Animal Life History Research Articles

Life history patterns shape energy allocation among fishes on coral reefs

Although critically important, the link between animal life histories and ecosystem energetics is seldom explored. In the pursuit of ecological simplification, ecosystem properties are typically described by models based on static counts, where organisms are aggregated into trophic- or size-based groups. Consequently, output is often based on an assumption that larger group biomass equals greater energetic contribution. Here, we modelled the individual growth of over 58,000 fishes from 74 genera within a coral reef ecosystem to investigate the role and importance of taxon-specific life histories to the division, spatial distribution and relative contribution of biomass production within 14 coral reef fish families. Rank changes among families in standing biomass to biomass production indicated that small cryptic families (e.g. Gobiidae and Blenniidae) exhibit collective growth potentials equal to or exceeding those of many other common families composed of individuals with body-sizes 1-3 orders of magnitude larger. Remaining at high risk of predation throughout their lives as a consequence of their small size, these cryptic fishes also provide a constant food resource and supply of reproductive energy to coral reefs throughout the year. Enhanced further by the strength and diversity of their trophic relationships within food webs, the highly productive nature of these small cryptic fishes suggests they make a substantial contribution to the flow of energy in coral reef ecosystems via predatory pathways. It appears that life histories leave a strong imprint on ecosystem energy fluxes and illustrate the importance of incorporating taxon-specific features when assigning values to key ecosystem processes.

Effects of diet quality on energy budgets and thermogenesis in Brandt's voles

Food quality and availability play an important role in an animal's life history. The aim of this study was to examine the effect of diet quality [high-fiber diet (HF) or low-fiber diet (LF)] on energy budgets and thermogenesis in Brandt's voles (Lasiopodomys (Microtus) brandtii). Dry matter intake and gross energy intake increased and digestibility decreased in HF voles compared with LF voles, while the digestible energy intake was similar for both HF and LF voles. Nonshivering thermogenesis (NST) decreased in HF voles, while LF voles kept stable; no significant differences were detected in basal metabolic rate (BMR), BAT uncoupling protein 1 (UCP1) content and the levels of serum thyroid hormones (T3 and T4) between HF and LF voles. Although there were no differences in body fat content and serum leptin concentrations between HF and LF voles, serum leptin concentrations in HF voles were reduced to nearly half as those seen in LF voles after 4-weeks acclimation. These results support the hypothesis that Brandt's voles can compensate the poor quality diet physiologically by the means of increasing food intake and decreasing thermogenesis.

EARLY ONSET OF VEGETATION GROWTH VS. RAPID GREEN-UP: IMPACTS ON JUVENILE MOUNTAIN UNGULATES

Seasonal patterns of climate and vegetation growth are expected to be altered by global warming. In alpine environments, the reproduction of birds and mammals is tightly linked to seasonality; therefore such alterations may have strong repercussions on recruitment. We used the normalized difference vegetation index (NDVI), a satellite-based measurement that correlates strongly with aboveground net primary productivity, to explore how annual variations in the timing of vegetation onset and in the rate of change in primary production during green-up affected juvenile growth and survival of bighorn sheep (Ovis canadensis), Alpine ibex (Capra ibex), and mountain goats (Oreamnos americanus) in four different populations in two continents. We indexed timing of onset of vegetation growth by the integrated NDVI (INDVI) in May. The rate of change in primary production during green-up (early May to early July) was estimated as (1) the maximal slope between any two successive bimonthly NDVI values during this period and (2) the slope in NDVI between early May and early July. The maximal slope in NDVI was negatively correlated with lamb growth and survival in both populations of bighorn sheep, growth of mountain goat kids, and survival of Alpine ibex kids, but not with survival of mountain goat kids. There was no effect of INDVI in May and of the slope in NDVI between early May and early July on juvenile growth and survival for any species. Although rapid changes in NDVI during the green-up period could translate into higher plant productivity, they may also lead to a shorter period of availability of high-quality forage over a large spatial scale, decreasing the opportunity for mountain ungulates to exploit high-quality forage. Our results suggest that attempts to forecast how warmer winters and springs will affect animal population dynamics and life histories in alpine environments should consider factors influencing the rate of changes in primary production during green-up and the timing of vegetation onset.

