Home range and ecology of a palaearctic lacertid : Combining novel and old approaches to assess <em>Lacerta agilis</em> LINNAEUS, 1758 in the centre of its distribution with considerations for conservation

Effective species conservation requires a thorough understanding of a species’ ecology as it reveals the requirements a species has of its environment. In this thesis I combine established methods like visual encounter surveys and the processing of local weather data with novel methods like radio-telemetry on sand lizards and habitat mapping by UAV to make an ecological profile for a population of Lacerta agilis from the centre of its range. In several papers, me and my colleagues analyse different aspects of sand lizard ecology: The spatio-temporal patterns in microhabitat and weather preferences, the weather dependent detection probability, and the home range and habitat selection. Before that, I summarize previous studies of home range and habitat selection in vertebrates to identify the allocation of focus towards vertebrate orders and topics and to understand, where the study of Lacerta agilis fits into previous work. In summary, allocation of focus on vertebrate orders in home range and habitat studies is independent of species diversity within the order as well as relatedness between orders or portion of vulnerable species within orders. Furthermore, many marine turtles and mesocarnivores were among the most studied species and topics most studied in concordance with home range and habitat selection are conservation/human influence, intraspecific differences, and home range shifts and exploratory behaviour. In the following, the thesis focuses on establishing an ecological profile of L. agilis. First, the data shows, that the studied central population varies greatly in spatio-temporal patterns of microhabitat and weather preferences from much studied populations at the ranges edge. Overall, the spatio-temporal patterns in habitat selection of L. agilis in this population cannot be explained by season, weather or microclimate and only very minor differences between ontogenetic stages, sexes or daytime can be observed. Overall, L. agilis of this population occupy a broad niche but are most active in dry and sunny conditions with low windspeeds after air temperatures reached values around 20°C for a few hours. In terms of habitat, lizards favour incorporating blackberry bushes into their home range while avoiding large areas of sand and tall vegetation. My results show the need for local data in conservation and help improving conservation of local populations by detailing weather dependent encounter rates and fine-scale habitat selection. I furthermore supply a combination of methods many of which are designed to remain useful for a multitude of organisms and applicable in conservation and management work

The Lifecycle of Semidiurnal Internal Tides over the Northern Mid-Atlantic Ridge

The lifecycle of semidiurnal internal tides over the Mid-Atlantic Ridge (MAR) sector south of the Azores is investigated using in situ, a high-resolution mooring and microstructure profiler, and satellite data, in combination with a theoretical model of barotropic-to-baroclinic tidal energy conversion. The mooring analysis reveals that the internal-tide horizontal energy flux is dominated by mode 1, and that energy density is more distributed among modes 1-10. Most modes are compatible with an interpretation in terms of standing internal tides, suggesting that they result from interactions between waves generated over the MAR. Internal tide energy is thus concentrated above the ridge and is eventually available for local diapycnal mixing, as endorsed by the elevated rates of turbulent energy dissipation, ε, estimated from microstructure measurements. A spring-neap modulation of energy density on the MAR is found to originate from the remote generation and radiation of strong mode-1 internal tides from the Atlantis Meteor Seamount Complex. Similar fortnightly variability of a factor of 2 is observed in ε, but this signal’s origin cannot be determined unambiguously. A regional tidal energy budget highlights the significance of high-mode generation, with 81% of the energy lost by the barotropic tide being converted into modes &gt; 1, and only 9% into mode 1. This has important implications for the fraction of local dissipation to the total energy conversion, q, which is regionally estimated to be ~0.5. This result is in stark contrast with the Hawaiian Ridge system, where the radiation of mode-1 internal tides accounts for 30% of the regional energy conversion, and q &lt; 0.25

Observations of Nutrient Supply by Mesoscale Eddy Stirring and Small-Scale Turbulence in the Oligotrophic North Atlantic

Sustaining biological export over the open ocean requires a physical supply of nutrients to the mixed layer and thermocline. The relative importance of diapycnal mixing, diapycnal advection and isopycnal stirring by mesoscale eddies in providing this nutrient supply is explored using a field campaign in oligotrophic waters in the subtropical North Atlantic, consisting of transects over and off the mid-Atlantic ridge. Eddy stirring rates are estimated from the excess temperature variance dissipation relative to the turbulent kinetic energy dissipation, and using eddy statistics from satellite observations combined with 9-month-long mooring data. The vertical nutrient fluxes by diapycnal mixing, diapycnal advection and isopycnal mesoscale eddy stirring are assessed using nitrate measurements from observations or a climatology. Diapycnal mixing and advection provide a nutrient supply within the euphotic zone, but a loss of nutrients within the upper thermocline. Eddy stirring augments, and is comparable to, the diapycnal transfer of nutrients within the summertime upper thermocline, while also acting to replenish nutrients within the deeper parts of the thermocline. The eddy supply of nitrate is relatively small in the centre of the subtropical gyre, reaching up to 0.06 mol N m−2yr−1, but is likely to be enhanced on the flanks of the gyre due to larger isopycnal slopes and lateral nitrate gradients. The nutrient supply to the euphotic zone is achieved via a multi-stage mechanism: a diapycnal transfer of nutrients by small-scale turbulence to the euphotic zone, and an isopycnal stirring of nutrients by mesoscale eddies replenishing nutrients in the upper thermocline. Plain Language Summary Phytoplankton growth requires a supply of nutrients to the base of the euphotic zone, which is usually provided by a combination of vertical mixing or vertical upwelling of nutrients. However, in the oligotrophic waters of the central North Atlantic, it is unclear how the vertical supply of nutrients is sustained. Here we use field data to explore the roles of mixing across density surfaces, advection across density surfaces and mesoscale eddy stirring along density surfaces in supplying nutrients to some of the most nutrient-depleted surface waters in the central North Atlantic. Diapycnal mixing and advection are found to be important in supplying nutrients to the euphotic zone during summer, but at the expense of eroding the nutrients in the upper thermocline. In contrast, mesoscale eddy stirring augments the diapycnal supply of nutrients to the euphotic zone, and replenishes nutrients in the upper thermocline