Theses and Dissertations

Although the consequences of habitat fragmentation have been a rich field of inquiry for some time, the ecological legacies of past land use are only recently gaining much attention. Our work focused on the effects of patch size and historical land use on woodland ants and myrmecochores (plants species that have their diaspores dispersed by ants) in mesic forests of the southern Appalachian Highlands. The purpose of this study was to examine a potential mechanism, the presence and diversity of seed-dispersing ants, that might explain the reduced abundance and diversity of myrmecochores in small forest patches with high intensities of past land use (Pearson et al. 1998).

Small patches (200 ha) with minimal past land use. Overall, sites with greater myrmecochore species richness and abundance had less diverse ant communities and a lower abundance of ants. This negative correlation was most pronounced among small patches with high levels of prior land use. Ant species composition varied most between patches that differed in size. Large patches were dominated by one ant species, Aphaenogaster fulva, whereas small patches supported less A. fulva, but higher numbers of Aphaenogaster rudis and two Camponotus species. Large patches with low levels of past land use tended to have relatively lower numbers of conspecific immature myrmecochores when adult myrmecochores were more abundant. In contrast, higher immature abundance was correlated with greater numbers of adult myrmecochores in both small and large patches with high past land use intensity.

An absence of seed-dispersing ants cannot explain the reduced numbers of myrmecochores in small patches with high past land use because the mechanism of seed dispersal by ants still appears to be available in those patches. Land use legacies or fragmentation effects may be overriding any advantages offered by the increased diversity and abundance of ants at those sites. The long recovery time and slow recolonization rates, compounded with the low reproduction and slow growth rates of the herbs, may explain some of the myrmecochore patterns we have observed. It is possible that the reintroduction of adult myrmecochores might reverse extirpation in locations that currently support low numbers and diversities of these herbs.

Land use and land cover can have a significant impact on water chemistry, but the spatial scales at which landscape attributes exert a detectable influence on aquatic systems are not well known. This study quantifies the extent of the landscape influence using the proportion of wetlands in the watershed measured at different distances to predict dissolved organic carbon (DOC) concentrations in Wisconsin lakes and rivers, and to determine whether the watershed influence varies with season or hydrologic type of lake. The proportion of wetlands in the total watershed often explained the most variability of DOC in lakes when stepwise regression was used. However, best model techniques revealed that, for lakes, r2 values often only differed 1-3% between models using the proportion of wetlands in the total watershed and models using only the proportion of wetlands in nearshore riparian areas (25-100 m). In rivers, the proportion of wetlands in the watershed always explained considerably more of the variability in DOC than did the proportion of wetlands in the nearshore riparian zone. The watershed influence also varied seasonally in rivers, as the proportion of the watershed covered by wetlands explained more of the variability in DOC in the fall than in the spring. Overall, the proportion of wetlands in the landscape explained much more of the variability of DOC concentrations in rivers than in lakes.