Effect of Seasonality on the Behavior of an Insectivorous Primate, Tarsius spectrum

The distribution and quality of food resources is generally recognized as the preeminent factor explaining much interspecific and intraspecific variation in the behavior of nonhuman primates. Primates that live in seasonal environments often show predictable responses to fluctuating resources. In order to compensate for the reduction in resource availability, primates variously switch to alternative, poorer quality food sources, increase the amount of time they spend foraging, or increase their daily path length. Some primate species reduce their group size or maximize the group dispersion. I address whether spectral tarsiers (Tarsius spectrum), which are insectivores, modify their behavior in the same ways as frugivores and folivores in response to seasonal or scarce resources. My results indicate that wild spectral tarsiers modify their activity budget in response to seasonal resources. Specifically, during periods of low resource availability, spectral tarsier males and females spent more time traveling and foraging compared to their activity budget during the wet season. Males and females not only increased the amount of time they spent foraging during times of low resource abundance but also modified their foraging behavior. During the wet season, when resource abundance was high, they consumed Orthoptera and Lepidoptera with greater frequency than during the dry season. During the dry season, when resource abundance was low, spectral tarsiers still ate numerous Orthoptera and Lepidoptera, but they also increased consumption of Coleoptera and Hymenoptera. Spectral tarsiers were also more likely to be involved in territorial disputes during the dry season than during the wet season. Intragroup encounters decreased in frequency in the dry season versus the frequency of encounters during the wet season.     

Seasonal variation in patch use in a tropical African environment

We used giving-up densities (GUD) to study patch use decisions of small granivorous passerines throughout the year. We measured GUDs continuously in four sites for a period of 9–10 months per year during 2004 and 2005 in a savannah area in Jos, central Nigeria. The study thus covered a period from the middle of the dry season, through the wet season to the beginning of the next dry season in each year. We placed experimental food patches in both open areas and in cover to investigate possible effects of predation risk and thermal hazard on the foraging behavior of the birds. We found a difference in GUDs between the microhabitats, with a consistently lower GUD in cover throughout the year and for the two years. During both years GUDs followed a pattern coinciding with the seasonal change in local seed availability. An initial decline in GUDs late in the dry season was followed by a steady increase during and after the rains. A similar trend in GUDs observed for both years supports the conclusion that GUDs measure the feeding birds' assessment of environmental quality, possibly in combination with other factors changing predictably during the year. We conclude that food abundance may act with other environmental and ecological factors to affect foraging decisions throughout the year.     

Nest and foraging‐site selection in Yellowhammers Emberiza citrinella: implications for chick provisioning

Capsule Vegetation structure and invertebrate abundance interact to influence both foraging sites and nestling provisioning rate; when invertebrate availability is low, adults may take greater risks to provide food for their young.

Aims To investigate nesting and foraging ecology in a declining farmland bird whose fledging success is influenced by the availability of invertebrate prey suitable for feeding to offspring, and where perceived predation risk during foraging can be mediated by vegetation structure.

Methods Provisioning rates of adult Yellowhammers feeding nestlings were measured at nests on arable farmland. Foraging sites were compared with control sites of both the same and different microhabitats; provisioning rate was related to habitat features of foraging‐sites.

Results Foraging sites had low vegetation density, probably enhancing detection of predators, or high invertebrate abundance at high vegetation density. Parental provisioning rate decreased with increasing vegetation cover at foraging sites with high invertebrate abundance; conversely, where invertebrate abundance was low, provisioning rate increased with increasing vegetation cover.

Conclusions Vegetation structure at foraging sites suggests that a trade‐off between predator detection and prey availability influences foraging site selection in Yellowhammers. Associations between parental provisioning rate and vegetation variables suggest that where invertebrate abundance is high birds increase time spent scanning for predators at higher vegetation densities; however, when prey are scarce, adults may take more risks to provide food for their young.     

