Roost availability may constrain shorebird distribution: Exploring the energetic costs of roosting and disturbance around a tropical bay

High tides force shorebirds from their intertidal feeding areas to refuges known as roosts. This paper explores the energetic costs of roost disturbance of great knot (Calidris tenuirostris) and red knot (C. canutus) at Roebuck Bay, North-western Australia, assessing disturbance levels at different roost sites through direct observation and automatic radio-telemetry, and applying physiological equations and predictive roost choice models to estimate energetic costs of disturbance through a complete tidal cycle. The study area had a variety of roosts, but use of each was constrained by conditions of tide and time. The roost most suitable for shorebirds on daytime high tides of intermediate height experienced high levels of disturbance from both natural sources (birds of prey) and humans. Flight costs caused by disturbance at this site exceeded the costs of flying to and roosting at the nearest alternative roost, 25 km away. However, shorebirds did not roost at the alternate site, possibly because of the risk of heat stress in a prolonged flight in tropical conditions. Increases in disturbance levels at just one of the roost sites of Roebuck Bay would increase energetic costs substantially, and could easily reach the point at which feeding areas accessed from this roost cannot be used without incurring a net energy deficit. Roost availability can therefore limit access to feeding areas and hence limit population size. Adequate provision and management of roost sites is accordingly an important consideration in conservation of sites used by coastal shorebirds.     

Impact of West Nile virus and other mortality factors on American white pelicans at breeding colonies in the northern plains of North America

American white pelicans (Pelecanus erythrorhynchos) are colonial-nesting birds and their breeding sites are concentrated in a few small areas, making this species especially vulnerable to factors that can influence productivity, such as disease, disturbance, predation, weather events and loss of nesting habitat. Nearly half of the American white pelican population breeds at four colonies in the northern plains: Chase Lake National Wildlife Refuge (NWR) in North Dakota, Bitter Lake (Waubay NWR) in South Dakota, Medicine Lake NWR in Montana, and Marsh Lake in Minnesota. Thus, sustained productivity at these colonies is crucial to the health of the entire species. During the latter half of the 2002 and 2003 breeding seasons, unusually high mortality of pelican chicks was observed at these colonies. West Nile virus (WNv) was identified as one source of these losses. In 2004–2007 we monitored three major colonies in the northern plains to assess mortality of chicks during the late breeding season. We documented severe weather events, disturbance, and WNv as factors contributing to chick mortality. Before WNv arrived in the region in 2002, chick mortality after mid-July was 4%, and then jumped to as high as 44% in the years since WNv arrived. WNv kills older chicks that are no longer vulnerable to other common mortality factors (e.g., severe weather, gull predation) and typically would have survived to fledge; thus WNv appears to be an additive mortality factor. Persistence of lower productivity at American white pelican colonies in the northern plains might reduce the adult breeding population of this species in the region.     

Spatial variation in anthropic and natural factors regulating the breeding success of the cinereous vulture (Aegypius monachus) in the SW Iberian Peninsula

The management of the cinereous vulture (Aegypius monachus) populations, the largest bird of the Western Palæarctic and considered an umbrella species, requires the understanding of the factors limiting the breeding success. As part of a management program, we studied such factors in seven breeding colonies in Extremadura (SW Iberian Peninsula). Using a Geographic Information System and multivariate models, we analyzed the relationship of breeding success with anthropic and natural factors at the nest site and in the foraging area of the adults. We incorporated into the models density-dependent effects between pairs and the spatial autocorrelation of the environmental variables. The differences in breeding success resulted from spatial variations in natural and anthropic conditions, with present human disturbance to nests and future alteration of climate having an expected negative effect at all the sites. Management measures must set calendar restrictions for the immediate environment of the nests, mainly with respect to forestry and hunting activities. A second key element is the protection of the habitats at the nest sites and in their surrounding area, with the aim of there being both wooded areas available for the location of the nest and open environments for the availability of food. The Special Protection Areas showed a partial effectiveness of conservation measures for the species, and the need for future improvement. Lastly, in a scenario of global warming, management policies with respect to nesting habitats will have to be extended to higher altitude zones, actions that should be guided by the study of the selection of potential nesting habitat.     

