An individual behaviour‐based model can predict shorebird mortality using routinely collected shellfishery data

Food supply is widely considered to be a major factor in determining life history traits and reproductive performance of birds. However, large spatial and temporal variation in natural available food supply is not always paralleled by proportional changes in energy demand by breeding birds. This necessarily results in variation in the supply–demand ratio and the amount of food available per unit mass of nestling. Because reproductive performance should respond to increases in available supply as a saturation curve, reaching a plateau above a certain threshold of food supply, we predict that variation in supply should change the intensity of selection on reproductive traits. We first tested this prediction using long-term data on nestling growth and survival in Blue Tits (Parus caeruleus) breeding over a gradient of habitat richness in Corsica, France. This long-term data analysis evaluates the effect of variation in food supply available to breeding tits using three surrogate variables: interannual variation in peak caterpillar abundance (caterpillar frass fall), offset between breeding date and peak caterpillar abundance, and natural variation in clutch size. We also used an experimental brood size manipulation (±3 chicks) to test the effect of varying brood demand on nestling growth. Results of the long-term data analysis show that all three variables affect fledging mass and fledging success in poor habitats, while only fledging mass is affected by variation in offset in rich habitats. Moreover, mean annual fledging success and fledging mass is strongly affected by annual variation in peak caterpillar abundance at low levels of abundance, but these effects disappear when food becomes abundant (saturation threshold level of 373 and 560 mg frass·m−2·d−1 for fledging success and fledging mass, respectively). Brood size manipulations confirm these results. In rich habitats, breeding birds can raise three extra chicks without any apparent effects on chick growth, while in poor habitats, chick growth is significantly reduced with brood enlargement. Our study shows that although food limitation can play an important role, it may not always be the primary force shaping life history traits.

The hypothesis that migratory bird populations are limited during the non-breeding season is increasingly supported by empirical studies that also suggest consequences that carry-over into subsequent seasons. Although variation in food supply is the best supported explanation for non-breeding season limitation, the ecological mechanisms and physiological consequences are not well understood. We both supplemented and reduced Ovenbird (Seiurus aurocapilla) food availability on replicate plots in Jamaica in each of 3 years to determine the direct role of food in limiting the physical condition of Ovenbirds. Annual variation in rainfall and food supply created a natural experiment in parallel with manipulations. Sex and age-classes of Ovenbirds did not respond differently in terms of body condition to either food manipulation or natural variation in environmental conditions, suggesting that this population is not structured by strong dominance relationships. Ovenbird body mass, fat, and pectoralis muscle shape were positively and predictably related to manipulated food availability. Feather regrowth rate also responded positively to food supplementation and negatively to food reduction in the drier of 2 years. Prior to manipulation, annual variation in body mass corresponded to annual variation in food supply and rainfall, providing additional, correlational evidence of food limitation. Since multiple intercorrelated body condition indices of Ovenbirds responded directly to food supply, and since food supply influenced body condition independently of other habitat features, we argue that food is a primary driver of non-breeding season population limitation. Moreover, since these effects were observed during the late non-breeding period, when individuals are preparing to migrate, we infer that food availability likely initiates carry-over effects.

Summary1. In order to assess the future impact of a proposed development or evaluate the cost effectiveness of proposed mitigating measures, ecologists must be able to provide accurate predictions under new environmental conditions. The difficulty with predicting to new circumstances is that often there is no way of knowing whether the empirical relationships upon which models are based will hold under the new conditions, and so predictions are of uncertain accuracy.2. We present a model, based on the optimality approach of behavioural ecology, that is designed to overcome this problem. The model's central assumption is that each individual within a population always behaves in order to maximize its fitness. The model follows the optimal decisions of each individual within a population and predicts population mortality rate from the survival consequences of these decisions. Suchbehaviour‐basedmodels should provide a reliable means of predicting to new circumstances because, even if conditions change greatly, the basis of predictions – fitness maximization – will not.3. The model was parameterized and tested for a shorebird, the oystercatcherHaematopus ostralegus. Development aimed to minimize the difference between predicted and observed overwinter starvation rates of juveniles, immatures and adults during the model calibration years of 1976–80. The model was tested by comparing its predicted starvation rates with the observed rates for another sample of years during 1980–91, when the oystercatcher population was larger than in the model calibration years. It predicted the observed density‐dependent increase in mortality rate in these years, outside the conditions for which it was parameterized.4. The predicted overwinter mortality rate was based on generally realistic behaviour of oystercatchers within the model population. The two submodels that predicted the interference‐free intake rates and the numbers and densities of birds on the different musselMytilus edulisbeds at low water did so with good precision. The model also predicted reasonably well (i) the stage of the winter at which the birds starved; (ii) the relative mass of birds using different feeding methods; (iii) the number of minutes birds spent feeding on mussels at low water during both the night and day; and (iv) the dates at which birds supplemented their low tide intake of mussels by also feeding on supplementary prey in fields while mussel beds were unavailable over the high water period.5. A sensitivity analysis showed that the model's predictive ability depended on virtually all of its parameters. However, the importance of different parameters varied considerably. In particular, variation in gross energetic parameters had a greater influence on predictions than variations in behavioural parameters. In accord with this, much of the model's predictive power was retained when a detailed foraging submodel was replaced with a simple functional response relating intake rate to mussel biomass. The behavioural parameters were not irrelevant, however, as these were the basis of predictions.6. Although we applied the model to oystercatchers, the general principle on which it is based applies widely. We list the key parameters that need to be measured in order to apply the model to other systems, estimate the time scales involved and describe the types of environmental changes that can be modelled. For example, in the case of estuaries, the model can be used to predict the impact of habitat loss, changes in the intensity or method of shellfishing, or changes in the frequency of human disturbance.7. We conclude that behaviour‐based models provide a good basis for predicting how demographic parameters, and thus population size, would be affected by novel environments. The key reason for this is that, by being based on optimal decision rules, animals in these models are likely to respond to environmental changes in the same way as real ones would.

