Persistence,extinction, and critical patch number for island populations

Sufficient conditions are derived for persistence and extinction of a population inhabiting several islands. Discrete reaction-diffusion population models are analyzed which describe growth and diffusion of a population on a group of islands or a patch environment. A critical patch number is defined as the number of islands below which the population goes extinct on that group of islands. It is shown that population persistence on one island leads to population persistence for the entire archipelago. Both single-species and multi-species models are discussed.     

Lakes and rivers as islands: species-area relationships in the fish faunas of Ontario

Synopsis Fish species richness in 82 lakes in Ontario, Canada was significantly correlated with surface area. In this region, latitude explained only a small amount of the variation in fish species richness. Thus, our study provides a clear demonstration of the relation between fish species richness and lake area without the confounding effects of latitude and physiography inherent in analyses from broader geographic regions. By comparison with the species-area relationship obtained, we show that acidification clearly depressed the number of fish species in 66 acid-stressed lakes in Ontario. Fish species richness was also significantly correlated with both drainage and surface areas of 21 Ontario rivers. Slopes of species-area regressions of lakes and rivers did not differ significantly, suggesting that species are added to these habitats at similar rates. However, our regression analyses show that rivers support more species of fish per unit surface area of water. Although these results are consistent with some predictions of island biogeography theory, we suggest that fish species richness is more likely to be a simple function of habitat diversity, rather than an equilibrial balance between immigration and extinction.     

Habitat islands and the equilibrium theory of island biogeography: testing some predictions

Summary Species-area data from a study of marsh birds are used to test five predictions generated by the equilibrium theory of island biogeography. Three predictions are supported: we found a significant species-area relationship, a non-zero level of turnover, and a variance-mean ratio of 0.5. One prediction is rejected: the extinction rates were not greater on small islands. The results of one test are equivocal: the number of species on each island was not always the same. As Gilbert (1980) suggests, a strong species-area relationship alone does not validate the theory. The avian communities we studied were on habitat islands, not true islands, and underwent complete extinction annually. Thus caution must be used before applying the theory to these and other habitat islands.     

Leaves as islands for microbes

Summary The equilibrium theory of island biogeography provided a framework for describing the colonization of apple leaf islands by filamentous fungi. Surface sterilization of living leaves in situ by hydrogen peroxide allowed the colonization process to be followed from its inception. Numbers of species of filamentous fungi per leaf fluctuated from 6 to 21 during the first 2 weeks of colonization and equilibrated at about 12 by the third week. Turnover occurred in species composition at equilibrium. The equilibrium number of species was not related to leaf area.The presence of an equilibrium condition with turnover on the leaf surfaces is consistent with two key tenets of the theory of island biogeography. However, the apparent back of a species-area relationship is inconsistent with the island model.     

Species diversity preserved in different numbers of nature reserves of the same total area

The expected number of species occurring in different numbers of reserves of the same total area is examined on different assumptions of the spatial distribution and the probability of extinction. The advantage of one large reserve or several smaller ones of equal total area depends on the spatial distributions of species and the stage after the establishement of reserves. In general, several smaller reserves maintain more species immediately after the establishments unless the spatial distribution are uniform or random, whereas one large reserve excels several smaller ones after some rare species have gone extinct unless the spatial distributions are strongly contagious. Since the extinction of rare species must be facilitated as the size of each reserve reduces, the area of a reserve should be larger than the critical area that ensures the persistence of the species. Hence it is concluded that one or a few large reserves are a better strategy in order to maintain the species diversity.     

Incidence of Extrafloral Nectaries and Their Relationship with Growth and Survival of Lowland Tropical Rain Forest Trees

Mutualistic relationships between organisms have long captivated biologists, and extrafloral nectaries, or nectar‐producing glands, found on many plants are a good example. The nectar produced from these glands provides food for ants, which may defend the plant from potential herbivores in turn. However, relatively little is known about their impact on the long‐term growth and survival of plants that produce them. To better understand the ecological significance of extrafloral nectaries, we examined their incidence on lowland tropical rain forest trees in Yasuní National Park in Amazonian Ecuador, and collated data from two other tropical lowland forest sites (Barro Colorado Island, Panamá and Pasoh Forest Reserve, Malaysia). At Yasuní, extrafloral nectaries were found on 137 of 1123 species censused (12.2%), widely distributed among different angiosperm families. This rate of incidence is high but consistent with other tropical locations. Furthermore, this study adds 18 new genera and two new families (Urticaceae and Caricaceae) to the list of taxa exhibiting extrafloral nectaries. Using demographic data from long‐term forest dynamics plots at each site, we compared the growth and mortality rates of species with extrafloral nectaries to those without. After controlling for phylogeny, no general relationship between extrafloral nectary presence and demographic rates could be detected, suggesting little demographic signal from any community‐wide ecological effects.     

