilaceae. The predominant phyla in the entire bacterial community were Bacteroidota and Firmicutes while the most abundant genera harbor so far unknown bacteria. Temporal fluctuations at the entire community level were driven by consumption of fruits and flowers, and affiliative interactions. Changes in alpha diversity correlated only with the consumption of flowers and leaves. The composition of the entire and active bacterial community was not significantly different, but the most abundant taxa differed. Our study revealed that monthly changes in the bacterial community composition were linked to fruit and flower consumption and affiliative interactions. Thus, portraying the importance of longitudinal studies for understanding the adaptations and alterations of the gut microbiome to temporal fluctuations.

Seasonal elevational patterns and the underlying mechanisms of avian diversity and community structure on the eastern slope of Mt. Gongga

AbstractAimMountain ecosystems harbour significant biodiversity across elevations and seasons. This biodiversity, however, is increasingly under threat from climate change and human land use. While much work has been done to characterize biodiversity in tropical mountains, far less is known about the environmental, seasonal and spatial factors that impact diversity and community structure in subtropical and temperate regions.LocationMt. Gongga, Sichuan, China: the eastern‐most peak in Asia above 7000‐m elevation and the main peak of the Hengduan Mountains.MethodWe examined elevational patterns and ecological variables underlying taxonomic diversity (TD), phylogenetic diversity (PD), functional diversity (FD) and community structure in birds on the eastern slope of Mt. Gongga between 1100‐ and 4400‐m elevation. We assessed biodiversity patterns between species with different elevational range sizes (small‐ vs. large‐ranged species) and between seasons (breeding vs. non‐breeding season).ResultsWe recorded 230 bird species across seven field surveys. TD, PD and FD showed similar hump‐shaped elevational patterns in both seasons. In the breeding season, TD, PD and FD for small‐ranged species were highly correlated with climatic factors (mean daily temperature, seasonal temperature range) and vegetation factors (enhanced vegetation index), while large‐ranged species were correlated with spatial factors (mid‐domain effect). In the non‐breeding season, TD, PD and FD for all species groupings were positively correlated with climate factors. For small‐ranged species in both seasons, community structure was more overdispersed at low and high elevations, and more clustered at middle elevations. For large‐ranged species, community structure differed between seasons, showing a general trend towards clustering as elevations increase in the breeding season and trends towards overdispersion and/or evenness as elevations increase in the non‐breeding season.ConclusionsWe found that different factors shape elevational patterns of diversity for small‐ and large‐ranged species in the breeding season; small‐ranged species are shaped by climate and vegetation structure, while large‐ranged species are shaped by spatial factors. This difference is likely explained by differences in ecological niche breadth (physiological tolerance and/or habitat specialization) between small‐ranged species and large‐ranged species. In the non‐breeding season, however, when climate is seasonally harsher, we found that patterns of diversity for all range‐size groupings were driven by climatic factors. We also found that community structure generally becomes more overdispersed as resource availability decreases and environmental conditions become harsher, like at higher elevations and in the non‐breeding season, suggesting that competition for limited resources is important for shaping communities in seasonal environments. These findings highlight how avian diversity and community structure are dynamic across a local elevational gradient and seasonally, shifting across the annual cycle, which has implications for conservation strategies and land management.

Fire Impacts on Recruitment Dynamics in a Seasonal Tropical Forest in Continental Southeast Asia

The effects of forest fires on tree recruitment dynamics in tropical forests is important for predicting forest dynamics and ecosystem function in Southeast Asia. To our knowledge, no studies have examined the effects of fire intensity on community-level recruitment patterns in tropical forests due to the rarity of long-term observation datasets in fire-impacted tropical forests and the difficulty of quantifying fire intensity. We addressed two questions: (1) is tree recruitment among species affected by fire intensity? and if so, (2) are there specific plant functional traits associated with these responses? We used data from a long-term forest dynamics plot at the Huai Kha Khaeng (HKK) Wildlife Sanctuary in Thailand. The HKK plot occurs in a strongly seasonal tropical environment and has experienced several fires since its establishment in 1994. We found 46 tree species (52% of the 89 species analysed) showed evidence of reduced recruitment rates with increasing fire intensities during the most recent fire in 2005. Tree species in this flammable landscape have various leaf and wood functional traits associated with fire. Spatial and temporal variability in fire activity may lead to alterations in long-term taxonomic and functional composition of the forest due to selection on fire-related traits.

Evolutionary game of life-cycle types in marine benthic invertebrates: Feeding larvae versus nonfeeding larvae versus direct development

Many marine invertebrates have a benthic adult life with planktonic long feeding larval stages (planktotrophy). In other species, planktonic larvae do not eat, and after a rather short period, they settle and initiate their benthic stages (lecithotrophy). Still other species skip planktonic larval stages altogether, and adults produce benthic offspring (direct development). In this paper, we develop an evolutionary game among different life-cycle types and examine the conditions for each life-cycle type to win in a seasonal environment. The growth rate and mortality of benthic individuals are the same among all three life-cycle types, the local habitat (patches) for benthic individuals have a finite longevity, and adults may engage in a limited dispersal just before breeding. Planktotrophy evolves if the planktonic stages are more efficient in terms of biomass gain than benthic life. Otherwise, lecithotrophy or direct development should evolve. Among them, direct development is more advantageous than lecithotrophy if the cost of having planktonic larvae is large, the habitat for benthic individuals is stable, and adults engage in some dispersal.

