Testing generalizations about latitudinal variation in reproduction and recruitment patterns with sicyoniid and caridean shrimp species

Summary

Study of latitudinal variation in seasonality of reproduction and recruitment of benthic marine invertebrates is useful in generating and testing hypotheses about causal factors acting on reproduction such as temperature and larval food supply that might be altered by changes in world climate. Analysis of latitudinal variation in reproductive patterns might be made with comparisons (a) among species with a common phylogenetic history from different latitudes and habitats and (b) among phylogenetically different taxa from the same location. Hypotheses on variation of reproductive seasonality with latitude are tested here with results of a study on nine species of caridean and two species of sicyoniid shrimp sampled from a tropical seagrass meadow in Puerto Rico. Breeding condition was determined by the presence or absence of incubated embryos (carideans) and the state of ovarian development in both carideans and sicyoniids. Recruitment was estimated from the percentage of individuals of monthly population samples in the juvenile size classes. Comparison of reproductive patterns among tropical, subtropical, and cool temperate Sicyonia spp. supports the paradigm of continuous reproduction in the tropics with increased restriction of breeding season with an increase in latitude. A greater intensity of breeding effort appears to accompany the shorter breeding period associated with an increase in latitude. At the tropical site most females of all caridean species carried embryos during all months of the year. With the onset of sexual maturity, caridean females produced consecutive broods for the rest of their relatively short (< 6 month) life span. In both sicyoniid and caridean species, recruitment occurred throughout the year but was highly variable, i.e., episodic rather than truly continuous or seasonal. Patterns of recruitment were highly concordant among but not between sicyoniid and caridean species, indicating that different sets of environmental factors controlled recruitment in the two groups. It is suggested that simultaneous study of adult reproduction and larval ecology is necessary to understand patterns of reproduction and recruitment. Coordinated effort on a global scale in studying latitudinal variation in reproduction and recruitment is suggested in order to predict the consequences of climate change on commercially and ecologically important marine invertebrate species.     

Dietary overlap and seasonality in three species of mormoopid bats from a tropical dry forest

Competing hypotheses explaining species’ use of resources have been advanced. Resource limitations in habitat and/or food are factors that affect assemblages of species. These limitations could drive the evolution of morphological and/or behavioural specialization, permitting the coexistence of closely related species through resource partitioning and niche differentiation. Alternatively, when resources are unlimited, fluctuations in resources availability will cause concomitant shifts in resource use regardless of species identity. Here, we used next‐generation sequencing to test these hypotheses and characterize the diversity, overlap and seasonal variation in the diet of three species of insectivorous bats of the genus Pteronotus. We identified 465 prey (MOTUs) in the guano of 192 individuals. Lepidoptera and Diptera represented the most consumed insect orders. Diet of bats exhibited a moderate level of overlap, with the highest value between Pteronotus parnellii and Pteronotus personatus in the wet season. We found higher dietary overlap between species during the same seasons than within any single species across seasons. This suggests that diets of the three species are driven more by prey availability than by any particular predator‐specific characteristic. P. davyi and P. personatus increased their dietary breadth during the dry season, whereas P. parnellii diet was broader and had the highest effective number of prey species in all seasons. This supports the existence of dietary flexibility in generalist bats and dietary niche overlapping among groups of closely related species in highly seasonal ecosystems. Moreover, the abundance and availability of insect prey may drive the diet of insectivores.     