包头市达茂旗居民点空间分布变化及其影响因素分析

深刻把握居民点空间分布和变化规律及其与影响因素的关系,对居民点整治、优化布局及实施乡村振兴战略规划具有重要意义。以包头市达茂旗为例,综合土地利用、地名志、旗志等历史数据资料,采用核密度分析、重心迁移等空间分析方法,探索揭示居民点空间分布特征及演变规律,选取DEM、坡度、坡向、距水域距离及距道路距离、距城镇距离、民族文化、人口数量、政府政策因子,分析居民点空间分布与自然环境、社会经济影响因素的内在关系。研究表明:1)2012年达茂旗居民点分布集聚特征明显,达到集聚峰值1.416个/km2。1996-2016年间达茂旗居民点分布重心向东南部迁移,逐渐靠近百灵庙镇。2)在DEM和坡度对居民点分布的影响上呈倒"U"型特征,即先增加到峰值后逐渐减少,DEM的峰值为1 400～1 600m,坡度峰值为3.056°～5.446°。在坡向选择上逐渐倾向于南坡等阳坡,且比重逐年增大,但仍有部分居民点分布在阴坡。达茂旗居民点空间分布在距水域距离上并未呈现出明显的近水性,而在距水域7～10km区间分布数量最多。3)道路距离上呈现出明显的近道路取向,2016年居民点分布在距道路距离为0～1 000 m内的个数占98.77%,表明道路与居民点之间具有相互影响、相互作用的关系。中心城镇对居民点的辐射影响仅局限一定范围内,居民点空间分布远离中心城镇。达茂旗农区和牧区的居民点个数与其人口数量相关性呈现不同特征,1996年、2016年牧区蒙古族人口数量与居民点个数呈显著正相关。蒙古族游牧文化促使居民点分布呈"满天星"的高度分散特征,政府政策对达茂旗居民点空间分布及格局具有重要影响。     

Productivity affects the density–body mass relationship of soil fauna communities

The productivity of ecosystems and their disturbance regime affect the structure of animal communities. However, it is not clear which trophic levels benefit the most from higher productivity or are the most impacted by disturbance. The density–body mass (DBM) relationship has been shown to reflect changes in the structure of communities subjected to environmental modifications, so far, mainly in aquatic systems. We tested how different seawater inundation frequencies and cattle grazing, which both disturbed and impacted the productivity of a terrestrial system, a salt marsh, affected the size structure of soil fauna communities, expressed by their DBM relationship. We hypothesized that either: (1) all the trophic levels of soil fauna would benefit from higher productivity (i.e., amount of litter mass), reflected by a higher Y-intercept of the DBM relationship; (2) only smaller animals would benefit, reflected by a lower slope of the relationship; (3) or only larger animals would benefit, reflected by a higher slope of the relationship. We collected a large range of soil fauna from different elevation levels in grazed and ungrazed areas, thence subjected to different levels of productivity, represented by litter mass, with the most inundated and grazed area as the least productive one. Considering that pore size must be smaller in inundated and grazed areas, productivity seemed to be a greater factor influencing species distribution than soil structure. We found slopes lower than −0.75, showing that large animals dominated the community. However, a difference between the DBM relationships of the most and least frequently inundated ungrazed sites indicated that higher productivity benefited the smaller animals. Our findings show that high productivity does not equally affect the different trophic levels of this soil fauna community, suggesting inefficient transfers of energy from one trophic level to another, as smaller species benefitted more from higher productivity.     

Influence of disturbance and nitrogen addition on plant and soil animal diversity in grassland

