Probability Of Reproductive Success Research Articles

Predicting the probability of avian reproductive success and its components at a nesting site

Avian reproduction has four prime components: nesting, mating, hatching, and fledging. Predicting the probability of individual components helps in identifying the period of reproduction that would benefit from an increased conservation effort. Identification of biotic, abiotic, and sociological variables of the nesting sites is essential to calculate the component-wise success probabilities. There is no standard methodology to estimate these probability values separately. This study proposes a methodology to estimate the success probability of each component, identifies correlated environmental predictors, and provides a modelling framework to accurately predict the nesting success probabilities using Merops philippinus as a model species. Primary surveillance data and the proposed methodology indicate that the time window between the bird's nesting and mating is most vulnerable to environmental fluctuations. Both biotic and abiotic factors are crucial determinants of nesting success. Sociological factors also play a crucial role in determining the probabilities of these successes. Mating, hatching, and fledging success depend more on biotic factors than abiotic ones. Linear modelling frameworks are helpful in exploring which types of environments are better determinants of the success of a reproductive component. Artificial neural networks are useful in predicting mating, nesting, and overall reproductive success probabilities. Though the models in this study are developed using Merops philippinus data, the proposed methodology and modelling framework is also applicable for other bird species.

Dynamic multistate occupancy modeling to evaluate population dynamics under a scenario of preferential sampling

AbstractEffective conservation of animal populations depends on the availability of reliable data derived from rigorous monitoring protocols, which allows us to assess trends and understand the processes they are governed by. Nevertheless, population monitoring schemes are hampered by multiple sources of errors resulting from specific logistical and survey constraints. Two common complications are the non‐visitation of some sites in certain years and preferential sampling (PS), that is, the tendency to survey “better” sites disproportionately more often. Both factors can lead to serious biases unless accommodated into models. We used 22 yr of nest‐monitoring data to develop a dynamic multistate occupancy model, including a PS component to investigate occupancy and reproduction dynamics in a peripheral Black Stork (Ciconia nigra) population in Spain. We analyzed the effects of climate and nesting substrate (tree vs. cliff) on population dynamics and accounted for PS and non‐visitation biases using a model that distinguished three territorial states: unoccupied, occupied without, or occupied with successful reproduction. We found strong evidence for positive PS, and when accounting for this bias, lower population size estimates were generated. Black stork nests had a high probability of remaining in the same state from one year to the next, with successful nests more likely to be occupied again and to be successful the following year than occupied but unsuccessful or unoccupied nests. Nesting substrate and spring precipitation did not influence state transition probabilities or the probability of reproductive success; nevertheless, cliff nest occupancy was overall higher than tree nest occupancy. Our results highlight the importance of correcting for non‐visitation and PS in habitat occupancy models. If these potential biasing effects are not accounted for, inferences of population size may be overestimate. Multistate occupancy models with correction for PS offer a powerful analytical framework for data collected as part of population studies of unmarked animals. These models compensate for common methodological biases in biological surveys and can help implement efficient conservation strategies based on robust population dynamics estimates.

Decomposing fecundity and evaluating demographic influence of multiple broods in a migratory bird

Relevance of breeding season fecundity as a driver of population dynamics has been highlighted by many studies. Despite that, knowledge about how brood type specific (i.e. first, second or replacement) fecundity affects demography of multiple-brooded species is limited. In fact, estimation of brood type specific fecundity is often challenging due to imperfect detection of nesting attempts. We examined the demographic contribution and the feedback on population density of different components of fecundity, along with other vital rates, in a facultative multiple-brooded migratory bird. We used a novel formulation of a fecundity model that allows incorporating reproductive data for which information on the type of brood was unknown in some cases, and embedded it into an integrated population model (IPM) to obtain consensual estimates of all demographic rates, including brood type specific fecundities, reproductive success probabilities and proportion of breeding pairs that performed a second or replacement brood. We then conducted transient life table response experiments on IPM estimates to account for non-stationary environments. We applied the model to two 20-year datasets collected in a Swiss and a German local population of wrynecks Jynx torquilla. Brood type specific fecundities and temporal patterns of brood type specific probabilities of success, number of successful and unsuccessful first broods, probability of starting a second or a replacement brood and proportion of pairs that performed a second or a replacement brood differed between the two populations. However, changes in immigration rate and apparent survival were the dominant contributors to temporal variation and large sequential changes in realized population growth rates in both populations. In the Swiss population we also found that second brood fecundity declined when population size increased. Our study provides insight into the reproductive processes that affect population dynamics and mediate density-dependent fecundity in a migratory bird. In addition, the analytical approach proposed can be used in other studies of multiple-brooded species to maximize the use of available fecundity data through the estimation of unknown brood types, thus favouring a better understanding of the demographic contribution of brood type specific fecundity.