Diet and habitat use of frillneck lizards in a seasonal tropical environment

A population of frillneck lizards, Chlamydosaurus kingii, was monitored by mark-recapture and telemetry over a 2 year period in Kakadu National Park. The aims of the study were to document changes in diet, growth, condition and habitat use between the wet and dry seasons of northern Australia, in light of recent research examining seasonal variation in the physiology of this species. Frillneck lizards feed on a diverse range of invertebrates in both seasons, even though there is a substantial reduction in food avail-ability in the dry season. Harvester termites from the genus Drepanotermes constitute a major component of the diet, and the prevalence of termites in the diet of sedentary foragers in a tropical environment is unusual. Adult male body condition remained relatively stable throughout the year, but females experienced considerable variation. These differences are attributed to different reproductive roles of the sexes. Growth in C. kingii was restricted to the wet season, when food availability was high, and growth was minimal in the dry season when food availability was low. The method used in catching lizards was an important factor in determining seasonal habitat use. Telemetered lizards selected a significantly different distribution of tree species than was randomly available, and they selected significantly larger tree species during the dry season. Lizards spotted along roadsides showed little seasonal variation in the selection of tree species or tree sizes. The results suggest a comprehensive change in the ecology of this species, in response to an annual cycle of low food and moisture availability, followed by a period with few resource restrictions.     

Seasonal influence on reproduction in chimpanzees of gombe national park

Although wild chimpanzees are not seasonal breeders, there are seasonal effects on several aspects of chimpanzee reproduction. I examined the seasonal incidence of anogenital swelling in cyclic, pregnant, and acyclic female chimpanzees in Gombe National Park, May 1975–April 1992, and surveyed important reproductive events to determine whether there is a seasonal effect. I analyzed data by season (wet vs. dry) and seasonal quarter;early dry season = May–July;late dry = August–October;early wet = November–January;late wet = February–April. When data for the 17 years are combined, the percentage of females in each reproductive state remains consistent throughout the year. In a given month, 30–35% of subjects were in the cyclic category, 11–15% were pregnant, and 54–61% were acyclic. Cyclic females showed full swelling more often during the late dry season. Pregnant females exhibited anogenital swelling more often during the late dry and early wet seasons. Acyclic females also exhibited a seasonal effect with more anogenital swelling during the late dry season. There is no seasonal difference in frequency of live births (dry, 20;wet, 23). However, the timing of conception showed a seasonal effect (dry, 32;wet, 16). Consistent with earlier reports, the onset of postpartum cycles is highly seasonal;30 occurred during dry season, 9 during wet season. The occurrence of first full swellings for young females is also concentrated in the late dry season. It appears that the dry season is a time of great change for Gombe chimpanzee reproductive physiology. Previous studies indicated that seasonal changes in food availability play a role in increasing group size during the dry season and social contact between females can enhance cyclicity. Accordingly, I suggest that seasonal changes in diet may play a role, either directly (food content) or indirectly (social contact), to alter reproductive physiology.     

Female investment in offspring size and number shifts seasonally in a lizard with single-egg clutches

The timing of reproduction strongly influences reproductive success in many organisms. For species with extended reproductive seasons, the quality of the environment may change throughout the season in ways that impact offspring survival, and, accordingly, aspects of reproductive strategies may shift to maximize fitness. Life-history theory predicts that if offspring environments deteriorate through the season, females should shift from producing more, smaller offspring early in the season to fewer, higher quality offspring later in the season. We leverage multiple iterations of anole breeding colonies, which control for temperature, moisture, and food availability, to identify seasonal changes in reproduction. These breeding colonies varied only by the capture date of the adult animals from the field. We show that seasonal cohorts exhibit variation in key reproductive traits such as inter-clutch interval, egg size and hatchling size consistent with seasonal shifts in reproductive effort. Overall, reproductive effort was highest early in the season due to a relatively high rate of egg production. Later season cohorts produced fewer, but larger offspring. We infer that these results indicate a strategy for differential allocation of resources through the season. Females maximize offspring quantity when environments are favorable, and maximize offspring quality when environments are poor for those offspring. Our study also highlights that subtle differences in methodology (such as capture date of study animals) may influence the interpretation of results. Researchers interested in reproduction must be conscious of how their organism’s reproductive patterns may shift through the season when designing experiments or comparing results across studies.     

