Increasing Levels Of Disturbance Research Articles

Invasive-dominated grasslands in Hawai'i are resilient to disturbance.

Non-native-dominated landscapes may arise from invasion by competitive plant species, disturbance and invasion of early-colonizing species, or some combination of these. Without knowing site history, however, it is difficult to predict how native or non-native communities will reassemble after disturbance events. Given increasing disturbance levels across anthropogenically impacted landscapes, predictive understanding of these patterns is important. We asked how disturbance affected community assembly in six invaded habitat types common in dryland, grazed landscapes on Island of Hawai'i. We mechanically disturbed 100 m2 plots in six vegetation types dominated by one of four invasive perennial grasses (Cenchrus ciliaris, Cenchrus clandestinus, Cenchrus setaceus, or Melinis repens), a native shrub (Dodonaea viscosa), or a native perennial bunchgrass (Eragrostis atropioides). We censused vegetation before disturbance and monitored woody plant colonization and herbaceous cover for 21 months following the disturbance, categorizing species as competitors, colonizers, or a combination, based on recovery patterns. In addition, we planted individuals of the native shrub and bunchgrass and monitored survival to overcome dispersal limitation of native species when exploring these patterns. We found that the dominant vegetation types showed variation in post-disturbance syndrome, and that the variation in colonizer versus competitor syndrome occurred both between species, but also within species among different vegetation types. Although there were flushes of native shrub seedlings, these did not survive to 21 months within invaded habitats, probably due to regrowth by competitive invasive grasses. Similarly, survival of planted native individuals was related to the rate of regrowth by dominant species. Regardless of colonization/competitor syndrome, however, all dominant vegetation types were relatively resilient to change. Our results highlight that the altered post-agricultural, invaded grassland landscapes in Hawai'i are stable states. More generally, they point to the importance of resident communities and their effects on species interactions and seed availability in shaping plant community response to disturbance.

Species Composition and Diversity of Plants along Human-Induced Disturbances in Tropical Moist Sal Forests of Eastern Ghats, India

Plant biodiversity data are prerequisites for the sustainable management of a forest. We used quantitative ecological tools to determine the species composition, diversity (richness and evenness), population structure, distribution patterns, and regeneration status of trees in a Tropical Moist Sal Forest of Eastern Ghats, India. For this purpose, a field inventory was conducted during 2020–2022 in sixteen 1.0 ha forest stands along a human-induced disturbance gradient. A total of 161 species (61 trees, 40 shrubs, 60 herbs) belonging to 77 families and 143 genera were recorded in the 16.0 ha of forest area. The results revealed a significant (p < 0.01) decrease in the tree and shrub species density, basal area, species richness, and diversity along the gradient of disturbance. However, in the case of herbs, the Shannon–Weiner diversity index increased significantly (p < 0.01) with increasing disturbance levels. Irrespective of forest types and disturbance levels, the tree diameter class (10–30 cm) accounted for the highest stem density in the forest. A mixed trend was found in the case of the basal area; the >41 cm diameter class constituted the highest basal area in the Pure Sal Forest while the 10–30 cm class was in the Moist Deciduous Forest without Sal. Tree species richness was found higher in lower diameter classes. Disturbances impacted the distribution pattern of trees; in the Pure Sal Forest, the contagious distribution of trees were 61.54%, 40%, and 12.5% in undisturbed, low-disturbed, and moderately disturbed sites, respectively. The percent of trees showing random and regular distribution increased with the increased level of disturbance in all forest types. The number of tree species having good regeneration decreased with the increased disturbance intensity in all forest types. Frequent grazing, repeated forest fires, and poor soil seed banks at the Moderately Disturbed site were the main reasons for the poor/no regeneration of Pterocarpus marsupium, Adina cordifolia, Terminalia bellerica, and some other economical species. Significant changes in structural attributes of the tree community revealed the impact of human-induced disturbances in the Moist Sal Forests of Eastern Ghats. The disturbance mosaics promoted the growth of many invasive weed species and lianas, depleting the number of valuable species in the forest. This study suggests the adaption of sustainable biodiversity conservation approaches through the active participation of the tribal so that the remnants the Moist Sal Forests of Eastern Ghats can be controlled to prevent further degradation.