Two key determinants of biological diversity that have been examined in aboveground and aquatic systems are productivity, or resource supply, and physical disturbance. In this study, we examined how these factors interact under field conditions to determine belowground diversity using microarthropods (mites and Collembola) as our test community. To do this, we established a field manipulation experiment consisting of crossed, continuous gradients of nitrogenous (N) fertilizer addition (up to 240 kg N ha^?1) and disturbance (imitated trampling by cattle) to produce a gradient of soil nutrient availability and disturbance. Due to the relatively short-term nature of our study (i.e. 2 years), we only detected minimal changes in plant diversity due to the experimental manipulations; in the longer term we would expect to detect changes in plant diversity that could potentially impact on soil fauna. However, disturbance reduced, and additions of N increased, aboveground biomass, reflecting the potential effects of these manipulations on resource availability for soil fauna. We found that disturbance strongly reduced the abundance, diversity, and species richness of oribatid mites and Collembola, but had little effect on predatory mites (Mesostigmata). In contrast, N addition, and therefore resource availability, had little effect on microarthropod community structure, but did increase mesostigmatan mite richness and collembolan abundance at high levels of disturbance. Oribatid community structure was mostly influenced by disturbance, whereas collembolan and mesostigmatan diversity were responsive to N addition, suggesting bottom-up control. That maximal species richness of microarthropod groups overall occurred in undisturbed plots, suggests that the microarthropod community was negatively affected by disturbance. We found no change in microarthropod species richness with high N additions, where plant productivity was greatest, indicating that soil biotic communities are unlikely to be strongly regulated by competition. We conclude that the diversity of soil animals is best explained as a combination of their many varied life history tactics, phenology and the heterogeneity of soils that enable so many species to co-exist.     

Habitat selection of endangered and endemic large flying-foxes in Subic Bay, Philippines

Large flying-foxes in insular Southeast Asia are the most threatened of the Old World fruit bats due to high levels of deforestation and hunting and effectively little local conservation commitment. The forest at Subic Bay, Philippines, supports a rare, large colony of vulnerable Philippine giant fruit bats (Pteropus vampyrus lanensis) and endangered and endemic golden-crowned flying-foxes (Acerodon jubatus). These large flying-foxes are optimal for conservation focus, because in addition to being keystone, flagship, and umbrella species, the bats are important to Subic Bay’s economy and its indigenous cultures. Habitat selection information streamlines management’s efforts to protect and conserve these popular but threatened animals. We used radio telemetry to describe the bats’ nighttime use of habitat on two ecological scales: vegetation and microhabitat. The fruit bats used the entire 14,000 ha study area, including all of Subic Bay Watershed Reserve, as well as neighboring forests just outside the protected area boundaries. Their recorded foraging locations ranged between 0.4 and 12 km from the roost. We compared the bats’ use to the availability of vegetative habitat types, riparian areas, and bat trees. The fruit bats’ locations showed a preference for undisturbed forest types and selection against disturbed and agricultural areas. Bat locations also showed selection for particular fruiting/flowering bat trees. The bats showed strong preference for riparian areas; locations were in riparian areas over four times more than expected. From these results we recommend that management focus flying-fox conservation efforts on undisturbed forest and riparian areas.     

松嫩平原粮食主产区农村居民点格局及影响因素分析

揭示粮食主产区农村居民点格局及其影响因素,对城镇化背景下农村居民点整理有重要意义。该文综合运用GIS空间统计、核密度分析、全局聚类检验及空间热点探测法,从农村居民点规模、密度以及集聚特征分析农村居民点格局,并探索地形地貌、农业生产力水平及区位条件对农村居民点格局的影响。结果表明：1）微型、小型及中型居民点数量繁多,其公共基础设施不配套,破坏耕地完整性,已不适应农业生产力的发展及内部居民生活;2）农村居民点核密度最高值为1.58个/km2,整体分布密度相对较低,规模呈现全局低值集聚特征,符合粮食主产区特点。克山镇、双河镇北部、古北乡北部、向华乡东北部、北兴镇中部以及河南乡中部农村居民点呈小规模集聚,西联镇、西河镇、发展乡、克山农场、西建乡部分区域以及古城镇、向华乡、北联镇的零星区域的农村居民点呈大规模集聚;3）地形地貌是农村居民点初始区位形成的基础,但随着社会经济的转型,农业生产力水平的提高对粮食主产区农村居民点格局调整有较大的推动作用。区位因素中城镇辐射对居民点格局影响仅限于一定范围,交通道路显著改变居民点局部空间格局,具有明显的距离衰减效应。该研究可为松嫩平原粮食主产区农村居民点布局优化与调控提供参考。     

