Polar light regime and piscivory govern diel vertical migrations of planktivorous fish and zooplankton in a subarctic lake

Abstract –  Seasonal variation in light intensity has strong impacts on invertebrate and vertebrate habitat selection creating trade-offs between foraging gain and risk of death. Diel vertical migration (DVM) has received a particularly interest, but multitrophic level studies in lakes under polar light regime have not been conducted. Here, we examined habitat selection of pelagic zooplankton, planktivores and piscivores in subarctic Lake Muddusjärvi with polymorphic whitefish ( Coregonus lavaretus (L.)). Seasonal change in light was hypothesized to be the most important abiotic factor inducing DVM, whereas predation was considered as an ultimate biotic factor. During period of mid-night sun in June, no DVM was observed at any trophic level, whereas during normal day and night light in September planktivores and zooplankton migrated. DVM was top-down controlled, where piscivorous brown trout ( Salmo trutta L.) used pelagic habitat continuously inducing DVM of its main prey, pelagic whitefish morph, which cascaded to reverse DVM of zooplankton. Top-down control of lower trophic level DVMs by piscivores might be more general pattern in lakes than previously considered.     

Dissolved oxygen controls summer habitat of Clear Lake Hitch (Lavinia exilicauda chi), an imperilled potamodromous cyprinid

Clear Lake Hitch is an imperilled minnow endemic to Clear Lake, Lake County, California, United States listed as threatened under the California Endangered Species Act (ESA) and a candidate for listing under the United States ESA. It exhibits a potamodromous life cycle whereby adults, which reach up to 6 + years in age and over 350 mm in length, migrate into Clear Lake's ephemeral tributaries briefly during spring to spawn. Conservation and management of Clear Lake Hitch is inhibited, in part, by a lack of information on the lacustrine habitat of nonbreeding individuals within Clear Lake. To address this problem, we sampled Clear Lake Hitch with gill nets in a stratified random sampling design to determine the distribution and habitat associations in early summer 2017 and 2018. We identified abundance-habitat relationships for juveniles and adults using Bayesian zero-inflated negative binomial generalised linear mixed modelling. Results indicated that dissolved oxygen concentration was the most important habitat feature measured; juveniles and adults were substantially more abundant in normoxic (≥2 mg/l) than in hypoxic (<2 mg/l) habitat. Both also exhibited weak positive relationships with chlorophyll fluorescence, suggesting relatively productive habitats may support higher numbers of Clear Lake Hitch. Spatially, juveniles were most abundant in nearshore habitats while adults were ubiquitous, indicating an ontogenetic habitat expansion that may be associated with a resource availability-predation risk trade-off. Management actions undertaken to improve hypoxia problems in Clear Lake would also improve Clear Lake Hitch habitat.     

不同生境黑果枸杞实生苗生长及土壤养分空间差异的研究

研究不同生境黑果枸杞实生苗数量、生长状况、生物量分配及土壤养分空间差异,探讨环境因子对黑果枸杞实生苗生长的影响,为黑果枸杞种群恢复及持续经营提供理论依据。采用固定样地调查法,于2016年对张掖市甘州区、临泽县、肃南县及周边地区的农田地埂、水渠边、盐化沙地、盐碱荒地等各生境黑果枸杞进行调查。研究结果表明：不同生境均有黑果枸杞实生苗分布,农田地埂生境实生苗数量相对水渠边、盐化沙地、盐碱荒地分别增加66.67%、122.22%、215.79%。因环境条件差异,不同生境的黑果枸杞实生苗采取了不同的生存策略适应环境：农田地埂生境的黑果枸杞主要为增高生长,盐化沙地的黑果枸杞主要为冠幅的增长,而盐碱荒地的黑果枸杞主要为增粗生长。农田地埂生境0~20 cm土层有机质含量相对水渠边、盐化沙地、盐碱荒地分别增加28.50%、2.62%、10.13%;全氮含量分别增加44.08%、33.16%、72.41%;有效氮含量分别增加46.81%、0%、50%。空气湿度、土壤含水量对黑果枸杞幼苗数量及幼苗生长有显著影响。在今后的黑果枸杞栽培管理中,幼苗期应加强水分管理。     

Forecast skill for predicting distribution shifts: A retrospective experiment for marine fishes in the Eastern Bering Sea