Beyond species loss: How anthropogenic disturbances drive functional and phylogenetic homogenization of Neotropical dung beetles

Anthropogenic activities drive tropical forest loss and biodiversity decay. However, few studies have addressed how the biodiversity response varies between disturbance-adapted species (i.e., winners) and those highly susceptible to disturbance (i.e., losers), or whether such responses differ between the taxonomic, functional, or phylogenetic dimensions of diversity. Understanding these dynamics can help prevent or buffer biotic homogenization processes. Using a meta-analytical approach with dung beetles as model organisms, we evaluated how anthropogenic habitat disturbances influence the multiple diversity dimensions of winner and loser species relative to conserved forest sites in the Neotropics. Habitats were organized according to a disturbance gradient ranging from second-growth forests, shaded agroforestry, lowly-shaded agroforestry, living fences, and pastures. Our database included 30 studies, from which we calculated nine metrics divided into three alfa diversity aspects: richness, evenness, and divergence. We also evaluated the beta-diversity response to disturbance and forest protection. All dimensions of dung beetle diversity decreased significantly with increasing disturbance levels, with phylogenetic diversity showing the highest losses, whereas evenness metrics increased in second-growth forests and agroforestry systems. Loser dung beetles showed high diversity loss as well as functional and phylogenetic clustering, reflecting a pervasive biotic homogenization in the most severely disturbed habitats, whereas winner species were insensitive to anthropogenic disturbances. Beta diversity increased significantly with disturbance and forest protection. Our study showed that heavy disturbances erode and homogenized all diversity dimensions of loser dung beetles. However, second-growth forests and agroforestry systems mitigated diversity loss and homogenization processes by favoring the coexistence between functional and phylogenetically distant species and maintaining assemblages compositionally similar to those in conserved forests, highlighting their importance for conservation. We encourage natural resource managers to consider protection of disturbed off-reserve forests in management schemes as these are essential for maintaining biodiversity in an increasingly anthropized world.

Spatio-temporal distribution of gelatinous zooplankton in tropical mangrove estuaries: Environmental drivers and possible mangrove disturbance effects

The impacts of environmental changes and mangrove disturbance on the gelatinous zooplankton community structure were investigated monthly for one annual cycle at six stations in three estuaries in Matang, Malaysia. Tiram, Tinggi, and Sepetang estuaries were classified based on the Mangrove Quality Index (MQI) to represent the least (MQI 5 = excellent), moderately (MQI 4 = good), and highly disturbed (MQI 2 = bad) areas, respectively. Among the gelatinous zooplankton species, the holoplanktonic ctenophore, Pukia ohtsukai (formed 56%–58% of the total gelatinous zooplankton), was the most dominant species and showed increased densities with the increasing level of disturbance. On the other hand, a hydrozoan, Blackfordia sp. (39%–43%), which needs suitable substrates for the survival of polyploids, was found to be most abundant in the moderately disturbed area, indicating low densities in areas with too little or too much disturbance. Salinity, a parameter influenced by river discharge and tidal changes, was identified as the main environmental factor affecting the species' seasonal variability. The dry season was associated with an increase in gelatinous zooplankton density and prevalence of marine species. Also, factors related to water clarity (turbidity, transparency, and suspended solids) and nutrients (nitrogen and phosphorus) explained 91% of the variables that affected the gelatinous zooplankton community structure. The species diversity (H′) in the least and moderately disturbed areas were significantly higher than in the highly disturbed estuary. In contrast, the highest mean density was recorded in the highly disturbed estuary (34.4 ± 19.8 inds. m−3) followed by the moderately (21.6 ± 6.1 inds. m−3) and the least disturbed areas (9.7 ± 4.1 inds. m−3). The present study suggested that the gelatinous zooplankton biodiversity declines and the abundance escalates with increasing disturbance levels.