Patterns of protection and threats along productivity gradients in Canada

Productivity is an important driver of broad-scale diversity gradients and community composition. Surprisingly, it is rarely used as a biodiversity proxy in protected area network assessments. In this research, we evaluate if biases exist in the locations of Canada’s protected areas with respect to productivity and assess the distribution of anthropogenic threats to protection along productivity and topographic axes. Productivity was expressed as the annual minimum and integrated fraction of absorbed photosynthetically active radiation (fPAR) and related seasonality (defined as variation in fPAR over a year), as acquired by remote sensing. Results indicate that, overall, protected areas are slightly biased to lower productivities (higher seasonalities), but are relatively unbiased along elevation. Sites at high elevations, high seasonalities, or low productivities are extremely well represented, but they account for a very small proportion of Canada’s area overall and under protection. However, the productivity characteristics of protected areas are heterogeneous across reserve characteristics and space; biases are greater and more variable when considering individual International Union for Conservation of Nature (IUCN) categories, protected area size classes, or ecozones.The spatial and environmental correlates of anthropogenic pressures (proximity of roads and settlements in the greater park ecosystem) to protected areas in the forested ecozones were evaluated with partial linear regression models. Threats were strongly spatially structured. Reserve characteristics (productivity, elevation, size, IUCN category) shared about half of this spatial structure, explaining ∼25% of the variation in threat distributions. Small and productive protected areas tended to occur closer to human populations and roads, respectively, and are thus expected to face greater threats to biodiversity. High-elevation protected areas generally occurred farther from both roads and settlements.Systematic patterns between productivity, reserve size and management goals, and anthropogenic disturbances suggest that the most productive, biodiverse areas may not yet be sufficiently protected. These analyses highlight considerations for the management of existing parks and the expansion of Canada’s protected area network.     

The influence of disturbance and habitat on the presence of non-native plant species along transport corridors

The impact from transportation corridors on surrounding habitat often reaches far beyond the edge of the corridor. The altered disturbance regime in plant communities along corridor edges and vehicle traffic facilitate the spread and establishment of invasive non-native plant species. We compared the frequency of non-native plant species along highways and railways and the ability of these species to invade grasslands and dense forests along these corridors. We measured the frequency of several non-native plant species along transects 0-150 m from the edge of highways and railways in grasslands and forests, as well as at control sites away from corridors. Both transportation corridors had higher frequency of non-native species than respective control sites. Grasslands had higher frequency of non-native species than forested habitats, but the frequency did not differ between the highways and the railways. The frequency of non-native species in grasslands along highways and railways was higher than at grassland control sites up to 150 m from the corridor edge, whereas the frequency in forested habitats along corridors was higher than at forested control sites up to only 10 m from the corridor edge. There was a significant decrease in the frequency of non-native species with increasing distance from both corridors in the forest, while grasslands showed no significant change in non-native species frequency with distance from corridors. This suggests that corridor edges and grassland habitats act as microhabitats for non-native species and are more prone to invasion than forests, especially if disturbed. Our results emphasize the importance of minimizing the disturbance of adjacent plant communities along highways and railways during construction and maintenance, particularly in grassland habitats and in areas sensitive to additional fragmentation and habitat loss.     

Does whale watching in Southern New England impact humpback whale (Megaptera novaeangliae) calf production or calf survival?

There is growing concern about the effects of wildlife tourism on biologically important parameters in target species and/or populations. We tested whether whale watch vessel exposure affected either the calving rates or calf survival to age 2 in humpback whales (Megaptera novaeangliae) on their feeding grounds off of southern New England, where individually identified whales have been studied intensively for decades and whale watch pressure is intense. Whale watch exposure did not correlate with either the calving rate (# of calves/# of years sighted) or calf production and survival of individual females, although a breakpoint analysis showed a slight negative trend up to 1649 min (or 20 boat interactions). In some comparisons, whales with more exposure were significantly more likely to produce calves and to have those calves survive. Logistic regressions including exposure and prey variables also failed to show negative effects of exposure in predicting calf productivity or survival. A limited comparison of calves seen only in an alternate habitat without whale watching showed similar return rates to those in the exposed area. Our data include limited suggestions that some animals (i.e., females alive when whale watching started) might be more susceptible to impacts than others. However, we found no direct evidence for negative effects of whale watch exposure, and suggest that short-term disturbance may not necessarily be indicative of more meaningful detrimental effects on either individuals or populations.     

