• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 127
  • 59
  • 15
  • 12
  • 5
  • 4
  • 3
  • 2
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 272
  • 272
  • 73
  • 63
  • 46
  • 45
  • 43
  • 43
  • 39
  • 37
  • 37
  • 34
  • 32
  • 31
  • 29
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
81

Växtartrikedomens svar på restaurering av hävdade gräsmarker : En litteraturstudie / The Response of Plant Species Richness on Restoration of Semi-natural Grasslands : A Review

Bergström, Elin January 2021 (has links)
En av de naturtyper med flest antal växtarter i världen är hävdade gräsmarker som är präglade av traditionell skötsel. Denna naturtyp har minskat kraftigt i area och för att förhindra framtida artutdöenden är restaureringsåtgärder viktiga. Syftet med denna rapport var att med hjälp av vetenskapliga publikationer undersöka vilken effekt restaurering av före detta hävdade gräsmarker i norra och centrala Europa har på växtartrikedomen. Mer specifikt undersöktes effekten av olika restaureringsmetoder på totala antalet arter, arttätheten och artsammansättningen. Utöver detta undersöktes vilka faktorer som påverkar möjligheten till restaurering. Resultatet tyder på att restaurering med bete eller slåtter är mest framgångsrik av de olika undersökta metoderna. Restaurering med bete eller slåtter visade sig kunna ha en positiv effekt på totala antalet arter, arttätheten och artsammansättningen. Enbart rensning av träd och buskar var inte en långsiktigt hållbar metod för restaurering eller bevarandet av artrikedomen eller arter associerade med hävdade gräsmarker. Det finns många faktorer som påverkar möjligheten till restaurering och alla är inte entydiga. Något som kan vara intressant att vidare utforska är vilken betydelse de olika artrikedomsmåtten och artsammansättningen har för att kunna optimera restaureringsprojekt. Förutom att restaurering av hävdade gräsmarker både kan bidra till att utöka Natura 2000-nätverket och uppfylla de globala målen, ger det oss mängder med ekosystemtjänster och bevarande av kulturlandskap.
82

Predicting biodiverse semi-natural grasslands through satellite imagery and machine learning

Baggström, Adrian January 2021 (has links)
Semi-natural grasslands are amongst the most biodiverse ecosystems in Europe, though their importance they are experiencing a declining trend. To monitor and assess the health of these ecosystems is generally costly, personnel demanding and time-consuming. With satellite imagery and machine learning becoming more accessible, this can offer a cheap and effective way to gain ecological information about semi-natural grasslands.This thesis explores the possibilities to predict plant species richness in semi-natural grasslands with high resolution satellite imagery through machine learning. Five different machine learning models were employed with various subsets of spectral- and geographical features to see how they performed and why. The study area was in southern Sweden with satellite and survey data from the summer of 2019.Geographical features were the features that influenced the machine learning models most. This can be explained by the geographical spread of the semi-natural grasslands, as well as difficulties in finding correlations in the relatively noisy satellite data. The most important spectral features were found in the red edge- and the short-wave infrared spectrums. These spectrums represent leaf chlorophyll content and water content in vegetation, respectively. The most accurate machine learning model was Random Forest when it was trained using with all the spectral- and geographical features. The other models; Logistic Regression, Support Vector Machine, Voting Classifier and Neural Network, showed general inabilities to interpret feature subsets containing the spectral data.This thesis shows that with deeper knowledge about the satellite-biodiversity relationship and how to apply it with machine learning have the possibilities of cheaper, more efficient and standardized monitoring of ecologically valuable areas such as semi-natural grasslands.
83

Species Richness of Soil and Leaf Litter Tardigrades in the Great Smoky Mountains National Park (North Carolina/Tennessee, USA)

Nelson, Diane R., Bartels, Paul J. 02 August 2013 (has links)
A large database now exists for tardigrades in the Great Smoky Mountains National Park (GSMNP) consisting of 780 samples, 15,618 specimens, and 80 species including 14 new to science. We found 43 species of tardigrades in 150 soil/leaf litter samples. We calculated the Chao 1 species richness estimate with the species accumulation curve for the GSMNP and confirmed that our species list is virtually complete. Compared with soil data from mt. Fuji, Japan, estimated species richness in GSMNP was significantly higher. In our comparison of previous studies of soil/leaf litter tardigrades in other geographic areas, only the Kanagawa prefecture of Japan reported a higher number of species (47) than the GSMNP. Species richness estimators are valuable tools for comparing diversity in different habitats, even when sampling effort varies between studies.
84

Species Richness of Soil and Leaf Litter Tardigrades in the Great Smoky Mountains National Park (North Carolina/Tennessee, USA)