Disturbance of plateau zokor (Eospalax baileyi) mounds increase plant and soil macroinvertebrate richness by offering a diversified microenvironment

Habitat heterogeneity is expected to change community composition and diversity, with large implications for ecosystem processes and function. Understanding the potential mechanisms of habitat heterogeneity affecting community ecological processes is a central issue in biodiversity conservation. In this study, we use a spatial metrics analysis to quantify the spatial pattern of plateau zokor mounds. We integrated soil physicochemical variables and community characteristic data to understand the disturbance effect of plateau zokor mounds on community diversity at a microhabitat scale (400 m2). Results showed that plant species richness increased significantly with increasing disturbance levels. Increases in forb species were largely the reason for the increased plant diversity in the alpine meadow disturbed by plateau zokor mounds. Disturbance caused by the plateau zokor significantly increased the soil macroinvertebrate richness and abundance, with herbivorous taxa playing a key role. Mantel tests and redundancy analysis showed that the composition of plant and soil macroinvertebrate communities are significantly related to soil moisture and soil temperature, and the SEM model revealing soil moisture and soil temperature positive effects on plant and macroinvertebrate richness after plateau zokor disturbance. Furthermore, soil variables (moisture, temperature, and organic carbon) directly affected plant richness, and indirectly affected soil macroinvertebrate communities. Our results suggest that the spatial pattern of plateau zokor mounds facilitate greater biodiversity through increased habitat complexity and heterogeneity. Therefore, it can be regarded as a “key species” in the alpine grassland and researchers should pay more attention to the ecological effects of alpine rodent disturbance on grassland ecosystems.

Management‐mediated predation rate in the caribou–moose–wolf system: spatial configuration of logging activities matters

AbstractLandscape complexity can determine the population dynamics of interacting predators and prey. Yet, management plans are commonly developed from aspatial predictive models. This oversight may result in unexpected outcomes or the loss of opportunities to make spatial interventions that would increase a plan's effectiveness. The management of the threatened woodland caribou (Rangifer tarandus caribou), boreal population, provides an example of such shortcomings when using an aspatial approach. Currently, the most influential management recommendation is to maintain at least 65% of undisturbed forests in areas occupied by caribou populations, regardless of the spatial configuration of the forest cover. Using a spatially explicit individual‐based model (IBM), we evaluated the effects of the spatial configuration of cuts and roads on the mortality of boreal caribou living in sympatry with wolves (Canis lupus) and moose (Alces alces), an apparent competitor. Starting with a real forest landscape, we created forest management scenarios of the specific spatial distribution of cuts (mosaic, small, or large agglomeration) with increasing disturbance levels. We then ran the IBM with simulated agents, representing individuals of the three species, moving according to movement rules determined from radio‐collared individuals. We found that movement responses to land cover types and roads differed among species. For example, caribou and moose generally avoided areas close to roads, contrary to wolves. Those differences influenced the mortality of caribou agents, which not only depended on the levels of disturbance but also depended on the spatial distribution of cuts and roads. After controlling for disturbance level, wolves were more successful when forest management required an extensive road network resulting in relatively high habitat fragmentation. Caribou agents experienced lower mortality in landscapes with low densities of road and disturbance‐related edges. The effect remained much stronger, however, for the level than the spatial configuration of human disturbances. Still, our IBM demonstrated how landscape management could be used to manipulate species interactions, with the intent of either increasing or decreasing predation rates on specific populations, depending on management goals.

Impact of tourism on habitat use of black grouse (Tetrao tetrix)in an isolated population in northern Germany.

