Life History Phenomena Research Articles

Recent Advances in Endocrine and Neuroendocrine Systems.

The endocrine and neuroendocrine systems exert powerful and broad control over the regulation of homeostasis in animals. Secreted hormones play significant roles in lifetime-related events such as germ cell development, sexual maturation, development, metamorphosis, aging, feeding, and energy metabolism. Additionally, hormones, particularly sex steroid hormones, are involved in reproduction, including sexual behavior and dimorphism. Changes in body color protect against external enemies, and circadian rhythms direct physiology and behaviors in synchrony with light and dark cycles. Water and electrolyte metabolism are essential for survival in land or seawater. Both aquatic and terrestrial animals have developed a variety of endocrine and neuroendocrine systems that exquisitely manage water and electrolyte metabolism to support survival. In zoological science, many animal species are investigated for their unique life history phenomena, and many researchers bring original and unique research approaches to understand these phenomena. Exploring such a variety of animal species leads to an understanding of diversity and unity, and contributes to the development of comparative endocrinology. This Special Issue contains 15 papers focusing on the endocrine mechanisms involved in the aforementioned life phenomena.

Wearable reproductive trackers: quantifying a key life history event remotely

Advancements in biologging technology allow terabytes of data to be collected that record the location of individuals but also their direction, speed and acceleration. These multi-stream data sets allow researchers to infer movement and behavioural patterns at high spatiotemporal resolutions and in turn quantify fine-scale changes in state along with likely ecological causes and consequences. The scope offered by such data sets is increasing and there is potential to gain unique insights into a suite of ecological and life history phenomena. We use multi-stream data from global positioning system (GPS) and accelerometer (ACC) devices to quantify breeding events remotely in an Arctic breeding goose. From a training set of known breeders we determine the movement and overall dynamic body acceleration patterns indicative of incubation and use these to classify breeding events in individuals with unknown reproductive status. Given that researchers are often constrained by the amount of biologging data they can collect due to device weights, we carry out a sensitivity analysis. Here we explore the relative merits of GPS vs ACC data and how varying the temporal resolution of the data affects the accuracy of classifying incubation for birds. Classifier accuracy deteriorates as the temporal resolution of GPS and ACC are reduced but the reduction in precision (false positive rate) is larger in comparison to recall (false negative rate). Precision fell to 94.5%, whereas recall didn’t fall below 98% over all sampling schedules tested. Our data set could have been reduced by c.95% while maintaining precision and recall > 98%. The GPS-only classifier generally outperformed the ACC-only classifier across all accuracy metrics but both performed worse than the combined GPS and ACC classifier. GPS and ACC data can be used to reconstruct breeding events remotely, allowing unbiased, 24-h monitoring of individuals. Our resampling-based sensitivity analysis of classifier accuracy has important implications with regards to both device design and sampling schedules for study systems, where device size is constrained. It will allow researchers with similar aims to optimize device battery, memory usage and lifespan to maximise the ability to correctly quantify life history events.

Increase in protandry over time in a long-distance migratory bird.

Protandry is a widespread life‐history phenomenon describing how males precede females at the site or state of reproduction. In migratory birds, protandry has an important influence on individual fitness, the migratory syndrome, and phenological response to climate change. Despite its significance, accurate analyses on the dynamics of protandry using data sets collected at the breeding site, are lacking. Basing our study on records collected during two time periods, 1979 to 1988 and 2006 to 2016, we aim to investigate protandry dynamics over 38 years in a breeding population of willow warblers (Phylloscopus trochilus). Change in the timing of arrival was analyzed in males and females, and protandry (number of days between male and female arrival) was investigated both at population level and within breeding pairs. Our results show advancement in the arrival time at the breeding site in both sexes, but male arrival has advanced to a greater extent, leading to an increase in protandry both at the population level and within breeding pairs. We did not observe any change in sex ratio that could explain the protandry increase, but pronounced temperature change has occurred and been reported in the breeding area and along the migratory route. Typically, natural selection opposes too early arrival in males, but given warmer springs, this counteracting force may be relaxing, enabling an increase in protandry. We discuss whether our results suggest that climate change has induced sex‐specific effects, if these could be evolutionary and whether the timing of important life‐history stages such as arrival at the breeding site may change at different rates in males and females following environmental shifts.

