Spatial variation in trophic ecology of small mammals in wetlands: support for hydrological drivers

Abstract

Citation: van der Merwe, J., and E. C. Hellgren. 2016. Spatial variation in trophic ecology of small mammals in wetlands: support for hydrological drivers. Ecosphere 7(11):e01567. 10.1002/ecs2.1567Abstract. Food webs composed of similar consumers can vary based on nutrient input, habitat structure, and other factors. For wetland-associated species, fluctuating water levels can potentially affect habitat quality, which in turn can affect trophic diversity. Our objective was to determine spatiotemporal variation in the trophic structure of small mammals at two wetland complexes (floodplain and mineland) in southern Illinois. We live-trapped small mammals during 2011-2013 at nine wetland patches on the Mississippi River floodplain and 14 patches at a reclaimed mineland. We collected hair samples from six species of small mammals (n = 428) at these wetland complexes. We analyzed C and N stable isotopes for three mammal taxa (Oryzomys palustris, Peromyscus spp., Microtus ochrogaster) to compare diet between species, sites, and times. Food sources (vegetation and invertebrates) were collected to form the isotopic baseline. We found no seasonal difference in diet composition, but isotopic values varied between sites and species. At the floodplain site, both δ 15 N and δ 13 C isotopic values for Oryzomys were more variable and completely enclosed that of Peromyscus. At the mining site, Peromyscus were at a lower trophic level (δ 15 N) and had a separate and less variable δ 13 C values from Oryzomys. Microtus was at a lower trophic position than the other two species at both sites. These results point to reduced niche overlap between Oryzomys and Peromyscus at the mining site, perhaps due to lower habitat quality and limited suitable resources. At the floodplain site, we conclude that more dynamic hydrology gave rise to higher biodiversity and more resources allowing small mammals to use similar food items.

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

“…Isotopic partitioning of small mammal species is characteristic in other cases of limited space, such as under snow cover (Calandra et al, ; Merwe & Hellgren, ). The segregation of the isotopic niche spaces of small mammals, minimizing interspecific competition, allows sympatric species to coexist (Baltensperger et al, ), especially in grasslands, where small mammals are more plastic in their dietary preferences (Symes et al, ).…”

“…Areas subject to periodic flooding maintain a high small mammal diversity (Balčiauskas, Balčiauskienė, & Janonytė, ; Crnobrnja‐Isailović et al, ) as the dynamic hydrology supports a diversity of resources (Merwe & Hellgren, ). A greater number of species (Barnosky, Hadly, Maurer, & Christie, ; Hallett, ) or functional diversity of these species (Wood, McKinney, & Loftin, ) enhances the stability of a community, increasing the potential to withstand negative influences (Scheffer et al, ).…”

A review on homogeneity across hydrological regions

“…Several physical-established (or geomorphic) categorization of rivers carried out, containing some features of climate, geology, topography [9], and also mixed hydro-geomorphic typologies [10][11][12]. The categorizations are popular, however cannot reveal single hydrological difference since they contain further broad values regarding the origins of spatial difference in environmental features of rivers and streams [13]. To resolve these problems, defining patterns in hydrologic character are recognised directly via methods that are established on empirically features that can apply hydrologic metrics explaining several elements of the flow regime [14].…”

Dietary niche separation of rodents and shrews in an African savanna

“…This method provides quantitative records of an animal's feeding ecology based on the stable isotopes of nitrogen (d 15 N) and carbon (d 13 C) found in animal tissues. Values of d 13 C in animals reflect the carbon source (primary producer consumed), whilst d 15 N reflects the trophic positioning in a community (Symes et al 2013, van der Merwe & Hellgren 2016. In a stable community with coexisting species, taxon separation based on different dietary resources is detected by variation between species of 2.0& to 2.5& of d 13 C and d 15 N in their isotope signature, respectively (Crowley 2012).…”