Nelson, Diane R., Bartels, Paul J. 02 August 2013 (has links)
A large database now exists for tardigrades in the Great Smoky Mountains National Park (GSMNP) consisting of 780 samples, 15,618 specimens, and 80 species including 14 new to science. We found 43 species of tardigrades in 150 soil/leaf litter samples. We calculated the Chao 1 species richness estimate with the species accumulation curve for the GSMNP and confirmed that our species list is virtually complete. Compared with soil data from mt. Fuji, Japan, estimated species richness in GSMNP was significantly higher. In our comparison of previous studies of soil/leaf litter tardigrades in other geographic areas, only the Kanagawa prefecture of Japan reported a higher number of species (47) than the GSMNP. Species richness estimators are valuable tools for comparing diversity in different habitats, even when sampling effort varies between studies.
85

A Global Biodiversity Estimate of a Poorly Known Taxon: phylum Tardigrada

Bartels, Paul J., Apodaca, J. J., Mora, Camilo, Nelson, Diane R. 01 December 2016 (has links)
Although many estimates of species numbers have been attempted using various techniques, many smaller phyla remain poorly known without such estimates. For most of these it is unclear if they are species-poor or just poorly studied. The phylum Tardigrada is one of these phyla. Specialists have created a regularly updated checklist for the known tardigrade species, which as of 15 July 2013 listed 1190 taxa (species and subspecies). Of these, 1008 are limnoterrestrial and 182 are marine. These were the most up-to-date data at the time of our analysis. As species accumulation curves show little sign of levelling out, they do not provide a useful tool for estimating global tardigrade diversity from existing species numbers. A new technique has recently been developed that uses the more complete knowledge of higher taxonomic levels to estimate the asymptotic number of species. We applied this technique to limnoterrestrial and marine tardigrades. We estimate that the global total for limnoterrestrial tardigrades is 1145 (upper 95% CI = 2101), and the global total for marine tardigrades is 936 (upper 95% CI = 1803). This yields 87% completeness for our knowledge of limnoterrestrial tardigrades, and only 19% completeness for our knowledge of marine tardigrades. Thus, although many more marine species remain to be discovered, it appears that tardigrades are both poorly studied and relatively species poor.
86

A Large-Scale, Multihabitat Inventory of the Phylum Tardigrada in the Great Smoky Mountains National Park, USA: A Preliminary Report

Bartels, Paul, Nelson, Diane R. 01 March 2006 (has links)
An All Taxa Biodiversity Inventory (ATBI) is underway in the Great Smoky Mountains National Park (GSMNP), with the goal of attempting to identify all species of life in the 2000 km2 park. The GSMNP is a hotbed of biodiversity, a U.N. Biosphere Reserve, and one of the largest protected, deciduous forests in the temperate world. We have completed two field seasons of work on the tardigrades in the park (2001-2002). As of July 2003, we have collected 420 samples from soil/decomposed leaf litter, lichens and mosses on trees, and stream sediment and periphyton. A few samples from caves, bird nests, and lichens/mosses on rocks were also collected. Samples were taken from within permanent plots established for the ATBI, representing the major biological communities of the GSMNP. Tardigrades were extracted from samples using centrifugation with Ludox AM™, individually mounted on microscope slides in Hoyer's medium, and studied with phase contrast and DIC microscopy. We have examined 1524 slides from 60 samples as of July 2003. Prior to our work, only three species of tardigrades had been previously reported from a few samples in the park. We have now recorded 42 species, 8 of which we believe may be new to science. Species richness estimates were calculated using EstimateS 6 software for each of the major tardigrade habitats. Overall, we predict that there are 47 to 76 species in the GSMNP, with generally similar species richness in soil, lichen, moss, and stream habitats. Species richness estimates were also used to determine that the number of tardigrade species was greater in mosses at breast height on trees than in mosses at the base of trees.
87

The relationship of endoparasite diversity and feeding ecology in the seabird complex of South Florida

Nakama, Michael 06 December 2018 (has links)
Endoparasite community structure has been poorly studied in migratory birds, particularly among the seabirds of south Florida. We examined parasite communities in seven south Florida seabird species: brown pelican Pelecanus occidentalis (n=33), northern gannet Morus bassanus (n=31), double-crested cormorant Phalacrocorax auritus (n=33), osprey Pandion haliaetus (n=27), royal tern Thalasseus maximus (n=30), herring gull Larus argentatus (n=12), and laughing gull Leucophaeus atricilla (n=40). We identified 33 parasitic helminth species: 6 nematodes, 2 cestodes, 3 acanthocephalans, and 22 digeneans. Subsequent pairwise tests and similarity profile analysis identified four distinct clusters with similar parasite community structures: (1) pelican and gannet; (2) cormorant; (3) osprey; and (4) tern and both gull species. The mean infracommunity observed species richness differed among the several seabird host species with the highest observed values in pelicans (5.7±0.4) and gannets (5.1±0.4), while the lowest values were seen in herring (0.8±0.7) and laughing (0.4±0.4) gulls. RELATE analyses indicated that the factors of host phylogeny (Rho=0.564, p=0.017), host feeding range (Rho=0.553, p=0.005), and host feeding technique (Rho=0.553, p=0.039) were significant and had similar magnitudes of effect on the structure of observed parasite communities within the several seabird species of this study. Host prey preference was not significant from the RELATE analyses (Rho=0.124, p=0.278), suggesting that preferred prey items of the several seabird hosts had a negligible impact in the structuring of parasite communities. From our results, host phylogeny and host feeding ecology are important driving factors of parasite community composition and structure of these south Florida seabirds, while host prey preference had little influence on parasite communities.
88