Food and feeding ecology of the rock fowl Picatthartes oreas in Old Oyo National Park, Nigeria

The rock fowl is an endangered species and its food and feeding ecology was studied in the forest zone of Old Oyo National Park, Nigeria. The methods used were direct observation, and fragmentation analysis of faecal and crop content of samples collected during both the wet and dry seasons. The results showed that rock fowl feed on a wide range of species of insects, fruits and flower buds. In the wet season, animal resources represented 54 and 62% of the adult and chick diet, respectively, whereas in the dry season, animal food resources represented about 60% of both adult and the chick diets. There was a significant difference (P < 0.05) in the food composition of the birds between the dry and wet seasons. There was also a significant (P < 0.05) difference in food preference between adults and chicks. Food sharing was not common, although it was observed between rock fowl cockerels and hens. Food search and selection indices were directly related to season and food availability. It was concluded that food scarcity may not be a serious contributory factor in the threat to the rock fowl.     

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 Polyspecific Associations Among Callimico goeldii, Saguinus labiatus, and S. fuscicollis in Acre, Brazil

Polyspecific associations (PSA) occur when 2 or more species maintain proximity or coordinate activities. PSA may provide ecological benefits similar to those of monospecific groups, i.e., protection against predation and improved foraging efficiency, but may also impart costs, such as feeding competition. I studied 3 New World Callitrichidae—Callimico goeldii, Saguinus fuscicollis, and S. labiatus—in northwestern Brazil over 18 mo between April 1999 and August 2003, during which single primary study groups of C. goeldii, S. labiatus, and S. fuscicollis consistently associated with one another. I compared patterns of PSA participation to variation in plant diets during wet and dry seasons. All 3 species associated an average 61% of observation time, but with significant seasonal variation in PSA. During the dry season, April–September, PSA occurred significantly less frequently than during the wet season, October–March (37% vs. 88%). The variation in PSA corresponded with seasonal shifts in plant food diets, resulting in less dietary overlap among all 3 species during the dry season, particularly between Callimico goeldii and Saguinus labiatus. Dietary richness, diversity, and evenness were also lower in the dry compared to the wet season for each species. The results suggest a link between PSA participation and diet among the taxa; foraging-related costs or feeding competition may constrain PSA during the dry season.     

Maternal investment in reproduction and its consequences in leatherback turtles

Maternal investment in reproduction by oviparous non-avian reptiles is usually limited to pre-ovipositional allocations to the number and size of eggs and clutches, thus making these species good subjects for testing hypotheses of reproductive optimality models. Because leatherback turtles (Dermochelys coriacea) stand out among oviparous amniotes by having the highest clutch frequency and producing the largest mass of eggs per reproductive season, we quantified maternal investment of 146 female leatherbacks over four nesting seasons (2001–2004) and found high inter- and intra-female variation in several reproductive characteristics. Estimated clutch frequency [coefficient of variation (CV) = 31%] and clutch size (CV = 26%) varied more among females than did egg mass (CV = 9%) and hatchling mass (CV = 7%). Moreover, clutch size had an approximately threefold higher effect on clutch mass than did egg mass. These results generally support predictions of reproductive optimality models in which species that lay several, large clutches per reproductive season should exhibit low variation in egg size and instead maximize egg number (clutch frequency and/or size). The number of hatchlings emerging per nest was positively correlated with clutch size, but fraction of eggs in a clutch yielding hatchlings (emergence success) was not correlated with clutch size and varied highly among females. In addition, seasonal fecundity and seasonal hatchling production increased with the frequency and the size of clutches (in order of effect size). Our results demonstrate that female leatherbacks exhibit high phenotypic variation in reproductive traits, possibly in response to environmental variability and/or resulting from genotypic variability within the population. Furthermore, high seasonal and lifetime fecundity of leatherbacks probably reflect compensation for high and unpredictable mortality during early life history stages in this species.     

