Abstract
Species interactions between stygobites (obligate groundwater organisms) are poorly known, reflecting the difficulty in studying such organisms in their natural environments. Some insight can be gained from the study of the spatial variability in microcrustacean communities in groundwater-fed springs. Earthquakes can increase hydraulic conductivity in the recharge area of karstic aquifers and flow rates in discharge zones, thus dislodging stygobites from their original habitats to the spring outlets. Earthquakes are expected to alter species spatial niche overlap at the spring outlets, where stygobites coexist with non-stygobites living in benthic and subsurface habitats. We compared the abundance of stygobiotic and non-stygobiotic microcrustaceans in groundwater-fed springs before and after the 6.3-Mw earthquake that hit the karstic Gran Sasso Aquifer (Italy) in 2009. Pre-seismic (1997, 2005) overall niche overlaps were not different from null expectations, while post-seismic (2012) species mean niche overlaps were higher, following the redistribution of animals caused by the earthquake-triggered discharge. The reduced abundance of stygobites following their dislodgement from the aquifer and the concomitant displacement of non-stygobites led to a higher post-seismic co-occurrence of stygobites and non-stygobites. Changes in aquifer structure destroyed pre-seismic species segregation patterns by creating new or strengthening already existing interactions.
Highlights
According to classical ecological theory[6, 7], a differential utilisation of resources, i.e. low niche overlap, is considered essential for the coexistence of sympatric species
Karstic aquifers are complex systems whose parts are interconnected by water that flows from surface recharge areas to the aquifer outlets, such as springs
Our results indicate that the Tirino Springs (TS) subsurface copepod community is subjected to wide fluctuations in species abundances as a consequence of relatively small environmental changes, and to variations in niche overlap between species pairs determined by anomalous high disturbance events
Summary
According to classical ecological theory[6, 7], a differential utilisation of resources, i.e. low niche overlap, is considered essential for the coexistence of sympatric species. Of the aquifer should promote faunal homogenisation by favouring species drift, especially for non-stygobites that live on the surface, enter the aquifer through fast infiltration pathways and are dispersed by groundwater flows, especially during high-discharge periods[15, 16]. These species reach the spring environment via the surface water hydrological continuum. Groundwater environments can be altered by major disturbance events such as earthquakes[14, 19]
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