Call number: LD2668 .T4 1979 R617 / Master of Science

Land use is the major global driver of biodiversity loss and ecosystem change. In this thesis the impact of an important land use practice, livestock grazing, in the population dynamics of a keystone species of temperate grassland ecosystems, the field vole Microtus agrestis, was investigated in a manipulative grazing experiment in the UK uplands. Vole densities at different spatial scales declined with increasing grazing intensities. This decline was especially acute and non-linear at high altitudes, where the preferred habitat of voles is less abundant. The activity of an important vole predator, the red fox Vulpes vulpes, declined accordingly. The evidence suggested that the availability of voles to foxes changed between grazing treatments. A behavioural response to reduced habitat quality was the most likely mechanism to explain vole declines with grazing, while food limitation or increased predation received no support as valid mechanisms to explain vole declines. Grazing increased vole mobility, changed sex-specific patterns of natal dispersal, affected the age structure of the female population and led to biases in sex ratios amongst the adult population. Despite profound demographic changes, the dynamics of the vole population was unaffected by grazing. Neither direct nor delayed density dependent dynamics nor seasonal dynamics changed between grazing treatments. Apparent survival in adults was not direct density dependent and similar in ungrazed and grazed areas. Negative direct density dependence in reproductive and immigration rates, and population growth rates at different spatial scales was strong and did not change in response to grazing. Thus, livestock grazing reduced vole densities probably through a behavioural response to grazing, but it did not affect the demographic mechanisms of population regulation or vole population dynamics.

Theoretical studies have proposed that a critical threshold occurs below which a small change in the amount of habitat can cause an abrupt change in population persistence.  I tested the threshold concept using field voles (<i>Microtus agrestis</i>), their predator, the common weasel (<i>Mustela nivalis vulgaris</i>), and their ecto-parasites in a highly fragmented agro-ecosystem. I found strong support for a threshold in margin width, below which vole abundance was extremely low.  I also revealed that changes in the demography and behaviour of vole populations occurred in relation to the detected thresholds.  However, despite these responses, no effect was observed on their survival.  I found no evidence of a threshold response in either predator activity or parasite prevalence in relation to either prey/host abundance or habitat size.  Weasels may have been able to compensate for low vole abundances by consuming other rodents or by moving to areas with higher prey abundances.  The lack of any detectable effect of habitat loss on weasel activity may therefore be related to the scale of this study relative to their home range and their degree of diet specialisation.  The ecto-parasites observed infested all seven of the small mammal species trapped.  The high level of transiency and movement within this multi-host system may have facilitated the spread of parasites between margins.  The susceptibility of predators and parasites to habitat loss due to their trophic position may therefore have been offset by the high vagility of predators and the capability of both predators and parasites to predate/parasitise a range of host species.

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains ix, 114 p. : ill. (some col.), map. Includes abstract. Includes bibliographical references (p. 92-107).

Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Mar. 26, 2010). Includes bibliographical references.

Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Mar. 30, 2010). Includes bibliographical references.

No description available.

Evaluation of aerial photographs, LiDAR imagery and GPS survey points was conducted to characterise water vole habitat at Grains in the Water and Swains Greave, in the Peak District. Justification for the study is to explore an affective way to monitor water vole habitat in relation to water vole signs utilising GIS. The water vole is a rapidly declining native species (Strachan and Strachan, 2003). The geospatial data was evaluated in terms of integration and extraction. The aerial photography provided a basis for vegetation mapping after visual interpretation. The aerial photograph required geometric correction and an average control point RMSE of 4.17m for the Grains in the Water site, using a 2nd order polynomial model was achieved. Extraction of slope, aspect, stream proximity and elevation were achieved using LiDAR imagery. Pearson’s product moment correlation coefficient highlighted a significant relationship between water vole latrine density with slope at the 0.01 significance level for 4m and 6m resolution data (Grains in the Water). The Swains Greave site supported this result with a 0.01 significance level for 6m resolution slope data. Elevation and aspect did not show a significant correlation with latrine density at Grains in the Water. The main conclusion is that water vole habitat cannot be solely characterised by aerial photography and LiDAR data, as other habitat variables could affect water vole distributions, which cannot be extracted from these geospatial data e.g. pH, bank exposure and stream depth.