As many other wild living species, black grouse Tetrao tetrix has to cope with anthropogenic disturbances in many habitats. Impacts of tourism and outdoor recreation on grouse species Tetraoninae have been subject to several studies in mountainous habitats in Central Europe and the United Kingdom. The geographically isolated and critically endangered black grouse population of Lower Saxony (North Germany) has been consistently monitored but beyond that poorly studied. This also applies to the key habitats of the nature reserve Lüneburg Heath (Lüneburger Heide) which, in turn, serves as a recreational area as well. In this study, the impact of tourism activity on habitat use of black grouse was investigated using data of GPS-tracked individuals. Additionally, visitor numbers on public and (usually undisturbed) closed routes were monitored using infrared light barriers. The spatio-temporal distribution of locations and the recreational activity were evaluated by linear mixed-effects models. Tagged individuals avoided the vicinity of public routes and avoiding distances were directly related to intensity of human activity. There was no seasonal change of black grouse habitat use alongside public routes. However, towards closed routes, significantly higher distances appeared during peak phases of visitor numbers (August and September), implying temporary increased disturbance levels within a key refuge area. Diurnal adaptation of habitat use was strongly dependent on the route density within the home range. Individuals used the vicinity of public trails at night and dawn but evaded these habitats during peak human activity around noon and afternoon. Recreational disturbances appeared to significantly affect the effective habitat availability for black grouse in the nature reserve. Visual cover by vegetation, however, seemed to diminish negative effects emerging from hiking trails. This provides an effective protective measure which requires minimal effort for the local conservation management.

Dominance of competitors in riparian plant species composition along constructed banks of the German rivers Main and Danube

Hardening of shorelines has been extensively implemented in many parts of the developed world. This also applies to banks of German Federal Waterways, which are mostly fixed by ripraps to prevent bank erosion as a consequence of wave disturbance by shipping traffic. Since ripraps notably alter functions of riparian ecosystems and nature conservation demands recently gained in importance along waterways, alternatives for ripraps play an increasing role.Front-fixed banks are ripraps parallel to the shoreline and embedded in the waterway’s channel with an unsecured bank of low steepness behind them. Thus, they are suitable to prevent banks from erosion. However, it is unclear how they can contribute to the ecological enhancement of riparian vegetation along waterways.Therefore, we compared riparian vegetation of ripraps and front-fixed banks with unsecured banks along the German rivers Main and Danube to assess the ecological efficiency of front-fixed banks. Disturbance by alternating water levels was the lowest at ripraps, whereas disturbance levels were higher at front-fixed and unfortified banks. We used an ordination and indicator species analysis to reveal differences in species composition. The results of the indicator species analysis were analyzed regarding species’ biotope origin, light and moisture demand and life strategy. We analyzed species diversity and calculated functional diversity indices to display the prevalent ecosystem processes.Higher variation in species composition, common indicator species, a strong vertical layering of woody riparian vegetation and similar site conditions at front-fixed and unfortified banks revealed higher similarities in species composition between them than to other bank type combinations. Limnic species occurred with a higher frequency at unfortified and front-fixed banks, whereas terrestrial species were more frequent at ripraps. Light-tolerant species were more common at ripraps, whereas species’ demand for moisture was higher at front-fixed and unfortified banks than at ripraps. Cr-strategists occurred more frequently with increasing disturbance level, whereas c-strategists were more common at ripraps.Ripraps had the highest species diversity levels whereas functional diversity tended to be higher at front-fixed and unfortified banks. This indicates a higher trait complementarity and thus a higher specialization towards alternating water levels, wherefore a higher degree of naturalness can be assumed in these habitats.Nature conservation efforts along German Federal Waterways should focus on the restoration of flooding dynamics, as species typical for riverine habitats are more common at front-fixed and unfortified banks than at ripraps. Since front-fixed banks bear traits suited for the reconnection of rivers and their floodplains and for bank protection, they are a suitable alternative to promote biodiversity along German Federal Waterways.