Multidimensional natal isotopic niches reflect migratory patterns in birds

Naturally occurring stable isotope ratios in animal tissues allow estimation of species trophic position and ecological niche. Measuring multiple isotopes of migratory species along flyway bottlenecks offers the opportunity to sample multiple populations and species whose tissues carry information at continental scales. We measured δ2H, δ18O, δ13C, δ15N in juvenile feathers of 21 bird species captured at a migratory bottleneck in the Italian Alps. We examined if trends in individual isotopes reflected known migratory strategies and whether dietary (δ13C–δ15N) and spatially-explicit breeding origin (δ2H–δ18O) niche breadth (NB) differed among long-distance trans-Saharan (TS), short-distance (IP) and irruptive (IR) intra-Palearctic migrants, and whether they correlated with reported populations long-term trends. In both TS and IP groups, species δ2H declined with capture date, indicating that northern populations reached the stopover site later in the season, following a Type-I migration strategy. Values of δ2H indicated that breeding range of TS migrants extended farther north than IP and IR migrants. The breeding season was longer for IP migrants whose δ13C and δ15N values declined and increased, respectively, with time of capture. Average species dietary NB did not differ among migratory groups, but TS migrants displayed wider breeding origin niches, suggesting that long-distant migration is linked to broader ecological niches. Isotope origin NB well reflected species geographic range extent, while dietary NB did not correlate with literature accounts of species’ diet. We found no relationship between species breeding NB and population trends in Europe, suggesting that conditions in the breeding grounds, as inferred by stable isotopes, are not the only determinant of species’ long-term persistence. We demonstrate that ringing activities and isotopic measurements of passerines migrating through a bottleneck represents a unique opportunity to investigate large-scale life-history phenomena relevant to conservation.

Long‐term studies on restoration of Connecticut River anadromous sea lamprey,Petromyzon marinusLinnaeus 1758: Trend in annual adult runs, abundance cycle, and nesting

This study is the first to evaluate the results of 60 years of restoring anadromous sea lamprey, Petromyzon marinus, to historical spawning and rearing habitats using fish passage at barrier dams in the Connecticut River, USA. We obtained counts of pre-spawning adult P. marinus annually passed upstream at Holyoke Dam (river km 140), Connecticut River, MA, during 37 years (1978–2014), and we counted P. marinus nests during 25 years (1986–2010) in the Fort River, a tributary upstream of Holyoke Dam. These two data sets were used to study relationships between adult passage and subsequent nesting and to study nesting timing and ecology. During the 37 years, annual adult P. marinus abundance at Holyoke Dam ranged from 15,000 to 95,000, but regression analysis found no trend (p = .50) for increasing annual adult abundance with years. However, during the 37 years, adults gained access via fish passage at dams to an estimated double the amount of spawning and rearing habitat upstream compared to the 1970s. The lack of a trend for increased adult abundance is consistent with a hypothesis of non-natal river homing by adults. However, the lack of a trend in adult abundance, when many more larvae are likely present in the watershed compared to the 1970s, is inconsistent with the hypothesis that greater numbers of larvae (and greater concentration of larval pheromone) results in greater number of adults attracted to a river. Instead of an abundance trend of adults with years, we found a rare life history phenomenon occurs in anadromous adult P. marinus ─ an abundance cycle with peaks at 6 year intervals (autocorrelation analysis, p = .04). Comparison of passage timing with nesting timing found passage did not affect nesting initiation or duration (p = .61). Annual date of nesting initiation strongly affected the duration of nesting with earlier nesting resulting in longer nesting (p = .001). Time series comparing Fort River temperature and discharge with nesting found these factors did not clearly predict annual initiation of nesting. This suggests a role for day length (photoperiod) as the trigger for nesting initiation (most nesting began annually during 1–14 June, all year mean, 7 June), regardless of river conditions. However, river discharge may affect nesting ecology because most nesting occurred during decreasing discharge when variability in daily discharge was small (stable discharge). The present research on passage and nesting contributes to a new Connecticut River restoration program for P. marinus, which is a keystone fish species in the watershed.