The phenotype dynamics of arvicolid rodents during the terminal stages of the Vistualian glacial and the earliest Holocene was investigated with aid of a detailed morphometric analyses of extensive dental material from three sedimentary series of that age. The particular attention was paid to the record from a section in Býčí skála cave, Moravian karst, which demonstrated details of the Pleistocene/Holocene transition (12.4-8.4 ky BP) with extraordinary resolution. It revealed that dramatic rearrangements in community structure were accompanied by significant rearrangements of the phenotype dynamics in all arvicolid species. Despite some trends specific for particular species, some common features were identified as well. One of them was a rapid turnover in phenotype structure by the end of Younger Dryas, at time of the Preboreal event. (11.7-11 ky BP), the other was associated with the extensive shifts in community structure and habitat diversity at terminal stage of the Preboreal (9.7-9.3 ky). The core arvicolid species of Preboreal communities, Clethrionomys glareolus, Microtus arvalis, M.agrestis and Arvicola terrestris, exhibited repeated fluctuations during that stage (ll-9,3 ky BP) both in abundance and phenotype characteristics, supposedly related to serial invasion events during that time....

<p>Gustina populacija i sezonske fluktuacije u<br />brojnosti voluharica i mi&scaron;eva (Rodentia:<br />Muridae) predstavljaju najvažniji faktor u<br />diverzitetu, distribuciji i abundanci<br />ektoparazitskih vrsta. Epidemiolo&scaron;ki modeli<br />ukazuju da bi povećanje gustine populacija<br />glodara dovelo i do povećanja gustine<br />populacija ektoparazita zbog postojanja većeg<br />izbora preferentnih habitata (jedinke domaćina).<br />Voluharice i mi&scaron;evi predstavljaju grupu glodara<br />koja ima izuzetan vektorski potencijal za veliki<br />broj vrsta iksodidnih krpelja (Acari: Ixodidae),<br />naročito triksenih i diksenih vrsta. Ako se<br />gustina populacija potencijalnih domaćina<br />(voluharica i mi&scaron;eva) posmatra kao stani&scaron;te za<br />iksodidne krpelje, tada se i meĎu njima mogu<br />uočiti razlike koje u kvalitativnom ili<br />kvantitativnom smislu podržavaju različite<br />gustine populacija krpelja. Većina vrsta glodara<br />zbog svojih &scaron;irokih areala, sezonskih migracija i<br />fluktuacija brojnosti predstavlja jednu vrstu<br />specifičnog &bdquo;epidemiolo&scaron;kog mosta&ldquo; koji je<br />odgovoran za održavanje visokih gustina<br />populacija krpelja u okviru odreĎenih stani&scaron;ta,<br />ali, &scaron;to je jo&scaron; značajnije, i prostorno preno&scaron;enje<br />pojedinih vrsta iksodidnih krpelja van okvira<br />datog habitata. Na osnovu dokazanog<br />vektorskog potencijala glodara, utvrĎen je i cilj<br />istraživanja koji podrazumeva tačno<br />odreĎivanje sezonske fluktuacije i prostorne<br />disperzije voluharica i mi&scaron;eva na odabranim<br />lokalitetima, utvrĎivanje dinamike populacija<br />prikupljenih krpelja iz prirode i brojnosti krpelja<br />prisutnih na domaćinu, vektorsku i<br />ektoparazitsku povezanost glodara i krpelja u<br />odnosu na tip habitata, meteorolo&scaron;ke parametre<br />(sezonu), uzrasnu klasu i pol glodara. TakoĎe će<br />se razmatrati i četiri postavljene radne hipoteze<br />koje se tiču odnosa glodari &ndash; krpelji: (1) broj<br />različitih stadijuma krpelja na individuama<br />domaćina se povećava sa povećanjem starosne<br />grupe (mase tela) domaćina, (2) broj različitih<br />stadijuma krpelja na individuama domaćina se<br />smanjuje sa povećanjem gustine populacije<br />domaćina, (3) veći broj različitih stadijuma<br />krpelja na individuama domaćina se konstatuje<br />na ženkama, nego na mužjacima i (4) najveći<br />broj parazitirajućih stadijuma krpelja se nalazi<br />na glavi domaćina. Tokom četvorogodi&scaron;njeg<br />ispitivanja (od 2008. do 2011. godine) sezonske<br />dinamike glodara na lokalitetima Apatin,<br />Bogojevo, Labudnjača (Kamari&scaron;te) i Čelarevo<br />ukupno je izlovljeno 2.736 jedinki, od kojih je<br />najbrojnija vrsta A. terrestris, zatim slede: A.<br />agrarius, A. flavicollis, A. sylvaticus i C.<br />glareolus. Ukupan broj konstatovanih krpelja<br />iznosio je 257. Krpelji su pripadali sledećim<br />vrstama i razvojnim stadijumima: I. ricinus<br />(larve i nimfe), I. trianguliceps (larve), D.