Seasonal differences in egg size in three species of crabs from a tropical upwelling zone

Egg size and offspring size are fundamentally important aspects of the life histories of all animals. However the impact of environmental conditions on intraspecific variation in egg size of marine invertebrates is poorly documented. Here we followed three species of intertidal crabs Xanthodius sternberghii, Petrolisthes armatus and Clibanarius albidigitus to understand how seasonal environmental variation in temperature and salinity associated with seasonal upwelling impacts egg size. Ovigerous females of both P. armatus and C. albidigitus were found year round, while X. sternberghii has a limited reproductive season, with ovigerous females found only between November and February. In all three species more than half of the variation in egg size was attributable to variation among broods from different females. Eggs collected during the dry, upwelling season were significantly larger than those collected during the wet, non-upwelling season. Multiple regression analysis showed that average egg size from each brood was significantly negatively correlated with temperature for all three species. Egg size was also negatively correlated with salinity in P. armatus when we controlled for temperature. Overall these results support the idea that changes in environmental temperature caused by seasonal upwelling play a significant role in generating seasonal differences in egg size.     

It takes two: Seasonal variation in sexually dimorphic weaponry results from divergent changes in males and females

Sexually dimorphic weaponry often results from intrasexual selection, and weapon size can vary seasonally when costs of bearing the weapon exceed the benefits outside of the reproductive season. Weapons can also be favored in competition over nonreproductive resources such as food or shelter, and if such nonreproductive competition occurs year‐round, weapons may be less likely to vary seasonally. In snapping shrimp (Alpheus angulosus), both sexes have an enlarged snapping claw (a potentially deadly weapon), and males of many species have larger claws than females, although females are more aggressive. This contrasting sexual dimorphism (larger weaponry in males, higher aggression in females) raises the question of whether weaponry and aggression are favored by the same mechanisms in males and females. We used field data to determine whether either sex shows seasonal variation in claw size such as described above. We found sexual dimorphism increased during the reproductive season due to opposing changes in both male and female claw size. Males had larger claws during the reproductive season than during the nonreproductive season, a pattern consistent with sexual selection. Females, however, had larger claws during the nonreproductive season than during the reproductive season—a previously unknown pattern of variation in weapon size. The observed changes in female weapon size suggest a trade‐off between claw growth and reproduction in the reproductive season, with investment in claw growth primarily in the nonreproductive season. Sexually dimorphic weaponry in snapping shrimp, then, varies seasonally due to sex differences in seasonal patterns of investment in claw growth, suggesting claws may be advantageous for both sexes but in different contexts. Thus, understanding sexual dimorphisms through the lens of one sex yields an incomplete understanding of the factors favoring their evolution.     

Between‐individual variation drives the seasonal dynamics in the trophic niche of a Neotropical marsupial

The dynamics of population niches result from the variation in resource use within individuals and also from the variation between individuals. The prevalence of one mechanism or the other leads to competing hypotheses about the major mechanisms underlying the empirical observations of the contraction/expansion dynamics of the trophic niche in natural populations. In this study, we investigated how within‐ and between‐individual variation in resource use shapes the food niche dynamics of the woolly mouse opossum, Marmosa paraguayana (Didelphimorphia: Didelphidae), in a remnant of the highly seasonal Cerrado in south‐eastern Brazil. To do so, we analysed the faecal samples of live‐trapped individuals to determine their diets within the wet and dry seasons. In addition to a seasonal shift in the composition of the diet, the population trophic niche was significantly wider during the dry season than the wet season. This expansion resulted from larger between‐individual variation in the dry season that was not related to sex preferences, whereas the individual niche widths did not significantly increase from the wet to the dry seasons. Our findings add to the growing list of animal populations that show individual‐level variation in resource use. Furthermore, these results represent a pattern of individual‐level response to seasonal changes that is different from patterns reported for other organisms. We suggest that a pathway to build more realistic foraging models and produce more accurate predictions on population and community dynamics is to consider between‐individual variation and short‐term niche dynamics.     

