Reproductive Synchrony Research Articles

Phenology of a dipterocarp forest with seasonal drought: Insights into the origin of general flowering

Abstract Our understanding of the factors that shape reproductive phenology in Southeast Asian tropical forests comes almost exclusively from studies of everwet, general flowering (GF) forests. Therefore, we examined the phenology of an evergreen dipterocarp forest in a climate exhibiting seasonal drought in Southeast Asia, with the aim of evaluating what evidence it brings to bear on the hypothesis that reproductive phenology in contemporary dipterocarp forests is the product of evolutionarily conserved responses to seasonal drought. We hypothesized that (1) dipterocarp forests that experience seasonal drought would exhibit annual reproduction and seasonality similar to that of forests with similar climates in other parts of the world, (2) within species, flowering frequency would be climate‐dependent, not a fixed trait, and (3) climatic events that cue flowering in everwet forests would also cue flowering in seasonally dry forests. From 2001 to 2009, we monitored flowering and fruiting monthly for 1,344 trees (>300 spp.) in a forest in Khao Chong (KC), Thailand that experiences an annual 2–4 month dry season, assessing frequency, duration, seasonality and synchrony of reproduction. We also examined phenological records for trees in three dipterocarp‐dominated forests in everwet climates. Reproductive phenology of the KC forest was more similar to tropical forests with similar rainfall seasonality in other parts of the world than it was to dipterocarp‐dominated forests in everwet regions of Southeast Asia. The forest exhibited annual reproduction, with peak flowering occurring at the end of the dry season and peak fruiting occurring early in the wet season. Approximately half of all species and individuals reproduced annually, including several species that are known to exhibit “general flowering” in everwet climates. Short dry spells appeared to cue flowering for early flowering species, while later flowering species may have responded to either low precipitation or temperature, consistent with data from everwet forests. GF behaviour also showed significant phylogenetic signal. Synthesis. Our results support the hypothesis that the phenological behaviour of both seasonal and everwet dipterocarp forests may have initially evolved in response to seasonal drought and that the general flowering phenomenon is a product of evolutionary conservatism.

Home field advantage, not group size, predicts outcomes of intergroup conflicts in a social bird

Research on cooperatively breeding birds usually focuses on social dynamics within the breeding group, but conflict between groups can also affect individual fitness and the evolution of sociality. Here we investigate the causes and consequences of competition between groups of communally breeding greater anis, Crotophaga major , over a 10-year field study. Social groups were spatially clustered into loose aggregations that showed a moderate degree of reproductive synchrony. However, competition between neighbouring groups for nesting sites was intense, occasionally leading to wholesale destruction of a group's nesting attempt and abandonment of the site. We documented 18 cases in which a group's entire clutch of eggs was ejected from the nest during the laying or incubation period, often accompanied by behavioural observations of conflict with a neighbouring group. Clutch destruction typically occurred when two groups attempted to nest in close proximity on high-quality sites: nearest-neighbour distance and nest site type were the strongest predictors of clutch destruction. Surprisingly, group size did not predict whether or not a group's clutch would be destroyed, and small groups sometimes ousted larger groups. By contrast, ‘home field advantage’ did have a significant effect: groups that had previously nested on the site were more likely to destroy the clutches of newly established groups, and this effect increased with the number of years that the group had nested there. Together, these results support previous evidence that competition between groups for high-quality nesting sites is an important driver of communal breeding, and they highlight the importance of location and past history in determining the outcome of intergroup contests in social species.

How do seasonality and host traits influence the distribution patterns of parasites on juveniles and adults of Columba livia?

