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Ben-Gurion University of the Negev (2010)

Inter-specific competition between Negev rodents

Avetisyan Khoren

Titre : Inter-specific competition between Negev rodents

Auteur : Khoren Avetisyan

Université de soutenance : Ben-Gurion University of the Negev

Grade : Master of Science 2010

Two approaches based on regression models are proposed to estimate competition from census data. The static approach is based on censuses of population sizes among species at one point in time over many sites. This dynamic approach relies on a time series of species abundance data to examine whether per capita changes in one species are associated with the abundance of other species. In this paper I have tested the hypothesis that in desert environments that disrupt equilibrium, the dynamic approach indicates true (exploitation) competition, whereas the static approach reflects negative interspecific spatial association (interference). I estimated competition interactions of 3 populations of rodent species in the Ramon erosion cirque and vicinity, Negev Highlands, Israel, using both approaches and based on 2 years (4 half-year periods) of observations. From 2008 through 2009 I conducted experiments, where supplemental seeds were added. I examined the patterns of relationship between the competition coefficient and the population variance of the 3 species of rodents. I measured how adding millet seeds affected interference and exploitation competition. Experiment demonstrated the existence of interference competition between Dipodillus dasyurus and Mus musculus and between Dipodillus dasyurus and Gerbillus henleyi. In the cases when field census data indicates this type of competition and when this data indicates no competitive interaction. Cases of negative interactions recorded by the static approach were more frequent at peak and increase phases of population density dynamics, whereas there were not recorded by the dynamic approach. These results indicate that food is limited, but the relegation of subordinate species to less preferred microhabitats by the large Dypodillus dasyurus is the major factor underlying the spatial organization of this community. Results also demonstrated that strong interactions among species increase the probability that pathways of indirect interactions through intermediary species are important. Result suggests that there is a trade-off between interference competition and food to which gerbils respond behaviorally.

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