Use of Micro-Computed Tomography for Dental Studies in Modern and Fossil Odontocetes: Potential Applications and Limitations

Teeth are important elements in studies of modern and fossil Cetacea (whales, dolphins), providing information on feeding habits, estimations of age and phylogenetic relationships. The growth layer groups (GLGs) recorded in dentine have demonstrated application for aging studies, but also have the potential to elucidate life history phenomena such as metabolic or physiologic events. Micro-Computed Tomography (Micro-CT) is a non-invasive and non-destructive technique that allows 3-dimensional study of mineralized tissues, such as human teeth, and their physical properties. Teeth from extant dolphins (Cetacea: Odontoceti) and some fossil odontocetes were scanned in a Skyscan 1172 Micro-CT desktop system. X-rays were generated at 100 kV and 100 µA for extant samples, and at 80kV and 124 µA for fossils. 0.5 mm thick aluminum and copper filters were used in the beam. Reconstructed images were informative for most extant species, showing a good resolution of the enamel layer, dentine and pulp cavity. Greyscale changes in the dentinal layers were not resolved enough to show GLGs. Visualization of the internal structure in fossil cetacean teeth depended on the degree of diagenetic alteration in the specimen; undifferentiated enamel and dentine regions probably reflect secondary mineralization. However, internal details were finely resolved for one fossil specimen, showing the enamel, internal layers of dentine and the pulp cavity. Micro-CT has been proven to be a useful tool for resolving the internal morphology of fossil and extant teeth of cetaceans before they are sectioned for other morphological analyses; however some methodological refinements are still necessary to allow better resolution of dentine for potential application in non-destructive age determination studies.

Demography of a dormancy-prone geophyte: influence of spatial scale on interpretation of dynamics

Both temporal and spatial scales are important in the evaluation of population dynamics, but the latter often receives less attention in demographic analyses. We used a 5-year demographic data set for a long-lived geophyte, Calochortus lyallii, to investigate the pattern and components of spatial variation at two scales (population and microsite). We found that neither the projected population structure nor asymptotic population growth rate (λ) varied greatly across either scale, although the underlying contributors to the variation in λ, V(λ), did differ between scales. Life table response experiment analyses showed that V(λ) among populations came primarily from variation in seedling survival and progression of non-reproductive plants, whereas V(λ) among microsites was primarily due to the variable fertility of large adults. Prolonged dormancy was important in reducing V(λ) among quadrats at both the scales, partly countering fluctuations in other transitions such as recruitment. This result represents some of the first evidence that underground “bulb banks” could function to offset the effects of a spatially heterogeneous environment in a manner analogous to seed banks. Future work is needed to isolate the specific, sometimes idiosyncratic, life history phenomena acting to modulate plant population dynamics in a spatial context.

Predicting trait values and measuring selection in complex life histories: reproductive allocation decisions in Soay sheep

Accurate prediction of life history phenomena and characterisation of selection in free-living animal populations are fundamental goals in evolutionary ecology. In density regulated, structured populations, where individual state influences fate, simple and widely used approaches based on individual lifetime measures of fitness are difficult to justify. We combine recently developed structured population modelling tools with ideas from modern evolutionary game theory (adaptive dynamics) to understand selection on allocation of female reproductive effort to singletons or twins in a size-structured population of feral sheep. In marked contrast to the classical selection analyses, our model-based approach predicts that the female allocation strategy is under negligible directional selection. These differences arise because classical selection analysis ignores components of offspring fitness and fails to consider selection over the complete life cycle.