Effects of lions on behaviour and endocrine stress in plains zebras

Living under predation risk may alter both behaviour and physiology of potential prey. In extreme cases, such alterations may have serious demographic consequences, and recent studies support that non‐lethal effects of predation may have broad ecological consequences. However, behavioural and physiological responses to predation risk may be related to trade‐offs associated with resource acquisition and direct predation risk. We validated an enzyme‐linked immunoassay (EIA) for non‐invasive monitoring of stress in plains zebras (Equus quagga) from faecal material. We used this assay in combination with behavioural data to assess if plains zebras living with and without lions (Panthera leo) in a mountain savannah in southern Africa differed in behaviour and physiology, and if such differences were influenced by seasons with contrasting resource availability. Zebra group sizes did not differ between areas with and without lions, but zebra groups had more juveniles in an area with lions than groups in an area without lions, but only during the wet season. Similarly, we observed differences in individual vigilance, foraging behaviour and stress hormone concentrations, but all these differences were influenced by seasons. Despite these seasonal influences, our study did not suggest that zebras in an area with lions spent a higher proportion of time being vigilant, a lower proportion of time foraging, or had higher stress hormone levels. Our results instead suggest that zebras' responses to lion presence were highly context dependent and the result of complex interactions between resource abundance and cues about predation risk. Because of the obvious ecological and evolutionary ramifications of such findings, we argue that further research is needed to define the spatial and temporal scales over which predators impose indirect effects on their prey.     

Influence of Dry Season and Food Quality and Quantity on Behavior and Feeding Strategy of Propithecus verreauxi in Kirindy, Madagascar

According to optimal foraging theory, herbivores can base food choice mainly on the quality or the quantity of food, or both. Among herbivorous primates, folivorous lemurs living in the highly seasonal environment of Madagascar have to cope with the shortage of high-quality food during the dry season, at least in deciduous forests. We studied (Verreaux's sifaka) in Kirindy, western Madagascar, to understand the influence of dry season and food quality and quantity on behavioral patterns and feeding strategy (qualitative vs. quantitative dietary choice) of a folivorous lemur in a deciduous forest. We followed 7 groups (4 groups/period; 3 individuals/group/month) during 4 periods of the year (wet season: February–March; early/middle/late dry season: May–June; July–September; October–November). We collected samples of plants eaten and examined behavioral and feeding patterns, considering food quality (macronutrients, proteins/fibers ratio, and tannins) and abundance. We found 1) a significant reduction of home range, core area, and daily path length from the wet to the dry season, possibly related to dietary change and 2) a daily period of inactivity in the dry season for energy conservation. Regarding the feeding strategy, Kirindy sifakas showed 1) high variation and selection in choosing food items and 2) a dietary choice based mainly on quality: Kirindy sifakas fed on plant species/families independently from their abundance and tannins represented a feeding deterrent during the dry season. Overall, behavioral and dietary adaptations allow Kirindy sifakas to overcome the shortage of high-quality food in the lean period.     

Foraging ecology in the lizard Anolis oculatus (Iguanidae) from Dominica, West Indies

In general, populations of Anolis lizards on West Indian islands face few predators, are at high density and are thought to be limited by food. This paper describes how the foraging ecology of Anolis oculatus , a solitary species confined to the island of Dominica, Lesser Antilles, varies with habitat and season in relation to the quantity and quality of available food.
Availability of invertebrate food (determined using pitfall traps and sticky traps) was greater in a dry scrub woodland site, Cabrits National Park (CNP), compared with a montane rainforest site, Palmiste Ridge. In the former, there were general increases in abundance, volumes of softbodied prey and sizes of invertebrates from dry season to wet season. Concomitant dietary changes, as determined principally by stomach flushing, included an increase (by volume) in the proportion of soft-bodied prey. Dietary analyses confirmed the importance of ants (Formicidae) in the diet of A. oculatus , although for large individuals (mainly adult males) at the rainforest site, soft-bodied prey such as Oligochaeta and Orthoptera were, in volumetric terms, more important. Prey capture observations showed that large A. oculatus fed mainly above ground. Anolis oculatus at the montane rainforest site used higher perch heights than those in dry scrub woodland, although in both habitats, small individuals (mainly juveniles) fed mainly at ground level on ants. In the dry season in CNP, the diet (in volumetric terms) of smaller Anolis was dominated by hardbodied prey such as ants, springtails (Collembola), barklice (Psocoptera) and beetles (Coleoptera). large Anolis used springtails and barklice to a lesser extent, resulting in relatively low food niche overlap values between size classes and a reduced potential for intraspecific competition compared with the wet season.     