Intra‐ and inter‐individual variation show distinct trends as drivers of seasonal changes in the resource use of a neotropical marsupial

Individual specialization can influence important ecological and evolutionary traits and both inter‐ and intra‐individual variation in resource use can drive niche shifts in natural populations. We evaluated the predominance of these two factors for determining seasonal differences in the trophic niche of the didelphid marsupial Gracilinanus agilis (Burmeister, 1854) in the highly seasonal Brazilian savanna. In the three sampled sites, the population of G. agilis increased its dietary niche width in the warm–wet season, when food resources are more abundant, and there were no differences between sexes and no interaction between season and sex. However, the evaluation of intra‐individual variation indicated that females reduce the number of items consumed during the warm–wet season, whereas males show no seasonal differences. Inter‐individual variation nonetheless followed the overall population pattern because both sexes increased their spread with respect to food‐item consumption in the warm–wet season. Additionally, we found positive relationships between body length and diet only in the warm–wet season, when larger animals fed more on invertebrates and less on fruits than the small ones. Our results show a previously unknown pattern for mammals, in which the trophic niche is wider during the high‐resource season as a result of inter‐individual variation along the body‐size axis. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 737–747.     

Interannual Variation in Nut Abundance Is Related to Agonistic Interactions of Foraging Female Japanese Macaques (Macaca fuscata)

The importance of dominance status to foraging and ultimately survival or reproductive success in wild primates is known; however, few studies have addressed these variables simultaneously. We investigated foraging and social behavior among 17 adult female Japanese macaques (Macaca fuscata) on Kinkazan Island, northern Japan, from September to November in 2 consecutive years (2004 and 2005) to determine whether interannual variation in food availability was related to variation in agonistic interactions over food resources and the feeding behavior of individuals of different dominance rank. We compared energy obtained with daily energy requirements and also examined the effect of variation in feeding behavior on female survival and reproductive success. Fruiting conditions differed considerably between the 2 yr: of four nut-producing species, the nuts of only Torreya nucifera fruited in 2004, whereas all four species, particularly Fagus crenata, produced nuts in abundance in 2005. The abundance and average crown size of trees of Torreya nucifera were smaller than those of Fagus crenata, and there was a higher frequency of agonistic interactions during 2004, when dominant, but not subordinate, individuals were able to satisfy daily energy requirements from nut feeding alone through longer nut feeding bouts. In contrast, all macaques, regardless of their dominance rank, were able to satisfy their energy requirements by feeding on nuts in 2005. Subordinate macaques appeared to counter their disadvantage in 2004 by moving and searching for food more and maintaining larger interindividual distances. Several lower-ranking females died during the food-scarce season of 2004, and only one dominant female gave birth the following birth season. In contrast, none of the adult females died during the food-scarce season of 2005, and 12 females gave birth the following birth season. These findings suggest that an interaction between dominance rank and interannual variation in food availability are related to macaque behavior, survival, and reproduction.     

Habitat preferences,seasonal abundance and diets of rodents in Alage,Southern Ethiopia

To understand habitat preferences, seasonal abundance and diets of rodents in wet and dry season surveys were conducted in Alage, Southern Ethiopia. Sherman and snap traps were used to capture rodents from the four habitats: bushland, Acacia woodland, maize and wheat farmlands. A total of 3312 trap nights, from the four trapping habitats, yielded 776 individuals that represented 11 species of rodents. The distribution of rodents varied between habitats and seasons. Wet season rodent abundance was 52.3% while in the dry season it was 47.7%. Seasonal differences in species abundance were insignificant. Bushland habitat had high wet and dry season abundances with 137 and 211 individuals, respectively. Abundance was low in maize farm (57 individuals) in the wet season and wheat farm (10 individuals) in the dry season. Stomach content composition analysis of snap‐trapped rodents from different habitats showed differences between species and across seasons. Six rodent species were recorded as pests on the farmlands in this study area. In conclusion, variation in habitat preferences and diet of rodents in different habitats and across seasons might be due to the role of ground cover and food sources.     

