A study of the ecology of the bushpig (Potamochoerus porcus) showed that there were regional differences in relative investments made in reproduction and maintenance. Southern Cape populations had ...relatively low reproductive rates, but levels of energy storage and survival rates were high. The reverse applied to eastern Cape populations. The diets of the two populations differed, with a higher ratio of available production nutrients (NPK) to maintenance nutrients (C) in the eastern Cape. A life history model is developed which accommodates these regional differences by linking nutritional characteristics of the diet with metabolic turnover rates. According to this model, the rate of reproductive investment (number of viable young per unit of time) relative to somatic investment (energy storage, survival) is determined by the rate at which production nutrients (NPK) are procurable. For herbivorous animals this depends on the rate at which the nutrients are available to their food plants, which in turn is linked to soil fertility and thus to the geological parent material.
The population biology of the tropical marine gastropod Conus pennaceus was studied off the island of Oahu in the Hawaiian Islands. Growth, fecundity, and survivorship rates were determined in the ...field through a combination of mark—recapture studies, regular population censuses, and direct count of ova produced by individual females. Individuals of C. pennaceus grow to a shell length of 15 mm in their 1st yr, and females may reproduce by the end of their 2nd yr at a shell length of between 20 and 25 mm. Females probably produce 1 egg mass/yr, and age—specific fecundity increases with increasing female size. By year 10, annual fecundity of females has increased to over 6000 ova, while shell growth has slowed to <1mm/yr. Although C. pennaceus has no planktonic larval stage, over 99.93% of all fertilized ova fail to survive their 1st yr. Subsequent mortality is constant at an annual rate of 0.419, and very few animals survive to the end of their 10th yr. The population examined remained relatively constant in size during the 22—mo study. This stability is attributed to the shape of the reproductive value curve of the population and to the ability of C. pennaceus to utilize a wide variety of prey species.
1. Identifying which factors influence age and size at maturity is crucial for a better understanding of the evolution of life-history strategies. In particular, populations intensively harvested, ...hunted or fished by humans often respond by displaying earlier age and decreased size at first reproduction. 2. Among ungulates wild boar (Sus scrofa scrofa L.) exhibit uncommon life-history traits, such as high fertility and early reproduction, which might increase the demographic impact of varying age at first reproduction. We analysed variation in female reproductive output from a 22-year long study of an intensively hunted population. We assessed how the breeding probability and the onset of oestrus responded to changes of female body mass at different ages under varying conditions of climate and food availability. 3. Wild boar females had to reach a threshold body mass (27-33 kg) before breeding for the first time. This threshold mass was relatively low (33-41% of adult body mass) compared to that reported in most other ungulates (about 80%). 4. Proportions of females breeding peaked when rainfall and temperature were low in spring and high in summer. Climatic conditions might act through the nutritional condition of females. The onset of oestrus varied a lot in relation to resources available at both current and previous years. Between none and up to 90% of females were in oestrus in November depending on the year. 5. Past and current resources accounted for equivalent amount of observed variations in proportions of females breeding. Thus, wild boar rank at an intermediate position along the capital-income continuum rather than close to the capital end where similar-sized ungulates rank. 6. Juvenile females made a major contribution to the yearly reproductive output. Comparisons among wild boar populations facing contrasted hunting pressures indicate that a high demographic contribution of juveniles is a likely consequence of a high hunting pressure rather than a species-specific life-history pattern characterizing wild boar.
We assessed age-specific natural mortality (i.e., excluding hunting mortality) and hunting mortality of 1,175 male and 1,076 female wild boar (Sus scrofa) from Châteauvillain-Arc en Barrois (eastern ...France), using a 22-year dataset (1982–2004) and mark–recapture–recovery methods. Overall yearly mortality was >50% for all sex and age-classes. Low survival was mostly due to high hunting mortality; a wild boar had a >40% of chance of being harvested annually, and this risk was as high as 70% for adult males. Natural mortality rates of wild boar were similar for males and females (approx. 0.15). These rates were comparable to rates typical of male ungulates but high for female ungulates. Wild boar survival did not vary across sex and age-classes. Despite high hunting mortality, we did not detect evidence of compensatory mortality. Whereas natural mortality for males was constant over time, female mortality varied annually, independent of fluctuations in mast availability. Female wild boar survival patterns differed from those reported in other ungulates, with high and variable natural mortality. In other ungulates, natural mortality is typically low and stable across a wide range of environmental conditions. These differences may partly reflect high litter sizes for wild boar, which carries high energetic costs. High hunting mortality may induce a high investment of females in reproduction early in life, at the detriment to survival. Despite high hunting mortality, the study population increased. Effective population control of wild boar should target a high harvest rate of piglets and reproductive females.