Parasites may influence host fitness and consequently exert a selective pressure on distinct phenotypes of the host population. This pressure can result in an evolutionary response, maintaining only individuals with certain traits in the population. The present study was aimed at identifying the morphological characteristics of juveniles and adults of Columba livia that may influence the distribution patterns of lice, Pseudolynchia canariensis and Haemoproteus columbae and how the populations of these parasites vary throughout the seasons of the year. Between July 2012 and July 2014, 377 specimens of C. livia were captured. We observed a significant increase in the mean intensities of infestation by pigeon flies and lice, as well as in species richness of ectoparasites during the warmest seasons, suggesting a reproductive synchrony between ectoparasites and host species. Bill length, body mass, and body length did not affect the infestation levels of ectoparasites on adults and juveniles of C. livia with three distinct plumage colors. In juveniles, plumage color affected only the mean intensity of infestation by lice, with Spread individuals as the most infested. This indicates that melanin in feathers was not an effective barrier against ectoparasites.

Reproductive synchrony in a temperate damselfish, Chromis limbata

Synchronous reproduction has been reported in many tropical damselfishes, and it appears that temperature is the main driver of synchrony at these latitudes. However, reproductive synchrony and its relation to temperature is less well understood in temperate damselfish. The endemic Azores chromis (Chromis limbata) was chosen as a study species to address this topic. First, an ethogram of the reproductive behaviour and embryo development of the Azores chromis is provided. Then, are investigated (1) the reproductive dynamics at the colonial and inter-colonial levels, (2) how these are affected by temperature, and (3) the relation between reproductive dynamics and the social organization of temperate damselfish. In the Azores chromis, reproduction was cyclic with a high periodicity of 7.2 ± 0.63 days on average. Embryo development was synchronous within colonies towards the beginning and the end of incubation, but not at intermediate stages of development. Colonies that were closer were more synchronized than those located further apart, despite contrasting temperature and depth profiles. Embryo size differences were also greater between colonies that were further apart, and embryos tended to grow larger in warmer water. A literature review revealed that reproductive synchrony was common in colonial breeding damselfish species. Although these results suggest that within the breeding season, the timing and length of reproductive cycles cannot be explained by temperature alone, the observed changes in embryo size raise concern about the effects of changing oceanic conditions on this species.

How shrub encroachment under climate change could threaten pollination services for alpine wildflowers: A case study using the alpine skypilot, Polemonium viscosum.

Under climate change, shrubs encroaching into high altitude plant communities disrupt ecosystem processes. Yet effects of encroachment on pollination mutualisms are poorly understood. Here, we probe potential fitness impacts of interference from encroaching Salix (willows) on pollination quality of the alpine skypilot, Polemonium viscosum. Overlap in flowering time of Salix and Polemonium is a precondition for interference and was surveyed in four extant and 25 historic contact zones. Pollinator sharing was ascertained from observations of willow pollen on bumble bees visiting Polemonium flowers and on Polemonium pistils. We probed fitness effects of pollinator sharing by measuring the correlation between Salix pollen contamination and seed set in naturally pollinated Polemonium. To ascertain whether Salix interference occurred during or after pollination, we compared seed set under natural pollination, conspecific pollen addition, and Salix pollen addition. In current and past contact zones Polemonium and Salix overlapped in flowering time. After accounting for variance in flowering date due to latitude, Salix and Polemonium showed similar advances in flowering under warmer summers. This trend supports the idea that sensitivity to temperature promotes reproductive synchrony in both species. Salix pollen is carried by bumble bees when visiting Polemonium flowers and accounts for up to 25% of the grains on Polemonium pistils. Salix contamination correlates with reduced seed set in nature and when applied experimentally. Postpollination processes likely mediate these deleterious effects as seed set in nature was not limited by pollen delivery. Synthesis: As willows move higher with climate change, we predict that they will drive postpollination interference, reducing the fitness benefits of pollinator visitation for Polemonium and selecting for traits that reduce pollinator sharing.

Substantial variation in the timing of pollen production reduces reproductive synchrony between distant populations of Pinus sylvestris L. in Scotland.