Strict mast fruiting for a tropical dipterocarp tree: a demographic cost-benefit analysis of delayed reproduction and seed predation

1. Masting, the production of large seed crops at intervals of several years, is a reproductive adaptation displayed by many tree species. The predator satiation hypothesis predicts that starvation of seed predators between mast years and satiation during mast years decreases seed predation and thus enhances tree regeneration. 2. Mast fruiting comes at demographic costs such as missed reproduction opportunities and increased density-dependence of recruits, but it remains unknown if predator satiation constitutes a sufficiently large benefit for masting to evolve as a viable life-history strategy. So far, no studies have quantified the net fitness consequences of masting. 3. Using a long-term demographic data set of the dipterocarp Shorea leprosula in a Malaysian forest, we constructed stochastic matrix population models and performed a demographic cost–benefit analysis. 4. For observed values of mast frequency and seed predation rates, we show that strict masting strongly increases fitness compared with fruiting annually. Model results also show that the demographic costs of mast fruiting are very low compared to the demographic losses due to seed predation in a scenario of annual fruiting. Finally, we find that mast fruiting would still be selected for even at low levels of seed predation and when including additional costs such as decreased adult growth rates, limiting crop size and density-dependent seedling survival. 5. Synthesis. Our results are consistent with the predictions of the predator satiation hypothesis: mast fruiting increases fitness for a range of seed predation levels. Under seed predation pressure annually fruiting species are at a strong disadvantage and as a result a mast fruiting strategy may swiftly confer a fitness advantage. Our study shows that demographic modelling allows the weighing of fitness benefits and costs of life-history phenomena such as strict masting.

The metabolic theory of ecology: prospects and challenges for plant biology

The metabolic theory of ecology (MTE) as applied to the plant sciences aims to provide a general synthesis for the structure and functioning of plants from organelles to ecosystems. MTE builds from simple assumptions of individual metabolism to make predictions about phenomena across a wide range of scales, from individual plant structure and function to community dynamics and global nutrient cycles. The scope of its predictions include morphological allometry, biomass partitioning, vascular network design, and life history phenomena at the individual level; size-frequency distributions, population growth rates, and energetic equivalence at the community level; and the flux, turnover and storage of nutrients at the ecosystem level. Here, we provide an overview of MTE, by considering its assumptions and predictions at these different levels of organization and explaining how the model integrates phenomena among all of these scales. We highlight the model's many successes in predicting novel patterns and draw attention to areas in which gaps remain between observations and MTE's assumptions and predictions. Considering the theory as a whole, we argue that MTE has made a significant contribution in furthering our understanding of those unifying aspects of the structure and function of plants, populations, communities, and ecosystems.

The evolution of seeds

The evolution of the seed represents a remarkable life-history transition for photosynthetic organisms. Here, we review the recent literature and historical understanding of how and why seeds evolved. Answering the 'how' question involves a detailed understanding of the developmental morphology and anatomy of seeds, as well as the genetic programs that determine seed size. We complement this with a special emphasis on the evolution of dormancy, the characteristic of seeds that allows for long 'distance' time travel. Answering the 'why' question involves proposed hypotheses of how natural selection has operated to favor the seed life-history phenomenon. The recent flurry of research describing the comparative biology of seeds is discussed. The review will be divided into sections dealing with: (1) the development and anatomy of seeds; (2) the endosperm; (3) dormancy; (4) early seed-like structures and the transition to seeds; and (5) the evolution of seed size (mass). In many cases, a special distinction is made between angiosperm and gymnosperm seeds. Finally, we make some recommendations for future research in seed biology.

