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The ecological consequences of homogenization remain relatively unexplored. One example of landscape-homogenizing is the establishment
of plantations. We studied the effect of human-made forests by contrasting plant and small-mammal community composition between
planted tree stands and adjacent natural habitat in two different Mediterranean habitats in Israel: (1) inland habitat where
we focused on pine (Pinus halepensis) and carob (Ceratonia siliqua) stands, and (2) coastal sand dune habitat where we focused on planted acacia (Acacia saligna) stands. We first wanted to verify whether planted trees modify plant species composition, and second, if and how the small-mammal
community is affected by the different habitat conditions created in plantations with different canopy cover. We were especially
interested in the abundance of the commensal house mouse (Mus musculus). All tree stands underwent biotic homogenization indicated by abundance of house mice coupled with lower diversity of indigenous
vegetation and small-mammal abundances and diversities. Habitat structural diversity was positively related with small-mammals
diversity and was lower in artificial tree stands in both habitats. Our results suggest that using the abundance of commensal
generalist species such as the house mouse relative to other more specialist small-mammals is a good approach to determine
ecosystem integrity. Pre-commercial thinning treatment is a potential management tool to maintain a proportion of native tree
species within the canopy of planted tree stands. However, until sufficient data is available for making generalizations,
the exact level of thinning necessary to reverse the homogenization processes in man-made plantations and keeping indigenous
small-mammal communities diverse and less prone to invasion must be determined empirically. 相似文献
64.
Integrative analyses of genetic variation in enzyme activities of primary carbohydrate metabolism reveal distinct modes of regulation in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> 下载免费PDF全文
65.
Density dependent habitat selection at the community level is regarded as a major determinant of biodiversity at the local
scale, and data on these processes and how they are affected by human activities is highly applicable to conservation. By
studying the competitive relationships between a specialist and a generalist we can acquire valuable insights about how different
environmental elements determine species abundance and distribution and consequently biodiversity. Here we describe a study
of density dependent processes that determine the community structure of two rodents: a specialist—the broad toothed mouse
(Apodemus mystacinus), and a generalist—the common spiny mouse (Acomys cahirinus) in a Mediterranean maqui habitat, and how this structure is impacted by anthropogenic planting of pine stands. We carried
out two field experiments: The first, based on open field trapping, looking at how rodent communities change with habitat
structure. The second experiment was an enclosure study aimed at validating the habitat preferences and competitive relationship
between the specialist and the generalist. We identified asymmetric competition relationships in which the specialist was
dominant over the generalist. Competition intensity was lower in maqui with >10% oak cover, although both species abundances
were high. Competition was found only during the limiting season (summer). Based on these findings we produced management
recommendations to keep indigenous small mammals’ biodiversity high. Density dependent habitat selection processes play a
central role in determining biodiversity, and understanding the mechanisms motivating these processes is needed if alterations
in biodiversity in response to human disturbance are to be understood. 相似文献
66.
