古田山常绿阔叶林物种生境关联及其对物种共存的贡献

物种共存机制一直是群落生态学研究的核心内容。解释物种共存的假说很多，近年来最引人注目的是生态位分化假说和群落中性理论。这两种理论对群落内物种共存的相对重要性是目前群落生态学研究的热点。国际上这方面的研究基本集中在热带森林大样地内，而针对亚热带森林大样地的相关研究却非常少见。本文以浙江古田山24公顷常绿阔叶林永久固定监测样地第一次调查数据为基础，研究样地内木本植物与生境关联和与地形因子梯度相关，目的在于探讨物种生境生态位分化在亚热带常绿阔叶林内物种多样性维持中的作用，也为了解决当前物种生境关联相关研究中的一些不足之处。 本研究首先采用Torus转换检验分析古田山样地内90种常见木本植物与5类生境关联，结果表明有75种（83.3%）至少与一类生境类型显著相关，说明大部分亚热带森林群落内物种具有生境特化的特性。与CTFS全球大样地类似研究结果相比，古田山样地内生境特化的物种比例更高，这与古田山样地复杂的地形条件密切相关。通过本研究，证明地形条件越复杂，物种特化比例越高的趋势确实存在。在古田山样地，虽然83.3%的物种有生境特化的特性，但生境特化没有排他性，即并不完全排斥其他生境，在非最适生境也能稳定与其他物种共存。根据本研究与生境负相关的平均物种数与被检测的物种比例估算，古田山样地内生境异质性对物种多样性维持的贡献率约为19.6%，说明物种生境特化对于物种共存有一定的作用，但贡献并不大，除了生境异质性，仍有其他因素决定物种共存。 目前有关物种生境关联的研究都假设同一物种的个体对于生境偏好一致，不管胸径大小是否相同，很少有人研究不同生长阶段生境偏好的变化。本研究利用Torus转换检验比较样地内60种常见木本植物在3个生活史阶段（幼苗阶段、小树阶段和成熟阶段）与5类生境关联的变化，结果表明大部分物种在其幼苗和小树阶段的生境偏好比较一致，但成熟阶段与前两个阶段差别比较大，说明物种在生活史不同阶段的生境偏好可能发生改变。 由于生境划分没有统一的标准，不同学者用不同的方法划分生境类型和数量，主观性很大，造成不同研究地点、不同研究者之间的研究结果可比性差。本研究尝试利用直接梯度分析方法重新分析物种空间分布与地形梯度相关，用以代替生境关联分析。利用CCA分析检验样地内90种常见木本植物与4种地形因子梯度（海拔、凹凸度、坡度和坡向）的相关情况，发现有76个（84%）物种的空间分布与地形梯度相关，说明大部分物种具有沿地形因子梯度分布的特性。4种地形因子梯度变化对90个物种空间分布的解释量约为20%，说明地形异质性对于物种共存有一定作用，但贡献并不大。对生境关联分析和直接梯度法分析结果进行比较，两种方法分析结果一致，得到的结论也一致。直接梯度分析方法可以避免生境划分对研究结果的影响，是今后类似研究中值得采纳的方法。 本研究的结果表明地形异质性引起的生态位分化在古田山样地群落内物种多样性维持中起一定的作用，但贡献不大，因此需要更深入地研究其他环境因素引起的生态位分化在物种多样性维持中的作用，同时也需要进一步研究中性过程在物种多样性维持中的作用，以更全面地探讨生态位分化假说和中性理论在亚热带常绿阔叶林内物种共存的相对重要性。

Rarity and decline in bumblebees - A test of causes and correlates in the Irish fauna