A Global Baseline for Spawning Aggregations of Reef Fishes

Species that periodically and predictably congregate on land or in the sea can be extremely vulnerable to overexploitation. Many coral reef fishes form spawning aggregations that are increasingly the target of fishing. Although serious declines are well known for a few species, the extent of this behavior among fishes and the impacts of aggregation fishing are not appreciated widely. To profile aggregating species globally, establish a baseline for future work, and strengthen the case for protection, we (as members of the Society for the Conservation of Reef Fish Aggregations) developed a global database on the occurrence, history, and management of spawning aggregations. We complemented the database with information from interviews with over 300 fishers in Asia and the western Pacific. Sixty-seven species, mainly commercial, in 9 families aggregate to spawn in the 29 countries or territories considered in the database. Ninety percent of aggregation records were from reef pass channels, promontories, and outer reef-slope drop-offs. Multispecies aggregation sites were common, and spawning seasons of most species typically lasted <3 months. The best-documented species in the database, the Nassau grouper (Epinephelus striatus), has undergone substantial declines in aggregations throughout its range and is now considered threatened. Our findings have important conservation and management implications for aggregating species given that exploitation pressures on them are increasing, there is little effective management, and 79% of those aggregations sufficiently well documented were reported to be in decline. Nonetheless, a few success stories demonstrate the benefits of aggregation management. A major shift in perspective on spawning aggregations of reef fish, from being seen as opportunities for exploitation to acknowledging them as important life-history phenomena in need of management, is urgently needed.

Life history perspectives on pest insects: What's the use?

In his seminal 1954 paper on the ‘population consequences of life history phenomena’, Cole noted that ‘these computations may have practical value in dealing with valuable or noxious species’. In the present paper, the question is asked: ‘is research based on evolutionary perspectives in general, and life history theory specifically, really useful for dealing with insect pests?’ Perhaps such theory-based research is rather a luxury: time and resources would be better spent on entirely applied aspects of the problem. The conclusion of the present discussion is that having an evolutionary perspective guiding research is actually a very cost-effective way of dealing with applied problems, as it provides a clear basis for interpretations, generalizations and predictions. Life history theory is a very central and necessary part of both population ecology and general evolutionary theory, and its specific usefulness in pest forecasting and management are discussed. Nevertheless, our ability to predict insect population dynamics is still limited, and so is our ability to make use of an insect’s life history traits to predict its propensity to become a pest. I suggest that the former shortcoming is largely due to poor understanding of insect life history plasticity. This, in turn, may partly be due to a paucity of studies where reaction norms are investigated as putative adaptations. I suggest that the latter shortcoming is due to problems inherent with studying life history traits as adaptations, for example the lack of an independent fitness model and the fact that life histories tend to form syndromes of coadapted traits. These points are illustrated with examples from my own work on non-pest butterflies and from insect–Eucalyptus systems.

State-dependent energy allocation in cod (Gadus morhua)

Growth and maturation are processes that are tuned to the external environment that an individual is likely to experience, where food availability, the mortality regime, and events necessary to complete the life cycle are of special importance. Understanding what influences life history strategies and how changes in life history in turn influence population dynamics and ecological interactions are crucial to our understanding of marine ecology and contemporary anthropogenic induced change. We present a state-dependent model that optimises life-long energy allocation in iteroparous fish. Energy can be allocated to growth or reproduction and depends in the individual's age, body length, and stored energy and the state of the environment. Allocation and the physiological processes of growth, energy storage, and reproduction are modelled mechanistically. The model is parameterised for Atlantic cod (Gadus morhua), more specifically the Northeast Arctic cod stock. Growth and maturation predicted by the model fit well with field observations, and based on a further investigation of cod reproduction in the model, we conclude that the model has the ability to recapture complex life history phenomena, e.g., indeterminate growth and skipped spawning, and therefore provides an important tool that can improve our understanding of life history strategies in fish.

THE FIRST BASIC PROBLEM REVISITED: REPLY TO COMMENTARIES ON HOWELL ET AL. (2003)

Abstract In this issue, Jenni and Winkler, Piersma, Thompson, and Willoughby offer commentaries on our modifications (Howell et al. 2003) to the Humphrey-Parkes system for naming molts and plumages (Humphrey and Parkes 1959; the H-P system). Piersma generally accepts our revision and outlines how its use could improve our ability to understand other cyclic life-history phenomena. Both Jenni and Winkler and Willoughby disagree with the philosophy of the H-P system, particularly its ability to reveal homologies. Thompson accepts the H-P system but argues that our elaboration on the system is faulty. However, we believe that despite a diversity of opinion concerning our proposal there is much common ground, including agreement regarding the homology of juvenal and basic plumages across species and the utility of the new term “formative.” The main points we review here are the potential dichotomy between homologies of molt and homologies of plumage coloration; the caution that should be applied when using plu...