Ecological Risk Aversion and Foraging Behaviors of Juvenile Squirrel Monkeys (Saimiri sciureus)

The ‘ecological risk aversion hypothesis’ [C.H. Janson and C.P. van Schaik, Juvenile Primates, Oxford Univ. Press, New York (1993), pp. 57–74] proposes that the pattern of slow growth characteristic of juvenile primates is a response to ecological risks (predation and starvation) experienced by juveniles. Juveniles are thought to avoid predation risk by positioning themselves near conspecifics, therefore experiencing high levels of feeding competition with older individuals, reduced access to resources and, consequently, high starvation risks during periods of food scarcity. The present study compared the foraging behaviors of juvenile and adult squirrel monkeys, a small neotropical primate characterized by a long juvenile period, to determine how predation and starvation risks affected juvenile behaviors. The study was conducted in Eastern Amazonia, in a seasonal environment. Due to their slow development, small body size and large group sizes, it was expected that juveniles in this species would behave in a manner consistent with the risk aversion hypothesis. However, age differences in foraging efficiency and foraging success were smaller than predicted. There was also no evidence that juveniles sacrificed access to food for predator protection. Adults did not have preferential access to fruit patches and direct competition was rare. Feeding competition for prey, the most common resource in the troop's diet, was negligible. Therefore, the slow growth and long juvenile period of squirrel monkeys do not correspond with evidence of predation or starvation risk, as predicted by the risk aversion hypothesis.     

The influence of temporally variable predation risk on indirect interactions in an aquatic food chain

We know little about how temporally variable predation risk influences prey behavior. The risk allocation hypothesis predicts that prey facing more frequent risk should show weak anti-predator responses, and should be particularly active foragers during rare periods of safety, compared to prey facing infrequent risk. Several studies offer support for the risk allocation hypothesis, but how these responses might propagate through the larger ecological community remains largely unknown. We experimentally investigated the relative strength of trait- and density-mediated indirect effects of a predator on its prey’s resource across predation treatments that varied the lethality (caged or free-swimming predators) and temporal variability (always, often, or sometimes present) of predation. We performed this experiment in pond mesocosms using a giant water bug predator (Belostoma lutarium), an herbivorous pond snail (Physa gyrina), and algae as the basal resource. Snails greatly reduced the abundance of their algal resource when in the absence of predation. Lethal predation at low and medium intensities had significant positive indirect effects on the abundance of algae, mostly by reducing snail density. Snails responded behaviorally to high levels of deadly predation by foraging more and hiding less than in other situations, as predicted by the risk allocation hypothesis, and thus ameliorated the density-mediated indirect effects of predators on algae. Behavioral responses to caged predators, and the subsequent trait-mediated indirect effects, were negligible regardless of predation intensity. Our previous work has demonstrated that trait-mediated indirect effects are weak when resources are abundant, as they were in this experiment. This work demonstrates that temporal variation in predation intensity plays a key role in determining the relative strength of TMIIs and DMIIs in an aquatic food chain.     

