Life History Implications Research Articles

Effects of Habitat Fragmentation on Effective Dispersal of Florida Scrub‐Jays

Studies comparing dispersal in fragmented versus unfragmented landscapes show that habitat fragmentation alters the dispersal behavior of many species. We used two complementary approaches to explore Florida Scrub-Jay (Aphelocoma coerulescens) dispersal in relation to landscape fragmentation. First, we compared dispersal distances of color-marked individuals in intensively monitored continuous and fragmented landscapes. Second, we estimated effective dispersal relative to the degree of fragmentation (as inferred from two landscape indexes: proportion of study site covered with Florida Scrub-Jay habitat and mean distance to nearest habitat patch within each study site) by comparing genetic isolation-by-distance regressions among 13 study sites having a range of landscape structures. Among color-banded individuals, dispersal distances were greater in fragmented versus continuous landscapes, a result consistent with other studies. Nevertheless, genetic analyses revealed that effective dispersal decreases as the proportion of habitat in the landscape decreases. These results suggest that although individual Florida Scrub-Jays may disperse farther as fragmentation increases, those that do so are less successful as breeders than those that disperse short distances. Our study highlights the importance of combining observational data with genetic inferences when evaluating the complex biological and life-history implications of dispersal.

Nephila clavipes females have accelerating dietary requirements

Abstract Nephila spiders are famous for extreme sexual size dimorphism, with females an order of magnitude larger than males. The proximal developmental mechanism for the sexual size dimorphism is extended development in females: they have many more juvenile instars than males. During an experimental rearing of Nephila clavipes (Linnaeus 1767) from two populations, we discovered that females cannot reach sexual maturity on diets that are qualitatively and quantitatively sufficient for male maturation. Here we describe the dietary regimes that produced sexually mature females and the life history implications of these requirements.

Missing claws in a commercial catch of the American lobster: Implications for life history and the fishery

In most crustaceans, including the American lobster ( Homarus americanus), a high frequency of individuals with missing claws is often reported. As lobsters with missing claws (“culls”) are less valuable in terms of weight and market value than uninjured lobsters, returning of culls to the sea has been suggested as a conservation strategy. To assess the potential benefits of such strategy, the frequency and types of claw loss were documented during the fishery season of 2007 (34 days, 6900 trap hauls) in an area of Prince Edward Island, southern Gulf of St. Lawrence. On average, culls accounted for ∼7% of the total catch in weight and such percentage remained fairly constant along the study period. The raw frequency of culls, however, was higher in the first 9–12 days of the study and decreased progressively afterwards, reflecting the pattern followed by actual total catches. A single missing claw (pincher or crusher in similar proportions) was the most common type of injury for both males and females, followed by the presence of a single regenerating claw. The male:female ratio for the culls (∼1:2) did not deviate from the one estimated for uninjured lobsters of the same size range (canners). These results are used to further discuss life history implications and the potential benefits and limitations of a conservation strategy based on the return of culls to the water.

Trade-offs between time, predation risk and life history, and their implications for biogeography: A systems modelling approach with a primate case study

Group sizes are often considered to be the result of a trade-off between predation risk and the costs of feeding competition. We develop a model to explore the interaction between different ecological constraints on group sizes, using a primate (baboons) case study. The model uses climatic correlates of time budgets to predict maximum ecologically tolerable group size, and climatic predictors of predation risk (reflected mainly in predator density and female body mass) to predict minimum tolerable group size for any given habitat. As well as defining the range of sustainable group sizes for a given habitat, the model also allows us to reliably predict our exemplar taxon's biogeographical distribution across Africa. We also explore the life history implications of the model to ask whether baboons form group sizes which maximise survival or fecundity in the classic trade off between these two key life history variables. Our results indicate that, within the range of study sites in our sample, baboons prefer to maximise fecundity. However, the data indicate that in higher predation risk habitats they would switch to maximising survival at the expense of fecundity. We argue that this is due to the fact that interbirth interval and developmental rates have a ceiling that cannot be breached. Thus, while females can shorten interbirth intervals to compensate for increased predation risk, there is a limit to how much these life history variables can be altered, and when this is reached the best strategy is to maximise survivorship.