The impact of natural resource use on bird and reptile communities within multiple-use protected areas: evidence from sub-arid Southern Madagascar

Multiple-use protected areas, in which sustainable levels of extractive livelihood activities are permitted, play an increasingly important role in the global protected area estate, and are expected to rise in prevalence. However, we know little about their effectiveness at conserving biodiversity. We surveyed bird and reptile communities in three areas across a forest disturbance gradient resulting from charcoal production and shifting cultivation within a multiple-use protected area in Madagascar’s sub-arid spiny forest. We scored individual species using a Conservation Value Index (CVI; a simple metric based on rarity, threat and distinctiveness), and estimated the total conservation value of each treatment by calculating the sum of frequency-weighted CVI scores across all present species. Bird and reptile community responses to forest disturbance were idiosyncratic. Bird richness was greatest in the moderate-disturbance treatment, but the low-disturbance treatment had the superior conservation value due to higher frequencies of locally-endemic species. Reptile richness was the same in low- and moderate-disturbance treatments, but the conservation value of the latter was greater. The high-disturbance areas had lowest richness and conservation value for both groups. For birds, increasing disturbance levels were accompanied by community turnover from high-value to low-value species, a pattern highlighted by CVI that is masked by assessing species richness alone. Although some endemic species appear to be resilient to degradation, multiple-use protected areas in Madagascar may lose biodiversity since most endemic species are forest-dependent. Stricter protected area models may be more appropriate in areas where much of the high-value biodiversity is sensitive to habitat degradation.

Extended Kalman filter application for high-noise cancelation in control telemetry channels of oil electric submersible pump

Electro Submersible Pump (ESP) telemetry system allows getting information of different types of heavy electromagnetic noise: random, pulsing, harmonic etc. in the neighborhood They are pump unit's intake pressure, temperature and most importantly its insulation resistance for submersible motor stator coil reliability – for the successful exploitation of the oil complexes. The change from analog to digital communication techniques is going at a fast rate in almost all technical fields. But increasing disturbance levels with corrupted analog communication result in an increased noise level, but are often still “audible” or the control system is still reliable. With increasing disturbance levels, the analog signal will be audible, but will remain low. However beyond a certain disturbance level, the so called “digital cliff”, the digital communication and the control stop abruptly. In this study, the extended Kalman filter (EKF) is designed and examined under severe noise conditions for the high-noise cancelation in control telemetry channels of oil ESP. The results approve a high performance of the developed EKF.

PHYSICAL DISTANCES AMONG INDIVIDUALS IN FLOCKS OF GREATER FLAMINGOES (PHOENICOPTERUS RUBER) ARE AFFECTED BY HUMAN DISTURBANCE

ABSTRACT Use of flock members to reduce individual levels of vigilance has been the focus of many studies that have attempted to explain the relationship among vigilance, group size, and distance covered by using foraging or preening as indicators. To avoid the confounding variables associated with foraging and preening, the effects of increasing levels of disturbance on vigilance by measuring distances among individuals (D) in flocks of greater flamingoes was studied. During 61 h, reactions to 112 disturbances were recorded. Undisturbed flamingoes exhibited no relationship between D and flock size. When joggers appeared, birds became alert but continued to feed. D was uninfluenced by flock size when jeeps drove past, but was different in value from that in undisturbed flocks. However, when tours stopped and occupants got out of their vehicles, D was significantly reduced and flock size was positively correlated with flock cohesiveness, i.e., smaller flocks had smaller D values than larger flocks. Flaming...

