Echidnas have a low metabolic rate, and energy expenditure is reduced even further by the use of torpor and hibernation. Thus, echidnas appear to lie at the slow extreme of the fast–slow continuum, and this is reflected in many aspects of echidna life history: a long life, a long lactation period, and a single young that matures late. Reproductive activity occurs in mid-winter, shortly after arousal from hibernation. After a pregnancy of about 3 weeks the female lays a single egg into her pouch that hatches after 10–11 d. Initially, the young is incubated in the pouch. Later, it is left in the nursery burrow while the mother forages for ants, termites, and other invertebrates. Lactation lasts for 150–200 d, the duration differing significantly between geographic regions. Growth rates during late lactation are very high, and, when weaned, the young has reached about 40% of adult mass. The young loses mass before entering its first hibernation, which extends from early autumn to late spring. The young echidna reaches adult mass after about 3–5 years.

I reviewed studies of small mammals in order to assess the methodological constraints in documenting nest mortality in the wild, to identify the major causes of nest mortality, and to consider the impact of nest mortality on population dynamics. Population-level studies are not sufficiently intensive to monitor nest mortality accurately, and the best data are from individual-level studies. The most reliable estimates of nest mortality average over 50% in most populations and range from less than 30% to over 90%. The potential for nest mortality to have a significant impact on population dynamics is high. However, the extent of nest mortality has rarely been studied, and the actual impact of nest mortality on population dynamics is not clear. Multiple causes, including predation on adults and nestlings, infanticide, food constraints, and weather-related events appear to affect nest mortality at any given time, with no single cause predominating. It is suggested that future long-term studies with a focus on nest mortality be conducted, with mortality partitioned to distinguish between losses due to the mortality of adults and the direct mortality of nestlings. Such studies are needed to adequately assess the role of nest mortality in population dynamics.

Studies of life histories often compare species to discern patterns in the evolution of traits. Major components of life histories appear to involve important aspects of species biology, and the first such component appears to be body size. We tested whether the second major component of variation in life histories of mammals is a continuum from species with short lives to long lives, the “fast–slow continuum.” Mammalian populations (n = 143) representing 109 species were examined, and life histories were summarized using 5 key variables that reflect reproduction and survival. Body size and phylogeny were significant influences on life histories. Once these influences were removed statistically, a major axis of life history variation that reflected the fast–slow continuum was revealed in a principal components analysis. This component of life history was poorly but significantly associated with indices of the fast–slow continuum, such as the ratio of reproduction to age at maturity and generation time. Fast and slow species were identified among several orders and families of mammals, and one species exhibited fast and slow populations. These results may indicate that fast and slow life cycles are highly phenotypically plastic. Degree of precociality did not appear to be a third major component of life histories.

Nomenclature: Wilson & Reeder, 2005.

In short-lived mammals, age at maturity is a particularly important parameter influencing lifetime fitness. Age at maturity proves highly variable in altricial rodents, but little is known for small precocial rodents of the order Caviomorpha. Even though extreme precociality implies early maturation, female cavies and guinea-pigs (genus Cavia) advance puberty considerably in the presence of males. We briefly review earlier findings and compare them to data from altricial rodents. We report experiments on 2 very similar species of cavy, the dark-backed (C. magna) and the wild cavy (C. aperea). In the dark-backed cavy, we tested whether the male signal responsible for acceleration of maturity is a chemical in urine, as demonstrated for mice. Females exposed twice daily to male urine on their nares matured at the same age (73–75 d) and mass (around 330 g, 4 times birth mass) as females treated with water. Thus, chemicals in urine did not replace the effect of male presence. Two experiments with wild cavies showed that male presence without physical contact was sufficient to accelerate puberty, even though physical interaction leads to even earlier maturation. Presence of a male during the first 10 d of life only did not lead to advanced maturation in young females. Functionally, it may be more correct to speak of a delay in the onset of maturity in the absence of males rather than considering male presence to stimulate early maturation. Comparative evidence suggests that precocial species generally mature earlier than altricials.