Conservation of intron and intein insertion sites: implications for life histories of parasitic genetic elements

BackgroundInteins and introns are genetic elements that are removed from proteins and RNA after translation or transcription, respectively. Previous studies have suggested that these genetic elements are found in conserved parts of the host protein. To our knowledge this type of analysis has not been done for group II introns residing within a gene. Here we provide quantitative statistical support from an analyses of proteins that host inteins, group I introns, group II introns and spliceosomal introns across all three domains of life.ResultsTo determine whether or not inteins, group I, group II, and spliceosomal introns are found preferentially in conserved regions of their respective host protein, conservation profiles were generated and intein and intron positions were mapped to the profiles. Fisher's combined probability test was used to determine the significance of the distribution of insertion sites across the conservation profile for each protein. For a subset of studied proteins, the conservation profile and insertion positions were mapped to protein structures to determine if the insertion sites correlate to regions of functional activity. All inteins and most group I introns were found to be preferentially located within conserved regions; in contrast, a bacterial intein-like protein, group II and spliceosomal introns did not show a preference for conserved sites.ConclusionsThese findings demonstrate that inteins and group I introns are found preferentially in conserved regions of their respective host proteins. Homing endonucleases are often located within inteins and group I introns and these may facilitate mobility to conserved regions. Insertion at these conserved positions decreases the chance of elimination, and slows deletion of the elements, since removal of the elements has to be precise as not to disrupt the function of the protein. Furthermore, functional constrains on the targeted site make it more difficult for hosts to evolve immunity to the homing endonuclease. Therefore, these elements will better survive and propagate as molecular parasites in conserved sites. In contrast, spliceosomal introns and group II introns do not show significant preference for conserved sites and appear to have adopted a different strategy to evade loss.

Relationship between mRNA secondary structure and sequence variability in Chloroplast genes: possible life history implications

BackgroundSynonymous sites are freer to vary because of redundancy in genetic code. Messenger RNA secondary structure restricts this freedom, as revealed by previous findings in mitochondrial genes that mutations at third codon position nucleotides in helices are more selected against than those in loops. This motivated us to explore the constraints imposed by mRNA secondary structure on evolutionary variability at all codon positions in general, in chloroplast systems.ResultsWe found that the evolutionary variability and intrinsic secondary structure stability of these sequences share an inverse relationship. Simulations of most likely single nucleotide evolution in Psilotum nudum and Nephroselmis olivacea mRNAs, indicate that helix-forming propensities of mutated mRNAs are greater than those of the natural mRNAs for short sequences and vice-versa for long sequences. Moreover, helix-forming propensity estimated by the percentage of total mRNA in helices increases gradually with mRNA length, saturating beyond 1000 nucleotides. Protection levels of functionally important sites vary across plants and proteins: r-strategists minimize mutation costs in large genes; K-strategists do the opposite.ConclusionMrna length presumably predisposes shorter mRNAs to evolve under different constraints than longer mRNAs. The positive correlation between secondary structure protection and functional importance of sites suggests that some sites might be conserved due to packing-protection constraints at the nucleic acid level in addition to protein level constraints. Consequently, nucleic acid secondary structure a priori biases mutations. The converse (exposure of conserved sites) apparently occurs in a smaller number of cases, indicating a different evolutionary adaptive strategy in these plants. The differences between the protection levels of functionally important sites for r- and K-strategists reflect their respective molecular adaptive strategies. These converge with increasing domestication levels of K-strategists, perhaps because domestication increases reproductive output.

Implications of life history for genetic structure and migration rates of southern African coastal invertebrates: planktonic, abbreviated and direct development

The amount of genetic structure in marine invertebrates is often thought to be negatively correlated with larval duration. However, larval retention may increase genetic structure in species with long-lived planktonic larvae, and rafting provides a means of dispersal for species that lack a larval dispersal phase. We compared genetic structure, demographic histories and levels of gene flow of regional lineages (in most cases defined by biogeographic region) of five southern African coastal invertebrates with three main types of larval development: (1) dispersal by long-lived planktonic larvae (mudprawn Upogebia africana and brown mussel Perna perna), (2) abbreviated larval development (crown crab Hymenosoma orbiculare) and (3) direct development (estuarine isopod Exosphaeroma hylecoetes and estuarine cumacean Iphinoe truncata). We hypothesized that H. orbiculare, having abbreviated larval development, would employ a strategy of larval retention, resulting in genetic structure comparable to that of the direct developers rather than the planktonic dispersers. However, regional population structure was significantly lower in all species with planktonic larvae, including H. orbiculare, than in the direct developers. Moreover, nested clade analysis identified demographic histories resulting from low levels of gene flow (isolation by distance and allopatric fragmentation) in the direct developers only, and migration rates were significantly higher in all three species having planktonic larvae than in the direct developers. We conclude that the amount of genetic structure within marine biogeographic regions strongly depends on the presence or absence of free-swimming larvae. Whether such larvae are primarily exported or retained, whether they have long or short larval duration, and whether or not they are capable of active dispersal seems to have little effect on connectivity among populations.

