The influence of spring floods on small mammal communities in the Nemunas River Delta, Lithuania

Abstract

The influence of the annual spring floods on small mammal communities was studied in the Nemunas River Delta, SW Lithuania. The aim of the investigation was to compare the diversity of small mammals inhabiting springflooded meadows, meadows not subjected to flooding and spring-flooded forest in years characterized by differing heights and durations of spring flood. In the years of the high flood, the number of species and diversity index were higher, while index of dominance was less than in the years of low flood. Significantly, the highest proportions of Apodemus agrarius were recorded in spring-flooded meadows in years of high flood (41.7%), while Microtus oeconomus occurred in the highest proportions in spring-flooded meadows in years of low flood (66.8%) and in meadows not subjected to flooding (47.1%). In non-flooded areas, M. oeconomus is not expelled by the floods and outcompetes other species. After high levels of flooding, during the process of re-population, the voles may be outcompeted by A. agrarius. In the absence of dominant species, greater opportunities existed for the establishment of more species (13 species in flooded meadows). Micromys minutus accounted for up to 19.5-30.1% in the years of high flood. We concluded that the annual spring floods in the Nemunas Delta had no long-term negative effects, the number of small mammal species and their abundance had been restored in just a few months. The worst consequences of the high flood were recorded in forest habitat. Spring floods, and especially the higher floods, are natural environmental agents, maintaining the high diversity of small mammals in meadows and reed-beds.

Resource partitioning confirmed by isotopic signatures allows small mammals to share seasonally flooded meadows

“…This corresponds to the situation described by Brown et al (), where environmental perturbations can fully reorganize ecosystems, exceeding the ecological tolerances of dominant or keystone species; though changes may be buffered due to the compensatory dynamics of complementary species. In the investigated area, the 2010 flood in particular was very high (Balčiauskas et al, ), and it was in this year that the two most abundant species were granivores A. agrarius and M. minutus . A. agrarius was shown to be the best colonizer of previously flooded areas within agricultural land (Zhang et al, ).…”

“…We analyzed how several small mammal species, representing insectivores, granivores, herbivores, and omnivores, share a seasonally flooded meadow of limited size. With the re‐occupation of the habitat after the spring flood, spatial arrangement may “pack” species of small mammals tightly, high floods giving chances to uncommon species to establish (Balčiauskas et al, ). We identified separation of dominant species by time and by isotopic partitioning of sympatric species, but not by intraspecific differences in diet (with one exception).…”

“…Mediterranean shrew ( Neomys anomalus ) was found in flooded meadows at Rusnė (<100 m from the investigated site) living sympatrically with three other shrew species, water shrew ( Neomys fodiens ), S. araneus, and S. minutus (Balčiauskas & Balčiauskienė, ). Two other small mammal species that are uncommon in Lithuania, namely M. oeconomus and M. minutus , may also reach high densities in the Rusnė meadows (Balčiauskas et al, ). These species are not common in Lithuania (Balčiauskas & Juškaitis, ; Balčiauskas, ; Balčiauskas, Čepukienė, & Balčiauskienė, and references therein), but are not rare in flooded meadows and river valleys in other European countries (Ambros et al, ; Crnobrnja‐Isailović et al, ; Tast, ; Zub et al, ).…”

“…We previously found that flood height was a key factor influencing diversity and dominance in the small mammal community in the Rusnė flooded meadows. After low‐level floods, A. agrarius was the dominant species, while high‐level floods increased the chances for other species to dominate the meadow (Balčiauskas et al, ). This corresponds to the situation described by Brown et al (), where environmental perturbations can fully reorganize ecosystems, exceeding the ecological tolerances of dominant or keystone species; though changes may be buffered due to the compensatory dynamics of complementary species.…”

“…Two other small mammal species that are uncommon in Lithuania, namely M. oeconomus and M. minutus, may also reach high densities in the Rusnė meadows (Balčiauskas et al, 2012b). These species are not common in Lithuania (Balčiauskas & Juškaitis, 1997;Balčiauskas, 2005; Balčiauskas, Čepukienė, & Balčiauskienė, 2017 and references therein), but are not rare in flooded meadows and river valleys in other European countries (Ambros et al, 2016;Crnobrnja-Isailović et al, 2015;Tast, 1966;Zub et al, 2012).…”