Changing vulnerability to predation related to season and sex in an African ungulate assemblage

The consequences of predation for prey population dynamics depend on the extent to which this mortality is predisposed by malnutrition or senescence, or additive in the sense that animals that would otherwise not have died at that time were killed. In places lacking effective predators, few adult ungulates die during the summer or wet season months when food is plentifully available. Hence the seasonal distribution of predator kills as well as the age and sex classes of the prey indicates the extent to which malnutrition contributes to mortality as well as other influences on vulnerability. Using records of animal deaths assembled over 35 years in South Africa's Kruger National Park, these patterns were investigated for 12 ungulate species forming the prey of lions, and for three other large predators with respect to one prey species. Buffalo, kudu and giraffe were more strongly represented in kills made during the late dry season, while wildebeest and zebra made relatively greater contributions during the wet season. Impala, waterbuck, warthog and rarer antelope species became more prominent in kills during transitional periods between seasons. Five prey species showed an elevation in representation of males in lion kills during the mating season, as well as impala for all predator species. Females were more prominently represented in kills during the time of late gestation and parturition for three prey species. Hence reproductive activities as well as changing vegetation cover and food resources affected vulnerability to predation. Shifts in susceptibility to predation over the seasonal cycle corresponded with rainfall‐related variation in the annual representation of these ungulate species in lion kills. The availability of vulnerable prey species, age and sex classes at different stages of the seasonal cycle helps maintain a high abundance of lions. These factors contribute to the strong additive impact that predation has had on the abundance of some of these ungulate populations.     

Detecting predators and locating competitors while foraging: an experimental study of a medium-sized herbivore in an African savanna

Vigilance allows individuals to escape from predators, but it also reduces time for other activities which determine fitness, in particular resource acquisition. The principles determining how prey trade time between the detection of predators and food acquisition are not fully understood, particularly in herbivores because of many potential confounding factors (such as group size), and the ability of these animals to be vigilant while handling food. We designed a fertilization experiment to manipulate the quality of resources, and compared awareness (distinguishing apprehensive foraging and vigilance) of wild impalas (Aepyceros melampus) foraging on patches of different grass height and quality in a wilderness area with a full community of predators. While handling food, these animals can allocate time to other functions. The impalas were aware of their environment less often when on good food patches and when the grass was short. The animals spent more time in apprehensive foraging when grass was tall, and no other variable affected apprehensive behavior. The probability of exhibiting a vigilance posture decreased with group size. The interaction between grass height and patch enrichment also affected the time spent in vigilance, suggesting that resource quality was the main driver when visibility is good, and the risk of predation the main driver when the risk is high. We discuss various possible mechanisms underlying the perception of predation risk: foraging strategy, opportunities for scrounging, and inter-individual interference. Overall, this experiment shows that improving patch quality modifies the trade-off between vigilance and foraging in favor of feeding, but vigilance remains ultimately driven by the visibility of predators by foragers within their feeding patches.     

Coping with Spatial Heterogeneity and Temporal Variability in Resources and Risks: Adaptive Movement Behaviour by a Large Grazing Herbivore

Movement is a key mean for mobile species to cope with heterogeneous environments. While in herbivorous mammals large-scale migration has been widely investigated, fine-scale movement responses to local variations in resources and predation risk remain much less studied, especially in savannah environments. We developed a novel approach based on complementary movement metrics (residence time, frequency of visits and regularity of visits) to relate movement patterns of a savannah grazer, the blue wildebeest Connochaetes taurinus, to fine-scale variations in food availability, predation risk and water availability in the Kruger National Park, South Africa. Wildebeests spent more time in grazing lawns where the grass is of higher quality but shorter than in seep zones, where the grass is of lower quality but more abundant. Although the daily distances moved were longer during the wet season compared to the dry season, the daily net displacement was lower, and the residence time higher, indicating a more frequent occurrence of area-concentred searching. In contrast, during the late dry season the foraging sessions were more fragmented and wildebeests moved more frequently between foraging areas. Surprisingly, predation risk appeared to be the second factor, after water availability, influencing movement during the dry season, when resources are limiting and thus expected to influence movement more. Our approach, using complementary analyses of different movement metrics, provided an integrated view of changes in individual movement with varying environmental conditions and predation risk. It makes it possible to highlight the adaptive behavioral decisions made by wildebeest to cope with unpredictable environmental variations and provides insights for population conservation.     