Energetic requirements during reproduction are important determinants of the onset of reproduction and of breeding strategy (e.g., breeding post-partum) and therefore affect female reproductive output in seasonally varying environments. To balance the energetic needs of breeding with energy availability, females must optimize energy allocation between their own energy use and energy allocated to their litter. Here, we studied energetic costs and potential energetic trade-offs of reproduction in female bank voles (Clethrionomys glareolus). We measured energy consumption, i.e., metabolic rates as determined from carbon dioxide production of females either with their pups (breeding unit) to find the total energy expenditure of breeding or alone (maternal energy use), to find potential trade-offs between energy allotted to offspring and to maintenance metabolism. We found that energy used by breeding units remained on the non-pregnant level during pregnancy and increased during lactation but did not increase further during post-partum pregnancy. Maternal energy use remained unchanged through the breeding cycle. Carbon dioxide produced per gram of tissue decreased throughout the reproductive cycle for both breeding units and females alone, suggesting that energy use efficiency improved with advancing pregnancy and lactation. Our study supports the idea that in small mammals reproduction does not increase female energetic costs beyond the costs involved in increasing body mass. We found further that offspring body mass did not differ between lactating non-pregnant and lactating pregnant females and that there were no trade-offs between female energy use and offspring body mass. We conclude that energy allocation by breeding iteroparous females allows for an optimal breeding strategy, i.e., fertilization of new ova post-partum.

Studies of plasticity in vole reproductive traits in response to changing predation risk have produced conflicting results. Predator-induced breeding suppression observed in laboratory experiments has not been fully supported by other studies. Here, data from a 9-y field study of Microtus oeconomus in a strongly fluctuating population and under variable predation risk imposed by a specialist predator, Mustela nivalis, were used to assess plasticity of reproduction. The age (body mass) at maturity and 2 indices of the reproductive effort of females were measured during the summer. In years of high vole density, increased predation risk resulted in early maturation and increased reproductive effort of females. In years of low vole density the effect of increased predation risk was not evident, probably because the reproductive performance of females was significantly enhanced by low density alone. These results do not support the predator-induced breeding suppression hypothesis, but are in agreement with models that predict increased investment in reproduction under decreased probability of survival in fluctuating environment.

The “terminal investment” hypothesis predicts that reproductive effort should increase with age as life expectancy, and therefore residual reproductive potential, decreases. Several studies, however, have found that reproductive success decreases with age because of senescence. We monitored the age–specific reproductive success of individually marked bighorn sheep ewes at Sheep River, Alberta, from 1982 to 2006. Lamb production increased from 2 to 4y of age, then remained at approximately 88% until age 13 y, when it began to decline. Lamb survival was higher for ewes aged 4 to 12 y than for ewes aged 2 or 3 y. Reproductive senescence began at 13 y of age but was restricted to a decrease in lamb production. There were no differences in lamb survival between prime–aged and older ewes. The onset of reproductive senescence is about 5 y later than the onset of survival senescence. Positive correlations between reproductive success before 9 y of age and longevity, and between reproductive success before and after 9 y of age, suggest that ewes that survived to the onset of reproductive senescence were mostly of high phenotypic quality. Our data provide no clear support for the terminal investment hypothesis. Future tests of this hypothesis should account for individual heterogeneity in phenotypic quality.

Survival conditions over the winter and determinants of variability in the onset of reproduction are major factors shaping the life history of most organisms in strongly seasonal environments. During the long non-breeding season availability and quality of food may be major constraints determining the onset of reproduction. We studied the effects of supplemental animal protein over winter on the onset of reproduction in the bank vole, Clethrionomys glareolus, an iteroparous seasonal breeder, granivorous-herbivorous, with small amounts of animal food in its diet. We predicted that animal protein would be especially important during spring, when energy demands are increasing due to the onset of reproduction and availability of new plant food is still limited. Field experiments were conducted in 6 open forest plots (2.25 ha each), and bank voles were fed supplemental whey protein during the winter and spring. Supplemented males were heavier at the onset of reproduction than non-supplemented males. Maturation and parturition of first litter occurred significantly earlier in females fed supplemental animal protein. No differences in litter size and litter mass were detected between treatments. We conclude that animal protein in the form of whey may play an important role in the timing of spring reproduction. Therefore, natural animal protein food sources like insects, pupae, and possibly carcasses of mammals and birds gain importance for the onset of breeding even in an granivorous-herbivorous species like the bank vole.

