Anthony M. Davis

Urban Ecosystems and Island Biogeography

In urban areas, continuing fragmentation of natural habitat, disturbance, and increasing isolation of individual ‘habitat islands’, has brought on almost general reduction in species richness. Sensitive species are being replaced by aggressive synanthropic ones. Continued loss seems inevitable, but reducing the rate of that loss is a worthwhile conservation goal. It is imperative that the numerous and varied habitats within each urban area be considered as interrelated and not as separate units. Island biogeography models supply the means for unifying the disparate elements in urban ecological studies and can provide a useful strategy for conservation. It is difficult to define colonization, extinction, and equilibrium, in disturbed, often transient, urban habitats. Pseudo- and successional turnover dominate. The occupation of each ‘habitat island’ is a function of its own geography and of its position relative to other ‘islands’. Each habitat may serve as isolated ‘island’, ‘stepping-stone’, or ‘corridor’, depending on its spatial relationships with other ‘habitat islands’ and with the nature of each organism present. ‘Habitat islands’ in small cities appear to function like large or near oceanic islands, while those in large cities seem to respond like small or distant oceanic islands. In all cases, the analogy with land-bridge islands is appropriate. Continuing urbanization is leading to reduced ‘habitat island’ size, and increasing the isolation of units from one another and from the surrounding rural ‘reservoir’.

Ombrotrophic peatlands in Newfoundland, Canada: Their origins, development and trans-Atlantic affinities☆

Abstract The ombrotrophic peatlands of Newfoundland are morphologically and phytosociologically similar to those of northwest Europe. They have a geography that is largely dictated by climate, but that may be regionally constrained by topography and substrate. Pollen, macrofossil, and elemental analysis of the peats, and physical and chemical analysis of their mineral substrates allow reconstruction of their paleoecologies, and some determination of the roles of climate and pedogenesis in their initiation and development. As in northwest Europe, paludification appears to be episodic rather than regularly continuous. The most pronounced episode of peat growth and climate change is at ∼3000−2500 B.P., the sub-Boreal—sub-Atlantic transition. It is marked by massive expansion of peatlands and by autogenic changes that convert minerotrophic systems to ombrotrophic ones.

Floodplains and Agricultural Origins: A Case Study in South-Central Ontario, Canada

AbstractHuman interaction with riverine ecology is an important component of recent modelling of agricultural origins in eastern North America. Recent research on the ancestral Ontario Iroquoian Princess Point Complex (A.C. 500–900) in south-central Ontario, Canada, demonstrates that the floodplain of the Grand River was an important setting for initial maize production in this region. This paper presents a case study of an archaeological occupation in relation to its floodplain setting during the transition front hunting and gathering to agriculture. Previous interpretation of the Princess Point occupation of the lower Grand River Valley suggested that maize cultivation was grafted onto a Middle Woodland pattern of seasonally scheduled foraging. In particular, the old model proposed that floodplain disruption by substantial annual flooding and ice rafting limited use of the floodplain; exploitation of floodplain habitats was limited to the late spring, summer, and early autumn when maize cultivation coul...

Sedimentology and palynology of Middle Wisconsinan deposits in the Pecatonica River valley, Wisconsin and Illinois

Abstract The bedrock valley of the Pecatonica River north of Freeport, Illinois, contains a thick valley-fill complex of alluvium and drift. Within the valley, loess-capped benches surround hills of silty Illinoian drift. Beneath these benches lie thick deposits of poorly sorted stony silt interbedded with thin lenses of silt, sand, and organic-rich loam. Channel deposits and peat cap the diamicton in places. We interpret the stony silts as solifluction debris shed from silty slopes within the valley-fill during the Early or Middle Wisconsinan (Altonian). Top and bottom radiocarbon dates from a 2.5-m section of peat overlying the diamicton are 26,820 ± 200 and 40,500 ± 1700 yr B.P., respectively. We informally refer to the stony silts, channel sediments, and peat as the “Martintown unit.” Geomorphic position, sediment input, and macrofossils suggest that the dated peat was deposited in a floodplain pond (oxbow?). The pollen record from the peat indicates that a boreal forest dominated this area during the Middle Wisconsinan (late Altonian and Farmdalian). Two pollen zones are recognized: a basal Zone I with Pinus slightly more abundant than Picea and with few herbs and shrubs, and an upper Zone II dominated by Picea and with a larger representation of herbaceous and shrub taxa. Little displacement of vegetation zones is indicated, even though ice advanced to within 100 km of the site during the time of peat accumulation. Because of the problems involved in clearly defining Middle Wisconsinan forest-tundra in mid-latitudes by using analogs of Holocene forest-tundra in high latitudes, caution is required in making geomorphic inferences solely from vegetation data. Together, though, pollen and sediment data indicate that during the Middle Wisconsinan, Pecatonica hillslopes progressed through a sequence of instability-stability-instability related to climatic fluctuations.

