Food resources influence spatial ecology, habitat selection, and foraging behavior in an ambush-hunting snake (Viperidae: Bothrops asper): an experimental study

Prey availability affects many aspects of predators' life history and is considered a primary factor influencing individuals' decisions regarding spatial ecology and behavior, but few experimental data are currently available. Snakes may represent ideal model organisms relative to other animal groups for addressing such resource dependency, due to a presumably more direct link between food resources and many aspects of behavior and natural history. We experimentally investigated the relationship between food intake and spatial behavior in a population of the snake Bothrops asper in a Costa Rican lowland rainforest. Six adult snakes were allowed to forage naturally while six were offered supplemental food in the field, with both groups monitored using radiotelemetry. Mean home range size did not differ between groups presumably due to small sample size, but supplementally fed snakes demonstrated altered patterns of macro- and microhabitat selection, shorter and less frequent movements, and increased mass acquisition. Fed snakes also devoted less time to foraging efforts, instead more frequently remaining inactive and utilizing shelter. Because snakes were always fed in situ and not at designated feeding stations, observed shifts in habitat selection are not explained by animals simply moving to areas of higher food availability. Rather, B. asper may have moved to swamps in order to feed on amphibians when necessary, but remained in preferred forest habitat when food was otherwise abundant. The strong behavioral and spatiotemporal responses of snakes in this population may have been influenced by an overall scarcity of mammalian prey during the study period.     

Condition‐dependent ejaculate production affects male mating behavior in the common bedbug Cimex lectularius

Food availability in the environment is often low and variable, constraining organisms in their resource allocation to different life‐history traits. For example, variation in food availability is likely to induce condition‐dependent investment in reproduction. Further, diet has been shown to affect ejaculate size, composition and quality. How these effects translate into male reproductive success or change male mating behavior is still largely unknown. Here, we concentrated on the effect of meal size on ejaculate production, male reproductive success and mating behavior in the common bedbug Cimex lectularius. We analyzed the production of sperm and seminal fluid within three different feeding regimes in six different populations. Males receiving large meals produced significantly more sperm and seminal fluid than males receiving small meals or no meals at all. While such condition‐dependent ejaculate production did not affect the number of offspring produced after a single mating, food‐restricted males could perform significantly fewer matings than fully fed males. Therefore, in a multiple mating context food‐restricted males paid a fitness cost and might have to adjust their mating strategy according to the ejaculate available to them. Our results indicate that meal size has no direct effect on ejaculate quality, but food availability forces a condition‐dependent mating rate on males. Environmental variation translating into variation in male reproductive traits reveals that natural selection can interact with sexual selection and shape reproductive traits. As males can modulate their ejaculate size depending on the mating situation, future studies are needed to elucidate whether environmental variation affecting the amount of ejaculate available might induce different mating strategies.     

Immediate and delayed life history effects caused by food deprivation early in life in a short‐lived lizard

Detailed studies of the mechanisms driving life history effects of food availability are of prime importance to understand the evolution of phenotypic plasticity and the capacity of organisms to produce better adapted phenotypes. Food availability may influence life history trajectories through three nonexclusive mechanisms: (i) immediate and long‐lasting effects on individual quality, and indirect delayed effects on (ii) intracohort and (iii) intercohort interactions. Using the common lizard (Zootoca vivipara), we tested whether a food deprivation during the two‐first months of life influence life history (growth, survival, reproduction) and performance traits (immunocompetence, locomotor performances) until adulthood. We investigated the underlying mechanisms and their possible interactions by manipulating jointly food availability in a birth cohort and in cohorts of older conspecifics. Food deprivation had direct immediate negative effects on growth but positive long‐lasting effects on immunocompetence. Food deprivation had also indirect delayed effects on growth, body size, early survival and reproduction mediated by an interaction between its direct effects on individual quality and its delayed effects on the intensity of intercohort social interactions combined with density dependence on body size. These results demonstrate that interactions between direct and socially mediated effects of past environments influence life history evolution in size‐structured and stage‐structured populations.     