Sex-specific reproductive benefits of early arrival to the breeding colony in a seabird

Territorial protandry, or early season male-biased settlement at breeding sites, is a widespread phenomenon in a range of animal breeding systems. While protandry is common across several avian lineages and has been linked with increased reproductive success of earlier breeding males in terrestrial species, the selective advantage of breeding protandry has only rarely been studied in seabirds. We assessed the seasonal changes in the sex ratio at the breeding site and sex-specific correlates of arrival date with reproductive success during 2 breeding seasons of a colonial seabird, the Australasian Gannet (Morus serrator), at Cape Kidnappers, New Zealand. We found no biases in overall sex ratios of adults and fledglings but detected a male sex bias during nest site establishment, and a significantly higher probability of reproductive success for earlier-settling males. In contrast, the reproductive success of females did not correlate with the timing of arrival. Our findings provide an assessment of the sex differences in reproductive correlates of the timing of breeding settlement in gannets and are consistent with selective advantages as suggested by indirect selection hypotheses. This study contributes to our understanding of the fitness benefits of protandry, and its linkages with sex differences in breeding philopatry and mate fidelity, in a long-lived seabird species with obligate and extended biparental care.

Plasticity in dormancy behaviour of Calanoides acutus in Antarctic coastal waters

Abstract Copepods that enter dormancy, such as Calanoides acutus, are key primary consumers in Southern Ocean food webs where they convert a portion of the seasonal phytoplankton biomass into a longer-term energetic and physiological resource as wax ester (WE) reserves. We studied the seasonal abundance and lipid profiles of pre-adult and adult C. acutus in relation to phytoplankton dynamics on the Western Antarctic Peninsula. Initiation of dormancy occurred when WE unsaturation was relatively high, and chlorophyll a (Chl a) concentrations, predominantly attributable to diatoms, were reducing. Declines in WE unsaturation during the winter may act as a dormancy timing mechanism with increased Chl a concentrations likely to promote sedimentation that results in a teleconnection between the surface and deep water inducing ascent. A late summer diatom bloom was linked to early dormancy termination of females and a second spawning event. The frequency and duration of high biomass phytoplankton blooms may have consequences for the lifespan of the iteroparous C. acutus females (either 1 or 2 years) if limited by a total of two main spawning events. Late summer recruits, generated by a second spawning event, likely benefitted from lower predation and high phytoplankton food availability. The flexibility of copepods to modulate their life-cycle strategy in response to bottom-up and top-down conditions enables individuals to optimize their probability of reproductive success in the very variable environment prevalent in the Southern Ocean.

Environmentally mediated reproductive success predicts breeding dispersal decisions in an early successional amphibian

Dispersal is a central mechanism in ecology and evolution. Dispersal evolution is driven by a trade-off between costs and benefits, which is influenced by interindividual variability and local environmental conditions (context-dependent dispersal). Many studies have investigated how dispersal decisions may be influenced by environmental factors, including density, predation and interspecific competition. Yet few have attempted to examine how habitat disturbance may affect the dispersal process in spatially structured populations. In early successional species, one might expect individuals to adjust their dispersal decisions based on two main factors that potentially have an influence on reproductive success: patch size and the level of patch disturbance. In this study, we examined how these two factors affect breeding success and dispersal decisions in an early successional amphibian, the yellow-bellied toad, Bombina variegata. To this end, we used capture–recapture data collected on a spatially structured population occupying 28 breeding patches. We took advantage of recent developments in multievent capture–recapture models to detect signs of context-dependent dispersal. The results revealed that the probability of successful reproduction and the number of newly metamorphosed individuals increased with both the size and the proportion of disturbance of a patch. In addition, our results showed that the factors affecting breeding success also influenced breeding dispersal probability. Large patch size negatively influenced emigration probability; in contrast, it positively influenced immigration probability. Equally, higher disturbance had a strong negative influence on emigration probability and slightly positively affected immigration probability. These findings strongly suggest that individuals make context-dependent dispersal decisions, adjusted to maximize future fitness prospects in a patch, allowing them to better cope with rapid changes in environmental conditions resulting from the ecological succession process. This opens new areas of potential research into the role of dispersal in organism specialization along an ecological succession gradient.