Exploring Linkages between Abiotic Oceanographic Processes and a Top-trophic Predator in an Antarctic Ecosystem

Climatic variation affects the physical and biological components of ecosystems, and global-climate models predict enhanced sensitivity in polar regions, raising concern for Antarctic animal populations that may show direct responses to changes in sea-ice distribution and extent, or indirect responses to changes in prey distribution and abundance. Here, we show that over a 30-year period in the Ross Sea, average weaning masses of Weddell seals, Leptonychotes weddellii, varied strongly among years and were correlated to large-scale climatic and oceanographic variations. Foraging success of pregnant seals (reflected by weaning mass the following pupping season) increased during summers characterized by reduced sea-ice cover and positive phases of the southern oscillation. These results demonstrate a correlation between environmental variation and an important life history characteristic (weaning mass) of an Antarctic marine mammal. Understanding the mechanisms that link climatic variation and animal life history characteristics will contribute to understanding both population dynamics and global climatic processes. For the world’s most southerly distributed mammal species, the projected trend of increasing global climate change raises concern because increasing sea-ice trends in the Ross Sea sector of Antarctica will likely reduce populations due to reduced access to prey as expressed through declines in body condition and reproductive performance.

Equipment and Techniques for Nocturnal Wildlife Studies

Many biologists speculate on the nocturnal behavior of wildlife. Night-vision technologies may provide ways to move beyond speculation to observation of nocturnal activity. Nocturnal activity data collection is often secondary to broader study objectives; consequently, techniques for such studies are poorly understood and infrequently used. We reviewed 53 papers to examine image enhancement (i.e., night vision) and assess trends in nocturnal research techniques. We also conducted a field study on nocturnal behavior of roosting cranes (Grus spp.) to evaluate equipment function and efficacy for wildlife studies. A third-generation night-vision scope greatly outperformed a pair of first-generation night-vision binoculars, and we were able to identify cranes by species and observe and record their behaviors while they were on their nocturnal roost sites. Techniques reported in the literature included use of moonlight or natural ambient light, spotlight or simulated luminosity, remote photography, surveillance radar, infrared thermal imaging, and image enhancement. With the many techniques available, scientists can select the procedure or a combination of strategies explicit to their purpose. We believe night-viewing technologies are an exceptional, nonintrusive, functional tool for wildlife ecology studies. However, even the best equipment will have problems or issues with contrast, inclement weather, and large group size and density. Regardless of the specific method used and the inherent challenges, we believe third-generation, American-manufactured night-vision equipment can provide valuable insight into the complete life history of animals and can promote a more comprehensive approach to wildlife studies.

Applications, Considerations, and Sources of Uncertainty When Using Stable Isotope Analysis in Ecotoxicology

Stable isotope analysis (SIA) has become a powerful tool for ecotoxicologists to study dietary exposure and biomagnification of contaminants in wild animal populations. The use of SIA in ecotoxicology continues to expand and, while much more is known about the mechanisms driving patterns of isotopic ratios in consumers, there remain several considerations or sources of uncertainty that can influence interpretation of data from field studies. We outline current uses of SIA in ecotoxicology, including estimating the importance of dietary sources of carbon and their application in biomagnification studies, and we present six main considerations or sources of uncertainty associated with the approach: (1) unequal diet-tissue stable isotope fractionation among species, (2) variable diet-tissue stable isotope fractionation within a given species, (3) different stable isotope ratios in different tissues of the animal, (4) fluctuating baseline stable isotope ratios across systems, (5) the presence of true omnivores, and (6) movement of animals and nutrients between food webs. Since these considerations or sources of uncertainty are difficult to assess in field studies, we advocate that researchers consider the following in designing ecotoxicological research and interpreting results: assess and utilize variation in stable isotope diet-tissue fractionation among animal groups available in the literature; determine stable isotope ratios in multiple tissues to provide a temporal assessment of feeding; adequately characterize baseline isotope ratios; utilize stomach contents when possible; and assess and integrate life history of study animals in a system.