Relative importance of hydrological and climatic controls on Holocene paleoenvironments inferred using diatom and pollen records from a lake in the central Hudson Bay Lowlands, Canada:

Postglacial paleoenvironmental changes and landscape development in the Hudson Bay Lowlands in subarctic Canada were inferred using sediment properties and diatom and pollen assemblages in the sediments of a lake raised above the surrounding peatlands in an ice-marginal landform. Coarse-grained, inorganic sediments at the base of the Lake AT01 core suggest a high-energy periglacial environment, following isostatic emergence from Hudson Bay around 6840 cal. BP. Initial diatom assemblages dominated by Fragilaria spp., and pollen of Shepherdia canadensis, indicate early successional conditions in a recently deglaciated environment. Around 6200 cal. BP, tychoplanktonic Fragilarioid diatoms are replaced by large benthics. Coincident increases in Equisetum spores, Cyperaceae pollen and sediment organic matter suggest the establishment of a more productive macrophyte-rich shallow lake. While the Holocene Thermal Maximum and subsequent Neoglacial may have contributed to these shifts, pollen and diatom records suggest only subtle responses to Holocene climatic changes. A core chronology inferred from radioisotopes suggests a hiatus in sediment accumulation between 3650 and 200 cal. BP. Peaks in carbonate inferred from loss-on-ignition and increases in bulk density in that section of the core suggest some effect of erosional or thermokarst processes, or the breaching of a sandbar, now a remnant island in the lake, in the drainage of the lake and ensuing hiatus. Sediment accumulation resumed within the past two centuries; diatom assemblages in the uppermost section are characterized initially by benthic diatoms of smaller valve size compared with the pre-hiatus assemblages. More recently, increases in the planktonic diatom Cyclotella stelligera are recorded, signaling significant environmental changes.

MODERN POLLEN RAIN AND DIATOM ASSEMBLAGES IN A LAKE ERIE COASTAL MARSH

We present an analysis of modern pollen and diatom assemblages in surficial sediments in a coastal marsh at Rondeau Provincial Park, on the northern shore of Lake Erie in southwestern Ontario, Canada. The objectives of the study were (1) to determine how pollen and diatom assemblages in surface sediments vary as a function of the dominant vegetation community and moisture availability at the sampling site and (2) to analyze pollen-vegetation relationships of four dominant wetland plants: Cephalanthus occidentalis, Phragmites australis, Typha spp., and Zizania aquatica, in order to improve interpretations of fossil sequences. Canonical variate analysis (CVA) was used to compare pollen and diatom spectra from sampling sites in three marsh zones delineated on the basis of moisture availability. Using the pollen or the diatom datasets, the resulting discriminant functions correctly classified 86% of the wettest sites, 72% of those with intermediate moisture availability, and only 25% of the sites in the driest parts of the wetland. Since 35% of the sampling sites were misclassified by the CVA on the basis of pollen assemblages, a representation factor approach is needed to complement the comparative approach when analyzing pollen datasets from wetland contexts. Percent cover vegetation data at sediment sampling sites are used to illustrate pollen-vegetation relationships for the ecologically important wetland plants at the site. Phragmites australis and Typha spp. produce small amounts of pollen relative to their abundance, while Cephalanthus occidentalis and Zizania aquatica produce abundant pollen, which is deposited highly locally in the case of Cephalanthus. These data will enable improved interpretations of fossil pollen and diatom sequences from wetland contexts.