Predation risk of artificial ground nests in managed floodplain meadows

Nest predation highly determines the reproductive success in birds. In agricultural grasslands, vegetation characteristics and management practices influences the predation risk of ground breeders. Little is known so far on the predation pressure on non-passerine nests in tall swards. Investigations on the interaction of land use with nesting site conditions and the habitat selection of nest predators are crucial to develop effective conservation measures for grassland birds.In this study, we used artificial nests baited with quail and plasticine eggs to identify potential predators of ground nests in floodplain meadows and related predation risk to vegetation structure and grassland management.Mean daily predation rate was 0.01 (±0.012) after an exposure duration of 21 days. 70% of all observed nest predations were caused by mammals (Red Fox and mustelids) and 17.5% by avian predators (corvids). Nest sites close to the meadow edge and those providing low forb cover were faced with a higher daily predation risk. Predation risk also increased later in the season. Land use in the preceding year had a significant effect on predation risk, showing higher predation rates on unmanaged sites than on mown sites. Unused meadows probably attract mammalian predators, because they provide a high abundance of small rodents and a more favourable vegetation structure for foraging, increasing also the risk of incidental nest predations. Although mowing operation is a major threat to ground-nesting birds, our results suggest that an annual removal of vegetation may reduce predation risk in the subsequent year.     

Yellow‐chevroned Parakeet (Brotogeris chiriri) abundance and canopy foraging at a dry forest in western Brazil

I studied Brotogeris chiriri abundance and foraging activity at a dry forest of the Urucum mountains in western Mato Grosso do Sul, Brazil, to evaluate their relationships with food resource production. Brotogeris chiriri abundance sharply increased during the early wet season (mainly October 2001) when it mostly foraged for fleshy fruits. At that time Protium heptaphyllum, one of the most common tree species, bore a large crop of fruits, the arils of which were extensively consumed by B. chiriri. Conversely, only a few parakeets were recorded foraging from the late wet to the late dry season, when dry fruit production predominated. The monthly pattern of parakeet abundance paralleled both its monthly pattern of foraging activity and fleshy fruit availability. Moreover, the variations in foraging activity were highly correlated to fleshy fruit production. Thus, data presented here evidenced the effect of both fruiting pulses and a common tree species that produced a large and ephemeral fruit crop, on the dynamic of a small and mobile canopy forager at a primary dry forest.     

Effects of season, water and predation risk on patch use by birds on the African savannah

Birds from semi-arid regions may suffer dehydration during hot, dry seasons with low food availability. During this period, both energetic costs and water requirements for thermoregulation increase, limiting the scope of activity. For granivorous birds feeding on dry seeds, this is a major challenge and availability of water may affect the value of food. Water availability could (1) increase the value of a food patch when the surrounding environment is poor, due to an increase in the marginal value of energy, and (2) increase the value of the entire environment to the forager when environmental quality increases, due to an increase in the marginal value of time. We aimed to test this by measuring giving-up densities (GUDs, remaining food densities after foraging) of granivorous birds in the presence or absence of filled water pots, at different seasons differing in background food and water availability. We predicted that GUDs will increase with water provision during the dry season with moderate food, but in the early wet season with low food and water availability, GUDs will decrease with water provision. Later in the wet season, our experimental addition of water should have no effect. During seasons with low water availability but differing in food availability, results confirmed our predictions. However, when water became more abundant as the wet season progressed, birds still foraged more intensely during days with added water. In all seasons, birds fed more intensely in cover than in exposed areas, suggesting that predation risk rather than heat influenced microhabitat selection.     