Condition indices for conservation: new uses for evolving tools

Biologists have developed a wide range of morphological, biochemical and physiological metrics to assess the health and, in particular, the energetic status of individual animals. These metrics originated to quantify aspects of human health, but have also proven useful to address questions in life history, ecology and resource management of game and commercial animals. We review the application of condition indices (CI) for conservation studies and focus on measures that quantify fat reserves, known to be critical for energetically challenging activities such as migration, reproduction and survival during periods of scarcity. Standard methods score fat content, or rely on a ratio of body mass rationalized by some measure of size, usually a linear dimension such as wing length or total body length. Higher numerical values of these indices are interpreted to mean an animal has greater energy reserves. Such CIs can provide predictive information about habitat quality and reproductive output, which in turn can help managers with conservation assessments and policies. We review the issues about the methods and metrics of measurement and describe the linkage of CIs to measures of body shape. Debates in the literature about the best statistical methods to use in computing and comparing CIs remain unresolved. Next, we comment on the diversity of methods used to measure body composition and the diversity of physiological models that compute body composition and CIs. The underlying physiological regulatory systems that govern the allocation of energy and nutrients among compartments and processes within the body are poorly understood, especially for field situations, and await basic data from additional laboratory studies and advanced measurement systems including telemetry. For now, standard physiological CIs can provide supporting evidence and mechanistic linkages for population studies that have traditionally been the focus of conservation biology. Physiologists can provide guidance for the field application of conditions indices with validation studies and development of new instruments.

Activity patterns of Asiatic black bears (Ursus thibetanus) in the Central Mountains of Taiwan

AbstractShifts in activity patterns and time budgets in response to environmental variables may yield insights into key factors affecting animal life histories. Activity data on wild Asiatic black bears Ursus thibetanus are limited, and non‐existent in tropical portions of their geographic range. During November 1998–November 2000, we monitored the activity (active vs. inactive) of bears within a national park in the tropics of central Taiwan. On the basis of 4630 readings from motion‐sensitive transmitters obtained in 24‐h monitoring sessions, bears were active 54–57% of the time over the course of the year. However, bears were more active during summer (60±15%sd) and fall (60±15%) than in spring (47±13%). They were active mainly during daylight hours in spring and summer, and also during fall when acorns, a principal fall food, were scarce. However, extensive nocturnal activity occurred in fall when acorns were abundant. Increased nocturnal activity in fall is consistent with studies of the related American black bear Ursus americanus, and suggests that this behavior is not necessarily driven by preparation for winter denning or because of disturbance by hunters (as posited in previous studies), as bears in our study did not den (except parturient females) and were not hunted or otherwise disturbed by people.

Controls on marine animal biomass through geological time

ABSTRACTTotal animal biomass depends on four factors: (1) food supply, (2) the efficiency with which animals consume available food, (3) the efficiency with which animals convert consumed food into biomass, and (4) the rate at which animals lose biomass to the environment through respiration or death. Each of these factors may change through geological time because each is a function of animal ecology and physiology. Animal ecology and physiology, in turn, are products of interacting evolutionary and environmental factors. The direction of change in animal biomass through time may be predicted given knowledge of environmental and ecological change. At a finer level, physiological differences among phyla or other higher taxa suggest that they would have had differential responses to specific environmental changes. Physiological features shared by all of life, such as the dependence of metabolic rate on ambient temperature, suggest that even a coarse time‐series of relative changes in animal biomass may enrich understanding of biogeochemical cycling among all organisms, including phytoplankton and microbes. Changes in the abundance of skeletal material in shallow marine deposits through geological time indicate that the biomass of benthic skeletal invertebrates has fluctuated significantly on timescales from millions to hundreds of millions of years. During the Ordovician radiation, increase in the complexity of animal food webs and increase in the efficiency of animal communities in removing available food from the water column and sediment appear most likely to account for a secular increase in animal biomass. Decrease in animal biomass after the end‐Permian extinction appears to have been driven by a combination of factors but particularly decreased aggregate growth efficiency and consumption efficiency. Comparing biomass and diversity trends through other major transitions in the history of animal life has the potential to shed light on the relationship between physical environmental change and ecosystems evolution.

