Prolonged Breeding Season Research Articles

Precocious maturation and semi-multivoltine lifecycle in a subtropical grass lizard, Takydromus toyamai

Abstract There are many short-lived animals, but those displaying a lifecycle with more than one generation per year (multivoltine lifecycle) are rare among terrestrial vertebrates. The multivoltine lifecycle requires rapid growth and maturation and a long active season. Thus, small lizards in humid tropical or subtropical areas are candidates for multivoltine lifecycles. To test this prediction, we conducted a capture-mark-recapture study of a subtropical grass lizard, Takydromus toyamai, endemic to Miyako Islands, Japan. Juveniles grew very quickly, averaging 0.3 mm/day in the warm season, and attained sexual maturity at 2.5 months post-hatching. The breeding season was very long, and hatchlings emerged from May to November. The prolonged breeding season and rapid growth to maturity allowed some individuals to produce a second generation in their first year. Estimates of hatching date from growth rates indicated that many females that hatched in May–June became gravid 76–120 days after hatching and 122–165 days after oviposition of the eggs from which they hatched. Analyses of juvenile survivorship and month of hatching suggest that nearly half of breeding adults were members of multivoltine generations, although the 2 generations were not discrete. The species is short-lived, with only 16% of individuals surviving beyond 12 months, and few individuals reproduced in a second year. We refer to this condition as a “semi-multivoltine lifecycle.” Individuals that hatch late in the season defer reproduction until the following year and become founders of the next season’s cohort. This putative advantage of late-hatching individuals may have driven the evolution of this lifecycle.

Concentrations of zearalenone and its metabolites in female wild boars from woodlands and farmlands

As a valuable food base and safe shelter, large agricultural fields create favourable living conditions for wild boars for most of the year. The occurrence of mould in these fields, causing hormonal disturbances, may lead to a lower age of sexual maturity and a prolonged breeding season, and therefore, the population growth in farmlands can be markedly higher than that in extensive woodlands. This study was initiated because of reproductive cycle disturbances in wild boar populations, which were presumably linked with habitat and food types, especially rotten maize. To determine if the major sources of zearalenone (ZEN) in female wild boars are maize cobs infected with mycotoxins, we compared the concentrations of ZEN and its metabolites in organs, tissues and body fluids of wild boars hunted in extensive maize fields and in extensive woodlands where no large maize fields were located within a distance of several km. Samples of blood, bile, liver, kidneys, muscles, urine, stomach and colon contents as well as ovaries from young female wild boars (40–60 kg) were collected in 2011–2014 and prepared for liquid chromatography tandem mass spectrometry (HPLC-MS/MS). The results showed that ZEN was present in most of the samples, from both farmlands and woodlands, but its concentration within individual types of the analysed body fluids or tissues differed depending mainly on habitat type. In nearly all the analysed cases, higher concentrations of ZEN and its derivatives were detected in the samples collected from wild boars in farmlands, suggesting that wild boars living and feeding in extensive maize fields take in markedly higher amounts of mycoestrogens.

Reproductive Biology and Sexual Dimorphism in Bokermannohyla alvarengai (Anura: Hylidae)

The general pattern of sexual size dimorphism (SSD) in amphibians is characterized by females being larger than males. However, the reverse pattern, a male-biased SSD, may be widespread within some particular groups, as seems to be the case for the Neotropical treefrog genus Bokermannohyla. Although SSD is commonly associated with factors influential to breeding success, the evolutionary determinants of SSD remain controversial. Thus, the study of SSD, particularly on lesser-known species, remains critical to advance our understanding of the evolution of body size and other traits associated with the reproductive biology of amphibians. Herein, we examined the occurrence of sexual dimorphism in body size and other morphometric attributes in Bokermannohyla alvarengai and provided a detailed account of its reproductive biology. This species is endemic to a threatened habitat, occurs at low densities, and has a poorly documented natural history. We found that, at maturity, males of B. alvarengai were larger than females, with hypertrophied forelimbs and larger prepollex spines. This set of features, common to other Bokermannohyla species, is often attributed to the occurrence of male territorial defense and aggression between males. We found that B. alvarengai has a prolonged breeding season that extends from the middle of the dry season to the middle of the rainy season. Adult males did not form breeding aggregations and seemed to establish and defend territories; these males often had skin scars indicative of male–male combat. However, alternative interpretations for differences in body size and secondary sexual characters cannot be ruled out and are discussed.