Self-harm caused by an insect's innate immunity

It has been a long-held assumption that the innate immune system of insects causes self-harm when used to combat an immune insult. We show empirically that this assumption is correct. Invertebrate innate immunity relies heavily on effector systems which, on activation, produce cytotoxins that kill pathogens. Reliance on these robust, fast-acting, generic killing mechanisms ensures a potent and rapid response to pathogen invasion, but has the potential disadvantage of causing self-damage. We show that the innate immune response against an immune insult produces measurable phenotypic and functional damage to self-tissue in the beetle Tenebrio molitor. This type of self-harm (autoreactivity) and the life-history implications that arise from it are important to understand evolutionary phenomena such as the dynamics between hosts and parasites as well as the nature of immune system costs.

Gastropod predation on egg cases of skates (Chondrichthyes, Rajidae) in the southwestern Atlantic: quantification and life history implications

Mean predation rates (± SD) on egg cases of the skates Bathyraja macloviana, B. albomaculata, Amblyraja doellojuradoi, and Psammobatis spp. from the southwestern Atlantic were estimated to be 0.151 (±0.230), 0.423 (±0.344), 0.254 (±0.390), and 0.150 (±0.288), respectively. These estimates are within the ranges reported earlier (14–40%). Egg cases of B. albomaculata were preyed on in higher proportion than expected from their abundance and suffered a heavier predation rate where the snail Trophon acanthodes was present. Predation rates were not correlated with the thickness of the egg case wall, which indicates that other factors (ecological or chemical) could explain this pattern. Five types of boreholes were found in the egg cases: one was attributable to muricid gastropods, one to naticid gastropods, and a third type to an unknown gastropod (probably Fusitriton magellanicus); the remaining were of unknown origin. Cladistic analyses showed that skates are secondarily oviparous and have maximized adaptations for living in deep water. We suggest that oviparity in skates appeared as an adaptation to maximize fecundity (40–160 eggs per year, as compared to 2–18 pups annually or biannually in viviparous guitarfishes, the plesiomorphic sister clade of skates). If a predation rate of 24% (the mean of predation rates of all skate species studied to date) is applied to the range of fecundities reported for skates, the result is that 18–114 viable pups are produced annually per female skate. Even with a high mortality rate of 64% (the only direct estimate of natural mortality for any elasmobranch), each female skate produces 17–54 eggs annually. These values are higher than most elasmobranch fecundities. This maximization of fecundity is possible mainly because the fecundity of oviparous species is not limited by body size, as in viviparity. The protracted egg-laying season (4–12 months) of most skates (as in many other deep-sea fishes) maximizes the number of eggs laid.

An evolutionary model of stature, age at first birth and reproductive success in Gambian women.

We have built a model to predict optimal age at first birth for women in a natural fertility population. The only existing fully evolutionary model, based on Ache hunter-gatherers, argues that as women gain weight, their fertility (rate of giving birth) increases-thus age at first birth represents a trade-off between time allocated to weight gain and greater fertility when mature. We identify the life-history implications of female age at first birth in a Gambian population, using uniquely detailed longitudinal data collected from 1950 to date. We use height rather than weight as an indicator of growth as it is more strongly correlated with age at first birth. Stature does not greatly influence fertility in this population but has a significant effect on offspring mortality. We model age at first reproduction as a trade-off between the time spent growing and reduced infant mortality after maturation. Parameters derived from this population are fitted to show that the predicted optimal mean age of first birth, which maximizes reproductive success, is 18 years, very close to that observed. The reaction norm associated with variation in growth rate during childhood also satisfactorily predicts the variation in age at first birth.