WHEN NOT TO AVOID INBREEDING

Avoidance of incestuous matings is widely reported across many animal taxa, and the adaptive value of such behavior is explained through inbreeding depression. However, an old and somewhat neglected theoretical result predicts that inbred matings offer another, positive effect on the inclusive fitness of parents: an individual who mates with a relative will help that relative to spread genes identical by descent. This benefit can be substantial, if the additional mating achieved by the relative does not harm his mating success otherwise, and in the context of selfing in plants the phenomenon is well known. Here, we develop a model that derives expected values of inbreeding tolerance, that is, the magnitude of inbreeding depression that is required to make individuals avoid inbreeding, for different animal life histories and parental investment patterns. We also distinguish between simultaneous and sequential mate choice, and show that inbreeding tolerance should often be remarkably high in the latter scenario in particular, although egalitarian parental care will lead to lower tolerance. There is a mismatch between theory and data: the almost complete lack of cases where individuals prefer to mate incestuously is at odds with a large overlap between the predicted range of inbreeding tolerance and estimates of inbreeding depression found in nature. We discuss four different solutions to this enigma, and suggest that inbreeding tolerance, where it is found, should not always be attributed to a simple constraint that has prevented finding any other mate.

WHEN NOT TO AVOID INBREEDING

Avoidance of incestuous matings is widely reported across many animal taxa, and the adaptive value of such behavior is explained through inbreeding depression. However, an old and somewhat neglected theoretical result predicts that inbred matings offer another, positive effect on the inclusive fitness of parents: an individual who mates with a relative will help that relative to spread genes identical by descent. This benefit can be substantial, if the additional mating achieved by the relative does not harm his mating success otherwise, and in the context of selfing in plants the phenomenon is well known. Here, we develop a model that derives expected values of inbreeding tolerance, that is, the magnitude of inbreeding depression that is required to make individuals avoid inbreeding, for different animal life histories and parental investment patterns. We also distinguish between simultaneous and sequential mate choice, and show that inbreeding tolerance should often be remarkably high in the latter scenario in particular, although egalitarian parental care will lead to lower tolerance. There is a mismatch between theory and data: the almost complete lack of cases where individuals prefer to mate incestuously is at odds with a large overlap between the predicted range of inbreeding tolerance and estimates of inbreeding depression found in nature. We discuss four different solutions to this enigma, and suggest that inbreeding tolerance, where it is found, should not always be attributed to a simple constraint that has prevented finding any other mate.

From Physiology to Fitness: The Costs of a Defensive Adaptation in Rattlesnakes

The costs of using and maintaining presumed adaptations are unknown for most animals. Energetically expensive traits, such as some agonistic and antipredator behaviors in animals, may incur trade-offs with other aspects of an animal's life history, such as feeding and reproduction. However, infrequent and brief use may reduce the costs of vigorous behaviors. The shaker muscles in the tails of rattlesnakes are an excellent system for studying the potential costs of a specialized defensive system. The high energetic cost of rattling may increase feeding requirements or use energy that could otherwise be available for reproduction. I used energetic modeling to test whether the cost of rattling in western diamond-backed rattlesnakes (Crotalus atrox) can be high enough to increase feeding demands or reduce fecundity and fitness. Only very frequent and prolonged rattling would increase feeding needs and perhaps reduce fecundity to some degree. Typically, rattling probably incurs very low costs to feeding, reproduction, and hence fitness. These and other results suggest that many seemingly expensive adaptations may have minimal costs to energy budgets, reproduction, and fitness.

Genetic covariance between indices of body condition and immunocompetence in a passerine bird

BackgroundCondition-dependence is a ubiquitous feature of animal life histories and has important implications for both natural and sexual selection. Mate choice, for instance, is typically based on condition-dependent signals. Theory predicts that one reason why condition-dependent signals may be special is that they allow females to scan for genes that confer high parasite resistance. Such explanations require a genetic link between immunocompetence and body condition, but existing evidence is limited to phenotypic associations. It remains unknown, therefore, whether females selecting males with good body condition simply obtain a healthy mate, or if they acquire genes for their offspring that confer high immunocompetence.ResultsHere we use a cross-foster experimental design to partition the phenotypic covariance in indices of body condition and immunocompetence into genetic, maternal and environmental effects in a passerine bird, the zebra finch Taeniopygia guttata. We show that there is significant positive additive genetic covariance between an index of body condition and an index of cell-mediated immune response. In this case, genetic variance in the index of immune response explained 56% of the additive genetic variance in the index of body condition.ConclusionOur results suggest that, in the context of sexual selection, females that assess males on the basis of condition-dependent signals may gain genes that confer high immunocompetence for their offspring. More generally, a genetic correlation between indices of body condition and imuunocompetence supports the hypothesis that parasite resistance may be an important target of natural selection. Additional work is now required to test whether genetic covariance exists among other aspects of both condition and immunocompetence.