Bees are believed to be in decline across many of the world's ecosystems. Recent studies on British bumblebees proposed alternative theories to explain declines. One study suggested that greater dietary specialization among the rarer bumblebee species makes them more susceptible to decline. A second study disputed this theory and found that declines in British bumblebees were correlated with the size of species' European ranges, leading to the suggestion that climate and habitat specialization may be better indicators of the risk of decline. Here we use a new and independent dataset based on Irish bumblebees to test the generality of these theories. We found that most of the same bumblebee species are declining across the British Isles, but that, within Ireland, a simple food-plant specialization model is inadequate to explain these declines. Furthermore, we found no evidence of a relationship between declines in Irish bumblebees and the size of species' European ranges. However, we demonstrate that the late emerging species have declined in Ireland (and in Britain), and that these species show a statistically significant westward shift to the extremity of their range, probably as a result of changing land use. Irish data support the finding that rare and declining bumblebees are later nesting species, associated with open grassy habitats. We suggest that the widespread replacement of hay with silage in the agricultural landscape, which results in earlier and more frequent mowing and a reduction in late summer wildflowers, has played a major role in bumblebee declines. (C) 2006 Elsevier Ltd. All rights reserved.

First assessment of the endoparasitic nematode fauna of four psammophilous species of Tropiduridae (Squamata: Iguania) endemic to north-eastern Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Microhabitat and plant structure of Characeae (Chlorophyta) populations in streams from São Paulo State, southeastern Brazil

Microhabitat distribution was investigated in five populations of Characeae (two of Chara guairensis, two of Nitella subglomerata and one of Nitella sp.) to determine the distributional patterns, the morphometric and reproductive adaptations to varying environmental conditions and niche width on a scale of few centimeters. Variations in physical variables revealed some general trends of microhabitat distribution for the Characeae populations studied, with occurrence under the following conditions: slow and narrow current velocities; substrata predominantly composed of small particle size (sand-clay); variable and generally low depths. In terms of morphological adaptations, we found some general patterns: plants with longer whorl branchlets also had longer internodes in all populations studied, whereas longer plants had also thicker axis. The former were generally associated with higher biomass (percent cover). Few correlations of morphological characters were observed with environmental variables (e.g. plant length with irradiance: negative in two populations and positive in one population). Despite the general patterns of occurrence mentioned above, our results also indicated that each population differed in its responses to environmental variables and had particular morphological and reproductive adaptations. The Characean populations occurred under a narrower range of microhabitat conditions than other macroalgae from lotic habitats, particularly lower current velocity (6.7-9.8 cm s(-1)) and a more specific substratum type (sand-clay). Niche width values (0.60-0.99) of the Characeae populations studied indicate a high degree of habitat specialization and are among the highest yet found in lotic macroalgae. The relatively narrow variations in microhabitat conditions and high niche widths here reported for Characean populations, suggest a lower tolerance to variations in current velocity, depth, irradiance and substratum type. These characteristics probably explain the relatively restricted distribution of Characeae species in streams of S (a) over tildeo Paulo State with low frequency of records in most regions.

A new and threatened species of Scinax (Anura: Hylidae) from Queimada Grande Island, southeastern Brazil

We describe a new species of hylid frog, Scinax peixotoi, from Queimada Grande Island, southeastern Brazil. The new species belongs to the Scinax perpusillus species group, in which all known forms inhabit bromeliads, and is diagnosed by the following set of characters: moderate-size (males 18.8-20.7 mm SVL, females 22.4-25.1 mm SVL); canthus rostralis distinct; dorsal skin slightly rugose; and a distinct advertisement call with relatively low dominant frequency. The new species is known from a single population on Queimada Grande, an island of 43 ha, approximately 33 km distant from the coast of São Paulo State, where it inhabits scattered patches of bromeliads. The highly specialized and patchy habitat of S. peixotoi, associated with its small range size, make this species highly susceptible to stochastic or anthropogenic habitat disturbances, which could lead it to extinction. Copyright © 2007 Magnolia Press.