Theories for optimal life history strategies in variable environments have until now focused on cases where the individuals have either no information about the environment (models maximizing geometric mean fitness) or full information about the environment (models predicting optimal reaction norms). In this paper I investigate the optimal time for multivoltine organisms to commence seasonal reproduction in a more general and realistic case where animals perceive the state of their environment through cues that are measured with varying degrees of precision. If there were only a trade-off between early reproduction and high reproductive success, and if animals had perfect information about their environment, it would be optimal to commence reproduction when the rate of change in reproductive success relative to its current value equals the difference between population growth during the reproductive and non-reproductive seasons. This implies that reproductive success at the optimum is independent of when (but not how) the environment improves over the season. However, because it is optimal to respond conservatively to uncertain cues, we should expect higher reproductive success during years when breeding conditions improve early than when they improve late. Nevertheless, a phenotypic correlation between reproductive success and timing of reproduction will probably not be detectable in a stochastic environment. Data from a cyclic population of field voles (Microtus agrestis L.) in northern England show a negative correlation between reproductive success and timing of reproduction among out-of-phase locations. Such a pattern may occur when there is a convex trade-off between pre-breeding survival and timing of reproduction, or if animals precipitate reproduction to avoid senescence when the environment improves late.

With the exception of a positive relationship between energy expenditure and number of offspring per litter, few links have been made between energy expenditure and life history attributes in mammals. The purpose of this study was to examine relationships between basal metabolic rate (BMR) and life history attributes among 26 species within the Neotomine–Peromyscine rodents. Specifically, I used independent contrasts to determine whether variation in BMR is related to variation in life history attributes that represent reproductive effort and maturation, and I determined if there is an offspring size versus offspring number trade-off. My results demonstrate that within the Neotomine–Peromyscine rodents, 1) there exists an offspring number versus offspring size trade-off whereby taxa that have a large residual number of offspring per litter have a small residual neonate mass, 2) BMR is related to this trade-off whereby taxa that have large residual BMR have small residual neonate mass and a trend towards a large number of offspring per litter, and 3) BMR is not related to total reproductive effort as represented by total litter mass, total weanling mass, or total growth rate of the litter from birth to weaning. My results suggest that high BMR facilitates a large number of small offspring per reproductive event. A large number of small offspring may confer a fitness advantage for taxa with compensatory growth mechanisms for weaned young that minimize fecundity trade-offs with small offspring size.

A growing body of evidence shows that lactation is energetically costly for mammals. Although lactation costs are positively correlated with litter size, the shape of this relationship remains largely unexplored. Understanding physiological efficiencies of metabolic investment in reproduction should provide valuable insight concerning trade-offs between number and size of offspring and limits to litter size. I used data from northern grasshopper mice (Onychomys leucogaster) to explore these constraints. The relationship between litter size and cost of lactation was best described by a non-linear regression such that intermediate litter sizes were the most cost-effective. Lactation costs at the upper range of natural litters for this species required mothers to ingest more than twice as much food as non-reproductive females. Young at 15 d of age from the largest litters were smaller than same-age young from smaller litters. In contrast, young from litters at the lower end of the species range were larger than average. These data suggest that the distribution of litter sizes within this species is selected against at the lower end by inefficient conversion of energy into viable offspring and at the upper end by simple limits on digestive efficiency or capacity.

The potential importance of life history traits to population growth rates has been well explored theoretically but has rarely been documented in wild mammals. In this study we used 18 consecutive years of data from a population of North American red squirrels (Tamiasciurus hudsonicus) in the southwest Yukon, Canada, to examine variation in female life history traits and their consequences for population growth rate. Red squirrels in this population experienced severe juvenile mortality, but survivorship beyond age 2 followed a Type I relationship where the annual survival probability decreased with age. Maximum lifespan was 8 y. Some females initiated breeding as yearlings, but most delayed first breeding until 2 y of age or in some cases even later. Annual reproduction generally involved the production of a single litter averaging 3.1 offspring (range: 1 to 7); however, some females attempted a second litter within a single breeding season, either following reproductive failure or, in rare circumstances, after a successful first breeding attempt. Life table characteristics for the 11 cohorts born between 1987 and 1997 indicated a population growth rate close to zero (r = 0.009). Elasticity analysis as well as individual population projection matrices and lifetime reproductive success data indicated that early survival and not age at first reproduction was most strongly associated with a female's contribution to population growth. Lifespan accounted for 83.9% of the variation in population growth rate and was positively correlated with age at first reproduction, such that females who bred as yearlings suffered decreased longevity. Collectively, these results emphasize the importance of female survival and not reproductive output to population growth and lifetime fitness in this system.