The Evolution of Life Histories in Holo-anhydrobiotic Animals: A First Approach

The life histories of holo-anhydrobiotic animals differ from those of all other organisms by a regular or irregular entrance into an ametabolic state induced by desiccation. Such ametabolic periods will arrest growth and reproduction completely and thus affect primary life history parameters dramatically. The selective forces and the genetic and physiological trade-offs acting on anhydrobiotic animals are to a large extent unknown. Assuming low growth rates and low juvenile to adult survival, general theoretical models on life history responses to stress predict that anhydrobiotic animals will be selected for a high degree of iteroparity, with low fecundity, large egg size, and low total reproductive investment. A high degree of variability in growth and reproduction should create a selective force in the same direction. Although basic empirical data on life history parameters are very scarce, available observations seem to be consistent with this prediction.

Desiccation Tolerance in Encysted Embryos of the Animal Extremophile, Artemia

Encysted embryos (cysts) of the primitive crustacean, Artemia franciscana, are among the most resistant of all animal life history stages to extremes of environmental stress. These embryos, extremophiles of the animal kingdom, are the main focus of this paper. Previous work has revealed the importance of biochemical and biophysical adaptations that provide a significant part of the basis of their resistance, and I consider some of these here. In the present paper the critical role played by the outer layer of the shell in desiccation tolerance will be one focus. Another involves studies on the response of dried cysts to high temperatures that, among other things, implicate one or more volatile factors released from the cysts that determines the extent of thermotolerance under a given heating regime. A hypothetical scheme is given to account for these peculiar results. Based on western immunoblotting analysis, and data from the literature, the scheme also implicates the heat-induced translocation of the stress protein p26 to nuclei as a potential cause of the reduction in hatching level.

Temperature‐dependent ovariole and testis maturation in the yellow dung fly

AbstractTemperature is one of the abiotic environmental factors most strongly affecting animal behaviour, physiology, and life history. In insects, lower temperatures generally slow down most physiological processes, reducing growth rate and prolonging the juvenile period. Here, we investigate temperature‐dependent ovariole and testis maturation in the anautogenous yellow dung fly, Scathophaga stercoraria L. (Diptera: Scathophagidae), and relate it to corresponding temperature effects on pre‐adult development time and the adult pre‐reproductive period. Flies were reared in the laboratory at three constant temperatures (18, 22, and 26 °C), and the size of the developing ovarioles and testes (reflecting sperm production) was measured over time (i.e., age). Ovariole size increased asymptotically over the first 12 days of adult life, while the testes continued to fill after day 10. In accordance with the temperature‐size rule, warmer temperatures resulted in smaller ovarioles (eggs) and smaller testes, independent of body size. Warmer temperatures also greatly reduced pre‐adult development time by more than half, from 12 to 25 °C, the larger males always taking 1–3 days longer than the females. Corresponding temperature effects on the adult pre‐reproductive period were small (<1 day between 15 and 25 °C), with males taking 5–6 days and females 10–13 days to first reproduction. Time lost by males during the pre‐adult stage, when ovaries and testes are produced, can thus be more than compensated‐for by time gained during the pre‐reproductive period, when eggs and sperm are produced, so males can nevertheless start reproducing sooner than females.

Evaluating body condition of striped skunks using non-invasive morphometric indices and bioelectrical impedance analysis

Abstract Assessment of the body composition and body condition of animals in the wild is an important aspect of animal ecology. We were interested in understanding the seasonal changes in body condition in order to investigate the effects of adaptive strategies on life histories of animals. We investigated the merit of morphometric condition indices and bioelectrical impedance analysis (BIA) to predict fat reserves in striped skunks (Mephitis mephitis, n = 26). We took BIA and morphometric measurements following chemical immobilization in the field and completed chemical analyses of whole carcasses postmortem. We determined relationships between body lipid and water using multiple linear regression techniques and performed model selection using Akaike's Information Criterion (AIC). Bioelectric volume (L2/Rs) and chest circumference (CC) best predicted total body water (TBW=–1.1+0.058*CC+0.25 * L2/Rs; r2 = 0.91, SEE=0.15, P <0.001). Lean dry mass (LDM) was significantly correlated with total body mass (LDM...