Sex‐biased dispersal in a salmonid fish: implications for growth rate and survival

I tested the hypothesis that dispersal is sex‐biased in an unexploited population of brook trout (Salvelinus fontinalis Mitchill). Based on the assumptions that trout are promiscuous and that reproductive success is limited primarily by either number of mates (males) or fecundity (females), I predicted that males would disperse greater distances than females. I also tested the hypothesis that trout populations comprise stationary and mobile individuals, predicting that males have greater mobility than females. Based on a 5‐year, mark‐recapture study of almost 1000 fish, there was strong support for the hypothesis of male‐biased dispersal. On average, males dispersed 2·5 times as far as females; during the spawning period only, male dispersal exceeded that by females almost four‐fold. Both sexes were heterogeneous with respect to movement, with a lower incidence of mobility among females than males. Sex differences in dispersal may have been responsible for sex biases in seasonal growth. Importantly, growth rate was positively associated with survival, independent of the effects of body size. Sex‐biased dispersal may (1) reduce mate competition among male kin, (2) decrease the probability that males will reproduce with related females, and (3) have important implications for life history.

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

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

11-Oxygenated androgens in female teleosts: prevalence, abundance, and life history implications

Although 11-ketotestosterone (11-KT) has been found in blood of females of several diadromous fish species, the importance, abundance, and prevalence of this and related 11-oxygenated androgens in females have not been investigated. To address this issue and to determine whether the differences among androgen profiles relate to specific life history strategies, particularly diadromous migrations, fish (males and females) of around 30 species were sampled and 5 androgens were measured by radioimmunoassay. Levels of 17β-estradiol and cortisol were also determined to evaluate ovarian and interrenal activity at the time of sampling. Testosterone (T) was the predominant androgen in most sexually recrudescent females. Only in female eel and sturgeon were 11-oxygenated androgens present in levels as high as, or higher than, those of T, although substantial amounts were also found in blood of mullet and salmonids. 11-KT was generally the most abundant 11-oxyandrogen, levels being higher than those of 11β-hydroxytestosterone or 11β-hydroxyandrostenedione. It is concluded that 11-oxygenated androgens are quantitatively minor steroids in most female fish. There was no convincing evidence to support the notion that the presence of 11-oxygenated androgens in blood is an adaptation specific to migratory fishes.

Life History Implications of Complete and Incomplete Primary Molts in Pelagic Cormorants

Abstract We describe the rules of primary flight-feather replacement for Pelagic Cormorants (Phalacrocorax pelagicus), and contrast the completeness of primary replacement in individuals from Asia and North America. In adult Pelagic Cormorants primary replacement is stepwise, with multiple waves of molt, each initiated at the innermost primary (P1), proceeding simultaneously toward the tip of the wing. Shugart and Rohwer's (1996) ontogenetic model for generating and maintaining stepwise primary replacement depended upon incomplete molts. In each new episode of molt, waves of primary replacement were thought to be initiated at P1 and at each arrested wave that had failed to replace all old feathers in the preceding molt. Because most adult Pelagic Cormorants from North America completely replace their primaries but maintain stepwise primary molts, the latter assumption must be relaxed. In contrast to the present-day situation in North America, Pelagic Cormorants from northeastern Asia have incomplete molts of their primaries, and may be forced to skip breeding in some years to clear their wings of overworn primaries. Young birds from Asia start the replacement of their juvenile primaries later than North American birds and replace more feathers simultaneously. Implicancias de la Muda Primaria Completa e Incompleta en la Historia de Vida de Phalacrocorax pelagicus Resumen. Describimos las reglas de reemplazo de plumas primarias para Phalacrocorax pelagicus y contrastamos la totalización del reemplazo de primarias entre individuos de Asia y América del Norte. En individuos adultos, el reemplazo de primarias ocurre en varias etapas, con múltiples secuencias de muda cada una iniciada en la primaria más interna (P1), procediendo simultáneamente hacia la punta del ala. El modelo ontogenético de Shugart y Rohwer (1996) para la generación y mantenimiento del reemplazo en etapas de las plumas primarias depende de mudas incompletas. Se pensaba que en cada nuevo episodio de muda las secuencias de reemplazo de primarias eran iniciadas en P1 y en cada punto de interrupción de la muda precedente que hubiera impedido el reemplazo de todas las plumas viejas. Debido a que la mayoría de los individuos adultos de P. pelagicus de Norteamérica reeemplazan completamente sus primarias pero aún lo hacen en etapas, la última suposición debe ser re-evaluada. En contraste con la situación actual en Norteamérica, individuos del noreste de Asia tienen mudas incompletas de sus primarias y pueden verse forzados a no reproducirse en algunos años para despojarse de la presencia de primarias desgastadas. Las aves juveniles de Asia comienzan el reemplazo de sus primarias más tarde y reemplazan más plumas simultáneamente que las aves de Norteamérica.

