Low Litter Mass Research Articles

The persistent effects of corticosterone administration during lactation on the physiology of maternal and offspring mitochondria.

Reproduction and environmental stressors are generally thought to be associated with a cost to the individual experiencing them, but the physiological mechanisms mediating costs of reproduction and maternal effects remain poorly understood. Studies examining the effects of environmental stressors on a female's physiological state and body condition during reproduction, as well as the physiological condition of offspring, have yielded equivocal results. Mitochondrial physiology and oxidative stress have been implicated as important mediators of life-history trade-offs. The goal of this investigation was to uncover the physiological mechanisms responsible for the enhanced trade-off between self-maintenance and offspring investment when an animal is exposed to stressful conditions during reproduction. To that end, we manipulated circulating corticosterone (CORT) levels by orally supplementing lactating female mice with CORT and investigated mitochondrial physiology and oxidative stress of both the reproductive females and their young. We found that maternal CORT exposure resulted in lower litter mass at weaning, but mitochondrial performance and oxidative status of females were not impacted. We also found potential beneficial effects of maternal CORT on mitochondrial function (e.g. higher respiratory control ratio) and oxidative stress (e.g. lower reactive oxygen species production) of offspring in adulthood, suggesting that elevated maternal CORT may be a signal for early-life adversity and prepare the organism with a predictive, adaptive response to future stressors.

Litter quality and microtopography as key drivers to topsoil properties and understorey plant diversity in ancient broadleaved forests on decalcified marl

In forest ecosystems, litter quality is a major driver for soil and understorey characteristics, but elevation, microtopography and subsoil properties may also be important. We tested the importance of each factor in two ancient mixed forests on decalcified marl, dominated by trees with different litter quality such as European hornbeam, with high-palatable litter, and beech, with low-palatable litter. We mapped elevation, differences in local height (microtopography), tree distribution and understorey cover on slopes ranging from crest to bottom, and sampled 200 7 × 7 m grid cells for characteristics of litter input, understorey, topsoil and subsoil. In both forests, elevation decreased gradually, but microtopography showed irregular patterns of depressions and mounds of a few cm below or above average local height. Tree distribution was not affected by elevation or subsoil properties, but clearly by microtopography. Adult beech was abundant on local mounds, while hornbeam was more common in local depressions. Topsoil and understorey characteristics were mainly affected by litter quality (tree species dominance) and microtopography. Litter quality had separate effects from microtopography, but could reinforce this. High litter quality (hornbeam) and low local height both led to high earthworm activity, low litter mass, high erosion, impermeable clay layers close to the surface, high pH, high soil moisture and high diversity of the understorey. Low litter quality (beech) and high local height both led to low earthworm activity, high litter mass, low erosion, low pH, low soil moisture and low plant diversity. Beech and hornbeam may act as ecosystem engineers, which change habitat conditions and local hydrology, and make habitats more suitable to themselves, and/or unsuitable to the other. However, they also increased spatial complexity of the forest and length of the habitat gradient. This may increase forest biodiversity as a whole, but also resilience to prolonged wet or dry periods.

Food restriction affects maternal investment but not neonate phenotypes in a viviparous lizard.

Food availability significantly affects an animal's energy metabolism, and thus its phenotype, survival, and reproduction. Maternal and offspring responses to food conditions are critical for understanding population dynamics and life-history evolution of a species. In this study, we conducted food manipulation experiments in field enclosures to identify the effect of food restriction on female reproductive traits and postpartum body condition, as well as on hatchling phenotypes, in a lacertid viviparous lizard from the Inner Mongolian desert steppe of China. Females under low-food availability treatment (LFT) had poorer immune function and body condition compared with those under high-food availability treatment (HFT). The food availability treatments significantly affected the litter size and litter mass of the females, but not their gestation period in captivity or brood success, or the body size, sprint speed, and sex ratio of the neonates. Females from the LFT group had smaller litter sizes and, therefore, lower litter mass than those from the HFT group. These results suggest that female racerunners facing food restriction lay fewer offspring with unchanged body size and locomotor performance, and incur a cost in the form of poor postpartum body condition and immune function. The flexibility of maternal responses to variable food availability represents an important life strategy that could enhance the resistance of lizards to unpredictable environmental change.

Why does land-use history facilitate non-native plant invasion? A field experiment with Celastrus orbiculatus in the southern Appalachians

Although historic land use is often impli- cated in non-native plant invasion of forests, little is known about how land-use legacies might actually facilitate invasion. We conducted a 2-year field seeding experiment in western North Carolina, USA, to compare germination and first-year seedling sur- vival of Celastrus orbiculatus Thunb. in stands that had been cultivated and abandoned a century earlier and were dominated by tulip poplar (Liriodendron tulipifera L.), and in paired stands that had never been cultivated and were dominated by oaks (Quercus spp.). Experiments were conducted at five sites with paired tulip poplar and oak stands by varying litter mass (none, low, or high) and litter type (tulip poplar or oak). We also performed reciprocal soil translocations using pots seeded with C. orbiculatus. Soil moisture and temper- ature were measured throughout the growing season. Germination and survival were highest in the tulip poplar stands. Germination was also higher in plots with low litter mass. Seedling survival was highest in plots with low litter mass or no litter. Soil moisture was higher in tulip poplar stands and under low-mass litter. Differences in germination and survival among the potted plants were minimal, suggesting that soil type and ambient site conditions were less important than litter conditions for C. orbiculatus establishment. Our results suggest that the low litter mass and mesic soil conditions that are characteristic of tulip poplar stands may confer higher invasibility and explain the higher abundance of C. orbiculatus in areas with successional overstory communities associated with historically cultivated forests.

