Fire-driven dynamic mosaics in the Great Victoria Desert,Australia – II. A spatial and temporal landscape model

An explicitly spatial, large scale, high resolution model of fire driven landscape dynamics in the Great Victoria Desert is constructed and parameterized to simulate frequency distributions of fire size and shape obtained from previous analyses of satellite chronosequences. We conclude that probabilities of fire spread cannot be constant over time, and that realistic distributions of fire size and plausible rates of fire spread can be obtained by assuming that fire spread is conditional on observed durations of windy conditions. Landscapes subject to this form of disturbance show large scale correlation structure many times greater than the average dimensions of single fires, and exhibit low frequency quasi-periodic stochastically driven oscillations in proportions of the landscape at different successional states over spatial scales exceeding 100,000 km². Average fire return intervals are 30 yrs. Analysis of patch structure suggests that this landscape is composed of few large younger patches, embedded in a mature sea of surrounding habitat. Intermediate and late successional habitat must exist in more abundant patches somewhat smaller than young habitat. Numerous small patches of mature habitat are likely to be scattered throughout this younger habitat. The model predicts that fire size frequency distributions are relatively insensitive to changes of as much as ±50% of observed fire ignition frequency.     

Patch size but not short‐term isolation influences occurrence of westslope cutthroat trout above human‐made barriers

Habitat fragmentation in aquatic systems has led to widespread isolation of stream fishes. Metapopulation theory predicts that persistence is directly related to local patch size and its characteristics, but because these relationships tend to be taxon‐specific, empirical data are important. We assembled 246 observations of occurrence of westslope cutthroat trout (WCT), a taxon of concern in the western U.S. and Canada, in stream networks isolated for up to 100 years (median 40 years) above human‐made barriers, mostly culverts, at road crossings within U.S. National Forests. We used logistic regression to analyse how WCT occurrence varied with patch size, isolation time and stream‐level covariates. Occurrence was positively related to stream length and habitat quality within the isolated stream network and negatively related to elevation and channel gradient. Unexpectedly, the probability of occurrence was not related to how long a habitat patch had been isolated. At the median elevation (1354 m) and channel gradient (14%), and where habitat quality was poor, WCT were likely to occur (probability >0.5) if an isolated stream network was at least 1.7 km. If habitat quality was high, about 0.2 km of habitat produced the same probability. Although there are important limitations, this analysis provides the first empirical estimate for how patch size and patch‐level characteristics influence persistence of WCT in isolated stream networks.     

焉耆绿洲景观格局变化分析

对焉耆绿洲近30年3期遥感数据（1973年MSS．1990年TM，2000年ETM）应用遥感与地理信息技术进行解译和拓扑后，在fragstats景观格局分析软件中，计算出不同时期景观指数，根据计算结果从类型水平和景观水平上进行了分析，分析认为，人类活动对焉耆绿洲景观格局尤其是天然植被和耕地有很大影响，耕地面积在近30年问增长了增长120％。2000年耕地已经成为面积最大的景观类型，其最大斑块指数，达到16．24％。天然植被斑块密度由1973年0．0213增大到2000年0．0505，斑块数从120增加到284个，面积减少了68％，破碎化程度提高，在空间上趋于离散。1973～1990年，城镇面积增加了373．95％。1990-2000年又增加了38．36％，近30年问城市和农村居民点的斑块数增加了65个。博斯腾湖周边的芦苇沼泽地，1973～1990年，面积减少了17．52％．1990～2000年，又恢复了14．80％。从景观水平上整个研究区的斑块数在增长，平均斑块面积在减小，这3个时期的斑块密度分别为0．098，0．135，0．158，斑块密度的提高表明了斑块破碎化增加。香农多样性指数值在1990年上升到1．96后又在2000年下降到1．93，绿洲整体的异质性和多样性在1990年上升2000年下降。     

Immune challenge of mating effort: steroid hormone profile,dark ventral patch and parasite burden in relation to intrasexual competition in male Iberian red deer

Testosterone secretion may regulate the reproductive effort and the development of sexual traits, but it may also involve costs at the immunological and metabolic levels. However, the evidence for this trade‐off in wild populations is scarce. Cortisol also plays an important role in mediating the reproductive and immune functions. In this study, we analyzed whether the endoparasite burden relates to hormonal levels (fecal testosterone and cortisol metabolites) and/or morphological sexual traits (size of the dark ventral patch, a trait that indicates reproductive effort in males) in male Iberian red deer. For this purpose, we sampled male red deer harvested during hunting actions in 2 types of populations in south western Spain that differed in structure, affecting the level of male–male competition for mates. We used coprological analyses to estimate the parasite burden mainly of gastrointestinal and bronchopulmonary nematodes and of protozoa, and assessed testosterone and cortisol metabolite levels from fecal pellets. We found a positive relationship of host parasitation with both testosterone levels and the size of the dark ventral patch, but these relationships depended on the intensity of male–male competition in the population, being only found under the high‐competition scenario. These results are discussed under the hypothesis of the testosterone immunocompetence handicap, suggesting a cost at the immunological level, and, therefore, higher susceptibility to parasite infection in males that make a greater reproductive effort. However, this effect seems to be modulated by the social environment (male–male competition) that might lead to different optima in testosterone production and sexual trait development.     

