For the majority of large ungulates living in temperate regions winter is the limiting season, because of the combined effects of lack of resource availability and severity of climatic conditions. Those species that did not develop any particular morphological and physiological adaptation to cope with winter severity may adopt movement and space use tactics instead (like e.g. migration). Specifically, these space use patterns may emerge at different spatiotemporal scales to allow individuals to accede the resources they need and escape unfavourable conditions, thus determining both individual fate and population dynamics. A detailed understanding of the relationship between limiting factors in wintertime, and individual movement response, is remarkable to preserve and manage wildlife successfully, especially in the context of fast-occurring climate change that induces important alterations in landscape and resource distribution (e.g. changes of snow cover patterns). The comparison of movement tactics under different environmental scenarios, e.g. by means of large -scale analysis at the species distribution range, represents a valuable approach to work in that direction and to assess the effects of landscape alteration on individual movement. Roe deer (Capreolus capreolus) is an excellent model species to investigate these issues, because its distribution range covers most of Europe, thanks to its high ecological plasticity. For those populations that live in northern and mountain environments, winter is the limiting season because roe deer lack any morphological and physiological adaptations to cope with winter severity. In spite of the adoption of specific movement tactics such as partial migration from summer to winter ranges, roe deer may still face limiting conditions in some areas of the distribution range exposed to winter severity. Wildlife managers therefore have developed supplemental feeding programs to sustain roe deer (and other ungulate) populations. Regardless of the pervasiveness of this practice and the potential negative ecological consequences (such as for example the enhanced probability of disease transmission), if and how the interplay between distribution of supplemental feeding sites and winter severity may shape roe deer spatial ecology remains mostly unknown. During my PhD, I provided a contribution to investigate in this direction. First, I relied on the data stored and managed in the EURODEER database (www.eurodeer.org) to evaluate across a wide latitudinal and altitudinal gradient how individuals responded to the presence of these patchily distributed resources under different environmental conditions and supplemental feeding management. The comprehensiveness of large scale datasets such as EURODEER is counterbalanced by some limitations in terms of data resolution of some potentially meaningful environmental variables, such as snow cover. To overcome these limitations, I empirically collected accurate data on snow cover and snow sinking-depth to assess the combined effect of snow and of the distribution of feeding stations on winter resource selection in an Alpine population of roe deer. The investigation of the effect of feeding stations on individual space use tactics should go hand in hand with a proper assessment of the inter-individual relationships occurring at feeding stations, which in turn correspond to contacts btween animals. Measurements of contact rates is a relatively new ecological interest, and could be performed either by visual recording of observers, or by means of proximity loggers or, as alternative, using tr acking data that permit to infer spatial relationships from individual trajectories. The latter two approaches are more practical in terms of application, but both need to be carefully calibrated to avoid biased ecological inference derived from the obtained contact measurements. In this context, I performed a detailed analysis and modelling of the factors influencing the connectivity of recently introduced proximity loggers (WSN, Wireless Sensor Network). In parallel, I explored the potential applicability of SECONDO spatiotemporal database for the investigation of spatial relationships among individuals through the more widespread GPS tracking data. The large-scale comparative analyses I conducted along a wide latitudinal and altitudinal gradient showed that the use of feeding sites by roe deer is highly seasonal, and specifically associated to low temperatures and activation of the feeding stations, but not to snow cover. Moreover, I found some indications that winter use of feeding stations was negatively affected by the presence of competitors. Finally, I found a strong signal of the reduction of individual home range size in relation to feeding site use. Local assessment of roe deer winter resource selection partially supported these results: the main drivers of roe deer resource selection included the proximity to feeding stations (although to a lesser extent than expected) and, a more strong inverse relationship with snow sinkng depth. The main driver of roe deer habitat use was presence of forest canopy. The absence of any statistically significant effect of the index used for measuring snow at a large scale (MODIS) supported the importance of local measurements of snow to complement remotely-sensed data. The finding that the use of feeding stations leads individuals to concentrate their movements around these sites supports the hypothesis of high contact rate between individuals at feeding sites. i.e. as they would work as attractive points. The assessment of encounters is preliminary to the evaluation of such hypothesis. I have demonstrated Wireless Sensor Network proximity loggers as tools with high potentiality for assessment of encounters. At the same time, my work has strongly indicated the need to carefully calibrate these tools before applying them for any biological investigation, and provided practical guidelines on how to proceed, including how to model the error probability. Alternatively, I laid the first technical premises to assess encounters from the more widespread GPS tracking data, by means of high-performance queries within an appropriate spatiotemporal database. I conclude that roe deer use feeding stations, but only when winter conditions are particularly harsh (i.e. low temperature, abundant snow cover). In a context of climate change with an alteration of snow pattern distribution due to a general increase of temperatures, it would be essential to understand whether supplemental feeding management will still be a reasonable and effective tool to manage roe deer. More generally, it would be necessary to assess whether roe deer indeed need feeding stations for overwinter survival. This work clearly provides evidence that the distribution of feeding stations modifies roe deer spatial behaviour. A full understanding of the patterns of animal aggregation, derived from the correct measurement of contact rates, is thus fundamental to understand the consequences of supplemental feeding practices on animal welfare, and ecosystem consequences (e.g., disease transmission). Research in these directions would ultimately permit to understand the tradeoff between benefits and costs, both for wildlife, and as a human action, of supplemental feeding practices, thus helping wildlife managers to take the right decisions.
|Citation:||Ossi, Federico (2015-01-13). Ecological determinants of roe deer (Capreolus capreolus) spatial behavior and movement in limiting conditions. (Doctoral Thesis). Université Claude Bernard, Lyon 1, a.y. 2013/2014, FIRST. handle: http://hdl.handle.net/10449/26494|
|Organization unit:||Biodiversity and Molecular Ecology Department # CRI_2011-JAN2016|
|Title:||Ecological determinants of roe deer (Capreolus capreolus) spatial behavior and movement in limiting conditions|
|External Tutor:||Gaillard, Jean Michel|
|University:||Université Claude Bernard, Lyon 1|
|Scientific Disciplinary Area:||Settore BIO/07 - Ecologia|
|Appears in Collections:||08 - Doctoral thesis|