On-station comparative analysis of reproductive and survival performance between Red Maasai,Dorper, and Merino sheep breeds

The reproductive performance of ewes and the survivability of lambs to weaning have a critical economic impact on sheep farming worldwide. Further, knowledge of major mortality causes allows an opportunity for improved flock management to evade financial losses. The maximum likelihood estimates for generalised linear mixed models and chi-square test methods were used to examine 971 mating records, 839 and 763 lambs born and weaned (singles or twins) from the Naivasha Sheep and Goats station in Kenya for the years 2011 to 2020 consisting of Dorper, Red Maasai (RedM), and Merino breeds. The RedM (P < 0.05) outperformed Dorper and Merino in weaning rate, whereas reproductive performance between the three breeds was not significantly different (P > 0.05) in litter size and multiple lambings per ewe lambing. On the one hand, Dorper significantly (P < 0.05) outperformed the other two breeds only in weaning weight per lamb born. In addition, among all the major causes of death, pneumonia appeared to be the one to which Dorper breeds were most susceptible (chi-square test, P < 0.05). According to the findings of this study, neither the Dorper nor the Merino sheep breeds were reproductively superior to the RedM in an extensive semi-arid production environment. In addition, Dorper's susceptibility to the leading causes of mortality, particularly pneumonia and sheep pox, were relatively high compared to other breeds and could be a precursor to massive economic losses for Dorper sheep producers. In contrast to the indigenous RedM breed, imported sheep breeds appeared to be more susceptible to major mortality-related under an extensive production system. Therefore, regardless of weaning weight, RedM breed production appears to be a more viable investment for small-scale farmers, particularly in semi-arid regions.     

Conifer seedling recruitment in a southeastern Canadian boreal forest: the importance of substrate

Abstract. In order to explain conifer species recruitment in Canada's southeastern boreal forest, we characterized conifer regeneration microsites and determined how these microsites vary in abundance during succession. Microsite abundance was evaluated in deciduous, mixed and coniferous stands along a 234-yr postfire chronosequence. Conifers were most often found in relatively well-illuminated microsites, devoid of litter, especially broad-leaf litter, and with a reduced cover of lower vegetation (< 50 cm tall). Although associated with moss-rich forest floor substrates, Abies balsamea was the most ubiquitously distributed species. Picea glauca and especially Thuja occidentalis seedlings were frequently found on rotten logs. Light measurements did not show differences among seedling species nor between stand types. The percentage cover of broad-leaf litter decreased significantly during succession. Also, rotten logs covered with moss occupied a significantly larger area in the mid-successionnal stands than in early successional deciduous or late successional coniferous stands. The results suggest that the presence of specific forest floor substrate types is a factor explaining low conifer recruitment under deciduous stands, conifer codominance in the mid-successional stage, and delayed Thuja recolonization after fire. Results also suggest that some facilitation mechanism is responsible for the observed directional succession.     

The ecology of very small-seeded shade-tolerant trees and shrubs in lowland rain forest in Singapore

A study was made in Bukit Timah Nature Reserve of niche differentiation among 11 woody species that have very small seeds (22–460 µg) and establish in deep shade, i.e., where the indirect site factor (isf) under cloudy conditions is 2%, and one taxonomically related light-demander (seed mass 33 µg). Comparative observations were made on changing light requirement with age. The species varied from shrubs and treelets (Urophyllum) via small to medium-height trees (Ficus, Pternandra) to tall trees (Gynotroches and Pellacalyx). In general, the shorter species fruited in deep shade while the taller needed direct irradiance. All produced ripe fruit at least once a year.In 1–3% isf seedling mortality over 11 months was 24% for Urophyllum hirsutum and 57% for Pternandra echinata (two strongly shade-tolerant species); survivors produced appreciable new stem and leaf tissue. For two more light-demanding species (Ficus grossularioides and F. fistulosa) mean lamina area was much larger in small gaps (10% isf) than in the understorey (<3% isf), while for Urophyllum hirsutum it was much smaller. These three species showed the greatest difference in SLA. There were few significant intraspecific differences between gaps and understorey in concentrations of N, P or K. In a valley where there was no significant difference in isf between a path and adjacent understorey, seedlings of species with seeds <1 mg mean dry mass were five times as dense on transects along steep pathside banks as in the understorey 5 m upslope. The mean mid-bank slope was 66° (cf. 20° upslope). On mid-bank transects litter had a cover of 36% (cf. 95% upslope), and was thinner (0.8 vs 3.2 cm). The soil at 0–7 cm depth into the mid-bank had much lower concentrations of organic matter, total N and P (but not total K) and fine roots than that of upslope transects. All species were found to have vesicular-arbuscular mycorrhiza when 1–2 m tall in deep shade, several having very dense infections. Seedling form and responses are discussed in relation to potential adaptive value and possible evolutionary origin.     

