Coastal Dune Sites Research Articles

Long-term effects of anthropogenic habitat disturbance on a lizard assemblage inhabiting coastal dunes in Argentina

We studied abundance and habitat use in two species of Liolaemus (Squamata: Tropiduridae) at a coastal dune site in eastern Argentina before and 7 years after a road was built at the site. Before disturbance, lizards exhibited similar abundances and a wide segregation in microhabitat use. Liolaemus multimaculatus used flat dunes scarcely covered by Spartina ciliata, while Liolaemus gracilis used the grass Panicum racemosum as cover. After disturbance, the mean number of L. multimaculatus detected by month was significantly less than that observed in the predisturbance period, owing to a drastic reduction in S. ciliata microhabitat patches. The mean number of L. gracilis was similar to that seen during the first period. These differences were clearly linked to habitat loss at the site. We concluded that human impact on the habitat structure of foredunes induced changes in the structure of the lizard assemblage, including shifts in the relative abundance of species and the proportional use of their preferred microhabitats.

Population dynamics of an Egyptian desert shrub, Thymelaea hirsuta

Natural populations of the evergreen shrub, Thymelaea hirsuta (L.) Endl., were studied over 6 years at five desert habitats, in terms of seedling recruitment and adult survival and as a function of plant size and gender class. Habitat and time significantly influenced mortality of both reproductive and non-reproductive plants. Plant size also significantly affected adult mortality. Seedling recruitment varied significantly with habitat and year and approached zero some years. Significant among-year and among-population variation in population growth rates were observed over the 6 years of study, and all populations declined in size (ranging from −1.7% per year at the coastal dune site to −10.9% per year at the inland plateau site). Spearman rank correlation analysis between habitats ranked according to a north–south gradient and demographic variables indicates that this gradient is associated with a pattern of lower seedling emergence and survival and a lower population growth rate and greater mortality for all size-classes of Thymelaea plants. In experimental botanic garden plots, germination of seed collected from five natural populations, and seedling survival in the following year were assessed under conditions of high, medium, and low seedling density. Seedling emergency differed significantly according to maternal habitat. With regular watering, seeding survival to one year was 72% (averaged across habitats and densities). This compares with 64% for seedlings grown at the highest density, suggesting that the intense mortality observed under field conditions is more likely to be a result of water shortage than intraspecific competition. Key words: Egyptian desert, Thymelaea hirsuta, germination and establishment, seedlings, recruitment, competition, population growth rate.

Interpretation of archaeological material eroded from coastal dune sites

Abstract THE archaeologist may sometimes extract useful cultural data from coastal midden sites in eroding sand dunes. An understanding of the dune feature, the “blow-out”, is considered a prerequisite to understanding the various phases of midden erosion. A model is described based on observations in the field and it is used to explain the erosional processes that destroy middens. A method of dealing with the eroded material is outlined.