Forecasting distribution shifts under novel environmental conditions is a major task for ecologists and conservationists. Researchers forecast distribution shifts using several tools including: predicting from an empirical relationship between a summary of distribution (population centroid) and annual time series (“annual regression,” AR); or fitting a habitat‐envelope model to historical distribution and forecasting given predictions of future environmental conditions (“habitat envelope,” HE). However, surprisingly little research has estimated forecast skill by fitting to historical data, forecasting distribution shifts and comparing forecasts with subsequent observations of distribution shifts. I demonstrate the important role of retrospective skill testing by forecasting poleward movement over 1‐, 2‐ or 3‐year periods for 20 fish and crab species in the Eastern Bering Sea and comparing forecasts with observed shifts. I specifically introduce an alternative vector‐autoregressive spatio‐temporal (VAST) forecasting model, which can include species temperature responses, and compare skill for AR, HE and VAST forecasts. Results show that the HE forecast has 30%–43% greater variance than predicting that future distribution is identical to the estimated distribution in the final year (a “persistence” forecast). Meanwhile, the AR explains 2%–6% and VAST explains 8%–25% of variance in poleward movement, and both have better performance than a persistence forecast. HE and AR both generate forecast intervals that are too narrow, while VAST models with or without temperature have appropriate width for forecast intervals. Retrospective skill testing for more regions and taxa should be used as a test bed to guide future improvements in methods for forecasting distribution shifts.     

半荒漠地区灌木饲料林营造技术研究

本文对半荒漠地区灌木饲料林的树种选择、经营管理等问题进行了初步探讨，给出了花棒、杨柴、柠条、沙柳、毛条、毛柳、白沙蒿、油蒿８个半荒漠地区灌木饲料林树种的造林适宜立地类型、最适造林季节、最佳造林密度、最适收获期以及最佳平茬年龄。     

基于MaxEnt模型的检疫性害虫小蔗螟在中国的潜在分布预测

小蔗螟是重要的检疫性害虫,许多国家将其列入检疫性害虫名录,主要危害甘蔗、玉米等作物。本研究基于小蔗螟分布记录,结合环境数据,采用MaxEnt软件对其在中国潜在分布区进行预测。结果表明：小蔗螟在我国的高度和中度适生区主要分布在海南、云南、广东、广西及福建等。影响小蔗螟分布的最主要环境变量是最暖季平均降雨量和温度变化方差。阐明小蔗螟在我国潜在地理分布及限制其分布的环境变量,可为我国的检疫工作提供理论依据。     

塔里木河中游塔里木马鹿种群数量及其栖息地现状的初步分析

为了查明塔里木河中游野生塔里木马鹿种群数量及栖息地资源,2006年10月1～15日,采用截线抽样法和地理信息系统相结合,对塔里木马鹿种群及其栖息地进行了研究.结果表明,现有野生种群数量大约在21～71头,集中分布在离人类干扰比较远的依明且克和托胡拉克阔坦一带.同时采用地理信息系统分析方法对研究地区的LANDSAT TM 遥感影像进行了监督分类处理,把研究区影像土地覆被分成了农田、水体、高密度林地、中密度林地、低密度林地、草地、沙漠、盐碱地、荒漠等9类型.其中塔里木马鹿主要分布在中,高覆盖度胡杨林、红柳灌丛和胡杨红柳混交林带中.同时根据在不同类型栖息地中马鹿粪便、卧迹、足迹的出现频率并结合地理信息系统分析结果,把研究地区生境划分为4种适宜栖息地等级.其中不适宜区占62.6;;较差区占3.76;;适宜区占3.38;;非常适宜区占30.23;.     

西双版纳自然保护区鼷鹿生境选择的初步研究

对中国仅见于西双版纳勐腊县鼷鹿（ＴｒａｇｕｌｕｓｊａｖａｎｉｃｕｓｗｉｌｉａｍｓｏｎｉＫｌｏｓ）栖息地生境因子的调查分析，初步得出鼷鹿栖息环境与植被类型、下木、地被、坡度、坡向、海拔、土质的相关程度。对各生境因子的优先选择顺序分别为：下木郁闭度，地表覆盖物，坡度，植被类型，土质，海拔，坡向。并初步划分出鼷鹿的４个生境等级为：（１）最佳生境地；（２）良好生境地；（３）一般生境地；（４）劣等生境地。并在此基础上提出相应的保护对策。     

高山红景天的繁殖生态学研究 Ⅰ生态因子与植物学、物候学特性分析

本研究对生长在新疆天山１号冰川观测站附近的高山红景天，从生境土壤的理化性质、气象因子等方面进行了观测与统计，并对其植物学及物候学特性进行了较详细的观察，结果表明：高山红景天植株的形态特征、生长发育节律与其特殊的生态环境是相适应的。