Quantitative evaluation of temporal similarity in abundance of animal species

Summary A quantitative method is suggested for measuring the similarity of seasonal abundance patterns of different animal species. The method was applied to two sets of field data and produced biologically meaningful and interesting results.     

Land use and climate influences on waterbirds in the Prairie Potholes

Aim We examined the influences of regional climate and land‐use variables on mallard (Anas platyrhynchos), blue‐winged teal (Anas discors), ruddy duck (Oxyura jamaicensis) and pied‐billed grebe (Podilymbus podiceps) abundances to inform conservation planning in the Prairie Pothole Region of the United States. Location The US portion of Bird Conservation Region 11 (US‐BCR11, the Prairie Potholes), which encompasses six states within the United States: Montana, North Dakota, South Dakota, Nebraska, Minnesota and Iowa. Methods We used data from the North American Breeding Bird Survey (NABBS), the National Land Cover Data Set, and the National Climatic Data Center to model the effects of environmental variables on waterbird abundance. We evaluated land‐use covariates at three logarithmically related spatial scales (1000, 10,000 and 100,000 ha), and constructed hierarchical spatial count models a priori using information from published habitat associations. Model fitting was performed using a hierarchical modelling approach within a Bayesian framework. Results Models with the same variables expressed at different scales were often in the best model subset, indicating that the influence of spatial scale was small. Both land‐use and climate variables contributed strongly to predicting waterbird abundance in US‐BCR11. The strongest positive influences on waterbird abundance were the percentage of wetland area across all three spatial scales, herbaceous vegetation and precipitation variables. Other variables that we included in our models did not appear to influence waterbirds in this study. Main conclusions Understanding the relationships of waterbird abundance to climate and land use may allow us to make predictions of future distribution and abundance as environmental factors change. Additionally, results from this study can suggest locations where conservation and management efforts should be focused.     

Environmental factors affecting the distribution of aquatic invertebrates in temporary ponds in Mammoth Cave National Park,Kentucky, USA

Despite a recent surge of interest in temporary lentic systems, a strong theory linking the biota to its environment has not emerged. Using data from 10 temporary ponds at Mammoth Cave National Park, Kentucky, USA, we investigated how invertebrate communities were structured along environmental gradients, both between and within ponds. Samples were collected with a benthic corer in winter and spring, and a sweep net in spring. Six between-pond and two within-pond datasets were created. Between-pond analyses yielded significant CCA’s with only one of the six data sets. The ranges of environmental variables (EV’s) within ponds were often similar to the ranges of EV’s when averaged and compared between ponds. Some taxa were aggregated in a single pond, and richness increased with pond area. The theory that richness increases with hydroperiod did not apply to these systems. Within-pond analyses yielded more consistent relationships, with both CCA’s being significant. Sample depth was the best predictor of invertebrate richness and abundance, with most taxa preferring shallow habitats. Richness and abundance were higher in both shallow ponds and shallow areas of deep ponds than in deep areas of deep ponds. Standardizing sample depth may be an effective way to remove this gradient as a confounding variable in future research. The presence of within-pond gradients, possibly coupled with the limited dispersal and random colonization of tolerant taxa, makes between-pond comparisons difficult. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorised users. Handling editor: S. Declerck     

Climatic seasonality, resource bottlenecks, and abundance of rainforest birds: implications for global climate change

We demonstrate that within-year climatic variability, particularly rainfall seasonality, is the most significant variable explaining spatial patterns of bird abundance in Australian tropical rainforest. The likely mechanism causing this pattern is a resource bottleneck (insects, nectar, and fruit) during the dry season that limits the population size of many species. The patterns support both the diversity–climatic–stability hypothesis and the species–energy hypothesis but clearly show that seasonality in energy availability may be a more significant factor than annual totals or means. An index of dry season severity is proposed that quantifies the combined effect of the degree of dryness and the duration of the dry season. We suggest that the predicted increases in seasonality due to global climate change could produce significant declines in bird abundance, further exacerbating the impacts of decreased range size, increased fragmentation, and decreased population size likely to occur as a result of increasing temperature. We suggest that increasing climatic seasonality due to global climate change has the potential to have significant negative impacts on tropical biodiversity.     