Kutryk MJ Wardeh AJ Knook AH Foley DP Giessen WJ Hamburger JN Brand Mv Feyter PJ Becker GJ Serruys PW 《International journal of cardiovascular interventions》1999,2(3):163-169
BACKGROUND: Coronary stents have been used with increasing frequency and in increasingly complex coronary disease. A new 316 LVM stainless steel coronary stent, the R Stent, has been designed to provide maximum flexibility for tracking and high radial strength post-deployment. PURPOSE: To assess the clinical feasibility of the R Stent in a tertiary referral population of patients with coronary heart disease. Specific objectives are to assess the R Stent's deployment success, angiographic and procedural success (<20% residual stenosis and >TIMI 2 flow), safety (absence of complications), and 30-day clinical success (angiographic/procedural success plus no major adverse coronary events). METHODS: Between April and November 1998, stent deployment was attempted in 27 patients with stable (46%) or unstable (54%) angina pectoris who qualified for percutaneous transluminal coronary angioplasty. Eighty per cent of patients had a pre-existing history of myocardial infarction, coronary bypass surgery or percutaneous transluminal coronary angioplasty, and several of the lesions were anatomically complex (totally occluded, n 32; thrombus present, n 32; heavily calcified, n 33; ostial, n 31; >20 mm long, n 39; angulation >45 degrees, n 37). Lesions in aortocoronary saphenous vein grafts were excluded. Adjunctive medical management included intraprocedural aspirin and heparin and post-procedural aspirin and ticlopidine. After deployment, patients were followed up in the hospital and at 30 days post procedure. RESULTS: Stent deployment was achieved in 32 of 33 attempts (26 of 27 patients). There was one deployment failure in a long, calcified ostial and proximal left coronary lesion. In the 26 successful deployments, TIMI 3 flow was achieved. One other patient experienced a painless increase in creatine kinase to 375 (CK-MB of 59) at 12 h without ECG changes. At 30 days, there were no deaths, no myocardial infarctions, no subacute thromboses, no repeat interventions, no bypass surgeries and no bleeding complications. Only the patient with post-procedural CK-MB elevation experience recurrence of CCS class 2 angina within the 30 days. CONCLUSION: The R Stent is a promising new device for the treatment of complex coronary heart disease. A larger, more broadly-based study is warranted. 相似文献
67.
We consider three case studies of long-term plant population dynamics in Makhtesh Ramon erosion cirque in the central Negev desert of Israel. We show that rainfall is the major driving variable in this system, and that it creates large temporal and spatial variation in plant species diversity and vegetation community composition. This variability makes it extremely difficult to distinguish `signal' (= pattern in vegetation) from `noise' (random spatial and temporal variance). Our long-term vegetation studies in permanent plots arranged along the length of the cirque, initiated in 1990 and continuing, show that there is high spatial and temporal variance in plant species' incidences and abundances. This is particularly true of annual plant species. However, using pairs of fenced and unfenced plots arranged along the major abiotic gradient, altitude (which mirrors changes in rainfall), we were able to tease apart the effects of variance in rainfall and herbivory. We found significant negative effects of herbivory by the re-introduced Asiatic wild ass (Equus hemionus) on plant cover and on vegetation community composition. In a study of the effects of herbivory by dorcas gazelles (Gazella dorcas) on the lily Pancratium sickenbergeri, we found that there was little inter-annual fluctuation in lily population size in two sand dunes in Makhtesh Ramon in spite of the high percentage of lilies that is removed by the gazelles and the almost complete herbivory of flowers by these herbivores. This result indicates that the dune lily populations may be maintained by dispersal of seed from other lily populations elsewhere in Makhtesh Ramon where gazelles are rare or absent. 相似文献
68.
Abstract. Asiatic wild asses, Equus hemionus, were driven to extinction in Israel in the early 20th century. In 1983, a herd of these animals was re-introduced to the wild in Makhtesh Ramon, a large erosion cirque in the central Negev desert, Israel. The population has grown steadily ever since and now numbers some 100 animals. In order to determine whether the wild asses are having a significant impact on the vegetation, we have monitored the plant communities in Makhtesh Ramon since 1992, using McAuliffe's log-series survey method. Our study involves 11 pairs of plots along the length of the altitudinal gradient in Makhtesh Ramon. The altitudinal gradient results in a rainfall gradient from an average of 95 mm rain per year to an average of about 40 mm per year. Each pair of plots consists of: (1) an unfenced plot, and (2) a fenced plot that excludes wild asses but not the other large mammalian herbivore, the dorcas gazelle Gazella dorcas. The wild asses have not had a significant impact on vegetation cover, species richness, diversity or dominance. Three plant species showed significant increases in percentage cover in fenced plots, while one species showed a significant increase in percentage cover in unfenced plots. Furthermore, eight plant species invaded fenced plots, three species invaded unfenced plots and one species disappeared from unfenced plots during the study. Using Detrended Correspondence Analysis, we found that the major differences among plots are due to position along the altitudinal gradient. The Detrended Correspondence Analyses indicated that the wild asses have had no significant effect on vegetation community structure. 相似文献
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