Forcing the TIEGCM model with Birkeland currents from the Active Magnetosphere and Planetary Electrodynamics Response Experiment

Geomagnetic field‐aligned currents from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) satellite mission are used to drive the Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM). We present a comparison between ground magnetic signatures computed by the model and observations at four different geomagnetic observatories, for different magnetic disturbance levels. Results show the ability of the model to pick up the gross features of the magnetic variations, improving its performance with increasing disturbance level and from low to high latitudes. During geomagnetically quiescent conditions a baseline noise of about 5 nT is evident in reconstructed ground magnetic field signatures, which we attribute to the baseline noise level in the AMPERE currents. For variations shorter than about 30 min the modeled signals are often significantly lower than observed by a factor up to 3 to 4, possibly reflecting localized ionization structures not captured in the TIEGCM conductance modules, or missing small‐scale and rapid temporal variations in auroral currents. While the observed horizontal field variations are reflected in the model, the vertical component is consistently underestimated, possibly indicating errors in the estimates for ground induction currents. Comparison with the standard version of the TIEGCM is also carried out, showing that time variations shorter than 6 h and down to the 10 min resolution of the AMPERE data (which do not appear in the standard version of TIEGCM) are now reflected in the AMPERE‐driven model.

Multi‐level functional responses for wildlife conservation: the case of threatened caribou in managed boreal forests

Summary1. The selection for particular habitat patches can vary as a function of local and regional levels of anthropogenic disturbance. Although such functional responses can better reveal habitat loss for species of precarious status faced with dwindling resources, they remain rarely used in conservation planning. We show that functional responses can occur at multiple levels, even as nested hierarchies, and that they can explain the plasticity in habitat selection observed in threatened forest‐dwelling caribou Rangifer tarandus caribou, within and among home‐ranges.2. Twenty‐seven caribou were followed with global positioning system collars between 2005 and 2010. Generalized linear mixed models served as the basis from which we built multi‐level functional responses characterizing how caribou alter their selection for closed‐canopy conifer forests, depending upon the availability of these forests and the amount of cutovers and roads.3. Caribou increased their selection for closed‐canopy conifer forests in areas of their home‐range that were comprised of a high proportion of recent cutovers during calving and summer and of high closed‐canopy conifer forests during winter. Also, caribou that were established in highly disturbed areas displayed an overall stronger selection for conifer forests. These individuals further adjusted their selection for conifer forests in areas of their home‐ranges that were largely comprised of recent cutovers. This concurrent response to local and global anthropogenic disturbances provides evidence of nested‐hierarchical functional responses.4. Synthesis and applications. Reliable characterization of disturbance effects on animals is necessary for conservation planning. Multi‐level functional responses can accurately describe animal distribution, and we provided a framework for modelling these responses. Our multi‐level functional responses indicate that fixing habitat requirements based on patterns of habitat selection for the average amount of disturbance can be misleading because it overlooks plasticity in the response of animals to habitat heterogeneity. For example, selection of closed‐canopy conifer forests by caribou generally became stronger with increasing disturbance levels. Anthropogenic disturbance thus could not only lead to the functional loss of residual habitat, but it can also increase the ‘relative value’ of residual patches. Our study provides a tool for more thorough assessments of spatial variation in the attractiveness of resource patches and, presumably, in the fitness benefits.

The intermediate disturbance hypothesis and plant invasions: Implications for species richness and management

The intermediate disturbance hypothesis (IDH) predicts a hump-shaped pattern between community diversity and disturbance, and is central to understanding patterns of species diversity. Here, we examine IDH in the context of alien plant invasions. IDH can offer insight into the role of disturbance in facilitating plant invasions and the effect of these invasions on floristic diversity. Early stages of succession are most susceptible to invasion because resources and colonisation opportunities are elevated after disturbance. This trend is accentuated by human-mediated dispersal, a bias towards early successional species in the alien species pool, the tendency for fast-growing species to profit most from enemy release, and increased disturbance levels in human-modified habitats. Human disturbance, coupled with plant introductions, extends the diversity–disturbance curve and shifts peak diversity towards higher disturbance levels. However, invasive aliens can reduce native diversity at the community scale, especially in mid succession where competitive interactions structure communities. Certain invasive plants may have higher impacts because they overcome some life history tradeoffs as a result of their association with humans or novel evolutionary histories, e.g. enemy release. This may directly or indirectly (e.g. through plastic reallocation of resources from defence into growth) enable invasive plants to colonise earlier or persist into later stages of succession. By modifying disturbance regimes, invaders that transform the environment may also interfere with succession and precipitate low diversity communities. Low introduction rates of late successional species may currently limit impacts of aliens under infrequent disturbance. IDH is a useful framework for understanding ecological communities. However, because of the novel evolutionary histories of alien species and the anthropogenic context in which they invade, disturbance levels that maximise total diversity in invaded communities can differ from those that maximise native diversity. Joint consideration of IDH and alien invasion patterns suggests a range of strategies can be used to manage diversity.