泥河沟流域农林复合生态系统景观格局变化研究

以淳化县泥河沟流域为研究对象,利用该区1986年和2004年的土地利用现状图,在A rc/in fo和A rcveiw软件支持下,对该流域18 a来农林复合生态系统景观格局的变化进行了研究。结果表明,除水域不变外,林地、草地和未利用地面积均减少,其他用地面积有所增加,尤其是居民地企业及交通用地增幅最大,达47.48%;流域的斑块数量减少,斑块形状趋于复杂,多样性指数增加,景观的破碎程度加大,景观格局正朝多极化和破碎化方向发展。     

高寒草甸不同斑块草地土壤微生物多样性特征研究

本文以矮嵩草（Kobresia humilis）高寒草甸及退化后形成的不同退化斑块群落类型草地土壤为研究对象,利用Illumina MiSeq高通量测序技术分析了不同斑块草地土壤中微生物群落结构组成和多样性变化特点,并分析了土壤微生物与土壤养分之间的相关性。结果表明：以矮嵩草为优势植物的高寒草甸群落变为以细叶亚菊（Ajania tenuifolia）、黄帚橐吾（Ligularia virgaurea）和甘肃马先蒿（Pedicularis kansuensis）为优势的群落或斑块后,土壤真菌群落丰富度和多样性未呈现出显著差异,但土壤细菌群落表现出了差别,表现为细叶亚菊和黄帚橐吾斑块土壤细菌丰富度指数显著高于矮嵩草草甸,而甘肃马先蒿斑块的低于矮嵩草高寒草甸。优势植物种类变化和土壤养分含量显著下降引起土壤真菌营养类型的分化,草地退化降低了腐生营养型真菌丰度,增加了共生营养型真菌丰度。土壤养分、pH和水分含量对真菌群落影响相对较小,对细菌群落影响相对较大。     

Matrix effects on bird assemblages in fragmented Afromontane forests in South Africa

We examine the effects of matrix type on forest bird species richness in historically fragmented forests of the KwaZulu-Natal midlands, South Africa. Bird species-area relationships for forest fragments within natural grassland were compared with those surrounded by plantation forestry (Pinus spp.). While fragments in grasslands displayed a species-area effect, no such effect (slope ∼0) was detected for fragments in plantations. The critical fragment size to avoid an island effect on species richness was 302 ha for fragments in grasslands, and contained 51 of the 61 forest bird species encountered. Small forest fragments (<50 ha) within grasslands were less species-rich than those surrounded by plantation, while the reverse was true for forests larger than 50 ha. Bird density was significantly lower in larger forest patches within plantation when compared to those in grassland. However, a slight decline in species density with increasing species richness in a patch (i.e. weak density compensation) characterised only those bird assemblages surrounded by a grassland matrix, suggesting these are approaching species saturation. Commercial plantations may increase the likelihood of colonisation of, and immigration from, small forest fragments by birds, reducing the incidence of area-dependent extinction in small fragments, but may also result in lower species richness in larger fragments. The latter is likely a consequence of the promotion by plantations of a wider distribution of generalist species in, and the loss of some specialised or rare species from, large patches. Management options are to avoid planting plantations near large forest patches and to increase the size of small patches where possible. Where afforestation is unavoidable, placing plantations in the vicinity of small forest patches rather than large forest patches may be preferable.     

侧柏风景林美景度的林内色彩斑块非线性模型研究

利用景观生态学的景观空间格局分析原理,以照片的色彩斑块结构为基础,开展风景林林内景观质量评价研究。分析美景度等级和14个斑块指数的关系,利用简相关法筛选出对美景度影响大的SPLIT、SHDI、DIV、SIEI、ACOV和LPI 6个指数,研究表明:随着美景度等级的降低,DIV、SIEI、ACOV和LPI呈曲线变化趋势;SPLIT、SHDI呈线性增大的变化趋势。依据6个指标,利用聚类方法将侧柏人工林分为4种类型。以指数为自变量分别构建了线性和非线性美景度模型。对比结果表明:非线性模型拟合精度高于线性模型,所以选用二次多项式逐步回归模型从总体上较好地反映出景观指数与美景度间的关系。      

放牧强度对黄土丘陵沟壑区生物土壤结皮分布格局的影响

【目的】明确放牧强度对生物土壤结皮（生物结皮）分布格局的影响。【方法】以黄土丘陵沟壑区4个典型的退耕还林（草）县（市）的退耕草地为对象,以单位面积羊粪球数(羊粪球密度)表征放牧强度,将放牧强度划分为轻度（羊粪球数0~10个/m²）、中度（羊粪球数＞10~20个/m²）、重度（羊粪球数＞20个/m²）3个强度,分别记作G1、G2、G3,以退耕封禁草地为对照(G0),基于景观生态学方法,通过拍照和GIS图像处理,采用景观格局指数定量分析了生物结皮分布格局的变化。【结果】放牧影响退耕草地生物结皮的盖度及组成,其中G2和G3处理藓结皮盖度显著低于G0和G1处理;藻结皮盖度随放牧强度的增加呈增大趋势,地衣结皮盖度无显著变化。放牧降低了生物结皮厚度,其中G3处理生物结皮厚度显著低于G0和G1处理。随着放牧强度的增加,藻生物量呈增大趋势,但各处理间差异不显著;而藓生物量呈降低趋势。与G0处理相比,放牧显著降低了生物结皮斑块的连结度,而增加了分离度,其中G3处理斑块连结度显著降低,而分离度显著增加。随着放牧强度的增加,生物结皮斑块密度变化不显著,斑块盖度、斑块连结度降低,而景观形状指数、分离度增加。放牧强度与生物结皮斑块盖度、斑块连结度、斑块分离度之间显著相关,拟合结果显示均呈二次函数关系。【结论】中度和重度放牧强度（羊粪球数>10个/m²）导致生物结皮斑块破碎化及退化。