Importance of seed size for the establishment of seedlings of five deciduous broad-leaved tree species

Effects of seed size and phenology on the establishment of five deciduous broad-leaved tree species were examined in deciduous woodland. Treatments included absence and presence of litter in the forest understory, a small gap, and a large gap. Seedling emergence of large-seeded speciesQuercus mongolica var.grosseserrata andAcer mono was not reduced by accumulation of litter in the forest understory, but was promoted in the large gap where litter was less. Seedling emergence of small-seeded species,Alnus hirsuta, Cercidiphyllum japonicum andBetula platyphylla var.japonica, was reduced by the litter in almost all of the sites. Seedlings of large-seeded species avoid shade stress phenologically by unfolding all of their large leaves in a short period before canopy closure in the forest understory. These species had little mortality after seedling emergence. In contrast, small-seeded species have a longer duration of leaf emergence, shorter leaf longevity, and rapid leaf turnover in all the sites. These seedlings attained similar height to those of the large-seeded species at the end of the second year in the large gap, but survival and height growth rate decreased after canopy closure in the forest understory. We suggest that the importance of seed size in determining seedling establishment largely depends on the relationships between seasonal changes of environmental conditions and phenological traits of seedlings, which are related to seed size.Abbreviations Ah Alnus hirsuta - Am Acer mono - Cj Cercidiphyllum japonicum - Bp Betula platyphylla var.japonica - Qm Quercus mongolica var.grosseserrata     

A comparative study on nutrient cycling in wet heathland ecosystems

Summary The concept of the relative nutrient requirement (L _n) that was introduced in the first paper of this series is used to analyse the effects of the dominant plant population on nutrient cycling and nutrient mineralization in wet heathland ecosystems. A distinction is made between the effect that the dominant plant species has on (1) the distribution of nutrients over the plant biomass and the soil compartment of the ecosystem and (2) the recirculation rate of nutrients. The first effect of the dominant plant species can be calculated on the basis of the /k ratio (which is the ratio of the relative mortality to the decomposition constant). The second effect can be analysed using the relative nutrient requirement (L _n). The mass loss and the changes in the amounts of N and P in decomposing above-ground and below-ground litter produced by Erica tetralix and Molinia caerulea were measured over three years. The rates of mass loss from both above-ground and below-ground litter of Molinia were higher than those from Erica litter. After an initial leaching phase, litter showed either a net release or a net immobilization of nitrogen or phosphorus that depended on the initial concentrations of these nutrients. At the same sites, mineralization of nitrogen and phosphorus were measured for two years both in communities dominated by Molinia and in communities dominated by Erica. There were no clear differences in the nitrogen mineralization, but in one of the two years, phosphate mineralization in the Molinia-community was significantly higher. On the basis of the theory that was developed, mineralization rates and ratios between amounts of nutrients in plant biomass and in the soil were calculated on the basis of parameters that were independently measured. There was a reasonable agreement between predicted and measured values in the Erica-communities. In the Molinia-communities there were large differences between calculated and measured values, which was explained by the observation that the soil organic matter in these ecosystems still predominantly consisted of Erica-remains.     

Reproductive effort during gestation and lactation by Richardson's ground squirrels

Summary Reproductive effort by yearling and older female Richardson's ground squirrels was studied over a 4-year period in southern Alberta by obtaining serial weight records from marked individuals to compare the mother's mass at critical points in the annual cycle (emergence from hibernation, estrus, parturition, and litter emergence) with her litter's mass at birth and weaning. Yearlings weighed only 80% of older adults at emergence from hibernation, but they mated at the same time as older females, attained adult mass coincident with pregnancy, and weaned litters that were not significantly smaller in size or mass than those of older females. Age and maternal mass were weak predictors of litter size and litter mass. Of the net increase in mass of the combined mother-litter unit during gestation, over half (60% of 139 g for yearlings; 52% of 127 g for older females) was attributable to an increase in the mother's own mass, whereas during lactation almost all of the net increase (93% of 545 g for yearlings; 96% of 567 g for older females) was attributable to an increase in the litter's mass. On a daily basis, deposition of mass in the litter was 6 times greater during lactation than gestation. On average, neonates weighed 2.3% (6.5 g) of maternal mass at birth and 23.1% (81 g) at emergence from the natal burrow; offspring masses at birth and at emergence were significantly negatively correlated with litter size. On average, litters weighed 16.3% (48 g) of maternal mass at birth and 157.5% (578 g) at emergence from the natal burrow. Compared with other hibernating sciurids, Richardson's ground squirrels have a similar offspring mass relative to maternal mass both at birth and at emergence from the natal burrow. However, because of the large litter size (typically 6–8), absolute reproductive effort, measured either as litter mass at birth or at natal emergence, is large for the body size of the species.     

