The Effect of Increased Productivity on Species Diversity
Investigators (most current known information)
In order to investigate the relationship between species diversity and productivity, we proposed to test three hypotheses that might explain the declining phase of the productivity-diversity pattern: Inter-taxon competition, habitat heterogeneity and intra-taxon competition. These hypotheses provide conflicting predictions that can be explored experimentally. We predicted that directing food enrichment towards either rodents or ants, should be expressed by:
- Changes in population abundance of at least some populations of that taxon;
- Changes in the overall species diversity of that taxon;
- Lower population sizes and increased food generality of the other taxon.
We set up nine experimental plots (three control plots, hereafter "control plots," three rodent-oriented plots, hereafter "rodents plots," and three ant-oriented plots, hereafter "ants plots") at Mashabim-Sands Nature Reserve, located 35 km south of Beer Sheva, Israel. To allow for a higher diversity of species we have located the plots mainly in the most preferred habitats for rodents the semi-stabilized sands habitat while a small proportion of each plot also included the stabilized sands habitat. In each plot, four trapping lines were set up, each line having 10 rodent-trap stations (altogether 40 stations in each plot). Each station was marked with an iron stake having a colorful tape, and aluminum tag with the number of the station, and a light reflector to help finding the station when working at night. Twenty feeding stations were uniformly located in each of the six experimental plots. We have used a 30 x 30 x 30-cm meshed cage (with a 5-mm hole size), which allows only ants to go in and out, as feeders for ants to prevent rodents from consuming the seeds supplied for ants only. Each meshed cage was buried 25 cm in the ground, leaving only 5 cm above sand surface. A quantity of 3.4 gr. of seeds has been added manually at each of the feeding stations daily. (Due to the risk of theft and vandalism we have decided not to use the electronic feeders mentioned in our original proposal). The seeds have been added at sunset, just before dark, so rodents, which forage efficiently at the beginning of the night, would consume the added seeds quickly. However, because rodents could not reach the seeds inserted into the ant-oriented meshed feeders, these seeds were left available for the ants during both night and day time.
We started with rodent trapping in September 1999. We have been able to complete five trapping sessions (September 1999, December 1999, June 2000, September 2001, and February 2002). Each trapping session included 3-4 nights of rodent capturing using live Sherman traps. Each captured rodent had been identified for species and sex, and had been weighted using standard Pezola weights. Data on reproductive status (males: young, reproductive phase; females; young, labor, post labor, lactating) have been recorded. Rodents have been marked by individual toe clipping in the first two years of the research and by temporary marking using color permanent markers in the last year of the research. All individuals have been released immediately in the field after the short-term data recording.
A graduate student, Mr. Udi Sogavker, began studying the ant community of the experimental system since August 2000. Udi has been focusing on the effect of seed enrichment on species diversity and community structure of the ant species living in the studied sandy habitats. This focus has been consistent with the goal of the research to test potential competition between ants and rodents as well as species interactions within each group of organisms. The ant study included: 1) Detection and identification of the different species co-occurring at "Mashabim Sands Nature Reserve"; 2) characterization of the spatial arrangement of the different species in both experimental and control plots; 3) Characterization of the temporal behavior of the different species along 24-hour intervals as well as across seasons throughout the year; 4) Censussing species abundance of all species in the different treatments along the spatial and temporal axes.
Ant observations have taken place at each of the feeding stations as well as at six random stations that were randomly placed in each experimental plot to prevent bias by censussing ants where they have been fed on a daily basis. Ants have been observed for 24 hours every two months at the feeding stations and along three consecutive days every three months at the randomly placed stations.
Articles in Journals
Sogavker, U. and Y. Ziv. 2005. "Ant species richness - productivity relationship along a rainfall gradient in the sandy soils of Israel." Global Environment and Biogeography (in review).
Abramsky, Z., M.L. Rosenzweig, M. Elbaz and Y. Ziv. 2005. "Is interspecific competition from congeners cause the scarcity of Gebillus henleyi in productive desert habitats?" Journal of Animal Ecology (in review).
Pragai, G. and Y. Ziv. 2005. "Testing the scale-dependence hypothesis of the species-productivity relationship within the sandy habitat in Israel." (in preparation).
Sogavker, U. and Y. Ziv. 2005. "Ant competition on productivity-enriched patches in a sandy habitat of Israel." (in preparation).
Ziv, Y. and A. Tsairi. 2004. "The diversity-productivity relationship:the danger of looking for short cuts. Community Ecology (in press).
Rosenzweig, M. L. and Y. Ziv. 1999. "The echo pattern of species diversity: Pattern and processes." Ecography 22:614-628.
Pragai, G. and Y. Ziv. 2004. "Is there scale dependence in beetle-species diversity -productivity relationship in the sandy habitat of Israel?" British Ecological Society. September. Lancaster University, UK
Sogavker, U. 2004. "Ant competition on productivity-enriched patches in a sandy habitat of Israel". Zoological Society of Israel, December. Haifa, Israel. (in Hebrew).
Pragai, P. 2004. "Scale independence in the beetle species-productivity relationship in a sandy habitat of Israel". Zoological Society of Israel. December. Haifa, Israel. (in Hebrew).
Ziv, Y. 2003. "The search for the "true" species richness-productivity pattern: The danger of looking for shortcuts." Zoological Society of Israel. December. Sede Boker, Israel. (in Hebrew).
Sogavker, U. 2003. "The effect of productivity on ant-species assemblage at regional and local scales." Zoological Society of Israel. December. Sede Boker, Israel. (in Hebrew)
Hill, N. 2003. "Effects of food distribution and predation on the foraging behavior of Messor arenarius." Zoological Society of Israel. December. Sede Boker, Israel. (in Hebrew)
Sogavker, U. and Y. Ziv. 2002. "The influence of productivity on ant-species diversity and assemblage at regional and local scales." British Ecological Society. December. University of York, UK.
Pragai, G. 2004. Is There Scale Dependence in the Beetle-Species Diversity-Productivity Relationship in the Sandy Habitat of Israel? M.S. Thesis.
Hill, N. 2003. Effects of food distribution and predation on the foraging behavior of Messor arenarius. M.S. Thesis.
Sogavker, U. 2003. The effect of productivity on ant-species assemblage at regional and local scales. M.S. Thesis.