寒害后珠海淇澳岛红树林群落水土生要素的CCA分析

选取2008年寒害后和恢复重建5年后红树林群落水土生要素进行纵向对比,选取水域pH、化学需氧量(COD)、溶解氧(DO)、总悬浮物(TSS)、总无机氮(TIN)、正磷酸盐(PO_4-P)等水环境指标和(S)pH、氧化还原电位(Eh)、有机质(OM)等沉积物指标进行不同类型红树林群落间的横向对比。自变量指标中水环境指标所占比例较大,约为2—3,弥补了红树林湿地植被、沉积物和水文等3个自然因素中水文条件研究较为缺乏的现状。结合各类红树林群落水、土、生三要素进行典范对应分析(CCA)的结果表明:1)典范对应分析方法用于分析淇澳岛大围湾各类红树林典型群落寒害后及寒害5年后的群落生物过程特征与各种生境因子间的相关关系,效果良好,前4组自变量的典型变量可以解释标准变量中绝大部分(约80%以上)的信息。2)恢复重建5年后,淇澳岛大围湾各类红树林群落中中潮位的无瓣海桑(Sonneratia apetala)群落和高潮位的桐花树(Aegiceras comiculatum)群落拓展最快,面积分别增加26.58hm~2和23.1 hm~2,而互花米草(Spartina alterniflora)群落因无瓣海桑群落的扩张而受到抑制,面积下降31.51hm~2。3)水域pH、沉积物(S)pH、OM、DO、COD等水土指标与冠幅、胸径、基径、盖度和高度等生物过程指标依次正相关,而PO_4-P、TSS和TIN等水域指标与生物过程指标依次负相关。4)珠海淇澳岛大围湾红树林湿地生态系统对水域悬浮物和营养元素的固定效果明显,但其植被生物过程受水土因素,尤其是水文因素,影响较大,其中影响最大的生境因素是pH值(包括水域pH值和沉积物(S)pH值)。低中潮位、中性至弱碱性的表层沉积物生境条件较为适合无瓣海桑和老鼠簕(Acanthus ilicifolius)等红树植物群落的初期恢复。     

平潭岛典型海岸草丛沙堆植物群落水势日变化特征及其影响因素

水势是反映植物受到环境胁迫的重要指标之一,可用来确定其受胁迫的程度和适应能力大小。以福建省平潭岛海岸典型沙生植物老鼠艻(Spinifex littoreus)形成的草丛沙堆为研究对象,选取晴朗无云的天气,采用PSYPRO水势测量系统对其植物叶、茎水势及其所形成的沙堆土壤水势进行测定,同时采用HUMIPORT10手持式温湿度计对当日的气象要素进行同步观测。结果表明:(1)老鼠艻的叶水势呈现出与早晚高午间低相反的反梯度现象,叶、茎水势的日变化均表现为"M"型变化趋势,除18:00后,其它时间均表现为叶片水势下降、茎干水势上升,并且发现叶、茎水势的变化趋势存在位相后移现象;(2)老鼠艻的叶、茎水势在10:00时差异达到最大的0.65MPa,且茎水势高于叶水势,在14:00左右,植物茎水势出现低于叶水势的反常现象,在18:00时叶、茎水势趋于相同;(3)除表层30cm外,其它层土壤水势日变化特征总体表现为从早晨开始下降,14:00达到最低,但总体变化不明显;(4)随着深度增加,草丛沙堆土壤水势呈现为依次增加的趋势,但80cm以下土壤水势变化不显著(P0.1);(5)叶水势与大气水势具有较好的相关性,且变化显著(P0.1),与茎水势及浅层土壤水势有一定相关性,但变化不显著(P0.1),与50cm以下土壤水势均无相关性。     

海南岛自然保护区对土壤保持服务功能的保护效果

自然保护区建设是保护生态系统服务的重要手段,在防治土壤侵蚀和维持生态安全方面具有不可替代的作用。以1988年、1998年和2008年3期遥感影像为基础,分析海南保护区对土壤保持功能的长期保护效果,探讨引起保护区土壤保持功能变化的影响因素。结果表明:(1)海南岛保护区内部平均单位面积土壤保持量是1951.59 t hm-2a-1,分别是区外0—5、5—10km和海南岛全省平均水平的2.4、3.2、2.9倍,保护区在土壤保持功能的保育方面发挥着重要作用;(2)在时间尺度上,1988—2008年保护区内外土壤保持功能呈现不同程度的退化趋势,其中保护区外围退化程度显著高于保护区内部(P0.05),后10年的退化程度显著高于前10年(P0.05);(3)从驱动因素上看,1988—2008年经济发展、人口增加和耕地扩张是影响保护区土壤保持功能退化的主要因素,其中在前10年,土壤保持功能与单位面积地区生产总值、单位面积第一产业生产总值、人口密度和耕地比例呈显著负相关(P0.05),而在后10年,土壤保持功能与单位面积地区生产总值、人口密度和耕地比例呈显著负相关(P0.05),由此,应权衡土壤保持功能保护与人为活动的关系,实现生态环境保护与社会经济的协调发展。