Impacts of volcanic eruptions and early recovery in freshwater environments and organisms

Volcanic eruptions modify environments physically and chemically with serious consequences for the biota. In this review, we analysed 80 papers reporting the effects of volcanic eruptions in freshwater environments and on freshwater organisms. An increase in water turbidity is the most common reported physical effect while increases in concentrations of inorganic elements, many representing nutrients for primary producers, are the most common chemical effects. Bacterial growth is usually stimulated, while autotrophs can be either positively or negatively affected depending on the type of impact. A persistent effect reported in the biota is changes to the assemblage, which could generate further changes in terms of ecosystem functions. This analysis also identifies some information gaps, particularly involving the effects of eruptions on heterotrophic biofilms in streams and on invertebrates and fish in lakes. Most studies were carried out soon after the volcanic eruption, so it is difficult to assess the recovery of the ecosystems. Eruptions present unique opportunities for scientific discovery, although such studies are often hindered by a lack of pre-eruption data, which would allow for a more comprehensive assessment of the effects.     

Regional differences in kelp-associated algal assemblages on temperate limestone reefs in south-western Australia

Abstract. Ecklonia radiata (C. Agardh) J. Agardh kelp beds — a characteristic feature of the nearshore environment along the south‐west Australian coastline — contribute significantly to the coastal biodiversity in temperate Australia, yet, little is known about the organization of these macroalgal assemblages. By compiling existing and new data sets from habitat surveys, we have characterized and compared the structure of kelp‐associated macroalgal assemblages in three regions (Marmion Lagoon, Hamelin Bay and the marine environment neighbouring the Fitzgerald River National Park) across more than 1000 kilometres of the south‐west Australian coastline. 152 macroalgal taxa had been recognized within the three regions and this is in the range of species richness reported from other Australian and African kelp beds. The kelp‐associated algal assemblages were regionally distinct, 66% of all taxa were only found in one region and only 17 taxa were found in all three regions. Adjacent regions shared an additional 13–15 taxa. The regional shifts in assemblage structure were evident in species composition of both canopy and understorey. The organization of assemblages followed a spatial hierarchy where differences in assemblage structure were larger among regions (hundreds of kilometres apart) than among sites within regions (kilometres apart) and differences among sites within region were larger than differences among quadrats within sites (metres apart). Despite this hierarchy each level of nesting contributed approximately the same to total variation in assemblage structure and these spatial patterns were stronger than temporal differences from seasons to 2–3 years. Our results suggest that local and small‐scale processes contribute considerably to heterogeneity in macroalgal assemblages throughout south‐western Australia, and, in particular, our results are consistent with E. radiata exerting a strong influence on macroalgal assemblage structure. Further, our study contradicts the existence of a general south‐west Australian kelp assemblage, although a few species may form the core of E. radiata associations across regions.     

Origin of the lichen–spruce woodland in the closed-crown forest zone of eastern Canada

Aim We investigate the timing and factors responsible for the transformation of closed‐crown forests into lichen–spruce woodlands. Location The study area extends between 70° and 72° W in the closed‐crown forest zone from its southern limit near 47°30′ N to its northern limit at the contact with the lichen–spruce woodland zone around 52°10′ N. A total of 24 lichen–spruce woodlands were selected. Methods Radiocarbon dating of charcoals at mineral soil contact and within the organic horizons allowed the principal factors causing the degradation of the closed‐crown forest to be identified, i.e. light fires, successive fires and the occurrence of a spruce budworm epidemic followed by a fire. Results Charcoals dated in the organic horizon were less than 200 years old, suggesting a recent transformation of the closed‐crown forest following surface fires. Before their transformation into lichen–spruce woodlands, stands were occupied by old, dense forests that originated from fires dating back to 1000 yr bp . The radiocarbon dating of charcoals in the organic horizon indicated that several stands burned twice in less than 50 years, while others burned shortly after a spruce budworm epidemic. Light fires are frequent within the lichen–spruce woodlands according to multiple charcoal layers found within the organic matter horizon. Main conclusions While closed‐crown forests are predicted to expand under climate warming, compound disturbances diminish the natural regeneration of the closed‐crown forests in the south and favour the expansion of lichen–spruce woodlands. As black spruce germinates on mineral soils, surface fires accentuate the expansion of the lichen–spruce woodlands southward. Under global warming, warmer springs will lead to earlier low‐intensity fires that do not remove as much organic matter, and hence prevent conditions suitable for black spruce regeneration. Also, spruce budworm reduces seed production for a certain time. The occurrence of fire during this period is critical for regeneration of black spruce.     