Host-associated variation in sexual size dimorphism and fitness effects of adult feeding in a bruchid beetle

We studied the effect of larval host (two Convolvulus L. species, Convolvulaceae) on sexual size dimorphism and on the fitness consequences of adult feeding in the bruchid beetle Megacerus eulophus (Erichson) (Coleoptera: Bruchidae). Whereas Convolvulus chilensis Pers. occurs in low density in semiarid habitats, Convolvulus bonariensis Cav. occurs in less stressful environments and exhibits higher population density. Host plants neither differ in seed mass nor in seed nitrogen content, and there were no consistent host‐associated differences in female fitness. Consequently, host quality was considered to be similar. Sexual size dimorphism, expressed as the female:male ratio of body size, was significantly greater in C. chilensis than in C. bonariensis. A greater female size in the C. chilensis population could be selectively advantageous due to higher survival during host‐plant search in stressful environments. Female longevity was affected by food availability (starvation vs. honey‐pollen solution) and by the interaction between food availability and larval host. Fed females lived longer than starved females. This trend was found in both hosts, but it was of greater magnitude in C. chilensis than in C. bonariensis. Fecundity was significantly affected by adult feeding and larval host, and marginally affected by their interaction. Fed females laid more eggs than starved females. However, the increase in fitness of fed females was greater in C. chilensis. Results might be explained by differential selection on plasticity in life‐history traits in contrasting environments. Females in stressful environments should take a greater advantage of the transient availability of resources.     

Resource availability modulates the effect of body size on reproductive development

Within-species variation in animal body size predicts major differences in life history, for example, in reproductive development, fecundity, and even longevity. Purely from an energetic perspective, large size could entail larger energy reserves, fuelling different life functions, such as reproduction and survival (the “energy reserve” hypothesis). Conversely, larger body size could demand more energy for maintenance, and larger individuals might do worse in reproduction and survival under resource shortage (the “energy demand” hypothesis). Disentangling these alternative hypotheses is difficult because large size often correlates with better resource availability during growth, which could mask direct effects of body size on fitness traits. Here, we used experimental body size manipulation in the freshwater cnidarian Hydra oligactis, coupled with manipulation of resource (food) availability to separate direct effects of body size from resource availability on fitness traits (sexual development time, fecundity, and survival). We found significant interaction between body size and food availability in sexual development time in both males and females, such that large individuals responded less strongly to variation in resource availability. These results are consistent with an energy reserve effect of large size in Hydra. Surprisingly, the response was different in males and females: small and starved females delayed their reproduction, while small and starved males developed reproductive organs faster. In case of fecundity and survival, both size and food availability had significant effects, but we detected no interaction between them. Our observations suggest that in Hydra, small individuals are sensitive to fluctuations in resource availability, but these small individuals are able to adjust their reproductive development to maintain fitness.     

Effects of food availability on reproductive output,offspring quality and reproductive efficiency in the apple snail <Emphasis Type="Italic">Pomacea canaliculata</Emphasis>

Phenotypic plasticity in life history traits favors the establishment of invaders and may magnify their ecological impacts. Pomacea canaliculata, the only freshwater snail listed among the 100 worst invaders worldwide, is able to complete its life cycle within a wide range of conditions, a capacity attributed to its life history plasticity. Using snails from their native range in Argentina we investigated the changes in fecundity, egg mass traits, offspring quality, and efficiency of food conversion into eggs in response to different levels of food availability throughout different life stages. Pre-maturity mortality was not affected by chronic reductions of up to 80% in food availability. Females fed ad libitum demonstrated no significant reproductive output differences when mated with males raised at different food availability levels. For females, the number and total weight of eggs and the size of egg masses decreased at high levels of food deprivation. Their efficiency of conversion into eggs of the food ingested during the reproductive period increased with deprivation, as did the survival time of their offspring. In contrast, the egg mass laying rate and the individual egg weight did not differ under different food availability regimes. Reductions in food availability have been suggested as a control method but our results indicate that fecundity would be lessened only at deprivation levels higher than 50% and would be partially compensated by an increase in hatchling survival.     

Resource dependent growth and body condition dynamics in juvenile snakes: an experiment

We examined the manner in which animals adjust the proportion of energy allocated to growth and storage in response to food availability. We compared univariate growth and length-mass relationships between juvenile adders (Vipera berus) reared under two different feeding regimes. Animals in the low- and high-food experimental groups were fed suckling mice once and twice weekly, respectively. Snout-vent length, body mass, and body condition (residual scores from log-log regression of body mass on snout-vent length) were measured shortly after birth, and at 4, 9, and 14 weeks. We found that growth in length and mass, as well as changes in length-mass relationships, differed between treatments; snakes with access to more food not only increased faster in length but were also heavier at the completion of the experiment than were similar sized less frequently fed snakes. There was no association between body condition of individuals measured at birth and at the end of the experiment, whereas size at birth was a good predictor of final size. Our results provide evidence for resource-dependent allocation strategies in V. berus, and suggest that somatic growth is less sensitive to environmental fluctuations than body condition, presumably because body size is of greater importance for fitness.     

