Oral Session - Assessing the Consequences of Landscape Change on Ecological and Hydrological Processes Chair(s): Semmens, Darius ¹, ¹ Department of Watershed Management, Tucson, AZ
Friday, April 2, 2004 3:00 PM - 4:20 PM Apollo Room 3

The effects of anthropogenic changes in landscape physiognomy on a desert lizard assemblage. Hawlena, Dror^*,1, Bouskila, Amos^{1, 2}, Abramsky, Zvika¹, ¹ Department of Life Sciences, Beer-Sheva, Israel, Israel² Mitrani Department of Desert Ecology, Midreshet Ben-Gurion, Israel, Israel

ABSTRACT- Spatial heterogeneity in desert ecosystems has tremendous effects on basic ecological processes. The characteristics of patches and their distribution in the landscape affect the flow of resources between patches, species richness and population densities. Recently, large areas in the Negev desert have been altered to crop runoff in order to support planted trees, altering the natural patch mosaic. I found that the landscape alteration induced significant changes in the lizard assemblage structure, including local extinction of two desert species. Following these findings, I examined the role of predation as a possible mechanism for the observed pattern. I manipulated patch heterogeneity in a natural loess plane. Five pairs of plots were marked, and in each of these, a grid of 64 pitfall traps was established. In one plot of each pair, 16 metal trees were planted in order to mimic the management practices being used. I used artificial trees to rule-out all possible biological effects of trees except the use as avian predator perches. Lizards were trapped each month for two years, were measured and individually marked. The perches increased the presence of shrikes (the main lizard predator) and altered the assemblage structure. The population of the endangered lizard A. beershebensis decreased in the manipulated plots. The mosaic of areas with different predation pressure generates a source-sink patch dynamics that affects the A. beershebensis populations in the whole area. The study has important implications on the role of desert habitat manipulation on the survival of this endangered lizard and provides a basis for sustainable planning of afforestration.

KEY WORDS: Predation, Patch mosaic, Population dynamics, Assemblage structure, source-sink