Contrasting dynamics of ciliate communities in sandy and silty sediments of an estuarine intertidal flat

During a 1-year study of the ciliate faunas of a silty and a sandy site on an intertidal flat in the Westerschelde estuary, a total number of 107 taxa were recorded belonging to at least 52 genera and 15 orders. Our results suggest that physical properties of the sediment were more important in regulating ciliate abundance, diversity and community composition than food availability, predation, temperature or oxygen concentration. Ciliate abundance and diversity were positively related to sediment grain size and the ciliate community of silty sediments was found to be a subset of that of sandy sediments. At the sandy site, where the sediment composition was stable, seasonal changes in the ciliate community were related to changes in food availability and/or temperature. At both the sandy and silty sites, a clear vertical gradient in the ciliate community was observed that appeared to be linked to gradients in food availability and oxygen concentration. These vertical gradients in ciliate community composition, however, were less steep than the measured oxygen gradients, probably due to the presence of oxic microniches in the anoxic zone.     

A new statistical approach for assessing similarity of species composition with incidence and abundance data

The classic Jaccard and Sørensen indices of compositional similarity (and other indices that depend upon the same variables) are notoriously sensitive to sample size, especially for assemblages with numerous rare species. Further, because these indices are based solely on presence–absence data, accurate estimators for them are unattainable. We provide a probabilistic derivation for the classic, incidence‐based forms of these indices and extend this approach to formulate new Jaccard‐type or Sørensen‐type indices based on species abundance data. We then propose estimators for these indices that include the effect of unseen shared species, based on either (replicated) incidence‐ or abundance‐based sample data. In sampling simulations, these new estimators prove to be considerably less biased than classic indices when a substantial proportion of species are missing from samples. Based on species‐rich empirical datasets, we show how incorporating the effect of unseen shared species not only increases accuracy but also can change the interpretation of results.     

东海水母类丰度的动力学特征

本文根据1997-2000年东海23°30′-33°N、118°30′-128°E海域4个季节海洋调查资料,探讨了东海水母类数量变化特征和相应的动力学。结果表明:水母类是东海浮游动物的第三大类群,其丰度仅次于桡足类和海樽类;其数量有明显的季节变化,春季丰度最高(5·37ind·/m3),秋季次之(2·23ind·/m3),冬季(1·82ind·/m3),夏季最低(0·88ind·/m3);其平面分布特征为近海高于外海;其数量变化首先来自优势种大西洋五角水母(Muggiaeaatlantica)和双生水母(Diphyeschamissonis)的贡献,前者是近岸暖温种,后者是近岸暖水种;春季丰度变化与表层和底层盐度二元线性相关,夏季与底层水温相关,秋季与底层盐度相关,冬季与表层盐度相关,4季总丰度与10m层盐度相关。盐度是影响水母类数量变化的主要环境动力学因子,水温是次要因子;水母类高丰度区往往位于台湾暖流与长江径流交汇处偏冲淡水水团一侧。长江冲淡水在不同季节入海后的流向是决定高丰度分布区位置重要的动力学因子。该类浮游动物对沿海海域生物安全、生态安全和环境安全都有重要的影响,引起全球的普遍关注。     

