Modelling Recolonisation of Heterogeneous River Floodplains by Small Mammals

Abstract

Riverine landscapes are characterised by recurrent flooding events and successional landscape mosaics with high habitat heterogeneity, providing species-specific patterns of suitable and unsuitable biotopes. Landscape characteristics, like distance, barriers and their specifications (e.g. cumulative barrier width, barrier number) and the spatial arrangement of suitable habitat areas, are expected to affect the dispersal of animals in landscapes. The distribution of voles, shrews and mice in a floodplain was monitored for 2 years using live traps. Recolonisation was found to be a slow process, resulting in a heterogeneous distribution of small mammals in the floodplains. Microtus arvalis was found just after the floods in low densities and on or near non-flooded areas only. From summer to autumn densities gradually increased, and specimens could be observed on larger distances from the non-flooded areas. The density development pattern of Crocidura russula was similar to that of M. arvalis, but densities increased faster. In contrast, Clethrionomys glareolus and Sorex araneus could immediately be observed in the former flooded areas just after the floods, but throughout the year these species were not trapped on distances further than 120 m from the non-flooded areas. Micromys minutus and Apodemus sylvaticus were trapped only occasionally in spring and summer after which those species could be found throughout the floodplain in larger densities in autumn. To analyse the influence of landscape characteristics on recolonisation, the floodplain was classified into suitable, marginal and unsuitable habitat landscape units for each of the small mammal species, based on the trapping results. Landscape characteristics relating to monitoring sites were measured from an aerial photograph using a geographic information system. After that, presence and recolonisation time of small mammals at monitoring sites could be described by multiple regression models based on these measured landscape characteristics. The predictive power of these models was tested in another floodplain by determining the species distribution after 35 weeks. Multiple regression models appeared to be useful in analysing recolonisation patterns and determining the importance of landscape characteristics for recolonisation by small mammals after flooding events. Available distribution data suggest three different types of recolonisers: (1) Gradual, density induced colonisers; (2) Active dispersers and (3) Long-distance dispersers after a lag. Results of regression models confirmed that M. arvalis could be characterised as a type 1 and A. sylvaticus as a type 3 species. The classification of the other species was not possible due to the relatively short time available for recolonisation.

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

“…Conditions did not prove advantageous to A. flavicollis or M. minutus. After high flood levels, the dominant species in the forest was S. araneus, this conforming to rapid re-populating abilities of the species found by Wijnhoven et al (2006).…”

“…Myodes glareolus and A. flavicollis may survive even major floods, while M. arvalis tends to be the most affected (Jacob 2003). Re-colonization abilities also differ: M. arvalis, S. araneus and M. glareolus appear in the area immediately after the flood, but M. glareolus manages to re-colonize only about 120 m in the first year after the flood, while M. minutus restore their densities in autumn (Wijnhoven et al 2006). Microtus oeconomus does not immediately reappear in areas after flood, but does so much later in the summer (Tast 1966).…”

“…The absence of dominant species in the area gave rise to opportunities for chances more species to establish due to reduced competition. As a natural disturbance process, flooding leads to a decline in small mammal populations (Golet et al 2011) and a later restoration of communities, though it was shown that in areas where flooding exceeding one kilometer, not all the area might be re-colonized in the same year (Wijnhoven et al 2006).…”

Persistence of fishers in riparian forests in North Dakota, USA following a severe flood event

“…Because of the difficulty in predicting when and where a flood will occur, the majority of information gathered on the topic was not acquired as part of a designed project, but instead the result of studies that were in progress when flooding occurred-as was the case with our investigation. Most published information on the topic is based on studies and observations of small mammals (Anderson et al 2000;Batzli 1977;McCarley 1959;Stickel 1948;Wijnhoven et al 2006;Williams et al 2001;Yeager and Anderson 1944) with the exception of opossums (Didelphis virginiana; Yeager and Anderson 1944), raccoons (Procyon lotor; Gehrt et al 1993;Yeager and Anderson 1944), and white-tailed deer (Odocoileus virginianus; Samuel and Glazener 1970).…”

“…Species with arboreal capabilities (e.g., Peromyscus spp., fox squirrels [Sciurus niger], opossums, and raccoons) initially are known or presumed to take refuge in trees located within the floodplain (Anderson et al 2000;Batzli 1977;Gehrt et al 1993;McCarley 1959;Stickel 1948;Williams et al 2001 and Anderson 1944) but may perish or move beyond flooded areas if the flood persists for a long duration (Anderson et al 2000;Blair 1939 Samuel and Glazener 1970). Little is known about survival or recolonization rates of individuals that disperse beyond flooded areas, except for a few studies of small mammals (Anderson et al 2000;Batzli 1977;Stickel 1948;Wijnhoven et al 2006), and we located no documentation describing the effects of flooding on forest-dependent mammalian species occupying areas where forests occur almost exclusively in riparian habitats. The limited information available suggests that most small mammal species that leave the floodplain are slow to recolonize (>9 months) the area after the water recedes (Wijnhoven et al 2006).…”