Effect of intensity and duration of anthropic noises on European mink locomotor activity and fecal cortisol metabolite levels

Human activities involving noise emission can affect wild animals. European mink was exposed to road noise and human voice playbacks to analyze how sound intensity level and duration of both noises altered the time that individuals were active and if their fecal cortisol metabolite (FCM) levels varied. A Hierarchical Analysis Cluster was performed to establish 2 mink groups with respect to both noise source type: short duration/low intensity (SL) and long duration/high intensity (LH). We performed general linear mixed models to evaluate the variation in locomotor activity duration (s) and FCM (nanogram per gram) levels, respectively. The results showed both road noise and human voices decreased locomotor activity duration in SL more sharply compared with LH, and human voices were the triggers that induced the most pronounced response to both exposure conditions. FCM (ng/g) levels increased in SL compared with LH during road noise while the opposite happened during human voices. Differences based on sex and age of individuals were observed. In conclusion, noise characteristics given by the sound type determined the variations in locomotor activity duration while noise exposure level determined the variations in FCM (ng/g) levels. Attention should be paid to noisy activities (e.g., recreational activities for visitors in protected natural areas) and loud groups of people to conserve wildlife, especially noise sensitive species.     

Gastric Bypass in a Low‐Income,Inner‐City Population: Eating Disturbances and Weight Loss

Objective: To examine the prevalence of eating disturbances and psychiatric disorders among extremely obese patients before and after gastric bypass surgery and to examine the relationship between these disturbances and weight outcomes. Research Methods and Procedures: Sixty‐five women patients (ages 19 to 67) with a mean BMI of 54.1 were assessed by semistructured psychiatric interview before surgery and by telephone interview after surgery (mean follow‐up: 16.4 months) to determine psychiatric status, eating disturbances, and weight and health‐related variables. Results: Patients lost a mean of 71% of their excess BMI, with significantly poorer weight loss outcomes among African Americans. Psychiatric disorders remained prevalent before (37%) and after (41%) surgery. In contrast, binge eating disorder dropped from 48% to 0%. Psychiatric diagnosis did not affect weight outcomes. Instead, more frequent preoperative binge eating, along with greater initial BMI, follow‐up length, and postoperative exercise, predicted greater BMI loss. Postsurgical health behaviors (exercise and smoking) and nocturnal eating episodes were also linked to weight loss. Exercise frequency increased and smoking frequency tended to decrease after surgery. Discussion: These findings indicated that eating and psychiatric disturbances did not inhibit weight loss after gastric bypass and should not contraindicate surgery. Prior binge eating, eliminated after surgery, predicted BMI loss and, thus, may have previously been a maintaining factor in the obesity of these patients. The association between health behaviors and outcome suggests possible targets for intervention to improve surgical results. Poorer outcomes among African Americans indicate that these patients should be closely monitored and supported after surgery.     

Demographic patterns of a widespread long‐lived tree are associated with rainfall and disturbances along rainfall gradients in SE Australia

Predicting species distributions with changing climate has often relied on climatic variables, but increasingly there is recognition that disturbance regimes should also be included in distribution models. We examined how changes in rainfall and disturbances along climatic gradients determined demographic patterns in a widespread and long‐lived tree species, Callitris glaucophylla in SE Australia. We examined recruitment since 1950 in relation to annual (200–600 mm) and seasonal (summer, uniform, winter) rainfall gradients, edaphic factors (topography), and disturbance regimes (vertebrate grazing [tenure and species], fire). A switch from recruitment success to failure occurred at 405 mm mean annual rainfall, coincident with a change in grazing regime. Recruitment was lowest on farms with rabbits below 405 mm rainfall (mean = 0–0.89 cohorts) and highest on less‐disturbed tenures with no rabbits above 405 mm rainfall (mean = 3.25 cohorts). Moderate levels of recruitment occurred where farms had no rabbits or less disturbed tenures had rabbits above and below 405 mm rainfall (mean = 1.71–1.77 cohorts). These results show that low annual rainfall and high levels of introduced grazing has led to aging, contracting populations, while higher annual rainfall with low levels of grazing has led to younger, expanding populations. This study demonstrates how demographic patterns vary with rainfall and spatial variations in disturbances, which are linked in complex ways to climatic gradients. Predicting changes in tree distribution with climate change requires knowledge of how rainfall and key disturbances (tenure, vertebrate grazing) will shift along climatic gradients.     

Tree mortality episodes in the intact Picea abies‐dominated taiga in the Arkhangelsk region of northern European Russia

Question: What were the temporal patterns and rates of tree mortality in a recent episodic tree mortality event? Have similar events occurred in the past, and does climatic variability play a role in the disturbance regime? Location: Intact Picea abies‐dominated taiga in the Arkhangelsk region, northwestern Russia. Methods: We reconstructed the past tree mortality and disturbance history by applying dendroecological methods in five forest stands and related these to climatic data. The role of other potential causes of tree mortality was assessed in a field inventory. Results: The recent episode lasted from 1999 to 2004, influenced all stands studied, and killed on average 21% of trees with a diameter of over 10 cm at 1.3‐m height. The annual tree mortality rate in the decades preceding this episode was 0.49%. During the past 200 years, the stands have experienced chronic small‐scale disturbances, with several irregular disturbances of moderate severity. The recent episode was associated with abundant signs of the bark beetle Ips typographus. Furthermore, the timing of both the recent tree mortality episode and the past disturbance events was associated with dry summers. Conclusion: The results indicate a connection between climatic variability and forest dynamics, the likely driving factors being droughts and bark beetles. In the context of the past 200 years, the recent episode was potentially at the higher end of the range of disturbance variability in terms of severity and spatial extent. This has ecological implications in a changing climate, potentially influencing ecosystem structure and long‐term dynamics.     