Ungulate flight responses to human disturbance: A review and meta-analysis

As human recreation in natural areas increases, so does the potential for disturbance to wildlife, and many factors (environmental, disturbance type, experience with humans) influence the impact of disturbance. However, there exists no comprehensive examination of the effects of human disturbance on ungulate escape responses. I conducted a comprehensive review of studies measuring Artiodactyl escape responses (e.g., flight initiation distance, distance moved) to experimental harassment by humans and vehicles, and meta-analyses aimed at predictive questions about the impact of human disturbance on ungulate behavior under an optimization framework. I found evidence across studies that ungulates pay attention to approacher behavior, have greater perceptions of risk when disturbed in open habitats, and females or groups with young offspring show greater flight responses than adult groups. Increased group size and the presence of hunting showed weak but positive heterogeneous effects on flight behavior both between and within species. Humans on foot were more evocative than other stimuli (vehicles, noises). Populations in areas with higher levels of human traffic showed reduced wariness but a lack of alternative sites to move to may explain some of this effect. Hunted populations showed significantly greater flight responses than non-hunted populations. Finally, I suggest five factors to consider when forming predictive models of ungulate flight behavior: (1) how seasonal variation in reproductive status and body condition effects wariness, (2) the relative impacts of lethal and non-lethal human contact, and (3) unique natural history traits that may cause differences in flight behavior between populations, (4) the availability of alternative sites, and (5) shorter distances between feeding sites and refugia can reduce the impact of other factors on flight responses.     

High levels of spatial heterogeneity in the biodiversity of soil prokaryotes on Signy Island, Antarctica

In a previous study, soil bacterial diversity at environmentally distinct locations on Signy Island was examined using denaturing gradient gel electrophoresis (DGGE) profiling, and a range of chemical variables in soils was determined in order to describe variations between them. The dominant bacterial communities of all locations were found to be significantly different, although higher levels of similarity were observed between locations with similar physico-chemical characteristics, such as at penguin rookeries, seal wallows and vegetated soils. Extending this study, here soil prokaryote biodiversity was compared between 15 distinct locations in order to elucidate any interaction between four general habitat types on Signy Island (South Orkney Islands, maritime Antarctic) and any influence of previous human impacts at these sites. Specific sites were selected to represent the range of different soil environments present and to cover a range of environmental factors present in the maritime Antarctic which are known to influence bacterial community composition in soils elsewhere. A diverse prokaryote community is described, again with the majority of excised and sequenced bands belonging to the Bacteroidetes. Although DGGE profiling identified significant differences in prokaryotic biodiversity between all sampling sites, aggregations of banding patterns were also apparent across the different soil environments examined. Correlations between specific DGGE profiles and 10 selected soil parameters suggested that much of this variation could be explained by differences in the levels of environmental disturbance and soil pH. In particular, a greater proportion of variation in soil bacterial diversity was explained by differences in soil properties at human-disturbed locations than at undisturbed locations, with higher explanatory values by edaphic factors in the former and soil metal content in the later. In general, our data indicate that small-scale variation is an important factor in understanding patterns of prokaryotic distributions in soil habitats in the maritime Antarctic environment.     

A test of the hierarchical model of habitat selection using eastern massasauga rattlesnakes (Sistrurus c. catenatus)

Understanding the process animals follow to select habitat, rather than just documenting the habitat they use, will improve our ability to predict how the animals use habitat in other locations and how they will respond to changes in habitat. Animals are usually assumed to select habitats hierarchically, preferentially using specific macrohabitats at a landscape scale and specific microhabitats within the preferred macrohabitats. We used four years of telemetry data from 34 individuals to test this hierarchical model of habitat selection with eastern massasauga rattlesnakes (Sistrurus c. catenatus) in Ontario. Snakes were selective at the microhabitat scale, preferentially using locations with closer retreat sites and shrubs than random. Gravid females were most selective, using sites with more rock cover and less canopy closure than sites used by males and nongravid females. Snakes preferred forested habitats for hibernation and steadily increased their use of open, wetland, and edge habitats to a peak in mid-summer. Landscape-scale habitat preferences were generally mild and could be explained by the relative availability of suitable microhabitat within habitats, suggesting habitat selection was primarily driven by microhabitat preferences. The lack of selectivity at the landscape scale may be a consequence of fine-grained differences between habitats that allow massasauga rattlesnakes to find suitable microhabitats in all available macrohabitats. For species that select habitat primarily at the microhabitat scale (e.g., the rattlesnakes we studied), landscape-scale modeling of habitat use will only be effective to the extent habitats reflect the availability of suitable microhabitat within.     

