Climate and longleaf pine (Pinus palustris P. Mill.) radial growth relationships have been documented within its southern and western distribution. However, knowledge of this relationship is lacking along its northern latitudinal range margin (NLRM). Based on the principles of ecological amplitude, limiting factors, and studies of coniferous species in eastern temperate forests of the U.S., we hypothesized that the radial growth of longleaf pine in mixed pine-hardwood forests is responding to winter temperatures in southeastern Virginia. Two longleaf pine chronologies were developed to determine the relationship between radial growth and monthly temperature, precipitation, and Palmer Drought Severity Index (PDSI) via response function analysis (RFA). Results at the 0.05 level yielded significant response function coefficients with a positive response to current winter temperature and precipitation and a negative response to prior August PDSI. In studies of climate and longleaf pine radial growth in other parts of its range, winter temperature and precipitation have not shared a significant positive association with radial growth. Instead current spring and summer precipitation usually share this positive association. These findings add more evidence to an emerging pattern suggesting that winter temperatures contribute to limiting the radial growth of temperate conifers at northern range margins in the Northern Hemisphere.

Plant populations near the northern limits of their geographic distribution may experience different biotic pressures than southern populations. For instance, if herbivores are scarce in northern populations, performance of their host plants may benefit. In this study, I looked at populations of burdock (Arctium minus) along an 815 km latitudinal gradient from the northern range limit to more southern populations. I found that plant height, stem diameter, and number of seeds all increased on approaching the northern limit. In addition, I also found significant decreases in herbivory by generalist and specialist leaf and seed predators, even though northern plants invested less in physical and possibly chemical defenses. In an experiment in which seeds were planted in different soils, marginal soil initially produced smaller plants, but subsequently larger plants than soil from southern populations. These results indicate northern populations experience relaxed pressure from natural enemies and may benefit as a result.

Plant populations near the northern limits of their geographic distribution may experience different biotic pressures than southern populations. For instance, if herbivores are scarce in northern populations, performance of their host plants may benefit. In this study, I looked at populations of burdock (Arctium minus) along an 815 km latitudinal gradient from the northern range limit to more southern populations. I found that plant height, stem diameter, and number of seeds all increased on approaching the northern limit. In addition, I also found significant decreases in herbivory by generalist and specialist leaf and seed predators, even though northern plants invested less in physical and possibly chemical defenses. In an experiment in which seeds were planted in different soils, marginal soil initially produced smaller plants, but subsequently larger plants than soil from southern populations. These results indicate northern populations experience relaxed pressure from natural enemies and may benefit as a result.

Conservation is plagued by the issue of prioritization - what to conserve and where to conserve it - which relies on identification and assessment of risks. In this body of work, I identify some of the risks related to climate change impacts on biodiversity, as well as potential solutions. Climate changes are underway across nearly all terrestrial areas and will continue in response to greenhouse gas emissions over centuries. Other extinction drivers, such as habitat loss due to urbanization, commonly operate over localized areas. Urbanization contributes, at most, less than 2% of the total range loss for terrestrial species at risk when averaged within an ecodistrict (Chapter 2). Documented impacts of climate change, to date, include: extinction, population loss, reduction in range area, and decreased abundance for multiple taxonomic groups. Examining species’ and populations’ physiological limits provides insight into the mechanistic basis, as well as geography, of climate change impacts (Chapter 3). Climate changes, and the ecological impacts of climate changes, are scale-dependent. Thus, the biotic implications are more accurately assessed through comparisons of local impacts for populations. Under a scenario of climate change, equatorward margins may be strongly limited by climatic conditions and not by biotic interactions. Yet, geographic responses at poleward margins do not appear directly linked to changes in breeding season temperature (Chapter 4). New ideas on how regions with attenuated climate change (climate refugia) may be used to lower species climate-related extinction risk while simultaneously improving habitat connectivity should be considered in the context of potential future consequences (i.e. range disjunction, alternative biological responses) (Chapter 5). Contemporary climate refugia are identifiable along multiple climatic dimensions, and are similar in size to current protected areas (Chapter 6). Determining how, when, and where species distributions are displaced by climate change as well as methods of reducing climatic displacement involves integrating knowledge from distribution shift rates for populations, occurrence of climate refugia, and dispersal barriers. Such assessments, in the Yellowstone to Yukon region, identify dramatically different pathways for connectivity than assessments that are not informed by considerations of species richness and mobility (Chapter 7).

Climate change is one of the most important factor determining species ranges. In Europe there is now evidence for northward areal expansion in many Mediterranean insects including the praying mantis (Mantis religiosa). This species is the only representative of the order Mantodea inhabiting central Europe. The northern edge of the species distribution currently reaches latitude 53ř North. Although, the praying mantis is well known insect there is not enough evidence about its phylogeography. In this work three mitochondrial genes (COI, COII, Cyt b) were selected for phylogenetic study. Results indicate three statistically supported distinct lineages in Europe: Eastern European, Central European and Western European. Presumably these lineages are consistent with isolation during the last glacial and re-colonization from glacial refugia. Reduced haplotype diversity on the northern edge suggests currently established populations at the northern distribution border. To validate mtDNA results it was also considered four microsatellite loci. Due to different type of inheritance mtDNA and nuclear DNA it is possible to compare two independent genetic datasets. Microsatellite analysis confirmed results obtained on mitochondrial data. Three major genetic clusters were found: east, west and central. Spatial...