Growth patterns in euconodont crown enamel: implications for life history and mode-of-life reconstruction in the earliest vertebrates

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Armstrong H. A. and Smith C. J. 2001Growth patterns in euconodont crown enamel: implications for life history and mode-of-life reconstruction in the earliest vertebratesProc. R. Soc. Lond. B.268815–820http://doi.org/10.1098/rspb.2001.1591SectionRestricted accessGrowth patterns in euconodont crown enamel: implications for life history and mode-of-life reconstruction in the earliest vertebrates H. A. Armstrong H. A. Armstrong Department of Geological Sciences, University of Durham, South Road, Durham DH1 3LE, UK [email protected] Google Scholar Find this author on PubMed Search for more papers by this author and C. J. Smith C. J. Smith Department of Geological Sciences, University of Durham, South Road, Durham DH1 3LE, UK Google Scholar Find this author on PubMed Search for more papers by this author H. A. Armstrong H. A. Armstrong Department of Geological Sciences, University of Durham, South Road, Durham DH1 3LE, UK [email protected] Google Scholar Find this author on PubMed Search for more papers by this author and C. J. Smith C. J. Smith Department of Geological Sciences, University of Durham, South Road, Durham DH1 3LE, UK Google Scholar Find this author on PubMed Search for more papers by this author Published:22 April 2001https://doi.org/10.1098/rspb.2001.1591AbstractEuconodonts were the first vertebrates to produce a mineralized skeleton. It is concluded that the minor increments in the crown enamels of Protopanderodus varicostatus and Drepanodus robustus are probable homologues of the cross striations in hominoid enamel, although they are much more variable in thickness and represent daily to weekly growth. Major increments are superficially similar to lines of Retzuis, but represent a check in growth that is likely to have occurred at monthly intervals. Periods of above– and below–average growth are likely to have been seasonally moderated. The growth of P.varicostatus' elements are characterized by two distinct phases: the production of a triangular, asymmetrical juvenile ‘proto–element’ followed, in a second phase, by the development of the curved and twisted geometry of the adult element. These fundamentally different morphologies imply that juvenile and adult animals had different modes of life and/or feeding strategies. In these animals the growth of the elements was indeterminate. The growth model for euconodonts is clearly different from that of hominoid teeth as the enamel organ must have reformed repeatedly throughout life. Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Jain S (2020) Conodonts Fundamentals of Invertebrate Palaeontology, 10.1007/978-81-322-3962-8_5, (93-115), . Shirley B, Bestmann M and Jarochowska E (2020) The cono-dos and cono-dont’s of phosphatic microfossil preparation and microanalysis, Micron, 10.1016/j.micron.2020.102924, 138, (102924), Online publication date: 1-Nov-2020. Van houcke J, Geeraerts E, Vanhunsel S, Beckers A, Noterdaeme L, Christiaens M, Bollaerts I, De Groef L and Moons L (2018) Extensive growth is followed by neurodegenerative pathology in the continuously expanding adult zebrafish retina, Biogerontology, 10.1007/s10522-018-9780-6, 20:1, (109-125), Online publication date: 1-Feb-2019. Shirley B, Grohganz M, Bestmann M and Jarochowska E (2018) Wear, tear and systematic repair: testing models of growth dynamics in conodonts with high-resolution imaging, Proceedings of the Royal Society B: Biological Sciences, 285:1886, Online publication date: 12-Sep-2018. Terrill D, Henderson C and Anderson J (2018) New applications of spectroscopy techniques reveal phylogenetically significant soft tissue residue in Paleozoic conodonts, Journal of Analytical Atomic Spectrometry, 10.1039/C7JA00386B, 33:6, (992-1002) Fraser G, Cerny R, Soukup V, Bronner-Fraser M and Streelman J (2010) The odontode explosion: The origin of tooth-like structures in vertebrates, BioEssays, 10.1002/bies.200900151, 32:9, (808-817), Online publication date: 1-Sep-2010. JIANG H, ALDRIDGE R, LAI X, SUN Y and LUO G (2008) Observations on the surface microreticulation of platform elements of Neogondolella (Conodonta) from the Upper Permian, Meishan, China , Lethaia, 10.1111/j.1502-3931.2007.00052.x, 41:3, (263-274), Online publication date: 1-Sep-2008. Armstrong H and Brasier M (2013) Conodonts Microfossils, 10.1002/9781118685440.ch21, (249-272) Girard C, Renaud S and Feist R (2007) Morphometrics of the Late Devonian conodont genus <i>Palmatolepis</i>: phylogenetic, geographical and ecological contributions of a generic approach, Journal of Micropalaeontology, 10.1144/jm.26.1.61, 26:1, (61-72) Świś P (2018) Population dynamics of the Late Devonian conodont Alternognathus calibrated in days , Historical Biology, 10.1080/08912963.2018.1427088, (1-9) Gregory F, Armstrong H, Boomer I, Gersonde R, Harding I, Herrle J, Lazarus D, Schmidt D, Schoenfeld J and Young J (2006) Celebrating 25 years of advances in micropalaeontology: a review, Journal of Micropalaeontology, 10.1144/jm.25.2.97, 25:2, (97-112) Terrill D, Jarochowska E, Henderson C, Shirley B and Bremer O (2022) Sr/Ca and Ba/Ca ratios support trophic partitioning within a Silurian conodont community from Gotland, Sweden, Paleobiology, 10.1017/pab.2022.9, (1-21) Leonhard I, Shirley B, Murdock D, Repetski J and Jarochowska E (2021) Growth and feeding ecology of coniform conodonts, PeerJ, 10.7717/peerj.12505, 9, (e12505) This Issue22 April 2001Volume 268Issue 1469 Article InformationDOI:https://doi.org/10.1098/rspb.2001.1591PubMed:11345326Published by:Royal SocietyPrint ISSN:0962-8452Online ISSN:1471-2954History: Published online22/04/2001Published in print22/04/2001 License: Citations and impact Keywordsmode of lifeenamel rrowtheuconodonts Large datasets are available through Proceedings B's partnership with Dryad