UNDERSTANDING EVOLUTION OF PLUMAGES AND OTHER CYCLIC AVIAN LIFE-HISTORY PHENOMENA: ROLE FOR AN IMPROVED MOLT TERMINOLOGY

Abstract Birds show quite distinct changes in both external and internal appearance. An evolutionary interpretation of these cyclic life-history phenomena would benefit from a system of description aimed at mapping shared ancestries of arguably the “easiest” of traits: the molts and seasonal plumage changes. By 1959, Humphrey and Parkes had already provided the basis of such a system, but its development and application, especially with regard to the confusing first plumage cycle, by Howell et al. (2003), adds considerably to its power. I hope this leads to an upsurge of evolutionary studies of molt and plumage cycles that in turn provide the basis for analyses of other aspects of the flexible phenotype of birds. With such an increase, the study of molts and plumages could once again be at center stage of avian biology. Entendiendo la Evolucion de los Plumajes y Otros Fenomenos Ciclicos de las Historias de Vida de las Aves: El Papel de una Terminologia Mejorada para la Muda Resumen. Las aves muestran camb...

Life history perspectives on pest insects: What’s the use?

AbstractIn his seminal 1954 paper on the ‘population consequences of life history phenomena’, Cole noted that ‘these computations may have practical value in dealing with valuable or noxious species’. In the present paper, the question is asked: ‘is research based on evolutionary perspectives in general, and life history theory specifically, really useful for dealing with insect pests?’ Perhaps such theory‐based research is rather a luxury: time and resources would be better spent on entirely applied aspects of the problem. The conclusion of the present discussion is that having an evolutionary perspective guiding research is actually a very cost‐effective way of dealing with applied problems, as it provides a clear basis for interpretations, generalizations and predictions. Life history theory is a very central and necessary part of both population ecology and general evolutionary theory, and its specific usefulness in pest forecasting and management are discussed. Nevertheless, our ability to predict insect population dynamics is still limited, and so is our ability to make use of an insect’s life history traits to predict its propensity to become a pest. I suggest that the former shortcoming is largely due to poor understanding of insect life history plasticity. This, in turn, may partly be due to a paucity of studies where reaction norms are investigated as putative adaptations. I suggest that the latter shortcoming is due to problems inherent with studying life history traits as adaptations, for example the lack of an independent fitness model and the fact that life histories tend to form syndromes of coadapted traits. These points are illustrated with examples from my own work on non‐pest butterflies and from insect–Eucalyptus systems.

Mechanistic and Selective Causes of Life History Trade-Offs and Plasticity

We discuss the mechanistic (proximate) and selective (ultimate) factors that cause life history trade-offs such as the trade-off between offspring quality and quantity and that between current and future reproduction. We point out that key concepts in life history theory and evolutionary biology such as negative genetic correlations and trade-offs can be understood in terms of physiological mechanisms. More specifically, negative genetic correlations causing trade-offs between life history traits are caused by hormones and their regulatory genes that have multiple and opposing, pleiotropic effects on two or more traits. Consequently, investigations of these mechanisms is a natural complement to the classical population genetical approach. We critically dissect the argument, put forward by other workers, that experimental manipulations of organismal physiology or other phenotypic traits do not reveal genetic life history trade-offs, but only reflects phenotypic plasticity. We reject this idea and discuss the proposed alternative approach: laboratory selection experiments. We point out some problems associated with laboratory selection experiments and suggest that experimental manipulations of life history traits and secondary sexual characters in natural populations is an important and invaluable empirical method if one aims to get a better understanding of life history evolution in the wild. Finally, we discuss the proximate-ultimate dichotomy, the physiology of phylogenetic constraints, the role of physiological mechanisms in population differentiation in life history trade-offs and the importance of phenotypic plasticity in shaping such trade-offs. We suggest that life history plasticity in many cases may stem from the same endocrine mechanisms (gonadotropin, gonadal steroids, and adrenal glucocorticoids) as those involved in life history trade-offs. In particular, attempts to dichotomize life history trade-offs and life history plasticity may be unrealistic as the hormones governing both life history phenomena are likely to share key mechanisms in common.