Demography, range use, and behavior in black lemurs (Eulemur macaco macaco) at Ampasikely, northwest Madagascar

We studied a black lemur population over a 2-year period (1992-1993) and 8 years later (2000) in a 50-ha secondary forest in northwest Madagascar. All of the animals were marked to investigate population dynamics and seasonal variation in ranging and behavior, and new data on black lemurs were obtained. Our data on demographic characteristics were expanded to include other forest sites and contrasted with those collected in other Eulemur macaco macaco field studies, in relation to human activity and the presence of introduced and cultivated plant species. Density is affected by deforestation and hunting. Group size and home range depend on the composition of the forest and probably food patches. Sex ratio at birth varies according to the number of females per group, a result that fits the local resource competition model. Groups are multimale-multifemale, and adult females form the core of the groups. Reproductive parameters indicate sharply defined seasonal breeding, a high female reproductive rate, and birth synchrony. Changes in group composition reveal male and female juvenile dispersal, male transfer between groups at the time of mating, and adult female transfer and group fission when groups exceed a critical size. At mating and birth, intergroup agonistic encounters occurred at home-range boundaries, and larger groups were dominant over smaller groups. Patterns of intragroup interactions suggest that males compete for access to groups of females during the mating season, and that females may compete for food resources during the birth season. Our study also reports female social dominance and lack of sexual weight dimorphism in this species.     

Resource tracking in aphids: programmed reproductive strategies anticipate seasonal trends in habitat quality

Most aphids show cyclical parthenogenesis, have short generation times and complete several generations each season. Two hypotheses have been proposed to account for the adaptive seasonal trends observed in the reproductive strategies of aphids. Firstly, individuals of each generation modify their reproductive strategy in direct response to the conditions they experience during their development. Secondly, the reproductive strategies of the different generations are to a large extent programmed and anticipate seasonal trends in habitat quality. These hypotheses were tested by rearing individuals of three generations of the host-alternating willow-carrot aphid, Cavariella aegopodii, on both willow and carrot. This revealed that the way this aphid allocates resources to gonads and lipid reserves is independent of an aphid's weight and the host plant on which it is reared. In addition each generation shows a specific relationship between offspring size and adult size, which tends to keep the absolute investment in individual offspring relatively constant from generation to generation, inspite of the big differences in adult size between generations. That is, through programmed allometric engineering aphids anticipate the predictable seasonal trends in habitat quality and so more closely track their resources, investing relatively more in gonads when food quality is high and relatively more in lipoidal reserves when food quality is poor. Received: 25 August 1997 / Accepted: 19 October 1997     

FACTORS DETERMINING A CLUTCH SIZE REDUCTION IN CALIFORNIA GULLS (LARUS CALIFORNICUS): A MULTI-HYPOTHESIS APPROACH

In the thirty-five years since David Lack first highlighted the importance of clutch size, a large number of hypotheses have been proposed relating clutch size variation to various environmental and demographic factors. Despite a great deal of both empirical and theoretical work on clutch size, there has been very little effort to test many of the competing hypotheses in explaining a clutch size difference between two populations of the same species. I have taken the latter approach in an effort to explain a clutch size reduction in the California Gull (Larus californicus) population at Mono Lake, California. I compared the breeding biologies of the gulls at Mono Lake and at Great Salt Lake, Utah, collecting data for three breeding seasons at Mono Lake and one breeding season at Great Salt Lake. These data included measurements of the conditions of 60 adults, growth and mortality measurements for approximately 900 chicks, 4450 nest-hours of parental care observations, and the results of egg-removal experiments on 40 females. I tested seven hypotheses to explain the clutch size reduction: age structure, egg predation, bet-hedging, effort reallocation, most productive brood size, parental mortality, and pre-egg food limitation. Each of these hypotheses is described in detail in the introduction. The pre-egg food limitation hypothesis is best able to explain the clutch size reduction at Mono Lake, although the egg-removal experiments show that the resource limitation is relative and not absolute. Clutch size variation at each site need not be viewed as the result of fine-scaled evolutionary adjustment, although the general clutch size decision machinery is presumably molded by selection. Future research must focus on the details of this clutch size decision machinery and its application to the concept of reproductive effort.     