Zooplankton nutrition: recent progress and a reality check

Evidence suggests that marine and freshwater zooplankton generally experience food levels above subsistence values in terms of carbon. However, the quality of this food may be poor due to an insufficiency of other essential nutrients. In this review, we examine recent progress in three main areas of food quality research: (1) elemental (especially P) limitation, (2) digestion resistance, and (3) biochemical (especially fatty acids) limitation. We evaluate laboratory and field evidence in each of these areas, look at new evidence about the life history implications of the elemental limitation hypothesis, and suggest future avenues for research. From a rather large number of seemingly heterogeneous studies, a single consistent picture of food quality emerges: both P and essential fatty acids are predicted to be important dietary factors, but at different places and times. Nevertheless, despite an abundance of valuable laboratory studies, our knowledge of food quality limitation in the field is still poor.

Mortality estimates from repeated visual censuses of a parrotfish ( Sparisoma viride ) population: demographic implications

Repeated visual censuses of different categories (juveniles, females, territorial and group males) of the stoplight parrotfish (Sparisoma viride, a protogynous hermaphrodite) over a 3-year period indicated a relatively stable size and structure of the adult population. This allowed estimates of size-specific mortality, sex change, and territory acquisition probabilities from previously reported growth rates. Comparison of the predicted number of survivors, sex changers, and territory take overs with field observations indicates that our estimates are quite reliable. However, rather large differences in mortality are obtained for the largest three size classes (>25 cm), which may be due to reduced accuracy of length estimates of large fish. A pooled mortality for these classes is therefore suggested as a more realistic estimate. The life-history implications of our findings are investigated by comparing the predicted survival and future reproductive success of fish that change sex at different sizes. Ten percent of the adults reach an age of ca. 17 years, once a length of 20 cm is attained, as predicted from the pooled estimates. Calculations based on these estimates indicate that the predicted reproductive output of a 15-year-old fish (2500 matings) is the same for early (i.e. at 20 cm) and late (>30 cm) sex changers and for an average fish subject to the estimated daily sex change and territory acquisition probabilities. These findings suggest that S. viride individuals are able to flexibly adjust the timing of sex change in an adaptive way to unpredictable local conditions. However, independent mortality estimates are needed to corroborate our present findings.

