用空间多样性指数分析辽河三角洲野生动物生境的格局变化

在利用遥感(RS)和地理信息系统(GIS)对辽河三角洲土地覆被变化进行研究的基础上,引用空间多样性指数(Sd)对本区野生动物的生境格局进行了定量描述,并分析了其1988～1998年间的生境格局变化,结果表明,研究区野生动物生境格局受人为和自然干扰的双重影响而发生了较明显的变化,整体趋势是生境适宜性逐渐降低,适宜生境和较适宜生境(Sd≥0．35)的面积10年间减少7637hm^2。且破碎化程度加深,在空间上呈现由北向南推进、由东向西压缩之势,生境质量呈下降趋势,同时,空间多样性指数能够定量地反映野生动物生境的适宜程度,并能直观地描述生境的空间格局,为进一步揭示生境格局的变化规律及原因提供了有效措施和依据,对于协调区域经济发展与生物多样性保护具有重要意义。     

Restocking a keystone species in a biodiversity hotspot: Recovering the European rabbit on a landscape scale

Rabbit populations in Iberia remain at low densities in several areas in which their endangered predators still coexist, and the recovery of these populations is therefore urgent if the integrity of Iberian Mediterranean ecosystems is to be maintained. The enhancement of wild rabbit populations has been attempted through the use of in situ extensive rabbit captive breeding enclosures (restocking plots), which reduce mortality caused by terrestrial predators and dispersal movements and permit the breeding of young individuals which can then naturally disperse to settle in the surrounding areas. However, their effectiveness, the role of its size, the optimal habitat management that should be promoted around them and the habitat features remains uncertain. Here, we show results from a four year study of an ambitious rabbit restocking plan on a landscape scale. We measured rabbit abundance in a vast area in which thirty-two restocking plots were built to create an initial rabbit population for further dispersion, in addition to an intensive habitat management program. We also compared rabbit abundance between managed and unmanaged UTM cells of 2.5 km × 2.5 km. Our results showed that rabbit abundance was three times higher in managed cells, but four years after restocking, rabbit abundances had only reached the threshold needed to support stable Iberian lynx presence (at least 10 latrines per km^?1) in 9 of the 23 managed cells. Rabbit abundance was strongly affected by habitat treatment and scrub coverage. The increase of shelter was useful in low cover areas but ineligible in places with high scrub cover, where the increase of refuge plus scrub clearing to create pastures improve rabbit abundance more effectively. In the light of our results, restocking plots should be built only in places with suitable habitat, whereas pastures should be created in dense scrublands and refuge in low cover areas.     

The Effect of Habitat Fragmentation on Cyclic Population Dynamics: A Numerical Study

Through four spatially explicit models, we investigate how habitat fragmentation affects cyclic predator–prey population dynamics. We use a Partial Differential Equation (PDE) framework to describe the dispersal of predators and prey in a heterogeneous landscape made of high quality and low quality habitat patches, subject to increasing fragmentation through habitat separation and/or habitat loss. Our results show that habitat fragmentation decreases the amplitude of the predator–prey population cycles while average population density is not as strongly affected in general. Beyond these simple trends however, the four models show differing responses to fragmentation, indicating that when making predictions about population survival and persistence in the face of habitat fragmentation, the choice of model is important. Our results may inform conservation efforts in fragmented habitats for cyclic species such as the snowshoe hare and Canada lynx. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorised users.     

粪样在野生动物研究中的作用

野生动物数量少,取样难度大;在野外工作时,动物肌肉和血液样品还难以保存。这些给野生动物研究带来很大不便。由于动物粪样容易收集,易于保存,对动物的影响小,在野生动物研究中得到了广泛的应用。粪样分析已经应用在动物的领域、食性、消化动态、疾病与寄生虫、种群数量和遗传结构、有效种群大小、食物链与食物网、能量流与物质流的研究等方面。研究证明,在野生动物的研究和保护中,通过粪样可以得到许多关键性问题的答案。     

On moment closures for population dynamics in continuous space

A first-order moment closure, the mean-field assumption that organisms encounter one another in proportion to their spatial average densities, lies at the heart of much theoretical ecology. This assumption ignores all spatial information and, at the very least, needs to be replaced by a second-order closure to gain understanding of ecological dynamics in spatially structured populations. We describe a number of conditions that a second-order closure should satisfy and use these conditions to evaluate some closures currently available in the literature. Two conditions are particularly helpful in discriminating among the alternatives: that the closure should be positive, and that the dynamics should be unaltered when identical individuals are given different labels. On this basis, a class of closures we refer to as 'power-2' turns out to provide a good compromise between positivity and dynamical invariance under relabelling.     