The competitive nature of today's scientific environment requires the availability of ranking indicators that are both fair and easy to compute. An ecologist's publication record is the paper-trail that defines his/her scientific output, and assessment of that record hinges heavily on the popularity and prestige of the journal(s) where the research is published. Although highly criticized, the ISI® Impact Factor is still recognized as the primary measure of journal “quality”. In this study, I apply a recent bibliometric measure, Hirsch's h index, to rank the scientific quality of 111 journals in the ecological sciences and to track changes in journal performance over the past 25 y. Among the top-ranked ecological journals, I found that Trends in Ecology and Evolution has the highest h index, followed closely by journals including Ecology, Molecular Ecology, Evolution, and American Naturalist. A moderate positive relationship between a journal's ISI® Impact Factor versus h index (54% explained variation) suggests that the h index provides an alternative perspective on the citation performance of journals by measuring significance and sustainability in scientific production over longer time periods. Trends in h values over the past 25 y suggest that sharp increases in the performance of specialized journals have been in response to popularity and shifting research priorities in ecology (e.g., Molecular Ecology, Global Change Biology), whereas sustained growth for other journals reflects prestige and the continued popularity that comes with publication excellence. A Hirsch-based ranking of ecological journals, either alone or in combination with the Impact Factor, provides a robust indicator for assessing scientific achievement and tracking the performance of journals over time.

Florida scrub is a pyrogenic shrubland ecosystem occurring on well-drained sands derived from contemporary and relictual beach dunes. Despite average annual precipitation > 1300 mm, Florida scrub is dominated by xeromorphic plants. We monitored spatio-temporal variation in soil moisture to determine if the distribution of Florida scrub communities reflects patterns in soil moisture variation. Using frequency domain reflectometry, we measured soil moisture at 24 sampling stations (3 depths per station) in 3 Florida scrub communities (rosemary scrub, scrubby flatwoods, and oak–hickory scrub) at Archbold Biological Station for 3y (October 1998–September 2001). Stations were arrayed to sample 2 microhabitats (gaps, shrubs) and 2 burn histories. Soil moisture closely tracked cumulative rainfall across widely varying precipitation in the 3 y studied. Soil moisture changed through time and differed significantly among habitats; it was generally highest in scrubby flatwoods, particularly during the wettest periods, and lowest in oak–hickory scrub. Soil moisture was generally greater at deeper depths, in more recently burned sites, and in gaps. Burn effects were particularly pronounced in rosemary scrub, where lack of resprouting dominants after fire maintains more distinct, larger gaps. Burn and gap effects were small in absolute terms, but burned sites and gaps consistently had greater soil moisture than unburned and matrix sites. These small differences may be critical to the germination, establishment, and growth of narrowly endemic plants, particularly in Florida rosemary scrub. However, factors such as competition for nutrients, cryptobiotic soil crusts, litter accumulation, gap size, and allelopathy may be more important in influencing distributions of endemic scrub plants.

We examined how population structure affects seed set and recruitment in the dioecious plant Antennaria dioica, which is a declining species inhabiting semi-natural grasslands in Sweden. Flowering and sex ratio in A. dioica were studied over 4 y at a local (1.2 km²) scale and over 1 y at a regional (742 km²) scale in southern Sweden. Antennaria dioica was also hand-pollinated during 2y to examine whether sex ratios, male abundance, and distance to nearest male influence the degree of pollen limitation. Seed-sowing experiments were conducted to assess whether recruitment is limited by seed or microsite availability. There was a considerable spatio-temporal variation in both flowering and sex ratios. The regional scale survey showed that patch size and number of patches per site were positively correlated, and small patches of A.dioica tended to have biased sex ratios. Experimental hand-pollinations showed that the degree of pollen limitation increased with increasingly female-biased sex ratios in the closest vicinity of the experimental plants. Thus, even though A. dioica is pollinated by many different insects, a fragmented population structure has a large influence on reproductive performance of A. dioica. The seed-sowing experiments showed that recruitment is limited by a combination of seed and microsite availability. It is therefore plausible that reduced seed production due to pollen limitation translates into reduced recruitment. The results from the local and the regional scale indicate that a large fraction of local patches and populations of A. dioica have decreased sexual reproduction. The conclusion is that A. dioica is likely to be particularly sensitive to habitat fragmentation.