Unexpected reproductive fidelity in a polygynous frog.

Polygynous mating systems with group fidelity are a common animal organization, typically consisting of multiple females in a mated group with a single male for an extended period (sometimes referred to as harem polygyny). Single-male polygyny with reproductive fidelity occurs in invertebrates, bony fishes, and some tetrapods, such as lizards, mammals, and birds. In amphibians, reproductive fidelity in polygynous groups is not fully demonstrated. Combining data on larval development, molecular paternity assignment, and in situ behavioral observations, we reveal high fidelity during a prolonged breeding season in a Neotropical polygynous frog. Males dominate scarce breeding sites, guarding offspring, and mating exclusively with multiple females that exhibit dominance rank. This system likely evolved in response to intense competition for breeding sites and intrasexual competition for mates.

Feeding behaviour and reproductive biology of the shrimp scad Alepes djedaba(Forsskal, 1775) off Cochin coast, Kerala, south India

Food and feeding habits, sex ratio, spawning behaviour, size at first maturity, fecundity and ova diameter of the shrimp scad Alepes djedaba (Forsskal, 1775) exploited off Cochin coast, Kerala are presented in this study. A. djedabat is a pelagic carnivore, with a preference for fishes. Low gastrosomatic index (GaSI) values and very low feeding intensity during spawning season indicated poor feeding behaviour during the period. The sex ratio did not deviate from the expected 1:1 ratio. Size at first maturity was estimated to be193 mm for male and 174 mm for female. Monthly gonadosomatic index (GSI) values, monthly distribution of gonadal maturation stages and ova diameter revealed that the species had a prolonged breeding season from June to September with a peak in July. Estimated absolute fecundity was 59,744 to 3,30,190 with an average of 1,94,965 eggs.

Reproductive behavior of White-tailed Kites (Elanus leucurus) in the Pampas of Argentina

The White-tailed Kite (Elanus leucurus) is a raptor that has been less studied in the Neotropics than in the Nearctic region, especially in relation to its reproductive behavior. In this study, we report information about the phenology and activity patterns of this raptor at the Pampas of Argentina. We found that White-tailed Kites have a prolonged breeding season, from October to May. Time-activity budgets of mating pairs indicated a pronounced division of roles in parental care between sexes. Females devoted most of their time to nest construction, incubation and chick care (80% of total time) and males to food provisioning and vigilance (70% of total time). We registered 11 cases of prey transfer from the male to the female. In four cases the transfer occurred in flight and in the remaining seven cases while individuals were perched. Our results agree with general patterns on breeding behavior of White-tailed Kites from North America, suggesting a consistent behavioral pattern throughout the species’ distribution.

Biología reproductiva de <i>Boana pulchella</i> y <i>Boana punctata</i> (Anura: Hylidae) en poblaciones simpátricas de humedales templados

Boana pulchella habita principalmente climas templados y B. punctata principalmente climas tropicales, lo que permitiría suponer la presencia de estrategias reproductivas diferentes, aún en la región en la que sus poblaciones son simpátricas. En el presente estudio se analizaron y compararon los ciclos reproductivos, parámetros reproductivos y desarrollo de cuerpos grasos (CG) de Boana pulchella y B. punctata en humedales templados del río Paraná Medio. Boana pulchella presentó óvulos maduros de marzo a diciembre. En machos no hubo variación del volumen testicular a lo largo del año y el mayor desarrollo de CG de los machos se observó en invierno. Esta especie presentó un patrón reproductivo continuo. La vitelogénesis de B. punctata se inició en enero, alcanzando el mayor desarrollo ovárico en febrero (verano) y decreciendo hacia mayo (otoño). Los machos presentaron crecimiento testicular en verano, decreciendo hacia otoño y los CG presentaron su máximo desarrollo en enero para ambos sexos. Esta especie mostró un patrón reproductivo continuo. Ambas especies presentaron dimorfismo sexual con hembras que poseen una relación proporcional entre la talla y la inversión reproductiva. Boana pulchella presentó un mayor esfuerzo reproductivo (ER = 20,48 ± 12,9) y factor de tamaño ovárico (FTO = 25,73) que B. punctata (ER = 10,06 ± 4,45; FTO = 8,99). También se encontraron diferencias interespecíficas en la masa ovárica, complemento ovárico y volúmen testicular, siendo estas variables proporcionalmente mayores en B. pulchella. Las diferencias observadas en las poblaciones simpátricas podrían relacionarse con el desarrollo de estrategias reproductivas bajo diferentes presiones evolutivas.Material suplementario: https://doi.org/10.15446/caldasia.v41n2.80604