The social and mating system of the herbivorous reef fishSparisoma viride: one-male versus multi-male groups

We present a detailed description of the social and mating system of the protogynous reef herbivoreSparisoma viride at the fringing reef of Bonaire (Netherlands Antilles). Initial phase (IP) fish and terminal phase (TP) males occur either in one- or in multi-male groups, which are compared quantitatively with respect to the use of space, size composition, social interactions and sexual activity. One-male groups consist of one TP male plus 1–14 IP females, whereas in multi-male groups up to 14 TP males and about twice as many IP fish share a common home range. The two social units further show marked differences in vertical distribution (one-male groups are restricted to depths between 3 and 22 m, multi-male groups mainly residing < 3 m), size composition (a larger proportion of small adults live in multi-male groups), size and stability of the range (larger in one-male groups) and sexual activity (daily spawning of one-male group members inside their normal home range; no activity in multi-male groups on the shallow reef). Sexual activity occurred daily, throughout the year, with no evidence for tidal tracking or major seasonal or lunar patterns. The one-male groups constitute less than 20% of the adult stock but control up to 77% of the inhabited reef. As a result they have access to higher-yield food patches and to suitable spawning sites inside their home range. Although members of both units appear to defend their common home range against intruding conspecifics, the degree of territoriality is clearly higher in one-male groups. We discuss the relative importance of food, shelter, mates and mating sites as defended resources and some life history implications. The complex social and mating system ofS. viride shows much resemblance to that of another Caribbean scarid,Scarus iserti. This complexity seems to reflect the capacity of individuals to flexibly adapt their feeding, mating and life history styles to an unpredictable environment. We propose thatS. viride is a good study animal to test adaptive explanations for its territorial organization and complex life history patterns.

The meanings of weaning: Growth, lactation, and life history

Hooded seal pups are suckled for a total of four days; chimpanzees and elephants sometimes are suckled for as long as eight years. This enormous range suggests considerable diversity in reproductive strategies. Lactation represents early maternal effort, whereas weaning is the infant's transition to nutritional independence. Weaning behavior is thus important from two interconnected perspectives: that of the infant during this transition and that of the mother with the cessation of lactation and the resumption of her reproductive capacity. What controls such diversity in the duration of lactation? What are the consequences of this diversity for mothers in terms of reproduction and for infants in terms of their growth and survival? How are differences in lactation reflected in behavioral interactions? The answers to these questions involve consideration of weaning and growth, and have implications for life histories.

Population Demography of Antarctic Fur Seals: The Costs of Reproduction and Implications for Life-Histories

1. This study examined the costs of reproduction in terms of future survival and reproduction in female Antarctic fur seals from Bird Island, South Georgia. It used mark-recapture data from 11 consecutive years, including 3 years when several indices showed that food availability was well below average. 2. Population age structures were used, in conjunction with the measured age-specific survival rates, to estimate the rate of increase of the population as 10.7% per annum. 3. The average annual survival rate was 0.83 (SD = 0.10) with a range from 0.65 to 0.93. Survival rate showed no trend through time but was weakly correlated with pup growth rate, suggesting that it may be influenced by availability of food. Survival rate was unrelated to any other environmental or demographic parameter including population size. 4. There was no evidence of senescence. Survival rate was not related to year of birth or age, after accounting for variation due to pregnancy and calendar year. Survival was reduced as a result of pregnancy which accounted for 40-50% of adult female mortality. This effect was greatest in the age classes with the highest reproductive output (ages 5-8 years). 5. Mean pregnancy rate was 0.70 (SD = 0.11) with an interannual range of 0.59-0.88. Although females normally produced their first pups at age 3-4 years, pregnancy rate peaked at age 8 years and declined thereafter. Otherwise pregnancy rate was unrelated to the environmental or demographic variables we tested. Food availability during the pup-rearing period had no effect on pregnancy rate. 40-50% of failures to become pregnant related to animals having been pregnant in the previous year. 6. Reproduction incurs costs to females, in terms of reduced survival and future fecundity, and consequently, on average, females which survive longest tend to do so because they have lower fecundity.