<br />marginatus (larve i nimfe), H. concinna (larve i<br />nimfe) i R. sanguineus (larve i nimfe). U okviru<br />proučavanih ekosistema, glodari imaju značajnu<br />ulogu u održavanju krpeljskih populacija<br />različitih vrsta, omogućavajući i olak&scaron;avajući<br />transstadijalni kontinuitet u ciklusu razvića.<br />Dalje, na osnovu bioekolo&scaron;kih karakteristika, a<br />naročito arela kretanja za vreme perioda<br />intenzivne ishrane i parenja, sve ispitivane vrste<br />glodara predstavljaju i veoma dobre vektore<br />determinisanih vrsta iksodidnih krpelja izmeĎu<br />različitih tipova stani&scaron;ta, obezbeĎujući im<br />prostornu i vremensku disperziju, &scaron;to je od<br />velikog ekolo&scaron;kog, medicinskog i veterinarskog<br />značaja.</p> / <p>The population density and seasonal fluctuations<br />of voles and mice (Rodentia: Muridae) are the<br />most important factors in the diversity,<br />distribution and abundance of ectoparasites.<br />Epidemiological models indicate that an increase<br />in the rodent population density could stimulate<br />an increase in population density of ectoparasites<br />due to the greater variety of preferred habitat<br />(individual hosts). Voles and mice are a group of<br />rodents that have exceptional vector potential for<br />a large number of ixodid ticks species (Acari:<br />Ixodidae), especially tree-host and two-host<br />species. If the densities of the potential host<br />population (voles and mice) are observed as the<br />habitats for ixodid ticks, the qualitative and<br />quantitative differences among them are<br />noticeable, so as different species diversity and<br />population densities of ixodid ticks. Because of<br />the wide ranges of activity, seasonal migrations<br />and population size fluctuations, most rodent<br />species represent a specific type of an<br />&quot;epidemiological bridge&quot; which is responsible<br />for the maintenance of high population density<br />of ticks within certain habitats, but more<br />importantly, the spatial transfer of certain ixodid<br />tick species beyond the boundaries of the certain<br />habitat. Based on the proven vector potential of<br />rodents, the aims of the research were to<br />determine: the seasonal fluctuations and spatial<br />dispersion of voles and mice at selected<br />localities, the dynamics of tick populations<br />collected from nature and obtained from the<br />hosts, vector and ectoparasitic relation between<br />rodents and ticks concerning the type of habitat,<br />meteorological parameters (season), age classes<br />and gender. The four hypotheses will be<br />reviewed: (1) the number of different stages of<br />ticks on the hosts increases with the age group<br />(body mass) of the host, (2) the number of<br />different stages of ticks on the hosts decreases<br />with increasing host population density, (3) a<br />larger number of ticks obtained from the hosts<br />are found on the females than on the males, and<br />(4) the highest number of ticks could be found<br />on the host&rsquo;s head. The four year study (2008 to<br />2011) of seasonal dynamics of voles and mice<br />was conducted at four localities: Apatin,<br />Bogojevo, Labudnjača (Kamari&scaron;te) and<br />Čelarevo. The total of 2.736 rodent specimens<br />were caught. The most numerous species was A.<br />terrestris, followed by: A. agrarius, A .<br />flavicollis, A. sylvaticus and C. glareolus. The<br />total number of identified ticks was 257,<br />belonging to the following species and<br />developmental stages: I. ricinus (larvae and<br />nymphs), I. trianguliceps (larvae), D.<br />marginatus (larvae and nymphs), H. concinna<br />(larvae and nymphs) and R. sanguineus (larvae<br />and nymphs). Within the studied ecosystems,<br />rodents play a significant role in maintaining<br />different species of tick populations, enabling<br />and facilitating transstadial continuity in the life<br />cycles. Furthermore, based on bio-ecological<br />characteristics, especially areal activity during<br />the period of intensive feeding and mating, all<br />observed rodent species were very good vectors<br />of certain ixodid tick species among different<br />types of habitats, providing them spatial and<br />temporal dispersion, which is of great<br />ecological, medical and veterinary importance.</p>