Habitat selection models for European wildcat conservation

Populations of the European wildcat (Felis silvestris) are only slowly recovering in Central Europe after a severe decline in the last centuries and require specific conservation plans in many areas. However, detailed information on wildcat occurrence and habitat requirements is still scarce and controversial. We present a fine-scale habitat selection model for wildcats based on detailed species and land use information and evaluate its accuracy to predict habitat distribution in new areas. We analysed habitat use within home ranges using single locations of 12 radio-tracked individuals from south western Germany. Several competing models were fitted and compared using generalised linear mixed models (GLMM) and information-theoretic approaches. Radio-tracking data of 9 and 10 wildcats from two distant areas were used to evaluate the models. The selected model predicted habitat associated to close distance to forest, watercourses and meadows and a critical distance to villages, single houses and roads. To predict area suitable for home ranges we superimposed rules derived from home range attributes at a higher level of selection. Predictions from the combination of the fine-scale habitat model and home range rules matched well with more than 2000 wildcat observations of south-western Germany. We discuss the application of the model in wildcat conservation for finding potential reintroduction sites, identifying small isolated populations and aiding in the evaluation of the needs of mitigation and compensation within the scope of the European Habitats Directive.     

Comparison of breeding bird and vegetation communities in primary and secondary forests of Great Smoky Mountains National Park

We compared breeding bird communities and vegetation characteristics at paired point locations in primary (undisturbed) and mature secondary forest (70-100 years old) sites in Great Smoky Mountains National Park, USA to understand how sites logged prior to creation of the park compare to undisturbed sites following 70 years of protection from human disturbance. We found that bird and vegetation communities are currently similar, but retain some differences in species composition. Rank abundance curves for primary and secondary forest bird communities showed very similar patterns of species dominance. Species composition was also similar on the two sites which shared 24 of the 25 most frequently recorded species. Nonetheless, comparisons of density estimates derived from distance sampling showed three bird species were more abundant on primary forest sites and that one bird species was significantly more abundant on secondary forest sites. Notably, comparisons based on raw counts (unadjusted for potential differences in detectability) produced somewhat different results. Analyses of vegetation samples for the paired sites also showed relative similarity, but with some differences between primary and secondary forests. Primary forest sites had more large trees (trees greater than 50 cm diameter at breast height) and late successional species. Primary forest sites had a denser tall shrub layer while secondary forest sites had a denser canopy layer. Nonetheless, tree species richness, basal area of live trees and number of standing snags did not differ between primary and secondary forest sites. Results indicate that breeding bird communities on sites within the park that were logged commercially 70 years ago are currently quite similar to bird communities on sites with no history of human disturbance. Similarities between the bird communities on previously disturbed and undisturbed sites in Great Smoky Mountains National Park may exceed those on more fragmented landscapes because large patches of primary forest, adjacent to commercially logged sites, remained in the park when it was established in 1935. These patches of primary forest may have served as source areas for commercially logged sites.     

Dampened behavioral and physiological responses mediate birds’ association with humans

The study of the mechanisms involved in phenotypic adaptations or plasticity to environmental stressors may serve to evaluate contemporary ecological and evolutionary dynamics in threatened or growing wildlife populations. By addressing human disturbance as a main stressor agent, we investigated antipredator response (flushing distance), social behavior (degree of gregarism), health (fecal pathogens), and endocrine status (fecal corticosterone levels) as potential mechanisms that permit birds to cope with anthropogenic impact in tourist areas. Our study models were species that are neither urbanized nor invasive, and that are typical of the high mountains of the Palearctic: the Alpine and the Red-billed chough (Pyrrhocorax graculus and P. pyrrhocorax), and the surrounding alpine bird community. Both chough species showed habituation, reduced flushing distances, fewer parasites and lower corticosterone levels in tourist than in non-tourist sites, and a significant variation in gregarious behavior. Behavioral and physiological adjustments permitted these corvids to optimize resource exploitation depending on habitat quality and in conditions of continuous disturbance. Human-induced changes in chough social behavior had no effect on local avian species richness, a surrogate measure for community diversity. Irrespectively of chough aggregations, bird diversity decreased significantly in recreational areas, thus not all community members tolerated human impact as choughs did. Our findings suggest that species that manage to coexist with humans primarily adjust traits that influence ecological interactions (social, foraging or antipredatory responses) and that vary rapidly (learned behaviors and physiological mechanisms that promote homeostasis).     