Mammals of the northern Philippines: tolerance for habitat disturbance and resistance to invasive species in an endemic insular fauna

AbstractAim Island faunas, particularly those with high levels of endemism, usually are considered especially susceptible to disruption from habitat disturbance and invasive alien species. We tested this general hypothesis by examining the distribution of small mammals along gradients of anthropogenic habitat disturbance in northern Luzon Island, an area with a very high level of mammalian endemism.Location Central Cordillera, northern Luzon Island, Philippines.Methods Using standard trapping techniques, we documented the occurrence and abundance of 16 endemic and two non‐native species along four disturbance gradients where habitat ranged from mature forest to deforested cropland. Using regression analysis and AICc for model selection, we assessed the influence of four predictor variables (geographic range, elevational range, body size and diet breadth) on the disturbance tolerance of species.Results Non‐native species dominated areas with the most severe disturbance and were rare or absent in mature forest. Native species richness declined with increasing disturbance level, but responses of individual species varied. Elevational range (a measure of habitat breadth) was the best predictor of response of native species to habitat disturbance. Geographic range, body size and diet breadth were weakly correlated.Main conclusions The endemic small mammal fauna of northern Luzon includes species adapted to varying levels of natural disturbance and appears to be resistant to disruption by resident alien species. In these respects, it resembles a diverse continental fauna rather than a depauperate insular fauna. We conclude that the long and complex history of Luzon as an ancient member of the Philippine island arc system has involved highly dynamic ecological conditions resulting in a biota adapted to changing conditions. We predict that similar responses will be seen in other taxonomic groups and in other ancient island arc systems.

Changes in the decapod fauna of an Arctic fjord during the last 100 years (1908–2007)

Whereas Arctic benthic decapods are not a species-rich group, they can dominate the local epifauna and play important roles in the ecosystem. We studied the decapod fauna from Isfjorden (Svalbard, Norway, 78°N) by sampling from 22 stations and comparing with 50 and 100-year-old data from the same localities. Our data provide no evidence of changes in the species composition of decapods during the last 50 years. Hence, we do not observe the poleward shift of species found in several pelagic communities in the North Atlantic. However, there is statistical evidence for changes in the community structure between 1908 and both 1958 and 2007. The main change is a shift towards communities more dominated by the spider crab Hyas araneus and the hermit crab Pagurus pubescens in 2007, and with a corresponding decrease in the two shrimp species Lebbeus polaris and Spirontocaris spinus. These shrimps are specialist predators compared to the more opportunistic, scavenging crabs. We argue that increased disturbance levels may be a causal factor behind the observed community change, with likely sources of disturbance including trawling and climatic fluctuations.

Sleep disturbance mediates the relationship between perceived racism and depressive symptoms.

To examine the effects of racism on sleep disturbance and depression and to examine whether sleep disturbance mediates the effects of racism on depression. Cross-sectional questionnaire study. Community. 168 Hispanic-American immigrants, 45% female, average age 33 years, average length of time living in the United States was 5 years. The Perceived Racism Scale for Latinos, the Pittsburgh Sleep Quality Index, and the Center for Epidemiologic Studies-Depression (CES-D) Scale. Using hierarchical linear regression analyses, perceived racism was related to increased sleep disturbance (b=.21, P<.01) and higher levels of depressive symptoms (b=.24, P<.01). When sleep disturbance was included in the regression equation, perceived racism was no longer a significant predictor of depressive symptoms (b=.10, nonsignificant), indicating that sleep disturbance mediated the relationship between perceived racism and depressive symptoms. This study adds to the research literature by identifying sleep disturbance as a potential pathway through which perceived racism may affect health.

