The effect of distance from human disturbance on ant communities

Background/Question/Methods

Urban ecosystems lead to biological homogenization, through habitat degradation and support of invasive species. The urbanized habitat is extremely modified due to dense human population, creating high concentration of food, water, energy, pollution, garbage, etc. The proportion of invasive species is higher in cities, compared with rural or forest areas, and so is the frequency of disturbance events, which in turn creates disturbed habitats, where invasive species thrive.  

Invasive ants are known to have a complex negative impact on their new ecosystem, mainly on other ant species. As ants are an important component of natural ecosystems, this may have substantial consequences on many other organisms.

In two separated experiments I studied the effect of human disturbance on ant communities under Mediterranean conditions. In the first experiment, I compared 12 native habitats, with and without human disturbance (=close proximity to a settlement), in the Coastal Plains of Israel. In the second experiment I focused on one area in San Francisco Bay, California, studying the effect of disturbance on ant communities over an urban-rural gradient. My main hypothesis was that invasive ant species have an advantage at disturbed habitats, while native species have an advantage in preserved habitats.  

Results/Conclusions

According to the first experiment, over a large geographic scale, ant abundance and species richness were not significantly different adjacent to a settlement or away from it. However, in a different experiment, over a finer geographic scale, vast differences were found between ant communities along a gradient of disturbance. In the pristine native habitats, which are remote from disturbance, only native species were found. In similar habitats, that are closer to buildings, roads, and irrigation, most native species are displaced by invasive ones. The invasive species thrive in the urban environment, exploiting the excessive availability of food and water. However, even in the middle of a heavily disturbed habitat, some pockets of native species are still present.