We studied recruitment age (i.e. the age that a gull bred for the first time) and the probability that an adult reproduced during its life in three cohorts of Western Gulls Larus occidentalis breeding on southeast Farallon Island. We examined the effects of sex, hatching date, hatching order, brood size and annual variation in food supply during the recruitment period. Modal recruitment ages of males and females were 4 and 5 years, respectively, a difference that was significant. None of the factors examined, including hatching date, hatching order and brood size, had a significant effect on recruitment age. The probability of breeding in males who experienced low food supply in their fourth and fifth years was lower than that of males who experienced favourable food supply in their fourth and fifth years. Recruitment probability (the proportion of the sample group that recruited among those available to recruit during a given year) of 4‐ and 5‐year‐old males was lower in the food‐poor 1983 El Nino than in years of favourable food supply. The only variable affecting recruitment probability of females was age: recruitment probability was greater among 5‐year‐olds than 4‐year‐olds. Recruitment age in males was more sensitive to annual variation in food supply, probably because females have more difficulty recruiting due to an excess of adult females in the population and because of the different roles in reproduction in which males are primarily responsible for provisioning chicks and maintaining the territory.

Individual‐based models (IBMs) predict how animal populations will be affected by changes in their environment by modeling the responses of fitness‐maximizing individuals to environmental change and by calculating how their aggregate responses change the average fitness of individuals and thus the demographic rates, and therefore size of the population. This paper describes how the need to develop a new approach to make such predictions was identified in the mid‐1970s following work done to predict the effect of building a freshwater reservoir on part of the intertidal feeding areas of the shorebirds Charadrii that overwinter on the Wash, a large embayment on the east coast of England. The paper describes how the approach was developed and tested over 20 years (1976–1995) on a population of European oystercatchersHaematopus ostraleguseating musselsMytilus edulison the Exe estuary in Devon, England.The paper goes on to describe how individual‐based modeling has been applied over the last 10 years to a wide range of environmental issues and to many species of shorebirds and wildfowl in a number of European countries. Although it took 20 years to develop the approach for 1 bird species on 1 estuary, ways have been found by which it can now be applied quite rapidly to a wide range of species, at spatial scales ranging from 1 estuary to the whole continent of Europe. This can now be done within the time period typically allotted to environmental impact assessments involving coastal bird populations in Europe.The models are being used routinely to predict the impact on the fitness of coastal shorebirds and wildfowl of habitat loss from (i) development, such as building a port over intertidal flats; (ii) disturbance from people, raptors, and aircraft; (iii) harvesting shellfish; and (iv) climate change and any associated rise in sea level. The model has also been used to evaluate the probable effectiveness of mitigation measures aimed at ameliorating the impact of such environmental changes on the birds. The first steps are now being taken to extend the approach to diving sea ducks and farmland birds during the nonbreeding season.The models have been successful in predicting the observed behavior and mortality rates in winter of shorebirds on a number of European estuaries, and some of the most important of these tests are described. These successful tests of model predictions raise confidence that the model can be used to advise policy makers concerned with the management of the coast and its important bird populations.