Reproductive Strategies in a Population of Gobiosoma bosci (Osteichthyes: Gobiidae) with Slow and Fast Maturing Individuals

The reproductive biology of Gobiosoma boscicollected from November 1986 to October 1987 in the McFaddin Wildlife Refuge in southeast Texas was studied by using morphometric data. Males achieved greater weights per unit length than females, and longevity was about 12 to 13 months. GSI values and mean monthly ovum diameters indicated that the breeding season ran from April to September, with a major activity peak in May and a minor peak in September. Significant differences in male and female standard lengths (SL), ovum diameter, and egg number existed for sexually mature specimens between the first and second peaks of reproductive activity. An egg versus length analysis produced a positive linear relationship. An accessory gonadal structure index (ASGI) was developed and revealed that maximal AGS development corresponded with the male GSI, but did not produce discemable peaks. Two reproductive strategies were followed and depended upon time of hatching and growth rate. Some individuals that hatched early in the breeding season grew rapidly and were capable of egg laying by August or September. Individuals hatched late in the breeding season delayed breeding until the following season. The distribution of the naked goby, Gobiosoma bosci, extends from Long Island, New York, to the state of Carnpeche, Mexico (Hoese and Moore 1977). In view of the markedenvironmentaldifferellces throughout its range, G. boscimay be expectedto vary its reproductive strategies. In a review of life history phenomena, Cole (1954) stated that the age at which reproductionbegins is one of the most significant characteristics, and as such will influence the reproductive success of an individual. Therefore, southerly populations of G. bosci have at least two potential reproductive strategies available to them (Steams and Crandall1984). First, an individual may grow throughout the non-reproduc tive season after hatching and thenengage in breeding during the subsequent breeding season. Alternatively, young-of-the-year may grow rapidly enough to reproduce before the end of the breeding season, and thereby gain a breeding season not available to fish with delayed breeding. As such, individuals within the same populationmay employ one strategy or the other depending upon their time of hatching and environmental conditions. * Corresponding author; current address is Dept. of Biology, Valdosta State University, Valdosta, GA 31698 Gobiosoma bosci, a cavity nester preferring hard substrates (Bechler et al. l99O), has been studiedextensively along the Atlantic Coast. Dahlberg and Conyers (1973), who reviewed much of the literature, postulated that spawning seasons for different populations of G. bosci were variable, and depended on location. They related initiation and termination of spawning to water temperature and indicated peak spawning activity was in the warmest months, May through August. However,they didnot discuss any variations inbreeding strategies. Other reports on G. bosci byNem(lW6),CrabtreeandMiddaugh(l982),and~rnimm and Seok (1989) revealedmany h t s about the life history and ecology of G. bosci. However, none of the above studies examined reproductive strategies of the naked goby -in fthelargest,ClamLake, was the primary siteof this study.

The National Trust and nature conservation: prospects for the future

The range and extent of nature conservation interests on land owned by the National Trust are reviewed and the high level of protection which can be afforded to such features is stressed. Some of the threats to such interests are examined and possible conflicts between management for nature conservation and for other Trust objectives are considered. The importance of survey and monitoring are emphasized. It is argued that nature conservationists need to adopt a view of plant communities which recognises their dynamic nature and which accepts the possibility of change. Evidence is reviewed which supports the non-equilibrium state of some communities, the impact of rare events and the importance of life history phenomena. Some possible future directions of nature conservation in the Trust are discussed.