Light pollution in a rocky desert community: Foraging behavior, activity patterns, and inter- and intraspecific interactions in spiny mice

Background/Question/Methods

We capitalized on two decades of ecological and physiological research of temporally partitioned desert spiny mice to ask how artificial illumination during the earlier hours of the night will impact both nocturnal and diurnally active species.  Ecological light pollution is considered to have a negative influence on ecosystems, yet was rarely studied at the community level.  In our study system the common spiny mouse (Acomys cahirinus) is nocturnal, while the golden spiny mouse (A. russatus) is diurnally active; previous research suggests that the golden spiny mouse was competitively excluded into diurnal activity by its congener.  We hypothesized that in response to artificial illumination, A. cahirinus will decrease their activity, A. russatus may use it to expand theirs, and thus temporal overlap and interspecific competition may increase.

Our study took place in four field enclosures at the Ein Gedi nature reserve which is located at a rocky desert near the Dead Sea.  The first and third months were controls with natural light, and in the second month artificial illumination, simulating low levels of light pollution, was set for the first three hours of the night.  We implanted temperature-sensitive radio transmitters to monitor mouse activity, and individual identification tags with auto-monitored foraging patches were used to track foraging behaviour in artificial foraging patches placed in each enclosure in three microhabitats: under boulder (UB), between boulders (BB), and open microhabitat (O).  These microhabitats constitute a gradient in shelter and hence predation risk for spiny mice.

Results/Conclusions

A. cahirinus decreased activity and foraging with artificial lighting, particularly in less sheltered microhabitats, probably because of increased predation risk.  As illumination restricted both activity time and space, A. cahirinus intraspecific encounters over foraging patches increased during and following the illuminated hours.  Under illumination intraspecific encounters increased in the more sheltered under boulder (UB) microhabitat.

A. russatus did not expand their activity into the illuminated hours, possibly due to the presence of competing A. cahirinus, non-favourable environmental conditions, or low illumination.  Therefore, overt interspecific competition was not affected by experimental light pollution.  Light pollution had a negative influence by: a) reducing overall activity and producing a relatively underexploited temporal niche, which may promote invasion of alien species that are less light sensitive, and b) increasing intraspecific overlap in A. cahirinus foraging.