The adult sex ratio (ASR) is an important property of populations. Comparative phylogenetic analyses have shown that unequal sex ratios are associated with the frequency of changing mates, extrapair mating (EPM), mating system and parental care, sex-specific survival, and population dynamics. Comparative demographic analyses are needed to validate the inferences, and to identify the causes and consequences of sex ratio inequalities in changing environments. We tested expected consequences of biased sex ratios in two species of Darwin's finches in the Galápagos, where annual variation in rainfall, food supply, and survival is pronounced. Environmental perturbations cause sex ratios to become strongly male-biased, and when this happens, females have increased opportunities to choose high-quality males. The choice of a mate is influenced by early experience of parental morphology (sexual imprinting), and since morphological traits are highly heritable, mate choice is expressed as a positive correlation between mates. The expected assortative mating was demonstrated when the Geospiza scandens population was strongly male-biased, and not present in the contemporary Geospiza fortis population with an equal sex ratio. Initial effects of parental imprinting were subsequently overridden by other factors when females changed mates, some repeatedly. Females of both species were more frequently polyandrous in male-biased populations, and fledged more offspring by changing mates. The ASR ratio indirectly affected the frequency of EPM (and hybridization), but this did not lead to social mate choice. The study provides a strong demonstration of how mating patterns change when environmental fluctuations lead to altered sex ratios through differential mortality.

Interference is an important component of food competition but is often difficult to detect and measure in natural animal populations. Although interference has been shown to occur between oystercatchersHaematopus ostralegusL. feeding on musselsMytilus edulisL., four previous studies have not detected interference between oystercatchers feeding on cocklesCerastoderma eduleL. In contrast, this study detected interference between cockle‐feeding oystercatchers in the Baie de Somme, France. Prey stealing (kleptoparasitism), one of the main causes of interference between mussel‐feeders, also occurred between oystercatchers in the Baie de Somme. The kleptoparasitism rate was related to the natural variation in the food supply, tending to be higher when cockles were rare. Feeding rate was negatively related to competitor density, so providing evidence for interference, but, as in mussel‐feeders, only above a threshold density of about 50–100 birds ha−1. The strength of interference at a fixed competitor density was related to the cockle food supply, usually being greater when cockles were rare. Previous studies probably failed to detect interference between cockle‐feeders because competitor densities were too low, or cockles were too abundant, or because they were not conducted during late winter when interference is most intense. The study shows that natural variation in the food supply can influence the strength of interference within an animal population and provides support for those behaviour‐based interference models which predict that the strength of interference will be greatest when competitor densities are high and prey scarce.

Xenohormesis: Sensing the Chemical Cues of Other Species

(1) We report some effects of an annually variable and unpredictable rainfall upon Darwin's Finches on the Galápagos. Finch numbers, foraging and food supply were studied on I. Daphne Major in December of 1973 and 1977, and compared. 1973 was the second of two successive wet years and 1977 was a drought year. (2) Seed numbers and biomass were approximately one order of magnitude lower in the drought year than in the wet year. Small and soft seeds were absolutely and relatively rarer in the drought year than in the wet year. (3) Similarly finch numbers and biomass were approximately one order of magnitude lower in the drought year than in the wet year. Numbers of G. scandens declined less than did number of G. fortis. Both species exhibited unabalaced sex ratios, in favour of males, in the dry year in contrast to balanced sex ratios in the wet year. Male scandens were heavier on average in the wet year, but male fortis were heavier in the dry year. (4) The foraging of scandens, a cactus (Opuntia) specialist, was similar in the two years. The foraging of fortis in the dry year differed from foraging in the wet year in three important respects: fortis devoted a disproportionate amount of time to feeding on small seeds while tending to avoid seeds of Opuntia, they fed more on floral and extra-floral parts of Opuntia and they fed on Tribulus cistoides, a large and hard fruit which was absent from their diet in the wet year. As a consequence of feeding more on Opuntia, fortis foraging was more similar to scandens foraging in the dry year than in the wet year. (5) The results are discussed in relation to expectations from competition theory. The decline in numbers in relation to a decline in food supply was expected, but a convergence in diets was not. The convergence is attributed to the recent renewal of a single resource, Opuntia flowers, against a background of general resource scarcity. Diet overlap and limitation of numbers by food provide indirect evidence of interspecific competition; scandens, with an included niche, was competitively superior to fortis.