The ability of a population to genetically adapt to a changing environment is contingent not only on the level of existing genetic variation within that population, but also on the gene flow received from differently adapted populations. Effective pollen‐mediated gene flow among plant populations requires synchrony of flowering. Therefore differences in timing of flowering among genetically divergent populations may reduce their ability to adapt to environmental change. To determine whether gene flow among differently adapted populations of native Scots pine (Pinus sylvestris) in Scotland was restricted by differences in their flowering phenology, we measured timing of pollen release among populations spanning a steep environmental gradient over three consecutive seasons (2014–2016). Results showed that, over a distance of 137 km, there were as many as 15.8 days’ difference among populations for the predicted timing of peak pollen shedding, with the earliest development in the warmer west of the country. There was much variation between years, with the earliest development and least synchrony in the warmest year (2014) and latest development and greatest synchrony in the coolest year (2015). Timing was negatively correlated with results from a common‐garden experiment, indicative of a pattern of countergradient variation. We conclude that the observed differences in reproductive synchrony were sufficient to limit gene flow via pollen between populations of P. sylvestris at opposite ends of the environmental gradient across Scotland. We also hypothesize that continually warming, or asymmetrically warming spring temperatures will decrease reproductive synchrony among pine populations.

Gametogenesis and reproductive dynamics of Rhinella schneideri (Anura: Bufonidae): Influence of environmental and anthropogenic factors

AbstractThis is the characterisation of the reproductive dynamics of Rhinella schneideri in an urban area during two non‐consecutive periods. Germ cells are similar to those of other anuran species, but some characteristics were more marked for R. schneideri, such as the morphological similarity of spermatogonia and oogonia, which may be related to their potential for development into both stem cell types. The presence of lampbrush chromosomes, the extensive variation in number and organisation of the nucleoli and the organisation of the nuclear cortex are also characteristic of this species. All of these features appear to work together, participating in the dynamic growth of the oocyte. In some specimens, previtellogenic oocytes were also observed in the seminiferous tubules, which may be related to anthropogenic changes induced in the study area. In the first study period, reproductive dynamics revealed synchrony between the sexes, with the preparation of the gonads from October to December and the reproductive season from October to January, coinciding with the rainy season. In the second period, reproductive synchrony was also observed, but gonad preparation occurred from February to June and the reproductive season was from August to November, before the rainy season. These changes in the reproductive cycle suggest that urbanisation affects the reproduction of this species.

Long-term analysis on the variance of extra-group paternities in rhesus macaques

Extra-group paternity (EGP) has been described in various mammalian species; however, little is known about which factors contribute to the variation in EGP, as the majority of studies were restricted in time and the number of groups considered. Using longitudinal demographic and genetic data, we aim to investigate which factors predict rates of EGP in the free-ranging rhesus macaque population of Cayo Santiago, Puerto Rico (USA). Of the 1649 infants considered which were born into six social groups over 9 years, we identified an average of 16% of infants resulting from EGPs. We tested the influence of group size, breeding group sex ratio, female reproductive synchrony, and group instability on the occurrence of EGPs. Our results suggest a tendency for EGPs to increase as the proportion of females increased in larger groups, but no such effect in smaller groups. Furthermore, as group instability and female reproductive synchrony decreased, the number of EGPs tended to increase. Our results support the hypothesis that group structure affects the occurrence of EGPs, which might be mediated by male mating opportunities, male monopolization potential, and/or female choice.Significance statementIn several species, both sexes seek alternative reproductive strategies to enhance their reproductive success. For instance, females may pursue EGPs to potentially increase genetic compatibility with males, or males may seek EGPs to improve their mating opportunities. Our longitudinal analysis, including demographic and genetic data over 9 years of six social groups of rhesus macaques, revealed high variation in the occurrence of EGPs across groups and years, and this variation tended to depend on group characteristics such as breeding group size, sex ratio, female synchrony, and group instability. The data suggest that group structure affects the number of EGPs in this group-living primate. Our results show that EGPs can affect the distribution of paternity within social groups and should be taken into account when assessing reproductive success.