黄、东海生态系统中鱼卵、仔稚幼鱼种类组成与数量分布

2000年秋季和2001年春季“北斗号”生物资源调查船利用大型浮游生物网采用表层水平拖网的调查方式对黄、东海鱼卵、仔稚幼鱼种类组成与数量分布进行了调查。秋季和春季分别设置66个(黄海26个,东海40个)和98个(黄海46个,东海52个)调查站。每站拖网10min,拖网速度为3.0nmile/h。调查结果表明:秋季和春季所采集到的鱼卵和仔稚幼鱼样品共62种以及鳗鲡目和飞鱼类两大类,鉴定到种的44种,隶属于9目33科40属;还有10种仅能鉴定到属,6种和飞鱼类仅能鉴定到科,1种和鳗鲡目一大类仅能鉴定到目以及1种不能识别。优势种为、鲐、带鱼、棱、黑鳃梅童鱼、绿鳍鱼以及多鳞、鼠、大泷六线鱼、细纹狮子鱼等。2000年秋季,从黄海和东海分别采集到16粒鱼卵、107尾仔稚幼鱼和495粒鱼卵、116尾仔稚幼鱼。鱼卵、仔稚幼鱼的出现频率分别为26.92%、38.46%和65.00%、40.46%,平均密度分别为0.6粒/站、3.6尾/站和12.4粒/站、2.8尾/站。2001年春季,从黄海和东海分别采集到3粒鱼卵、61尾稚幼鱼和17587粒鱼卵和1560尾仔稚幼鱼,鱼卵、仔稚幼鱼的出现频率分别为2.17%、39.13%和57.69%、48.08%,平均密度仅分别为0.07粒/站、1.3尾/站和338.2粒/站、30.0尾/站。秋季,黄海区的硬骨鱼类进入产卵末期,而东海区才刚刚进入产卵末期。春季,黄海区的硬骨鱼类刚刚进入产卵初期,而东海区已进入产卵盛期。此外,对秋季和春季鱼卵和仔稚幼鱼的数量分布以及鼠、、棱、多鳞、少鳞、黑鳃梅童鱼、小黄鱼、鲐、带鱼、绿鳍鱼、大泷六线鱼和细纹狮子鱼等优势种类的鱼卵和仔稚幼鱼数量分布进行了详尽的描述。2000年和2001年黄海区鱼卵、仔稚幼鱼的种类组成与1985年和1986年发生了明显的变化,这与黄海区渔业资源和鱼类群落结构的变化是相符合的。从而说明人类的长期捕捞活动对海洋生态系统中鱼类资源的种群交替和鱼类群落结构的变化产生了较大的影响     

Moss Responses to Elevated CO2 and Variation in Hydrology in a Temperate Lowland Peatland

We studied the effects of elevated CO₂ (180–200 ppmv above ambient) on growth and chemistry of three moss species (Sphagnum palustre, S. recurvum and Polytrichum commune) in a lowland peatland in the Netherlands. Thereto, we conducted both a greenhouse experiment with both Sphagnum species and a field experiment with all three species using MiniFACE (Free Air CO₂ Enrichment) technology during 3 years. The greenhouse experiment showed that Sphagnum growth was stimulated by elevated CO₂ in the short term, but that in the longer term (≥1 year) growth was probably inhibited by low water tables and/or down-regulation of photosynthesis. In the field experiment, we did not find significant changes in moss abundance in response to elevated CO₂, although CO₂ enrichment appeared to reduce S. recurvum abundance. Both Sphagnum species showed stronger responses to spatial variation in hydrology than to increased atmospheric CO₂ concentrations. Polytrichum was insensitive to changes in hydrology. Apart from the confounding effects of hydrology, the relative lack of growth response of the moss species may also have been due to the relatively small increase in assimilated CO₂ as achieved by the experimentally added CO₂. We calculated that the added CO₂ contributed at most 32% to the carbon assimilation of the mosses, while our estimates based on stable C isotope data even suggest lower contributions for Sphagnum (24–27%). Chemical analyses of the mosses showed only small elevated CO₂ effects on living tissue N concentration and C/N ratio of the mosses, but the C/N ratio of Polytrichum was substantially lower than those of the Sphagnum species. Continuing expansion of Polytrichum at the expense of Sphagnum could reduce the C sink function of this lowland Sphagnum peatland, and similar ones elsewhere, as litter decomposition rates would probably be enhanced. Such a reduction in sink function would be driven mostly by increased atmospheric N deposition, water table regulation for agricultural purposes and land management to preserve the early successional stage (mowing, tree and shrub removal), since these anthropogenic factors will probably exert a greater control on competition between Polytrichum and Sphagnum than increased atmospheric CO₂ concentrations.     

The scaling of colony size with nest volume in termites: a role in population dynamics?

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