Ecologia de peixes de riachos da bacia do rio Machado, RO: padrões, processos e conservação

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

First assessment of the endoparasitic nematode fauna of four psammophilous species of Tropiduridae (Squamata: Iguania) endemic to north-eastern Brazil

Tropiduridae (Squamata: Iguania) is a lizard taxon widely distributed in the neotropics. Among its representatives, some species are classified as generalists regarding habitat usage. Others exhibit a very restricted and probably relict distribution, and are strongly associated with predominantly sandy and dry habitats. Within this rather ecologically similar than phylogenetically closely related group we examined specimens of Eurolophosaurus amathites, E. divaricatus, Tropidurus hygomi, T. psammonastes for endoparasites. In all four species examined we recorded parasitic nematodes (Nemathelminthes: Nematoda). At least three nematode species were recovered: Parapharyngodon sp., Physaloptera lutzi and Strongyluris oscari, with Ph. lutzi being the most abundant parasite encountered in all lizard species examined. In spite of the hosts' habitat specialization, these parasites are also found frequently in non-psammophilous tropidurid species as well as in other squamates. Individual species richness per lizard was low, with usually just one species parasitizing at a time. These are the first parasites registered for these tropidurids and constitute a total of six new host records.

Soil-mediated effects on potential Euterpe edulis (Arecaceae) fruit and palm heart sustainable management in the Brazilian Atlantic Forest

Euterpe edulis is an endangered species due to palm heart overharvesting, the most important non-timber forest product of the Brazilian Atlantic Forest, and fruit exploitation has been introduced as a low impacting alternative. However, E. edulis is a keystone species for frugivores birds, and even the impact of fruit exploitation needs to be better investigated. Since this species occurs over contrasting habitats, the establishment of site-specific standards and limits for exploitation may also be essential to achieve truly sustainable management. In this context, we sought to investigate how soil chemical composition would potentially affect E. edulis (Arecaceae) palm heart and fruit exploitation considering current standards of management. We studied natural populations found in Restinga Forest and Atlantic Rainforest remnants established within Natural Reserves of Sao Paulo State, SE Brazil, where 10.24 ha permanent plots, composed of a grid of 256 subplots (20 m x 20 m), were located. In each of these subplots, we evaluated soil chemical composition and diameter at breast height of E. edulis individuals. Additionally, we evaluated fruit yield in 2008 and 2009 in 20 individuals per year. The Atlantic Rainforest population had a much higher proportion of larger diameter individuals than the population from the Restinga Forest, as a result of habitat-mediated effects, especially those related to soil. Sodium and potassium concentration in Restinga Forest soils, which have strong negative and positive effect on palm growth, respectively, played a key role in determining those differences. Overall, the number of fruits that could be exploited in the Atlantic Rainforest was four times higher than in Restinga Forest. If current rules for palm heart and fruit harvesting were followed without any restriction to different habitats, Restinga Forest populations are under severe threat, as this study shows that they are not suitable for sustainable management of both fruits and palm heart. Hence, a habitat-specific approach of sustainable management is needed for this species in order to respect the demographic and ecological dynamics of each population to be managed. These findings suggest that any effort to create general management standards of low impacting harvesting may be unsuccessful if the species of interest occur over a wide range of ecosystems. (C) 2012 Elsevier B.V. All rights reserved.

Evidence for sympatric speciation by host shift in the sea

The genetic divergence and evolution of new species within the geographic range of a single population (sympatric speciation) contrasts with the well-established doctrine that speciation occurs when populations become geographically isolated (allopatric speciation). Although there is considerable theoretical support for sympatric speciation [1, 2], this mode of diversification remains controversial, at least in part because there are few well-supported examples [3]. We use a combination of molecular, ecological, and biogeographical data to build a case for sympatric speciation by host shift in a new species of coral-dwelling fish (genus Gobiodon). We propose that competition for preferred coral habitats drives host shifts in Gobiodon and that the high diversity of corals provides the source of novel, unoccupied habitats. Disruptive selection in conjunction with strong host fidelity could promote rapid reproductive isolation and ultimately lead to species divergence. Our hypothesis is analogous to sympatric speciation by host shift in phytophagous insects [4, 5] except that we propose a primary role for intraspecific competition in the process of speciation. The fundamental similarity between these fishes and insects is a specialized and intimate relationship with their hosts that makes them ideal candidates for speciation by host shift.