Seasonal testosterone and corticosterone patterns in relation to body condition and reproduction in a subtropical pitviper, Sistrurus miliarius

Seasonal constraints on the timing and intensity of reproductive events shape observed variation in life history strategies across latitudes. Selection acts on the endocrine mechanisms that underlie reproductive investment. It is therefore important to examine the seasonal relationship between hormones and reproduction in geographically and phylogenetically diverse taxa. Snakes have proven to be a valuable model in investigations of seasonal hormone production and behavior in field-active vertebrates, but most research has focused on temperate populations from highly seasonal environments. To reduce this bias, we provide a description of the seasonal relationships among testosterone, corticosterone, body condition, and reproductive behavior in a subtropical population of Pygmy Rattlesnakes, Sistrurus miliarius. In central Florida, Sistrurus miliarius exhibits a prolonged breeding season (September-January) compared to most temperate zone snakes. Despite the extended breeding season, the pattern of testosterone in the population was highly seasonal and very similar to temperate pitvipers with a shorter mating season. Testosterone declined steadily through the mating season, but males sampled while engaging in mating behaviors had higher testosterone compared to solitary males throughout the mating season. Testosterone was negatively related to corticosterone throughout the breeding season and during times of year when the gonads were presumed to be quiescent and no mating behavior was observed. Testosterone was positively related to individual body condition both within and outside of the breeding season. A review of the literature reveals no consistent pattern regarding the relationship between corticosterone and testosterone in snakes, but suggests that the condition-dependence of steroid production may be consistent across snake taxa.

Corticosterone profiles in northern cardinals (Cardinalis cardinalis): Do levels vary through life history stages?

As animals move through life history stages, energy requirements for each stage will vary. Both daily and annual variation in the glucocoriticoid hormones (specifically corticosterone, or CORT, in birds) helps provide the variable energy needed through life history stages. In many bird species, CORT is higher in the breeding season when energy demands can be quite high and is often lower in the non-breeding season. Additionally, CORT has a role to play in the response to stressful stimuli and the level to which CORT is elevated following stressful events can vary through the annual cycle as well. Here we report on baseline and stress-induced CORT levels in both sexes of northern cardinals, Cardinalis cardinalis, a non-migrating, year-round territorial species across life history stages. Corticosterone is overall higher in the non-breeding season than the breeding season in both sexes. Males tend to have higher levels of stress-induced CORT than females, although the observed patterns are complex. Our findings differ from one of the more common profile reported in songbirds where breeding season CORT tends to be higher than non-breeding levels. A strong influence may be the prolonged breeding season seen in cardinals; lower levels of CORT during breeding may guard against adverse maternal effects, interruptions in breeding behaviors, or egg production. Additional investigation of species with similar ecologies to northern cardinals, and more populations of cardinals, may show that annual glucocorticoid profiles are more labile than previously appreciated.

Assessment of Maturity, Reproduction and Reproductive Potentials of Torpedo Scad, Megalaspis cordyla (Linnaeus, 1758) from Northern Arabian Sea Coast of Pakistan

Port landing specimens of torpedo scad, Megalaspis cordyla were collected at monthly intervals from August 2013 to June 2014 from the northern Arabian Sea coast of Pakistan. The life history characteristics revealed that torpedo scad has a prolonged breeding season which occurred with two peaks: from May to June and from November to February. The spawning seasonality was also validated with microscopic gonad examination.The highest GSI value was noted in May and January whereas the lowest in November was recorded for both sexes. The age at which individuals of both sexes become 50% mature (t50) was estimated as 2.44 year. Life span (tmax) calculated as 3.96 years for male and females. The size of 270 and 265 mm at which 50% individuals attained sexual maturity (L50) was determined for males and females respectively. The reproductive potential (fecundity)was made from ten ripe females ranged from 29–43.8 cm TL and weighing 220–540 g of IV–V developmental stage was enumerated as 32306–236677 eggs (CV = 2.135) with an average number of eggs 86544 counted per ripe female/season. This study contains fundamental data of an important fish species in the northern Arabian Sea coast of Pakistan. It provides vital information to the fisheries managers for implementation on sustainable use of the resource during spawning season.

