Human-disturbed Areas Research Articles

Effects of Human Disturbance on the Dune Vegetation of the Georgia Sea Islands

This research investigates how human disturbance has affected foredune vegetation of the Georgia Sea Islands (GSI) in the United States. The cover of native dunebuilding grasses (Uniola paniculata L. and Panicum amarum Ell.) was more abundant within less-disturbed sites than in sites that had higher levels of human disturbance. In contrast, dunes in human-disturbed areas had significantly higher cover of alien plants and native generalist taxa, and they also had higher overall species diversity. Additionally, the cover of native dune-building grasses was significantly greater on protected National Wildlife Refuge islands than on more frequently visited and developed tourist islands. In addition to the ANOVA, nonmetric multidimensional scaling (NMS) analysis showed that the vegetation composition differed between disturbed and less-disturbed plots and between plots on tourist islands and protected islands. Both ANOVA and NMS analyzes agree that dunes in human-modified areas have lower dune-grass cover and greater cover of species that are not adapted to building and stabilizing dunes. Therefore, human disturbance may indirectly reduce dune stability by altering the dune vegetation.

Phylogeny and Adaptation in the Encelia Alliance (Asteraceae: Helliantheae)

The three related genera Encelia, Enceliopsis, and Geraea comprise the alliance. The first consists primarily of shrubs and the latter two of herbaceous perennials and an annual. With the exception of two Encelia species of arid South America, all inhabit southwestern North America. Enceliopsis and Geraea are sister groups, and together form the sister group to Encelia, which includes two major clades. Especially in Encelia, there are diverse morphologies and a variety of ecological strategies marked by differences in habitat, vestiture, water balance, and photosynthetic parameters. The North American species of all three genera are obligate outcrossers, all with n = 18 chromosomes. Although intergeneric hybrids are largely sterile, interspecific hybrids in Encelia are fertile in the wild and in cultivation. Hybrids in the wild are largely restricted to F1s, except in areas of human disturbance. Two true-breeding species are of homoploid hybrid origin, and are evidently isolated from the parent species through external ecological barriers involving selection against backcross progeny. Studies of the chloroplast genome and the intercistronic transcribed spacer (ITS) of nrDNA show clear differentiation of the genera, but much less variation within Encelia, even between phenotypically disparate species, suggesting recent divergence. Because the species are interfertile, it will be possible to study the genetics of the traits that distinguish the species and contribute to their differences.

Book Review

THERE IS A MYSTERY to be solved. Certain ants follow people. These “tramp” ants predictably are found in human habitations and areas of high human disturbance, but not in surrounding native habitats. For the past decade, I have been surveying the ant fauna of a rich Neotropical area (Costa Rica), and I constantly am amazed at the specificity and predictability of a handful of tramp species. I can spend person-years cataloging the diversity of a patch of rainforest and not find tramp species, yet I know that I can walk 20 m from the forest to a dining hall or laboratory and find them. These species are a myrmecologist's friends, because they allow me to impress people the world over with my knowledge. I can go to almost any tropical field station in the world, be it in Bolivia or Bali, look at the 1mm long ants running in the sugar bowl, and pronounce “Ah, Tapinoma melanocephalum (F.), I see.” God forbid they ask about the ants in the forest beyond!

Prehistoric Agricultural Ecosystems: Avifauna from Pottery Mound, New Mexico

Excavations at Pottery Mound, a large Pueblo ruin located on the banks of the Rio Puerco in New Mexico, have recovered over 4,000 bird bones representing 50 species. The habitats of these birds include grassland, marshland, canal- and riverbank, Pinyon-juniper forest, and coniferous forest. Instead of attributing this diversity to changing climate or long-distance hunting expeditions away from the pueblo, I employ the "garden hunting" model, which ascribes increased species biomass to areas of human disturbance. At Pottery Mound prehistoric agricultural fields increased insect populations and provided wild and cultivated seeds which attracted a variety of birds. Additionally, irrigation canals extended riparian growth from the river across the floodplain creating more available cover for predators. This ecotone effect allowed avian species to increase beyond their normal numbers and diversity in undisturbed areas. All 50 species at Pottery Mound could have been obtained within a small radius of the site.

Birds and prehistoric agriculture: The New Mexican pueblos

Analysis of faunal remains from prehistoric southwestern pueblo sites reveals certain commonly occurring species of mammals and birds, the latter including ducks and geese, hawks and eagles, American Kestrel, Mourning Dove, owls, Horned Lark, Common Raven, and jays. This phenomenon is examined with the analysis of bird bones from four New Mexican pueblos located in north-central and west-central New Mexico. Recovered faunal remains date to specific periods between A.D. 1250 and the present. Over 70 species of birds represent various ecological situations; many of these species presently do not occur near the pueblos and a few occur only in the extreme southeastern portion of the state. Marsh and riparian areas along the river systems and richer grasslands on the floodplains would account for most of these species occurring near the sites prehistorically. However, rather than attribute unusual species to climatic change, trade, or long-distance hunting expeditions by the Indians, an alternative explanation is offered which attributes high species diversity to areas of human disturbance. Disturbed areas such as agricultural fields can increase species diversity in an area and aid in the range extension of many animals. The primary factor in this situation, besides the crops themselves, is believed to be insects, which attract other animals, particularly birds and their predators. In addition, field irrigation systems act to extend riparian growth from the river across the floodplain, creating habitats for these animals. Finally, certain groups of birds and mammals have developed a natural attraction to human settlements and agricultural areas and these include species whose remains commonly occur in prehistoric pueblo sites. The avifauna from these sites also reveals information on the prehistoric use of birds as inferred from bone modification, cut marks, burials, and articulated wings.

Drug addiction and the pastor

The problem of drug addiction has, within recent months, received a great deal of notoriety in the newspapers. While most of the newspaper material seems to indicate that the problem is confined to under-privileged areas in large urban communities, here and there there are indications that drug addiction was but another escape mechanism resorted to by anxious individuals irrespective of their station in life. Thus, in a single newspaper issue the other day, appeared a report of an addict who was a high administrative officer of a large university, and another report of addiction on the part of an outstanding personality in the theater. From communications which we have received from our readers it was obvious that parish ministers, too, were concerned with this problem and wanted to know more about it. While the problem of drug addiction in itself may not be of major concern to the average minister, it is one of those areas of human disturbance with which we feel he ought to be acquainted. It was of particular interest to us to find that a number of ministers have been working in this field all through the country and are making a significant contribution to both the understanding and the treatment of this difficult problem. Chaplain Armen Jorjorian is one such person. We believe that the uniqueness of his article as well as his work lies in the fact that in his attempt to understand the problem of drug addiction he has not been content with the usual generalisations about the problem under discussion, but has instead attempted to locate the specific factors in the drug addict which are responsible for his choice of drug addiction as a particular method of solving his problems. We hope to publish another article by another minister working in this field in an early issue if we hear from our readers that this area is sufficiently important and interesting to them.—Ed.