Does testis weight decline towards the Subarctic? A case study on the common frog, Rana temporaria

Interpopulation comparisons of variation in resource availability and in allocation patterns along altitudinal and latitudinal gradients allow insights into the mechanisms shaping the life history of animals. Patterns of between-population differences in female life history traits have been studied intensively across a wide range of taxa, but similar investigations in males have remained scarce. To study if testis weight-a measure of reproductive investment-varies on a geographical scale in anurans, we focussed on the variation in relative testis weight (RelTW) and asymmetry in 22 populations of the common frog Rana temporaria along a 1,600-km latitudinal transect across the Scandinavian peninsula. We found that RelTW decreased towards the north. Body mass and body length both had independent positive effects on testes mass. We found evidence for directional asymmetry (DA) in testis weight with the right testis being larger than the left. The level of DA in testis weight was not related to latitude, but both body mass and testes mass had independent positive effects on asymmetry. We discuss the northwards decrease in RelTW in terms of a decreased reproductive investment as a possible consequence of harsher environmental conditions, and perhaps also, weaker sexual selection in the north than in the south.

Common waxbills use carnivore scat to reduce the risk of nest predation

For many animals, nest construction is a prerequisite for successful breeding. The choice of nesting materials is an important component of nest construction, because material properties can influence nest design and, potentially, reproductive success. Common waxbills are small African finches that select carnivore scat as a material to include in, on, and around their nests. I investigated the hypothesis that scat functions to reduce predation risk by documenting its use in a wild population of common waxbills and by conducting an artificial nest experiment. Among natural nests, scat was present in every nest that hatched young, and parents continued to add scat to nests throughout the nestling period. Among artificial nests, those that received experimental additions of carnivore scat survived at a significantly higher rate than did untreated nests, suggesting that scat functions to reduce predation risk. The mechanism by which nests are protected remains unclear, although it is likely that scat acts as an olfactory deterrent and/or camouflage. Researchers have long focused on the implications of nest site characteristics for avian life-history evolution. Results of the present study suggest that nest materials, similar to nest sites, may influence life histories of nest-building animals by affecting predation risk. Key words: artificial nest, carnivore scat, Estrilda astrild, life-history evolution, nest material, nest predation. [Behav Ecol]

Ecological and genetic evidence for impaired sexual reproduction and induced clonality in the hydroid Sertularia cupressina (Cnidaria: Hydrozoa) on commercial scallop grounds in Atlantic Canada

Colonial epifauna are vulnerable to the effects of bottom fishing, but impacts on the life histories of these non-target animals have not been examined extensively. Dredging potentially impairs sexual reproduction by invoking regeneration and induces clonality by severing colonies or through the abortion of damaged modules. This study investigated the potential for commercial-scale scallop dredging to alter sexual and asexual (“clonal”) reproduction in the hydroid Sertularia cupressina. In total, 1,071 colonies from 104 epizoic microhabitats (upper valves of live scallops relatively undisturbed by fishing) and 75 epilithic microhabitats (cobbles more severely disturbed by fishing) were collected from 53 to 94-m depths in the Bay of Fundy (Atlantic Canada). Colony abundance, injury frequency (proportion of colonies with sealed, snapped off stems), percentage of fertile colonies and sexual fecundity (number of gonophores and gonophore dimensions) were measured on all substrata. Ten randomly amplified polymorphic DNA (RAPD) primers were used to estimate clonal diversity. Field experiments found no significant effect of microhabitat differences between scallop and cobble substrata on fecundity and clonality in S. cupressina, while experimentally-induced injuries suppressed the percent of fertile colonies. On the fishing grounds, colonies on scallop valves were more abundant and sexually fertile than their counterparts on cobble, and all were sexually derived. In contrast, colonies on cobbles had a greater percentage of injury, were less fertile and were frequently clonally-derived. Impacts of fishing-related injuries on reproduction in colonial epifauna have been overlooked, yet the long-term consequences of such impacts could result in reduced adaptability, recruitment and recovery potential of these and dependent organisms.