Factors that enhance repeat breeder condition in a crossbred dairy herd submitted to reproductive synchronization protocols

O objetivo deste estudo foi avaliar a incidência vacas repetidoras (VR) leiteiras mestiças submetidas à inseminação artificial em tempo fixo (IATF) e protocolos de sincronização de estro. Dados de 371 novilhas e 997 vacas leiteiras mestiças foram analisados. Vacas com mais de 30 dias pós-parto, boa condição uterina, sem mastite clínica e com escore corporal ≥ 2,5 foram utilizadas. As vacas foram divididas em dois grupos, sendo: grupo 1: IATF – vacas sem corpo lúteo no exame ultrassonográfico e que foram submetidas ao protocolo de IATF, e grupo 2: sincronização de cio – aquelas vacas com corpo lúteo presente. A incidência de VR e seus fatores foram analisados por regressão logística pelo SAS. A incidência de VR foi maior em vacas em lactação em relação às fêmeas não-lactantes (P < 0,001). Ainda, uma tendência de um maior número de VR foi observada naquelas que pariram na primavera/verão quando comparadas às paridas no outono/inverno. O tipo de parto (normal vs. não normal) não influenciou na incidência de VR (P > 0,001), no entanto, foi detectado efeito do número de partos (P > 0.01). Dessa forma, nas categorias animais avaliadas, a incidência de VR foi maior em vacas leiteiras mestiças do que em novilhas. Uma tendência de VR foi observada naquelas que pariram na primavera/verão quando comparadas aquelas que pariram no outono/inverno, ainda a incidência de VR foi maior naquelas de segunda parição quando comparadas as de primeira, terceira ou quarta, ao passo que o tipo de parto (normal vs. não normal) não influenciou sobre a incidência de VR.

Assessing the effect of environmental factors on the spawning activity of the sea urchin Strongylocentrotus intermedius through video recording observations

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 588:101-119 (2018) - DOI: https://doi.org/10.3354/meps12436 Assessing the effect of environmental factors on the spawning activity of the sea urchin Strongylocentrotus intermedius through video recording observations Peter M. Zhadan1,*, Marina A. Vaschenko2, Sergey D. Ryazanov1 1V. I. Il’ichev Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, 43 Baltiyskaya Street, 690041 Vladivostok, Russia 2National Scientific Center of Marine Biology, A. V. Zhirmunsky Institute of Marine Biology, Far Eastern Branch, Russian Academy of Sciences, 17 Palchevsky Street, 690041 Vladivostok, Russia *Corresponding author: pzhadan@poi.dvo.ru ABSTRACT: We used video recordings of spawning behaviour of the sea urchin Strongylocentrotus intermedius conducted in parallel with an analysis of gonadal state and measurement of environmental variables (tidal level, phytoplankton, temperature, salinity and oxygen concentration) in situ to study the role of environmental factors in triggering sea urchin spawning. The observations were performed during 3 reproductive seasons, each of 2 mo duration, in 2 bays with different levels of phytoplankton (measured as chlorophyll a [chl a]). The only significant positive correlation found was between sea urchin spawning frequency and chl a concentration. Despite a high level of gonad maturity, sea urchin spawning was rarely recorded in the bay with low levels of chl a whereas mass spawning occurred in the bay with higher chl a concentration, with the peak of spawning activity centred around the full moon. Spawning was predominantly nocturnal. Immediately before and during spawning, males actively moved. Females began to spawn only when there were several spawning males nearby. In both sexes, each spawning event included several episodes of gamete release of different duration and with different intervals between them. The same male likely can participate in several spawning events. The following hierarchy of drivers of S. intermedius spawning activity was revealed: (1) increasing the phytoplankton concentration induced active motion and spawning in males, (2) both an elevated phytoplankton level and the presence of sperm stimulated spawning in females and (3) the night time and the new and full lunar phases increased the probability of spawning. KEY WORDS: Broadcast spawning · Echinoderms · Reproductive synchrony · Phytoplankton · Temperature · Circadian rhythm · Lunar cycle Full text in pdf format Supplementary material PreviousNextCite this article as: Zhadan PM, Vaschenko MA, Ryazanov SD (2018) Assessing the effect of environmental factors on the spawning activity of the sea urchin Strongylocentrotus intermedius through video recording observations. Mar Ecol Prog Ser 588:101-119. https://doi.org/10.3354/meps12436 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 588. Online publication date: February 08, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Every-Other-Day Clutch-Initiation Synchrony In Ring-Billed Gulls (Larus Delawarensis)