The effects of supplemental food on reproduction in parental male smallmouth bass

Synopsis We provided supplemental food for parental male smallmouth bass,Micropterus dolomieu, to determine if food supply limits the reproductive performance of nesting males as measured by care duration, reproductive success and survival of adult males. Although supplementing the diet of parental males had a positive effect on all three reproductive measures, the experiment generated contrasting results in different years. In the first year, supplemental feeding only improved the survival of fed males versus unfed males. In the second year, supplemental feeding increased care duration and reproductive success of fed males but reduced their survival relative to unfed males. Our supplemental feeding improved current or future measures of reproductive performance, but not both simultaneously. The results appear to demonstrate phenotypic plasticity in the extent to which energy from supplemental feeding can be allocated to present or future reproduction.     

Short and chubby or long and slim? Food intake,growth and body condition in free‐ranging pythons

Abstract An animal's sex and body size can influence not only its rate of food consumption, but also the way in which it allocates the resultant energy among the competing demands of maintenance, growth, reproduction and storage. A 13‐year mark–recapture study of pythons (Liasis fuscus) in tropical Australia provides extensive data on these topics. Rates of food intake and growth were highest in small pythons, and decreased more rapidly with body size in males than in females. Allocation to storage (as measured by the snake's mass relative to its body length) showed a more complex pattern. Body condition was high at hatching, but dropped rapidly as energy was allocated to growth rather than storage. Condition then increased through juvenile life, was at a maximum close to maturation, and was higher in females than in conspecific males. Body condition thereafter decreased with increasing body length. These allocation ‘decisions’ reflect the relative advantages of growth versus energy storage at different body sizes. Hatchling snakes grow rapidly (and hence become thin) because greater body size enables the snake to ingest larger prey items. Adult females amass larger energy reserves than males, because they need reserves to produce the clutch. Large snakes become thinner because their feeding rates are low, and they cannot compensate with increased prey size because large‐bodied mammalian prey are rare in our study area.     

Life history implications of allocation to growth versus reproduction in dynamic energy budgets

We compare the implications of determinate vs. indeterminate growth of a parthenogenetic iteroparous ectotherm at constant food density in the context of the dynamic energy budget theory, which specifies the tight links between life history traits, such as feeding, aging, growth and reproduction. We do a comparative analysis using, as measure of fitness, the life span reproduction, the population growth rate, and the conversion efficiency of food to biomass. When extrinsic mortality is constant, indeterminate growth cannot maximize fitness if measured by the population growth rate or the conversion efficiency, except when mortality is low, in which case both types of animals are similar. If the fitness measure is life span reproduction, indeterminate growth maximizes fitness even with constant mortality, provided it is not very high. When mortality decreases with size, indeterminate growth maximizes fitness for almost all measures of fitness. Finally, we suggest an evolutionary link between allocation strategies and expected life span. In populations of long living species, each type of animal can establish in the population of the other. In populations of short living species, determinate growers can invade, and displace, a population of indeterminate ones. However, when the mortality risk of organisms with small size is much higher than those of large size, indeterminate growers can be superior.     

Comparing food limitation among three stages of nesting: supplementation experiments with the burrowing owl

Food availability is an important limiting factor for avian reproduction. In altricial birds, food limitation is assumed to be more severe during the nestling stage than during laying or incubation, but this has yet to be adequately tested. Using food‐supplementation experiments over a 5‐year period, we determined the degree and timing of food limitation for burrowing owls (Athene cunicularia) breeding in Canada. Burrowing owls are an endangered species and food limitation during the nestling stage could influence reproductive performance of this species at the northern extent of their range. Supplemented pairs fledged on average 47% more owlets than unfed pairs, except during a year when natural food was not limiting (i.e., a prey irruption year). The difference in fledgling production resulted from high nestling mortality in unfed broods, with 96% of all nestling deaths being attributed to food shortage. Supplemental feeding during the nestling period also increased fledgling structural size. Pairs fed from the start of laying produced the same number of hatchlings as pairs that received no supplemental food before hatch. Furthermore, pairs supplemented from egg laying to fledging and pairs supplemented during the nestling period alone had the same patterns of nestling survival, equal numbers of fledglings, and similar fledgling mass and structural size. Our results provide empirical support for the hypothesis that the nestling period is the most food‐limited phase of the breeding cycle. The experimental design we introduce here could be used with other altricial species to examine how the timing of food limitation differs among birds with a variety of life‐history strategies. For burrowing owls, and other species with similar life histories, long‐term, large‐scale, and appropriately timed habitat management increasing prey abundance or availability is critical for conservation.     