Alternate migration strategies of eastern monarch butterflies revealed by stable isotopes

Abstract Alternative life history strategies are mechanisms by which organisms are able to maximize fitness across a range of environmental conditions. Fitness is maximized by different strategies depending on context, resulting in trade-offs between life history strategies. Monarch butterflies (Danaus plexippus) employ both migratory and resident life history strategies. Since residents breed throughout the year, but migrants overwinter in reproductive diapause, there are fitness trade-offs between the two strategies. We used stable isotope analysis to evaluate the geographic origins of monarchs in a yearround population in south Florida. Based on stable isotope profiles of hydrogen and carbon (δ2H and δ13C values), we found that 48% (16/33) of monarchs collected in south Florida are migrants that originated from outside the sampling region. Migrants had a larger wing length than residents; thus, switching to a resident strategy could alter their probability of reproductive success. Further work is needed to investigate the mechanism underlying this pattern, but these findings show that alternate life history strategies and sex-specific behaviors are underexplored factors influencing monarch migration and evolution.

Relative growth and onset of morphological sexual maturity of the freshwater crab Sylviocarcinus pictus in a river of the Caatinga of northeastern Brazil

ABSTRACTThe aim of this study was to investigate the relative growth and onset of morphological sexual maturity of the freshwater crab Sylviocarcinus pictus. Specimens were collected every month from October 2013 to September 2014, at night, on a stretch of the river Guaribas, Piauí, Brazil. Crabs were sexed and their carapace width (CW, independent variable), carapace length (CL), cheliped propodus length (PL) and height (PH), gonopod length (GL), and abdomen width (AW) (dependent variables) were measured. These measurements were related to characterise relative growth and possible sex differences. On average males were larger than females (p = 0.0001). Size at the onset of morphological sexual maturity was defined by relating CL vs. PL for males (30.82 mm) and CL vs. AW for females (28.63 mm). These are considered secondary sexual characters and reflect initial size at morphological sexual maturity with greater precision. The differential cheliped growth of males may be related to courting and disputes with other males, while the allometric growth of the abdomen of females indicates increased probability of reproductive success.

Aridity promotes bet hedging via delayed hatching: a case study with two temporary pond crustaceans along a latitudinal gradient.

Climate change does affect not only average rainfall and temperature but also their variation, which can reduce the predictability of suitable conditions for growth and reproduction. This situation is problematic for inhabitants of temporary waters whose reproductive success depends on rainfall and evaporation that determine the length of the aquatic phase. For organisms with long-lived dormant life stages, bet hedging models suggest that a fraction of these should stay dormant during each growing season to buffer against the probability of total reproductive failure in variable environments. Thus far, however, little empirical evidence supports this prediction in aquatic organisms. We study geographic variation in delayed hatching of dormant eggs in natural populations of two crustaceans, Branchinella longirostris and Paralimnadia badia, that occur in temporary rock pools along a 725km latitudinal aridity gradient in Western Australia. Consistent with bet hedging theory, populations of both species were characterised by delayed hatching under common garden conditions and hatching fractions decreased towards the drier end of the gradient where the probability of reproductive success was shown to be lower. This decrease was most pronounced in the species with the longer maturation time, presumably because it is more sensitive to the higher prevalence of short inundations. Overall, these findings illustrate that regional variation in climate can be reflected in differential investment in bet hedging and hints at a higher importance of delayed hatching to persist when the climate becomes harsher. Such strategies could become exceedingly relevant as determinants of vulnerability under climate change.

Survivorship and longevity of Diamesa mendotae Muttkowski (Diptera: Chironomidae) under snow

<em>Diamesa mendotae</em> Muttkowski commonly grow and emerge from groundwater dominated streams in winter. Previous estimates of longevity for adults of <em>D. mendotae </em>collected from the snow surface averaged 18.6 days post-collection, with 76.9% of individuals dying between Day 10 and Day 30 post-collection and 4.4% surviving over 40 days. Maximum longevities for males and females were 48 and 54 days, respectively. In this paper, we report survivorship and longevity of fieldcollected adults of <em>D. mendotae</em> kept at ambient snow temperature conditions. Adults (n=140) were collected in February from snow along groundwater-dominated sections of the Kinnickinnic River (Wisconsin, USA). All individuals were placed in vials, buried in snow, and retrieved in batches of 10 males and 10 females at 4-day intervals for 28 days. Once retrieved, adults were maintained at 6°C in controlled environmental chambers to determine survivorship and longevity. All individuals survived snow burial treatment, indicating they are capable of surviving sub-freezing field conditions for at least 28 days. Estimates of adult maximum longevity were as high as 66 days, higher than previous estimates for this genus. Our results suggest adults of <em>D. mendotae</em> can persist under snow cover, with high survivorship and longevity, potentially increasing their probability of successful reproduction in regions where lethal winter air temperatures occur.