Variation in predation pressure as a mechanism underlying differences in numerical abundance between populations of the poeciliid fish Heterandria formosa

We explored whether a variation in predation and habitat complexity between conspecific populations can drive qualitatively different numerical dynamics in those populations. We considered two disjunct populations of the least killifish, Heterandria formosa, that exhibit long-term differences in density, top fish predator species, and dominant aquatic vegetation. Monthly censuses over a 3-year period found that in the higher density population, changes in H. formosa density exhibited a strong negative autocorrelation structure: increases (decreases) at one census tended to be followed by decreases (increases) at the next one. However, no such correlation was present in the lower density population. Monthly census data also revealed that predators, especially Lepomis sp., were considerably more abundant at the site with lower H. formosa densities. Experimental studies showed that the predation by Lepomis gulosus occurred at a much higher rate than predation by two other fish and two dragonfly species, although L. gulosus and L. punctatus had similar predation rates when the amount of vegetative cover was high. The most effective predator, L. gulosus, did not discriminate among life stages (males, females, and juveniles) of H. formosa. Increased predation rates by L. gulosus could keep H. formosa low in one population, thereby eliminating strong negative density-dependent regulation. In support of this, changes in H. formosa density were positively correlated with changes in vegetative cover for the population with a history of lower density, but not for the population with a history of higher density. Our results are consistent with the hypothesis that the observed differences among natural populations in numerical abundance and dynamics are caused in part by the differences in habitat complexity and the predator community.     

A participatory counting method to monitor populations of large mammals in non-protected areas: a case study of bicycle counts in the Zambezi Valley, Zimbabwe

The sustainable use of wildlife resources within community-based programmes is considered as a valuable option to enhance development and conservation objectives. The application of such a concept in communal lands requires the strong support of local communities through their active involvement in wildlife management. Precise and regular information on wildlife abundance is also essential for effective conservation. In this paper, we present an innovative participatory monitoring method based on bicycle counts developed within the framework of an integrated conservation and development project in the Zambezi Valley, Zimbabwe. Results from the 1999 count of population density and structure of common species as well as diversity of large to medium size species are presented. We demonstrate the efficiency of this method, which allowed a high census intensity with efficient animal detection, and hence appeared appropriate for use in a non-protected area. The method gave high levels of precision for the density estimates obtained (10–30% cv) and is therefore useful as a repeatable monitoring tool. In addition, this method is inexpensive to run and is easy to implement for local people. We emphasise the technical and financial autonomy offered by the bicycle counts for communities to monitor their wildlife resources, and we discuss the contribution of this method to the wildlife management process.     

The impact of diffusion and stirring on the dynamics of interacting populations

We investigate the combined effects of diffusion and stirring on the dynamics of interacting populations which have spatial structure. Specifically we consider the marine phytoplankton and zooplankton populations, and model them as an excitable medium. The results are applicable to other biological and chemical systems. Under certain conditions the combination of diffusion and stirring is found to enhance the excitability, and hence population growth of the system. Diffusion is found to play an important role: too much and initial perturbations are smoothed away, too little and insufficient mixing takes place before the reaction is over. A key time-scale is the mix-down time, the time it takes for the spatial scale of a population to be reduced to that of a diffusively controlled filament. If the mix-down time is short compared to the reaction time-scale, then excitation of the system is suppressed. For intermediate values of the mix-down time the peak population can attain values many times that of a population without spatial structure. We highlight the importance of the spatial scale of the initial disturbance to the system.     

Downscaling indicators of forest habitat structure from national assessments

Downscaling is an important problem because consistent large-area assessments of forest habitat structure, while feasible, are only feasible when using relatively coarse data and indicators. Techniques are needed to enable more detailed and local interpretations of the national statistics. Using the results of national assessments from land-cover maps, this paper demonstrates downscaling in the spatial domain, and in the domain of the habitat model. A moving window device was used to measure structure (habitat amount and connectivity), and those indicators were then analyzed and combined with other information in various ways to illustrate downscaling.     

Regional persistence of an endemic plant, Erigeron acer subsp. decoloratus, in disturbed riparian habitats

Regional persistence of species requires a positive balance between colonizations and local extinctions. In this study, we examined the amount of colonizations and extinctions and their likelihood as a function of patch size, isolation, and habitat characteristics of a riparian perennial plant, Erigeron acer subsp. decoloratus. We also studied the importance of patch dynamics to the regional population growth. Over five successive years, we counted the number of plant patches along 43 km of riverside. Most patches were small in area and population size. The annual finite growth rate in the number of patches varied between years, but the geometric mean was close to 1.0, indicating a viable patch network in spite of local extinctions. Extinction rate was highest on steep slopes and for small patches with few individual plants and a small patch area. When the patches were classified into different stage classes, the most common fate was stasis, i.e., the patch remained at the same stage. Patch survival and local, within-patch dynamics were most important during this five-year period. Between-patch dynamics (including colonization for example) accounted for 5–10% of annual transitions. The overall dynamics were relatively similar to those of other plant species subjected to riparian disturbance regimes. In the long run, the survival of the species depends on how well it is able to escape from competition from forest and meadow species and track the availability of suitable habitats. This kind of habitat tracking differs from classical metapopulation dynamics. In the former, local extinctions occur as a consequence of adverse changes in the habitat and recolonizations are rare, whereas metapopulation models assume a highly persistent habitat structure with frequent recolonizations. In this respect, the regional dynamics of perennial plants in disturbed riparian habitats may differ from classical metapopulations.     