Dispersal capacity and diet breadth modify the response of wild bees to habitat loss

Habitat loss poses a major threat to biodiversity, and species-specific extinction risks are inextricably linked to life-history characteristics. This relationship is still poorly documented for many functionally important taxa, and at larger continental scales. With data from five replicated field studies from three countries, we examined how species richness of wild bees varies with habitat patch size. We hypothesized that the form of this relationship is affected by body size, degree of host plant specialization and sociality. Across all species, we found a positive species–area slope (z ¼ 0.19), and species traits modified this relationship. Large-bodied generalists had a lower z value than small generalists. Contrary to predictions, small specialists had similar or slightly lower z value compared with large specialists, and small generalists also tended to be more strongly affected by habitat loss as compared with small specialists. Social bees were negatively affected by habitat loss (z ¼ 0.11) irrespective of body size. We conclude that habitat loss leads to clear shifts in the species composition of wild bee communities.

Remotely sensed hydroacoustics and observation data for predicting fish habitat suitability

This paper investigates the use of using remotely sensed observation and full coverage hydroacoustic datasets to quantify habitat suitability for a marine demersal fish, the blue-throated wrasse. Because of issues surrounding the detection of species using remotely sensed video techniques, the application of presence-only techniques are well suited for modeling demersal fish habitat suitability. Ecological-Niche Factor Analysis is used to compare analyses conducted using seafloor variables derived from hydroacoustics at three spatial scales; fine (56.25 m²), medium (506.25 m²) and coarse (2756.25 m²), to determine which spatial scale was most influential in predicting blue-throated wrasse habitat suitability. The coarse scale model was found to have the best predictive capabilities with a Boyce Index of 0.80±0.26. The global marginality and specialization values indicated that, irrespective of spatial scale, blue-throated wrasse prefer seafloor characteristics that are different to the mean available within the study site, but exhibit a relatively wide niche. Although variable importance varied over the three spatial scale models, blue-throated wrasse showed a strong preference for regions of shallow water, close to reef, with high rugosity and maximum curvature and low HSI-B values. Generally the spatial patterns in habitat suitability were well represented in the Marine National Park compared to adjacent waters. However, some significant differences in spatial patterns were observed. Interspersion and Juxtaposition Indexes for unsuitable and highly suitable habitat were significantly smaller inside the Marine National Park, while the Mean Shape Index of unsuitable habitat in the Marine National Park was significantly larger.

Habitat use throughout migration : linking individual consistency, prior breeding success and future breeding potential

1. Habitat use can influence individual performance in a wide range of animals, either immediately or through carry-over effects in subsequent seasons. Given that many animal species also show consistent individual differences in reproductive success, it seems plausible that individuals may have consistent patterns of habitat use representing individual specializations, with concomitant fitness consequences.

2. Stable-carbon isotope ratios from a range of tissues were used to discern individual consistency in habitat use along a terrestrial–aquatic gradient in a long-distance migrant, the Bewick’s swan (Cygnus columbianus bewickii). These individual specialisations represented <15% of the isotopic breadth of the population for the majority of individuals and were seen to persist throughout autumn migration and overwintering until aquatic habitats were no longer available.

3. Individual foraging specialisations were then used to demonstrate two consecutive carry-over effects associated with macroscale habitat segregation: consequences of breeding season processes for autumn habitat use; and consequences of autumn habitat use for future reproductive success. Adults that were successful breeders in the year of capture used terrestrial habitats significantly more than adults that were not successful, revealing a substantial cost of reproduction and extended parental care. Use of aquatic habitats during autumn was, however, associated with increased body condition prior to spring migration; and increased subsequent breeding success in adults that had been unsuccessful the year before. Yet adults that were successful breeders in the year of capture remained the most likely to be successful the following year, despite their use of terrestrial habitats.