The gregarious feeding behaviour of Wood‐pigeons Columba palumbus was studied in the January‐March period in a Cambridgeshire study area when the birds were feeding on clover fields; many individuals were marked with wing tags enabling them to be identified under field conditions. Normal and underweight (arbitrarily under 450 g) adults survived equally well provided they remained in the flocks living within the study area, where they held dominant positions in the social hierarchy. Juveniles weighing over 450 g had a poorer survival and underweight juveniles the lowest survival of all within the area. Juveniles were more likely than adults to move to places outside the study area (5 to 53 miles) where they had the same survival rate as any adults of similar weight which moved more than five miles. Displaced adults presumably lost the advantages of their position in the established hierarchy and of local experience and now competed on more equal terms with the juveniles. The mean weight of pigeons was highest in those flocks feeding where clover leaf density was highest. Smaller flocks, containing a higher proportion of under‐weight birds and fewer juveniles, were found on fields where the leaf density was low (less than 100 leaves/ft2 Dominant birds co‐ordinated their searching (paces/min.) and pecking actions to obtain the best components of the feed. Subordinate birds were probably inexperienced individuals which preferred to frequent the front of the flock in order to determine what experienced birds were eating and some other experimental evidence for this view is discussed. It is shown that the number of pecks/min. taken by subordinate birds depended almost entirely on the pecking rate of dominant birds, although subordinates took fewer peckslmin. In addition, subordinates had to avoid supplanting attacks and, because they progressed by stops and starts, were prevented from co‐ordinating their feeding and searching movements and in consequence were relatively unselective in what they ate. These differences became greater if numbers were high relative to clover density so that a mechanism is demonstrated which adjusted flock size to the amount of food available; adjustment of numbers occurred when the total quantity of food available appeared to be non‐limiting judged by superficial impressions. Subordinate birds had lower weights and reduced survival prospects compared with dominant birds. Moreover, the adrenal cortex of subordinates became hypertrophied with the cortical cells exhibiting an increase in nuclear volume and RNA activity. Subordinate birds unable to feed successfully in one flock attempted to establish themselves in other feeding groups but if low food densities prevented this they were eventually forced to feed alone. It was found that birds feeding in isolation obtained even less food per unit time than subordinate individuals living in the flock. Nevertheless, solitary birds can feed successfully if the food supply is adequate. Solitary birds devoted much time to looking around as if afraid of being surprised by a predator. But it is more probable that when feeding on certain items pigeaons benefit from the combined from the combined feeding experience of the group and this possibility is discussed. Because a solitarily feeding Wood‐pigeon cannot exploit clover efficiently, social feeding behaviour improves the survival chances of the individual and in turn enables population size to be increased; social behaviour does not limit numbers before environmental resources become limiting and any apparent self‐regulatory processes are shown to be artifacts.

Food availability is likely to influence body condition and, in turn, fitness. The intensity of this response may vary between populations of the same species on a small spatial and temporal scale. We used 5 yr of data from 6 Eurasian red squirrel Sciurus vulgaris populations from the southern Alps to explore differences in body size and body mass among neighbouring populations, in relation to habitat type and variation in food supply. We also investigated sexual dimorphism in these traits and whether phenotypic variation affects local survival and female reproductive success. Mean hind foot length, a measure of body size, did not differ between sexes but differed between areas. Seasonal variation in body mass was small with no evidence for fattening in autumn. Females were slightly heavier than males, but this difference was largely explained by mass gain of females during reproduction. The size of conifer seed crops, the major food supply, varied strongly over years and between habitats, but this variation corresponded only weakly with autumn body mass. Differences in size and mass between populations were partially explained by habitat-related differences in body size and variability of seed-crops, suggesting differential selection for smaller squirrels in spruce-larch forests against selection for larger and heavier animals in mixed broadleaves and conifer forests and in Scots pine forests with more stable seed production. The probability of reproduction by females increased with body mass, but varied strongly between habitats and years, with more females reproducing in years with rich seed-crops. In both sexes, body mass positively affected probability of settlement and length of residency. Our results suggest that in temporally variable environments that differ in overall amount of food resources, individual variation in body mass is related to habitat type, and that having a relatively high body mass, within each population, positively affects male and female settlement success and local survival, and female reproductive success.