High-density populations of diamondback moth have broader host-plant diets

Although ecological specialists exploit a relatively limited resource base, it is unclear whether specialization limits local population density. Here, we focus on the relationship between diet specialization and local population density of a phytophagous insect, the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae). We compared key life history traits and food plant use among five pairs of high- and low-density populations from widely separate geographical areas. Moths from populations that persist at high densities were more generalized in food plant use than moths from low-density populations. In particular, the oviposition preference and larval performance of moths from some high-density populations were less variable across a suite of food plants, suggesting that moths from high- density populations had a broader diet. In addition, low- density populations were less similar to each other, exhibiting opposing preferences for particular plant species. Hence diet breadth may explain some of the persistent differences in the population density of diamondback moths in the field, consistent with the idea that ecological specialization may be generally associated with population density. Received: 19 December 1996 / Accepted: 2 May 1997     

Species Survival in Fragmented Landscapes: Where are We Now?

We present a brief introduction to current attempts to understand and mitigate the effects of fragmentation on species survival. We provide a short overview of the contributions of empiricists, modellers, and practitioners in this issue of Biodiversity and Conservation, which were initiated during a workshop held in Australia in February 2002 on the topic ‘Species Survival in Fragmented Landscapes: Where are we now?’. These contributions address the themes ‘uncertainty in research and management’, ‘tools for quantifying risk and predicting species sensitivity to fragmentation’, and ‘tools for reassembling fragmented landscapes’. A final contribution provides a synthesis across the contributions and highlights the most important areas for future research on species survival in fragmented landscapes.     

三峡大坝下游残存疏花水柏枝种群结构和动态

在三峡大坝下游的湖北宜都关洲设立1个40 m×40 m的固定样地,利用高度分级,比较2008与2009年两年间的疏花水柏枝（Myricaria laxiflora）种群数量动态,并运用点格局的Ripley＇s K函数分析了其空间格局变化及种群更新特征。结果表明,疏花水柏枝幼苗数量较少,种群更新存在一些障碍。空间分布格局与空间尺度及植株的大小密切相关。种群总体呈集群分布,各大小级多在9 m时出现最大的聚集强度,随着大小级的增加,聚集强度有减弱的趋势。幼苗与中株有较强的正关联。由于种群现有生境变化较大,应考虑迁地保护,并对原生种群加强长期动态监测;同时,开展疏花水柏枝适应机理研究,实施科学保护。     

Viability and Management of an Endangered Capercaillie (Tetrao urogallus) Metapopulation in the Jura Mountains, Western Switzerland

The populations of Capercaillie (Tetrao urogallus), the largest European grouse, have seriously declined during the last century over most of their distribution in western and central Europe. In the Jura mountains, the relict population is now isolated and critically endangered (about 500 breeding adults). We developed a simulation software (TetrasPool) that accounts for age and spatial structure as well as stochastic processes, to perform a viability analysis and explore management scenarios for this population, capitalizing on a 24 years-long series of field data. Simulations predict a marked decline and a significant extinction risk over the next century, largely due to environmental and demographic stochasticity (average values of life-history parameters would otherwise allow stability). Variances among scenarios mainly stem from uncertainties about the shape and intensity of density dependence. Uncertainty analyses suggest to focus conservation efforts on enhancing, not only adult survival (as often advocated for long-lived species), but also recruitment. The juvenile stage matters when local populations undergo extinctions, because it ensures connectivity and recolonization. Besides limiting human perturbations, a silvicultural strategy aimed at opening forest structure should improve the quality and surface of available patches, independent of their size and localization. Such measures are to be taken urgently, if the population is to be saved.     

Large-scale forest fragmentation increases the duration of tent caterpillar outbreak

I examined historical data (1950–1984) on the duration of outbreaks of the forest tent caterpillar (Malacosoma disstria) in northern Ontario, Canada. Outbreak duration was compared to host tree species dominance and forest structure over large areas of boreal forest partially cleared for agriculture. Abundance of the principal host tree species Populus tremuloides had no consistent effect on duration of outbreak within forest districts, and was negatively correlated with duration of outbreaks among the eight forest districts examined. The amount of forest edge per km² was the best, and most consistent, predictor of the duration of tent caterpillar outbreaks both within individual forest districts and among forest districts. Because forest tent caterpillar populations are driven largely by the impact of parasitoids and pathogens, results here suggest that large-scale increase in forest fragmentation affects the interaction between these natural enemies and forest tent caterpillar. Increased clearing and fragmentation of boreal forests, by agriculture and forestry, may be exacerbating outbreaks of this forest defoliator.