Fraser Darling suggested that reproductive synchrony enhances reproductive success of colonial seabirds as a result of predator satiation. However, the cost of yearly reproductive synchrony is high for colonial species for which intraspecific predation is the primary cause of egg and chick loss. A few studies indicate that egg-laying synchrony on a daily time scale within the annual breeding pulse may be an adaptive response to intraspecific predation. Here, we report every-other-day clutch-initiation synchrony in densely nesting cohorts of Ring-billed Gulls (Larus delawarensis). This is the second known case of clutch-initiation synchrony on a daily time scale in larids, the first being for Glaucous-winged Gulls (L. glaucescens). In both Ring-billed Gulls and Glaucous-winged Gulls, the degree of clutch-initiation synchrony is inversely related to nearest neighbor distance. Further studies are needed to test whether clutch-initiation synchrony in Ring-billed Gulls is adaptive in the presence of cannibalism, or if it is simply a neutral byproduct of colonial nesting.

Reproductive synchrony in a diverse Acropora assemblage, Vamizi Island, Mozambique

AbstractMulti‐specific synchronous spawning has never been documented for East Africa, but coral spawn‐slicks are observed annually around Vamizi Island, Northern Mozambique. We monitored gamete development in Acropora species from July 2012 to October 2013 and from August to September 2014 to describe patterns of reproductive seasonality and synchrony within and amongst species of Acropora. Gamete maturation was highly synchronized within and amongst Acropora species and culminated in multi‐specific spawning events lasting 1–3 nights in each year of the study, in late August or September. In 2013 and 2014, 50% or more of the colonies of over 50% of the species sampled prior to the spawning events had mature gametes. In all years, 91–99% colonies sampled after the spawning events had no visible gametes. The percentage of colonies with mature gametes was up to 100% for some species. In other species, the absence of mature gametes throughout the study period indicates that they might not spawn in certain years. The analysis of a 8‐year record of observations of spawn‐slicks showed that spawning generally occurred once a year for a few consecutive days between September and December, during periods of rising sea surface temperature and low wind speed and rainfall. This study is the first to quantitatively document coral reproduction in Mozambique and multi‐specific synchronous spawning off the coast of Africa. These findings contrast with the asynchronous breeding reported for Kenyan reefs and support the absence of breakdown in coral reproductive synchrony towards low latitudes.

Efficacy of gonadorelin hydrochloride or gonadorelin diacetate tetrahydrate 7 days after AI in field conditions to boost progesterone levels, a randomized clinical trial

The ability of some reproduction synchronization protocols to increase conception rates (CR) is reported as being in part due to increased progesterone (P4) levels in the diestrus phase before breeding. This has been demonstrated mostly in an experimental context and was linked to GnRH increasing the proportion of cows luteinizing a second corpus luteum (CL). A pilottrial was conducted to determine if an injection of gonadorelin hydrochloride (Factrel®) or gonadorelin diacetate tetrahydrate (Cystorelin®) given 7 days after AI to all cows on a farm in field conditions resulted in a significant increase of P4 levels 14 days after AI, compared to a placebo. If an increase in P4 levels was to be observed, a second larger trial was to be conducted testing the effect of post-AI GnRH on CR at return to estrus.

Infanticide and within-clutch competition select for reproductive synchrony in a cooperative bird.

Reproduction among members of social animal groups is often highly synchronized, but neither the selective advantages nor the proximate causes of synchrony are fully understood. Here I investigate the evolution of hatching synchrony in the Greater Ani (Crotophaga major), a communally nesting bird in which several unrelated females contribute eggs to a large, shared clutch. Hatching synchrony is variable, ranging from complete synchrony to moderate asynchrony, and is determined by the onset of incubation of the communal clutch. Data from a 10-year field study indicate that individual reproductive success is highest in synchronous groups, and that nestlings that hatch in the middle of the hatching sequence are most likely to survive. Nestling mortality is high in asynchronous clutches because early-hatching nestlings are more likely to be killed by adult group members, whereas late-hatching nestlings are more likely to starve due competition with their older nest-mates. Therefore, the timing of hatching appears to be under stabilizing selection from infanticide and resource competition acting in concert. These results provide empirical support for models predicting that synchrony may evolve as an adaptive counter-strategy to infanticide, and they highlight the importance of competition in shaping the timing of reproduction in social groups.

