The streams of the southeastern United States are both hotspots for biodiversity and centers of imperilment. The specific spatiotemporal scales at which stressors impact biota are often unknown, partly due to inadequate knowledge about many species' life-histories. I conducted two complementary studies to investigate the habitat associations of an imperiled highland stream fish, the Candy Darter Etheostoma osburni. In Chapter 2, I asked (1) does micro-habitat suitability correlate with the "robustness" (i.e., viability) of four distinct populations? In Chapter 3, I expanded the extent of investigation, and asked (2) which environmental factors, expressed at what spatial scales, best explain in-stream conditions, and (3) do stream segments where Candy Darters persist have cooler temperatures and less fine-sediment than segments where the species is extirpated or historically went undetected? Chapter 2 revealed Candy Darters demonstrate ontogenetic habitat shifts, with age-0 individuals selecting slower water velocities than adults. Despite, clear habitat selection for multiple habitat variables, suitability attributed to fine-sediment avoidance most strongly correlated with population robustness across streams. Chapter 3 indicated Candy Darters are extirpated from most areas in Virginia and southern West Virginia. Land use and natural catchment features, including geology, elevation, and stream geomorphology, predominantly explained instream conditions. Populations persist in segments with cool stream temperatures and low embeddedness year-round. To recover Candy Darters, managers will need to remedy pervasive land-use threats and restore stream habitat, while operating within the impending context of warming air and water temperatures and the existential threat of the introduced Variegate Darter E. variatum. / M. S. / The Candy Darter is a small colorful stream fish only found in the New River Valley of Virginia and West Virginia. It was historically recorded throughout much of its range, but the species has since seemingly disappeared from many historical locations. Biologists, who are tasked with conserving declining species, know very little about the Candy Darter, which makes it difficult to determine the reasons for its decline. My goal was to clarify the habitats and streams used by the Candy Darter. In Chapter 2, my team recorded the habitats that Candy Darters preferred in four different streams where the species is either abundant (two streams), rare (1 stream), or has disappeared (1 stream). I determined individuals consistently avoid areas with high levels of fine sediment. I also discovered the streams where the species still exists had lower levels of fine sediment, indicating that high levels of fine-sediment may diminish habitat quality for individuals and eventually impact populations. In Chapter 3, I asked whether the conclusions from Chapter 2 were valid for most streams where Candy Darters have ever been recorded. In addition to less fine-sediment, I suspected the streams where Candy Darters still exist, would have cooler stream temperatures than the streams where they have disappeared. I surveyed 42 locations for Candy Darters and recorded stream temperatures and fine-sediment levels at each location. I confirmed that, on average, the streams where Candy Darters still exist have much cooler stream temperatures and fewer fine-sediments. Stream temperatures and fine-sediment levels could be explained by surrounding environmental conditions including geology, altitude, stream size, and the amount of pasture beside and upstream of each location. These findings are consistent with many other studies that have found non-natural land covers, including pasture, lead to higher amounts of fine-sediment washing into streams and create warmer stream temperatures. The decline of the Candy Darter is similar to the declines of dozens of other fish species throughout the southeastern United States. To restore Candy Darters, biologists will need to work with landowners to improve conditions adjacent to streams, while combatting other threats, such as warming air temperatures and non-native species.

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Member of the genus Sicista rank among the rarest and the least known European mammals. They exhibit a number of outstanding specificities (hibernation, aestivation etc.) and extreme capability of a rare range dynamics. Their fossil record is fragmentary and associated with numerous controversies. The present thesis summarizes results of a detailed revision of the fossil record of Sicista from Czech Republic, Slovakia and some other countries. It comprises of about 150 items of the Holocene and Vistualian age as well as from the Middle and Early Pleistocene including earliest records from MN17/Q1 boundary and type material of S. praeloriger from Q1 Betfia. Compared to a sample of extant population, variation dynamics of both metrical and nonmetrical dental traits was examined in details with particular attention to phenotype patterns of particular fossil samples. The results demonstrated extensive amount of both within- and between-population variation and rather limited validity of commonly used discrimination criteria of extant clades. Nevertheless, we succeeded in species identification of considerable part of numerous Holocene and Vistulian records which revealed (i) a range expansion of S. subtilis s.l. during MIS 3 with persistent distribution in lowland regions of Central Europe in the Late...