Life-history evolution in Anodonta piscinalis (Mollusca,Pelecypoda)

Summary The correlations between certain life-history parameters (reproductive effort, reproductive life-span, age of first reproduction, general growth index, variation in juvenile survival, availability of resources) were studied in 13 populations of the mussel Anodonta piscinalis in south-western Finland in 1975 and 1976Reproductive life-span correlated positively (r _s=0,823, P<0.001) with variation in juvenile survival. The average availability of resources correlated negatively both with the reproductive life-span (r _s=-0.841, P<0.001 after the variation by juvenile survival had been deleted) and variation in juvenile survival (r _s=-0.676, P<0.05).The reproductive effort for female mussels at each site was computed by comparing body weight of reproductive females with body weights of non-reproductive individuals. Availability of resources was much higher in 1976 than in 1975. Consequently, the reproductive effort, an index of the strain of reproduction, was higher in 1975 than in 1976. In 1975 there was a significant correlation between reproductive effort and the length of the reproductive life-span (-0.727, -0.806) and also with the reproductive effort and the variation in juvenile survival (-0.718, -0.758) in females of the length of 60 mm and 70 mm respectively. In 1976, when availability of resources was better, such correlations were not found.Spatial and temporal change in the intake of resources complicates applicability of the principle of resource allocation in the theory of life-history evolution. Studying the mere allocation is not enough if the intake of resources varies in the groups studied. The ratio ovary weight/body weight is a dubious measure of reproductive effort in comparative studies when the input of resources can vary, and this possibility can be ruled out only exceptionally.Correlation between growth and reproductive effort was positive, obviously because both are important components in creating high reproductive capacity. In 1975 reproductive effort increased with size (age). Change in reproductive effort correlated with reproductive life-span (r _s=-0.633, P<0.05).The following parameters occurred together: short reproductive life-span, low age of first reproduction, high reproductive effort, rapid growth and high clutch size. They were realized at sites where the availability of resources was good and variation in juvenile survival was low-i.e. the environment was stable. The results conflict with the prediction of the theory of r and K-selection.     

Effects of food restriction across stages of juvenile and early adult development on body weight,survival and adult life history

Organisms have to allocate limited resources among multiple life‐history traits, which can result in physiological trade‐offs, and variation in environmental conditions experienced during ontogeny can influence reproduction later in life. Food restriction may lead to an adaptive reallocation of the limited resources among traits as a phenotypically plastic adjustment, or it can act as an overall constraint with detrimental effects throughout reproductive life. In this study, we investigated experimentally the effects of food restriction during different stages of the juvenile and early adult development on body weight, survival and reproductive success in females and males of the European earwig Forficula auricularia. Individuals either received limited or unlimited access to food across three different stages of development (fully crossed) allowing us to identify sensitive periods during development and to test both additive and interactive effects of food limitation across stages on development and reproduction. Food restriction during the early and late juvenile stage had additive negative effects on juvenile survival and adult body weight. With regard to reproductive success of females which produce up to two clutches in their lifetime, restriction specifically in the late juvenile stage led to smaller first and second clutch size, lower probability of second clutch production and reduced hatching success in the second clutch. Reproductive success of females was not significantly affected when their male mates experienced food restriction during their development. Our findings in general support the ‘silver‐spoon’ hypothesis in that food restriction during juvenile development poses constraints on development and reproduction throughout life.