Food availability is likely to influence body condition and, in turn, fitness. The intensity of this response may vary between populations of the same species on a small spatial and temporal scale. We used 5 yr of data from 6 Eurasian red squirrel Sciurus vulgaris populations from the southern Alps to explore differences in body size and body mass among neighbouring populations, in relation to habitat type and variation in food supply. We also investigated sexual dimorphism in these traits and whether phenotypic variation affects local survival and female reproductive success. Mean hind foot length, a measure of body size, did not differ between sexes but differed between areas. Seasonal variation in body mass was small with no evidence for fattening in autumn. Females were slightly heavier than males, but this difference was largely explained by mass gain of females during reproduction. The size of conifer seed crops, the major food supply, varied strongly over years and between habitats, but this variation corresponded only weakly with autumn body mass. Differences in size and mass between populations were partially explained by habitat‐related differences in body size and variability of seed‐crops, suggesting differential selection for smaller squirrels in spruce‐larch forests against selection for larger and heavier animals in mixed broadleaves and conifer forests and in Scots pine forests with more stable seed production. The probability of reproduction by females increased with body mass, but varied strongly between habitats and years, with more females reproducing in years with rich seed‐crops. In both sexes, body mass positively affected probability of settlement and length of residency. Our results suggest that in temporally variable environments that differ in overall amount of food resources, individual variation in body mass is related to habitat type, and that having a relatively high body mass, within each population, positively affects male and female settlement success and local survival, and female reproductive success.

Central Equatorial Pacific benthic foraminifera during the mid-Brunhes dissolution interval: Ballasting of particulate organic matter by biogenic silica and carbonate

* Preface and Acknowledgments * Abbreviations * Chapter 1. Introduction * Human Population Growth * Environmental Changes * and Food Supply * Population, Crop Yield, and Crop Production * Summary * Chapter 2. Methods of Studying Effects of Environmental Change on * Correlations Between Observed Yield and Historical Patterns of Environmental Variation and Change * Experimental Control of Environmental Conditions * Methods for Salinity Studies * Summary * Chapter 3. Cellular Responses to the Environment * Membrane Structure and Function * Enzymes * Cellular Mechanisms of Stress Resistance * The Role of Calcium in Stress Responses * Specificity, Cross-Talk, and Cross-Tolerance * Summary * Chapter 4. Water Relations * The Future of Fresh Water Resources * Effects of Climate Change on Global Hydrology * Excess Precipitation * Drought * Water Uptake, Transport in Xylem, and Transpiration * The Plant Surface * Roots and Hydraulic Conductance * The Crop Canopy * Environmental Changes * Summary * Chapter 5. Photosynthesis, Respiration, and Biosynthesis * Photosynthesis * Effects of Environmental Conditions and Changes on Photosynthesis * Respiration * Effects of Environmental Conditions and Changes on Respiration * Biosynthesis * Summary * Chapter 6. Partitioning of Photosynthate * Source and Sink * Harvest Index * Methods for Studying Partitioning * Carbon Partitioning Within Source Leaves * Phloem Loading, Transport, and Unloading * Regulation of Whole Plant Carbon Partitioning * Environmental Changes * Summary * Chapter 7. Mineral Nutrition * Nutrient Passage from Soil to Root and Beyond * Regulation of Ion Uptake * Kinetics of Nutrient Uptake * Environmental Changes * Summary * Chapter 8. Vegetative Growth and Development * Growth Patterns * Meristems, Organs, and Development * Shoots * Roots * Developmental Stages * Environmental Changes * Summary * Chapter 9. Sexual Reproduction, Grain Yield, and Grain Quality * Sexually Reproductive Development * Yield Components and Variation * Environmental Changes * Interactive Effects of Environmental Changes on Yield * Summary * Chapter 10. The Biotic Environment * Weeds * Insect Pests and Diseases * Symbiotic Relationships with Soil Organisms * Multiple Environmental Changes and Implications for Biotic Interactions * Summary * Appendix A: List of Plant Species * Appendix B: Definition of U.S. Principal Crops * References * Index

The zooplanktivorous schooling fish sandeels A. marinus comprise a quarter of North Sea fish biomass and are essential food for a number of marine mammals and birds. However, in recent decades there has been a decline in the abundance of older sandeels, with increased overwinter mortality proposed as a contributor. To survive winter animals require a minimum energy reserve which is determined by temperature, prey abundance, and possibly prey size. Here a new dynamic energy budget model is created to determine the influence of food and temperature on sandeel energy dynamics. The model hindcasts changes in energy and survival between 2000 and 2008, a period of pronounced stock decline in the northwestern North Sea. Overwinter starvation mortality was a large contributor towards a recent decline in sandeels in northern UK waters. Highest over-winter mortality rates were recorded for juveniles and not individuals aged 1 or over due to the effect of weight-specific metabolism. However, a sensitivity analysis of the model suggests that mortality rates are more sensitive to changes in copepod abundance in the build up to overwintering rather than temperature during overwintering. Further, projections show that temperature rises are negated by increases in large, but not small copepods. The conclusion is that food-driven size-selective starvation mortality contributed to the northwestern North Sea stock decline and that indirect food web effects of climate change are greater than direct physiological effects on sandeels.