Temporal windows of reproductive opportunity reinforce species barriers in a marine broadcast spawning assemblage.

Prezygotic isolating mechanisms act to limit hybridization and maintain the genetic identity of closely-related species. While synchronous intraspecific spawning is a common phenomenon amongst marine organisms and plays an important role in reproductive success, asynchronous spawning between potentially hybridizing lineages may also be important in maintaining species boundaries. We tested this hypothesis by comparing reproductive synchrony over daily to hourly timescales in a sympatric assemblage of intertidal fucoid algae containing selfing hermaphroditic (Fucus spiralis and Fucus guiryi) and dioecious (Fucus vesiculosus and Fucus serratus) species. Our results confirm that gametes are released on semi-lunar cycles in all species. However, sister species with different mating systems showed asynchronous spawning at finer circadian timescales, thus providing evidence for a partial reproductive barrier between hermaphroditic and dioecious species. Finally, our data also emphasize the ecological, developmental, and/or physiological constraints that operate to restrict reproduction to narrow temporal windows of opportunity in the intertidal zone and more generally the role of ecological factors in marine speciation.

On the photoperiodic induction of diapause in first generation hybrids of Harmonia Axyridis (PALL.) (Coleoptera, Coccinellidae)

Background. Diapause is an important component of insect life cycle which ensures synchronization of reproduction and development with local seasonal climate. Genetic bases of this synchronization are particularly important for the analysis of biological invasions. Materials and methods. We investigated photoperiodic induction of diapause in hybrids between two populations of Harmonia axyridis (Pallas): autochthonous population from Irkutsk (Siberia) which shows a strong induction of diapause by short days and invasive population from Sochi (the Caucasus) which exhibits very weak photoperiodic induction of diapause. Results. Reciprocal crosses showed that the strong photoperiodic induction of diapause is dominant and the effects of male and female genotypes on progeny phenotype are equal.

Movilización y utilización de los sustratos energéticos de <i>Arca zebra</i> (Bivalvia: Arcidae) en relación con el ambiente

El análisis de los componentes bioquímicos en especies marinas para el consumo humano tiene una gran importancia, ya que permite conocer las propiedades alimenticias y energéticas del organismo. En el presente estudio, se evaluó el perfil bioquímico en tejidos de Arca zebra en relación con los factores ambientales, con la finalidad de ser utilizado como indicador de la dinámica reproductiva y de los periodos de engorde de este importante recurso pesquero. Se analizaron 20 organismos/mes, entre julio de 2010-julio de 2011. A cada organismo se le determinó el largo total (LT) y se separaron los tejidos, los cuales se llevaron hasta peso constante para realizarles los análisis bioquímicos mediante espectrofotometría. Se establecieron diferencias mensuales en la LT, con un promedio anual de 69.61 mm, manteniéndose por encima de la talla comercial. Los carbohidratos y las proteínas mostraron diferencias entre meses, con valores máximos en marzo y julio de 2011, siendo el músculo quien registró el mayor contenido de ambos sustratos energéticos, asociados a los altos niveles de clorofila a. Se observó una relación inversa entre los carbohidratos y las proteínas en los tres tejidos con respecto a la masa gonadal, sugiriendo una posible transferencia durante el proceso reproductivo de A. zebra. En las gónadas se registró el mayor contenido de lípidos, sin variación mensual, debido a la sincronía reproductiva de la especie. A. zebra muestra su mejor condición nutricional durante los periodos comprendidos entre septiembre-diciembre y marzo-junio, en estos meses se recomienda su comercialización e ingesta.