Flora of Espírito Santo: Pontederiaceae

Abstract Pontederiaceae is a small family of Monocots, composed of two genera (i.e., Heteranthera and Pontederia) and ca. 40 species. Two genera and 27 species are accepted for Brazil. In the state of Espírito Santo, Heteranthera is represented by two species and Pontederia by four species. Its species are exclusively found growing in aquatic or paludal, perennial or seasonal environments. We present descriptions, comments, and illustrations for the species.

Seasonal occurrences, reproductive seasons, and habitat environments of an endangered damselfly Paracercion plagiosum (Odonata: Coenagrionidae) in ponds neighboring Lake Izunuma–Uchinuma, Japan

Seasonal occurrences, reproductive seasons, and habitat environments of an endangered damselfly <i>Paracercion plagiosum</i> (Odonata: Coenagrionidae) in ponds neighboring Lake Izunuma–Uchinuma, Japan

After the smoke has cleared: Extended low fruit productivity following forest fires decreased gregariousness and social tolerance among wild female Bornean orangutans (Pongo pygmaeus wurmbii)

As climate change continues to fundamentally alter resource landscapes, the ability to flexibly respond to spatio-temporal changes in the distribution of preferred food sources is increasingly important for the overall health and fitness of animals living in seasonal, variable, and/or changing environments. Here, we investigate the effects of an uncharacteristically long period of fruit scarcity, following widespread thick haze caused by peat and forest fires in 2015, on the behaviour and sociality of female Bornean orangutans (Pongo pygmaeus wurmbii). We collected data from 2010 to 2018 at Tuanan, Central Kalimantan, Indonesia, and compared the activity, diet, and association patterns of adult females during low-fruit periods before the fires, i.e., regular, seasonal periods of low fruit availability (“pre-fire”), and after the fires, i.e., during the extended period of low fruit availability (“post-fire”). First, we found that, post-fire, female orangutans adopted a more extreme energy-saving activity pattern and diet — resting more, travelling less, and diet-switching to less-preferred foods — compared to pre-fire. Second, we found that the probabilities of association between females and their weaned immature offspring, and between related and unrelated adult females were lower, and the probability of agonism between unrelated females was higher, post-fire than pre-fire. This change in energetic strategy, and the general reduction in gregariousness and social tolerance, demonstrates how forest fires can have lasting consequences for orangutans. Fission–fusion species such as orangutans can mitigate the effects of changes in resource landscapes by altering their (sub)grouping patterns; however, this may have long-term indirect consequences on their fitness.

A cross-scale approach to unravel the molecular basis of plant phenology in temperate and tropical climates.

Plants have evolved to time their leafing, flowering and fruiting in appropriate seasons for growth, reproduction and resting. As a consequence of their adaptation to geographically different environments, there is a rich diversity in plant phenology from temperate and tropical climates. Recent progress in genetic and molecular studies will provide numerous opportunities to study the genetic basis of phenological traits and the history of adaptation of phenological traits to seasonal and aseasonal environments. Integrating molecular data with long-term phenology and climate data into predictive models will be a powerful tool to forecast future phenological changes in the face of global environmental change. Here, we review the cross-scale approach from genes to plant communities from three aspects: the latitudinal gradient of plant phenology at the community level, the environmental and genetic factors underlying the diversity of plant phenology, and an integrated approach to forecast future plant phenology based on genetically informed knowledge. Synthesizing the latest knowledge about plant phenology from molecular, ecological and mathematical perspectives will help us understand how natural selection can lead to the further evolution of the gene regulatory mechanisms in phenological traits in future forest ecosystems.

Mismatch-induced growth reductions in a clade of Arctic-breeding shorebirds are rarely mitigated by increasing temperatures.

In seasonal environments subject to climate change, organisms typically show phenological changes. As these changes are usually stronger in organisms at lower trophic levels than those at higher trophic levels, mismatches between consumers and their prey may occur during the consumers' reproduction period. While in some species a trophic mismatch induces reductions in offspring growth, this is not always the case. This variation may be caused by the relative strength of the mismatch, or by mitigating factors like increased temperature-reducing energetic costs. We investigated the response of chick growth rate to arthropod abundance and temperature for six populations of ecologically similar shorebirds breeding in the Arctic and sub-Arctic (four subspecies of Red Knot Calidris canutus, Great Knot C. tenuirostris and Surfbird C. virgata). In general, chicks experienced growth benefits (measured as a condition index) when hatching before the seasonal peak in arthropod abundance, and growth reductions when hatching after the peak. The moment in the season at which growth reductions occurred varied between populations, likely depending on whether food was limiting growth before or after the peak. Higher temperatures led to faster growth on average, but could only compensate for increasing trophic mismatch for the population experiencing the coldest conditions. We did not find changes in the timing of peaks in arthropod availability across the study years, possibly because our series of observations was relatively short; timing of hatching displayed no change over the years either. Our results suggest that a trend in trophic mismatches may not yet be evident; however, we show Arctic-breeding shorebirds to be vulnerable to this phenomenon and vulnerability to depend on seasonal prey dynamics.