Factors Controlling Compositional Changes in a Northern Andean Páramo (La Rusia,Colombia)

In this study, we aimed to assess the processes controlling compositional change in a Northern Andean páramo highly affected by human‐induced disturbances over the last few decades (La Rusia, Colombia). Along the 3000–3800 m asl altitudinal range, we randomly sampled fifty 10 × 10 m plots. Therein, we measured altitude and variables related to soil conditions (i.e., moisture, nutrient contents, bulk density, and texture), occurrence of human‐induced disturbances (i.e., fire, vegetation clearing, potato cultivation, and cattle grazing), and land‐use history. We also recorded richness and abundance of plant species, identifying them as exotic or native. We differentiated four groups of plots according to their species composition. The groups had significant differences in altitude, soil conditions, land‐use history, and particularly, in richness of exotic species and exotic/native cover ratio. They could be ascribed to shrub‐ and grass‐páramo vegetation types based on their relative dominance of woody and herbaceous species; however, these groups were not arranged according to the hypothetical composition of altitudinal belts, but rather formed a mosaic of patches. This mosaic was determined not only by altitude but also by soil conditions and disturbance history of sites. Our results corroborate recent findings which highlight shrub‐ and grass‐páramo vegetation types as patches of contrasting species composition and structure that depend on local environmental variables, as well as human‐induced disturbances as a major determinant of compositional discontinuities in these ‘high mountain’ tropical ecosystems.     

AGE-DEPENDENT CHANGES OF THE CIRCADIAN SYSTEM

This review summarizes the current knowledge on changes of the circadian system in advanced age, mainly for rodents. The first part is dedicated to changes of the overt rhythms. Possible causes are discussed, as are methods to treat the disturbances. In aging animals and humans, all rhythm characters change. The most prominent changes are the decrease of the amplitude and the diminished ability to synchronize with a periodic environment. The susceptibility to photic and nonphotic cues is decreased. As a consequence, both internal and external temporal order are disturbed under steady-state conditions and, even more, following changes in the periodic environment. Due to the high complexity of the circadian system, which includes oscillator(s), mechanisms of external synchronization and of internal coupling, the changes may arise for several reasons. Many of the changes seem to occur within the SCN itself. The number of functioning neurons decreases with advancing age and, probably, so does the coupling between them. As a result, the SCN is unable, or at least less able, to produce stable rhythms and to transmit timing information to target sites. Initially, only the ability to synchronize with the periodic environment is diminished, whereas the rhythms themselves continue to be well pronounced. Therefore, the possibility exists to treat age-dependent disturbances. This can be done pharmacologically or by increasing the zeitgeber strength. So, some of the rhythm disturbances can be reversed, increasing the magnitude of the light-dark (LD) zeitgeber. Another possibility is to strengthen feedback effects, for example, by increasing the daily amount of activity. By this means, the stability and synchronization of the circadian activity rhythm of old mice and men were improved. (Chronobiology International,17(3), 261–283, 2000)     

Changes of vascular plant diversity along a chronosequence of beech coppice stands,central Apennines,Italy

Abstract

This research sought to understand the patterns of vegetation recovery after disturbances because of coppice management in beech forests. Eighty sampling units from the mountain belt of the Marche region (Apennines, Italy) were collected according to a stratified sampling based on their geological setting (limestone, sandstone), elevation classes and age after last coppicing (to represent a chronosequence, from 1 to 90 years). The expected successional trend of decreasing species richness was confirmed, together with some stabilisation processes for older stand ages. However, more complex diversity patterns were found when total species richness was decomposed into the species richness of five social behaviour types (SBTs), defined based on the species' habitat preference. On both bedrocks, temporal gradients explained the observed diversity changes at the stand level: forest specialists increased whereas non-forest species decreased. A relatively long time after coppicing (40–60 years), the contribution of the beech specialist species doubled, whereas non-forest and species from anthropogenic habitats decreased by about 50%. On sandstone, the contribution of gap species also decreased over a long-period, and the beech stands experienced stronger changes over time. We conclude that the decomposition of total species richness in terms of SBT affords the opportunity to identify temporal references for thresholds which can be used to assess plant diversity status in relation to management schedules and conservation policy decisions.