4. Our results uniquely demonstrate not only individual foraging specializations throughout the migration period, but also that processes during breeding and autumn migration, mediated by individual consistency, may play a fundamental role in the population dynamics of long-distance migrants. These findings, therefore, highlight the importance of long-term consistency to our understanding of habitat function, interindividual differences in fitness, population dynamics and the evolution of migratory strategies.

Comparative gas exchange performance during the wet season of three Brazilian Styrax species under habitat conditions of cerrado vegetation types differing in soil water availability and crown density

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Habitat use and foraging ecology of a batoid community in Shark Bay, Western Australia

Worldwide declines in populations of large elasmobranchs and the potential cascading effects on marine ecosystems have garnered considerable attention. Far less appreciated are the potential ecological impacts of changes in abundances of small to medium bodied elasmobranchs mesopredators. Crucial to elucidating the role of these elasmobranchs is an understanding of their habitat use and foraging ecology in pristine conditions. I investigated the trophic interactions and factors driving spatiotemporal variation in abundances of elasmobranch mesopredators in the relatively pristine ecosystem of Shark Bay, Australia. First, I describe the species composition and seasonal habitat use patterns of elasmobranch mesopredator on the sandflats of Shark Bay. Juvenile batoids dominated this diverse community and were extremely abundant in nearshore microhabitats during the warm season. Stomach content analysis and stable isotopic analysis revealed that there is a large degree of dietary overlap between common batoid species. Crustaceans, which tend to be found in seagrass habitats, dominated diets. Despite isotopic differences between many species, overlap in isotopic niche space was high and there was some degree of individual specialization. I then, investigated the importance of abiotic (temperature and water depth) and biotic (prey and predator abundance) factors in shaping batoid habitat use. Batoids were most abundant and tended to rest in shallow nearshore waters when temperatures were high. This pattern coincides with periods of large shark abundance suggesting batoids were seeking refuge from predators rather than selecting optimal temperatures. Finally, I used acoustic telemetry to examine batoid residency and diel use of the sandflats. Individual batoids were present on the sandflats during both the warm and cold seasons and throughout the diel cycle, suggesting lower sandflat densities during the cold season were a result of habitat shifts rather than migration out of Shark Bay. Combined, habitat use and dietary results suggest that batoids have the potential to seasonally impact sandflat dynamics through their presence, although foraging may be limited on the sandflats. Interestingly, my results suggest that elasmobranch mesopredators in pristine ecosystems probably are not regulated by food supply and their habitat use patterns and perhaps ecosystem impacts may be influenced by their predators.

Does variation in movement tactics and trophic interactions among American alligators create habitat linkages?

1. Highly mobile top predators are hypothesized to spatially and/or temporally link disparate habitats through the combination of their movement and feeding patterns, but recent studies suggest that individual specialization in habitat use and feeding could keep habitats compartmentalized. 2.  We used passive acoustic telemetry and stable isotope analysis to investigate whether specialization in movement and feeding patterns of American alligators (Alligator mississippiensis) in an oligotrophic subtropical estuary created habitat linkages between marine and estuarine/freshwater food webs. 3.  Individual alligators adopted one of the three relatively distinct movement tactics that were linked to variation in diets. Fifty-six per cent of alligators regularly travelled from the upstream (freshwater/mid-estuary) areas into the downstream (marine-influenced) areas where salinities exceed those typically tolerated by alligators. Thirty-one per cent of the alligators made regular trips from the mid-estuarine habitat into the upstream habitat; 13% remained in the mid-estuary zone year-round. 4.  Stable isotopic analysis indicated that, unlike individuals remaining in the mid-estuary and upstream zones, alligators that used the downstream zone fed at least partially from marine food webs and likely moved to access higher prey abundance at the expense of salt stress. Therefore, ‘commuting’ alligators may link marine food webs with those of the estuary and marshes in the coastal Everglades and create an upstream vector for allochthonous nutrient inputs into the estuary. 5.  This study lends further support to the hypothesis that large-bodied highly mobile predators faced with trade-offs are likely to exhibit individual specialization leading to habitat linkages, rather than compartmentalization. However, the conditions under which this scenario occurs require further investigation.