Lipid dynamics in the viperine snake, Natrix maura, from the Ebro Delta (NE Spain)

Body reserves play a major role in several aspects of vertebrate biology. Accurate identification and quantification of body reserves constitute a useful contribution to the better understanding of the energetic costs of reproduction and the implication of food availability in life history traits of organisms. In this study, lipid content in fat bodies, liver and muscle of the viperine snake (Natrix maura) were measured along an active season. Samples were collected monthly from a natural population of the Ebro Delta Natural Park (NE Spain). This methodology pointed out that lipids stored in fat bodies were the main energetic source during reproduction. In addition, lipids stored in liver appeared to be critical for vitellogenesis, while lipids stored in muscle turned out to be a supplementary energetic resource to fuel reproductive effort. Relationships between changes in body reserves and prey availability in canals of the Ebro Delta were also considered. In males, lipid reserves presented a positive correlation with food availability. On the contrary, lipid reserves in female viperine snakes decreased during vitellogenesis even though food availability increased in this period, which suggests a quick transfer of body lipids to clutch. In April, when rice fields of the Ebro Delta were dry and aquatic prey was scarce for viperine snakes, males and females presented a lower lipid content in fat bodies, liver and muscle than they did in other months, showing a clear link between prey availability and body reserves during food shortage. Thus, patterns of variation in fat levels indicated that Natrix maura is a capital breeder since it acquires resources in advance and stores them until they are invested during the reproductive period. Nevertheless, the shortage in April forces Natrix maura to turn into a facultative income breeder to fuel vitellogenesis. Finally, fat reserves in body components were compared with an estimate of body condition calculated by the residuals from the regression of body mass on body length. In male viperine snakes, the estimate of body condition was correlated with fat levels, revealing that this index is useful to measure condition in living individuals. On the contrary, body condition in females was not correlated with fat levels, which suggests that it is not appropriate to infer condition in female viperine snakes since it depends on the reproductive status of the individuals.     

Components of productivity in black-legged kittiwakes Rissa tridactyla: response to supplemental feeding

In contrast to the high productivity of black-legged kittiwakes in Britain, kittiwakes at many colonies in Alaska have failed chronically to reproduce since the mid 1970s. To determine if food is limiting productivity and, if so, at what stages of nesting food shortages are most severe, in 1996 and 1997 we supplementally fed kittiwakes nesting on an abandoned building. The effects of feeding were stronger in 1997 than in 1996, possibly because naturally occurring prey were of poorer quality in 1997. Consumption of supplemental herring declined as egg laying approached then increased slowly during incubation and more rapidly after hatching. All of the six components of productivity we studied were improved by supplemental feeding to some degree. Supplemental food did not significantly alter laying success in either year, although fed pairs bred at slightly higher rates than unfed pairs in 1997, the poorer food year. In 1996 and 1997, extra food noticeably increased clutch size and hatching success, but significantly so only in 1997. Fledging success and productivity were substantially augmented by feeding in both years. Fed pairs fledged twice as many chicks per nest as did unfed pairs in 1996 and three times as many in 1997. Fed and unfed pairs lost most of their potential productivity through the inability to hatch eggs, and secondarily because of their poor success at raising chicks. The benefits of supplemental feeding did not carry over from one stage of breeding to another. Pairs cut off from supplemental food after laying or hatching performed similarly to pairs that had not been previously fed. This study provides benchmark values of breeding performance attainable by kittiwakes in Alaska under optimal conditions. These values are comparable to highly productive colonies in Britain and suggest that differences in life-history characteristics between Pacific and Atlantic breeding populations are primarily controlled by food supply.     