Microbial decomposition of leaf litter as influenced by fertilizers

Summary A urea and NPK-mixture at concentration of 5, 10 and 15 mg g^–1 air dry litter stimulated microbial populations, microbial activity and rate of decomposition of the litter. The stimulation was more pronounced as the concentration of the fertilizers was increased. However, this trend was reverse after two months in case of urea except for bacterial population. Fewer fungal species were isolated from the fertilizer-treated litter, together with a certain degree of alteration in the composition of mycoflora.     

Leaf-litter and changing nutrient levels in a seasonally dry tropical hardwood forest,Belize, C.A.

Summary Total above ground plant biomass in a 45 year old seasonally dry tropical hardwood forest was estimated to be approximately 56,000 kg/ha oven dry weight. Nutrients immobilized in the standing vegetation were: N, 203 kg/ha; P, 24 kg/ha; K, 234 kg/ha; Ca, 195 kg/ha; Mg, 47 kg/ha; Na, 9 kg/ha; Mn, 1 kg/ha; Cu, 0.5 kg/ha; Zn, 3 kg/ha; Fe, 4 kg/ha. Total nutrients returned each year through the litter were: N, 156 kg/ha; P, 9 kg/ha; K, 59 kg/ha; Ca, 373 kg/ha; Mg, 32 kg/ha; Na, 5 kg/ha; Mn, 1 kg/ha; Al, 21 kg/ha; Zn, 0.3 kg/ha; Fe, 9 kg/ha. Half of the nutrients immobilized in the standing vegetation were found in the leaves and are returned annually to the soil. Although litter fall is interrupted during the year, the mean nutrient content of the litter was high –5.2%.A decomposition rate of 0.48 percent per day was considered high for a seasonally dry tropical hardwood forest. Fluctuations in soil nutrient levels showed a sharp increase at the start of the rainy season. Later during the dry season nutrient levels decreased to concentrations similar to what they were just prior to the rainy season. Soil organic matter levels were very high –20% in the top 12 cm.     

Litterfall,litter decomposition,and flux of particulate organic material in a coastal plain stream

Import of allochthonous material in terms of litterfall in a 3rd order stream in Mississippi coastal plain was 386g dry wt/m²/yr. Litter materials consisting of deciduous leaves, pine needles, and woody twigs collected during different seasons showed some differences in ash-free dry weight, caloric, carbon, hydrogen, nitrogen and phosphorus contents. In situ decomposition to particulate form of deciduous and pine litter enclosed in nylon litter bags showed 15% and 65%, respectively, of the litter remaining after 334 days. Downstream net transport of suspended particulate organic material in the river averaged 688,290 kg dry wt/yr with a range of 456,061 to 920,518 kg dry wt/yr. There was a tendency for the particulate organic matter load of the water to increase during ebbtide and to decrease during floodtide.Supported by the National Aeronautics and Space Administration (NASA Grant No. NGL-25-001-40) and by the National Science Foundation Biological Oceanography Section (NSF Grant No. GA-35715).     

Genetic effect of mottled locus on reproduction and preweaning growth in laboratory mice

Summary An experiment was conducted to study the maternal and fetal effects of the sex-linked gene tortoise on litter size, birth weight, body weight from birth to 30-day of age, and mortality in normal (N) and mutant (M) mice (Mus musculus). The experiment involved two mating types: (1) N x N (dam x sire) which produced normal male and normal female offspring and (2) M X N which produced mutant males that died in utero, mutant females and normal male and female offspring. Comparison 1 consisted of all phenotypically normal male and female offspring from both N X N and M X N mating types born in 2 parities. The data supports the hypothesis that the tortoise gene, when present in the dam, did not significantly affect the body weight of normal progeny prior to 18 days old. There is also evidence for a negative maternal effect of the tortoise gene on body weight from 21 to 30 days of age postpartum. Mating type X parity interaction was not significant prior to 9 day postpartum. Sex of mice did not influence body weight of siblings prior to 18 day old, but males were heavier than females there-after. Normal and mutant females born in six parities from the M X N mating type constituted Comparison 2. The birth weight of the offspring in Comparison 2 was not significantly influenced by the presence of the tortoise gene. All other body weight measurements, however, were lower for mutant females when compared to normal females. Parity affected all body weight measurements in both comparisons. Mortality rate of the offspring was not influenced by parental mating type or parity, but sex differences were observed. Mutant females had higher mortality than normal sisters. This study provides evidence that the mottled locus in the tortoise dam and progeny influences growth and survival.Reference to a company and/or product named by the USDA is only for purposes of information and does not imply approval or recommendation of the product to the exclusion of others