Actuarial and reproductive senescence in a long-lived seabird: preliminary evidence

The evolutionary theory of aging predicts that pelagic seabirds, which have low extrinsic mortality, should show exceptional longevity. These taxa appear to show the lowest rates of actuarial senescence among birds yet display declining reproductive performance at advanced ages. We have studied survival and reproduction of Nazca boobies ( Sula granti) in the remote Galápagos Islands since 1984. We found a slight but detectable increase in mortality rate in the oldest (≥19 yrs) cohort, indicating minimal actuarial senescence. The probability of successful reproduction (eggs or fledglings) declined from mid-life to the age of the oldest cohort. We are currently investigating the causal relationship between physical (foraging) performance, components of reproductive success, and longevity at our pristine study site.

Density and Reproductive Success of Florida Grasshopper Sparrows following Fire

Information on the response of the endangered Florida grasshopper sparrow (Ammodramus savannarum floridanus Mearns) to range management, especially prescribed fire, is needed to determine conservation strategies. Intensive management of grasslands for cattle grazing and conversion of grassland to other agricultural use is considered the greatest threat to the sparrow. Territory spot-mapping and estimates of reproductive success were examined in relation to time post-burn in managed cattle pastures at Avon Park Air Force Range, Highlands County, Florida from 1997-1999. We tested the hypothesis that sparrow density and reproductive success did not depend on time following fire. Contrary to previous work, there was no evidence that Florida grasshopper sparrow territory density depended on years post-burn (P = 0.842). The probability of reproductive success was significantly higher 0.5 year post-burn than at 1.5 years post-burn (P 0.27 for each pairwise comparison between years). No simple trend or highly significant polynomial relationship between reproductive success and territory density was indicated (P > 0.41). Compared to other subspecies, Florida grasshopper sparrows exhibited relatively low density (0.22 territories/ha or less) and reproductive success (20%). Our results suggest increased reproductive success at a population level 0.5 year following fire, and did not suggest an association between territory density and individual reproductive success. Additional information is needed on the effects of seasonality of fire on Florida grasshopper sparrows. DOI:10.2458/azu_jrm_v55i4_delany

Density and reproductive success of Florida grasshopper sparrows following fire

Information on the response of the endangered Florida grasshopper sparrow (Ammodramus savannarum floridanus Mearns) to range management, especially prescribed fire, is needed to determine conservation strategies. Intensive management of grasslands for cattle grazing and conversion of grassland to other agricultural use is considered the greatest threat to the sparrow. Territory spot-mapping and estimates of reproductive success were examined in relation to time post-burn in managed cattle pastures at Avon Park Air Force Range, Highlands County, Florida from 1997-1999. We tested the hypothesis that sparrow density and reproductive success did not depend on time following fire. Contrary to previous work, there was no evidence that Florida grasshopper sparrow territory density depended on years post-burn (P = 0.842). The probability of reproductive success was significantly higher 0.5 year post-burn than at 1.5 years post-burn (P < 0.05) and 2.5 years post-burn (P < 0.01). No other significant differences were observed among years post-burn (P > 0.27 for each pairwise comparison between years). No simple trend or highly significant polynomial relationship between reproductive success and territory density was indicated (P > 0.41). Compared to other subspecies, Florida grasshopper sparrows exhibited relatively low density (0.22 territories/ha or less) and reproductive success (20%). Our results suggest increased reproductive success at a population level 0.5 year following fire, and did not suggest an association between territory density and individual reproductive success. Additional information is needed on the effects of seasonality of fire on Florida grasshopper sparrows.

Can experiments on caloric restriction be reconciled with the disposable soma theory for the evolution of senescence?

