Master of Science / Department of Diagnostic Medicine and Pathobiology / Ram K. Raghavan / Dermacentor variabilis (Say) (Acari: Ixodidae), commonly known as the American dog tick is a medically important tick species in N. America, which has been implicated as a competent vector for several diseases, including tularemia, bovine anaplasmosis and canine tick paralysis. This tick is also the primary suspect for the transmission of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever (RMSF). The spatial distribution and geographic extent of D. variabilis territory in N. America is suspected to have changed in the recent times due to natural and anthropogenic, non-stationary forces. A clear understanding of the spatial distribution and environmental factors contributing to the distribution has public health significance, allowing us to make informed management decisions and for setting robust future research goals aimed at understanding vector-biology and disease management. Additionally, ongoing climate-change is expected to alter species spatial distribution and abundance within distribution range. In this research, I studied the current and likely future spatial distribution of D. variabilis ticks in N. America based on two representative concentration pathways, RCP 4.5 and RCP 8.5, representing lower and higher emission scenarios, respectively, under several global circulation models (GCM). The spatial distribution models were constructed using MaxEnt program and BioClim data was used as environmental data for modeling. Best models were selected based on Partial ROC curves, AIC, and omission rates. Median prediction of these models indicate a wider spread of D. variabilis from its currently known extent, and much further spread as a result of climate change. Different environmental variables that significantly influenced current and future D. variabilis distribution included annual mean temperature, mean diurnal range, maximum temperature of the warmest month, annual precipitation, precipitation seasonality, and precipitation of the wettest quarter.

Abstract In this thesis, I studied spatial and temporal variability of macroinvertebrate assemblages of boreal streams. The main objectives were (i) to characterize macroinvertebrate assemblage types across large geographical extents, and to assess the utility of assemblage types and landscape and stream type classifications as the basis of stream bioassessment and conservation programs (ii, iii). I also examined the relative roles of large-scale spatial trends and local environmental conditions in structuring macroinvertebrate assemblages (iv). Finally, I assessed (v) if assemblage classifications produce temporally stable and predictable assemblage types. Stream macroinvertebrate assemblage structure exhibited continuous variation instead of distinct assemblage types. Although ecoregions clearly accounted for a considerable amount of variation of macroinvertebrate assemblage characteristics, a combination of regional stratification and prediction from environmental factors would probably yield the most comprehensive framework for the characterizations of macroinvertebrate assemblages of boreal headwater streams. Differences in macroinvertebrate assemblage structure, as well as a group of effective indicator species for different stream types, suggest that landscape classifications could be used as a preliminary scheme for the conservation planning of running waters The strength of the relationship between assemblage structure and local environmental variables increased with decreasing extent, whereas assemblage variation related to spatially variables showed the opposite pattern. At the largest scale, spatial variation was related to latitudinal gradients, while spatial autocorrelation among neighbouring streams was the likely mechanism creating spatial structure within drainage systems. These results suggest that stream bioassessment should give due attention to spatial structuring of stream assemblage composition, considering that important assemblage gradients may not only be related to local environmental factors, but also to biogeographical constraints and neighbourhood dispersal processes. The classification strengths of macroinvertebrate assemblages based on data of three years were overall rather weak, and more importantly, the compositions of the site groups varied considerably from year to year. Such wide and continuous variation was also mirrored by low and inconsistent predictability of classifications from environmental variables. The observed level of temporal variation in assemblage structure may not be a serious problem for predictive approaches frequently used in bioassessment of freshwater ecosystems. For conservation purposes, however, alternative approaches (e.g. physical surrogates of biodiversity) need to be considered.