Effects of supplementary feeding on growth and reproduction of three carnivorous plant species in a subarctic environment

1 The effect of supplementary feeding on growth and reproduction of three carnivorous plants species was investigated over a 6‐year period. Pinguicula alpina , P. villosa and P. vulgaris populations growing at two altitudes in a subarctic environment were fed with fruit flies ( Drosophila melanogaster ).
2 Fed plants increased in size relative to control plants during the first years. Subsequently a stable size difference between feeding levels was established. The weight of the over‐wintering part was higher in fed plants than in control plants.
3 The flowering frequency (i.e. proportion of plants in a population carrying flowers) was also higher in the fed plants. The proportion of flowering plants increased in the feeding treatment compared to control plants during more‐or‐less the whole experimental feeding period (5–6 years). Seed production also increased slowly in response to feeding.
4 No feeding effect on nitrogen and phosphorus concentrations in seeds and over‐wintering parts was found.
5 In most characteristics the high‐altitude populations were less responsive than populations growing at low altitude. In the high‐altitude population reproduction failed repeatedly, suggesting that seed output may be more dependent on abiotic factors than on resource availability in cold environments.
6 Pinguicula villosa and P. vulgaris used the new resources the same summer for increased leaf rosette growth and current reproduction, showing these species to be income breeders, while the third species ( P. alpina ) allocated a larger proportion to storage and future reproduction, characteristic of a capital breeder.     

Length–mass allometry in snakes

Body size and body shape are tightly related to an animal's physiology, ecology and life history, and, as such, play a major role in understanding ecological and evolutionary phenomena. Because organisms have different shapes, only a uniform proxy of size, such as mass, may be suitable for comparisons between taxa. Unfortunately, snake masses are rarely reported in the literature. On the basis of 423 species of snakes in 10 families, we developed clade‐specific equations for the estimation of snake masses from snout–vent lengths and total lengths. We found that snout–vent lengths predict masses better than total lengths. By examining the effects of phylogeny, as well as ecological and life history traits on the relationship between mass and length, we found that viviparous species are heavier than oviparous species, and diurnal species are heavier than nocturnal species. Furthermore, microhabitat preferences profoundly influence body shape: arboreal snakes are lighter than terrestrial snakes, whereas aquatic snakes are heavier than terrestrial snakes of a similar length. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ●● , ●●–●●.     

Reproductive Energetics of Female Mantled Howlers (<Emphasis Type="Italic">Alouatta palliata</Emphasis>)

The energetic costs of reproduction have an important influence on the life histories of female primates. At present, however, the interplay of female reproductive state, food availability, and strategies aimed at maintaining energy balance has been described for only a few species, limiting our ability to understand intra- and interspecific variation in female life histories. We assessed how female mantled howlers (Alouatta palliata) are affected by reproductive seasonality, and whether they alter their behavior to cope with the energetic demands of reproduction. From August 2013 to July 2015 we measured the reproductive state, behavior (1100 h of focal animal observations), and energetic condition (312 urine samples collected for C-peptide analysis) of 7 adult females, and assessed food availability (weekly phenological sampling of 397 food trees). Female behavior did not vary with reproductive state or reproductive seasonality. There were, however, differences in how females responded to variation in food availability according to reproductive state. Cycling and gestating females spent more time feeding than lactating females, and cycling females less time resting than females in other reproductive states, when food was more available. C-peptide concentrations were unaffected by either individual or overall variation in reproductive state, except for cycling females, whose concentrations increased during periods of high food availability. The energetic condition of female mantled howlers is broadly maintained over different stages of reproduction, but is sensitive to variation in food availability.     

Variation in the diet of the viperine snake Natvix mama in relation to prey availability

The diet of the viperine snake was compared with food availability in the Ebro Delta, a wetland largely occupied by rice fields, in 1990 and 1991. Snake selection of prey type and size was studied seasonally and by snake group: males, females and immature snakes. Overall, feeding activity (percentage of individuals with prey and number of prey per stomach) increased with food availability. Diet analysis showed that viperine snakes mainly foraged on the green frog Rana perezi (adults and tadpoles) and the carp Cyprinus earpio. Conversely, viperine snakes rejected the mosquito fish Gambusia holbroki which is the most abundant species in autumn, when Natrix maura has a low feeding activity. Statistical comparisons between viperine snake diet and prey availability showed that males selected small carp, immature snakes selected tadpoles and, in spring, females selected frogs. The selection of small carp by males may reflect a sexual divergence of trophic niche related to sexual size dimorphism, as females are larger than males. As tadpoles are presumably easier to catch than fish, tadpole selection by immature individuals may reflect variance in capture abilities. In spring, the selection of frogs by females overlapped with vitellogenesis, suggesting that females compensate for the cost of reproduction by selecting green frogs, which have a greater biomass and higher energy content than fish. Carps eaten in spring were smaller than in summer. Moreover, in summer viperine snakes selected smaller carp than the available mean size. This divergent tendency between carp size selection and carp size availability reveals how seasonal diet shifts in prey size selection may be a response to an increase in prey size.     