A 4‐year study of the proportional distribution of male reproductive organ abnormalities in cattle slaughtered at Nyagatare abattoir, Eastern Rwanda

Male reproductive performance has more impact on overall herd productivity than in the female. In order to assess herd productivity in cattle in Nyagatare, Eastern Rwanda, the proportional distribution of male reproductive organ abnormalities was investigated in 3087 bulls slaughtered over a 4‐year period. The aim of the study was to investigate the proportional distribution of male reproductive organ abnormalities in exotic and indigenous bulls slaughtered over a 4‐year period at Nyagatare abattoir in Eastern Rwanda. Positioning of the testicles was observed and recorded as the animals were assembled before slaughter. After slaughter, the internal and external reproductive organs of all bulls were removed, labelled and analysed for pathology. Significantly more indigenous (79.01%) than exotic (20.99%) animals were slaughtered (P < 0.05; N = 3 087). Overall occurrence of abnormalities was significantly higher in exotic (20.83%) than in indigenous (10.33%) animals (P < 0.05). Overall, abnormal location of testicles was the most common abnormality (4.08%) followed by abnormal prepuce and penis (2.33%), orchitis (1.94%), enlarged vesicular gland (0.91%), scrotal hernia (0.87%), unilateral cryptorchidism (0.81%), testicular hypoplasia (0.81%) and hydrocoele (0.78%). Abnormal location of testicles, abnormal prepuce and penis, orchitis, testicular hypoplasia and enlarged vesicular glands had significantly higher prevalence in exotic animals than in indigenous animals (P < 0.05). There was no significant difference in the prevalence of unilateral cryptorchidism, hydrocoele and scrotal hernia between the exotic and indigenous breeds. The encountered reproductive abnormalities result in poor herd fertility manifesting as low first‐service conception rates, prolonged breeding seasons and reduced weaning weights accompanied by inevitable financial losses in beef production. The observed high proportion of male reproductive abnormalities in exotic breeds might offset the professed benefits from introduction of these exotic breeds with the aim of improving productivity.

BEHAVIORAL TYPES AND SYNDROMES IN THE NEOTROPICAL PASSERINE BLUE-BLACK GRASSQUIT (Volatinia jacarina)

Recent studies focusing on animal personality have been limited to model species found mainly in temperate regions. Selection pressures upon tropical species differ markedly from those of temperate regions ( e.g., higher predation, prolonged breeding seasons) and may influence the evolution of behavioral syndromes. We investigated animal personality using a Neotropical bird model Volatinia jacarina and tested for the presence of behavioral types and a context-general behavioral syndrome. Birds were captured in the field, held in captivity and tested for three different behaviors: feeding, exploration and sexual receptivity of females within two contextual conditions. Birds showed different behavioral types for exploration behavior, but not for feeding behavior. Besides, birds showed no context-general syndrome. We conclude that the blue-black grassquit does not follow any model predicting a long-term association between different behaviors, such as genetic models predicting syndromes.

Sperm Mass Longevity and Sperm Storage in the Female Reproductive Tract ofPlethodon shermani(Amphibia: Plethodontidae)

Abstract: In salamanders in the seven families composing the Salamandroidea, sperm storage allows a female to obtain male sperm months before oviposition. This study reveals the ability of captive female Red-legged Salamanders, Plethodon shermani (Plethodontidae), to store and retain viable sperm for long periods of time. By staging male–female courtship trials, we found that a female’s retention of the male sperm mass is visible in her cloaca for up to 4 d (X = 2.8 d). Given the prolonged breeding season exhibited by this species (>10 wk), it is unlikely that the sperm mass functions efficiently to prevent female remating in that season. In addition, oviposition and egg-rearing in the laboratory revealed that P. shermani females can store viable sperm in their sperm storage organs (spermathecae) for ≥9 mo. Histology and microscopy showed that a subset of females even retained sperm in their spermathecae after oviposition, but significantly less of their lumina were occupied by sperm compared with the...