Herbaceous plant strategies in disturbed habitats

A systematic theoretical evaluation has been made of three important plant life history traits: adult longevity, seed longevity and seed mass, where seed mass is interpreted as being indicative of dispersal distance and seedling vigour. This model study examined the role of these three traits in relation to environmental disturbance. We chose temperate grasslands, widespread in north Western Europe and northern and eastern America, as our reference system for our simulations. Eight plant strategies were defined by allowing two levels in each of the three and combining them in all eight possible ways. A simple, spatially explicit model was developed to simulate competition among individuals with these eight trait combinations at different levels of disturbance. Simulation results were compared with the actual occurrence over a disturbance gradient of species with similar plant trait combinations in a large database from the Sheffield area (UK). This showed that with increasing disturbance level, non‐dormant perennials, dormant perennials, non‐dormant annuals and dormant annuals, respectively, became dominant but only if small‐seeded, indicating the relative viability of these particular strategies with respect to disturbance. A new prediction from the model was that stable coexistence occurs between plant strategies with dormant and with non‐dormant seeds over a range of levels of disturbance. Plant strategies with large seeds were inferior to small‐seeded ones if competitive ability of seedlings is proportional to seed weight. This difference was highest at low seed densities and low germination probabilities, indicating that large‐seeded species secure no advantage from being dormant (i.e. having a low germination probability). Finally, the results indicated that dormancy is superior to dispersal as a method of coping with disturbance.

Experimental evidence for effects of human disturbance on foraging and parental care in oystercatchers

We carried out two experiments to quantify effects of human disturbance on foraging and parental care in European oystercatchers ( Haematopus ostralegus). In experiment 1, pairs incubating a clutch were disturbed on their feeding territory on the mudflat. Disturbance significantly reduced the proportion of time that the clutch was incubated, but also the proportion of time that the pair spent on the mud flat. In experiment 2, foraging oystercatcher pairs with chicks were disturbed by two observers at different distances from the edge of the salt marsh where the chicks resided. Total food collected was independent of disturbance, but a smaller proportion of the food collected was allocated to the chicks with increasing disturbance level. Both experiments demonstrate that human disturbance of foraging in breeding oystercatchers reduced the amount of parental care, and thus presumably reproductive success.

Local and Regional Effects of Pedestrians on Forest Birds in a Fragmented Landscape

Abstract I assessed the effects of pedestrians on the distribution of forest bird species in wooded parks in the city of Madrid within and between fragments. Within fragments, increasing levels of pedestrians reduced species richness and overall abundance of individuals within circular plots. The abundance of foraging individuals of four species (Magpies Pica pica, Blackbirds Turdus merula, Starlings Sturnus unicolor, and Woodpigeon Columba palumbus) diminished when pedestrians walked near sampling plots, as well as their breeding densities in relation to increasing disturbance levels. Between fragments, after controlling for fragment size effects, pedestrian rate was negatively related to species richness in two breeding seasons. Species turnover was positively associated to mean pedestrian rate and inter-annual variability in pedestrian rate. At the species level, pedestrian rate negatively affected the probabilities of fragment occupation of 16 species beyond the effects of fragment size and isolation. Locally, the short-term behavioral responses to visitors may reduce the suitability of highly disturbed parks in such a way as to decrease breeding densities and the probabilities of fragment occupation and persistence. The effects of human disturbance in fragmented landscapes should be incorporated into management decisions as another relevant factor that may reduce habitat quality.