Phenotypic plasticity of life history traits in relation to reproductive strategies in <Emphasis Type="Italic">Boa constrictor occidentalis</Emphasis>

The close connection between reproductive ecology and life history in snakes leads to trade-offs between reproductive and other life-history traits. Optimal energy allocation to growth and reproduction is a key factor to determine life history structure. Therefore, elucidating the relationship between body size variations and reproductive characters is essential for a better understanding of life-history plasticity. The aim of this work was to determine to what extent life-history differs among populations of Boa constrictor occidentalis and to identify possible life-history trade-offs between morphological and reproductive traits. We compared two populations from areas that are separated latitudinally, with different climatic conditions and vegetation landscape structure. Reproductive and morphological data of specimens were recorded. Although populations had a similar mean length of mature snakes, the frequency of some size classes tended to be different. Size at sexual maturity differed between populations for females, generating variations in the proportion of mature individuals. Reproductive threshold and follicular size also varied, but female reproductive frequency was similar between populations. Reproductive frequency of males varied between populations although their body condition was similar. We discussed two major issues: (1) implications of size at sexual maturity for body size and fecundity; (2) trade-offs in reproductive characters.     

Factors affecting fledging weight of Adélie penguin (Pygoscelis adeliae) chicks: a modeling study

An individual-based model is developed to examine mechanisms that potentially underlie the observed constancy in fledging weight (2.8-3.2 kg) of Adélie (Pygoscelis adeliae) penguin chicks, in spite of large variability in the abundance of Antarctic krill (Euphausia superba), the primary food source. The model describes the energetic requirements of the chick, with growth resulting from the difference between assimilated energy and respiration. Parameterizations of these metabolic processes are based upon experimental and field observations. Ingestion of Antarctic krill by the chick is dependent on the frequency of food delivery to the chick by the adults, which is based on measured foraging times. The mass, size, and size frequency distribution of Antarctic krill fed to the chick are specified using empirical data. The energy content of the Antarctic krill provided to the chick is taken to be constant or allowed to vary with size. The simulations show that food availability is most critical in the latter portion of chick development, when growth rates and food demands are high. Low food availability during this time must be compensated by either feeding chicks with larger krill of higher caloric value or by increased assimilation efficiency. Periods when small krill with lower caloric value dominate require more frequent feeding of the chicks in order to attain their observed fledging weight. Thus, although the total food energy given to the chick is the main factor determining chick growth, the distribution of food availability relative to chick size (i.e., different net growth rates) and food quality are also factors influencing the fledging weight of penguin chicks. The simulations provide insight into the compensating effects of food delivery, food quality, and metabolic processes that allow Adélie penguin chicks to reach their observed fledging weight in spite of considerable environmental variability in food supply.     

Capital and income breeding and the evolution of colony founding strategies in ants

Ability to store resources that will be used for reproduction represents a potential life history adaptation because storage permits feeding and reproduction to be decoupled spatially and/or temporally. The two ends of a continuum involve acquiring all resources prior to reproduction (capital breeding) or acquiring all resources during the reproductive period (income breeding). Traditional life history theory examines tradeoffs between costs and benefits of such strategies, but this theory has not been integrated into life history studies of ants, even though founding queens have the analogous strategies of fully claustral (capital breeding) and semi-claustral (income breeding). This study demonstrates that facultatively semi-claustral queens of the seed-harvester ant Pogonomyrmex desertorum exhibit phenotypic plasticity during colony founding because unfed queens produced few, small minims, whereas ad libitum fed queens produced larger, heavier minims and additional brood. Fed queens also lost less mass than unfed queens despite their producing more brood. Overall, foraging provides queens with a suite of benefits that likely offset potential negative effects of foraging risk. Life history studies across a diverse array of taxa show that capital breeding is consistently associated with low availability and/or unpredictability of food, i.e., environmental conditions that favor prepackaging of reproductive resources. Such a broad and consistent pattern suggests that similar factors favored the evolution of fully claustral (capital breeding) colony founding in ants. Overall, these data suggest that ant researchers should revise their conventional view that fully claustral colony founding evolved because it eliminated the need for queens to leave the nest to forage. Instead, colony founding strategies should be examined from the perspective of environmental variation, i.e., availability and predictability of food. I also provide a functional scenario that could explain the evolution of colony founding strategies in ants. Received 16 November 2005; revised 1 March 2006; accepted 29 March 2006.