The distribution of disturbance-dependent rare plants in a coastal Massachusetts sandplain: Implications for conservation and management

Rare plants in coastal New England sandplains are often restricted to anthropogenically disturbed sites including plowed and mowed firelanes at the Manuel F. Correllus State Forest on Martha’s Vineyard. Little is known about pre-colonial rare plant habitat or how modern management impacts these species. To understand the factors influencing rare plant distribution, we examined the influence of vegetation structure, species composition, environmental characteristics and disturbance history on rare plant populations and potential natural habitat in the 2100-ha Forest. We sampled >100, 100 m² plots - in firelanes and forested/shrubland areas - and conducted extensive searches for rare plants.Linum intercursum and Scleria pauciflora var. caroliniana were frequent in firelanes including in recently plowed areas, whereas Nabalus serpentarius, Sisyrinchium fuscatum, and Aristida purpurascens generally occurred in isolated, locally-abundant patches in firelanes not plowed for many decades. The former group may be characterized by an ability to rapidly establish following disturbances while the latter may take longer to establish and develop large populations. In some respects, rare plants were associated with environmental conditions reflecting the disturbance histories of sites they occupied (e.g., L. intercursum with lower duff depth and N. serpentarius with greater litter cover/depth).In forests and shrublands undisturbed for decades, rare plants only occurred on well-worn paths. Although scrub oak stands supported conditions more similar to those found in firelanes than other native vegetation types, disturbances - far more severe than those in forests/shrublands of the past century - are probably required to create suitable rare plant habitat in sandplain forests and shrublands.     

Negative and positive effects of topsoil biological crusts on water availability along a rainfall gradient in a sandy arid area

Drylands are regarded as highly sensitive to climatic changes. A positive relationship between rainfall and environmental factors (water availability for plants, productivity, species diversity, etc.) is often assumed for areas with an annual rainfall of 100–300 mm. This assumption disregards the fact that a climatic change in arid and semi-arid areas is not limited to climatic factors. This change is often accompanied by a parallel change in surface properties. The alteration of surface properties may have opposite effects on the water regime and ecosystem characteristics. Data on rainfall, runoff, soil moisture regime, and vegetation cover were collected at five monitoring sites in a sandy area along the Israeli–Egyptian border, where average annual rainfall varies from 86 to 160 mm. Data obtained show a decrease in water availability for perennial plants with increasing annual rainfall, clearly expressed by a lower survival of perennial plants in the wetter area. Results obtained cast doubt of the prevailing idea regarding the positive relationship between average annual rainfall and ecosystem characteristics. The findings are attributed to the decisive role played by the non-uniform properties of the topsoil biological crusts along the rainfall gradient considered. Under wetter conditions a thick topsoil biological crust develops. This crust is able to absorb large rain amounts, limiting thus the depth of rainwater infiltration and water availability for the perennial vegetation. A better water regime was found in the drier area, where a thin crust allows deeper water infiltration and water concentration by surface runoff. The process described may be regarded as a desertification process with increasing annual rainfall.     

Colony site selection and abandonment by least terns Sterna antillarum in New Jersey,USA

To develop habitat and management procedures to protect declining populations of least terns, colony site selection and abandonment by this species was investigated at 26 sites in New Jersey. Multivariate analysis was used to compare (1) colony sites to adjacent unused areas, (2) those located on beaches to dredge spoil sites and (3) abandoned to occupied colony sites.The presence of shells or pebbles in a sandy substrate, and short, sparse vegetation, were the habitat characteristics of New Jersey least tern colony sites most strongly correlated with colony site selection. Dredge spoil sites had significantly greater evidence of human disturbance, distance to water, and proportion of coarse particles in the substrate than beach sites. These differences may have contributed to the smaller colonines and greater colony turnover rates at spoil sites relative to beach sites. Overall, abandoned colony site characteristics did not differ significantly from occupied sites. However, human disturbance, over-growth of vegetation, predation, and flooding were all prevalent at colonies prior to abandonment. The results of this study suggest techniques for habitat management of both least and little terns.