Reproductive seasonality of Geophagus steindachneri Eigenmann &amp; Hildebrand, 1922 (Perciformes: Cichlidae) in a tropical mountain river

Reproductive seasonality in tropical freshwater fishes is strongly influenced by rainfall. In lowlands, floods spill laterally to floodplains and fishes usually breed during the flooding season. In mountain rivers, floods are sudden and flush out aquatic organisms. Fishes in mountain rivers usually breed during dry seasons, what has been hypothesized as a strategy to reduce mortality due to strong floods. If that is the case, mouth-brooding fishes should suffer less from strong floods and should have more prolonged breeding seasons in mountain rivers. Here we investigated the breeding activity of a mouth-brooding cichlid (Geophagus steindachneri) in a mountain river in Colombia using three kinds of evidence: monthly variation of gonad weight, macroscopic and histological observations of the gonads, and occurrence of mouth-brooding females. Analysis was made on adults captured monthly throughout a year. The results indicate that G. steindachneri breeds during the dry season in the mountain river studied. Female mouth brooding was related with a halt in the maturation of their ovaries. Other factors than the flushing-out effect of floods on offspring may be determining dry-season breeding of fishes in tropical mountain rivers.

Predator-induced renesting and reproductive effort in indigo buntings: more work for less pay?

Renesting after nest predation is ultimately an adaptive response to increase productivity in birds. However, renesting also increases reproductive effort to replace lost clutches. We investigated the consequences of this increased reproductive effort by determining whether renesting in female indigo buntings (Passerina cyanea) is associated with a decline in body condition (size-corrected mass) and haematocrit and an increase in stress hormones and whether renesting or maternal body condition is associated with a decline in productivity (clutch size, nestling body condition). Next, because a consequence of multiple renesting attempts is a prolonged breeding season and later timing, we predicted that a population of post-breeding females and juveniles would have lower body condition in fragmented forest than in contiguous forest owing to higher nest predation and frequency of renesting. Both forest types were settled by females of similar condition. Nest survival was lower in fragmented forest, where a higher proportion of females failed their first attempt and the breeding season was 2 weeks longer. Compared with females on their first attempt, renesting females had lower body condition and haematocrit and higher corticosterone concentrations. Lower maternal body condition was associated with higher concentrations of corticosterone, lower nestling body condition and smaller clutches. Clutch size was lower in renests and in fragmented forest. Nestling condition was lower in renests but did not vary greatly with forest type. Despite a prolonged breeding season in the fragmented forest, post-breeding females and hatch-year birds were in similar condition in both forest types. Our results suggest that the indirect effects of nest predation on maternal and offspring condition pose additional individual-level costs that have not been considered in the context of fragmentation studies. We discuss how predator-induced renesting could have additional demographic consequences by prolonging the breeding season and prompting seasonal interactions or carry-over effects that could impact populations.

Reproductive Dynamics of the Neotropical TreefrogHypsiboas albopunctatus(Anura, Hylidae)

Abstract To understand the seasonal reproductive dynamics of Hypsiboas albopunctatus, a Neotropical treefrog, we studied the following components: 1) the influence of abiotic factors on seasonality, 2) how this seasonality relates to population dynamics, and 3) male breeding recruitment. We conducted fieldwork every month from August 2007 to July 2008 within an ecotone connecting semideciduous Atlantic Forest and Cerrado (Brazilian Savanna) in Sao Paulo State, southeastern Brazil. Over the course of the prolonged breeding season, we recorded the maximum number of calling males and measured their snout–vent lengths; we then compared our data from the beginning and the end of the breeding season. We found that the breeding pattern of H. albopunctatus is correlated with climatic, physical, and biological factors. Male competition and aggression varied according to the population density, most likely as a function of resource availability. There appears to be a social hierarchy among males of H. albopunctatus...

Stronger Sexual Selection in Warmer Waters: The Case of a Sex Role Reversed Pipefish

In order to answer broader questions about sexual selection, one needs to measure selection on a wide array of phenotypic traits, simultaneously through space and time. Nevertheless, studies that simultaneously address temporal and spatial variation in reproduction are scarce. Here, we aimed to investigate the reproductive dynamics of a cold-water pipefish simultaneously through time (encompassing variation within each breeding cycle and as individuals grow) and space (by contrasting populations experiencing distinct water temperature regimes) in order to test hypothesized differences in sexual selection. Even though the sampled populations inhabited locations with very different water temperature regimes, they exhibited considerable similarities in reproductive parameters. The most striking was the existence of a well-defined substructure in reproductive activity, where larger individuals reproduce for longer periods, which seemed dependent on a high temperature threshold for breeding rather than on the low temperatures that vary heavily according to latitude. Furthermore, the perceived disparities among populations, such as size at first reproduction, female reproductive investment, or degree of sexual size dimorphism, seemed dependent on the interplay between seawater temperature and the operational sex ratio (OSR). Contrary to our expectations of an enhanced opportunity for sexual selection in the north, we found the opposite: higher female reproductive investment coupled with increased sexual size dimorphism in warmer waters, implying that a prolonged breeding season does not necessarily translate into reduced sexual selection pressure. In fact, if the limited sex has the ability to reproduce either continuously or recurrently during the entire breeding season, an increased opportunity for sexual selection might arise from the need to compete for available partners under strongly biased OSRs across protracted breeding seasons. A more general discussion on the effects of climate change in the pressure of sexual selection is also presented.