The phytotelmata and foliage macrofauna assemblages of a bromeliad species in different habitats and seasons

Abstract. 1. The macrofauna living inside the phytotelmata or on the foliage of bromeliads could be directly affected by habitat and seasonality. Habitat may also have indirect effects by affecting plant morphology.2. In Chaco forests, a facultative epiphytic bromeliad (Aechmea distichantha) shows different morphology when growing in sun and shade conditions. Therefore, the abundance and assemblage composition of the macrofauna living on this bromeliad were analysed in different habitats and seasons.3. Sun plants were shorter, had higher tank water content, but lower litter mass than shade ones. Phytotelmata water temperature and pH were similar between habitats.4. In the phytotelmata, the macrofauna abundance and richness per plant, as well as total richness, were similar between habitats and among seasons. Detritivores were more abundant than predators in all habitats and seasons. Shade plants had a higher proportion of detritivores than sun plants in spring and summer, but not in winter.5. On the bromeliad foliage, the macrofauna abundance and richness per plant were lower in winter. There were no differences in abundance between habitats, but shade plants had higher species richness than sun plants. In spring and summer, total richness was higher in shade plants than in sun plants. In spring and summer, detritivores were more abundant for shade, whereas ants were more abundant in sun plants. The proportion of hunting spiders was higher in the shade in spring and summer.6. Our study showed that habitat mainly affects bromeliad‐foliage macrofauna, but not the phytotelmata macrofauna.

Patterns of microarthropod abundance in oak–hickory forest ecosystems in relation to prescribed fire and landscape position

We examined patterns of microarthropod abundance in oak–hickory ( Quercus–Carya) forest ecosystems in southern Ohio (USA) in relation to landscape position and fire frequency. Abundances of various suborders of Acari and Collembola were determined in samples taken in June 1999 in three forested watersheds, one that had been burned annually for four consecutive springs (1996–1999), one that had been burned periodically (1996 and 1999), and an unburned control. Microarthropod abundance was significantly lower in the annually burned watershed than the periodically burned and control watersheds. Since both the periodically burned and annually burned watersheds were burned in April 1999, the lower microarthropod abundance in the annually burned watershed was not simply an immediate effect of burning. At the landscape scale, the abundance of oribatid mites was greater in xeric than intermediate or mesic landscape positions. Within any single watershed, there was no significant linear relationship between litter mass and microarthropod abundance. However, when all three watersheds were combined, there was a significant, positive relationship between litter mass and microarthropod abundance, mainly due to the annually burned watershed where there was very low litter mass and low microarthropod abundance. Both fire frequency and landscape position have significant effects on microarthropod abundance; however, those effects cannot be robustly predicted based solely on forest floor litter mass differences.

Species Richness of Experimental Productivity Gradients: How Important is Colonization Limitation?

The biodiversity of a site should depend on the interplay of local colonization (gain) and extinction (loss) rates, but few theoretical explanations of diversity patterns on productivity gradients have included effects of productivity on colonization. In an 11—yr study, experimental increases in productivity via nitrogen addition generally led to decreased species richness in four grassland fields. Decreased diversity in productive plots was caused as much by lower rates of species gain as by greater rates of loss of existing species. Annual grasses and forbs had high gain and loss rates, but these were independent of productivity. In contrast, the rates of gain of perennial grass and forb species declined with productivity, and their rates of loss increased. Species richness was dependent on litter mass and on light penetration, but not on aboveground living plant mass, suggesting that there was no direct effect of productivity on diversity. Diversity in periodically burned prairie, which had low litter mass, was independent of productivity by the 10th and 11th yr of the study. Results suggest that diversity is lower in productive grasslands because accumulated litter, and possibly lower light penetration, inhibit germination and/or survival of seedlings, and thus decrease rates of establishment by new species. Higher productivity also leads to higher rates of loss, presumably via competitive displacement, of existing species. Results do not support the hypothesis that soil N heterogeneity controls diversity on the temporal and spatial scales of this study.

Fertility and Disturbance Gradients: A Summary Model For Riverine Marsh Vegetation

Although freshwater shorelines occupy extensive areas of the temperate zone, we still have few conceptual models for pattern and process in shoreline vegetation. This study uses multivariate vegetation data to describe vegetation—environment relationships in a set of riverine wetlands and then explores general relationships between pattern and process. Samples were collected from five marshes along the Ottawa River (eastern Canada) (n = 94 sample units). Detrended correspondence analysis was used to described major gradients, and TRWINSPAN was used to classify vegetation types. TWINSPAN produced four major classes dominated by Sparganium eurycarpum, Eleocharis smallii, Scirpus americanus, and Typha latifolia. Within each class, two associations could be recognized, differing in the degree to which one species managed to dominate the vegetation. Ordination showed that these vegetation types were arranged along two major axes: a standing crop and litter gradient, and a water depth gradient. Species richness was greatest just above the late August waterline in Eleocharis smallii vegetation that had low fertility, intermediate total biomass (250g/m2) and low littermass (30 g/m2). Very high biomass (>400g/m2) was observed where indices of high fertility and low disturbance coincided. Low species richness in this Typha—dominated vegetation is thought to be a result of competitive exclusion. Exposure to waves, ice, and flowing water produced a fertility gradient. The least fertile sites had small evergreen species such as Eriocaulon septangulare and Ranunculus flammula. These species possessed traits associated with Grime's "stress tolerator" strategy. The three main factors controlling vegetation competition were water depth, the effects of spring flooding in removing litter, and the fertility gradient produced by waves and flowing water. These were incorporated into a conceptual model including both patterns and processes observed along the Ottawa River.