Season‐modulated responses of Neotropical bats to forest fragmentation

Seasonality causes fluctuations in resource availability, affecting the presence and abundance of animal species. The impacts of these oscillations on wildlife populations can be exacerbated by habitat fragmentation. We assessed differences in bat species abundance between the wet and dry season in a fragmented landscape in the Central Amazon characterized by primary forest fragments embedded in a secondary forest matrix. We also evaluated whether the relative importance of local vegetation structure versus landscape characteristics (composition and configuration) in shaping bat abundance patterns varied between seasons. Our working hypotheses were that abundance responses are species as well as season specific, and that in the wet season, local vegetation structure is a stronger determinant of bat abundance than landscape‐scale attributes. Generalized linear mixed‐effects models in combination with hierarchical partitioning revealed that relationships between species abundances and local vegetation structure and landscape characteristics were both season specific and scale dependent. Overall, landscape characteristics were more important than local vegetation characteristics, suggesting that landscape structure is likely to play an even more important role in landscapes with higher fragment‐matrix contrast. Responses varied between frugivores and animalivores. In the dry season, frugivores responded more to compositional metrics, whereas during the wet season, local and configurational metrics were more important. Animalivores showed similar patterns in both seasons, responding to the same group of metrics in both seasons. Differences in responses likely reflect seasonal differences in the phenology of flowering and fruiting between primary and secondary forests, which affected the foraging behavior and habitat use of bats. Management actions should encompass multiscale approaches to account for the idiosyncratic responses of species to seasonal variation in resource abundance and consequently to local and landscape scale attributes.     

Foraging speed in staging flocks of semipalmated sandpipers: evidence for scramble competition

Foraging speed is a key determinant of fitness affecting both foraging success and predator attack survival. In a scramble for food, for instance, evolutionary stable strategy models predict that speed should increase with competitor density and decrease when the risk of attack by predators increases. Foraging speed should also decrease in richer food patches where the level of competition is reduced. I tested these predictions in fall staging flocks of semipalmated sandpipers (Calidris pusilla) foraging for an evasive prey. Capture rate of these prey decreased with sandpiper density as the presence of competitors reduced the availability of resources for those behind. Foraging speed was evaluated indirectly by measuring the time needed to cross fixed boundaries on mudflats over 6 years. As predicted, foraging speed increased with sandpiper density and decreased with food density, but, unexpectedly, increased closer to obstructive cover where predation risk was deemed higher. When foraging closer to cover, from where predators launch surprise attacks, the increase in foraging speed may compensate for an increase in false alarms that interrupted foraging. While foraging in denser flocks decreases foraging success, joining such flocks may also increase safety against predators. In semipalmated sandpipers that occupy an intermediate position in the food chain, foraging behavior is influenced simultaneously by the evasive responses of their prey and by the risk of attack from their own predators.     

Seasonal variation in foraging conditions for Ring Ouzels Turdus torquatus in upland habitats and their effects on juvenile habitat selection

Recent studies indicate that variation in juvenile survival may be particularly important in driving avian population dynamics. The quality of habitats available to inexperienced juveniles of migrant species is critical to their survival because they must obtain enough food to build up fat reserves for migration, while avoiding predation. We radiotracked 110 juvenile Ring Ouzels Turdus torquatus, a species of high conservation concern in the UK, to quantify for the first time seasonal patterns in foraging habitat and food abundance during this potentially key life‐history period. Key attributes of foraging plots were compared with those on control plots (representing the broad habitat types selected by foraging juveniles) during 2007–08. Birds foraged on invertebrates in grass‐rich plots during June to mid‐July and then shifted to foraging mainly on moorland berries in higher‐altitude, heather‐rich plots during mid‐July to early‐September. Juveniles selected invertebrate foraging plots with low soil acidity, and increasingly selected plots with high earthworm (an important food) biomass and grass cover, but low grass and all vegetation height as the season progressed. In contrast, earthworm biomass and grass cover remained constant, and grass and all vegetation height increased, on control plots. Juveniles selected berry foraging plots with higher abundance of ripe Bilberries Vaccinium myrtillus and Crowberries Empetrum nigrum than found on control plots. Juvenile Ring Ouzels thus appear to require access to short, grass‐ and invertebrate‐rich habitat during early summer, and taller, heather‐dominated and berry‐rich areas in late summer. The use of two distinct habitat types during the pre‐migratory period illustrates the need for a detailed understanding of the requirements of juvenile birds.     