A publication by Shanley and Kirkwood (2000) attempts to explain data on caloric restriction (CR) and life extension in the context of the Disposable Soma (DS) theory for the evolution of senescence. As the authors concede, this juxtaposition appears at first to offend intuition: According to the DS theory, senescence is the result of a tight budget for caloric energy, such that repair and maintenance functions are shortchanged; yet, in CR experiments, it is found that longevity decreases smoothly as the total caloric budget is increased. In the Shanley-Kirkwood model, an optimized allocation of resources causes energy to be diverted away from somatic maintenance at a greater rate than caloric intake increases, with the net result that more total energy is associated with less energy available for maintenance. In the present critique, the limitations of this model are detailed and its special assumptions reviewed. While the CR experiments find comparable life extension for males and females, measured relative to nonbreeding controls, the Shanley-Kirkwood model draws its energy budget from data on breeding females. In addition, the success in reproducing the observed relationship between feeding and longevity depends crucially on a mathematical relationship between food availability and the probability of reproductive success which may be difficult to justify.

CAN EXPERIMENTS ON CALORIC RESTRICTION BE RECONCILED WITH THE DISPOSABLE SOMA THEORY FOR THE EVOLUTION OF SENESCENCE?

A publication by Shanley and Kirkwood (2000) attempts to explain data on caloric restriction (CR) and life extension in the context of the Disposable Soma (DS) theory for the evolution of senescence. As the authors concede, this juxtaposition appears at first to offend intuition: According to the DS theory, senescence is the result of a tight budget for caloric energy, such that repair and maintenance functions are shortchanged; yet, in CR experiments, it is found that longevity decreases smoothly as the total caloric budget is increased. In the Shanley-Kirkwood model, an optimized allocation of resources causes energy to be diverted away from somatic maintenance at a greater rate than caloric intake increases, with the net result that more total energy is associated with less energy available for maintenance. In the present critique, the limitations of this model are detailed and its special assumptions reviewed. While the CR experiments find comparable life extension for males and females, measured relative to nonbreeding controls, the Shanley-Kirkwood model draws its energy budget from data on breeding females. In addition, the success in reproducing the observed relationship between feeding and longevity depends crucially on a mathematical relationship between food availability and the probability of reproductive success which may be difficult to justify.Corresponding Editor: T. Mousseau

The effects of mating probability on the population genetics of nematodes.

We review how constraints on the mating probability of female worms by segregation within individual host guts form a critical element in the parasite population structure of nematodes. We consider the effects of these constraints on the population genetics of nematodes under various assumptions regarding worm competition as reflected in the relationship between the abundance of a certain genotype within the gut and the probability of reproductive success. The consequences for the emergence of resistance to drugs and immunotherapy and implications for host-parasite coevolution are discussed. We also review evidence for genetic heterogeneity in parasite populations as a necessary prerequisite for the applicability of mating probability models designed to assess the population genetics of nematodes.

Dominance, Age, and Reproductive Success in a Complex Society: A Long-Term Study of the Mexican Jay

Observations of mate guarding by males and robbing of nest material by fe- males suggest the hypothesis that dominance should be related to reproductive success in the Mexican Jay (Aphelocoma ultramarina). We analyzed the probability of successful reproduction in this plural-breeding, group-territorial species with respect to variation in social rank, sex, age, flock territory, and year. We examined the correlates of dominance rank at two stages of nesting, early (before and during laying) and late (after laying). The correlates of rank differed between the sexes and nesting stages. In the early or prelaying stage, success in getting a mate and initiating laying was correlated with rank in males but not in females, and with age in both females and males. In the late stage, given that a bird had a nest with eggs, fledging success was not significantly related to rank overall. In females, however, a significant inter- action was found between rank and age such that top rank was associated with greater suc- cess in older but not younger females. These effects of dominance at two stages of the nesting cycle (i.e. before and after egg laying) are consistent with the mate-guarding behavior of males and the nest-robbing behavior of females during nesting. Received 30 January 1996, accepted 19 December 1996.

Reproduction by virgin queen fire ants in queenless colonies: Comparative study of three taxa (Solenopsis richteri, hybridS. invicta/richteri, S. geminata) (Hymenoptera: Formicidae)

In the fire ant,Solenopsis invicta, some winged virgin queens are known to shed their wings (dealate) upon removal of the mated mother queen. These virgin queens then develop their ovaries and begin to lay eggs, thereby foregoing the option of leaving on mating flights and attempting to found their own colonies. Such a response of virgin queens to queenlessness has not been reported for other ants. In order to determine if virgin queens of some other fire ants (subgenusSolenopsis) would respond in the same way, experiments were conducted onS. richteri, hybridS. invicta/richteri andS. geminata, a member of a species complex different from that of the other taxa. Just as inS. invicta, virgin queens ofS. richteri and the hybrid dealated and began to lay eggs within days of the removal of the queen. In addition, workers executed many of the reproductively active virgin queens, a phenomenon also found inS. invicta. In contrast, virgin queens ofS. geminata did not dealate or quickly begin to lay eggs upon separation from the queen. Reasons for the variability in the response of virgin queens of the different species may be 1) higher probability of reproductive success for unmated dealated queens compared to normal claustral founding inS. invicta andS. richteri linked to relatively frequent loss of the mother queen; or 2) phylogenetic constraint.