Sympatric fish morphs diversifying in their feeding pattern in fresh waters typically implement alternative migratory tactics so that omnivores become migrants and specialists‐residents. Charrs of ...the genus Salvelinus populating the lower Kamchatka River (Northeast Asia) are a rare example wherein two related sympatric morphs both implement a variety of life‐history tactics in parallel. Here the authors analyse the ecological diversity in the endemic piscivorous “white” morph that exploits resources of the Kamchatka River in sympatry with the partially anadromous invertivorous “Dolly Varden” (DV) morph. Eco‐morphological criteria allowed the authors to validate the morph identification. The white charr (WC) was found to subdivide into the small‐sized (up to 1.6 kg) fish inhabiting the lacustrine part of the ecosystem and the large‐sized (up to 3.4 kg) fish inhabiting the main river channel. The persistent spatial segregation of the sub‐groups was confirmed by significant differences in the life span, muscle δ13С signature and parasite load. According to contrasting patterns of strontium accumulation in otoliths, the riverine WC is represented by resident and semi‐anadromous individuals. At the same time, the lack of microsatellite DNA differentiation and allometric nature of the morphometric discrepancy point to the intra‐population source of the WC polymorphism. The authors suggest that WC diverged from DV as a result of feeding specialization on the threespine stickleback numerous in the ecosystem since the temporary flooding by marine waters in the middle Holocene. The modern stickleback division into local stocks following the ecosystem differentiation into a river, side lake and estuary resulted in the WC life‐history split and ecological radiation.
Large horns or antlers require a high energy allocation to produce and carry both physiological and social reproductive costs. Following the principle of energy allocation that implies trade-offs ...among fitness components, growing large weapons early in life should thus reduce future growth and survival. Evidence for such costs is ambiguous, however, partly because individual hetero-geneity can counterbalance trade-offs. Individuals with larger horns or antlers may be of better quality and thus have a greater capacity to survive. We investigated trade-offs between male early horn growth and future horn growth, baseline mortality, onset of actuarial senescence, and rate of ageing in an Alpine ibex (Capra ibex ibex) population. Horn growth of males in early life was positively correlated to their horn length throughout their entire life. Cohort variation and individual heterogeneity both accounted for among-individual variation in horn length, suggesting both long-lasting effects of early life conditions and individual-specific horn growth trajectories. Early horn growth did not influence annual survival until 12 years of age, indicating that males do not invest in horn growth at survival costs over most of their lifetime. However, males with fast-growing horns early in life tended to have lower survival at very old ages. Individual heterogeneity, along with the particular life-history tactic of male ibex (weak participation to the rut until an old age after which they burn out in high mating investment), are likely to explain why the expected trade-off between horn growth and survival does not show up, at least until very old ages.
It is commonly assumed that the propensity to disperse and the dispersal distance of mammals should increase with increasing density and be greater among males than among females. However, most ...empirical evidence, especially on large mammals, has focused on highly polygynous and dimorphic species displaying female-defence mating tactics. We tested these predictions on roe deer, a weakly polygynous species of large herbivore exhibiting a resource-defence mating tactic at a fine spatial scale. Using three long-term studies of populations that were subject to the experimental manipulation of size, we did not find any support for either prediction, whether in terms of dispersal probability or dispersal distance. Our findings of similar dispersal patterns in both sexes of roe deer suggest that the underlying cause of natal dispersal is not related to inbreeding avoidance in this species. The absence of positive density dependence in fine-scale dispersal behaviour suggests that roe deer natal dispersal is a pre-saturation process that is shaped by heterogeneities in habitat quality rather than by density per se.
Studying between-sex differences in body growth has strong implications for understanding life-history tactics of animals. We used age and carcass mass data from 2,312 female and 2,622 male alpine ...chamois (Rupicapra rupicapra) harvested in the French Alps to model the sex-specific body growth patterns of this species. Males were heavier (asymptotic body mass: 29.6 kg) than females (22.3 kg), with an adult sexual size dimorphism of 32.4%. Sexual size dimorphism originated from both differences in body growth after 1.5 years of age and differences in length of the growth period. Females reached asymptotic body mass almost 3 years earlier (3.5 years) than males (6.2 years). We also found that females 1st reproduced before achieving asymptotic growth, at 78% of their asymptotic body mass. Between-sex differences in growth patterns in this species are most likely due to stronger selection pressure for larger size in males than in females due to intrasexual competition.
Salmonids are known for the occurrence in sympatry of two life-history forms, one that undergoes migration to sea before returning to freshwater to reproduce (anadromous) and one that inhabits ...freshwater without a migration phase (resident). Whereas one breeding population is often suggested by population genetic studies, mating patterns have rarely been directly assessed, especially when both sexes are found within each life-history form. By using highly polymorphic microsatellite loci and parentage analysis in a natural population of sympatric anadromous and resident brook charr (Salvelinus fontinalis), we found that gene flow occurred between the two forms and was mediated by resident males mating with both resident and anadromous females. Determinants of reproductive success, estimated by the number of surviving juveniles (ages 1 and 2 years), differed between the sexes. No strong evidence of the influence of size on individual reproductive success was found for males, whereas larger females (and hence most likely to be anadromous) were more successful. The higher individual reproductive success of anadromous fish compared to residents was mainly explained by this higher reproductive success of anadromous females. We suggest that resident males adopt a “sneaking” reproductive tactic as a way of increasing their reproductive success by mating with females of all sizes in all habitats. The persistence of the resident tactic among females may be linked to their advantage in accessing spatially constrained spawning areas in small tributary streams unavailable to larger females.
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