Breeding Phenology of Birds: Mechanisms Underlying Seasonal Declines in the Risk of Nest Predation

Seasonal declines in avian clutch size are well documented, but seasonal variation in other reproductive parameters has received less attention. For example, the probability of complete brood mortality typically explains much of the variation in reproductive success and often varies seasonally, but we know little about the underlying cause of that variation. This oversight is surprising given that nest predation influences many other life-history traits and varies throughout the breeding season in many songbirds. To determine the underlying causes of observed seasonal decreases in risk of nest predation, we modeled nest predation of Dusky Flycatchers (Empidonax oberholseri) in northern California as a function of foliage phenology, energetic demand, developmental stage, conspecific nest density, food availability for nest predators, and nest predator abundance. Seasonal variation in the risk of nest predation was not associated with seasonal changes in energetic demand, conspecific nest density, or predator abundance. Instead, seasonal variation in the risk of nest predation was associated with foliage density (early, but not late, in the breeding season) and seasonal changes in food available to nest predators. Supplemental food provided to nest predators resulted in a numerical response by nest predators, increasing the risk of nest predation at nests that were near supplemental feeders. Our results suggest that seasonal changes in foliage density and factors associated with changes in food availability for nest predators are important drivers of temporal patterns in risk of avian nest predation.     

Seasonal selection of soil types and grass swards by roan antelope in a South African savanna

Roan antelope are distributed mainly in regions characterized by infertile soils, offering food of low quality. We hypothesized that roan may select localities with higher soil nutrient levels and/or grass swards with more favourable properties in terms of food abundance or quality than generally available in those regions. Roan antelope were observed in a savanna region in South Africa where soils of widely varying nutrient status occurred. Roan favoured open grassland over wooded savanna areas. During the wet season, roan preferred sites with felsite‐derived soil of intermediate soil nutrient status. Grasslands growing on nutrient enriched alluvial soils were preferred outside of the early wet season, although most of the favourable sward characteristics were present in other landscape units. Food quantity, rather than quality appeared to attract roan to foraging sites in the late wet and early dry seasons. Food quality appeared more important in the early wet and late dry seasons. The higher degree of clustering of leafy material within foraging swards seemed to be an additional discriminating factor. The factors governing the selection of foraging sites by roan did not seem notably different from those influencing other species of grazing ruminant, but roan nevertheless seemed tolerant of stemmy grasslands growing on nutrient richer substrates.     

Rainbow trout in seasonal environments: phenotypic trade‐offs across a gradient in winter duration

Survival through periods of resource scarcity depends on the balance between metabolic demands and energy storage. The opposing effects of predation and starvation mortality are predicted to result in trade‐offs between traits that optimize fitness during periods of resource plenty (e.g., during the growing season) and those that optimize fitness during periods of resource scarcity (e.g., during the winter). We conducted a common environment experiment with two genetically distinct strains of rainbow trout to investigate trade‐offs due to (1) the balance of growth and predation risk related to foraging rate during the growing season and (2) the allocation of energy to body size prior to the winter. Fry (age 0) from both strains were stocked into replicate natural lakes at low and high elevation that differed in winter duration (i.e., ice cover) by 59 days. Overwinter survival was lowest in the high‐elevation lakes for both strains. Activity rate and growth rate were highest at high elevation, but growing season survival did not differ between strains or between environments. Hence, we did not observe a trade‐off between growth and predation risk related to foraging rate. Growth rate also differed significantly between the strains across both environments, which suggests that growth rate is involved in local adaptation. There was not, however, a difference between strains or between environments in energy storage. Hence, we did not observe a trade‐off between growth and storage. Our findings suggest that intrinsic metabolic rate, which affects a trade‐off between growth rate and overwinter survival, may influence local adaptation in organisms that experience particularly harsh winter conditions (e.g., extended periods trapped beneath the ice in high‐elevation lakes) in some parts of their range.