Spatiotemporal analysis of interactions between seasonal water, climate, land use, policy, and socioeconomic changes: Hulun-Buir Steppe as a Case Study

Increased grazing and agricultural production, industrialization, population growth, and consequent land use land cover (LULC) changes considerably increase water consumption. Global climate change exaggerates the uncertainty of water sources and supplies. Unfortunately, most current examinations are either confined within disciplinary silos or not integrated for considering wide-ranging socioenvironmental, management, and policy factors. The paper develops an integrated regional water environment modeling framework, examining how climate, LULC, socioenvironmental, and policy factors interact with the water environment. It also adopts a block-based econometric panel data analysis to quantify this framework. The paper extracts seasonal water area and LULC data through image processing from 2000 to 2014 in the Hulun-Buir watershed, Inner Mongolia of China. The paper quantitatively analyzed the interactions between seasonal water changes and major driving factors, such as climatic, land-use, socioeconomic, policy, space, and time. Many of these driving factors were interacting with the seasonal water environment and showing long-term causal relationships. The socioeconomic variables explained 71% of the variance of seasonal water change, the environmental and climatic factors about 9%, the regional disparities around 13%, and the yearly differences about 4%. The findings confirm that it is critical to carry out a time-series examination of causal relationships between seasonal water change and its manifold driving factors at the scale of regional watershed studies. This integrated watershed modeling framework is suitable for adaptation in other geographic areas or for integrated studies of other socio-environmental systems.

To minimize foraging time, use high-efficiency, energy-expensive search and capture methods when food is abundant but low-efficiency, low-cost methods during food shortages.

Based on a mathematical model, I show that the amount of food in the habitat determines which among alternative methods for search of prey, respectively, for pursuit‐and‐capture give the shortest daily foraging time. The higher the locomotor activity, the higher the rate of energy expenditure and the larger the habitat space a predator can search for prey per time unit. Therefore, I assume that the more efficient a foraging method is, the higher its rate of energy expenditure. Survival selection favors individuals that use foraging methods that cover their energy needs in the shortest possible time. Therefore, I take the optimization criterion to be minimization of the daily foraging time or, equivalently, maximization of the rate of net energy gain. When time is limiting and food is in short supply, as during food bottleneck periods, low‐efficiency, low‐cost foraging methods give shorter daily foraging times than high‐efficiency, energy‐expensive foraging methods. When time is limiting, food is abundant and energy needs are large, as during reproduction, high‐efficiency high‐cost foraging methods give shorter daily foraging times than low‐efficiency low‐cost foraging methods. When time is not limiting, food is abundant, and energy needs are small, the choice of foraging method is not critical. Small animals have lower rates of energy expenditure for locomotion than large animals. At a given food density and with similar diet, small animals are therefore more likely than large ones to minimize foraging time by using high‐efficiency energy‐expansive foraging methods and to exploit patches and sites that require energy‐demanding locomotion modes. Survival selection takes place at food shortages, while low‐efficiency low‐cost foraging methods are used, whereas reproduction selection occurs when food is abundant and high‐efficiency energy‐expensive foraging methods do better. In seasonal environments, selection therefore acts on different foraging methods at different times. Morphological adaptation to one method may oppose adaptation to another. Such conflicts select against foraging and morphological specialization and tend to give species‐poor communities of year‐round resident generalists. But a stable year‐round food supply favors specialization, niche narrowing, and dense species packing.

Soil-Water Characteristics and Creep Deformation of Unsaturated Expansive Subgrade Soil: Experimental Test and Simulation

The creep deformation of expansive soil has been considered as a vital threat to the safety in engineering construction because it may cause serious slope diseases in geological engineering. Meanwhile, since expansive soil usually remains in unsaturated state, its mechanical property is significantly affected by the seasonal environment. Therefore, the nonlinear deformation of expansive soil has received increasing attention, especially the humidity-dependent creep properties. This study focused on the stability of the unsaturated expansive soil subgrade considering rainfall and the creep behavior. Pressure plate extractor and direct shear tests were performed to investigate the hydro-mechanical and creep characteristics of the unsaturated expansive soil. Both the Van-Genuchten and Burgers models were applied to analyze the test results and inserted into the numerical model of the slope under rainfall infiltration. Results show that the compaction degree and the stress state was closely related to the water holding capacity of the expansive soil. The nonlinearity of the creep behavior became increasingly obvious with the increase of time and the stress level. The safety factor of the slope decreased as the rainfall time increased, and the most dangerous slide of the slope moved toward the foot of the slope. Considering the long-term creep process, there was a period of rapid growth in horizontal displacement that is detrimental to the stability of the slope. Besides, the rainfall infiltration could accelerate the slope failure before and after this creep process.