Behavioral adjustments of a pipefish to bacterial Vibrio challenge

Animals can profit from increasing temperatures by prolonged breeding seasons and faster growth rates. However, these fitness benefits are traded off against higher parasite load and increased virulence of temperature-sensitive pathogens. In thermally stratified habitats, behavioral plasticity can allow hosts to choose the optimal temperature to enhance individual fitness and to escape parasite pressure. To test this idea, we performed a temperature choice experiment with the host-parasite system of the sex-role reversed broad-nosed pipefish (Syngnathus typhle) and its bacterial pathogen Vibrio spp. In this species, pregnant males are expected to face a trade-off between shortening their brooding period in warm water and decreasing the effect of the infection in cold water. We found that exposure to Vibrio changed the temperature preference for both pregnant and nonpregnant males, as well as females compared to nonchallenged fish that tended to prefer warm water. This study shows that behavioral plasticity is one option for avoidance of higher bacterial prevalence, as expected due to rising ocean temperatures.

A comparison of life‐history and parental care in temperate and tropical wrens

Comparing closely related species that live in different environments is a powerful way to understand selective pressures that influence life‐history evolution. We examined a suite of life‐history traits and parental care in neotropical buff‐breasted wrens Cantorchilus leucotis and north‐temperate Carolina wrens Thryothorus ludovicianus (Family Troglodytidae), to test hypotheses about life‐history evolution. As expected, buff‐breasted wrens exhibited smaller clutch sizes and higher annual adult survival than Carolina wrens. We found minimal support for the nest predation hypothesis, as nest survival and age‐corrected provisioning rates to whole broods were similar between species, and number of breeding attempts and breeding season length were greater in temperate wrens. Critical predictions of the food limitation hypothesis were not supported; in particular age‐corrected provisioning rates per nestling were higher in the tropical than temperate species. The adult survival and offspring quality hypothesis garnered the most support, as buff‐breasted wrens exhibited greater age‐corrected provisioning rates per nestling, a longer nestling period, longer re‐nesting intervals following nest success, and lower annual fecundity than Carolina wrens. Despite similarly prolonged breeding seasons, reproductive strategies differ between species with buff‐breasted wrens investing considerably in single broods to optimize first‐year survival and Carolina wrens investing in multiple small broods to optimize annual fecundity.

Effects of size and size structure on predation and inter-cohort competition in red-eyed treefrog tadpoles

Individual and relative body size are key determinants of ecological performance, shaping the strength and types of interactions within and among species. Size-dependent performance is particularly important for iteroparous species with overlapping cohorts, determining the ability of new cohorts to invade habitats with older, larger conspecifics. We conducted two mesocosm experiments to examine the role of size and size structure in shaping growth and survival in tadpoles of the red-eyed treefrog (Agalychnis callidryas), a tropical species with a prolonged breeding season. First, we used a response surface design to quantify the competitive effect and response of two tadpole size classes across three competitive environments. Large tadpoles were superior per capita effect competitors, increasing the size difference between cohorts through time at high resource availability. Hatchlings were better per biomass response competitors, and maintained the size difference between cohorts when resource availability was low. However, in contrast to previous studies, small tadpoles never closed the size gap with large tadpoles. Second, we examine the relationship between body size, size structure, and predation by dragonfly nymphs (Anax amazili) on tadpole survival and growth. Hatchlings were more vulnerable to predation; predator and large competitor presence interacted to reduce hatchling growth. Again, the size gap between cohorts increased over time, but increased marginally more with predators present. These findings have implications for understanding how variation in resources and predation over the breeding season will shape population size structure through time and the ability of new cohorts to invade habitats with older conspecifics.