Age‐Specific Weaning Success of Northern Elephant Seals in Relation to Previous Breeding Experience

We studied the effect of age and previous breeding experience on the probability of successful reproduction in female northern elephant seals (Mirounga angustirostris). Reproductive data, collected over a 12—yr period, were analyzed by multiple logistic regression to describe the functional relationships among the variables. We also examined the relationships among age, experience, date of breeding, and reproductive success to determine if differences in timing explain age—specific productivity. Finally, we investigated the relationship among age, experience, and maternal behavior to determine if correlates of reproductive effort could be related to age— and experience—specific patterns of reproductive success. Reproductive success increased between the maternal ages of 3 and 7 yr and then levelled off, demonstrating an asymptotic relationship. However, the relationship between reproductive success and age, after statistically controlling for previous experience, showed instead that success increased linearly throughout an animal's lifetime. In contrast, after statistically controlling for age, reproductive success was related to experience in a parabolic fashion; success increased with experience for the first few breeding attempts, but declined later in an animal's reproductive lifetime. The effects of experience depended on age: among young animals experience was apparently beneficial, but among old animals greater experience was deleterious. These results suggest experience—related senescence. Timing of breeding was related to experience, rather than age, in a curvilinear fashion; arrival and parturition dates were later for inexperienced and very experienced females, and were earliest for moderately experienced animals. Young animals that gave birth later in the season experienced reduced reproductive success; we observed no such decline in older animals. Thus, among young females, arriving and giving birth earlier each year was adaptive. Aggressiveness and dominance increased with age and experience, but we were unable to separate the effects of age and experience. We contend that the experience—related drop in reproductive success reflects the cost of reproduction. Breeding at a young age and/or continuously appears to result in lower reproductive success later in life. Furthermore, curvature in age—specific reproductive success can be explained by experience—related senescence. This result has general applicability, suggesting that age—related senescence instead may be due to reproductive "burn—out". These results indicate that previous breeding experience and differences in individual quality do not explain the pattern of increasing reproductive success with age in northern elephant seals, and provide indirect support for the hypothesis that animals increase reproductive effort as they age to offset a concomitant decrease in residual reproductive value.

The Role of Reproduction and Life Histories in Models of Small Rodent Population Dynamics

Mammalian reproduction consists of internal fertilization, a period of intrauterine development, parturition, a period of postnatal dependence (lactation), and weaning. Quantitative aspects of this process include the time for development (both intrauterine and postnatal), the number of offspring raised, the age at maturation and the frequency of breeding. These characteristics are governed, within the constraints of morphology, physiology and genetics, by natural selection. Life historians have attempted to understand how organisms are adapted to their environments by considering age specific breeding patterns and the probability of reproductive success in relation to the survival costs of reproduction. Their studies have emphasized the constraints on reproductive patterns, the coevolved nature of reproductive characteristics, and the relationships between these patterns and nutritive resources or social systems (see Clutton-Brock and Harvey 1979, Zeveloff and Boyce 1980, Stearns 1983, Gittleman 1986, Harvey 1986 for examples). Population processes represent the cumulative effects of life history patterns. Many of the consequences of life histories (e.g. population growth) are too far removed from the immediate environment of organisms to be of great interest to life historians. Similarly, some aspects of life histories (e.g. neonatal weights and development) have no direct effects on population growth or density and are of little interest to population ecologists. Nevertheless, there are areas of mutual interest where improved communication may be beneficial. These comments will be restricted to life history principles that may be useful to population ecologists, particularly those who incorporate individual responses into their hypotheses. Reproductive processes are fueled by energy, with specific requirements dictated by the rate of metabolism and number of offspring raised. Among small mammals, reproduction is energetically expensive because basal metabolic rates are generally high (McNab 1986) and several young are produced per litter. Small mam-