An Inventory of Terrestrial Vertebrates in Aldesa Valley and Estimating Factors that affect Avian Species Richness and Occurrence

Alatawi, Abdulaziz Subhi 07 May 2016 (has links)
Conducting species inventories is important to provide baseline information essential for management and conservation. Furthermore, understanding the effects of anthropogenic and environmental factors on species richness and occurrence are crucial to conserve species. Aldesa Valley lies in the Tabuk Region of Saudi Arabia, and because of the presence of permanent water and vegetation, is thought to contain high biodiversity. I estimated avian species richness and occurrence in Aldesa Valley during May 10–August 10 in 2014 and 2015 to detect bird species richness and occurrence. I used generalized linear models and occupancy models for six commonly detected bird species. I recorded 24 bird species, and found that species richness and occupancy was affected by numerous anthropogenic and environmental factors that influenced species detection and presence. I encourage more biological inventories to further document species occurrences and facilitate conservation of the unique species assemblages in Aldesa Valley.
89

Spillningslevande bladhorningar (Scarabaeoidea) kring Varbergs kustslätt, en återinventering

Malmström, Klara January 2022 (has links)
Dyngbaggar tillhör en av de mest studerade insektsgrupperna inom ekologiska undersökningar på grund av deras förekomst i ett spritt förekommande habitat som spillning. Förekomsten av denna grupp skalbaggar har präglats av det kulturhistoriska brukandet av marker som under en längre tid hävdats genom bete med domesticerade djur på marker av olika karaktär. Idag är dessa habitat sparsamt förekommande i ett landskap präglat av fragmentation och förändrad markanvändning vilket ställer betesberoende populationers överlevnad på prov. För att kartlägga vilken påverkan dessa landskapsförändringar har på insektsfaunan är långsiktig miljöövervakning av stor vikt för att bromsa oåterkalleliga förluster. Syftet med den här studien är att undersöka dyngbaggefaunans artsammansättning och individtäthet under vår-och högsommar på tidigare inventerade lokaler 1997 i utkanten av Varberg i mellersta Hallands län. Sedan 1997 har den totala diversiteten ökat med fem tillkomna arter på de fem undersökta lokalerna där ingen art har försvunnit helt. Det fanns ingen statistisk skillnad mellan art- och individantal men artsammansättningen skilde sig på lokalerna där vissa har ökat i antal, tillkommit eller blivit färre. Detta visar på en potentiellt positiv trend men fortgående övervakning krävs för att detta skall bekräftas. De förändringar som har skett i betesmarkernas lokala klimat avspeglar förändringar i artsammansättningen på grund av att betestrycket blivit lägre, marker har betats över längre tid samt restaureringar som har lett till en positiv utveckling. Lokalerna har blivit mer distinkta och skiljer sig både från varandra och hur de såg ut 1997 vilket skapat en större artrikedom. För en gynnsam bevarandestatus krävs en variation av mikroklimat för att även de habitat-specifika arterna ska ha möjlighet att etablera sig.
90

The Impact of Human Presence on Terrestrial Mammals in Secondary Regenerating Forest of the Peruvian Amazon

Pandya, Duncan January 2023 (has links)
Human disturbance is becoming an ever-bigger threat to biodiversity across the globe and should continue to be a field of conservation priority. Urbanisation, research and tourism put unavoidable pressure on the surrounding flora and fauna, therefore we need to gain knowledge on how to reduce future harm. Here we investigated the effects of human presence on medium-large terrestrial mammals in the south-eastern Peruvian Amazon, using camera traps to measure the number of human and mammal observations at varying distances from our research centre and the hiking trails. Species richness and the Shannon and Inverse Simpson diversity indices were also calculated during the four-month study period. Nineteen species were detected across fourteen camera sites. Distance from camp was positively correlated with species richness and the diversity indices, but showed no correlation with total mammal observations. Distance from nearest trail was negatively correlated with species richness, total mammal observations and the diversity indices. Total human observations was negatively correlated with species richness and the diversity indices, but had no impact on total mammal observations. Nevertheless, these results often had high p-values and low sample size and therefore should be interpreted with caution. Omnivores were the most sensitive trophic guild, showing a statistically significant negative correlation with total human observations, and a statistically significant positive correlation with distance from nearest trail. It is important then to assess these responses to human disturbance at the community and species level, as to truly understand the impact we are having.

Page generated in 0.0622 seconds