Birth dates vary with fixed and dynamic maternal features, offspring sex, and extreme climatic events in a high-latitude marine mammal.

Reproductive synchrony tends to be widespread in diverse species of plants and animals, especially at higher latitudes. However, for long‐lived mammals, birth dates for different individuals can vary by weeks within a population. A mother's birth timing can reveal useful information about her reproductive abilities and have important implications for the characteristics and survival of her offspring. Despite this, our current knowledge of factors associated with variation in birth dates is modest. We used long‐term data for known‐age Weddell seals in Antarctica and a Bayesian hierarchical modeling approach to study how birth dates varied with fixed and temporally varying features of mothers, whether sex allocation varied with birth timing, and annual variation in birth dates. Based on birth dates for 4465 pups born to 1117 mothers aged 4–31, we found that diverse features of mothers were associated with variation in birth dates. Maternal identity was the most important among these. Unlike most studies, which have reported that birth dates occur earlier as mothers age, we found that birth dates progressively occurred earlier in the year in the early part of a mother's reproductive life, reached a minimum at age 16, and then occurred later at later ages. Birth dates were positively related to a mother's age at primiparity and recent reproductive effort. The earliest birth dates were for pups born to prime‐age mothers who did not reproduce in the previous year but began reproduction early in life, suggesting that females in the best condition gave birth earlier than others. If so, our finding that male pups tended to be born earlier than females provides support for the Trivers–Willard sex‐allocation model. Average birth dates were quite consistent across years, except for 2 years that had notable delays and occurred during the period when massive icebergs were present and disrupted the ecosystem.

A juvenile–adult population model: climate change, cannibalism, reproductive synchrony, and strong Allee effects

ABSTRACTWe study a discrete time, structured population dynamic model that is motivated by recent field observations concerning certain life history strategies of colonial-nesting gulls, specifically the glaucous-winged gull (Larus glaucescens). The model focuses on mechanisms hypothesized to play key roles in a population's response to degraded environment resources, namely, increased cannibalism and adjustments in reproductive timing. We explore the dynamic consequences of these mechanics using a juvenile–adult structure model. Mathematically, the model is unusual in that it involves a high co-dimension bifurcation at which, in turn, leads to a dynamic dichotomy between equilibrium states and synchronized oscillatory states. We give diagnostic criteria that determine which dynamic is stable. We also explore strong Allee effects caused by positive feedback mechanisms in the model and the possible consequence that a cannibalistic population can survive when a non-cannibalistic population cannot.

Stable Isotopes Reveal Long-Term Fidelity to Foraging Grounds in the Galapagos Sea Lion (Zalophus wollebaeki).

Most otariids have colony-specific foraging areas during the breeding season, when they behave as central place foragers. However, they may disperse over broad areas after the breeding season and individuals from different colonies may share foraging grounds at that time. Here, stable isotope ratios in the skull bone of adult Galapagos sea lions (Zalophus wollebaeki) were used to assess the long-term fidelity of both sexes to foraging grounds across the different regions of the Galapagos archipelago. Results indicated that the stable isotope ratios (δ13C and δ15N) of sea lion bone significantly differed among regions of the archipelago, without any significant difference between sexes and with a non significant interaction between sex and region. Moreover, standard ellipses, estimated by Bayesian inference and used as a measure of the isotopic resource use area at the population level, overlapped widely for the sea lions from the southern and central regions, whereas the overlap of the ellipses for sea lions from the central and western regions was small and non-existing for those from the western and southern regions. These results suggest that males and females from the same region within the archipelago use similar foraging grounds and have similar diets. Furthermore, they indicate that the exchange of adults between regions is limited, thus revealing a certain degree of foraging philopatry at a regional scale within the archipelago. The constraints imposed on males by an expanded reproductive season (~ 6 months), resulting from the weak reproductive synchrony among females, and those imposed on females by a very long lactation period (at least one year but up to three years), may explain the limited mobility of adult Galapagos sea lions of both sexes across the archipelago.